The prevention of dust explosions caused by high explosive bombs in flour mills

The heavy loss of flour mills under enemy attack from the air was shown to be largely attributable to extensive fires resulting from dust explosions initiated by high-explosive bombs, and a scheme of protection was worked out by Professor G. I. Finch in the capacity of Scientific Adviser to the Fire Research Division of the Research and Experiments Department, Ministry of Home Security. According to this scheme, propagation of the secondary dust explosion was to be prevented by packets of incombustible dust so placed in the mill buildings as to be broken open, and their contents dispersed by the high-explosive simultaneously with the liberation of combustible dust (flour, etc.) from damaged plant. Refinements to the original scheme were made as a result of the experimental work described. Flame propagation tests showed that a mixture of 90% powdered limestone with 10% sodium bicarbonate would be a suitable incombustible dust for the purpose; the small addition of bicarbonate greatly enhancing the 'flame-suppressing power of the mineral dust. Investigations into the agglomerating, caking and segregating characteristics of this and related mixtures, mainly in relation to mixture composition and particle size, were carried out, and indications are given of the way in which these factors may be adjusted to give the best all-round specification for the mixture. An experimental installation in a flour mill is described.