What is a combustible dust?
It is any loose and dainty material that has the ability to catch fire and explode when mixed with air. Combustible dusts can be from:
- most solid organic materials (such as sugar, flour, grain, wood, etc.)
- many metals, and
- some nonmetallic inorganic materials.
Although some of these materials are not usually combustible, but if they are the right size and concentration they can burn or explode.
Dust can collect on surfaces such as rafters, roofs, suspended ceilings, ducts, crevices, dust collectors, and other equipment. When the dust is disturbed and under specific situations, there is the potential for a serious explosion to take place. Even the build-up of a very fine amount of dust can produce serious damage. Therefore, any activity that creates dust should be examined for risk of a combustible dust.
Examples of materials that can be a combustible dust hazard:
There are many types of materials can become combustible if under specific situations. Examples include:
- agricultural products such as egg whites, powdered milk, cornstarch, sugar, flour, grain, potato, rice, etc.
- metals such as aluminum, bronze, magnesium, zinc, etc
- chemical dusts such as coal, sulphur, etc.
What workplaces are at risk for a dust explosion?
Dust explosions can occur in a variety of workplaces and industries, some of them are:
- Grain elevators,
- Food production,
- Chemical manufacturing (e.g., rubber, plastics, pharmaceuticals),
- Woodworking facilities,
- Metal processing (e.g., zinc, magnesium, aluminum, iron),
- Recycling facilities (e.g., paper, plastics, metals), and
- Coal-fired power plants.
Dust is created when materials are transported, handled, processed, polished, ground and shaped. Dusts are also created by abrasive blasting, cutting, crushing, mixing, sifting or screening dry materials. The buildup of dried residue from the processing of wet materials can also generate dusts. Essentially, any workplace that generates dust is potentially at risk.
How do combustible dust explosions happen?
Any fire needs three elements. These elements are known as the “fire triangle”:
1. Fuel to burn
3. Ignition source (heat, spark, etc.)
A dust explosion needs two additional elements – known as the “dust pentagon”:
4. Dispersion of dust particles in the right concentration, and
5. Confinement of the dust cloud.
Dispersion means the dust particles are suspended in air. Confinement means the dust is in an enclosed or limited space. This restriction allows pressure to build up, increasing the likelihood of an explosion.
Figure 1Figure 1 shows the dust explosion pentagon. Figure from Occupational Safety and Health Administration (OSHA).