Coal Dust and Gas Explosion Suppression by Barriers

Abstract

Explosion suppression barriers are devices that contain fire extinguishants that are activated to disperse at some critical point during the propagation of an explosion to suppress it. Suppression of coal dust explosions using barriers (both triggered and passive) has been investigated by the U.S. Bureau of Mines. The work reported in the present study is an update of the continuing study of passive barriers of both rigid and flexible construction. Suppressants tested were water and ABC powder (ammonium phosphate). The coal dust mixtures contained 60 to 65% total incombustible matter and were distributed in the Bureau's single entry experimental mine for a total distance of 111 m (365 ft). Dust explosions were initiated by a 7% methane-air gas zone at the face. The passive barriers were located at distances of 60 to 108 m (200 to 356 ft) from the face. At these distances, the magnitude of the explosion pressure pulse was about 0.70 to 1.14 bar (70 to 114 kPa) at the time the flame front arrived at the barrier. With the exception of the powders, the pressure pulse was sufficiently energetic to fracture the troughs and disperse the suppressants. The powder (approximately 180 kg per test) was almost totally ineffective when used with the rigid barrier because it did not disperse. One to four troughs of water effectively suppressed explosions. It was found that the mounting arrangement for the flexible troughs was most important for successful operation and release of the suppressant. Triggered barrier systems for protection against incipient gas explosions were tested in a simulated longwall panel. Results show that ABC powder was much more effective in suppressing the developing explosion than equal amounts of water released from the same pressurized reservoir. Although water was effective in stopping fully developed dust explosions, it had little effect against an explosion during its incipient stage.

Laboratory and large‐scale dust explosion research

“…In previous laboratory [46 -47] and full-scale tests [48] of other inhibitor dusts, the Bureau determined that ammonium phosphate was the most effective inhibitor powder against coal dust and/or methane gas explosions. Ammonium phosphate is not cost effective as a replacement in general rock dusting, but it has been tested and found to be feasible in explosion suppression systems such as triggered barriers [28]. Water has also been shown to be an effective inhibitor in barrier type suppression systems against both coal dust and methane gas explosions [30].…”