02/02/2010

Dust Busters, Combustibles and Explosions

They can seem like harmless substances - sugar, coal, wood dust, flour -
however in certain conditions and across many industrial processes, dust from
these - and other substances can become the fuel for an explosion. Many workers
have died and hundreds have been injured over the past few decades as a result
of dust explosions. Part of the problem is that dust explosion hazards are
often unrecognized. Investigations of such accidents have shown that the
material safety data sheets (MSDSs) did not adequately describe dust hazards
for the substances involved in these explosions.

MSDSs must identify this hazard and disclose information on appropriate
engineering controls to be used to prevent these explosions. Unfortunately the
dust explosion hazard is not always declared, contributing to a general lack of
awareness of this hazard amongst workers, and potentially putting them at risk
for injury or even death.

Industries and substances at risk of dust explosions

A combustible dust explosion hazard may exist in a variety of industries,
including:


  • metal processing

  • wood product manufacturing

  • chemical manufacturing

  • food and pharmaceutical production

  • grain storage

  • fabrication of rubber and plastic products

  • coal-fired power plants

Combustible materials connected with dust explosions include dusts from coal,
chemicals, wood, rubber, grain, sugar, flour, and metals. Most natural and
synthetic organic materials, as well as some metals, can form combustible dust
if they are processed in powdered form.

How dust can explode

For a dust explosion to occur, five conditions must be present at the same
time. The five elements are referred to as the explosion pentagon, and include:

  • combustible dust (fuel)

  • ignition source (spark or heat)

  • oxygen in air (oxidizer)

  • dispersion of dust (into the air forming a dust cloud)

  • confinement of the dust cloud (building or ceiling)

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
building. An initial explosion that occurs in processing equipment or in an
area where there is an additional accumulation of dust, may shake excess 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
explosion.

Although suppliers cannot predict every possible use of their products, they
can help prevent explosions and injuries by ensuring that MSDSs contain the
complete hazard information workers need to work safety with substances and
materials that could potentially combust and/or explode.

Further Information:


AplusA-online.de - Source: Canadian Centre for Occupational Health and Safety