OFR-76(2)-75 Mine Electrical Systems Evaluation - Explosion-Proofing Of Mine Containers - Introduction

In the context of the following report, an hazardous location can be described as any industrial area in which flammable or explosive gases, vapors, and dusts can be encountered. When electrical apparatus is used in such hazardous atmospheres, the chance of a dust or gas ignition is ever present. Consequently, in an effort to reduce the ignition hazard, several protection systems have been devised. Such systems are termed electrical hazard reduction techniques. The most widely accepted and used of these, the explosion-proof enclosure, is the principal subject of this report. However, other techniques are briefly mentioned. Hazard reduction techniques used in coal mine atmospheres (which can contain methane, coal dust, and air mixtures) are classified as Group I. The explosion-proof enclosure commonly used in mines is defined by the USBM Schedule 2G as a device that can contain internal explosions of methane-air mixtures without undergoing damage or excessive distortion and without an ignition of a surrounding methane-air mixture or discharge of flame. (100) Internationally, the definition remains the same except the words "discharge of flame" are not present. (4,5,31,42,52,76,102) The latter description often refers to flame-proof enclosure construction, but the terms "flameproof: and "explosion-proof" commonly have the same connotation. These enclosures which may not be vapor tight, are distinguished by heavy-wall cast or welded construction and bolted or threaded close fitting flanges.