The Ex p protection method is used on panels when large components or systems are to be located in a hazardous area. The inner parts are for the most part industrial equipment such as PLC’s, contactors, transformers, PC’s or other ignition sources.
Ex p panels are produced according to EN/IEC 60079-2 and basically use a technique where you make a higher internal pressure inside the enclosure than you have on the outside, thus preventing the external potential explosive atmosphere from entering into the enclosure.
The panels are made so that they first have a purge period to ensure that any explosive internal atmosphere is ventilated out prior to energising the internal non-explosion protected parts. There are basically 3 different types available, these are Px for zone 1 applications, Py for zone 1) applications (internal parts are zone 2 rated) and Pz for zone 2 applications. There are also 3 methods that can be used for pressurization, but the most common is leakage compensation, where you automatically re-fill according to the leakage rate of the panel. But you may also use continues air flow or static pressurization.