Improvements to the Hartmann Dust Explosion Equipment for MEC Measurements that Are Compatible with Gas Lean Limit Measurements

Literature results for the MEC of dusts show that the MECs in g/m3 convert to lean equivalence ratios of 0.2–0.3 for many HCO dusts, compared with 0.45 for hydrocarbons and alcohols. This indicates that HCO dusts are more reactive than hydrocarbons, but it could be that it is the measurements of MEC for dusts that are suspect. The measurement of the minimum explosible concentration of dusts is reviewed together with measurement methods for the lean flammability limit of gases. There is considerable uncertainty over the concentration of dusts at the lean limit in the 1 m3 MEC method, as most of the dust injected in the 1 m3 does not burn. It is shown for gases that a vertical tube equipment operated as a closed vessel will give the same lean limit of 0.46O for methane/air as the European standard method, but large spheres will not, and thus, the use of the 1 m3 dust explosion vessel is unlikely to give MEC data that is compatible with lean limits for gases. A study of the MEC of polyethylene dusts was carried out at various ignition delays in the Hartmann, and an ignition delay of 50 ms was recommended for polyethylene dust to give reliable MEC measurements.