Purge and pressurization is a method of explosion protection for equipment enclosures installed in hazardous environments that is performed prior to power-up to ensure the enclosure is free of any flammable gases. It is generally used when explosion-proof or intrinsically-safe enclosures are unsuitable or impractical.
There are two basic methods of purge and pressurization, constant flow and leakage compensation. In constant flow systems, compressed air first is pumped into an enclosure to displace hazardous gases, then a steady flow of pressurized air is used to maintain a constant positive pressure that prevents gases from entering. Leakage compensation provides an initial high flow rate to purge gases, then reduces and maintains the flow at just-above leakage level. Leakage compensation is the preferred method as it minimizes compressed air consumption and is less expensive to run.
Depending on the classification of the hazardous location, regulations dictate the number of purging volume changes, minimum pressure differential, and system status indication. Most systems are equipped with alarms and will interrupt power when pressure loss is detected to prevent explosion.
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