PRACTICAL IGNITION PROBLEMS RELATED TO INTRINSIC SAFETY IN MINE EQUIPMENT.

The most easily ignitible mixture of propane-air in a PTB break flash apparatus is approximately 5. 2 percent propane. Miniature lamp bulbs used in intrinsically safe circuits are about as incendive to coal dust-air as to methane-air and should be tested in gas mixtures containing about 7. 0 to 7. 5 percent methane. The sodium amalgam contained in high-pressure sodium lamps does not present an ignition hazard for coal dust or methane, where the lamps contain no more than 30 milligrams of amalgam. The maximum allowable surface temperature of permissible electrical enclosures should remain at 150 degree C.