The primary requirement is for the operator to prevent conditions where a flammable mixture is released to the atmosphere. However, as there is some risk of such a situation taking place, special measures need to be taken in respect of electrical and non-electrical apparatus, to prevent the possible ignition of flammable or explosive atmospheres. The employment of these measures should safeguard both the plant (or installation) and more importantly human life, as ignition can only occur when both a flammable atmosphere and the means for an ignition exist simultaneously.
Such ignition may occur following an arc, spark or hot surface during the use of electrically powered equipment. It should also be recognized that non-electrical equipment may also be the source of ignition
In addition ignition could also be initiated by frictional sparking and electrostatic action. Arcs can result from the discharge of stored energy or from switching contacts. Hot surfaces sufficient to cause ignition can arise from electrical enclosures or components.
Other sources of ignition energy are open flame, stray electric currents, lightning, compression, engine exhausts, heat from chemical reactions, spontaneous combustion, friction or heat from mechanical equipment & heat from the sun.
The three ingredients which together will give rise to an explosion taking place :-a. Flammable material
b. Air and
c. Ignition source
form what is commonly known as the Fire Triangle.