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Evaluation of Active Suppression in Simulated Post-Collision Vehicle Fires.


pdf icon Evaluation of Active Suppression in Simulated Post-Collision Vehicle Fires. (60615 K)
Hamins, A.

NISTIR 6379; 175 p. November 2000.

Available from:

National Technical Information Service (NTIS), Technology Administration, U.S. Department of Commerce, Springfield, VA 22161.
Telephone: 1-800-553-6847 or 703-605-6000;
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Order number: PB2001-102011

Keywords:

passenger vehicles; automobile fires; compartment fires; experiments; postcrash fires; nozzles; fire suppression; fuels

Abstract:

An investigation of the effectiveness of fire suppressants in simulated post-collision vehicle fires is presented. Two distinct fire scenarios were considered. The first configuration was a simulated engine compartment fire. The second configuration was a simulated underbody fire. The configurations were defined based on geometric and fire-related pammeters. Experiments were performed using both laboratory test devices and a mid-size passenger vehicle. A set of criteria was constructed for selection of suppressants for use in the suppression tests. The criteria were based on information from the fire literature and engineering judgement. Commercially available fire suppressants and several emerging suppressants were evaluated in terms of the criteria and a number of representative suppressants were selected for testing. Both traditional and emerging active fire suppressants were tested. These included dry powders, inert suppressants, compressed liquefied halogenated compounds, and a number of unique devices. The suppressants tested in the engine compartment suppression experiments were HFC-125 (C2HF5), HFC-227ea (C3HF7), ABC powder (NH4H2PO4, mono-ammonium phosphate), BC powder (NaHCO3, sodium bicarbonate), a tubular suppression system, solid propellant generators, and aerosol generators. The suppressants tested in the underbody fire suppression experiments were HFC-125, ABC powder, BC powder, solid propellant generators, and aerosol generators. A number of experimental protocols were developed to appraise the feasibility of fire suppression using the representative suppressants. The apparatus in each of the experimental configurations included a fire zone and a suppressant delivery system. The experimental procedure in each of the four configurations was essentially the same. A fire was established and after a specified duration, a controlled mass of suppressant was delivered to the fire zone. Suppressant distribution was optimized through careful nozzle selection, placement, and discharge duration. After suppressant delivery, observation determined whether the fire was suppressed or not suppressed. A number of experiments were conducted to test the importance of operating conditions on suppressant effectiveness in the simulated vehicle fires. These included geometrical factors and suppressant delivery parameters. Long fuel trails extending beyond the confines of the vehicle and environmental factors such as wind were considered. The results showed that it is highly improbable that an on-board fire suppression system will be able to extinguish all engine compartment and underbody fires. Many suppressant types were found to be impractical for post-collision engine compartment applications. The experiments have shown, however, that under certain conditions, fire suppression is feasible. A unique pyrotechnic device, the solid propellant generator, was the most effective suppressant tested in the full-scale engine compartment scenario. These devices rapidly deliver a gas/particulate effluent. Full-scale suppression experiments in the engine compartment of an uncrashed stationary vehicle in the absence of forced ventilation (radiator fan off) showed that suppression of a 200 mL/min gasoline fire was achievable with less than 500 g of the solid propellant generator. Full-scale underbody experiments showed that suppression of a (333 mL volume) gasoline pool fire was achieved with less than 300 g of ABC and BC powder suppressants when the fuel was located under the vehicle footprint for low wind conditions. If a fuel puddle in an underbody fire extended beyond the vehicle footprint and if moderate to high winds were present, then the powder suppression system failed to reliably extinguish the fire.