Dust Explosion Protection
Treatment of Fire and Dust Explosions in ATEX
The inadequate treatment of the differences between clouds of combustible dust and explosive gas clouds has resulted in deficiencies in two ATEX directives, which, therefore, need to be revised.
There are two basic differences between explosive gas mixtures and explosive dust clouds, which are of substantial importance in design of electrical apparatuses for use in explosive atmospheres. Firstly, the physics of generation and sustainment of dust clouds and premixed gas/vapour clouds are substantially different. This means that in most situations where accidental explosive gas clouds may be produced quite readily, generation of explosive dust clouds would be highly unlikely. Secondly, contrary to premixed gas flame propagation, the propagation of flames in dust/air mixtures is not limited only to the flammable dust concentration range of dynamic clouds. The state of stagnant layers/deposits offers an additional discrete possibility of flame propagation.
In reality the two European Directives 94/9/EC (1994) and 1999/92/EC (1999) primarily address gases/vapours, whereas the particular properties of dusts are treated rather inadequately. Some recent IEC and European dust standards resulting from this deficiency are discussed, and the need for revising the two directives accordingly is emphasized.
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