Fire Safety Science Digital Archive

The extent to which dusts that are marginally explosible according to small-scale tests are able to propagate explosion in large-scale equipment has been investigated. Mixtures of an explosible and an inert dust were made up in various proportions to give a range of explosibilities, and were dispersed in air in a vertical explosion tube. The range of concentration in air over which the mixtures were explosible was measured, and the proportion of inert dust required in the mixture to prevent explosion was determined. The dust mixtures were also tested in the small-scale apparatus. Most marginally explosible dusts from the small-scale tests (i.e. marginally Class I) would propagate explosion on the larger scale. Dusts that required a large source of ignition in small-scale tests did not propagate explosion on the larger scale. Good agreement was obtained between the calculated and the experimental values of the minimum amount of inert dust required to prevent propagation, when mixed with the explosible dust. The calculated values of the· explosible limits of dust mixtures were lower than those determined experimentally, after allowing for the velocity of fall of the dust particles, but evidence was obtained that a substantial proportion of the dust suspension remained unburnt.