Evaluation of the explosion hazard of powders by the maximum explosion pressure and maximum rate of explosion pressure rise
II. Methods for testing the powder  explosibility characteristics

Abstract

A method for assessing the powder explosibility was developed using analysis of suspended powder particle distribution in reaction vessels and combustion front propagation and comparative tests of atomizers. Dependences of the maximum explosion pressure on the concentration of suspended particles and oxygen content in mixture with nitrogen and other inert gases determined employing a four-liter test unit of the Frantsevich Institute for Problems of Materials Science (IPM) were examined. The experimental data were used to study the effect of reaction vessel sizes on the maximum explosion pressure and maximum rate of explosion pressure increase. The applicability of cube root law for geometrically similar vessels, the similarity criteria for gas suspension flows, including the homochronism criterion for turbulent flows, was indicated. The metal powders were categorized by the modified explosibility index, calculated in comparatively quantities relative to the explosibility of silicon powders and based on combustibility and explosibility characteristics. The irregular gas distribution substantially influenced the accuracy of the explosibility characteristics. In accordance with the IPM method, analyses of explosibility characteristics are corrected by the content coefficient, characterizing the suspended powder distribution in the reaction vessel. Incomplete disintegration of powder particle aggregations by a toroidal atomizer and their incomplete combustion (apparatus of the United States Bureau of Mines) leads to underestimation of the maximum explosion pressure and overestimation of the lower concentration ignition limit since the concentration of the suspended powder was calculated as the ratio between the atomized powder mass and vessel volume.