HAZARDOUS AREA ZONING

DSEAR (Dangerous Substances and Explosive Atmospheres Regulations, 2002) is concerned with the protection of workers against risks of fire and explosion arising from dangerous substances used in the workplace. DSEAR requires risk assessments to be carried out on all workplaces where dangerous substances are present in order to assess the risks to personnel from dangerous substances.

Part of a DSEAR Risk Assessment aims to examine how releases of dangerous substances (and hence risks) can be reduced. If risks cannot be effectively eliminated using this approach, and residual risks remain, then risks can be further reduced by the control of sources of ignition. This requires the classification of hazardous areas where there remains a risk of the generation of a flammable mixture which might be ignited by such a source of ignition.

The classification of hazardous areas is now based upon the 'ATEX' approach (link to the ATEX section). Where the risk is due to gases and vapours, then the approach is detailed in BS EN 60079-10: 2003 Electrical apparatus for explosive gas atmospheres. Classification of hazardous areas. Hazardous areas due to gases and vapours are classified as zones 0, 1 or 2 depending generally on whether the release is always present, present periodically during normal operations or not present during normal operations but present at other times.

Where the risk is due to a mixture of flammable dust and air, the approach is as per BS EN 50281-3: 2002 Electrical apparatus for use in the presence of combustible dust. Part 3: Classification of areas where combustible dusts are or may be present. Hazardous areas due to clouds of combustible dust are classified as zones 20, 21 or 22 depending generally on whether the release of dust is always present, present periodically during normal operations or not present during normal operations but present at other times.

Hazardous areas are classified in terms of the zone (0,1,2,20,21 or 22), the temperature which surfaces should not exceed (given a designation between T1 and T6) and, for the case of gases and vapours, a gas group (ranging from IA to IIC). All equipment installed in the hazardous areas must be certified suitable for use in such an area. Despite the title of the two British Standards above, this requirement applies to both electrical and non-electrical sources of ignition.