- Author
-
Ames, S. A.
|
Purser, D. A.
|
Fardell, P. J.
|
Ellwood, J.
|
Murrell, J.
|
Andrews, S.
- Title
- Cabin Water Sprays for Fire Suppression: An Experimental Evaluation.
- Coporate
- Civil Aviation Authority, London, England
- Report
-
CAA Paper 93009
March 1993
139 p.
- Keywords
-
mist
|
water sprays
|
aircraft compartments
|
fire suppression
|
evaluation
|
physiological effects
|
exposure
|
large scale fire tests
|
experiments
|
boeing 707 aircraft
|
cabin atmospheres
- Identifiers
- fire atmospheres; fire development within the cabin; life threat analysis
- Abstract
- This report describes the results of a series of experiments to investigate the effectiveness of on-board low volume water sprays in reducing the risk to passengers in an aircraft cabin exposed to a severe external fire. The risk to passengers arises from exposure to the effects of fire, including radiated and convected heat, toxic and irritant gases and particulates and reduced visibility due to smoke. these may cause harm directly or, indirectly, by impeding escape and increasing the probability of exposure to other effects. The nature of these effects and the manner in which they may combine to cause varying degrees of incapacitation have been examined and criteria set for the tenability of the cabin atmosphere. A number of preliminary experiments were undertaken to isolate and examine some of these mechanisms under laboratory conditions. The results of these indicated that fine water sprays could substantially reduce thermal radiation and that, as expected from theoretical considerations, performance increased with smaller diameter droplets and increased flow rate. The principal experimental programme consisted of a series of full-scale tests undetaken using a Boeing 707 fuselage. A severe fire scenario was chosen, representing an external 12 MW fuel fire adjacent to an opening in a fuselage resting directly on the ground. Without water spray, survival time was less than 2.5 minutes. Based upon observation of the fire development in the cabin, the measured levels of fire products and the degree of damage to furnishings and fittings, the primary effect of water sprays was found to be to reduce fire penetraion into the cabin and to inhibit fire spread in the cabin contents. Life threat analysis, based solely on the measured levels of toxic components showed, in all cases, the use of water sprays increased the time for incapacitation of standing passengers, some 8 metres from the fire, by about 4 minutes. However, when the effect of air temperature, including the maximum potential latent heat content of fully saturated air, was included, this improvement was reduced to 1.7 minutes for the fully sprayed cabin and to 0.7 minutes for reduced flow rate, zoned spray. These levels were improved to 3 and 1.5 minutes respectively at crouching height. When a full flow rate zoned spray was used no degradation in the extension of survival time occurred when air temperature was considered. The use of water sprays considerably reduced the amount of solid particles and liquid droplets capable of penetrating the lungs, and also the irritants attached to them, thereby reducing the risk of lung damage. However, there was little effect on visibility by smoke removal, when the full cabin was sprayed the water spray tended to pull down the developing hot smoke layer in the cabin reducing visibility at lower levels earlier than in the unsprayed case. When the spray was restricted to the zone near the fire the smoke quickly re-established a buoyant layer, the effect of this combined with the reduced burning rate was for visibility to be improved in the full flow rate zoned test. Overall, the most effective spray arrangements of those tested was found to be the zoned spray, with nozzles delivering water at a rate of 1 litre per minute per square metre of floor area and with mean droplet diameter (measured as Sauter mean diameter) of about 250 mum.