Dust Explosion and Fire Prevention Handbook
Airborne dust created by the handling of many industrial materials can combine in an air/dust mixture that could result in a violent, damaging explosion. A combustible dust is defi ned by the NFPA (Standards 68 and 654) as “any fi nely divided solid material 420 microns or smaller in diameter which presents a hazard when dispersed or ignited in air.” ISO is even more conservative and reports any fi nely divided solid material smaller in diameter 500 microns may present an explosion hazard. Most organic (carbon containing) and metallic dust will exhibit some combustibility characteristics. Th erefore, if dust is present in any form within a working environment eff orts should be taken to assess whether the potential for a hazard exists or not, and to devise appropriate practices and safeguards to mitigate the risks.
Preventing dust explosions has gained increased attention in recent years. In the United States the Chemical Safety Board has proposed new regulations to reduce the dangers of combustible dust. Th e European Community has already implemented two directives for that same purpose. Directive 94/9/EC, oft en referred to as ATEX-95 (Atmosphères Explosives), defi nes the safety requirements concerning equipment and protective systems intended for use in potentially explosive atmospheres. Th e other EC directive, 1999/92/EC (ATEX 137), outlines the minimum requirements for the protection and safety of workers at risk from explosive atmospheres.
Dust explosions can result when a fl ame propagates through combustible particles that have dispersed in the air and formed a fl ammable dust
cloud. Whether an explosion happens or not depends on the supply of oxygen to the fi re and the concentration of the fuel. If the concentration of the
oxygen or the fuel is too high or low, then an explosion is very unlikely.
