A combustible dust explosion hazard may exist in a variety of industries,
including: food (e.g., candy, starch, flour, feed), plastics, wood, rubber,
furniture, textiles, pesticides, pharmaceuticals, dyes, coal, metals, and
fossil fuel power generation. Most natural and synthetic organic materials, as
well as some metals, can form combustible dust. The safety bulletin prepared by
the U.S. Occupational Safety and Health Administration contains important
information on how to assess the risk in your facility.
Elements of a Dust Explosion
Experts agree that for a dust explosion to occur, five conditions must be
present at the same time. First, the three elements needed to cause fire (fire
These five elements make up the "explosion pentagon" that causes a dust
explosion. If one of the elements of the explosion pentagon is missing, a
catastrophic explosion cannot occur.
A dust cloud that is ignited within a confined or semi-confined vessel, area,
or building, burns very rapidly and may explode. This could cause fires,
additional explosions, flying debris, and the collapse of parts or all of the
An initial explosion that occurs in processing equipment or in an area where
there is an additional accumulation of dust, may shake the renegade dust loose,
or damage a containment system (such as a duct or vessel). The additional dust
released into the air, if ignited, can cause one or more secondary explosions
that can be even more destructive than the first.
Reducing the risk
Facilities should conduct a dust hazard assessment to carefully identify
materials that can be combustible, processes that use, consume, or produce
combustible dusts, open areas where combustible dusts may build up, hidden
areas where combustible dusts may accumulate, ways that dust may be dispersed
in the air, and potential ignition sources.
The key factor is whether or not the specific dust from your facility is a
combustible dust hazard. Although there is currently no combustible dust hazard
class under WHMIS, there is a requirement to declare all hazards of the product
on the Material Safety Data Sheet (MSDS). Unfortunately, the dust explosion
hazard is under-recognized and often not declared on MSDSs. In CCOHS' CHEMINFO
database, the potential for a material becoming a combustible dust hazard has
been identified. As well, any reports of dust explosions involving the chemical
are included. Laboratory testing of your specific dust will help tell you if
there is a hazard at your workplace. The facility analysis must also identify
areas requiring special electrical equipment classification due to the
potential combustible dust hazard.
The following safety practices are recommended:
Dust control - the most important step towards prevention of dust explosions
AplusA-online.de - Source: Canadian Centre for Occupational Health and Safety