The
minimum explosible concentration (MEC) in the air atmosphere at the
boundary between an explosion and no explosion in a dust cloud, has been
investigated for several particle sizes of oil shale and for mixtures
of oil shale and inert powder of different particle size. Limestone,
stone dust and coarse particle size of oil shale were used as inert
materials. Measurements were made in a standard small vertical tube
apparatus. The results obtained indicated that the minimum explosible
concentration is dependent on the particle size, i.e., values of MEC
decrease with a decrease in the size of the particles. Below 70μm,
values of MEC become almost constant. Admixture of limestone as low as
5% to oil shale is sufficient to reduce the MEC values significantly.