Limits of applicability
There are limits of applicability of the combustion and explosion characteristics specified in these tables. They are based on the wide variation possibilities in the nature of the dusts (e.g. composition, particle size distribution, surface structure, moisture content), on the one hand, and on the dependence of the numerical value of the characteristics on the test methods, on the other. Hence, the user must always be aware that the tabulated values can only serve as a guideline for the design of preventive and protective measures.
Above all, the data should indicate which substances have already been tested, whether the substances are dust-explosible and on what scale the most important data can be expected. They frequently illustrate the problem involved with combustible dusts, i.e. that very different values can occur for what appear to be the same dusts. This highlights the need to test the dust to be handled whenever it is unclear if certain important influencing factors, such as composition, fineness and moisture content, coincide completely with the existing conditions in the case to be assessed.
This applies also concerning the fact that despite careful compilation mistakes can not be excluded at this large extent of data.
In some cases where numerous data are available, however, it might be legitimate to "play safe" in that the assessment is based on the most critical values.
The characteristics listed are comparable both with each other and also with other characteristics determined by the same methods. They are not comparable, however, with values determined by other methods.
It should be noted that higher values for the maximum explosion pressure and the maximum rate of explosion pressure rise or the KSt value as well as lower values for the lower explosion limit, for the ignition temperature and for the minimum ignition energy may occur with diminishing particle size and moisture; hence the numerical values of the explosion characteristics vary towards the "more hazardous" side.
The characteristics in the tables apply to the following conditions in the operating plants:
Pressure from 0.9 bar to 1.1 bar
Oxygen approx. 21% V/V
Temperature from 0 °C to 30 °C.
If conditions other than these so-called "atmospheric conditions" exist in practice, special considerations should be made and, if necessary, the characteristics determined under the boundary conditions existing in the factory. Increased pressure, oxygen content and temperature also point to a more critical combustion and explosion behaviour.
The tabulated values do not apply if the simultaneous presence of combustible dust and gases, vapours or mists (hybrid mixtures) can be anticipated.Back