A hazardous area is an area where during normal operation a hazardous atmosphere is likely to be occurs in sufficient quantity to constitute a hazard.
A hazardous atmosphere contains any flammable gas or vapor in a concentration capable of ignition.
Remotely hazardous area is an area (excluding an air field) in which any flammable liquid, gas or vapor although processed, handled or stored is so well under conditions of control that its liability to produce a hazardous atmosphere in sufficient quantity to constitute a hazard is only likely to occur under abnormal conditions.
An atmosphere not facing within the definitions of hazardous atmosphere and incapable of ignition is called a safe atmosphere.
An area in which explosive gas/air mixtures or combustible dusts are or may be present in quantities such as to require special precautions for the construction and use of electrical apparatus.