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Finding the effect of ventilation on conveyor belt fire suppression systems.

Rowland J; Smith A; Verakis H; Hockenberry M
Coal USA Mag 2009 May; :27-28
Four different types of fire suppression systems were tested under two air velocity conditions, and two water-based fire suppression systems were able to suppress the fire under the test conditions. However, the amount of water needed to suppress the fire to the point where a miner could walk up to extinguish any smoldering belt was greater than current MSHA regulations require. MSHA regulations only require 10 minutes of water supply to the suppression system with all sprinklers or water sprays open. In the test, and based on the visual evaluation, it was unlikely that either system would have suppressed the fire had the water been turned off to the system after 10 minutes. The two dry chemical suppression systems provided mixed results. For example, System A did not extinguish the fire in either air-velocity condition. This system uses a nominal weight of 300lb of dry chemical agent (monoammonium phosphate-based) and 40 nozzles to protect the 50ft of drive area. Additionally, the primary failure mechanism was damage to the hoses from the fire prior to system activation. Several of the nozzles in System A did not discharge any dry chemical agent because the hoses leading to the nozzles were severely fire damaged. The dry chemical System B performed well at the lower air velocity. However, at the higher air velocity mixed results were obtained. System B required a nominal weight of 500lb of dry chemical agent (monoammonium phosphate-based) and 64 nozzles to protect the 50ft of drive area. One of the higher air velocity tests resulted in the fire not being extinguished, and there was a malfunction with one of the four dry chemical supply tanks that resulted in one tank not discharging any chemical to connected nozzles. This malfunction, however, would not have affected the extinguishment of the fire because the nozzles were located outby (downwind) of the fire area. The large-scale testing indicated the air velocity does, in fact, have a significant effect on the detection, activation, and suppression capabilities of the fire suppression system. The water-based systems each performed well under both sets of air velocity conditions, but required more time than the 10-minute requirement in 30 CFR. The dry chemical systems, however, did not perform as well, and resulted in failure to extinguish the test fires in some experiments. Several factors may have contributed to the dry chemical system's poor performance under the test conditions. The ventilation rate not only affects the discharge pattern of the dry chemical agent, but also contributes greatly to the system's detection and actuation. The increased air velocity condition has a cooling effect on the detection mechanisms, and this can allow the fire to grow and propagate further - before the system detects and actuates the dry chemical to discharge. The importance of early detection is imperative for any fire condition. The higher air velocity tests may have actually been larger fires by the time the system discharged, resulting in a more challenging suppression situation. A combination of the larger fire conditions under high air velocity because of detector cooling, detection location, the transference of dry chemical by the ventilation, and overall fire suppression system design, all may have affected the performance of each system.
Mining-industry; Mining-equipment; Fire-retardants; Fire-extinguishers; Fire-extinguishing-systems; Fire-extinguishing-agents; Fire-prevention
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Journal Article; Trade
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Coal USA Magazine
Page last reviewed: October 16, 2020
Content source: National Institute for Occupational Safety and Health Education and Information Division