Abstract
Since the development of laboratory apparatus for determining safety parameters in the form of the explosion pressure Pex and the maximum rate of pressure rise (dpex/dt)max a large number of dusts have been studied experimentally and the values obtained published in databases (GESTIS-DUST-Ex, 2018). It is assumed for the purpose of these studies that the parameters of a dust determined under ideal laboratory conditions are more critical - and therefore constitute a safer basis for the planning of safety measures - than the values actually arising in an explosion in an industrial installation. This generally holds true for the explosion pressure, which is attributable essentially to the basic thermodynamic variables of the heat of reaction, the specific heat capacity and the concentration. It is not the case however for the kinetic variable of the maximum rate of pressure rise, which is dependent upon the volume, as well as the turbulence and dust distribution. To facilitate comparison of the dp/dt values obtained with the use of different laboratory apparatus, the maximum rates of pressure rise are adjusted for the standard volume of 1 m3 by means of the cube law. The dpex/dt*V1/3 value calculated in this way also enables the dp/dt values to be applied to very large volumes. It must be noted here that application of the cube law to the laboratory test apparatus is subject to very strict conditions. Important criteria include the ignition geometry, sphere geometry, ignition delay time, etc. Even when these boundary conditions are observed, non-organic dusts frequently exhibit substantial deviations from the cube law. Systematic experimental studies of aluminium dust in a range of test volumes demonstrate that the cube law cannot be used without qualification. The reasons for this difference in reactive behaviour are discussed, and the limitations of the cube law thereby also revealed.
