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More than 50 per cent of fatalities in building fires result from the effects of smoke and toxic gases. A method of measuring visibility in smoke is discussed, and experiments on limiting smoke penetration to escape routes and occupied zones of a building are described. Because of their susceptibility to the influence of external weather conditions and the human element of misuse, smoke stop doors alone cannot be regarded as a satisfactory means of excluding smoke. The relative merits of natural and forced ventilation systems are discussed. The former are of uncertain effectiveness and give rise to discomfort conditions, but have economic advantages. With the latter it is shown that both pressure and exhaust systems can be effective in preserving smoke-free zones with quite modest pressure differentials, of the order of 1.3 mm (0.050 in.) of water, for continuous, and somewhat higher values for “on demand” systems. These, too, are susceptible to external weather conditions and the state of doors, though the brief opening of doors to permit the passage of persons escaping has no serious effect. Experimental work on the generation of toxic gases in building fires is described. It is shown that concentration of carbon monoxide far in excess of the acceptable safety limit can readily be obtained, the maximum concentration occurring for ventilation opening of 6 to 18 per cent of the area of one wall of the compartment.
fire tests, smoke, smoke control, toxic gases, ventilation, optical density, visibility, building fires, carbon monoxide
Silversides, R. G.
Assistant director, Fire Research Station, Boreham Wood, Herts.