NOM-032-STPS-2008, Safety for underground coal mines

That on 12 February 2008, in compliance with article 46, section I, of the Federal Act on Metrology and Standardisation, the Ministry of Labour and Social Welfare submitted to the National Consultative Committee for Standardisation on Occupational Safety and Health the Preliminary Draft Official Mexican Standard, and that Committee considered it correct and agreed that it be published as a Draft in the Official Gazette of the Federation; That to comply with the provisions of articles 69-E and 69-H of the Federal Act on Administrative Procedure, the corresponding Preliminary Draft was submitted for the consideration of the Federal Commission for Regulatory Improvement, which issued a favourable opinion on it; That on 15 August 2008, in compliance with the Agreement establishing the organisation and Operating Rules of the National Consultative Committee for Standardisation on Occupational Safety and Health, and with article 47, section I, of the Federal Act on Metrology and Standardisation, the Draft Official Mexican Standard PROY-NOM-032-STPS-2008, Safety for underground coal mines, was published in the Official Gazette of the Federation so that, within the 60 calendar days following that publication, interested parties could submit their comments to the Committee; That having received comments from two petitioners, the Committee proceeded to study them and resolved upon them in due course, this department publishing the respective responses in the Official Gazette of the Federation on 4 December 2008, in compliance with article 47, section III, of the Federal Act on Metrology and Standardisation; That as a result of incorporating the accepted comments submitted on Draft Official Mexican Standard PROY-NOM-032-STPS-2008, Safety for underground coal mines, as well as of the final review of the draft itself, various amendments were made for the purpose of providing clarity, consistency and legal certainty as regards the provisions applying in workplaces, and That in view of the foregoing considerations, and since the National Consultative Committee for Standardisation on Occupational Safety and Health granted its approval, the following is issued: OFFICIAL MEXICAN STANDARD NOM-032-STPS-2008, SAFETY FOR UNDERGROUND COAL MINES

To establish safety conditions and requirements for the installation and operation of underground coal mines, to prevent risks to workers who work in them.

This Official Mexican Standard is in force throughout the national territory and applies to all underground mines where activities related to coal mining are carried out.

To comply with this Standard, the following current Official Mexican Standards, or those replacing them, shall be consulted: NOM-002-STPS-2000, Safety conditions - Fire prevention, protection and fire-fighting in workplaces. NOM-006-STPS-2000, Materials handling and storage - Safety conditions and procedures. NOM-010-STPS-1999, Safety and hygiene conditions in workplaces where chemical substances capable of generating contamination of the working environment are handled, transported, processed or stored. NOM-011-STPS-2001, Safety and hygiene conditions in workplaces where noise is generated. NOM-015-STPS-2001, High or low thermal conditions - Safety and hygiene conditions. NOM-017-STPS-2001, Personal protective equipment - Selection, use and handling in workplaces. NOM-018-STPS-2000, System for the identification and communication of hazards and risks from hazardous chemical substances in workplaces. NOM-019-STPS-2004, Constitution, organisation and functioning of the safety and hygiene committees in workplaces. NOM-020-STPS-2002, Pressure vessels and boilers - Operation - Safety conditions. NOM-021-STPS-1994, Concerning the requirements and characteristics of the reports on occupational risks that occur, for compiling the statistics. NOM-024-STPS-2001, Vibration - Safety and hygiene conditions in workplaces. NOM-025-STPS-2001, Lighting conditions in workplaces. NOM-026-STPS-1998, Safety and hygiene colours and signs, and identification of hazards from fluids conveyed in pipework. NOM-030-STPS-2006, Preventive occupational safety and health services - Organisation and functions.

4.1 Hazardous activities: all tasks arising from work processes that generate unsafe conditions and overexposure of workers to physical, chemical or biological agents capable of causing harm to their health or to the workplace.

4.2 Timbering: a type of support for the roof and walls of a gallery or mine working by means of any support or anchoring system.

4.3 Self-rescuers: personal respiratory protection devices designed for escaping from contaminated atmospheres or atmospheres with oxygen deficiency.

4.4 Labour authority: the competent administrative units of the Ministry of Labour and Social Welfare that carry out inspection functions in respect of occupational safety and hygiene, and the corresponding units of the federal entities and the Federal District that act in support of them.

4.5 Boreholes: holes or perforations made for multiple purposes.

4.6 Misfired holes: explosive charges not detonated after a blast has been carried out.

4.7 Chinking: the application of small pieces of wood to the mine canvas, around the entire perimeter of the seal, to prevent leaks.

4.8 Cage: a hoisting conveyance used for the vertical transport of workers and materials.

4.9 Bell cavity: a cavity formed in the roof of a working, caused by the fall of rock material.

4.10 Keyway: a perimeter excavation made in the floor, roof and walls of the gallery, where the ventilation seal will be built.

4.11 Ventilation circuit: an arrangement designed to conduct air to the different districts of the mine, starting at the mine entrance and ending at the discharge of the main fan to the surface.

4.12 Spontaneous combustion of coal: the oxidation of coal resulting from an exothermic reaction that can reach a critical temperature and cause the coal to self-ignite.

4.13 Ventilation crosscut: the last crosscut developed through which the air flow of the circuit returns.

4.14 Disuse: temporarily out of operation or service.

4.15 Firing; blasting: the effect of detonating an explosive charge.

4.16 Duct: a conduit for carrying ventilation air to the working faces, with antistatic, flame-retardant or self-extinguishing properties.

4.17 Emergency: the occurrence of fires, explosions, spills, flooding, poisoning and collapses in the mine.

4.18 Interlock: the action of activating a mechanical device that prevents the unintended operation of the switch.

4.19 Plastering: the action of applying a construction mixture composed of cement, sand and water.

4.20 Exploration: the works and activities carried out to identify material deposits and to quantify and evaluate their content.

4.21 Mining: the works and activities intended for the preparation, development, breaking and extraction of materials in a mine.

4.22 Reinforcement: the strengthening of the roof, floor and walls of a mine working by means of any structural support system.

4.23 Face: the exposed wall of the gallery on which the ore is broken.

4.24 Long face: the exposed face of variable length on which ore is broken, bounded by two adjacent workings or galleries.

4.25 Gallery: a passageway made in underground mines for the extraction of minerals, ventilation, communication or drainage.

4.26 Crib: an interlocked timber or other material support arrangement, generally running from the floor to the roof of the gallery.

4.27 Non-combustible: the property of materials that prevents combustion.

4.28 Intrinsically safe: the designation used for electrical and electronic equipment that keeps its energy levels low enough always to remain below the level required for a gas-air mixture to ignite, under normal operating conditions and even where failures or abnormal conditions occur.

4.29 Mine canvas: a fabric that may be made of jute fibre or rubberised fibre, used to cover line stoppings, with antistatic, flame-retardant or self-extinguishing properties.

4.30 Hoist: equipment that, by means of one or more steel cables, enables materials, equipment and workers to be transported in skips, cars and cages.

4.31 Electrical material: the set of elements used, in whole or in part, for the use of electrical power. It includes, among others, the equipment intended for production.

4.32 Mine: an excavation made by means of vertical or inclined shafts and galleries for extracting coal.

4.33 Small-scale operation: an operation in which the distances between interconnected shafts do not exceed 100 metres and the development of its galleries does not exceed 150 metres from any of the shafts, in any direction, and which, in addition, has no electrical installation inside the mine.

4.34 Prop: timber, metal or other material posts used to support the timbering of galleries.

4.35 Dusting: the action of applying inert dust to the walls, roof and floor of the mine for the first time, as the workings or tunnels are developed.

4.36 Inert dust: material composed of calcium carbonate, or calcium and magnesium carbonate, used to reduce the combustibility of coal dust, having the following properties: a maximum content of 2% silicon dioxide (SiO2); a particle size of 80% below 200 mesh, and non-combustibility of more than 95% at 1000 ºC.

4.37 Pit: a vertical or slightly inclined mine working for the artisanal mining of coal.

4.38 ppm: parts per million.

4.39 Safety procedures: written instructions for carrying out a series of activities with the least risk to workers and the workplace.

4.40 Re-dusting: the action of reapplying inert dust to a section that had previously been dusted.

4.41 Higher-impact risks: those related to the instability and deformation of pits, galleries and mining faces, slopes and platforms of open cuts and waste dumps; scaling work; the transport and use of explosives; asphyxiant, toxic, flammable and explosive gases and dusts; flooding; those arising from the operation of motorised hoists, locomotives and extraction and loading machinery, and welding and cutting activities.

4.42 Maintenance routines: the activities, instructions or actions for carrying out preventive maintenance on machinery or equipment.

4.43 Preventive Occupational Safety and Health Services: a multidisciplinary group of specialists with essentially preventive functions, responsible for advising the employer, the workers and their representatives on compliance with the regulations on safety, hygiene and the working environment.

4.44 Disaster: a catastrophic event such as a fire, explosion, flood and/or collapse in a coal mine or pit.

4.45 Welding and cutting: activities involving the heating of materials and their localised coalescence, by raising their temperature, for the purpose of joining them, with or without the application of pressure and with or without the use of filler material.

4.46 Chairlifts: a system for transporting workers by means of an endless cable, with hanging chairs.

4.47 Shaft: the conduit, of a vertical or inclined mine working, through which workers, materials and equipment ascend and descend.

4.48 Verification unit: an individual or legal entity accredited and approved under the terms of the Federal Act on Metrology and Standardisation to verify the degree of compliance with this Standard.

4.49 Blasting: the action of blasting the working face of the mine with explosives.

4.50 Air volume (flow rate): the air supplied to a given location, the value of which is calculated by multiplying the air velocity by the cross-sectional area of the gallery.

4.51 Mined-out zones: the areas of the mine where extraction of recoverable coal has been completed.

5.1 To show the labour authority, when it so requests, the documents that this Standard requires it to prepare or hold.

5.2 To prohibit workers under 18 years of age and pregnant or breastfeeding women from working inside underground mines.

5.3 To comply, in all mines, with the applicable provisions contained in the chapters of this Standard, in accordance with the activities carried out and the type of installations, equipment, machinery and tools available.

5.4 To carry out an inspection of the safe conditions of the working faces inside the mine, before the start of the activities of each work shift, to ensure the safety of workers carrying out their work. The inspection shall at least consider the ventilation, reinforcement, equipment and dusting conditions. The person who carries out the inspection shall, where applicable, give the authorisation for the work of the corresponding shift to begin. A record of the inspections carried out shall be kept in printed or electronic form and retained for at least twelve months.

5.5 To provide all workers, including new recruits, with training and instruction to carry out their activities safely. Such training shall also be provided whenever the work processes, the equipment used by the worker or the worker's usual activity change, in accordance with the procedures referred to in the chapters of this Standard. To demonstrate the training and instruction provided, the corresponding proof of occupational skills shall be produced.

5.6 To inform all workers, at least once a year, of the risks to which they are exposed and, in particular, those related to the activities they carry out. This is without prejudice to compliance with the provisions of sections 5.5 and 5.7. A record of the information provided shall be kept, containing at least: the date on which the information was given; the name and position of the workers to whom the information was given, and the name of the instructor. Such a record shall be kept in printed or electronic form and retained for at least twelve months.

5.7 To provide workers who do not carry out activities inside underground mines, but who enter them for any reason, as well as other persons who enter them for any reason, with general information related to occupational safety and health and to the risks to which they are exposed. A record of the information provided shall be kept in printed or electronic form and retained for at least twelve months.

5.8 To grant written authorisation (permit to work) only to workers trained and instructed in accordance with this Standard to operate and maintain locomotives, machinery, vehicles, installations and equipment, and to those who store, transport or use explosives. A record of the authorisations granted shall be kept in printed or electronic form and retained for at least twelve months.

5.9 To keep a record, for each shift, of workers entering and leaving the mine, so that, at all times, the persons inside can be identified, together with their location by area or zone, in a way that allows them to be located on a plan. The location shall preferably be recorded in real time and, where possible, using current technology enabling compliance with this provision. Such a record shall be kept in printed or electronic form and retained for at least three months.

5.10 To comply with the provisions of NOM-006-STPS-2000 for the handling of materials.

5.11 To notify the Ministry of Labour and Social Welfare of occupational accidents that occur, in accordance with the provisions of NOM-021-STPS-1994.

5.12 To investigate accidents and disasters occurring in mines, to adopt preventive and corrective measures to prevent such accidents recurring, and to keep the corresponding records in printed or electronic form.

5.13 To assess the conditions of the mine after a disaster has occurred, before authorising the entry of the teams, and to resume routine activities only once the conditions ensuring workers' safety have been assessed and re-established. A record of the results of the assessments shall be kept in printed or electronic form and retained for at least twelve months.

5.14 To provide all workers with personal protective equipment, according to the risks to which they are exposed, in accordance with the provisions of NOM-017-STPS-2001.

5.15 To verify that all persons entering mines wear at least the following personal protective equipment: a) Protective helmets; b) A miner's lamp with a rechargeable battery lasting at least 1.25 times the worker's shift; c) Lamp belt; d) Rubber boots with toe caps or protective footwear with toe caps; e) Ear plugs or ear muffs; f) Safety glasses; g) Gloves; h) Particulate respirators; i) Cotton work clothing or clothing made of materials that do not generate static electricity; j) Self-rescuer, and k) Metal identification tag.

5.16 To verify that workers use personal protective equipment while carrying out their normal and emergency activities. It shall also verify that they maintain, safeguard, clean and, where applicable, replace it in accordance with the corresponding specific instructions.

5.17 To have safety data sheets (SDS) for all hazardous chemical substances used; to identify the deposits, containers and areas containing them or their waste, and to communicate their hazards and risks to all workers exposed to them, in accordance with the provisions of NOM-018-STPS-2000.

5.18 To have at least one Safety and Hygiene Committee, constituted, trained, with its activities scheduled and functioning, in accordance with the provisions of NOM-019-STPS-2004.

5.19 To follow up on the recommendations issued in the walk-through reports of the safety and hygiene committee(s).

5.20 To comply with the provisions of NOM-020-STPS-2002 for the operation of pressure vessels and steam generators or boilers.

5.21 To comply with the provisions of NOM-026-STPS-1998 for all signage referred to in this Standard and for the identification of pipework carrying fluids.

5.22 To carry out entrance (initial) and periodic medical examinations for occupationally exposed workers, according to the activities they carry out, and to monitor their health. At least the following shall be carried out: chest X-ray, audiometry and spirometry.

5.23 To have preventive occupational safety and health services carrying out the functions described in NOM-030-STPS-2006.

5.24 To have a permanently up-to-date potential risk analysis, available to workers, approved and signed by the employer and by the Preventive Occupational Safety and Health Services.

5.25 The potential risk analysis shall be carried out by area, process and activity throughout the mine and shall at least contain: a) The analysis of the work areas; b) The identification of workers and their activities by job, both under normal and emergency conditions; c) The identification of the higher-impact risks, their type of risk (to health, of flammability and of explosivity) and the hazardous activities to which workers are exposed, taking into account, at least, the safety procedures and the provisions to be considered in the emergency response plan; d) The possible impact, for which the magnitude of the harm that could occur to workers or to the mine shall be assessed; e) The probability of the risks occurring, using as a reference the statistics on risks that have occurred in that mine, so that a preventive measure is assigned to each potential risk; f) The number of events per unit of time that could occur. This result shall be combined with the comparative analysis that, where applicable, is made of the assessment of hazardous activities against their corresponding maximum permissible limits. If the results of the assessment are above the aforementioned limits, immediate prevention and control measures shall be established, modifying the safety conditions or procedures, the personal protective equipment or the training and, where applicable, applying the emergency response plan; g) The prioritisation of risks according to their probability of occurrence and possible impact, and h) The proposal of the occupational safety and health procedures and conditions to be implemented, to control the risks detected.

5.26 To be responsible for the physical integrity and health of their workers and of third parties while activities are being carried out.

5.27 To have a written emergency response plan available to workers, containing at least: a) The establishment of one or more teams or crews to deal with emergencies involving: 1) Fires; 2) Explosions; 3) Flooding; 4) Collapses, and 5) Sudden gas and coal outbursts. The document establishing the teams shall include: the name, position, shift, functions and responsibilities of their members. b) Procedures for: 1) Emergency alert and alarm, indicating the means the person(s) will use to raise the alarm for the emergency and to whom or where they shall report after raising the alarm; 2) Emergency response; 3) Evacuation of the mine; 4) First aid; 5) Rescue and salvage; 6) Coordination of the mine's teams with other external teams; 7) Control of access to the mine, and 8) Re-entry to the mine. There shall be at least two fully independent, redundant emergency alarm systems. The procedures shall define the functions, responsibilities and actions during and after the emergency, the length of time personnel shall remain and the declaration of the state of emergency. c) A programme for inspecting the equipment and materials required for each of the teams or crews, so that they are at all times fit for use and in good condition for operation; d) The determination of the personal protective equipment for each of the teams, in accordance with the provisions of NOM-017-STPS-2001; e) An indication that a first-aid kit is available, with the materials required to attend to injured persons according to the type of risks detected; f) An inventory of the rescue and salvage equipment and a copy of its most recent inspection; g) The determination of the location of the rescue and salvage equipment; h) The location of the operations and relief centres for emergencies; i) The training received and that which shall be received in accordance with each of the potential emergencies; j) Emergency response drills and exercises shall be carried out at least every six months. The results of the emergency response drills and exercises shall be recorded in a logbook or by electronic means and retained for at least twelve months. Such results shall include the improvement proposals and the problems detected, as well as the name and signature of the person designated by the employer to keep the record. In addition, the results of the record shall be made known to the workers; k) The medical examinations to which the members of the teams or crews shall be subjected so that they maintain the response capacity needed to deal with emergency tasks; l) In particular, for emergencies in mines susceptible to methane gas outbursts, the following specific information and actions to be taken shall be included: 1) The location of drilling machines; 2) The location of pipework and valves indicating the direction of flow; 3) The location of the degasification pumps; 4) The location of the methane gas monitoring equipment and its records; 5) A general description of the alarm system to be used; 6) The location and description of other means of communication for transmitting warning messages to other workplaces that could be endangered as a result of a methane gas escape in a given zone; 7) The types of immediate first aid to be given to injured persons; 8) The mechanisms for transporting and evacuating injured persons; 9) The procedures for responding to the emergency; 10) The means for rescuing injured or trapped persons; 11) The evacuation procedures; 12) The planning and coordination of the involvement of emergency services from outside the workplace, and 13) A description of the equipment and materials for controlling the emergency.

5.27.1 The emergency alert and alarm procedures shall contain, for each type of emergency, at least the following criteria for raising the alarm and taking immediate action: a) To raise the alarm: 1) The nearest supervisor shall be alerted immediately of the condition detected; 2) Where the person who becomes aware of the emergency at its outset - and is trained to deal with it - shall, if possible, attempt to tackle it and report the fact as quickly as possible to the nearest supervisor, and 3) The instructions for raising the alarm and responding to the emergency shall be followed. Following this, the personnel keeping watch from the surface and any persons who may be affected inside the mine shall be informed. b) To take immediate action in the event of fire: 1) Where an order is given for all workers to be evacuated immediately from all areas threatened by the emergency, only those who need to remain to control or fight the emergency shall, where applicable, be permitted to stay; 2) Where the emergency alarm is raised, the persons authorised to enter the mine to deal with emergencies shall coordinate their activities; 3) The application of the emergency response procedures shall be supervised, and 4) Where reasonably possible, in fire emergencies, inert dust shall be applied or the fire tackled by any other means so as to prevent the fire spreading to the parts adjoining the area of the fire in the mine.

5.28 To have a study confirming that, with the self-rescuers available to workers, it is possible to reach the surface from the most remote point of the mine. Otherwise, reserve or additional self-rescuers shall be available, one for each worker on the long faces and in the development workings, distributed at strategic locations, duly marked with reflective or fluorescent materials, and identified on a plan that shall be circulated for the information of all personnel.

5.29 To train and instruct workers in the use and replacement of self-rescuers in emergency situations, at least every six months. The record of the training provided shall be retained for at least twelve months.

5.30 To have signage for evacuation routes by means of lifelines with elements indicating the direction of the exit, and safety signs or notices made of reflective or fluorescent materials.

5.31 To verify that no worker is exposed to noise levels exceeding the maximum permissible exposure limits established in Appendix A of NOM-011-STPS-2001.

5.32 To prevent workers from being exposed to risks from high or low temperatures, in accordance with the provisions of NOM-015-STPS-2001.

5.33 To prevent workers from being exposed to risks from vibration, in accordance with the provisions of NOM-024-STPS-2001.

5.34 To provide individual methane gas detectors to personnel responsible for the safety of the mine (personnel in the chain of command).

6.1 To participate in the training and instruction provided by the employer.

6.2 To comply with the safety and health measures and procedures established by the employer.

6.3 To use personal protective equipment in accordance with the activity being carried out and the instructions for use.

6.4 To participate in the training and receive the information provided by the employer on the instructions for the system for identifying and communicating the hazards and risks of chemical substances of hazardous chemical substances.

6.5 To use and maintain the safety devices installed on machines, tools, installations and structures, refraining from arbitrarily connecting, disconnecting, changing or removing these devices.

6.6 To operate and maintain machinery, locomotives, vehicles and motorised hoists, and to transport, use or store explosives, only where they have specific training on the subject and written authorisation from the employer.

6.7 To be responsible for their own physical integrity and health, as well as for that of third parties who may be affected by their acts or omissions.

6.8 To keep the areas where they carry out their work, and those intended for service, clean and tidy.

6.9 To immediately notify their supervisor or the person in charge of safety of any situation of imminent risk that they cannot correct themselves, and to resume their activities only once the situation has been corrected.

6.10 To render assistance for as long as required in the event of an emergency or a situation of imminent risk.

6.11 To take part in evacuation drills and emergency response exercises when required to do so.

6.12 To undergo the medical examinations required according to their activities and to provide truthful information requested by the doctor carrying out the examination.

6.13 To observe the order and discipline required inside the mine's installations.

6.14 To report for work without being under the influence of alcoholic beverages, narcotics or psychotropic substances.

6.15 To make proper use of personal protective equipment, work tools, and the mine's electromechanical equipment and installations.

6.16 To observe and comply with safety signage.

To ensure a reduction in the risk of explosion in operations where explosives are received, stored, transported, handled, operated and detonated, the employer shall establish and implement procedures applicable in the areas where they are used, in accordance with the provisions of this Chapter.

7.1 The safety procedure for the receipt, storage, internal transport, handling and use of explosives in the mine shall contain at least the following: a) The safety measures for the receipt and storage of explosives; b) The safety measures for the issuing and internal transport of explosives; c) The safety measures for the handling and use of explosives; d) The control of the supply, consumption and return of explosives for the blast-charging process; e) The planning of drilling and blasting; f) The safety measures for charging and blasting with explosives, and g) The control and monitoring of access to blasting areas.

7.2 For the control of explosives, the employer shall designate the persons responsible for granting the corresponding authorisations for the receipt, storage, internal transport, handling and use of the explosives used.

7.3 The safety measures for the control of explosives shall at least address the following: a) Explosives and accessories shall be transported separately, from receipt through to their use or return; b) Materials not used for blasting shall be returned to the corresponding magazine outside the mine; c) The worker who moves explosive materials shall have been trained and authorised for that activity; d) The containers for transporting explosive material shall be closed and made of spark-proof material, and e) A minimum distance of 100 metres shall be maintained between the transport of the primer cartridges and the detonators, or one of these components shall be transported first and the other afterwards, kept separate from each other.

7.4 The employer shall designate a person in charge of the magazine, to receive, issue and oversee the handling of explosives, and to control their receipts, consumption and issues. A monthly report on these actions shall be prepared and kept by electronic means for at least twelve months.

7.5 Workers who use explosives inside the mine shall hold the corresponding written authorisation for that purpose. A copy of such authorisation shall be provided to the workplace's Safety and Hygiene Committee and to the preventive occupational safety and health services.

7.6 Work with explosives may only be started where the corresponding written authorisation is held and where the safety measures established for the activity to be carried out have been complied with.

7.7 The safety measures for obtaining explosive material shall at least comply with the following: a) The written request shall be only for the number of detonators and cartridges necessary to carry out the activity, and shall contain at least: 1) The name and authorising signature of the person in charge of the mine; 2) The name, signature and position of the worker receiving the material; 3) The name and position of the supervisor in charge of the blast; 4) The date of the request and of delivery; 5) The shift; 6) The type and quantity of material requested and delivered, and 7) A general description of the activity to be carried out. b) Instructions shall be available for returning unused explosives or accessories and for recording the reasons for the return; c) Both the issuing of materials and the return of unused materials shall be supervised by a person designated by the employer; d) Returned materials shall be placed in the corresponding magazines for storage, applying the applicable safety measures, and e) Records shall be kept, per shift, of explosives consumption.

7.8 The safety measures for the transport of explosives shall at least address: a) The workers responsible for transporting the explosives shall go underground before or after the rest of the personnel; b) Cartridges and detonators shall be transported separately; c) The same person shall not carry the detonators and the cartridges at the same time; d) Where the original containers are not used, cartridges shall only be transported in wooden containers, and detonators in rigid non-metallic or wooden containers; e) Workers transporting explosives shall never be separated from them until they are delivered for use; f) Detonators and cartridges shall not be placed near electrical conductors, moving equipment or unsafe locations. Where they are not used immediately, they shall be placed temporarily in previously authorised locations, kept at least 100 metres apart and returned to the corresponding magazines during the same work shift, and g) The transport of explosives on conveyor belts is prohibited, whatever their quantity or nature.

7.9 The safety measures for using, charging and tamping boreholes shall at least address: a) All the safety provisions established on the subject shall be observed; b) Only explosives, detonators and accessories approved for coal mines shall be permitted to be used; c) Only detonators of the same technical characteristics and make shall be used in the same shot; d) The firing line shall always be perfectly insulated and positioned in the centre of the gallery or, failing that, on the side opposite to where there are electrical cables or where personnel pass; e) The firing line shall be at least 100 metres long and in perfect condition for use; f) On straight faces the firing line shall be at least 150 metres long, where its length allows; g) The ends of the firing line shall remain joined together until one of them is connected to the detonators and the other to the exploder, the latter connection being made after the firing line has been connected to the detonators that are to be fired; h) The firing line used shall not be smaller than gauge 14; i) Before boreholes are charged, the authorised person shall inspect each borehole with the ordinary wooden tamping rod, to make sure it is clean and to check its direction and depth; j) It shall be verified that the resistance of the detonators, before and after charging the face, is less than or equal to 3 ohms. The ohmic resistance in a face that is about to be fired shall be less than or equal to the number of detonators multiplied by three; k) The detonator wires shall be handled carefully, without pulling or scraping them, and they shall only be permitted to be separated to test their ohmic resistance, using a galvanometer, and shall be rejoined immediately after the measurement; l) To pierce the primer cartridge, only special punches made of wood, copper, aluminium or another spark-free material shall be used; m) To insert the detonator into the cartridge that will serve as the primer, a hole shall be made in one end of the cartridge without opening the wrapper, and after inserting the detonator into the hole, the detonator wires shall be tied firmly around the cartridge; n) The primer shall be the first item inserted into the borehole, with the pierced end facing towards the bottom of the borehole, after which the remaining cartridges shall be inserted one by one; o) The remainder of the borehole shall be filled with inert-dust cartridges as stemming; p) While charging the borehole, the primer wires shall be held, allowing them to slide over the hand, to prevent the detonator coming out of the cartridge and to prevent the wires becoming tangled; q) When tamping the boreholes, only the personnel necessary to do so shall be present; r) Only wooden tamping rods shall be used to tamp the boreholes; s) The following safety rule shall be observed for tamping boreholes: the cartridges shall be pushed firmly with the tamping rod, and never struck; t) Before connecting the detonators to the firing line, the face, roof, floor and coal seam shall be thoroughly dusted, over a distance of at least 10 metres measured from the face; u) Before the safety condition in the preceding item is met, the accumulated fine coal dust shall be cleaned off or, failing that, dampened; v) The connection made between the detonators of a face that is to be fired shall be in a series circuit; w) The free end of the first and of the last detonator shall be connected to the firing line; x) Detonators shall never be tied to grating or to metal objects, and y) It shall be verified that boreholes have at least 60 cm of solid rim between their bottom and the point of breakthrough, where blasting is carried out in crosscuts or development workings close to breaking through.

7.10 The safety measures for firing boreholes shall at least address: a) Personnel authorised by the employer shall verify that the percentage of methane gas does not exceed 0.5% in faces where explosives are used; b) Measurements shall be taken across the entire section and at a distance of 30 cm from the face, before firing; c) Where a methane gas measurement detects a concentration above 0.5%, measures shall be applied to improve ventilation of the location before giving the go-ahead to fire; d) Before firing takes place, the personnel authorised for this activity shall notify the other areas and confirm that all workers have left the location (district or ventilation circuit) where firing is to take place; e) Danger notices shall be posted or personnel assigned to guard the entrances to the areas where firing is to take place; f) The personnel authorised by the employer for the safety measure in the preceding item shall remain in a safe place, at a distance of not less than 100 metres from the face; g) Where the location is prone to sudden outbursts, the distance at which personnel shall be positioned shall not be less than 500 metres; h) Before charging for a blast or shot begins, the electrical power to the machinery and electrical installations present in the heading where firing is to take place shall be cut off; i) The maximum number of detonators of the same number or delay period shall be twelve; j) The exploders used for firing shall only be those designed by manufacturers for coal mines; k) Only one shot at a time shall be fired per heading; l) Firing at the same time in two or more locations less than 100 metres apart shall not be permitted; m) Charging and firing operations shall preferably take place in the same shift. Should a face remain charged for any reason, danger signs shall be placed at least at 3 crosscuts before the air crosscut, and unauthorised personnel shall be prevented from accessing the charged face; n) Immediately after each shot, the ends of the firing line shall be removed from the exploder and short-circuited, that is, joined together; o) The firing lines shall be disconnected and short-circuited, coiled up and stored in a safe place; p) Exploders shall be controlled by workers authorised by the employer; q) The operating condition of the fan and the ducting, as well as the results of the shot, shall be checked; r) After each shot, the workers authorised by the employer for ventilation control and for safety control shall always be the first to enter and, on doing so, shall verify that the percentages of methane gas, nitrous oxide, carbon monoxide and oxygen are within limits that do not create risks for workers or for the workplace; s) The inspection shall be carried out 30 minutes after the shot; t) Where the inspection referred to in the preceding item finds concentrations above 1.5% methane gas, danger notices shall be posted at the entrance to the face and ventilation of the location shall be improved; u) Before the charge is lifted it shall be dampened with water to prevent dust being raised, and v) The operation of dampening with water referred to in the preceding item shall be carried out as many times as necessary.

7.11 The safety measures for inspecting and treating misfired boreholes shall at least address: a) Disconnecting the firing line from the exploder and verifying that there is no continuity in the circuit; b) Where there is no continuity in the circuit, the firing lines shall be short-circuited and the worker authorised by the employer to carry out shots shall inspect the location where the shot misfired, and connect the remaining detonators to fire the shot again; c) After each shot, the cartridges and detonators from misfired boreholes shall be located and recovered, based on a safety procedure that at least specifies the tools or implements for carrying out this activity, applied by trained personnel; d) Drilling into stub holes or leftover borehole stubs (portions of boreholes left over) is prohibited; e) Stub holes shall always be washed out and carefully inspected for explosives; f) Where misfired or unexploded boreholes are identified as a result of the inspection referred to in the preceding item, they shall be fired in accordance with the firing rules; g) To extract explosives from misfired boreholes, they shall be washed out with water until there is room to place a new primer. The use of compressed air and tools that could produce sparks is prohibited, and h) Explosive material recovered from a misfired borehole (explosive or accessory) shall be fired inside a new borehole or returned to the magazine, and a record shall be kept of this.

7.12 The safety measures for equipment and instruments shall at least address: a) Drilling shall be carried out using a rotary drill, auger-type rod and bit corresponding to the diameter of the explosives to be used; b) Where drilling is carried out in sandstone, a percussion drill may be used; c) Dry drilling with percussion machinery is prohibited, and d) To check the continuity of the circuit and the resistance of the detonators, only electrical-resistance measuring instruments approved for work in coal mines shall be used.

Ventilation control in coal mines is established to reduce contaminants to levels that do not represent a risk of fire, explosion or harm to personnel and installations. For this purpose, the employer shall have ventilation systems in accordance with this Chapter, so that at least the following conditions are met: a) In the design of new mines, at least the following shall be determined: 1) Air volumes at the workplaces; 2) Cross-section of the galleries; 3) Cross-section and number of mine entries; 4) Number of galleries in the headings; 5) Maximum distances between crosscuts and galleries; 6) Type of ventilation in the mine and in the development workings; 7) Location and number of ventilation shafts during the life of the mine; 8) Specifications of the main fans; 9) Specifications of the secondary fans; 10) Specifications of the ducts to be used with the secondary fans; 11) Maximum point capacities of the cutting equipment, and 12) Degasification requirements. b) No heading shall continue its development beyond its first crosscut unless its corresponding bridge or bridges are fully completed, where these are required; c) The development of headings shall not be permitted without the seal of the second-to-last crosscut having been completed with masonry; d) A circuit shall not be permitted to operate at the expense of maintaining another circuit with percentages higher than those established; e) Mine operation shall be suspended when all operating circuits are simultaneously approaching their established maximum methane gas limits; f) For machinery, procedures shall be established to maintain its permissibility rating during operation and after maintenance, and g) Calculation records shall be kept for the determination of air volumes at the workplaces, in accordance with a procedure prepared for that purpose, taking into account the information in section 8.1.a) and the ventilation plan referred to in section 8.1.1 of this Standard.

8.1 For the ventilation system, at least the following shall be in place: a) A general ventilation plan (as provided for in 8.1.1); b) Drawings of the ventilation system (as provided for in 8.1.2); c) Safety conditions for the outside fans - main and secondary - (as provided for in 8.1.3); d) Safety measures for when methane gas concentration limits are exceeded (as provided for in 8.1.4); e) Actions to be taken in the event of a stoppage of the main fan (as provided for in 8.1.5); f) Actions for restoring ventilation to the mine (as provided for in 8.1.6); g) Procedures, instructions and other safety actions for maintenance and operating work on the main and secondary fans (as provided for in 8.1.7); h) Safety conditions for diesel combustion engines in secondary fans or generating plants (as provided for in 8.1.8); i) Safety conditions for auxiliary fans (as provided for in 8.1.9); j) Safety conditions for air-volume control (as provided for in 8.1.10); k) Safety procedures for taking measurements in the ventilation system (as provided for in 8.1.11); l) Safety requirements for ventilation works (as provided for in 8.1.12), and m) Requirements for taking measurements of the mine atmosphere (as provided for in 8.1.13).

8.1.1 The general ventilation plan shall at least contain: a) The type of ventilation to be used (development workings or long faces, as applicable); b) The characteristics of the main and secondary fans; c) The dimensions of the galleries to be developed; d) The ventilation circuits; e) Details of the location of the line and closure stoppings; f) The schedule for installing the line and closure stoppings; g) Details of the location of the ventilation bridges and the schedule for constructing them; h) The approval signature of the person in charge designated by the employer; i) The air volumes at the workplaces; j) The cross-section of the galleries; k) The cross-section and number of mine entries; l) The number of galleries in the headings; m) The maximum distances between crosscuts between galleries; n) The type of ventilation in the mine and in the development workings; m) The location and number of ventilation shafts over the life of the mine; o) The specifications of the main fans; p) The specifications of the secondary fans; q) The specifications of the ducts to be used with the secondary fans; r) The maximum point capacities of the cutting equipment, and s) The degasification requirements.

8.1.2 Drawings of the ventilation system shall at least contain: a) The ventilation circuits; b) The location of the system's equipment; c) The dimensions of the ducts; d) The layout of the dampers of the main fan, of the secondary fans and of the other elements required by the system; e) Inspection doors and bridges; f) The closure stoppings; g) The degasification chart, where applicable; h) The points of interconnection with other mines; i) The air volume of the main fan (flow rate); j) The volume and velocity of the system's air; k) The direction of flow and its circuits (clean and vitiated air); l) The location of the regulators and reading sections (points where measurement is taken); m) The location of the auxiliary fans; n) The location of the mining equipment; o) The date of the survey or of the most recent update, and p) The name and signature of the person responsible for the proper functioning of the system.

8.1.2.1 The drawings showing the ventilation circuits shall be made known to workers and posted in the designated room, on the noticeboards at the mine entrance and chairlifts, or in any other location frequently used by workers.

8.1.2.2 The drawings showing the ventilation circuits shall be updated at least every month.

8.1.2.3 The drawings shall specify progress relative to the original plan or indicate any change made. Where a change to the original design is contemplated, it shall be analysed and signed by personnel designated by the employer.

8.1.3 Safety conditions for the outside fans (main and secondary) shall at least require that: a) The electric motor of the main fan is located outside the ventilation circuit; b) The building structure is built of non-combustible materials; c) The fans have at least the following: 1) A continuous methane gas monitoring instrument in the discharge area; 2) A temperature measuring instrument on the bearings (nose and coupling); 3) A vibration measuring instrument on the bearings (nose and coupling); 4) An automatic system for cutting off power inside the mine, when methane gas percentages are equal to or greater than 1.5% at the discharge of the main fan; 5) A fan pressure measuring instrument with a continuous recorder, and 6) An audible and visible alarm to indicate stoppage of the fan. d) The following criteria are applied to activate the safety devices on the main fan and automatically suspend its operation: 1) Where the depression readings are higher than that defined in the fan's design; 2) Where the temperatures are higher than the design temperature in any of the bearings of the main or secondary fan (based on the manufacturer's specifications), and 3) Where vibrations occur that are higher than those permitted by design in any of the bearings of the main or secondary fan.

8.1.4 Safety measures shall be applied when: a) A methane gas concentration of 1.0% is reached at the working faces (development workings); b) A methane gas concentration of 1.0% is reached at the long faces (end); c) A methane gas concentration of 1.5% is reached in secondary and general return airways, and d) The methane gas concentration reaches 1.5% in mines with no electromechanical equipment.

8.1.5 The actions to be taken in the event of a stoppage of the main fan shall at least address the following: a) An order shall be given immediately for all personnel to leave the mine, in the following cases: 1) Where the main fan stops and the communication systems between the interior and exterior of the mine simultaneously fail to function; 2) Where no fan (main or secondary) is working, or 3) Where faults or breakdowns are detected in the main fan; b) A safety procedure shall be applied for cases of unscheduled stoppages of the main fan, so that the secondary fan operates, which shall at least address the following: 1) After five minutes of the main fan stopping, all personnel shall proceed to the entrance of the secondary gallery; 2) Where the stoppage of the main fan continues for 15 minutes and the secondary fan is working, all personnel shall proceed to the inner landing; 3) Where the stoppage of the main fan continues for a period equal to or greater than 30 minutes, all personnel shall leave the mine, and 4) The person in charge of ventilation and safety, or those responsible for the work area, shall go around the workplaces to make sure that all personnel have left the mine, verifying together with the lamp-room attendant that all personnel are out; c) The maintenance staff responsible shall inform at least those responsible for safety and for the shift of the cause and likely duration of the fault, so that the information can be passed on inside the mine; d) It shall be verified that the electrical power inside the mine has been cut off; e) All diesel combustion equipment operating inside the mine shall immediately suspend operation; f) For the return to normal operating conditions, the persons authorised for ventilation and safety control shall confirm that the return airways are in safe condition, and shall also confirm the functioning of the main fan and the safety conditions, so as to be able to request the restoration of electrical power inside the mine; g) Reports on changes to the operation of the main and secondary fans at the vertical shaft shall be recorded by electronic means, indicating the times and causes, and shall be retained for at least twelve months; h) Before starting up electrical equipment located beyond the air crosscuts of a gallery, in a development area that has experienced a ventilation stoppage, the covers of the electrical controls shall be opened to release the gases inside them, and the safety procedure prepared for that purpose shall be applied, taking into account the methane gas concentration levels reached and the length of the stoppage, and i) The mine shall only be permitted to be left without ventilation for a maximum time of five minutes, which is sufficient time for the internal combustion engine of the secondary fan to start. Should the specified time be exceeded, the measure in item a) of this section shall be applied.

8.1.6 The actions for restoring ventilation to the mine, where both fans have stopped working, shall be carried out by the ventilation person in charge of the mine's shift designated by the employer, and shall address at least the following: a) When ventilation of the mine is started, it shall be done using the main fan, in such a way that the methane gas percentage is less than or equal to 1.5% at the discharge; b) Opening the airlocks or explosion doors to allow outside air to enter to dilute the mixture passing through the fan; c) Continuously measuring the methane gas percentage at the fan discharge to keep the mixture at 1.5% methane gas or less; d) Gradually closing the airlocks as the methane gas percentage decreases until they close completely, ensuring that the methane gas percentage is 1.5% or less, and e) Verifying, at the ventilation discharge of each circuit, that the methane gas percentage does not exceed 1.5%, before proceeding to restore electrical power to the interior.

8.1.7 Maintenance of the main and secondary fans shall include at least the following: a) Safety procedures that include at least: 1) A list of the tools and spare parts to be used, and 2) An instruction to check that all materials and tools have been collected after completing activities inside the fan mechanisms; b) Instructions for recording vibration readings, bearing temperature, electric motor current and fan depression according to the design, and c) Monthly inspections of: 1) The electrical substation; 2) The controls and electric motor; 3) The blades and fasteners; 4) The transmission system; 5) The lubrication system, and 6) The doors and airlocks.

8.1.7.1 The fan area shall have instructions indicating the actions to be taken by the fan operator in the event of an unforeseen stoppage of the main fan.

8.1.7.2 During maintenance activities, protective handrails at least 90 cm high shall be placed at all access points to the collar of the vertical shaft, when work is carried out near it.

8.1.7.3 The areas of the main fans shall be enclosed by a fence, with their access doors locked with a padlock.

8.1.7.4 The general air-extraction shaft shall not be used to take personnel or materials into the mine. In emergencies, it may only be used for personnel to exit, using the resources available, such as: mobile cranes, hoist, tractor, among others.

8.1.7.5 A written or electronic record of the equipment's operation shall be kept, noting observations and readings of vibrations, bearing temperatures, motor amperage and depression (suction pressure). All these parameters in accordance with the equipment's design. In addition, the operator shall verbally inform the incoming shift of the condition of the fans.

8.1.7.6 A written or electronic record shall be kept of the methane gas (CH4) and carbon monoxide (CO) values, remotely monitored from an outside console or computer connected to the measuring instruments.

8.1.7.7 Belt dressing shall not be applied to moving transmission belts.

8.1.8 The safety conditions for diesel combustion engines in secondary fans or generating plants shall specify at least: a) The diesel engine shall be run at least once a day, for a period of 15 minutes, to check that it is functioning correctly, and any variation or fault shall be reported to the relevant area; b) An automatic recharging system shall be available for the batteries, and c) The diesel tank shall: 1) Be located outside the mine; 2) Have sufficient capacity to run the combustion engine for at least eight continuous hours; 3) Have a fuel-level indicator, and its capacity shall not be exceeded by more than 90%; 4) Have a containment bund for spills; 5) Be connected to a physical earthing system; 6) Have a cable with a clamp (alligator type), connected to a physical earth, for filling operations; 7) Have signage for hazard identification, and indicate its capacity either on a label or on the body of the container; 8) Have a safety data sheet; 9) Have a flame arrester valve, and 10) Have an extinguisher of at least 9 kg of ABC-type dry chemical powder, for the purpose of tackling any incipient fire.

8.1.9 Auxiliary fans with an exhausting or forcing function, powered electrically (optionally pneumatically or hydraulically), shall at least meet the following safety conditions: a) Motors and connection boxes shall be explosion-proof; b) The cables feeding the motor shall be in clean air; c) Fans shall have a mesh guard at the air inlet to prevent any object from damaging their components; d) The bases of the fans shall be metallic; e) Auxiliary fans shall be installed so that there is no recirculation of air; f) Ventilation ducts shall be made of antistatic and flame-retardant or self-extinguishing materials: g) Ducts shall be properly assembled to prevent leaks; h) Ducts shall be arranged so that the air current always reaches the end of the face; i) Exhausting fans shall have a continuous methane gas monitor that suspends the fan's operation on measuring percentages above 1.0%; j) When the auxiliary fan stops operating, electrical power to all equipment located beyond the air crosscut shall be automatically cut off; k) Auxiliary fans shall have a control independent of the other equipment; l) Any change to the position of the auxiliary fan's blades shall be approved and authorised by the person in charge of the ventilation area; m) The fan's metal structure shall be earthed; n) When operation of the auxiliary fans is suspended, all personnel shall be withdrawn to at least the ventilation crosscut; o) To bring the auxiliary fans into operation, a procedure shall be applied containing at least the following: 1) Evacuating all workers before the ventilation crosscut; 2) Checking that the methane gas percentage in the return circuit of the development working does not exceed 1.5% for forcing ventilation and 1.0% for exhausting ventilation, and 3) All activities carried out to bring the auxiliary fans into operation shall be directly supervised by the person in charge of ventilation or the supervisor responsible for the area; p) The maximum distance between crosscuts or diagonals shall be 70 metres. For distances greater than 70 metres, this shall be determined by the ventilation capacity of the fans, the dilution of methane gas at the working face, and the support capacity of the type of timbering used in developing the gallery, without exceeding 200 metres; q) For galleries consisting of a single working, the fans shall supply air to the working faces to keep methane gas percentages below 1.0%, without prejudice to compliance with the other safety conditions established in this Standard, and r) When operation of the auxiliary fans in galleries consisting of a single working is suspended, where the ventilation crosscuts are more than 200 metres apart, the gallery shall be evacuated.

8.1.10 The safety conditions to be observed during air-volume control shall include at least:

8.1.10.1 Air volumes supplied inside coal mines, for diluting contaminants, controlling temperature and meeting workers' respiratory needs, shall comply with the following: a) The minimum quantity of air required for the activity shall be calculated on the basis of the largest shift, at a rate of three cubic metres per minute for each worker, and six cubic metres per minute for each brake HP (where diesel equipment is operated) and for mules or other draught animals; b) A methane gas content of 1.5% in the returns from headings in operation shall be measured at the crosscut before the operating face; c) The methane gas content in the air shall not exceed 1.0% at the working faces, measured one metre from the face end and 30 cm from the roof, and the sensor placed at this position shall cut off electrical power to the cutting machine and to the conveyors on reaching that limit. In the case of secondary and general return airways. The methane gas content shall not exceed 1.5%, and d) The ventilation system shall be divided into as many independent circuits as there are working areas established in the mine.

8.1.10.2 The minimum air velocity at workplaces shall be 0.5 metres per second, and the maximum air velocity shall in no case exceed 8.0 metres per second, except in vertical shafts and in locations not used by personnel.

8.1.10.3 Air volumes at the working faces shall be established to maintain a methane gas percentage below 1.0%.

8.1.10.4 All workings that reach their limit or are abandoned shall have a ventilation crosscut at their respective ends.

8.1.10.5 Where a ventilation circuit is detected with 1.5% methane gas or more, the appropriate measures shall be applied to restore normal conditions, without putting another circuit in the same condition.

8.1.10.6 The temperature inside the mine shall be maintained between 10 and 37 ºC, and the relative humidity between 20 and 95%, except at the mine entrances.

8.1.10.7 Any modification to the ventilation circuits shall be reviewed and approved by the person in charge of ventilation, and shall be made known to all personnel involved in the modification.

8.1.10.8 Electrical power shall be suspended to all areas that are affected when a modification is made to the ventilation circuits.

8.1.10.9 Any unforeseen change in ventilation, for any reason, shall be notified immediately to the area responsible for safety/ventilation.

8.1.10.10 To carry out work in “bell cavities”, the person in charge of ventilation shall use mine canvas or another air-movement system, to dilute the accumulated gas and reduce it to levels below 1.0%.

8.1.10.11 The direct use of compressed air for diluting methane gas is prohibited, except when used in auxiliary ventilation equipment, such as fans, air horns or nozzles.

8.1.10.12 To ensure the distribution of air inside the mine, the doors of the stoppings, elbows, ducts and other ventilation installations shall be kept in good condition.

8.1.10.13 All inspection access points for ventilation shall have two doors, to prevent opening one of them from causing a short circuit in the ventilation.

8.1.10.14 The materials used for managing ventilation in permanent stoppings shall be self-extinguishing, and the line and closure stoppings shall have non-combustible properties.

8.1.10.15 Ventilation shall be controlled by means of stoppings, doors and variable-area regulators.

8.1.10.16 All mined-out areas shall be sealed with stoppings resistant to ground pressure, made of non-combustible materials, based on 0.84 kg/cm2 sustained for 250 milliseconds.

8.1.10.17 Closure stoppings shall have devices for sampling gases from inside the mined-out area.

8.1.10.18 At the working faces, ventilation ducts shall be kept at distances such that the requirements of this Official Mexican Standard for controlling methane gas concentrations are met.

8.1.10.19 The ducts carrying air from the auxiliary fan shall not be regulated by placing loose objects in them, such as wood, canvas or belting.

8.1.10.20 The design and manufacture of the ducts shall have approvals for use in coal mines, offering antistatic, flame-retardant or self-extinguishing properties.

8.1.11 The safety procedures for taking measurements in the ventilation system shall take into account the actions to be carried out based on the results previously obtained, to correct earlier errors and prevent them from recurring. Such procedures shall at least address the following:

8.1.11.1 Measurements of all the mine's ventilation circuits shall be taken at least once a week.

8.1.11.2 At least the following data from the measurements referred to in the preceding item shall be recorded: a) Location and its area in m2; b) Volume; c) Velocity; d) Temperature; e) Relative humidity; f) % O2; g) % methane gas, and h) Gas emission in litres per second. The measurement data shall be signed by the person in charge of ventilation.

8.1.11.3 The minimum acceptable quantity of oxygen at any location where personnel are present shall be 19.5%.

8.1.11.4 Measurements at working faces in operation shall be taken every shift, and their results recorded in logbooks or by electronic means.

8.1.11.5 Ventilation measurement readings shall be taken and recorded in logbooks or by electronic means by the person in charge of the mine's ventilation, at least at: a) The development galleries; b) The long faces; c) The general headings; d) The air intake through the gallery or galleries; e) The air outlet through the return airways, and f) The areas considered necessary for identifying leaks.

8.1.11.6 For ventilation measurement, the location or section where the readings will be taken shall be prepared as follows: a) Select a location with a regular cross-section, free of nearby obstacles, and mark it with a label, leaving space to record the area value; b) Prepare the chosen section by boarding up the gaps between ribs and props, and between the timbering and the roof, to maintain a regular area; c) Take three readings to measure air velocities, each lasting one minute, each of which shall cover the entire section being measured; d) Apply the corresponding correction factor, and e) Average the readings, and the result shall be considered the actual velocity.

8.1.11.7 Where abnormalities are detected in air volumes, the cause shall be identified and corrected immediately, and the actions taken to restore normal conditions and, where applicable, prevent recurrence shall be recorded.

8.1.11.8 The recorded data shall be transcribed onto the ventilation drawing, which shall be updated monthly, or sooner if significant changes are made to the ventilation circuits;

8.1.11.9 After each equipment advance in development workings and before bringing the auxiliary fans into operation, or when the installation of another auxiliary fan is required, readings of the effective air volume shall be taken before the air crosscut, to prevent the possibility of recirculation by the fans.

8.1.11.10 Ventilation circuits in development workings shall have a surplus volume for ventilating the auxiliary fans.

8.1.12 The safety requirements for ventilation works shall at least address the following:

8.1.12.1 Permanent stoppings at the crosscuts separating the clean-air intakes from the vitiated-air returns shall be built of non-combustible materials, such as concrete, stone, block or brick and, where applicable, plastered to prevent air leaks, with sufficient strength to withstand pressures. The strength of the stoppings shall be estimated on the basis of a local rock-mechanics design study.

8.1.12.2 During the development of main or secondary headings, permanent stoppings shall be built in such a way that no more than one temporary stopping exists between the last of them and the end of the faces.

8.1.12.3 Stoppings shall be built at least every 200 metres (or more frequently if the needs of the mine so require), with inspection doors at the crosscuts between the intake and return air galleries. Stoppings shall be built in pairs, to prevent short-circuiting of the air while the inspection doors are in use.

8.1.12.4 Every mined-out area shall be isolated immediately after equipment recovery, by means of permanent closure stoppings that meet the following: a) Keyways shall be excavated wide enough to reach unweathered ground; b) Stoppings shall be built of reinforced concrete or solid block, at least one metre thick; c) The stopping built shall be protected against ground pressure by placing timber cribs on both sides. On the side of the active gallery, sufficient space shall be left between the cribs and the ribs to allow free access for the workers responsible for inspecting or repairing these stoppings; d) Pipes shall be provided to allow gas sampling, and e) Pipework of appropriate diameter shall be installed for drainage where necessary.

8.1.12.5 Every permanent closure stopping shall be plastered, paying particular attention to the joints around its perimeter.

8.1.12.6 Temporary stoppings in development areas shall be built as follows: a) Select the appropriate location for excavating the keyways; b) Build two in series to form airlocks, with self-closing doors, and c) Where the stopping is made of timber, it shall be covered with mine canvas, chinked and plastered to seal it and control the air.

8.1.12.7 Regulators for controlling each ventilation circuit shall be built as follows: a) Select an appropriate location for excavating the keyways; b) Always build two in series so that their location is between two consecutive crosscuts of the gallery; c) Air-circuit regulators that operate for more than two months shall be built of non-combustible material, and d) Air-circuit regulators used for a period of less than two months may be built of timber, lined with mine canvas, chinked and, where applicable, plastered.

8.1.12.8 Curtains shall not be used in locations where doors are required.

8.1.12.9 Degasification frames shall be built of non-combustible material.

8.1.12.10 Bridges for conducting air shall be built of non-combustible materials and with the cross-section calculated in the ventilation plan.

8.1.12.11 The mine's galleries shall be kept clean and free of obstacles that impede the free circulation of air, so as to maintain the cross-sectional area appropriate for efficient ventilation.

8.1.12.12 Operation of continuous miners in development workings and of cutting machines on the long face shall be stopped when a methane gas percentage of 1.0% is reached in the air.

8.1.12.13 Personnel shall not be permitted to be exposed in locations where carbon monoxide concentrations exceed 50 parts per million (ppm).

8.1.13 The requirements for taking measurements of the mine atmosphere shall at least address the following:

8.2.13.1 Operation of the equipment for breaking coal at the working faces shall only begin once the atmospheric conditions have been confirmed by the personnel in charge of ventilation or the person responsible for the location on that shift.

8.2.13.2 Methane gas concentration measurements shall invariably be taken at the start, during and at the end of each shift at all working faces, using portable methanometers.

8.2.13.3 On diesel- or battery-powered machinery and on coal-breaking machinery, methane gas concentration measurements shall be taken continuously using fixed methanometers installed and connected on the machinery, with sensors that only authorised personnel may operate for maintenance or adjustment, and with devices that automatically suspend operation on detecting methane gas concentrations equal to or greater than the permissible level (1%).

8.2.13.4 To take measurements of the mine atmosphere, instruments approved for use in coal mines shall be available, capable of determining the values of the atmospheric conditions.

8.2.13.5 Written procedures shall be available for operating the instruments and taking measurements of the mine atmosphere.

8.2.13.6 Air volume shall be measured using an anemometer that determines air velocity. If it is electronic, it shall be intrinsically safe with respect to methane gas.

8.2.13.7 To determine methane gas, an instrument shall be used that can record the percentage by volume of methane gas in the air, preferably over a range of 0-5%.

8.2.13.8 Instruments for recording oxygen shall preferably measure over a range of at least 0-25%, those for carbon monoxide over a range of 0-100 ppm, and those for hydrogen sulphide over a range of 0-100 ppm.

9.1 Drawings of the mining operations shall be available, showing the identification and location of at least: transformers, switches, electrical controls, distribution cells, pumps, battery chargers, and telephone and communications electrical circuits. Emergency generators shall be located outside the mines.

9.1.1 The electrical installation drawings shall meet the following conditions: a) Be in the Spanish language and specify the capacity of at least the transformers, battery chargers and circuit protection devices; b) Be updated monthly and whenever there are changes or new installations in the distribution of electrical power; c) Bear the name and signature of the persons in charge of the maintenance, safety and operation area; d) Be kept for a period of at least two months in document form and twelve months in electronic records, and e) Be available at the substations and control rooms for consultation by workers.

9.2 An up-to-date single-line diagram of the electrical installations shall be available, containing at least: a) The general load schedule; b) The type of connections in the primary and secondary windings of each transformer; c) The number of phases; d) The cable lengths between circuit elements; e) The gauges of the conductors, including earthing conductors, in mm2 or MCM (circular mil x103); f) The voltages of the primary and secondary windings of the transformers; g) The impedances and rated characteristics in kV or MVA of the transformers; h) The currents of the circuit breakers (branch-circuit protection); i) The emergency generating plants (located outside); j) The metering centres (located outside); k) The load centres or panels (located outside); l) The transfer switches (located outside); m) The signature of the person in charge of the maintenance area; n) The earth-fault detection devices or systems, and o) The design calculation record with the characteristics of the electrical equipment to be used in the electrical installations inside and outside the mine, and the calculations supporting the conductor gauge to be used, the capacity of the protection devices, the phase balancing, the circuit capacity, and the overload and short-circuit protection.

9.2.1 The single-line diagram shall: a) Be updated monthly or whenever there are new installations or changes to the distribution of electrical power; b) Bear the name and signature of the persons in charge of the maintenance area; c) Be kept for a period of at least two months in document form and twelve months in electronic records, and d) Be available at the substations and control rooms for consultation by workers.

9.3 An electrical engineer shall be available or, where applicable, the employer shall designate personnel trained in low- and high-voltage electrical installations for underground coal mines.

9.3.1 The electrician or the designated person shall have the following functions:

9.3.1.1 To coordinate the planning, design, installation and modification of the electrical installations, and to carry out tests on the equipment installed and to be installed in the underground coal mine.

9.3.1.2 To prepare an up-to-date list of all the electrical equipment operating at the working faces, including that which is out of operation.

9.3.1.3 To have safety procedures for carrying out activities involving the connection and disconnection of electrical circuits; the splicing of conductors; the extension of branch circuits; the maintenance of electrical equipment and installations, and all activities related to the use and handling of electrical power inside and outside underground coal mines.

9.3.1.4 To prepare and oversee execution of the annual programmes for: a) Maintenance of electrical equipment and electrical installations, and b) Inspection of electrical equipment and material in accordance with the manufacturer's specifications, to verify that they remain, as applicable, “explosion-proof”, “intrinsically safe” or “flameproof”, and to prepare the corresponding report, keeping the documentary evidence of the most recent inspection.

9.3.1.5 To assess the technical competence of the workers who carry out activities involving the connection and disconnection of electrical circuits; the splicing of conductors, and the extension of branch circuits for the maintenance of electrical equipment and installations.

9.3.1.6 To select the electrical equipment to be used in the electrical installations of underground coal mines, including the types of overload protection and power cut-off for each and every branch circuit.

9.3.1.7 To update, at least once a month, the drawings of the mining operations showing the identification and location of electrical equipment and installations.

9.3.1.8 To provide the approval of the person in charge of safety for any equipment coming from the workshop after repair and scheduled to be installed inside the mine. To keep documentary evidence of the most recent repair.

9.4 Safety conditions.

9.4.1 An up-to-date list, updated at least once a month, shall be available of all the electrical equipment operating at the working faces, including that not in use. Prohibitions:

9.4.2 Telephone and communications cables shall not be introduced into mines through the same boreholes used to introduce the cables of the power electrical circuits.

9.4.3 Batteries and diesel engines shall not be used beyond the last air crosscut, except in an emergency and with the prior authorisation of the safety department, in accordance with a procedure established for that purpose.

9.4.4 No person shall work on energised electrical circuits in locations inside the mine where explosives, or flammable or combustible substances, are used or handled.

9.4.5 Only authorised personnel may enter the areas where the substation or transformers are located and modify the operation of apparatus or equipment in those locations.

9.4.6 Workers shall not be permitted to carry out inspection or maintenance activities on energised equipment.

9.4.7 Gaskets of any type shall not be used at electrical control joints, except between metal and glass parts. In such cases, the gaskets shall be metal-clad and mechanically bonded to the glass. For the earthing system:

9.4.8 Mining installations shall have, outside the underground coal mines, an earthing system for discharging the fault currents of the underground electrical network.

9.4.9 Mining installations shall have, inside underground coal mines, an earthing system to discharge the static electricity generated by the processes and to discharge the currents generated by insulation faults or other types of electrical faults that need to be drained to prevent electrical risks to workers, fire risks or explosion risks. For equipment:

9.4.10 Electrical equipment (switches, power controls, motors, distribution cells and electric-motor pumps, among others) used in the electrical installations of underground coal mines shall have the corresponding certifications confirming that it is explosion-proof, in accordance with the provisions of the Official Mexican Standards or Mexican Standards issued for that purpose by the Ministry of Energy. Where no Official Mexican Standards or Mexican Standards exist, the employer shall have manufacturers' documents guaranteeing that the equipment is explosion-proof.

9.4.11 Electrical equipment, materials and overcurrent or short-circuit protection devices shall be suitable for the voltages of the supply lines of each branch circuit in which they are installed.

9.4.12 Electrical equipment such as transformers, cells, controls and switches used in underground coal mines shall bear identification on the equipment itself, painted on or by means of self-adhesive labels, indicating its electrical characteristics, at least the operating voltage, as well as the circuit or equipment it supplies.

9.4.13 Transformers used in underground coal mines shall have physical guards preventing unauthorised workers from coming into contact with the casing and external operating levers.

9.4.14 Devices shall be provided to cut off power to the entire electrical installation of the mine, and devices to cut off power for each of the branch circuits.

9.4.15 Mechanised equipment for breaking coal shall have methane gas monitoring devices and electrical power cut-off devices, for when the monitored methane gas concentration level is 1% or more.

9.4.16 At the flat contact joints of explosion-proof equipment, the parts shall be machined so that, once bolted together, it is not possible to insert a feeler gauge beyond the limit set out in the manufacturer's specifications. Flat joints with damaged surfaces shall be withdrawn from operation.

9.4.17 Where joints are made by means of explosion-proof threaded connections, at least the number of threads specified by the manufacturer shall be in direct contact for the joint to be accepted.

9.4.18 All electrical equipment inside the mine supplied by cables shall have cable glands in a condition that allows them to retain their design characteristics (for example: not broken, loose, deformed, or detached, among others), gasketed and secured to the base of the equipment with a complete set of fasteners, and sized (internal diameter) to match the size of the electrical cable (external diameter), so that the compartment retains its flameproof or explosion-proof properties. For motors:

9.4.19 Electric motors on remotely controlled equipment shall have emergency stops with mechanical interlocks, located next to the equipment itself and within reach of workers.

9.4.20 Electric motors installed inside the mine shall meet the following: a) The connections of the electrical cables shall have a cable gland suited to the characteristics of the cable diameter; b) The device for monitoring the continuity of the electrical cable shall be placed in the motor's connection box; c) A cooling system shall be provided; d) Motor connection boxes shall be protected against moisture, falling materials and operating movements of the machines; e) The starting and stopping circuit or circuits for the motors shall be located in the same area as the motors, and f) The area surrounding the electric motors shall be kept clean and tidy. For portable equipment:

9.4.21 Portable electrical equipment used with supply potentials of 440 volts or higher shall have automatic power cut-off systems in the event of an earth fault.

9.4.22 Electrical equipment installed in the underground coal mine shall have protection against overload, short circuit, earth fault and phase loss. The types of protection for each item of equipment shall be as indicated in the design calculation record for the single-line diagram. For electrical transformer substations:

9.4.23 Electrical transformer substations installed inside underground coal mines shall: a) Be located more than 100 metres from any quantity of explosives kept ready for immediate use; b) Have at least one 9 kg extinguisher of ABC-type dry chemical powder or its equivalent; c) Be located in ventilated areas; d) Be connected to an earthing system, and e) Have protective handrails at least 90 cm high, to prevent the passage of personnel, equipment or materials.

9.4.24 Transformers used in underground coal mines shall be designed and approved for use inside underground mines and shall be explosion-proof. The use of transformers with oil-based cooling systems is prohibited.

9.4.25 Transformers installed in underground coal mines shall be located in ventilated areas so that the heat they give off is dissipated.

9.4.26 Distribution transformers shall permanently have automatic insulation monitoring devices that disconnect the electrical power supply when they detect insulation defects.

9.4.27 Each transformer shall have an earth connection that meets the following: a) Have a resistance equal to or less than ten ohms, and b) Be made of copper, with a cross-sectional area of at least 40 mm2. For machinery:

9.4.28 Mobile or portable electrically powered machinery shall meet the following: a) Its supply cables shall: 1) Be of the flexible type; 2) Be of heavy-duty type; 3) Be securely attached to the machinery to prevent their terminals being damaged or accidentally disconnected; 4) Be positioned so that they are not mechanically stressed; 5) Be placed on supports to prevent them getting wet, and 6) Be kept on supports designed for that purpose where additional extensions are used; b) Electrical controls supplying machinery at 440 volts or more shall be installed on metal frames located in the galleries of the working faces; c) Junction boxes shall be hung securely and not exposed to impacts or water; d) Supply outlets of any voltage level shall not be located on headframes, at stations or hatches, or along shafts; e) In locations where electrical equipment or accessories are located, the possibility of increased explosivity from suspended coal particles shall be controlled through the application of inert dust; f) Devices shall be provided to cut off electrical power at workplaces where maintenance, operation or testing of electrical equipment is carried out, when methane gas concentrations reach 1%, and g) The use of equipment drawing its supply from bare (trolley) cables is prohibited. For electrical power distribution cables:

9.4.29 Cables used in underground coal mines shall be designed for use in this type of mine, with flame-retardant or self-extinguishing insulation, and shall meet the electrical characteristics indicated in the design calculation record attached to the single-line diagrams.

9.4.30 Electrical cables used to connect portable electrical equipment shall be of the flexible type, with flame-resistant insulation and of a gauge suitable to prevent overheating from electrical load.

9.4.31 The insulation of electrical cables installed in mines shall be of the flame-retardant or self-extinguishing type.

9.4.32 Electrical cables used in underground coal mines shall: a) Have protective elements such as: shielding per phase, pilot conductors and earth connections; b) Be protected from moisture and kept away from contact with water pipework; c) Be kept separate from compressed-air pipework and communication lines, and d) Be installed so that they are not subject to abnormal tension.

9.4.33 Electrical cables in underground coal mines shall be supported so that they do not rest on the floor of the underground mine. Those installed in shafts or inclined boreholes, where the conductors or sheaths cannot support their own weight, shall have supports capable of bearing their weight at intervals not exceeding 10 metres.

9.4.34 Cable splices inside the mine shall only be permitted to be made through explosion-proof connection boxes or boxes filled with dielectric resin, as well as splices approved for cold jointing. The connection boxes for splices shall be indicated on the single-line diagram.

9.4.35 Flexible cables used on hand-held or portable devices shall be multi-strand and shall have an earthing conductor with a cross-sectional area appropriate to the power they carry, and a pilot conductor.

9.4.36 The cables of electrical installations that are out of use shall have their ends wrapped with insulating tape. For telephony and communications:

9.4.37 Telephone and communication systems shall be of the intrinsically safe type.

9.4.38 Telephone and communications electrical circuits inside coal mines shall not be installed on the same side (same wall) as the conductors of the power electrical circuits.

9.4.39 All parts of the electrical network of the underground coal mine shall be effectively insulated from a physical earth, except for the equipment structures and earthing conductors. The electrical resistance of the earthing system shall be equal to or less than 10 ohms.

9.4.40 Measurements of earthing resistance shall be taken every six months and whenever changes or new installations are made, and recorded in a logbook or in electronic records. Records of the earthing resistance measurements shall be kept for at least twelve months. Where the measured resistance exceeds 10 ohms, extraordinary maintenance activities shall be carried out to bring the resistance to a value equal to or less than 10 ohms.

9.4.41 All conductors of the earthing network inside underground coal mines shall be positioned so that personnel do not come into contact with them. Safety signage:

9.4.42 Equipment such as transformers, motors, controls, switches and electrical power cables that are out of use shall bear signs indicating that they are out of service.

9.4.43 Electrical equipment, such as transformers, controls and switches used in underground coal mines, shall bear safety signs indicating, while in operation, that they are energised, for example by means of a presence lamp, voltage dial indicators or a notice.

9.4.44 Electrical equipment such as transformers and cells used in underground coal mines shall bear safety signs restricting unauthorised personnel from the areas where they are located.

9.4.45 At the entrance to the areas where substations or transformers are located, signs shall be posted prohibiting access to unauthorised persons. The signs used shall comply with the provisions of NOM-026-STPS-1998. Safety procedures:

9.4.46 Safety procedures shall be available for: a) The installation of conductors and electrical equipment; b) The splicing or connection of cables; c) The inspection of electrical installations, including checking that the branch-circuit protection devices are in good condition; d) The discharge of residual voltages from installed equipment; e) The verification of electrical continuity and measurement of the resistance of earthing conductors; f) The placing of safety tags and padlocks, and g) The measurement of cable insulation resistance.

9.4.47 The safety procedures shall at least contain: a) Instructions for applying safety measures; b) The sequence of actions personnel shall carry out for the activity; c) The type of tools, instruments or equipment to be used; d) The personal protective equipment that the worker shall wear, where applicable, and e) Instructions for acting in the event of an emergency.

9.4.48 Electrical equipment, such as transformers, used in underground coal mines shall have annual maintenance programmes that at least include: activity, start and completion date, frequency, person responsible, safety measures, and the procedure for placing safety tags and padlocks.

9.4.49 The results of the maintenance programmes shall be recorded in logbooks or by electronic means and kept for at least twelve months. The records shall contain at least the following information: a) The date on which the activity is scheduled; b) The date on which the activity is carried out; c) The name of the person carrying out the activity; d) The type of activity carried out, and e) The results of the activity carried out.

10.1 Welding and cutting activities are only permitted inside underground coal mines for equipment or machinery used for cutting or breaking coal, provided the following are complied with: a) It is not possible to move the equipment, machinery, or its parts or components, to the surface, owing to their dimensions, weight or the distance to be travelled; b) The risk analysis specified in section 10.6 of this Standard is available; c) The safety measures are implemented in the clean-air area, and d) The authorisation of the person in charge of safety is held. Where the result of the risk analysis is not favourable, welding and cutting shall be carried out outside the mine.

10.2 The use of liquefied petroleum gas for welding and cutting activities is prohibited, both inside and outside underground coal mines.

10.3 On long faces, welding and cutting activities are only permitted where clean air is present.

10.4 Where the main fan stops, all welding and cutting work using electrical and oxy-acetylene equipment, anywhere in the mine, shall be suspended and water applied to the hot parts.

10.5 Welding and cutting work is prohibited in return-air areas and beyond the last air crosscut in the gallery development area.

10.6 To carry out welding and cutting activities, a risk analysis of the specific activity to be carried out shall be available, to be used to establish preventive measures before, during and after it is carried out. The risk analysis shall contain at least the following: a) The characteristics of the welding or cutting equipment or machinery to be used; b) A list of the materials, elements and alloys used as base material and, where applicable, filler material for welding and cutting; c) A list of all the hazardous factors or agents and conditions that could affect the safety of the activity, of personnel and of the mine during welding and cutting operations, such as: 1) The methane gas concentrations at the location where the activities are to be carried out; 2) The quantity of coal dust present, both on the floor and in the atmosphere, at the location where the activities are to be carried out; 3) The fumes and gases from electric arcs and flames; 4) The radiation (infrared, ultraviolet and bright light, among others) from the high temperatures of flames and electric arcs; 5) The noise produced by flames and electric arcs; 6) Electric shocks, and 7) Splashes and sparks; d) The risk control measures to minimise or eliminate the risk, and e) The type of mandatory personal protective equipment workers shall use. Personal protective equipment shall be selected in accordance with the provisions of Official Mexican Standard NOM-017-STPS-2001.

10.7 Workers who are to carry out welding and cutting activities inside underground coal mines shall hold the written authorisation of the person in charge of safety of the mine, for which they shall: a) Complete the authorisation form; b) Obtain the corresponding authorisations; c) Attach to the form the results and recommendations of the risk analysis, and d) Deliver copies bearing all the signatures to the persons responsible for authorising it. The authorisation shall include copies for all those who sign it. The worker's copy shall be placed in a visible location while the work is being carried out, and the copy held by the person responsible for the authorisation shall be kept by the employer for at least one year.

10.8 Before starting the activity, the person responsible for safety in the mine, the person in charge of the activity, the safety and hygiene committee, and the operation and maintenance supervisors for the site, shall verify that all the applicable conditions are met and record this on a checklist.

10.9 The area where welding and cutting activities are carried out shall have: a) A first-aid kit including dressing materials for burns from slag splashes, cuts, bruises, blows and any others determined from the risk analysis; b) A first-aid manual and, where applicable, a rescue operations manual; c) One 9 kg extinguisher, or two (at least) 6 kg extinguishers, of ABC-type dry chemical powder. The extinguishers shall comply with the provisions of NOM-002-STPS-2000, and d) A portable methanometer or a continuous monitoring device, or both.

10.10 Safety procedures shall be available for carrying out welding and cutting activities inside underground coal mines, containing at least the following: a) The methane gas content shall not exceed 0.5% by volume. This entails assessing the area before and during the activity, in accordance with the procedures established for that purpose; b) The area where welding and cutting activities are to be carried out shall have signs prohibiting access by unauthorised persons. The signage shall comply with the provisions of NOM-026-STPS-1998; c) The area where welding and cutting activities are to be carried out shall have the floor, roof and walls wetted down with water; d) The area where the welding and cutting activity is to be carried out shall be covered with inert dust over a minimum radius of 10 metres from the site of the activity; e) The floor of the welding and cutting worksite shall be covered with a thick layer of inert dust, to prevent molten metal from coming into contact with coal dust; f) The area where the activity is to be carried out shall have a reserve of at least 250 kg of inert dust; g) The area where welding and cutting activity is to be carried out shall have a hydrant with a hose; h) In the area where welding and cutting work is to be carried out, the equipment shall be given a general clean, removing any material no longer in use and coal dust; i) Machinery, equipment or installations to be repaired shall be cleaned beforehand to remove accumulated coal dust or grease; j) There shall be no open deposits of lubricants or flammable substances near the activity, at a distance of at least 10 metres, and k) In the working area or district of the mine where welding and cutting activity is carried out, activities shall be suspended and personnel evacuated from that area or district, with only one representative from the safety and ventilation area, one from the area responsible for maintenance, and at least one representative of the safety and hygiene committee remaining, who shall supervise the activity and remain at the site for at least 30 minutes after it is completed, to verify that no risks remain from that activity.

10.11 On completion or cancellation of the activity, the authorised worker, under the supervision of the person in charge of the activity and the safety and hygiene committee, shall: a) Thoroughly wet down the area with water; b) Move the welding machine and cutting equipment out of the mine; c) Obtain the authorising signatures, and d) Forward copies to the persons responsible for the authorisation.

10.12 The person in charge of safety of the mine shall analyse the results of the activity and determine whether the conditions, procedures and recommendations provide sufficient safety for workers and, where applicable, propose modifications to the employer.

10.13 Before and during welding and cutting activity: a) The work area shall be monitored to confirm that there are no methane gas concentrations equal to or greater than 0.5%; b) It shall be supervised that permanent ventilation is provided; c) It shall be supervised, during the work, that the heat generated by the flame, as well as sparks or molten metal, are not transmitted to other areas or materials, cooling them as many times as necessary, and d) An insulation test shall be carried out on the electrical circuit supplying the welding machine. This item only applies before the welding machine is energised.

10.14 Before taking the equipment, machinery, accessories and materials to be used in welding and cutting activities down into the coal mine, the person responsible for safety of the mine, the person in charge of the activity, and the worker responsible, shall check that such equipment has the safety features indicated in the manufacturer's manuals.

10.15 Only the equipment, machinery, materials and substances required to carry out the specific welding and cutting activity shall be present inside the mines. On completion of the activities, they shall be removed and returned to the surface of the mine.

10.16 Storing welding and cutting equipment inside the mine is prohibited.

10.16.1 For the handling of compressed gas cylinders, the following shall be complied with: a) They shall be secured while being handled, to prevent them falling or coming into violent contact with each other; b) They shall be kept upright at all times while in use; c) They shall be protected against mechanical hazards such as cuts or abrasions; d) Gases shall not be mixed in cylinders, nor shall cylinders be used for purposes other than those intended by the supplier; e) Cylinders to be taken down into the mine shall bear a label identifying the gas they contain; f) All acetylene cylinders used inside the mine shall have the safety valve fitted at the top; g) Cylinders shall have their safety cap fitted; h) Where a fuel-gas cylinder is found to be dented or leaking, the following shall be carried out: 1) closing the valve; 2) taking the cylinder to a ventilated location, away from any source of ignition; 3) temporarily blocking the gas leak from the cylinder, where possible; 4) taking the cylinder out of service immediately; 5) marking or labelling it with the wording “leaking cylinder”, and 6) notifying the supplier immediately for its return; i) Where a leak occurs at a fusible plug or other safety device, the following shall be carried out: 1) taking the cylinder to a ventilated location away from any source of ignition; 2) opening the cylinder valve fully and allowing the fuel gas to escape slowly; 3) a supervisor remaining in the area until the pressure in the cylinder has been released, to make sure that no fire occurs; 4) taking the cylinder out of service immediately; 5) marking or labelling it with the wording “leaking cylinder”, and 6) notifying the supplier immediately for its return.

10.16.2 For the handling and operation of valves, instructions shall be available so that: a) They are not opened near sparks, open flame or other sources of ignition; b) It is verified that the regulator threads or connection correspond to those of the valve outlet, and mismatched connections are not forced; c) Oil or grease are not used as lubricants on the valves and accessories of oxygen cylinders; d) A cylinder is not used without the pressure-reducing regulator fitted to its valve, except where connected to a manifold, in which case the regulator shall be coupled to the manifold header; e) On completing the task, the cylinder valves are closed and the protective caps fitted; f) Where an outlet valve is blocked with ice or freezes, it is thawed using water applied only to the valve, and open flame is not used; g) Valves are opened slowly; h) Only cylinders fitted with valves are permitted to be taken down into the mine; i) Before making the connection to a cylinder outlet valve, it is opened slightly so that any dust particles or dirt in the opening are dislodged; j) The valve or its opening is not pointed towards oneself or another person; k) Where the cylinder is not connected for use, the metal cap is kept in place to protect the valve, and l) Once the valve has been closed, it is checked that there is no gas leak between the cylinder and the regulator.

10.16.3 For regulators, instructions shall be available so that: a) Gas cylinders are only used for their intended purpose, and regulators are not swapped between a cylinder containing one gas and another; b) It is verified that every oxygen or fuel-gas regulator is fitted with a pressure gauge and that these are in good condition (needle not broken, stuck or with unrestricted movement; dial fixed and visible; glass transparent; among others); c) It is verified that high-pressure oxygen gauges have safety caps and are marked with the word “oxygen” in green; d) It is verified that acetylene gauges are marked with the words “fuel gas” in red; e) The connections for oxygen regulators have a right-hand thread, and those for acetylene regulators a left-hand thread; f) It is verified that oxygen regulators are green and acetylene regulators are red; g) Before removing the regulator from a cylinder valve, the valve is closed and the gas released from the regulator; h) Where there is a leak in the regulator, the cylinder valve is closed and the regulator replaced; i) An operating procedure is followed, in accordance with the instructions of the equipment supplier or manufacturer, and j) Flashback arrestor valves are fitted between the regulator and the hoses, for both the oxygen and the acetylene.

10.16.4 For hoses and their connections, instructions shall be available so that: a) The oxygen and acetylene hoses and lines are purged, before and after completing the activity; b) It is verified, before starting the activity, that the hoses and connections have no leaks; c) Leaks detected in hoses are repaired by cutting them and inserting a splice, except for acetylene hoses, which shall be replaced with new hoses without splices; d) Where flashback occurs and the hose is burnt, it is replaced with one in good condition and purged again; e) It is verified that hoses are red for acetylene, green for oxygen, and blue for air and inert gases; f) The connections joining the hose to the torch handle and regulators are of the clamp or ferrule type. Gaskets shall not be used at these connections; g) Hoses with a metallic outer covering are not used; h) Flashback arrestor valves are fitted between the torch handle and the hoses, for both the oxygen and the acetylene, and i) Neither acetylene nor oxygen is used for cleaning.

10.16.5 For electric welding machines, instructions shall be available so that: a) The equipment, cables and accessories are kept in good condition, so that they present no risk to workers; b) Connections are handled with dry gloves, using suitable tools and on dry floors; c) Welding cables are kept dry, free of grease or oil; d) Only single-piece cables, without joints, are used; e) The earth-cable connection of the welding machines is located on the same piece being welded; f) The casing of the welding machine is earthed; g) Before starting welding and cutting activity, it is confirmed that the operation of the equipment is understood; h) On completing welding, the power source is switched off; i) Where the welding circuit remains energised at all times, care is taken with respect to electric shocks and arcs that form accidentally; j) The welding system is installed with care. The components of the equipment shall not be placed together; k) Electrodes that are wet or damp are not used; l) Where coated electrodes are used, it is checked that the current and polarity are correct; m) In electric welding, the attachment of the neutral or earth conductor to the piece being welded is verified, by means of a spring-loaded clamp firmly connected to the machine's earth or neutral; n) Electric welding of soft metals such as lead, tin and zinc, among others, is not used, and o) Energy isolation (lockout) is carried out for the machinery and equipment related to the machinery or equipment where the welding or cutting activity will be performed; safety tags are placed indicating that their use is prohibited while the activity is being carried out, and safety padlocks are also used.

11.1 A fire risk analysis shall be available, including: a) The areas, activities, equipment, machinery and materials with a risk of fire; b) A description of the material and human resources for preventing and controlling fire; c) The need for internal or external support from the company and how it will be requested; d) The actions to be taken during a fire emergency; e) The actions and acts to be prohibited under normal conditions or during the emergency; f) The name and signature of the person who prepared the risk analysis, and g) The date the fire risk analysis was prepared and reviewed.

11.2 The risk analysis shall be reviewed and, where applicable, updated at least every year, and shall also indicate the following: a) The type of general alarm system or mechanism to be used for fires. Any of the following types, or a combination of them, may be used: 1) Audible; 2) Visual; 3) Olfactory, or 4) By wired or wireless communication; b) The quantity and type of portable or mobile fire extinguishers to be placed strategically at: 1) The sites where flammable materials are stored; 2) The main electrical power distribution systems; 3) The mine access points, and 4) The fixed electromechanical installations; c) The quantity of inert dust distributed and placed strategically at: 1) The sites where flammable materials are stored; 2) The main electrical power distribution systems; 3) The mine access points, and 4) The fixed electromechanical installations.

11.3 Battery-charging areas shall be ventilated to dissipate the hydrogen generated during charging, and the ventilation airflow shall be directed to the return heading.

11.4 Every worker who goes down into the mine shall have self-rescue respirators (self-rescuers), guaranteeing a supply of oxygen for workers to reach the surface of the mine.

11.5 At least two 9 kg extinguishers of ABC-type dry chemical powder, or their equivalent in capacity, shall be available at belt transfer points, on electromechanical equipment, and in areas with electrical power control and distribution equipment.

11.6 The areas of the drive unit (head) and the terminals of belt conveyors shall be kept free of coal accumulation, free of inactive material and of lubricant deposits.

11.7 All coal conveyors shall have sequence stops, an emergency stop cable running the length of the belt, and an audible pre-start warning alarm.

11.8 On the drums of equipment used for cutting and breaking coal: a) The picks shall be kept complete; b) The cutting bit shall be fitted, and c) Water sprayers shall be fitted, with the distribution and type of nozzles enabling dust control and cooling of the picks.

11.9 Diesel-engined equipment shall be kept free of fuel and lubricant leaks and shall have a system for cooling the engine and the exhaust gases.

11.10 Equipment and/or materials used in the compressed-air and ventilation systems shall be made of materials with antistatic properties and/or be earthed.

11.11 Coal transport transfer points shall have dust guards and water sprayers.

11.12 At working faces, in timbered areas, in galleries and in all workings inside the mine: a) It shall be verified, at least once per work shift, that the methane gas percentage is below 1% at the working faces and below 1.5% in return airways; b) Inert dust shall be applied to the roof, walls and floors in gallery development, in accordance with a procedure that at least addresses: 1) The “cut, timber, dust” operating cycle; 2) The quantity of dust to apply per cut or metre advanced, and 3) The technique or method for applying the inert dust (this item does not apply to long faces); c) It shall be verified, at least once a month, that incombustibility is at least 85%, in accordance with a procedure established for that purpose that at least addresses: 1) Samples (mixtures of coal dust and inert dust) shall be taken from the walls, roof and floor; 2) Working back from the end of the development faces, samples shall be taken every 25 metres up to a distance of 300 metres, and 3) In the other areas of the mine, samples shall be taken at least every 100 metres. Areas checked where incombustibility is found to be below 85% shall be the first to be re-dusted.

11.13 Fixed fire-fighting systems shall be provided, which, outside the mine, shall at least meet the following: a) Water reservoirs shall be available; b) The water supply to the mine shall be exclusively for fire-fighting service, and independent of the water supply used for the process; c) The water supply shall guarantee at least two hours of continuous supply at a flow rate of 946 litres per minute; d) The pumping system shall be automatic and shall have at least two power sources, one electrical and the other internal combustion, and shall guarantee a minimum pressure of 7 kg/cm2 when the hydrants are opened; e) The network shall be permanently pressurised at 2 kg/cm2; f) It shall have a siamese connection for the fire brigade service, connected to the hydraulic network and not to the cistern or water supply source, and g) It shall have elements allowing the system to be tested without activating the fire suppression elements.

11.14 Hydrants shall be installed inside the mine meeting the following conditions: a) They shall be located at least every 200 metres in the galleries, with 100 metres of hose 3.81 cm (1.5”) in diameter; with a nozzle for jet and fog spray, and a valve for adjustment; b) They shall have “T”-type outlets every 100 metres in galleries where conveyor belts are present; c) They shall be installed at distances of 20 metres before the electrical controls at the coal-cutting and breaking faces with machinery, and d) They shall guarantee a minimum pressure of 7 kg/cm2 at the hydrant outlets.

11.15 Reserves of 400 kg of inert dust shall be kept in dry locations at a distance: a) Not exceeding 50 metres from the entrance to any gallery; b) Not exceeding 15 metres from the working faces, and c) Not exceeding 5 metres from belt transfer points and locations where electromechanical equipment is installed. For small-scale operations, the quantity of inert dust shall be 250 kg.

11.16 A permanent reserve of inert dust of at least 5 tonnes shall be maintained outside the mine for emergencies. For small-scale operations, the reserve shall be 750 kg.

11.17 Carbon monoxide fire detectors calibrated to 15 ppm shall be installed in the following locations: a) Where the take-up carriage of the conveyor belts ends; b) At the transfer points, downstream of the drive unit; c) At the electrical substations inside the mine; d) At each of the ventilation circuits downstream of the air crosscut, on the return side, at a distance not exceeding 20 metres, and e) At the outlet of the general return of the vertical shaft.

11.18 A drawing shall be available showing the location of the equipment (extinguishers, hydrants and detectors), the materials (inert-dust reserves) available for fire control inside the mine, and the communication equipment for reporting fires.

11.19 The functionality of the general fire-alarm system or mechanism shall be checked at least every six months, and it shall be given the maintenance needed to ensure it functions properly. The results of the checks shall be recorded in a logbook or by electronic means. The records shall contain at least the type of check carried out and its results, the name and signature of the person in charge of carrying out the check, and their comments, where any exist.

11.20 Monthly inspections shall be carried out on hydrants, extinguishers, detectors and self-rescuers, in accordance with procedures prepared for that purpose. The results of the inspections shall be recorded in a logbook or by electronic means. The record shall at least contain the identification of the equipment inspected, the name and signature of the person responsible for carrying out the inspection, the date of the inspection, and follow-up on any anomalies detected. For extinguishers, the entries shall specify the dates of maintenance and recharging carried out. All measuring equipment used to take measurements of the mine atmosphere shall have calibration certificates or comparison procedures against calibrated standards, describing the field adjustments justifying the reliability of the readings.

11.21 In locations inside the mine where preventive maintenance is carried out on equipment and installations, the oils, greases and other flammable substances used for these activities shall: a) Be stored in fireproof containers or cabinets, only in quantities limited to weekly consumption; b) Have their waste accumulated in closed containers and transported outside the mine at least twice a week, and c) Have their containers kept closed while not in use.

11.22 For maintenance work in which quantities of substances greater than weekly consumption are used, the authorisation of the mine's safety area shall be obtained.

11.23 To verify, before starting activities (after a non-working day, an emergency or a power cut, among others), that the methane gas percentage is below 1% at the workplaces and in the mine's galleries.

11.24 Combustion of coal dust shall be prevented at locations where shots are to be fired, by means of: a) The application of inert dust in accordance with a procedure that at least addresses the quantity of dust to be used and the technique or method for applying it; b) Wetting the area where the shots are to be fired by spraying water at a distance of at least 10 metres from the end of the gallery, and c) Verifying that methane gas levels are kept at concentrations of 0.5% or below.

11.25 Every underground coal mine shall have two general ventilation workings, separated in such a way that, if one of them becomes contaminated or obstructed as a result of a fire, the other can serve as a means of escape.

11.26 In all mines, two exits shall be provided for each workplace inside the mine, each of which shall be connected, at the exit, to different means leading to the surface, except for development faces beyond the last air crosscut.

11.27 The materials of the conveyor belts used to remove coal from the mine shall be self-extinguishing or fire-retardant materials.

11.28 Coal-breaking machinery at the operating faces shall have water sprayers in usable condition.

11.29 The bases and supports of electric motors, transformers and any other electrical equipment shall be made of non-combustible materials.

11.30 Electrical substations shall be kept clean and free of accumulations of combustible materials such as paper, coal dust, wood waste, lubricants or rags.

11.31 Galleries where coal transport systems, mainly conveyor belts, are installed shall be clean and free of accumulations of combustible materials such as paper, coal dust, wood waste, lubricants or lubricant-soaked rags.

11.32 The blades of the fans used for ventilating the mine, and of the equipment motors, shall be made of materials with spark-proof properties.

11.33 Mined-out zones shall be isolated with stoppings made of non-combustible materials capable of withstanding the pressures exerted by the isolated area. Stoppings shall have sampling ports for gas sampling. Sampling shall be carried out in accordance with a programme established for that purpose. The results shall be recorded in a logbook or by electronic means, including any deficiencies or anomalies detected, the preventive measures taken, and the name and signature of the person responsible for the ventilation area.

11.34 The use of open-flame equipment or devices and electrical or electronic apparatus shall be prohibited. This does not apply to the provisions of Chapter 10 of this Standard for the welding and cutting activities provided for therein. This prohibition shall be signposted at the entrance to the mine. The signs shall comply with the provisions of NOM-026-STPS-1998.

11.35 Workers shall be prohibited from taking aluminium cans, paper or aluminium foil wrappers, cigarettes, matches, lighters and similar items down into the mine. Compliance with this prohibition shall be supervised.

11.36 Fixed diesel fuel deposits shall be prohibited inside the mine. Only the quantity needed for the shift's consumption shall be taken down, with any surplus removed to the surface of the mine.

11.37 Coal shall be prohibited from being stockpiled in galleries, especially in return airways, to prevent spontaneous combustion.

12.1 Underground coal mines shall have a geological study, including a map showing the methane gas concentrations in the coal seams to be mined, as well as in the upper and lower seams to be mined.

12.2 Underground coal mines shall prepare a risk analysis to determine and identify the areas prone to sudden methane gas and coal outbursts.

12.3 The risk analysis shall at least have the following indicators: a) The history of outbursts in mining operations carried out in the region; b) The type of coal to be mined (bituminous or hard coal, sub-bituminous, anthracite, lignite, among others); c) The types of possible outbursts; d) Structural geological maps (isopachs, faults, deformations, among others); e) The distribution of methane gas content in the coal seam, in m3/tonne; f) The presence of mylonite (reactive layer) in the seam's stratigraphy; g) The geological structures in the upper and lower parts of the seam to be mined; h) The depth of the seam to be mined; i) The determination of the direction of the main fracturing of the coal seam to be mined, and j) The statistics on methane gas concentrations in the coal seam(s), in m3/tonne.

12.3.1 For small-scale operations, compliance with the following items is not required: a) Structural geological maps (isopachs, faults, deformations, among others); b) The distribution of methane gas content in the coal seam, in m3/tonne, and c) The presence of mylonite (reactive layer) in the seam's stratigraphy.

12.4 Where the risk analysis determines that the areas to be mined by any mining system are susceptible to sudden methane gas and coal outbursts, a degasification plan shall be applied.

12.5 During drilling and gas extraction to the surface by means of vacuum application, at least the following safety measures shall be adopted: a) Prevent leaks at boreholes by cementing them; b) Install valves, traps, hose fittings, among others, at the borehole head; c) Identify the pipework for gas extraction; d) Install pumps outside the mine, operated by means of a safety procedure that begins with stopping the pumps when the methane gas concentration during extraction is below 30%; e) Install the necessary safety devices on the installations (traps, flame arresters, pressure gauges, gas monitors, and provide earthing connections), and f) Keep the vacuum system in safe operating condition through a maintenance programme that at least addresses the frequency of execution, the personnel responsible, and the established routines.

12.6 Every underground coal mine that, according to the results of the risk analysis, is susceptible to sudden methane gas and coal outbursts shall have a work plan enabling it to manage actions to prevent the possible risks arising from this event and to continue mining the coal seams. The plan shall at least include: a) The safety measures to be applied during mining of the seams identified; b) Information on the risk indicators, the training all workers on the working faces shall receive to control them, the safe way to carry out their activities, the type of tools and, where applicable, the machinery they shall use, and c) The methodology for defining or determining the dimensions of the protective barriers to be maintained at the development faces, before continuing their advance in areas susceptible to sudden outbursts.

12.7 Up-to-date records shall be kept, in logbooks or by electronic means, of the behaviour of the indicators for the working faces referred to in the risk analysis of the areas being mined, at least addressing: a) Observations, deviations and actions taken during the work shift; b) The analysis and interpretation of geological conditions, reports, changes in geological structures, among others; c) The analysis of gases from exploratory boreholes drilled from the surface or from inside the mine, and d) The records, which may be kept in logbooks or on magnetic media. The analysis and interpretation shall be carried out by personnel trained for these tasks and designated by the employer.

13.1 An up-to-date list shall be kept of the machinery and equipment used for exploration, mining, extraction and transport, installed inside underground coal mines, indicating at least, for each item: a) The fleet or identification number; b) A general description of its use; c) The location (area or place); d) The type of fuel or energy used, and e) The type of use.

13.2 A maintenance programme shall be available for the machinery and equipment used in underground coal mines, at least addressing: a) The fleet or identification number; b) The scheduled dates for carrying out maintenance, and c) The maintenance routines, addressing the checking of safety devices. The result of the routines shall be signed by the person in charge of the activity.

13.3 Safety procedures shall be available for carrying out maintenance activities on the equipment and machinery used in underground coal mines, at least addressing: a) The equipment, tools and substances to be used; b) The safety measures to be adopted in the area where maintenance is carried out (cordoning off and marking the area, among others); c) The personal protective equipment the worker carrying out the maintenance shall wear; d) The safety measures to be applied to the equipment or machinery during maintenance (power cut-off, placing of safety padlocks and tags, among others), and e) The authorisations the worker shall obtain before starting work.

13.4 A risk analysis shall be available for the operation of the machinery and equipment in use inside underground coal mines, at least addressing a general description and, where applicable, specification of the risks and the safety conditions to be adopted to eliminate, reduce or control them.

13.5 Safety conditions

13.5.1 Coal-cutting machinery shall have: a) An automatic electrical power cut-off device, activated when methane gas percentages above 1% are detected, and b) A water spray system on the coal-cutting machinery.

13.5.2 In coal mines where roof bolting is used as timbering during normal development operations, or continuous miners in formal mining (using continuous miners or longwall), all cutting equipment (electric or self-propelled by diesel engine), as well as haulage cars and roof bolters, shall be fitted with protective canopies or cabs.

13.5.3 In the formal mining operating system (such as room-and-pillar or advancing pillar mining) using continuous miners, a remote control shall be available for operating the continuous miner.

13.5.4 All equipment used for roof bolting, roadheaders and continuous mining machines, and loading machines, shall have methane gas detectors installed. On longwall breaking equipment, at least one methane gas detector shall be installed at the air outlet of the face, and one on the fans where these are used as air extractors. In all cases, they shall be connected so as to cut off electrical power when the monitored methane gas concentration level is 1% or more.

13.5.5 Both the equipment used for roof bolting and continuous mining machinery, coal haulage cars and locomotives shall be fitted with lights.

13.5.6 All cutting equipment used to extract coal or to drill boreholes for shoring up the roof arches shall have technical risk-prevention devices, such as water sprayers, dust collectors or air-cleaning systems, to control the volume of respirable dust in coal mines.

13.5.7 All pulleys, gears, transmission systems, rotating shafts and other moving parts of a mine's machines and mechanical equipment shall have guards or fixed protective covers to prevent injury to personnel.

13.5.8 Where workers need to access certain areas or confined spaces inside a machine with moving parts, to carry out activities related to the operation or maintenance of such equipment or machinery, an energy isolation or de-energisation and signage procedure developed for that purpose shall be applied, ensuring that the machine cannot be started up inadvertently until the same worker who isolated it removes the guard.

13.5.9 All guards and protective devices on machinery and equipment, including emergency stops, shall be kept in operating condition.

13.5.10 Work procedures shall be available containing the safety measures and prohibitions applicable to operation, in accordance with the corresponding risk analysis.

13.5.11 Machinery powered by diesel engines shall have an audible and visible alarm warning the operator and automatically suspending operation of the equipment when methane gas percentages above 1% by volume are detected.

13.5.12 Conveyor belt systems shall have sequence stop systems with an emergency stop cable running the length of the belt, an audible pre-start warning alarm, and low-speed sensors calibrated to 10% below normal operating speed, fitted on any of the non-driving pulleys (idler pulleys).

13.5.13 Vehicles powered by diesel combustion engines shall be prohibited from being left running when the operator leaves them.

13.5.14 The area inside the mine where vehicles powered by diesel combustion engines undergo preventive and scheduled maintenance shall have two exits, be built of non-flammable materials, and be ventilated so that the vitiated air passes directly to a return airway.

13.5.15 Safety conditions for internal combustion engines: a) Internal combustion engines used to power equipment or machinery in underground mines shall be diesel engines of the compression-ignition type, designed with a catalytic converter and to run only on diesel fuel; b) Diesel-engined equipment shall be fitted with a device for cooling the exhaust gases and with spark control on the exhaust pipe; c) The diesel fuel used shall not contain more than 1.5% sulphur by weight; d) Where a vehicle powered by internal combustion engines shows abnormal running, additional engine noise, noticeable smoke emissions, water or fuel leaks, or throws off sparks, the engine shall be stopped immediately and taken out of service, and e) At locations where diesel combustion engines operate, assessments of exhaust gas concentrations shall be carried out, at least fortnightly, or where there is evidence of malfunction, after each major maintenance or tune-up, and at a maximum distance of 30 centimetres from the exhaust pipe outlet, such that the gas concentration does not exceed the following limits by volume: 1) Carbon monoxide: 0.0025%; 2) Nitrogen dioxide: 0.10%; 3) Sulphur dioxide: 0.10%, and 4) Aldehydes: 0.001%;

13.5.16 The results of the gas concentrations detected and the dates of the assessments shall be recorded in the corresponding logbooks or records.

13.5.17 Fuel supply stations shall be located outside the mine, at a distance of not less than 50 metres from the mine entrance, or shall meet the following: a) Be equipped with supply systems that prevent fuel spillage, and with a collection system, and b) Be surrounded by a bund so that, in the event of a fuel spill, it is prevented from spreading to other areas. The collection volume of the bund shall be at least 1.5 times the volume of the container.

13.5.18 The quantity of fuel stored inside the mine shall not exceed one shift's consumption, with any surplus removed.

13.5.19 Fuel shall only be taken into the underground mine in metal drums.

14.1 For the galleries, headings or other types of tunnel, faces and development workings of any underground coal mine, geological, hydrogeological and rock-mechanics studies shall be carried out prior to mining the seam. The studies shall be permanently updated to allow underground coal mines to be worked under safe conditions.

14.2 Based on the results of the studies referred to in 14.1, at least the following shall be established: a) The design and selection criteria for the timbering to be used, including among others: 1) Metal or timber arches or frames; 2) Shotcrete, reinforced or precast concrete timbering; 3) Bolts, screws or cables for confining the floor, roof and ribs; 4) Roof pre-stressing systems; 5) Metal or timber props and cribs; 6) A combination of any of the above types, and b) The materials to be used in the structural support; c) The drawings, sections and diagrams of the mine's structural support; d) The safety procedures for carrying out the excavation; e) The safety procedures for carrying out the reinforcement work and the safety conditions for preventing mechanical risks to workers, and f) The design or dimensions of the coal pillars that will serve as protection and will at the same time form the galleries.

14.3 The results of the studies shall be recorded in printed or electronic form and retained for at least twelve months.

14.4 The safety procedures for carrying out the excavation shall include: a) The machinery and equipment to be used; b) The characteristics of the excavation materials; c) The safety measures to prevent excavations from connecting to a source of water or saturated material, in accordance with the provisions of Chapter 15 of this Standard; d) That, where mining is carried out using a mechanised coal-extraction system, the following shall be available: 1) A type of timbering specific to the particular characteristics of the mining block; 2) The minimum space needed to safely operate the roof-support, breaking and material-transport equipment, which shall in no case be less than 40 centimetres, and 3) Instructions for installing and dismantling the machinery and equipment used; e) Instructions for activating the emergency response plan.

14.5 The safety procedures for carrying out the reinforcement work shall include at least: a) A direction-control method for maintaining the planned heading of the galleries, when reinforcing a development working; b) Safety instructions for when crosscut or diagonal breakthroughs are carried out, subject to prior compliance with the roof and wall stability control plan; c) Instructions for installing additional roof timbering where galleries have dimensions greater than those of the original design; d) The materials to be used for constructing the timbering; e) The types of timbering installation, manual or mechanised; f) The machinery, equipment or tools to be used; g) The sequence of activities in installing the timbering; h) Instructions on how to place the timbering where geological faults and defects are identified, such as: changes in soil or rock, plugs, petrified logs or excessive moisture; i) The frequency at which timbering inspections shall be carried out in underground coal mines, and j) The records of inspections carried out, which shall at least include the location of the timbering inspected, the dates of the inspections, the condition of the timbering, recommendations for remedying deficiencies found, and the name of the person responsible for carrying out the inspection.

14.6 A reinforcement plan shall be available, at least addressing: a) The control of displacements and maintenance of the stability of the mine's strata, through reinforcement of the roofs and walls of the galleries, to protect workers from hazards and maintain safety inside the mine; b) That the reinforcement is in accordance with the predominant geological conditions for the working system used in the mine, and is modified whenever the predominant geological conditions change; c) Roof control for securing the reinforcement, according to the applicable support method: 1) The spacing or density of the reinforcement; 2) The diameter and type of roof-consolidation bolt (roof bolts), including combination anchor bolts, and the anchoring depth; 3) The allowable load of the prop, of the type of frame and of other roof reinforcement used; 4) The size and distribution of the reinforcement, concrete blocks and other reinforcement of this type, and 5) The characteristics of the timber or metal lagging for covering the roofs and walls between sets of timbering; d) The dimensions of the gallery; e) The size or dimensions of the pillars; f) The pillar-recovery methods, and g) The reinforcement systems for the long face and the specific reinforcement for development workings and excavations.

14.7 To have a reinforcement procedure for areas at high risk of rockfall, following prior consultation with and approval of mining engineers, at least including: a) Instructions for recovering materials used to support and reinforce the roofs and ribs of mines where collapses occur; b) Instructions on the use of tools, safety devices, and positioning in a safe place of the persons involved in the operation, and c) Instructions for carrying out visual inspections on each shift to assess the behaviour and deformation of the reinforcement resulting from stresses in excess of its strength, so that the corresponding corrective measures can be taken.

14.8 The following safety conditions shall be adopted when installing reinforcement: a) All props used to reinforce the roofs or walls of faces or galleries shall be securely positioned and rest on firm ground; b) They shall be secured to the adjacent reinforcement element by means of ties or spacers; c) The timbering system shall be set tight against the roof, so that loads are distributed across the structure; d) On inclined seams, timbering shall be installed so as to ensure the loads are supported, taking into account the dip of the seams or the inclination of the galleries and possible movement of the strata; e) Additional reinforcement shall be installed to protect the closure stoppings of mined-out zones, installed on both sides of the stoppings; f) The cutting depth shall be that determined in the rock-mechanics study; g) The work procedure shall take into account the operating cycle of cutting followed by timbered cutting, and h) For development workings where the spacing between crosscuts is more than 70 metres, a special rock-mechanics study shall be carried out, addressing at least: 1) The cross-section of the gallery; 2) The density of the timbering; 3) The type and capacity of the timbering; 4) Additional reinforcement; 5) The depth of the cut, and 6) The quality of the immediate roof.

14.9 In areas with water seepage from the roof or ribs that affects ground stability, permanent checks of its behaviour shall be carried out to prevent landslips and deterioration of the mine's support systems. The results of the checks shall be recorded by electronic means; kept for at least twelve months; and contain at least the date of the check, a description of the location checked, the conditions detected, and the name and signature of the person who carried out the check.

14.10 Reinforcement shall be carried out on the support systems in locations where water seepage exists.

15.1 A geohydrological study shall be available, at least containing the following: a) Drawings of the coal-extraction operations showing the location of aquifers near the mining operation site and of surface water bodies (rivers, lakes, among others); b) The location of old or abandoned workings near the area to be mined, and c) The determination of the minimum permitted limits of proximity to old or abandoned workings for mining, based on the rock-mechanics study and the topography and geology of the location.

15.2 The study shall be updated when: a) The coal extraction processes are modified; b) New areas are assessed for mining, and c) The results of the inspections indicate high frequencies and quantities of water seepage into the mine.

15.3 Based on the results of the geohydrological study, the risk prevention and control measures shall be determined, where applicable, at least containing: a) The characteristics of the protective barriers or pillars between the mining operation and the old working or body of water; b) The operating procedures for extraction advance and for maintaining the protective barrier or pillar; c) Exploratory drilling near geological faults connecting to any aquifer or flooded mine; d) The characteristics of the pumping system, and e) The emergency response plan, in accordance with the provisions of section 5.27 of this Standard.

15.4 To make known to workers the hazard locations marked on the drawings showing the location of water accumulation zones near the mining areas.

15.5 Service pits and boreholes shall be timbered.

15.6 Where old workings exist in the area and no information is available on them, the following activities shall be carried out (see Figure 1): a) Drill boreholes at the end of the working, parallel to the ribs, one metre away from them and located in the coal seam. The spacing between boreholes shall not be more than 2.40 metres nor less than one metre; b) Always maintain a protective barrier of at least 4.5 metres in the mining workings, drilling again on reaching the barrier. The maximum drilling length is not restrictive, and c) Drill boreholes at 45º to the ribs, with a minimum length of three metres and a spacing of no more than 2.40 metres apart. Figure 1

15.7 Records shall be kept of the horizontal exploratory drilling work, at least containing: a) The drilling pattern; b) The dates of execution; c) The drilling lengths; d) The length of the protective barrier left after mining (before drilling); e) The diameter of the borehole; f) The shifts; g) The names of the worker and supervisor, and h) Where applicable, the presence of water or gas through the boreholes.

15.8 After the mining activities for each shift have been carried out, the length of the protective barrier left shall be recorded in the operating report.

15.9 Pumping systems shall be available to control the inflow of water inside the mine, shown on a drawing that shall at least contain: the location of the pumps; the diameters of the pipework; the types and capacities of the pumps, as well as the discharge points for the pumped water.

15.10 In areas where surface drilling connects with the coal seam, the boreholes shall be cemented to prevent water leaking into the mine.

15.11 To protect the entrances to mine workings with collars and keep them out of reach of surface water flows.

16.1 Installations and operations using rail-based personnel and materials transport systems shall have at least: a) Derailers on branch lines leading to stores, workshops, shaft collars, or connecting to the main line, where these have a downward gradient greater than 2%; b) Flags or hand lanterns for protecting persons working or passing near the rails; c) A signal code for the flags or hand lanterns, which shall be: 1) Red: danger, stop completely; 2) Amber: caution, proceed slowly, and 3) Green: clear to proceed.

16.2 A safe working procedure shall be available for transporting major equipment (longwall components or development equipment), at least containing: a) The condition that the equipment being transported may project, leaving a clear space of at least 40 cm on each side; b) Not permitting personnel to be present along the track between the origin and the destination; c) Limiting the locomotive's speed to suit the conditions of the route, and d) Having the operation supervised by the person in charge of traffic.

16.3 The most common rules from the operating manual for personnel or materials transport on tyres, rail or tracks shall be available and communicated. This may be communicated by means of signs, notices and posters located strategically in the areas designated for personnel, at the entrance to the mine, to ensure compliance.

16.4 To permit the use of skips (an alternative method to the use of cages) for transporting personnel through pits, a study shall be available indicating at least the following information: a) The diameter of the hoist drums; b) The diameter of the cables; c) The controlled ascent and descent speeds; d) The type of motor to be used; e) The diameter of the shafts; f) The characteristics of the hoist's braking guides, and g) The characteristics of the skips (diameter, volume capacity and weight).

16.5 All motorised materials-transport vehicles, on tyres, rail or tracks, shall: a) Have a braking system that guarantees the vehicle stops and remains stationary with the maximum load and under any other operating condition; b) Have clearly visible front, rear and warning lights; c) Have an audible warning signal that activates automatically when the vehicle reverses; d) Where used for transporting personnel, have a cab built or reinforced so that it can withstand damage caused by falling rocks or by the materials it will carry, as well as protection against impacts from the timbering; e) Prevent any reduction in the driver's visibility when the cab of these vehicles is modified or fitted out; f) Where diesel-engined equipment is used, position the engine's exhaust outlet away from the operator and from the air-conditioning intake (diesel locomotives); g) Have a comfortable seat that reduces equipment vibration for the driver, control levers with suitable devices, and access steps; h) Have at least one 4.5 kg "ABC"-type dry chemical powder extinguisher, and i) Have a materials-transport bed reinforced so that it can withstand the load and the impact of rocks or materials.

16.6 Vehicles used for the regular transport of personnel shall have functional seats.

16.7 The transport of persons is prohibited: a) Outside cabs and on platforms without side guards; b) In tipping-mechanism boxes, and c) In the boxes or platforms of vehicles loaded with any type of material.

16.8 Personnel transport in load-carrying vehicles shall only be permitted in disaster situations or situations of imminent risk, or for duly justified extraordinary circumstances, and where these are fitted with: a) Perimeter guarding on the platform preventing the accidental fall of any worker, and b) Devices allowing workers to hold on securely.

16.9 At locations where cars or gondolas are coupled or uncoupled, there shall be a clear space of at least 75 cm between the gondolas or the locomotive and the wall or timbering.

16.10 Locomotives used inside a mine shall be fitted with: a) Brakes that can be operated by the driver, regardless of whether other devices exist for operating them; b) A portable ABC-type dry chemical powder extinguisher of at least 4.5 kg, and a miner's lamp; c) A headlamp with an effective range of at least 60 m; d) Where applicable, a comfortable seat that reduces equipment vibration for the driver, and e) Control levers arranged so that the driver can operate them without distracting attention from the direction of travel.

16.11 All trains hauled by locomotives shall carry a luminous or reflective sign at the rear of the last car or gondola.

16.12 Cars or gondolas out of service shall be braked or chocked.

16.13 Locomotive batteries shall only be stored and replaced at charging stations fitted out for that purpose.

16.14 Vehicles with diesel combustion engines may only be refuelled at fuel supply stations.

16.15 Where a vehicle powered by diesel combustion engines shows abnormal running, additional engine noise or, in particular, where it noticeably emits smoke, throws off sparks, or has a water or fuel leak, the engine shall be stopped immediately and the vehicle taken out of service for repair.

16.16 Tracks and routes used by vehicles shall be signposted, indicating intersections, changes of direction and steep gradients. The signage shall comply with the provisions of NOM-026-STPS-1998.

16.17 Where workers are transported in motorised vehicles, the following safety measures shall be taken: a) Boarding and alighting stations shall be illuminated; b) Cars for transporting workers shall be fitted with sturdy sheet-metal roofs, perimeter guarding and bars or handrails to hold onto; c) Trains shall have a signal transmission system between the assistant and the locomotive operator, and d) Where remote-control devices are used to operate the motorised vehicles, the operators shall be trained and instructed.

16.18 Where conveyor belts are used for moving material, the following safety measures shall be taken: a) At the drive unit: 1) The support system for the gallery's roof or timbering and its supporting blocks shall be made of non-flammable materials or treated with fire-retardant material, and 2) At least one portable 9 kg extinguisher, or its equivalent, shall be available. b) On the conveyor belts: 1) An emergency stop cable shall be provided along the entire length of the belts; 2) Crossovers shall be installed at personnel crossing points, and 3) Safety guards shall be fitted on the pulleys of the drive unit and the tail end, and cleaning and maintenance of the belts shall only be carried out when they are not running.

16.19 Where chairlifts are used for transporting personnel, the following safety measures shall be taken: a) The cable used shall be of a type that requires no lubrication; b) Operation shall be in accordance with a safety procedures manual covering the probable risks; c) The boarding and alighting stations shall be spacious, illuminated, signposted, with a flat, non-slip floor; d) A maintenance programme shall be available, addressing cleaning and leak elimination, and inspection and testing of the steel cable, and e) Limit-switch-type emergency stops shall be provided in the alighting areas.

16.20 Conveyor belts shall have: a) An emergency stop cable along the entire length of the belts; b) Belt crossovers or bridges at personnel crossing points, and c) Safety guards on the pulleys of the drive unit and at the tail section.

16.21 A materials transport procedure shall be available, addressing at least: a) The equipment to be used; b) The materials to be transported; c) The method of loading and unloading materials; d) The communication systems to be used, and e) Traffic instructions.

16.22 Workers may only be transported in vehicles designed for that purpose or in unloaded load-carrying vehicles fitted with safety devices allowing workers to hold on, and which are platforms with side guards or boxes without a tipping mechanism.

16.23 Belts for transporting workers shall be equipped with boarding and alighting stations, shall operate at a speed of 2 metres/second or less, and shall have an emergency stop system along the entire route.

16.24 Where cages are used for transporting workers, they shall meet the following: a) Have a roof made of sturdy sheet metal; b) Be lined with sheet metal up to a height of at least 1.50 metres from the floor, with the remaining part up to the roof fitted with wire mesh; c) Have bars or handrails for workers to hold onto, and d) Have doors that can be secured while the cage is moving, to prevent them opening due to jolts or impacts.

16.25 For hoists, at least the following safety measures shall be adopted: a) Have signage prohibiting unauthorised personnel from entering the hoist control room; b) Be fitted with a depth indicator and a bell that operates on reaching each station, easily seen and heard by the operator; c) Have depth markers; d) Where friction sheaves are used, they shall be inspected to verify that the sheave and its liners are in good condition and, where necessary, the cable tension shall be adjusted each time the travel is adjusted or the cable or its attachment is changed; e) Hoists capable of disengaging the drums shall have a system preventing the drum from being disengaged without the brakes being fully applied, and which in turn prevents the brakes being released when the mechanism is not fully engaged; f) The clutch-engagement and disengagement controls shall be permanently guarded to prevent their accidental operation; g) Hoists with a speed exceeding 4 metres/second shall have an automatic speed control, braking the hoist before the cages, cars or skips overrun the upper or lower station, and preventing them from reaching the lower or upper station at a speed greater than 1.5 metres/second; h) The cable-winding drums shall be fitted with flanges or arms and, in the case of conical drums, shall have guides or other devices preventing the cable from slipping; i) The end of the cable shall be securely fixed to the drum, and at least three turns shall always remain on it when the cage or skip is at the deepest point of the shaft; j) The diameter of the cable-winding drums shall be at least 30 times the diameter of the cable; k) Where friction or traction sheaves are used, their diameter and guide shall be specific to the type and diameter of the cable used, but their diameter shall not be less than 30 times the diameter of the cable; l) The brakes of hoists used for raising and lowering workers shall: 1) Have two independent systems acting on the drum or sheave or on their shafts, capable of stopping the cage, car or skip at a retarded rate not exceeding 5 metres/second, nor at the maximum acceleration the hoist can produce with the maximum load, and 2) Engage automatically if the driving power fails or the pressure of the braking system drops, and, in the event of failure of one of the systems, the braking capacity of the other system shall remain available to control the cages, cars or skips; m) In the case of cages or cars supported by a single cable or with a single attachment point to the cable, these shall have a braking system that acts automatically on the guides in the event of the cable or its attachment breaking.

16.26 Safety procedures shall be available, at least addressing the following: a) At the start of each shift and after each stoppage for repairs, the empty cage shall be moved along the shaft, to ensure there are no obstacles or defects in its operation; b) Not permitting the simultaneous lowering or raising of material and workers on the same deck of a cage; c) Instructions for acting in the event of doubt about any signal; d) Instructions for when there is water at the bottom of a shaft; e) The precautions or measures the hoist operator shall take before leaving the controls; f) Inspections and tests shall be carried out only by workers trained and authorised by the employer, at the following intervals: 1) One day: for visual inspection of the cables, chains, connecting pieces and cable supports, and of the safety devices that prevent the free fall of cages or cars in the event of cable failure; 2) One week: for visual inspection of the external elements of the machines, the headframe, the cages and other elements required at these shafts; 3) Two weeks: for visual inspection of the timbering and the shaft walls, and 4) One month: for inspection of the motors, brakes, clutches, and testing of the safety devices that prevent cages or cars falling in the event of cable failure; g) The method for recording the results of the inspections, tests and maintenance of the shafts, hoists, cables, cages, cars, skips, safety devices and other accessories; h) The procedure to follow when the drum or sheave is disengaged, where two-ended hoists are used, and i) The frequency for cutting the ends of the cables at both extremities, in accordance with the inspection and test programme.

17.1 The employer may choose to engage an accredited and approved verification unit, as provided for in the Federal Act on Metrology and Standardisation, to verify or assess this Standard.

17.2 To obtain the current directory of verification units accredited and approved by the Ministry of Labour and Social Welfare, the employer may consult the following website: www.stps.gob.mx

17.3 Verification units verifying or assessing this Standard shall apply the compliance criteria established in the conformity assessment procedure in Chapter 18.

17.4 Accredited and approved verification units assessing compliance with this Standard shall issue a report, which shall contain: a) Workplace details: 1) Name, designation or business name; 2) Full address, and 3) Name and signature of the legal representative; b) Verification unit details: 1) Name, designation or business name; 2) Registration number granted by the accreditation body; 3) Approval number granted by the STPS; 4) Date on which accreditation and approval were granted; 5) Determination of the workplace's degree of compliance with this Official Mexican Standard and, where applicable, any qualifications determined by the verification unit; 6) Result of the verification; 7) Name and signature of the legal representative; 8) Place and date of signature of the report, and 9) Validity period of the report.

17.5 The report issued by the verification units shall be valid for five years, unless the work areas are modified.

18.1 This conformity assessment procedure applies both to verification visits carried out by verification units and to inspection visits carried out by the labour authority.

18.2 The aspects to be verified during the conformity assessment of this Standard are carried out, as applicable, by means of ocular verification, documentary review and confirmation through interview, in accordance with the following:

5.2 Documentary and physical The employer complies when: - It presents documentary evidence that no workers under 18 years of age or pregnant or breastfeeding women are working inside the small-scale operations or underground mines, and - When carrying out a walk-through of the interior of the small-scale operations or underground mines, it is confirmed that no workers under 18 years of age or pregnant or breastfeeding women are working there.

5.4 Documentary and interview. The employer complies when: - It

                interview                                                              be presented      in printed         or    by
                               -     It presents        the   records      of     the

                                                                                        compliance             with           this
                               conditions      of     ventilation,    reinforcement,

5.5 Documentary. The employer complies when it presents the occupational skills certificates for the training and instruction provided to

                               training     and     instruction      that     was interviewed            some
                               provided to all the workers of the workers                          about          the

5.6 Documentary. The employer complies when: - It presents

                               are exposed;                                         may         be supplemented              by
                                                                                        interviewing         some

5.7 Documentary The employer complies when: The records may

5.8 Documentary. The employer complies when: - It presents the authorisations it granted to trained and instructed workers, to operate and maintain locomotives, machinery, vehicles, installations and

                                    store, transport or use explosives;     may       be supplemented       by
                                                                                  interviewing      some

5.9 Documentary. The employer complies when: - It presents the record, for each shift, of the persons entering and leaving the small-scale operations or underground mine; - The record is kept for three

5.10 Physical and documentary. The employer complies when: - It

5.11 Documentary The employer complies when, in the event of having had accidents, it presents documentary evidence that it notified the Ministry of Labour and Social Welfare of them. The evidence may be presented in printed form or by electronic means.

5.12 Documentary. The employer complies when it presents documentary evidence that it investigated the causes of accidents or disasters, where these occurred. It shall keep the documents for all accidents that occur. The documents may

5.13 Documentary. The employer complies when: Where a disaster has occurred: - It presents the records of the assessments of the mine's conditions carried out to authorise entry by the teams;

5.14 Physical and documentary The employer complies when, on carrying out a walk-through of the interior of the small-scale operations or underground mines, it confirms that: - Workers have the personal protective equipment specific to carrying out their activities, and - It presents the following documentary and/or physical evidence: a) Determination of the personal protective equipment it provides to workers and/or b) Certificate from an accredited and approved certification body, or a guarantee that the equipment covers the risks for which it was acquired. The documentary evidence may be presented in printed form or by electronic means.

5.15 Physical. The employer complies when, on carrying out a walk-through of the interior of the small-scale operations or underground mines, it is confirmed that persons (workers or visitors) wear at least

5.16 Physical and interview. The employer complies when, on carrying out a walk-through of the installations of the small-scale operations or underground mine: - Workers use personal protective equipment while carrying out their activities or during emergency activities, and - When interviewing workers, it is confirmed that they maintain, safeguard and clean it, and, where applicable, replace it, in accordance with the corresponding instructions. The corresponding instructions relate to the use, damage or service life

5.17 Documentary and physical. The employer complies when: - It has safety data sheets (SDS) for all hazardous chemical substances used

5.18 Documentary and interview. The employer complies when: - It presents

5.19 Documentary and/or physical The employer complies when: - It presents documentary evidence that the recommendations issued by the safety and hygiene committee(s) are followed up, and/or - When carrying out a walk-through of the mine, their implementation is visually confirmed (where applicable).

5.20 Documentary and physical. The employer complies when: - It presents the list of equipment and/or, where applicable, the operating authorisations for pressure vessels or boilers operating at

5.21 Physical. The employer complies when, on carrying out a walk-through of the installations of the small-scale operations or underground mine, it is confirmed that: - The signage used complies with

5.22 Documentary The employer complies when: - It presents documentary evidence that medical examinations were carried out for occupationally exposed workers, and - The medical examinations carried out include at least: chest X-ray, audiometry and spirometry. The examinations may be entrance or periodic examinations, as applicable. The documents may be presented in printed form or by electronic means.

5.23 Documentary. The employer complies when it presents documentary evidence that NOM-030-STPS-2006 is applied. It may present a favourable report

5.24 Documentary. The employer complies when: - It presents the

                                  - It presents the current potential risk in printed      form    or     by
                                  analysis;                                      electronic means.

5.25 Documentary The employer complies when: - It presents the potential risk analysis, carried out by area, process and activity throughout the mine, and - The analysis includes at least the following: a) The analysis of the work areas; b) The identification of workers and their activities by job; c) The identification of the higher-impact risks; d) The possible impact; e) The probability of the risks occurring; f) The number of events per unit of time that could occur; g) The prioritisation of risks, and h) The proposal of the occupational safety and health procedures and conditions. For greater precision on the content of the elements referred to in items a) to h), it is advisable to review this section of the Standard. The risk analysis may be presented in printed form or by electronic means.

5.27 Documentary. The employer complies when: - It presents the emergency response plan; - The plan is available to

5.27.1 Documentary The employer complies when the emergency alert and alarm procedures include at least the criteria for: a) Raising the alarm, and b) Taking immediate action in the event of fire. For greater precision on the content of the elements referred to in items a) and b), it is advisable to review this section of the Standard. The emergency alert and alarm procedures may be presented in printed form or by electronic means.

5.28 Documentary or physical The employer complies when: - It presents the study confirming that the self-rescuers available to workers allow them to reach the surface from the most remote point of the small-scale operations or underground mine, or - It has reserve or additional self-rescuers, where the study is not available, or where its results indicate that they do not allow workers to reach the surface from the most remote point of the small-scale operations or underground mine. - The self-rescuers are provided under the following conditions: a) One for each worker on the long faces and in the development workings; b) Distributed at strategic locations; c) Marked with reflective or fluorescent materials, and d) Identified on a drawing circulated to all personnel. The study and the drawing may be presented in printed form or by electronic means.

5.29 Documentary. The employer complies when: - It presents the documentary evidence or

                                    - It presents the documentary evidence or        skills    certificates   or   diplomas,   among
                                    records of the training and instruction   others.

5.30 Physical. The employer complies when, on carrying out a walk-through of the small-scale operations or underground mine, the evacuation routes are found to be signposted by means of: a) Lifelines with elements indicating the direction of the exit, and b) Safety signs and notices made of reflective or fluorescent materials. The characteristics of the safety signs for evacuation routes are established in NOM-026-STPS-1998.

5.31 Documentary or physical. The employer complies when: - It presents

5.32 Documentary The employer complies when it determines the wind-chill index It may present a favourable report and the Temperature index of issued by a

5.33 Documentary The employer complies when: It may present a favourable report - It presents the study, as applicable, of the issued by a

5.34 Physical The employer complies when, on carrying out a walk-through of the interior of the small-scale operations or underground mines, it is confirmed that the personnel responsible for the safety of the mine (personnel in the chain of command) have individual methane

Chapter 7       Documentary and   The employer complies when:                     For greater precision on the
                 interview                                                  content of the elements

                                designates a person in charge of the magazine;         a     walk-through     of      the
                                - It presents the monthly report on receipt, small-scale  operations   or
                                issuing and oversight of the explosives, as underground      mine,      to
                                well as their receipts, consumption and issues;   confirm that the following is complied with

Chapter 8    Documentary, physical and The employer complies when:                            For greater precision on the
              interview                                                               content of the elements

                                      where      there are   changes      or    new safety of the installations
                                      installations;                                 electrical established by this

                                                                                     have     an     electrical
                                      a) General load schedule;                   engineer      or       personnel

                                    human resources      to     prevent       and   control
                                    fires;                                           For     greater      precision   on the

                                                                                       fire   risk,    the
                                    d)   Actions     to   be taken    during    the procedures and instructions,
                                    emergency;                                          it is advisable to review this

                                    normal and emergency conditions;                The      documents        may
                                    f) Name and signature of the person who prepared the be presented in printed form                       or   by
                                    risk analysis,                  electronic means.

                                    shows the methane gas concentrations in plans     and    programmes,     it     is
                                    the coal seams to be mined;             advisable to review this chapter

                                      - The record of the results of the studies mechanised      system      for
                                      is kept for twelve months;                     coal extraction;

Chapter 15   Documentary, physical and The employer complies when:                       For greater precision on the
              interview                                                          content of the elements

                                     - The hydrogeological study contains at records,        it    is advisable
                                     least:                                       to review this chapter of the

                                                                                 The    documents    may
                                      a)   That      the   equipment transported be presented in printed form or by

the person in charge of ventilation and carried out weekly; 2. The working faces, each shift; 3. The development galleries; 4. The long faces; 5. The general headings; 6. The air intake through the galleries; 7. The air outlet through the return airways; - It presents the instructions for the fan operator to carry out manoeuvres in the event of unforeseen stoppages of the main fan, and - When carrying out a walk-through of small-scale operations or the underground mine, it is physically confirmed that the safety measures and conditions for the ventilation systems are met. content of the elements - It presents drawings of the electrical installations; procedures, it is advisable to - The drawings include the identification and review this chapter of the location of the electrical equipment; Standard. it specifies the capacities, at least of, be presented in printed transformers; battery chargers, and form or by electronic means. protection devices of the electrical circuits; To assess compliance with - The drawings are updated every month or the conditions and measures of Chapter, a - The drawings bear the name and signature verification checklist may be drawn up including all those provisions maintenance, safety and operation; that can be confirmed by - The drawings are kept for two months in physical inspection, without the need to document form and twelve months in electronic use measuring equipment. records; In small-scale - The drawings are available at the operations, where no electrical installations are used, substations and control rooms; compliance with this Chapter shall not be required, nor - It presents the updated single-line diagram the obligation of the electrical installations, which includes: person in charge of handling b) Type of winding connections and the electrical installations. number of phases; c) Cable lengths and their gauges; d) Voltages, impedances and currents of the transformers; e) Emergency generating plants; f) Metering and load centres; g) Transfer switches; h) Earth-fault detection devices; i) Design calculation record, and j) Signature of the person in charge of the maintenance area; - The single-line diagram is updated every month, or when new installations exist or changes are made to the power distribution; - The single-line diagram bears the name and signature of the person in charge of the maintenance area; - The single-line diagram is kept for two months in document form and twelve months in electronic records; - The drawings are available at the substations and control rooms; - It presents documentary evidence that it has an electrical engineer or that the employer designates responsible personnel, trained in low- and high-voltage electrical installations, for handling electrical power in underground coal mines; - It presents documentary evidence that the electrical engineer or the designated person, electrical installations; - It presents documentary evidence that the electrician carries out tests on equipment installed and to be installed; - It presents the list of all the mine's electrical equipment, prepared by the electrician; - It presents the safety procedures for: a) Connection and disconnection of circuits; b) Splicing of conductors; c) Extension of circuits; d) Maintenance of electrical equipment and installations; e) Installation of conductors and electrical equipment; f) Inspection of electrical installations; g) Discharge of residual voltages; h) Verifying electrical continuity and measuring the resistance of earthing conductors; i) Placing of safety tags and padlocks, and j) Measurement of insulation resistance. - It presents the safety procedures containing at least the following information: a) Instructions for applying safety measures; b) The sequence of actions by personnel to carry out the activity; c) The type of tools, instruments or equipment to be used; d) Personal protective equipment, and e) Instructions for acting in the event of an emergency; - It presents the annual programmes for maintenance of electrical equipment and installations, and for inspection of electrical equipment and material; - The annual maintenance programme includes: a) Activity; b) Start and completion date; c) Frequency; d) Person responsible; e) Safety measures, and f) Procedure for placing safety tags and padlocks; - The programme for reviewing electrical equipment and material is in accordance with the intrinsically safe; explosion-proof, or flameproof - It presents documentary evidence that equipment coming from the repair shop and to be installed in the mine has the approval of the person in charge of safety, and keeps evidence of the last repair; - It presents documentary evidence that the following are prohibited: a) Introducing telephone and power cables through the same borehole; b) Using diesel batteries and motors beyond the last air crosscut, without authorisation from the safety department; c) persons working on energised electrical circuits in areas where explosives, or flammable or combustible substances, are present; d) The entry of unauthorised personnel into substation or transformer areas, and modifying the operation of apparatus and equipment; e) Carrying out inspection or maintenance activities on energised equipment, and f) Using gaskets at electrical control joints, except between metal and glass parts; - It presents documentary evidence of the certifications or the manufacturer's guarantee that they are explosion-proof; - It presents documentary evidence that it carries out earthing resistance measurements every six months, or when changes or new installations are made; - The earthing resistance measurements are kept for twelve months; - It presents the record of the results of the maintenance programme; - The record contains at least the following information: a) Date on which the activity is scheduled and carried out; b) Name of the person carrying out the activity; c) Type of activity carried out, and d) Results of the activity; - The record is kept for twelve months, and - When carrying out a walk-through of the mine, it is verified that the electrical equipment bears painted identification or an affixed label indicating at least the operating voltage and the circuit it supplies. verification of compliance - It presents documentary evidence that with this Chapter, when carrying out a only the activities of walk-through of the mine for welding and cutting for the equipment or machinery used for cutting are met that the coal, inside the mines, when safety measures and conditions established in the following conditions are present: this Chapter are met. a) That it is not possible to move to For greater precision on the the surface the equipment or machinery, its parts content of the elements or components; required in the risk analysis, the procedures and b) That the favourable results of the instructions, it is advisable to risk analysis are available; review this chapter of the Standard. c) That the safety measures in the clean-air area are available, and d) That the authorisation of the may be presented in printed person in charge of safety is available; form or by electronic means. - It presents documentary evidence that the To assess compliance with welding and cutting activities on the the safety conditions and long faces are carried out only where measures for the welding and clean air is present; cutting activities established - It presents documentary evidence that carrying out welding and cutting work by this Chapter, a in the return-air areas and beyond the verification checklist may be drawn up including all last air crosscut in the gallery development areas is prohibited; those provisions that can be confirmed by physical - It presents the risk analysis of the inspection, including those specific welding and cutting activities where measuring equipment carried out; needs to be used, where applicable. - The risk analysis includes at least: the welding or cutting process to be used; b) The list of materials used as base material and, where applicable, filler materials; c) The list of the hazardous factors, agents or conditions that could affect safety conditions; d) The risk control measures, and e) The personal protective equipment for the workers who carry out the welding and cutting activities; - It presents documentary evidence that the personal protective equipment of the workers who carry out the welding or cutting activities is selected in accordance with the provisions of NOM-017-STPS-2001; - It presents the authorisations for the workers who carry out welding and cutting activities inside the mine; - The authorisations: a) Bear the signatures of all persons responsible; b) Include the results and recommendations of the risk analysis; c) Are delivered (a copy) to the persons responsible for signing it; d) The worker's copy is placed in a visible location while the work is being carried out, and e) The copy held by the person responsible for the authorisation is kept for twelve months; - It presents a verification checklist including all the applicable conditions; - It presents documentary evidence that the person responsible for safety in the mine, the person in charge of the activity, the safety and hygiene committee and the operation and maintenance supervisors for the site confirm that the content of the checklist is met before starting the activity; - It presents the safety procedure for carrying out welding and cutting activities inside the mines; - It presents documentary evidence that the person in charge of safety in the mine analyses the results of the activity and determines whether the recommendations provide sufficient safety for the workers; - It presents documentary evidence that an insulation test is carried out on the electrical circuit supplying the welding machine before it is energised; - It presents evidence that storing welding and cutting equipment inside the mine is prohibited; - It presents, where applicable, the notifications of leaking cylinders to suppliers; - It presents the procedure for operating the regulators in accordance with the manufacturer's recommendations; - It presents instructions for: a) Handling and operation of valves; b) Regulators; c) Hoses and their connections, and d) Welding machines, and - When carrying out a walk-through of the mine, it is confirmed that, in the areas where welding and cutting activities are carried out, the following are available: a) First-aid kit; b) First-aid manual; c) One 9 kg extinguisher or two 6 kg extinguishers, and d) Portable methanometer and/or continuous monitoring device. verification of compliance - It presents the fire risk analysis; with this Chapter, when carrying out a - The fire risk analysis includes: walk-through of the mine to a) Areas, equipment, machinery and materials confirm that the safety with a risk of fire; conditions and measures established in it are met. b) Description of the material means and c) The need for internal or external support and content of the elements how it is to be requested; required in the risk analysis, e) Prohibitions on actions or acts involving g) Date of preparation and review of the this chapter of the Standard. risk analysis; To assess compliance with the safety conditions and h) General alarm system or mechanism; measures for the prevention and protection against fire and i) Quantity and type of portable or explosions established by this mobile fire extinguishers, and Chapter, a verification checklist may be drawn up including all - The fire risk analysis is those provisions that can be confirmed by updated every twelve months; using measuring equipment, where applicable. - It presents documentary evidence that the self-rescuers guarantee the supply of oxygen to the workers until they reach the surface from the small-scale operations or underground mine; - It presents the procedures for: a) Applying inert dust to roofs, floors and walls, non-combustibility; c) Applying inert dust, and d) Inspecting the hydrants, extinguishers, detectors and self-rescuers; - It presents evidence that it verifies the non-combustibility percentage every month; - It presents a drawing showing the location of the equipment and materials available for fire control, and of the communication equipment for reporting fires; - It presents the calibration certificates for the equipment, or the procedures for comparison against calibrated standards describing the field adjustments justifying the reliability of the readings; - It presents the programme for sampling gases at the seals of the mined-out zones; - It presents the records of the results of the gas sampling, in accordance with the programme; - It presents documentary evidence that maintenance is carried out to ensure the functioning of the general alarm system or mechanism; - It presents documentary evidence that: a) Checks on the functionality of the general alarm system or mechanisms are carried out every six months, and b) Inspections of hydrants, extinguishers, detectors and self-rescuers are carried out every month; - It presents the records of: a) The results of the checks on the functionality of the general alarm system or mechanisms, including: type of check; results; name and signature of the person in charge of the inspection and, where applicable, comments; b) The inspections of hydrants, extinguishers, detectors and self-rescuers, including: the equipment inspected; name and signature of the person responsible for carrying out the inspection; date of the inspection, and follow-up on any anomalies detected. For detectors, the dates on which maintenance and recharging were carried out shall be recorded; c) The results of the gas sampling carried out, and the name and signature of the person responsible for the ventilation areas; - When carrying out a walk-through of the interior of the small-scale operations or underground mine, it is confirmed that: a) all workers have self-rescuers; b) The use of open-flame equipment or devices and electrical or electronic apparatus is prohibited; c) A reserve of 400 kg of inert dust is kept in dry locations. Small-scale operations shall keep 250 kg, and d) A permanent reserve of inert dust of at least 5 tonnes is maintained outside the mine. For small-scale operations, the reserve shall be 750 kg. content of the elements - It presents the geological study; required in the risk analysis, the procedures, - The geological study includes a drawing showing of the Standard. - It presents the risk analysis for be presented in printed sudden methane gas and coal form or by electronic means. outbursts; - The risk analysis includes at least: To assess compliance with the safety conditions and a) History of outbursts in measures for preventing risks Chapter, a checklist may be drawn up including d) Structural geological maps; all those provisions e) Distribution of methane gas content that can be confirmed by in the coal seam; where measuring equipment f) Presence of mylonite; needs to be used, g) Geological structures in the upper where applicable. and lower parts of the seam to be mined; For small-scale operations, h) Depth of the seam to be mined; the history of sudden outbursts will not be required i) Direction of the main fracturing of the in mining operations carried out in coal seam to be mined, and the region; the types of j) Statistics on methane gas concentrations possible outbursts; the distribution in the coal seam. of methane gas contents in the coal seam; the presence of mylonite In small-scale operations, in the seam's stratigraphy, nor items d), e) and f) do not apply; sudden methane gas and coal outbursts; - It presents the degasification plan; - It presents the maintenance programme for the vacuum system; - The maintenance programme considers at least: a) Frequency of execution; b) Person responsible, and c) Established routines; - It presents a work plan, where the results of the risk analysis determine that the coal mines are susceptible to sudden methane gas and coal outbursts, enabling it to manage actions to prevent risks; - The work plan includes at least: a) Safety measures; b) Information on risk indicators; c) Training that the workers on the working faces shall receive to control them; d) Safety instructions for carrying out the activities; e) Type of tools to be used and, where applicable, machinery, and f) Methodology for determining the dimensions of the protective boreholes; - It presents the updated records of the behaviour of the risk indicators for the working faces, for the areas undergoing mining; - The records include at least: a) Observations, deviations and actions taken during the work shift; b) Analysis and interpretation of the geological conditions, reports, changes in the geological structure, among others; c) Analysis of gases from exploratory boreholes, and d) Records; - It presents documentary evidence that the analyses and interpretation are carried out by personnel trained for those tasks and designated by the employer, and - When carrying out a walk-through of the small-scale operations or underground mine, it is confirmed that the safety measures and conditions established in this Chapter are met. content of the elements - It presents the up-to-date list of the required in the risk analysis, the procedures and machinery and equipment used for exploration, mining, extraction and programmes, it is advisable to transport, installed in underground coal mines; review this chapter of the Standard. - The list indicates, for each item, be presented in printed a) Fleet or identification number; form or by electronic means. b) General description of its use; To assess compliance with c) Location; the safety conditions and measures for the operation of d) Type of fuel or energy used, and machinery and equipment in e) Type of use; underground coal mines - It presents the maintenance programme established by this Chapter, a for the machinery and equipment used in checklist may be drawn up including all those provisions underground coal mines; that can be confirmed by physical inspection, including - The maintenance programme includes at those where measuring least: equipment needs to be used, a) Fleet or identification number; where applicable. b) Scheduled dates for carrying out maintenance; c) Maintenance routines that take into account the checking of safety devices, and the person responsible for the activity; - It presents the safety procedures for carrying out maintenance activities on the equipment or machinery used in underground coal mines; - The safety procedures include at least: a) Equipment, tools and substances to be used; b) Safety measures for carrying out the maintenance; c) Personal protective equipment for the worker carrying out the maintenance; d) Safety measures to be applied during the maintenance, and e) Authorisations the worker shall obtain before carrying out the maintenance; - It presents the risk analysis for the operation of machinery and equipment inside the small-scale operations or underground coal mines, including at least a general or specific description, as applicable, of the risks and safety conditions; - It presents the procedure for energy isolation or de-energisation and signage, on the machinery and equipment; - It presents the work procedures including the safety measures and prohibitions applicable to the operation of machinery and equipment, in accordance with the risk analysis; - It presents the record of the results of the assessments of exhaust gas concentrations from diesel combustion engines; - The assessments are carried out every fifteen days, and - The records include the dates on which the assessments were carried out, and - When carrying out a walk-through of the small-scale operations or underground mine, it is confirmed that the safety measures and conditions established in this Chapter are met. content of the elements - It presents, the studies carried out before required in the studies, mining the seam: be presented in printed permanently; To assess compliance with - It presents, on the basis of the results of the the safety conditions and studies: measures for carrying out excavations and reinforcement a) The design and selection criteria for the in underground coal mines, timbering; established by this Chapter, a b) The materials to be used in the structural checklist may be drawn up including all support; those provisions that can be confirmed by manner c) The drawings, sections and diagrams of the physical, including those where structural support; measuring equipment needs to be used, in case d) The safety procedures for that applicable. carrying out the excavation; e) The safety procedures for In small-scale operations it shall not be required: carrying out the reinforcement work; a) That they include the machinery to be used, nor the safety f) The safety conditions for preventing conditions for when the mining mechanical risks to workers, and is carried out with a g) The design or dimensions of the coal b) That the equipment and machinery to be used in pillars; carrying out the excavation are not included in the safety procedures - The safety procedures for for carrying out the reinforcement work, when only a carrying out the excavation include: handsaw is used. a) Machinery and equipment to be used; c) That, in preparing the b) Characteristics of the excavation materials; reinforcement plan, the diameter and type of roof-bolt used for c) Safety measures to prevent the roof consolidation, the anchor excavations from connecting to a water source; depth, and the reinforcement systems for the d) Type of timbering; the minimum space needed development workings and to operate the roof-support, roof-caving e) Prohibition on removing the reinforcement of excavations, and personnel-transport equipment, and the instructions small-scale operations or any other type of for installing and dismantling the tunnel, unless the timbering; d) A special rock-mechanics study shall not be excavation is backfilled or supported by another type of required for when the spacing timbering, and between crosscuts is more than 70 f) Instructions for activating the metres, where the dimensions from emergency response plan; crosscut to crosscut or from - The safety procedures for diagonal to diagonal are 20 to carrying out the reinforcement work include at least: 25 metres, a) Direction-control method for maintaining the planned heading of the galleries; b) Safety instructions for crosscut or diagonal breakthroughs; additional; d) Materials for constructing timbering; e) Types of timbering installations; f) Machinery, equipment or tools to be used; g) Sequence of activities in installing timbering; h) Instructions for placing timbering where geological faults or defects are identified; i) Frequency at which timbering inspections shall be carried out, and j) Records of inspections carried out; - The records of inspections carried out include at least: a) Location of the timbering inspected; b) Dates of the inspections; c) Condition of the timbering; d) Recommendations for remedying deficiencies found, and e) Name of the person responsible for carrying out the inspection; - It presents the reinforcement plan; - The reinforcement plan considers at least: a) Control of displacements and maintenance of the stability of the mine strata; b) That the reinforcement is in accordance with the predominant geological conditions of the working system used in the mine, and that it is modified whenever the predominant geological conditions change; c) Roof control for securing the reinforcement; d) The dimensions of the gallery; e) The size or dimensions of the pillars; f) The pillar-recovery methods, and g) The reinforcement systems for the long face and the specific reinforcement for development workings and excavations. - It presents a reinforcement procedure for areas at high risk of rockfall, including at least: a) Instructions for recovering materials used to support and reinforce roofs; b) Instructions for the use of tools and safety devices; c) Instructions for positioning the persons involved in the operation in a safe place, and d) Instructions for carrying out visual inspections on each shift, to assess the behaviour and deformation of the timbering system; - It presents the work procedure for installing reinforcement, taking into account the operating cycle of cutting given timbered cutting; - It presents a special rock-mechanics study, where the spacing between crosscuts is more than 70 metres; - The special rock-mechanics study considers at least: a) The cross-section of the gallery; b) The density of the timbering; c) The type and capacity of the timbering; d) Additional reinforcement; e) The depth of the cut, and f) The quality of the immediate roof; - It presents the records of the results of ground stability behaviour, in areas with water seepage from the roof or ribs; - The records include at least: a) Date of the check; b) Description of the location checked; c) Conditions detected, and d) Name and signature of the person who carried out the check; - The records are kept for twelve months, and - When carrying out a walk-through of the small-scale operations or underground mine, it is confirmed that the safety measures and conditions established in this Chapter are met. It presents the hydrogeological study; required in the studies and a) The drawings of the operations of the Standard. aquifers and surface water deposits be presented in printed near the operation site; form or by electronic means. b) The location of old or To assess compliance with abandoned workings near the safety conditions and area to be mined, and the permitted proximity to old measures for flooding in or abandoned workings; underground coal mines established by this Chapter, a - It presents the updated study when: checklist may be drawn up including all a) The coal extraction processes are modified; those provisions that can be confirmed by manner New areas are assessed for mining, and physical, including those c) The results of the inspections indicate where measuring high frequencies and quantities of equipment needs to be used, water seepage into the mine or small-scale where applicable. operations; - It presents the records of the horizontal exploratory drilling work; - The records shall contain at least: a) The drilling pattern; b) The dates of execution; c) The drilling lengths; d) The length of the protective borehole left after mining; e) The diameter of the borehole; f) The shifts; g) The names of the worker and the supervisor, and h) Where applicable, the presence of water or gas through the boreholes; - It presents the operating report, after the mining activities for each shift have been carried out, recording the length of the protective barrier left; - It presents the drawing showing the location of the pumping systems; The drawings of the pumping systems shall include at least: a) The location of the pumps; b) The diameters of the pipework; c) Types and capacities of the pumps, and d) Discharge points for the pumped water; - When carrying out a walk-through of the small-scale operations or underground mine, it is confirmed that the safety measures and conditions established in this Chapter are met; and - When interviewing the workers, it is confirmed that they are informed of the hazard locations marked on the drawings showing the location of water accumulation zones near the mining areas. content of the elements - It presents a safe working procedure for procedures and programmes, it is transporting major equipment; advisable to review this - The safe working procedure for chapter of the Standard. transporting major equipment shall at least be presented in printed or by contain: they project, leaving a clear space of 40 electronic means. cm on each side; To assess compliance with b) That no personnel are present along the roadway the safety conditions and between the origin and the destination; measures for the transport of personnel and materials in d) That the operation is supervised by the underground coal mines person in charge of traffic; established by this Chapter, a - It presents the operating manual for those provisions that can be transporting personnel or materials on confirmed by physical inspection, tyres or on tracks; including those where measuring equipment needs to be used, a) That the most common rules where applicable. of the manual are communicated by means of signs, notices or posters, or b) Through an interview, that the workers receive the information; - It presents, if using this alternative method to the use of cages, the study permitting the use of skips for transporting personnel through small-scale operations; - The study on transporting personnel in skips through small-scale operations contains at least: a) The diameter of the hoist drums; b) The diameter of the cables; c) The ascent and descent speeds; d) The type of motor to be used; e) The diameter of the shafts; f) The characteristics of the hoist's braking guides, and g) The characteristics of the skips; - It presents documentary evidence of the training and instruction provided to the operators of remote-control devices for motorised vehicles, or confirms through an interview with the workers that they were trained and instructed; - It presents the manual of safety procedures for the operation of the chairlifts; - It presents the maintenance programme for the chairlifts; - The maintenance programme considers: a) Cleaning and elimination of leaks, and b) Tests on the steel cable; - It presents the materials transport procedure; - The materials transport procedure contains at least: a) Equipment to be used; b) Materials to be transported; c) Method of loading and unloading materials; d) Communication systems to be used, and e) Traffic instructions; - It presents the safety procedures for the operation of the hoists, which shall at least consider: a) That at the start of each shift and after each stoppage for repairs, the empty cage is moved along the shaft; b) That the simultaneous descent or ascent of materials and workers in the same cage is not permitted; c) The instructions for acting in the event of doubt about a signal; d) The instructions for when there is water at the bottom of a shaft; e) The precautions or measures the operator shall take before leaving the controls; f) That inspections and tests are carried out only by workers trained and authorised by the employer; g) The method for recording the results of the inspections, tests and maintenance of the shaft, equipment and accessories; h) The procedure to follow when the drum or pulley is disengaged, where two-ended hoists are used, and i) The frequency for cutting the ends of the cables at both extremities; - It presents an inspection and test programme; - The inspection and test programme includes the frequency in accordance with the following: a) One day for visual inspection of accessories and safety devices that prevent the free fall of cages or cars in the event of cable failure; b) One week for visual inspection of the external elements of the machines, the headframe, and elements required in the shafts; c) Two weeks for visual inspection of the timbering and the shaft walls, and d) One month for inspection of motors, brakes, clutches, and testing of safety devices that prevent the free fall of cages or cars in the event of cable failure; - When carrying out a walk-through of the small-scale operations or underground mine, it is confirmed that the safety measures and conditions established in this Chapter are met. To determine the number of workers to be interviewed in cases where this is required, except where the number is specified, the following table shall be applied: No. of workers at the workplace No. of workers to be interviewed 0-30 1 31-100 2 101-500 4 More than 500 5

Enforcement of compliance with this Standard is the responsibility of the Ministry of Labour and Social Welfare.

● Draft Code of Practice on Safety in Underground Coalmines. International Labour Organization. Geneva, 2006. ● Royal Decree 863, General Regulation of Basic Mining Safety Standards and Supplementary Technical Instructions. Ministry of Industry, Tourism and Trade. Madrid, Spain, 1995. ● Council Directive 92/91/EEC of 3 November 1992 concerning the minimum requirements for improving the safety and health protection of workers in the mineral-extracting industries through drilling. ● Council Directive 92/104/EEC of 3 December 1992 on the minimum requirements for improving the safety and health protection of workers in surface and underground mineral-extracting industries. ● Royal Decree 1389/1997, of 5 September, approving the minimum provisions intended to protect the safety and health of workers in mining activities. Ministry of Industry and Energy of Spain. ● Convention 176 of the International Labour Organization concerning Safety and Health in Mines. Geneva, 1995. ● R-183, Recommendation concerning Safety and Health in Mines. Geneva, 1995. ● Decree No. 1335 (15 July 1987), Safety in the mining industry, whereby the safety regulation for underground work is issued. Republic of Colombia. ● Regulation respecting occupational health and safety in mines. Canada, 1993. ● MSHA, USA, part 70 - Mandatory health standards - Underground coal mines subchapter O - Coal mine safety and health. ● Mining Works Regulations of the MICARE and MIMOSA Mines, Grupo Acerero del Norte. ● NOM-121-STPS-1996, Safety and hygiene for work carried out in mines, Official Gazette of the Federation, 21 July 1997. ● NOM-023-STPS-2003, Work in mines - Occupational safety and health conditions, Official Gazette of the Federation, 2 October 2003.

This Standard does not correspond to any international standard, as none existed at the time it was drafted.

FIRST. This Official Mexican Standard shall enter into force ninety calendar days after its publication in the Official Gazette of the Federation. SECOND. During the period referred to in the foregoing article, employers shall comply with the specific provisions for underground coal mines set out in Official Mexican Standard NOM-023-STPS-2003, Work in mines - Occupational safety and health conditions, published in the Official Gazette of the Federation on 2 October 2003, or shall make the adaptations needed to observe the provisions of this Official Mexican Standard, and, in the latter case, the labour authorities shall, at the request of the employers concerned, provide advice and guidance to help them implement compliance, without the employers becoming liable to penalties for non-compliance with the Standard in force. THIRD. As from the date on which this Official Mexican Standard enters into force, the specific provisions for underground coal mines set out in Official Mexican Standard NOM-023-STPS-2003, Work in mines - Occupational safety and health conditions, shall cease to have effect. Given in Mexico City, on the twenty-second day of the month of December two thousand and eight.- The Secretary of Labour and Social Welfare, Javier Lozano Alarcón.- Signature.