WHMIS 1988 - Hazard-Specific Issues - Dust Explosibility

Terminology

The term "explosible" is used to describe a dust which is able to cause a dust explosion. "Explosible" is preferred over the term "explosive" to avoid confusion with high explosives, whose explosion properties are different from those of dusts dispersed as a cloud and ignited. A dust explosion propagates by the combustion of particles with surrounding gas, whereas explosives do not require a surrounding atmosphere.

Although the term "combustible" is often used synonymously with the term "explosible", not all materials that will burn in air cause dust explosions even if finely divided and dry; i.e., not all combustible dusts are explosible, but all explosible dusts must be combustible.

Factors and Substances Implicated in Explosions

Like all fires, a dust fire occurs when fuel (the combustible dust) is exposed to a source of ignition in the presence of oxygen. Suspended dust burns more rapidly and confinement allows for pressure build-up. The initial explosion can cause dust that has settled over a period of years to become airborne resulting in a secondary explosion that propagates throughout the plant often with catastrophic results.

WHMIS Classification and Hazard Communication

Although the Controlled Products Regulations (CPR) do not set out criteria for the explosibility of dusts, a supplier or importer is still obligated to disclose information relating to this hazard as required by the existing requirements of the CPR:

12(11) A material safety data sheet shall disclose, in addition to the information required to be disclosed by subsection (2), all additional hazard information that is available to the supplier with respect to the controlled product or, if appropriate, a product, material or substance that has similar properties, including any evidence based on established scientific principles.

As such, where applicable, MSDSs should identify this hazard and disclose information on the appropriate engineering controls to prevent these explosions through, for example, information provided in pertinent guidelines.

While suppliers cannot predict every possible use of their products, the processes and substances implicated in dust explosions are well documented as are preventive measures. This information is subject to disclosure on the MSDS.

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