Problem: there are times when electrical equipment must be installed in a classified hazardous location but protection methods such as intrinsic safety or explosion-proof boxes are unsuitable or impractical.

Solution: applying a source of clean air or inert gas at a positive pressure to an equipment enclosure prevents the ingress of flammable gases and dust. Thus, the hazard classification of the atmosphere inside the enclosure may be reduced. Standards have been established which determine the degree of reduction, and stipulate initial purging volume changes, minimum maintained pressure differential, and system status indication. Alarm initiation and power interruption in the event of pressure loss are mandated for some situations.