Abstract
Recently, ultrafine particles which have several valuable properties, with diameters less than micro-meter, have been widely used. Although, ultrafine particles have special characteristics such as high reactivity and easy agglomerating property, the fire and explosion risks provoked by such particles have not yet been understood sufficiently. In order to estimate the explosion risks of the ultrafine particles, minimum explosion concentration MEC as an ignitability index and Kst-values as an explosion severity index were measured in this study. It was observed that MEC increased and Kst-values decreased when the particle diameter becomes sub-micron order, that is, the risk of dust explosion of sub-micron particles decreased. This result is contrary to the tendency for the particles of the diameters larger than a few tens microns. To examine the effect of size distribution on explosion characteristics, the size distribution of blew up particles were measured. The measurements of particle distribution indicate that the situation of agglomerates could have significant influence on explosion characteristics.
