Combustible Dust: An Airborne Hazard
On February 7, 2008, a large explosion occurred at a sugar refinery owned by Imperial Sugar, in Port Wentworth, Georgia. The accident killed 14 workers and injured another 40. The explosion, centered in the middle of the factory, was determined to have been caused by “combustible dust.”
Between 1980 and 2005 combustible dust explosion killed 119 people and injured an additional 718. This blog reviews the definition of combustible dust, and how to prevent it from becoming dangerous.
Combustible dust is any combustible material that can burn rapidly when in a finely divided form. If such dust is suspended in the air, at the right concentration, under certain conditions, it can become explosive.1
Many types of materials can be explosive when in dust form; these include but are not limited to: sugar, spice, starch, flour, grain, tobacco, plastics, wood, paper, pulp, rubber textiles, pesticides, dyes, coal and various metals (e.g. aluminum, chromium, iron, magnesium and zinc). OSHA has created a poster that lists many of the potentially combustible materials.2
Combustible dust requires several factors for an explosion to occur:
- Combustible dust must exist in the work environment
- High enough concentrations of the dust must be airborne to support combustion
- An ignition source is required
- The work area must be sufficiently enclosed to allow concentration of the combustible dust to increase
- Oxygen levels in the work environment must be sufficient to start and maintain combustion
Following are three, specific actions that can be taken to reduce the likelihood of a combustible dust explosion:
- Reduce the ability for material to become airborne. Many companies use collection systems to take dust from the point of generation to bins, or hoppers, for ultimate disposal. These systems must be designed by professionals to eliminate the risk of explosions within the dust collection system.
- Ensure that dust concentrations remain below levels that can combust, or explode, through air monitoring and interpretation by an industrial hygienist. Particle size (typically less than 420 microns), material type, and even the presence of other airborne materials can affect the potential for an explosion.
- Control ignition sources. OSHA requires areas where “dust” could potentially combust be considered a Class II Hazardous Location.3 In these areas, all sources of ignition such as lights, outlets, and machinery must be constructed and approved for that specific location.
Removing and/or controlling as many of these factors as possible is the best way to prevent dust from becoming explosive in your workplace.