NOM-022-STPS-2015, Static electricity in workplaces - Safety conditions

Whereas, in accordance with article 46, paragraph I, of the Federal Law on Metrology and Standardisation, the Ministry of Labour and Social Welfare submitted to the National Advisory Committee for Standardisation on Occupational Safety and Health, at its Twelfth Ordinary Session, held on 9 December 2014, the Draft amendment to Official Mexican Standard NOM-022-STPS-2008, Static electricity in workplaces - Safety conditions, so as to become PROY-NOM-022-STPS-2014, Static electricity in workplaces - Safety conditions, and that Committee found it to be appropriate and agreed that it should be published as a Draft in the Official Gazette of the Federation; Whereas, as determined by articles 69-E and 69-H of the Federal Law on Administrative Procedure, the corresponding Draft was submitted for consideration to the Federal Commission for Regulatory Improvement, which issued a favourable ruling on it; Whereas, in accordance with article 47, paragraph I, of the Federal Law on Metrology and Standardisation, the Draft amendment to Official Mexican Standard NOM-022-STPS-2008, Static electricity in workplaces - Safety conditions, so as to become PROY-NOM-022-STPS-2014, Static electricity in workplaces - Safety conditions, was published for public consultation for sixty calendar days in the Official Gazette of the Federation of 6 January 2015, so that during that period interested parties could submit their comments to the National Advisory Committee for Standardisation on Occupational Safety and Health; Whereas, having received comments from ten submitting parties, that Committee examined them and ruled on them in due course, and this Ministry accordingly published the respective replies in the Official Gazette of the Federation of 20 August 2015, on the basis of article 47, paragraph III, of the Federal Law on Metrology and Standardisation; Whereas, following the incorporation of the comments submitted on the Draft amendment to Official Mexican Standard NOM-022-STPS-2008, Static electricity in workplaces - Safety conditions, so as to become PROY-NOM-022-STPS-2014, Static electricity in workplaces - Safety conditions, and the final review of the draft itself, various amendments were made with the aim of giving clarity, consistency and legal certainty as regards the provisions that apply in workplaces, and Whereas, in view of the foregoing considerations, and given that the National Advisory Committee for Standardisation on Occupational Safety and Health, at its Third Ordinary Session of 2015, granted its approval, the following is hereby issued: OFFICIAL MEXICAN STANDARD NOM-022-STPS-2015, STATIC ELECTRICITY IN WORKPLACES - SAFETY CONDITIONS

REFERENCE GUIDE I. Examples of installations where static electricity is generated and measures intended to prevent accidents, and example cases in which the installation of a lightning protection system is suggested for consideration

To establish the safety conditions in workplaces to prevent the risks from static electricity and from atmospheric electrical discharges.

2.1 This Standard is in force throughout the national territory and applies in the areas of workplaces where flammable or explosive substances are stored, handled or transported, or in those which, by the nature of their processes, materials and equipment, are capable of storing or generating static electric charges.

2.2 This Standard does not apply to motor vehicles, railway vehicles, vessels and/or aircraft used for land, sea, river or air transport, which fall within the competence of the Ministry of Communications and Transport.

For the correct application of this Standard, the following Official Mexican Standards and the Mexican standard in force, or those replacing them, shall be consulted:

3.1 NOM-002-STPS-2010, Safety conditions - Fire prevention and protection in workplaces.

3.2 NOM-017-STPS-2008, Personal protective equipment - Selection, use and management in workplaces.

3.3 NOM-018-STPS-2000, System for the identification and communication of hazards and risks from hazardous chemical substances in workplaces.

3.4 NOM-026-STPS-2008, Safety and health colours and signs, and identification of hazards from fluids conveyed in pipework.

3.5 NMX-J-549-ANCE-2005, Lightning protection system - Specifications, materials and measurement methods.

For the purposes of this Standard, the following definitions are taken to apply:

4.1 Labour authority: The competent administrative units of the Ministry of Labour and Social Welfare that carry out inspection and enforcement functions in matters of occupational safety and health, and the corresponding units of the federal states and of Mexico City acting in support of them.

4.2 Static electric charge: The physical property of matter manifested by the loss or gain of electrons, generally in electrically insulating materials, or in conductive materials insulated from earth, that have been in contact or under pressure.

4.3 Earth connection; Earthing: The action and effect of electrically connecting one or more elements of an item of equipment or a circuit to an electrode or to an earthing system, in such a way that they are at zero (0) electrical potential.

4.4 Lightning current: The current that flows to the point where the lightning makes contact with the earth (with a structure or with the constituent elements of the lightning protection system), associated with the sudden process of neutralisation of the cloud charge through a flow of electrons in the ionised channel by which the movement of the cloud charge to earth takes place, formed by discontinuous discharges in air.

4.5 Electrical discharge: The flow of current generated between two bodies with a difference of potential when the dielectric of the air between them breaks down.

4.6 Atmospheric electrical discharge: The transfer of electric charges between cloud and cloud, or from cloud to earth.

4.7 Lightning ground flash density: The number of lightning strikes to earth per square kilometre per year in a specific region.

4.8 Static electricity: The electric charges that are generated and stored in solid materials, particles or fluids.

4.9 Earth electrode(s); Electrode(s) of the earthing network: The buried metal element(s) that establish an electrical connection to earth.

4.10 Lightning conductor; Air termination: The metal elements whose function is to offer a point of incidence to receive the lightning discharge.

4.11 Earthing network; Earthing system: The set of conductors and connections, electrode or electrodes, accessories and other buried metal elements which, interconnected with one another, are intended to drain to earth the currents of a lightning strike and those generated by static electric charges.

4.12 Lightning protection system: The set of elements used to protect an area against the effect of atmospheric electrical discharges. This set is composed of an external system and an internal protection system, on the following basis: a) External lightning protection system; Lightning conductor system: The set of elements to intercept (air terminations), conduct (down conductors) and dissipate (earthing network) the lightning current efficiently, and b) Internal lightning protection system: The set of elements formed by all those protective measures that make it possible to reduce the risk of harm to the workers and installations of the workplace, by means of earthing, equipotential bonding, electromagnetic shielding and surge suppressors.

4.13 Electrical bond; Equipotential bonding: The permanent connection of metal parts to form an electrically conductive path that ensures continuity and the capacity to conduct, so that they are at the same electrical potential.

5.1 To establish the safety conditions to control the generation and/or accumulation of static electric charges in the areas of the workplace, in accordance with Chapter 7 of this Standard.

5.2 To install a lightning protection system in the areas or installations of workplaces where flammable or explosive substances are stored, handled or transported, in accordance with Chapter 8 of this Standard.

5.3 To measure the earth resistance of the earthing network, in accordance with Chapter 9 of this Standard, to check the continuity at the earth connection points and, where applicable, to measure the relative humidity where this is a measure for controlling the generation and accumulation of static electric charges, on the basis of paragraph 7.3 of this Standard.

5.4 To inform all the workers and the Safety and Health Committee of the risks that static electricity represents and how to avoid them, taking into account, where applicable, contractors, suppliers and visitors.

5.5 To train and instruct the workers in the techniques for discharging or preventing the generation and accumulation of static electricity, in accordance with Chapter 10 of this Standard.

5.6 To record the values of the resistance of the earthing network, the check on electrical continuity and, where applicable, the relative humidity, in accordance with paragraphs 9.5 and 7.3, subparagraph a), respectively, of this Standard.

5.7 To show to the labour authority, at its request, the information and documentation that this Standard requires it to draw up or hold.

6.1 To observe the safety measures laid down in this Standard, and those established in the workplace for the prevention of risks from the generation and accumulation of static electricity.

6.2 To take part in the training and instruction that the employer provides them.

6.3 To notify the employer, in accordance with the procedure established for that purpose, of any abnormal situation they detect in the earthing systems and the lightning protection system.

7.1 The safety conditions for controlling the generation and/or accumulation of static electricity shall be determined on the following basis: a) The nature of the work (this refers to the stages of the process, the equipment, the presence of friction, the speed of conveying or pouring fluids and the types of working procedures, among other characteristics); b) The physicochemical characteristics of the substances (temperature, flash point, explosivity limit, viscosity, specific conductivity of the substance, density, among others) that are handled, stored or transported; c) The characteristics of the environment as regards relative humidity and temperature, and d) The characteristics of the construction materials of the machinery, equipment and building.

7.2 To control the generation or accumulation of static electricity, the following safety measures shall be adopted as applicable: a) Install earthing systems, devices or equipment to control static electricity, according to the types of processes and installations in place, such as: ionisers; static electricity neutralisers or eliminators; earthed devices; earthed mechanical brushes; static electricity dissipation bars, or by applying treatments to belts, among others; b) Ensure electrical bonding or equipotential bonding between machines, equipment, containers and metal components; c) Carry out the measurement of the earth resistance of the earthing network, in accordance with Chapter 9 of this Standard, and the check on continuity at the earth connection points, at least every twelve months. The values shall comply with the following: 1) Have a value of 10 ohms or less for the earth resistance of the electrode(s) in lightning conductor systems or lightning protection systems; 2) Have a value of 25 ohms or less for the earth resistance of the earthing network, and 3) Electrical continuity shall exist at the earth connection points of the equipment that may generate or store static electricity. Reference guide I indicates by way of illustration the points to be inspected and how to measure the electrical continuity of the connections; d) Lay antistatic or conductive floors; e) Humidify the environment, maintaining a relative humidity above 65%. This provision does not apply to those cases in which, by the nature of the substances, the humidity of the air poses a danger through reaction with the substance, in which case the control of the accumulation of static electricity shall be carried out by other means; f) Ionise the air in the vicinity of the charged equipment, container or object, and/or g) Increase the conductivity of the materials liable to generate and accumulate static electric charges by adding conductive additives (for example, carbon black, carbon additives, graphite and other electrically conductive products).

7.3 In enclosed work areas where relative humidity is the measure, or one of the measures, adopted to control the accumulation of static electricity, the following shall be carried out: a) Maintain the relative humidity at a level above 65%; b) Measure the relative humidity and record its value at least every twelve months and/or when modifications are made to the work area that may affect this condition, and c) Monitor, where applicable, the relative humidity of the areas or processes on a continuous basis where it constitutes a safety measure against the danger of fire or explosion. The monitoring shall be carried out by means of equipment fitted with an alarm indicating that the relative humidity has fallen to levels below that laid down in subparagraph a) of this paragraph. The equipment used for measuring and/or monitoring the relative humidity shall have a valid calibration certificate, under the terms laid down by the Federal Law on Metrology and Standardisation.

7.4 In work areas where the presence of static electricity on the worker's body represents a risk, antistatic or conductive materials, or devices to drain to earth the currents accumulated on the worker, shall be provided.

7.5 In the zones where flammable or explosive substances are handled, stored or transported, the metal parts that are not intended to carry electrical energy and that are not already inherently earthed, such as metal tanks, metal enclosures of equipment, machinery and pipework, shall be earthed.

8.1 Workplaces or areas classified as being at high fire risk in accordance with NOM-002-STPS-2010, or the standards that replace it, shall install a lightning protection system, such as a lightning conductor system. For the design and installation of the lightning protection system, Mexican Standard NMX-J-549-ANCE-2005, or the standards that replace it, may be consulted. Reference guide I presents some examples in which the installation of a lightning protection system is suggested for consideration.

8.2 To select an external lightning protection system, whether with conventional air terminations or with air terminations of alternative technologies, at least the following factors shall be taken into account: a) The general layout of the workplace (plan, sections and elevations); b) The flammable or explosive substances stored, handled or transported in the workplace, as regards their flammability or explosivity and their tendency to generate and accumulate static electric charges, on account of their physicochemical characteristics and those of the containers and/or pipework, and the nature of the processes to which they are subject and the prevailing conditions of the environment; c) The lightning ground flash density of the region, and d) The protection zone of the system.

8.3 The workplace shall have a study demonstrating that the coverage area of the external lightning protection system encompasses the building, premises or risk zone in which the flammable or explosive substances are handled. The study shall be drawn up by an electrical engineer or similar and shall contain at least the following: a) The type and characteristics of the system installed; b) The height of the air terminations projecting above any of the surrounding structures; c) The location of the system; d) The protection coverage area, with the methodology used for its calculation, and e) The name and signature of the person who drew it up, and their professional licence number.

8.4 To reduce the risk of electric shock arising from the flow of the lightning current in the down conductors and in the elements of the earthing network of the external lightning protection system, the following shall be adopted: a) Install an arrangement of the earthing system and provide a high-resistivity surface in the zone where workers move about, such as crushed gravel at least 0.10 metres thick, between the natural ground and the elements of the earthing system; b) Provide weather-resistant non-metallic ducting over the surface of the down conductor, so as to reduce the possibility of accidental or incidental contact by the workers; c) Place on the ducting warning notices reading “DANGER: POSSIBLE LIGHTNING CURRENT”, in accordance with NOM-026-STPS-2008, or the standards that replace it; d) Electrically bond to the earthing system (below floor level) all the metal elements and reinforcing steel of the structure to be protected, by means of horizontal earth electrodes placed at a minimum depth of 0.60 metres, and e) Install the down conductor in such a way that its route is as short as possible and crossings with electrical installations are avoided.

8.5 Workers who carry out activities in places where there is exposure to the incidence of lightning discharges and who are not protected against this risk, such as the roofs of buildings that project in height above other adjoining structures, lighting or cabling poles or towers, elevated platforms, antennas, among others, shall suspend the activity as soon as an electrical storm approaches.

8.6 The earthing network of lightning conductor systems shall be interconnected with other earthing networks, such as those of motors, substations or the electrical system in general.

8.7 The electrodes of the earthing network of lightning conductor systems shall allow their disconnection when the measurement referred to in Chapter 9 of this Standard is carried out. To that end, the electrodes shall have means allowing their disconnection and preventing false contacts.

8.8 The use of lightning conductors that are manufactured from, or operate on the basis of, radioactive materials is prohibited.

9.1 The measurement of the earth resistance of the earthing network shall be carried out by applying the fall-of-potential method, in accordance with paragraph 9.4 of this Standard. This measurement shall be made taking into account the most unfavourable condition as regards the degree of moisture of the ground in which the earthing network has been installed.

9.2 To carry out the measurement of the earth resistance of the earthing network, the following instruments shall be available: a) Earth resistance measuring equipment with the following characteristics: 1) A frequency range of 90 Hz to 200 Hz or greater, and 2) Able to supply current with values of at least 0.1 mA; b) Accessories supplied by the manufacturer of the measuring equipment or, where there are no accessories for the measuring equipment, use insulated copper cable or cord with a sheath appropriate to the conditions of use with a most common use designation of 2.08 mm 2 (14 AWG) or 1.307 mm2 (16 AWG), with accessories at its ends for the correct connection to the equipment, and auxiliary electrodes with a minimum length of 50 centimetres and a minimum diameter of 13 millimetres of one of the following materials: stainless steel, copper-clad steel or galvanised steel; c) An ohmmeter or earth resistance meter to check the continuity of the earth connections, with a resolution of at least 1 ohm; d) A voltmeter with a resolution of at least 1 volt, and e) A tape measure or similar length-measuring instrument.

9.3 The ohmmeter or earth resistance meter and the voltmeter shall have a valid calibration certificate, under the terms determined by the Federal Law on Metrology and Standardisation.

9.4 The measurement of the earth resistance of the earthing network shall be carried out as follows: a) Verify that the electrode under test (which corresponds to the earthing network) is disconnected from the earthing network, taking the following into account: 1) Carry out the disconnection of the earthing network with the electrical equipment de-energised, and 2) Make the measurement of the earth resistance by disconnecting each electrode individually, where it is made under normal operating conditions, so as not to leave the workers unprotected; b) Set the needle of the analogue measuring instrument to zero, or verify that the power source of the digital equipment has enough energy to carry out the set of measurements; c) Apply the fall-of-potential method as follows: 1) Pass a current between two electrodes: one called C1 (which corresponds to the earthing network) and an auxiliary electrode called C2, which is driven into the ground at a minimum distance of 20 metres from C1. To make the first measurement, another auxiliary electrode called P1 is driven into the ground, one metre away from C1, between the electrode under test C1 and the auxiliary electrode C2; 2) Move the auxiliary electrode P1 linearly 3 metres from the first measurement and in the direction of the auxiliary electrode C2 to make the second measurement, and 3) Make the subsequent measurements by moving the auxiliary electrode P1 every 3 metres until 19 metres are completed. Figure 1 shows the placement of the electrodes of the earthing network and the auxiliary electrodes; d) Record the values obtained from the measurements; e) Draw a graph on the basis of the values recorded, similar to the one illustrated in the lower part of Figure 1 below; D1 Distance between the electrode of the earthing network C1 and the auxiliary electrode P1. DT Distance between the electrode of the earthing network C1 and the auxiliary electrode C2. Figure 1 - Position of electrodes and graph of electrical resistance values vs. distance f) Obtain the value of the earth resistance of the earthing network from the intersection of the resistance axis with the part of the curve parallel to the distance axis; g) Repeat the measurements, moving electrode C2 away from electrode C1, where the curve obtained does not present a parallel stretch, until values parallel to the distance axis are obtained, and h) Verify that the values of the earth resistance of the earthing network obtained in this test are 10 ohms or less for the electrode(s) of the lightning conductor system, and/or have a value of 25 ohms or less for the earth resistance of the earthing network.

9.5 The result of the measurements shall be recorded; that record shall contain at least the following: a) The details of the workplace: 1) The name or company name of the workplace; 2) The address of the workplace; 3) The date on which the measurement was made, and 4) The name and signature of the person who made the measurement; b) The details of the measuring instruments: 1) The generic name of the instrument used; 2) The characteristics of the measuring equipment used (model, serial number, measuring ranges, precision, accuracy, etc.), and 3) A copy of the valid calibration certificate of the instrument used; c) The values of the measurements: 1) The values of the earth resistance of the earthing network and/or of the earth resistance of the electrode(s) of the lightning conductor system, and 2) An indication of whether electrical continuity exists at the connection points of the system; d) The sketch showing the measurement points of the earthing system and, where applicable, of the electrode(s) of the lightning conductor system, and e) The characteristics of the lightning conductor system used, where applicable, with at least the following: 1) The type of lightning conductor system; 2) The height of the air terminations; 3) The location, and 4) The protection coverage area.

10.1 Workers involved in activities in which static electricity is generated or accumulated, in the installation and inspection of earthing systems and lightning conductor systems, and in the determination of earth resistance and continuity of the networks, shall be provided with training and instruction to carry out these activities and to prevent the risks arising from them, which shall comprise at least the following: a) The technical fundamentals of the generation and accumulation of static electric charges; b) The processes in which the generation and accumulation of static electric charges occur, with emphasis on those carried out in their workplace, and the physical mechanisms by which this phenomenon occurs in each case; c) Solid and fluid materials - insulating, semiconducting and conducting - liable to become electrostatically charged; d) The risks caused by static electricity and the methods available for its control, dissipation and discharge; e) The risks arising from atmospheric electrical discharges and the safety measures to avoid them; f) The safety measures that this Standard sets out to prevent the risks from the generation and accumulation of static electricity; g) The safety conditions implemented in the workplace, in addition to the provisions of this Standard; h) The procedures, where applicable, for carrying out the installation and inspection of earthing systems and lightning conductor systems, and for the determination of earth resistance and continuity of the networks, and i) The proper use of the personal protective equipment supplied for the performance of their activities, in accordance with NOM-017-STPS-2008, or the standards that replace it.

10.2 The training and instruction provided to the workers shall be reinforced at least every two years.

10.3 Workplaces shall keep a record of the training and instruction they provide to the workers, which shall contain at least the following: a) The name and post of the workers to whom it was provided; b) The date on which the training and instruction were provided; c) The subjects taught, and d) The name of the instructor and, where applicable, the registration number as a training agent with the Ministry of Labour and Social Welfare.

11.1 The employer may choose to engage a verification unit and/or a testing laboratory, accredited and approved under the terms laid down by the Federal Law on Metrology and Standardisation and its Regulation.

11.2 Verification units engaged at the request of a party shall verify the degree of compliance with this Standard, in accordance with the conformity assessment procedure of Chapter 12 of this Standard and, where appropriate, issue an opinion of compliance, which shall contain: a) Details of the workplace verified: 1) Name, style or company name; 2) Federal Taxpayers Register; 3) Full address; 4) Telephone, and 5) Main activity; b) Details of the private body: 1) Name, style or company name; 2) Accreditation number; 3) Approval number granted by the Ministry of Labour and Social Welfare, and 4) Full address, and c) Details of the opinion: 1) Code of the standard; 2) Name of the verifier assessed and approved; 3) Services provided: preparation, execution and validation, in the case of opinions with a report of services; 4) Date of verification; 5) Number of the opinion; 6) Validity of the opinion; 7) Place of issue of the opinion, and 8) Date of issue of the opinion.

11.3 Testing laboratories may assess only what is determined by paragraphs 5.3 and 7.2 subparagraph c), Chapter 9 and, where applicable, paragraph 7.3 of this Standard.

11.4 Testing laboratories shall issue a report of results including the record, in accordance with paragraph 9.5 of this Standard and, where applicable, the result of the measurement of the relative humidity. The report of results shall contain: a) Details of the workplace assessed: 1) Name, style or company name; 2) Federal Taxpayers Register; 3) Full address; 4) Telephone, and 5) Main activity; b) Details of the private body: 1) Style or company name; 2) Accreditation number; 3) Approval number granted by the Ministry of Labour and Social Welfare, and 4) Full address, and c) Details of the report of results: 1) The code of the standard, the procedure for measuring the earth resistance of the electrode(s) of the lightning conductor system and of the earthing network, in accordance with paragraphs 9.1 and 9.4 of this Standard, the check on continuity at the earth connection points and, where applicable, the measurement and/or monitoring of the relative humidity; 2) The name of the signatory assessed and approved; 3) The equipment used and its serial number, on the basis of paragraphs 9.2 and 9.3 of this Standard; 4) The date on which the earth resistance of the electrode(s) of the lightning conductor system and of the earthing network was measured, the continuity at the earth connection points was checked and, where applicable, the relative humidity was measured and/or monitored; 5) The results of the measurements in accordance with paragraph 9.5 of this Standard; 6) The number of the report of results; 7) The validity of the report of results; 8) The place of issue of the report of results, and 9) The date of issue of the report of results.

11.5 The validity of the verification opinion and of the report of results, where these are favourable, shall be one year, provided that the conditions on which they were issued are not altered.

11.6 The directory of the verification units and testing laboratories approved by the Ministry may be consulted on the website of the Ministry of Labour and Social Welfare, via the Internet, at the electronic address: http://organismosprivados.stps.gob.mx/organismosprivados/index.html.

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

12.2 The report of results and the valid verification opinion, where applicable, shall be available to the labour authority at its request.

12.3 The aspects to be verified during the conformity assessment of this Standard shall be carried out, as applicable, by means of physical checks, documentary review, records or interviews, in accordance with the following: Type of Provision Acceptance criterion Observations Risk assessment

5.1 and 7 Physical. The employer complies when, on carrying out a walkthrough of the workplace, it is verified that it establishes safety conditions to control the generation and accumulation of static electric charges in the areas of the workplace. Serious. Documentary. The employer complies when it presents documentary evidence that it determines the safety conditions to control the generation and/or accumulation of static electricity on the basis of: - The nature of the work (this refers to the stages of the process, the equipment, the presence of friction, the speed of conveying or pouring fluids and the types of working procedures, among other characteristics); - The physicochemical characteristics of the substances (temperature, flash point, explosivity limit, viscosity, specific conductivity of the substance, density, among others) that are handled, stored or transported; - The characteristics of the environment as regards relative humidity and temperature, and - The characteristics of the construction materials of the machinery, equipment and building. Physical. The employer complies when, on carrying out a walkthrough of the workplace, it is verified that, to control the generation or accumulation of static electricity, the following safety measures, among others, are applied: Serious - It installs earthing systems, devices or equipment to control static electricity, according to the types of processes and installations in place, such as: ionisers; - It ensures equipotential bonding between machines, equipment, containers and metal components; - It lays antistatic or conductive floors; - It humidifies the environment, maintaining a relative humidity above 65%; - It ionises the air in the vicinity of the charged equipment, container or object, and/or - It increases the conductivity of the materials liable to generate and accumulate static electric charges by adding conductive additives (for example, carbon black, carbon additives, graphite and other electrically conductive products). This provision does not apply where, by the nature of the substances, the humidity of the air poses a danger through reaction with the substance, in which case the control of the accumulation of static electricity shall be carried out by other means. Documentary. The employer complies when it presents documentary evidence that: Serious - It carries out the measurement of the earth resistance of the earthing network and checks the continuity at the earth connection points, at least every twelve months; - The values are 10 ohms or less for the earth resistance of the electrode(s) in lightning conductor systems or lightning protection systems; - They have a value of 25 ohms or less for the earth resistance of the earthing network, and - Electrical continuity exists at the earth connection points of the equipment that may generate or store static electricity, and - In enclosed work areas where relative humidity is the measure, or one of the measures, adopted to control the accumulation of static electricity, it carries out the following: - It maintains the relative humidity at a level above 65%; - It measures the relative humidity and records its value, at least every twelve months, and - It monitors, where applicable, the relative humidity of the areas or processes on a continuous basis where this constitutes a safety measure against the danger of fire or explosion; - The monitoring is carried out by means of equipment fitted with an alarm indicating that the relative humidity has fallen to levels below 65%, and - The equipment used in measuring and/or monitoring the relative humidity has a valid calibration certificate, under the terms laid down by the Federal Law on Metrology and Standardisation. This provision does not apply to workplaces whose earthing network covers areas larger than 100 000 m2, for which the employer shall verify compliance. This provision does not apply to those cases in which, by the nature of the substances, the humidity of the air poses a danger through reaction with the substance, in which case the control of the accumulation of static electricity shall be carried out by other means. Physical. The employer complies when, on carrying out a walkthrough of the workplace, it is verified that: - In work areas where the presence of static electricity on the worker's body represents a risk, antistatic or conductive materials, or devices to drain to earth the currents accumulated on the worker, are provided, and - In the zones where flammable or explosive substances are handled, stored or transported, the metal parts that are not intended to carry electrical energy and that are not already inherently earthed, such as metal tanks, metal enclosures of equipment, machinery and pipework, are earthed.

   static electricity neutralisers or        does not apply to those
   eliminators; devices with an earth        cases in which, by the
   connection; earthed mechanical brushes;   nature of the
   static electricity dissipation bars, or   substances, the
   by applying treatments to belts, among    humidity of the air
   others;                                   poses a danger through
   - It ensures electrical bonding or        reaction with the substance, in

   - The values, the earth resistance of    by means of drawings
   the earthing network and the continuity   showing that the system
   at the earth connection points comply     covers that
   with the following:                       area
   - They have a value of 10 or less

5.2 and 8 Physical. The employer complies when, on carrying out a walkthrough of the workplace, it is verified that it installs a lightning protection system, such as a lightning conductor system, where the workplace or its areas are classified as being at high fire risk in accordance with NOM-002-STPS-2010, or the standards that replace it. This provision applies only where the workplace or its areas are classified as being at high fire risk in accordance with NOM-002-STPS-2010, or the standards that replace it. Documentary. The employer complies when it presents documentary evidence that: Serious - The general layout of the workplace (plan, sections and elevations); - The flammable or explosive substances stored, handled or transported in the workplace, as regards their flammability or explosivity and their tendency to generate and accumulate static electric charges, on account of their physicochemical characteristics and those of the containers and/or pipework, and the nature of the processes to which they are subject and the prevailing conditions of the environment, as provided for by NOM-018-STPS-2000, or the standards that replace it; - The study on the coverage area of the system covers the risk zone in which the flammable or explosive substances are handled, and - Specifications, materials and: the height of the air terminations projecting above any of the surrounding structures; the location of the system; the protection coverage area with the methodology used for its calculation; the name and signature of the person who drew it up, and their professional licence number. The selection, design and installation of the external lightning protection system, and the determination of its protection zone, may be carried out free of charge at the premises of the National Standardisation Body (Asociación) or directly at the electronic address http://www.ance.org.mx/NormalizacionOnLine/Index.aspx. Physical. The employer complies when, on carrying out a walkthrough of the workplace, it is verified that: - To reduce the risk of electric shock arising from the flow of the current in the down conductors and in the elements of the earthing network of the external lightning protection system, it adopts the following: - It installs an arrangement of the earthing system and provides a high-resistivity surface in the zone where workers move about, such as crushed gravel at least 0.10 metres thick, between the natural ground and the elements of the earthing system; - It provides weather-resistant non-metallic ducting over the surface of the down conductor, so as to reduce the possibility of accidental or incidental contact by the workers; - It places on the ducting warning notices reading “DANGER: POSSIBLE LIGHTNING CURRENT”, in accordance with NOM-026-STPS-2008, or the standards that replace it; - It electrically bonds to the earthing system (below floor level) all the metal elements and reinforcing steel of the structure to be protected, by means of horizontal earth electrodes placed at a minimum depth of 0.60 metres, and - It installs the down conductor in such a way that its route is as short as possible and crossings with electrical installations are avoided; - The earthing network of the lightning conductor systems is interconnected, where applicable, with other earthing networks, such as those of motors, substations or the electrical system in general; - The electrodes of the earthing network of the lightning conductor systems allow their disconnection when the measurement of the resistance of the earthing network is carried out, and have means allowing their disconnection and preventing false contacts, and - It uses lightning conductors that are not manufactured from, or do not operate on the basis of, radioactive materials. Interview. The employer complies when, on interviewing the workers selected in accordance with the sampling criterion of Table 2 of paragraph 12.4, it is verified that those workers who carry out activities in places where there is exposure to the incidence of lightning discharges, and who are not protected against this risk, such as the roofs of buildings that project in height above other adjoining structures, lighting or cabling poles or towers, elevated platforms, antennas, among others, suspend the activity as soon as an electrical storm approaches.

   - It takes into account, to select an    To identify whether
   external lightning protection system,    a substance is
   whether with conventional air            flammable or
   terminations or with air terminations    explosive, the
   of alternative technologies, at least    safety data sheets
   the following factors:                   shall be consulted

   - The lightning ground flash density of  in accordance with
   the region, and                          Mexican standard
   - The protection zone of the system;     NMX-J-549-ANCE-
   - It has a study demonstrating that      2005, Lightning
   the coverage area of the external        protection system
   lightning protection system covers the   against thunderstorms
   building, premises or

   external lightning protection system    measurement methods,
   was drawn up by an electrical engineer   or those replacing it.
   or similar, and contains at least the    This Mexican
   following:                               standard may be
   - The type and characteristics of the    consulted from
   system installed;

5.3 and 9 Documentary. The employer complies when it presents documentary evidence that: Serious - It measures the earth resistance of the earthing network and checks the continuity at the earth connection points and, where applicable, the relative humidity where this is a measure for controlling the generation and accumulation of static electric charges, on the basis of paragraph 7.3 of this Standard, and - The measurement of the earth resistance of the earthing network is carried out by applying the fall-of-potential method, in accordance with paragraph

9.4 of this Standard, and this measurement is made taking into account the most unfavourable condition as regards the degree of moisture of the ground in which the earthing network is installed. Physical. The employer complies when, on carrying out a walkthrough of the workplace, it is verified that, to carry out the measurement of the earth resistance of the earthing network, it has the following instruments: - Earth resistance measuring equipment with the following characteristics: - A frequency range of 90 Hz to 200 Hz or greater, and - Able to supply current with values of at least 0.1 mA; - Accessories supplied by the manufacturer of the measuring equipment or, where there are no accessories for the measuring equipment, it uses insulated copper cable or cord with a sheath appropriate to the conditions of use with a most common use designation of 2.08 mm2 (14 AWG) or 1.307 mm2 (16 AWG), with accessories at its ends for the correct connection to the equipment, and auxiliary electrodes with a minimum length of 50 centimetres and a minimum diameter of 13 millimetres of one of the following materials: stainless steel, copper-clad steel or galvanised steel; - An ohmmeter or earth resistance meter to check the continuity of the earth connections, with a resolution of at least 1 ohm; - A voltmeter with a resolution of at least 1 volt, and - A tape measure or similar length-measuring instrument. Demonstration of compliance with this requirement may also be made by presenting the original or a copy of the technical specifications of the equipment, instruments, electrodes and accessories used to carry out the measurement of the resistance of the earthing network, supplied by the manufacturer. Documentary. The employer complies when it presents documentary evidence that: Serious - The ohmmeter or earth resistance meter and the voltmeter have a valid calibration certificate, under the terms determined by the Federal Law on Metrology and Standardisation, and - The measurement of the earth resistance of the earthing network is carried out as follows: - It verifies that the electrode under test (which corresponds to the earthing network) is disconnected from the earthing network, taking the following into account: o It carries out the disconnection of the earthing network with the electrical equipment de-energised, and o It makes the measurement of the earth resistance by disconnecting each electrode individually, where it is made under normal operating conditions, so as not to leave the workers unprotected; - It sets the needle of the analogue measuring instrument to zero, or verifies that the power source of the digital equipment has enough energy to carry out the set of measurements; - It applies the fall-of-potential method as follows: o It passes a current between two electrodes: one called C1 (which corresponds to the earthing network) and an auxiliary electrode C2, which it drives into the ground at a minimum distance of 20 metres from C1. To make the first measurement it drives into the ground another auxiliary electrode called P1, one metre away from C1, between the electrode under test C1 and the auxiliary electrode C2; o It moves the auxiliary electrode P1 linearly 3 metres from the first measurement and in the direction of the auxiliary electrode C2 to make the second measurement, and o It makes the subsequent measurements by moving the auxiliary electrode P1 every 3 metres until 19 metres are completed. Figure 1 shows the placement of the electrodes of the earthing network and the auxiliary electrodes; - It records the values obtained from the measurements; - It draws a graph on the basis of the values recorded, similar to the one illustrated in the lower part of Figure 1; - It obtains the value of the earth resistance of the earthing network from the intersection of the resistance axis with the part of the curve parallel to the distance axis; - It repeats the measurements, moving electrode C2 away from electrode C1, where the curve obtained does not present a parallel stretch, until it obtains values parallel to the distance axis, and - It verifies that the values of the earth resistance of the earthing network obtained in this test are 10 ohms or less for the electrode(s) of the lightning conductor system, and/or have a value of 25 ohms or less for the earth resistance of the earthing network.

   o It makes the subsequent measurements
   by moving the

5.4 Documentary. The employer complies when it presents evidence - To the Safety and Health Committee. The evidence for the workers may be by means of leaflets, bulletins and/or posters.

5.5 and 10 Documentary. The employer complies when it presents documentary evidence that: - It trains and instructs the workers in the techniques for discharging or preventing the generation and accumulation of static electricity, and - The workers involved in activities in which static electricity is generated or accumulated, in the installation and inspection of earthing systems and lightning conductor systems, and in the determination of earth resistance and continuity of the networks, are provided with training and instruction to prevent the risks arising from these activities, which comprises at least the following subjects: - The technical fundamentals of the generation and accumulation of static electric charges; - The processes in which the generation and accumulation of static electric charges occur, with emphasis on those carried out in their workplace, and the physical mechanisms by which this phenomenon occurs in each case; - Solid and fluid materials - insulating, semiconducting and conducting - liable to become electrostatically charged; - The risks caused by static electricity and the methods available for its control, dissipation and discharge; - The risks arising from atmospheric electrical discharges and the safety measures to avoid them; - The safety measures that this Standard sets out to prevent the risks from the generation and accumulation of static electricity; - The safety conditions implemented in the workplace, in addition to the provisions of this Standard; - The procedures, where applicable, for carrying out the installation and inspection of earthing systems and lightning conductor systems, and for the determination of earth resistance and continuity, and - The proper use of the personal protective equipment supplied for the performance of their activities, in accordance with NOM-017-STPS-2008, or the standards that replace it, and - The training and instruction provided to the workers are reinforced at least every two years. The documentary evidence for compliance with this obligation consists of the certificates of occupational competence or skills under the terms laid down by the Federal Labour Law. Record. The employer complies when it presents evidence that it has the record of the training and instruction provided to the workers, which contains at least the following: - The name and post of the workers to whom it was provided; - The date on which the training and instruction were provided; - The subjects taught, and - The name of the instructor and, where applicable, the registration number as a training agent with the Ministry of Labour and Social Welfare.

   the generation and accumulation of      the certificates of
   static electricity, and                  competence or

5.6 and 9.5 Record. The employer complies when it presents evidence that it has the records of the values of the earth resistance of the earthing network, the check on electrical continuity and, where applicable, the relative humidity. The record contains at least the following: - The details of the workplace: - The name or company name of the workplace; - The address of the workplace; - The date on which the measurement was made, and - The name and signature of the person who made the measurement; - The details of the measuring instruments: - The generic name of the instrument used; - The characteristics of the measuring equipment used (model, serial number, measuring ranges, precision, accuracy, etc.), and - A copy of the valid calibration certificate of the instrument used; - The values of the measurements: - The values of the earth resistance of the earthing network and/or of the earth resistance of the electrode(s) of the lightning conductor system, and - An indication of whether electrical continuity exists at the connection points of the system; - The sketch showing the measurement points of the earthing system and, where applicable, of the electrode(s) of the lightning conductor system; - The characteristics of the lightning conductor system used, where applicable, with at least the following: - The type of lightning conductor system; - The height of the air terminations; - The location, and - The protection coverage area, and - The value of the relative humidity, where applicable.

12.4 For the selection of the workers to be interviewed, with the aim of verifying compliance with the provisions laid down by this conformity assessment procedure, the sampling criterion contained in Table 2 below shall be applied: Table 2 Sampling by random selection Total number of workers Number of workers to be interviewed 1-15 1 16-50 2 51-105 3 1 for every 35 workers up to a maximum More than 105 of 15

12.5 The documentary evidence or the records referred to in this Standard may be shown in printed form or on magnetic media, and shall be kept for at least one year.

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

14.1 Ministry of Labour and Social Affairs, Spain. National Institute for Occupational Safety and Health. NTP 567: Protection against electrostatic charges. 2000.

14.2 NFPA 77, Recommended Practice on Static Electricity. 2007 Edition.

14.3 NFPA 780, Standard for the Installation of Lightning Protection Systems. 2014 Edition.

14.4 NFPA 30, Flammable and Combustible Liquids Code. 2000 Edition.

14.5 Industrial Accident Prevention Association. A Health and Safety Guideline for Your Workplace. Static Electricity. 2008.

14.6 NOM-001-SEDE-2012, Electrical Installations (Utilisation).

This Official Mexican Standard does not correspond to any international standard, as no such reference existed at the time of its drafting.

FIRST. This Official Mexican Standard shall enter into force six months after its publication in the Official Gazette of the Federation. SECOND. During the period indicated in the preceding article, employers shall comply with Official Mexican Standard NOM-022-STPS-2008, Static electricity in workplaces - Safety conditions, or shall carry out the adaptations needed to observe the provisions of this Official Mexican Standard and, in the latter case, the labour authority shall provide, upon written request by the interested employers, advice and technical assistance under the terms laid down by the Federal Regulation on Federal Labour Inspection and the Application of Penalties, so as to put compliance into effect, without the employers becoming liable to penalties for non-compliance with the Standard in force. THIRD. From the date on which this Standard enters into force, Official Mexican Standard NOM-022-STPS-2008, Static electricity in workplaces - Safety conditions, published in the Official Gazette of the Federation on 7 November 2008, shall cease to have effect. Mexico City, on the seventeenth day of the month of March of two thousand and sixteen.- The Minister of Labour and Social Welfare, Jesús Alfonso Navarrete Prida.- Signed.

Examples of installations where static electricity is generated and measures intended to prevent accidents, and examples in which the installation of a lightning protection system is suggested for consideration. The content of this guide is a supplement for a better understanding of this Standard and is not mandatory. This guide mentions some examples of installations, equipment or processes that may be liable to accumulate or generate static electricity, and some of the safety measures that it is recommended be considered for the prevention of accidents arising from the generation and accumulation of static electricity. I.1 Installations, equipment or processes in which static electric charges may be generated or accumulated: a) The conveyor belt or pulley-driven transmission belt, and moving parts of machinery, where contact and friction occur; b) Rolled or woven material, such as metal, paper, fabric, etc., when passing between rollers; c) Equipment such as fans, pumps, dryers, motors, among others; d) Pipework conveying flammable or explosive substances, and its accessories; e) Installations equipped for spray painting or varnishing, and the objects to be painted or varnished and the walls of the booths, cubicles and vessels, and the extraction system; f) The equipment used in processes of decanting flammable and explosive substances, for example the transfer of non-conductive liquids through pipework, falling as a free jet; likewise where air or other gases bubble through liquids; g) Gases issuing at high speed from a nozzle, especially if they entrain liquid or solid particles; h) Pneumatic conveying and passage through hoppers of granulated or powdered product, such as seeds, powdered starch, metal powders, etc.; i) Operations of filling containers and mixing, filtering and stirring chemical substances, where static electricity may accumulate in the substance itself involved in one of these operations, and the extrusion of plastic films, and j) The use of dielectric footwear, such as insulating footwear with rubber and synthetic soles, and clothing of fibres such as silk, wool, acrylic fabric, rayon and synthetic fibres in general. Figure I.1 - Example of some equipment in which static electric charges may be generated and accumulated. I.2 General considerations on the safety measures to prevent accidents from the generation and accumulation of static electricity: I.2.1 One of the first aspects to be considered to prevent accidents from static electricity is to assess the risks that it may pose to the workers and to the workplace itself, as regards: a) Identification of the sites, equipment, machinery, processes, etc., where static electric charges may be generated and accumulated, some of which are mentioned in paragraph I.1 of this guide, and b) Assessment of the risks owing to the danger of fire or explosion, or any other of a different nature, related to the generation and accumulation of static electricity. It may at times be appropriate to measure the static electric charge, using a suitable instrument such as a voltmeter for an electrically conductive material, and a non-contact electrostatic voltmeter, or electric field meter, for non-conductive materials. The latter instrument detects the intensity of the electric field from the net charge on or in the non-conductive material. I.2.2 As regards the ignition risks arising from static electricity, these may be controlled by the following safety measures: a) Removing the flammable mixture from the area where static electricity may cause an electrical discharge capable of igniting that mixture; b) Reducing the generation or accumulation of static electric charges, or both, by means of changes in the process or materials, and c) Neutralising the static electric charges, the main means being the earthing of conductive materials and the ionisation of the air. I.2.3 The measures for controlling static electricity include those mentioned below; figure I.2 illustrates some of these measures: a) Earthing of the metal components of machinery, containers, pipework, hoppers, among other equipment; b) Equipotential bonding between machines, equipment, pipework, containers and metal components; c) Humidification of the environment or of the materials liable to accumulate static electric charges; d) Ionisation of the air in the vicinity of the charged object, so that the air becomes conductive enough to dissipate the static electric charges. The devices used are commonly called ionisers, neutralisers or static electricity eliminators; e) Increasing the conductivity of materials by adding additives such as carbon black to the rubber of tyres, hoses and conveyor belts, and carbon, graphite and other conductive products to reduce the electrical resistance of asphalts and synthetic floors; f) Use of conductive or antistatic footwear, and of wrist straps and ankle straps worn by the personnel and connected by cable to an earth; likewise, use of conductive materials in floors; g) Reduction of the flow velocity of a liquid conveyed by pipework, which in turn tends to reduce the rate of generation of static electricity; h) Extending the pipework for pouring flammable liquids through the top of a tank, so that this pipework ends within a distance of 150 mm from the bottom of the tank, to lessen the impact of the fall distance and the splashing, which tends to lessen the generation of static electricity; i) Reduction of the oxygen concentration, or inerting. For example, the values of the oxygen concentration below which no ignition of the substances indicated below occurs are: acetone 13.5 %; carbon disulphide and hydrogen 5.0 %; pea flour dust 15 % and aluminium powder 5 %. The gas most used for inerting is nitrogen; j) Implementing ventilation to prevent the formation of flammable or explosive atmospheres; when ventilation systems are implemented, precautions shall be taken, since these may themselves constitute a source of generation and accumulation of static electric charges; k) Pneumatic conveying of granulated or powdered material through earthed metal pipework; the equipment to which the pipework is connected should be metallic and earthed to dissipate the static electric charges that may be generated; a) Example of equipotential bonding and earthing in the transfer of flammable liquids. b) Example of static neutralisers in the vicinity of a roller and sheet. c) Typical earthing system for low-volume solvent dispensing via a drum connector. d) Typical earthing system for low-volume solvent dispensing via a drum pump. Figure I.2 - Example of some ways to provide equipotential bonding and earthing. For further information on types, materials and accessories for earthing, it is recommended that NOM-001-SEDE-2012, or the standards that replace it, be consulted. I.3 Example cases additional to those determined in this Standard, in which the installation of a protection system is suggested for consideration. I.3.1 Some of the cases in which the installation of a lightning protection system should be considered, such as those indicated below: a) Places where large crowds gather; b) Continuity of critical services; c) High density of lightning strikes to earth; d) Tall and isolated buildings or structures, and e) Premises or buildings containing an irreplaceable cultural heritage. ________________________________