Models to Estimate the Lower Explosion Limits of Dusts, Gases and Hybrid Mixtures

The present paper reports on the experimental and theoretical investigations on the lower explosion limits of single dusts, gases as well of two phase mixtures such as gas/dust, vapor/dust, spray/vapor and vapor/gas. The materials used were corn starch, lycopodium, toner and high density polyethylene as dusts, methane and hydrogen as combustible (perfect) gases and acetone and isopropanol as sprays or vapours (real gases). The experiments were performed in the standardized 20-lters spherical explosion chamber where modifications were done to allow input of spray, solvent and gas. The test protocol was according to EN 14034 with an electrical ignition source. The experimental results demonstrate a significant enhancement in explosion likelihood by solvent, gas or spray admixture with dust and vice versa. They also confirm that a hybrid mixture explosion is possible even when the concentrations of both components are lower than their minimum explosion concentration (MEC) respectively lower explosivity limit (LEL). For example, the MEC of starch decreases from 150 g/m decrease to 20, 30, 125g/m and 125g/m when small amounts of isopropanol spray, acetone vapor, methane gas and hydrogen gas respectively were added. These concentrations were all below the LEL of the individual substance. Comparisons have been done between the lower explosible limit of the experimental data and classical models such as those developed by Bartknecht, Le Chatelier, MKOPSC and our newly proposed models. With the exception of the Le Chatelier and MKOPSC model, the other models were in agreement with the experimental result for safety point of view.