4.4.2 Avoidance of ignition sources

If the formation of an explosive atmosphere cannot be prevented or the process operates with a flammable atmosphere, the next level of protection is the avoidance of ignition sources in areas where a flammable atmosphere may occur.  The hazardous areas where explosive atmospheres could be formed have to be identified and classified according to the likelihood of an explosive atmosphere being present.  For situations where hydrogen and/or other flammable gases or liquids may be present, the following classifications should be used where appropriate:

• Zone 0 – An area in which an explosive atmosphere is present continuously or for long periods. Only category 1 equipment should be used in these areas;
• Zone 1 – An area where an explosive atmosphere is likely to occur during normal operation. Only category 1 or 2 equipment should be used in these areas;
• Zone 2 – An area where an explosive atmosphere is not likely to occur during normal operation and, if it does occur, is likely to do so infrequently and will only last for a short period. Only category 1, 2 or 3 equipment should be used in these areas.

Guidance on identifying and classifying the hazardous areas is given in IEC 60079-10:2003 [32] and EN 1127-1:2007 [31].

 

Electrical and non-electrical equipment appropriate for use in the different areas of the workplace should be determined once the hazardous areas have been identified and classified.  The EN 60079 series of standards specifies the requirements and testing of electrical equipment for use in the different zones.  Part 0 [35] specifies the general requirements for the construction, testing and marking of electrical apparatus and components intended for use in hazardous areas where explosive gas/air mixtures exist under normal atmospheric conditions.  Part 14 [36] gives the specific requirements for the design, selection and erection of electrical installations in explosive gas atmospheres.  These requirements are in addition to those for installations in non-hazardous areas.  Part 17 [37] covers the maintenance of electrical installations in hazardous areas and Part 19 [38], the repair and overhaul for apparatus used in explosive atmospheres. Non-electrical equipment is covered by the EN 13463 series of standards, with Part 1 [39] specifying the basic method and requirements for the design, construction, testing and marking of equipment.  Methodology for the risk assessment of non-electrical equipment for use in potentially explosive atmospheres is given in EN 15198:2007 [40].

The hazardous area classification should also be used to ensure that suitable controls are placed on all other foreseeable sources of ignition including hot work, smoking, vehicles, mobile phones and work clothing.
Precautions should also be taken to prevent the build-up of static charges that may lead to an incendive discharge. These may include:

• Ensuring that all pipe work is conductive and has effective electrical continuity, especially over mechanical joints such as flanges;
• Ensuring that all pipe work and equipment is effectively earthed;
• Carrying out and documenting appropriate earthing/continuity checks;
• Wearing antistatic clothing and footwear in hazardous areas.

Further information on the avoidance of hazards due to electrostatics can be found in the code of practice PD CLC/TR 50404:2003 [41].

Appropriate protection is also required against the risk of lightning strike when designing outdoor fuel cell or hydrogen storage facilities.