Combat combustible dust
January 11, 2009
In November 2006, the U.S. Chemical Safety and Hazard Investigation Board (CSB) released the results of a three-year study regarding dust explosions. The organization concluded that dust explosions in factory and industrial-type settings were much more common and serious than had previously been believed.
Among their findings:
- There have been at least 281 dust-related fires/explosions in industrial facilities from 1980 to 2005
- Seven of these explosions were considered “catastrophic,” involved multiple facilities, and resulted in significant negative community economic impact
- No current OSHA standards comprehensively address the problem and how to prevent combustible dust explosions
“The combustible dust incidents included are likely only a small sampling, as no federal or state agency keeps specific statistics on combustible dust incidents, nor does any single data source provide a comprehensive collection of all these incidents.”
The basics on (industrial) dust
Many types of materials, including wood, metals, and nonmetallic materials can burn and possibly explode if small enough and in large enough concentrations. Polishing, grinding, cutting, and shaping materials cause the dust to become airborne and then settle on surfaces, equipment, and floors. If “stirred up,” it can cause dust clouds that potentially can cause an explosion.
It appears the amounts of accumulated dust necessary for an explosion can be far less than recognized. At one explosion in 2003 that killed six people, the dust accumulation was less than 0.25 inches deep. It is believed that once more than 1/32 of an inch of dust covers over five percent of a room’s surface, there is a hazard for a dust explosion.
But how does the fire or explosion actually occur? Accumulated dust can be viewed as fuel. Once exposed to heat, the ignition source, the “fuel” explodes. This scenario has been simplified, but with oxygen present, it creates the classic “fire triangle” combining all the elements necessary for a fire.
Facility managers should also know there are actually two types of dust explosions. A primary explosion occurs within a machine, a specific room, or area. A secondary explosion occurs when dust that has accumulated on floor surfaces becomes airborne and becomes ignited. This secondary, unconfined explosion can generate other explosions within the same facility.
Professor Bill Kauffman of the University of Michigan, a leading expert on dust explosions, says there is only one option: remove the dust. Since these explosions occur within equipment, silos, storage and other enclosed areas, cleaning and maintenance of these machines and areas is paramount. The goal is to keep the dust and dust accumulation away from ignition sources. Kauffman says that there are also various explosion protection methods. Among these are:
- Explosion relief venting (rupture disks)
- Explosion suppression
- Oxygen concentration reduction.
Develop a formalized housekeeping plan that applies to both your workers and cleaning professionals. Often, floor areas around work stations are swept to remove dust, however that can cause the dust to become airborne. Instead of sweeping, manual sweepers can be employed to gather and trap the dust. Because they are manually operated, there are no heat or ignition sources, which makes them safe to use.
Along with enhanced housekeeping, consider conducting more workforce training and education programs to help keep workers aware of the problem of dust. Additionally, canvass warehouse and industrial facilities for potential ignition sources and eliminate them wherever possible.