Combustible dust fires are an ever-present risk in processing industries across the country and are a much bigger problem than reported by the federal government. These combustible dust fires are often precursors to catastrophic explosions. In fact, most dust can be combustible under the right circumstances.
“If your facility generates dust — any kind of dust — consider it combustible until proven otherwise,” John Astad, founder of the Combustible Dust Policy Institute, told IMT.
In 2012, Astad’s institute reported results from a preliminary analysis of 2011 National Fire Incident Reporting System (NFIRS) data obtained from the U.S. Fire Administration (USFA). The report detailed 500-plus combustible-dust-related fires and explosions in many industrial sectors throughout the U.S. The majority of incidents were classified as “near-misses,” meaning they did not result in injuries or fatalities. NFIRS is a voluntary service in many states and not all fires are reported to the system.
The Occupational Health and Safety magazine reports that, although small dust-related fires might be the norm for some manufacturers, flames that don’t lead to deadly explosions or flash fires should be considered near-misses. Incidents are rarely reported to state and federal agencies because, aside from random inspections, the U.S. Occupational Safety & Health Administration (OSHA) only investigates incidents that involve fatalities or extensive injuries.
According to a 2006 study by the U.S. Chemical Safety Board (CSB), there were 281 combustible dust incidents between 1980 and 2005 that killed 119 workers and injured another 718.
Astad says the number from the CSB is much too low and combustible dust fires and explosions are a significantly bigger problem. In addition, his center’s analysis does not include many incidents that were not reported by fire departments to the USFA’s National Fire Data Center. Therefore, he contends that there are many more combustible-dust-related incidents that cannot be evaluated in determining whether they were near-misses or not.
According to an OSHA fact sheet, in many combustible dust accidents, employers and employees were unaware that a hazard even existed.
Jeffrey C. Nichols, managing partner of Industrial Fire Prevention LLC, a consulting and service company specializing is helping manufacturers reduce the risk of fires, explained to IMT that dust fires occur when three components of the fire triangle exist:
- Combustible dust (fuel)
- Ignition source (heat)
- Oxygen in air (oxidizer)
Nichols said, “Once you understand the fire triangle, you start to see where the fires can occur. Anytime there’s a moving part, a spinning part, a turning part, you’ll find something that’s creating combustible dust as well as friction,” the latter of which can become an ignition source. He also pointed out that human error and any mechanical machinery prone to breakdowns are potential causes for fire.
OSHA distinguishes the conditions that make a dust fire versus a dust explosion. Like a dust fire, an explosion occurs when there is fuel and oxygen. However, the ignition source may be something other than heat, such as static electricity. In addition, the dust must be dispersed into the air, while also being confined to vessel, room, or other enclosure.
Mysafetynews.com explains that dust explosions can occur “as a series.” For example, an initial explosion can damage equipment or preventative systems such as a dust collection unit. This can knock loose additional dust that leads to a larger, secondary explosion.
Preventing combustible dust explosions requires controlling the dust itself and potential ignition sources.
“Control of the hazard requires constant vigilance and constantly effective maintenance,” Len Welsh, chief of safety for the State Compensation Insurance Fund of California, the largest provider of workers’ compensation insurance in California, told IMT.
Mysafetynews.com and State Fund have the following recommendations for manufacturers:
- Install dust collection systems and filters to prevent explosions by removing dust from the air. Dust collectors should be hooked up outdoors or in a separate room.
- Lay out a facility so that machines with dust explosion hazards are enclosed or facing away from populated work areas to minimize the fire and energy impact if there is an explosion.
- Utilize surfaces that minimize dust accumulation and facilitate cleaning.
- Clean dust residue regularly. Before cleaning, shut down all flame and ignition sources. Use a cleaning method that does not generate dust clouds (i.e., vacuuming instead of blowing). Establish a routine cleaning schedule to remove dust from floors, ledges, beams, equipment, and other surfaces. Clean often enough to prevent dust buildup.
- Ensure that electrical wiring and equipment located in areas containing combustible dust are rated for use in Class II locations.
- Control static electricity sources as it is a serious explosion and fire ignition source. Grounding can help prevent this. Operate, service, and maintain equipment to ensure that the proper grounding is in place.
- Control potential heated surfaces, such as exhaust systems of mobile equipment, including forklifts.
Specific standards that deal with the prevention of combustible dust explosions are published by the National Fire Protection Association (NFPA).
OSHA continues to work toward a combustible dust standard. In the absence of a final rule, the agency offers guidance and information on its website.