A hazardous area is an area in which explosive atmospheres, or may be expected to be, present in quantities such as to require special precaution for the construction and use of electrical equipment. An explosive atmosphere consists of a mixture of flammable substances with air in the form of GAS, VAPOUR OR MIST in such proportions that it can be exploded by excessive TEMPERATURES or other ignition sources.
An Explosive Atmosphere is a mixture with air, under atmospheric conditions, of flammable substances in the form of gas, vapour, dust, fibres, or flyings that, after ignition, permits self-sustaining propagation.
Area classification is the mitigation of risk. The more likely an area is to have explosive or flammable mixtures present, the more stringent the types of equipment need to be that are allowed to be installed in that area.
Simply put, areas that have likely release of flammable or explosive substances need really safe equipment. Areas with low risk of these substances need less expensive and less protective equipment (for risk of ignition that is).
Are classification is the assignment of a risk threshold that determines the types of equipment and methods of installation that will provide and acceptable level of risk.