Gases, vapors, mists and dusts can all form explosive atmospheres with air.
Hazardous area classification is used to identify places where, because of the
potential for an explosive atmosphere, special precautions over sources of
ignition is needed to prevent fires and explosions.
Hazardous area classification should be carried out as an integral part of the
risk assessment to identify places (or areas) where controls over ignition
sources are needed (hazardous places) and also those places where they are
not (non hazardous places). Hazardous places are further classified in Zones
which distinguish between places that have a high chance of an explosive
atmosphere occurring and those places where an explosive atmosphere may
only occur occasionally or in abnormal circumstances. The definitions of the
zone also recognize that the chance of a fire or explosion depends on the likelihood
of an explosive atmosphere occurring at the same time as an ignition source becomes active.
Equipment Used in Hazardous Areas
Special precautions need to be taken in hazardous areas to prevent
equipment from being a source of ignition. CISI offers consultants with equipment zoning
experience to assure our customers of all safety precautions. In situations where an explosive
atmosphere has a high likelihood of occurring, reliance is placed on using
equipment with a low probability of creating a source of ignition. Where the
likelihood of an explosive atmosphere occurring is reduced, equipment
constructed to a less rigorous standard may be used. Equipment is
categorized (1, 2 or 3) depending on the level of zone where it is intended to
be used. A number of ways of constructing equipment to prevent ignition risks have
been published as harmonized European Standards, and in some cases,
additional requirements are set out in the Standards relating to installation and
use.
