Automating an industrial process is a complex problem when combustible vapors or dust are present in the work environment.
Two commonly used methods are Explosion Proof (EP) and Purged and Pressurized (PT). Explosion Proof devices are intended to withstand and contain an expected explosion, Purged and Pressurized systems are intended to prevent an explosion from occurring. While Explosion Proof is more widely known the Purged and Pressurized technique is more flexible and universally recognized.
The National Fire Protection Association publishes “Purged and Pressurized Enclosures for Electrical Equipment in Hazardous Locations”, (NFPA496), which describes the application of positive pressure with dry air or nitrogen to convert the interior of a motor to a non-hazardous area. A copy of the standard is available from the NFPA, (call 800/344-3555). Additional information is included in the National Electric Code, also written by the NFPA.