Combustible Dust Hazards
It was 2:30 a.m. on February 7, 2016, when something went disastrously wrong at the JCG Farms Feed Mill in Rockmart, Georgia. A skeleton crew of seven workers was on duty that Sunday morning when the accumulated grain dust in the hammer mill exploded, killing 25-year-old Justin Deems and sending five other workers to the hospital.
A federal OSHA investigation of the incident resulted in more than $100,000 in proposed fines against JCG Farms, as well as citations against two contractors at the facility.
It’s not uncommon for a manufacturing facility to be dusty, and dusts of various types have long been identified as respiratory irritants or as substances that can cause serious lung disease—but what makes dust a potentially explosive hazard? And how can you prevent combustible dust explosions?
Federal OSHA has issued a new fact sheet that can help you answer these questions.
Dust as fuel
Liquids aren’t directly flammable. It’s their vapors, dispersed in air, that form flammable or explosive mixtures.
Dust is similar. Dust that’s piled on a beam probably won’t explode until it’s dispersed into the air. At that point, it may form a combustible mixture that can result in a flash fire or explosion. In fact, combustible dust fires often involve multiple explosions. The dust in one area is dispersed into a cloud and explodes; the initial explosion, even if it is a small one, can jar loose more dust, which is then ignited by the initial fireball.
Increasing the risk is the fact that many substances that aren’t explosive—that may even be difficult to ignite—when in larger, aggregate form can be explosive as dusts. For example, a bar of soap isn’t a serious fire hazard, but finely divided soap dust is potentially explosive.
Likewise, sugar isn’t a highly flammable substance, but an accumulation of finely divided sugar dust exploded and killed 14 people at the Imperial Sugar refinery just outside Savannah, Georgia, in 2008.
Some materials, such as cement, gypsum, limestone, sand, and salt, won’t form combustible dust.
Preventing dust explosions
Workers in many industries may not realize that the dust in their workplace is a potentially explosive hazard. Potentially hazardous dusts can be formed by:
- Agricultural products like cellulose, egg white, or spices;
- Carbonaceous materials like coal, charcoal, and lignite;
- Metals like magnesium, iron, and aluminum;
- Plastics like melamine, polyethylene, and polypropylene; and
- Other products like pharmaceuticals and dyes.
To protect workers, employers should first determine the explosive potential of dusts in the facility. OSHA has an extensive list of products and materials at risk of a combustible dust explosion at http://bit.ly/2aOBMph.
California already has a standard regulating combustible dust, General Industry Safety Orders (GISO) Section 5174. The standard requires employers to reduce combustible dust hazards by controlling sources of ignition, practicing good housekeeping, and collecting and segregating dusts at the point of generation. These requirements are in line with OSHA’s recommendations for further reducing the risk of dust explosions.
OSHA recommends that employers control fuel dust by:
- Capturing dust before it escapes into a work area by using properly designed, installed, approved, and maintained dust collection systems.
—Dust collection systems should prevent leakage so fugitive dust doesn’t accumulate in the work area.
—Duct systems, dust collectors, and dust-producing machinery must be bonded and grounded to minimize accumulation of static electrical charge.
—Dust collectors shouldn’t be located inside buildings.
—Dust collector systems should have spark detection and explosion/deflagration suppression systems.
- Containing dust within equipment, systems, or rooms that are built and operated to safely handle combustible dust.
—Isolation devices should prevent the propagation of dust explosions between connected pieces of equipment.
—Separator devices should remove foreign materials capable of igniting combustible dusts.
—Rooms, buildings, or other enclosures (dust collectors) should have explosion-relief venting distributed over the exterior wall of buildings and enclosures.
—Explosion venting should be directed to a safe location away from employees.
- Cleaning work areas, overhead surfaces, and concealed spaces frequently and thoroughly using safe housekeeping methods to remove combustible dusts not captured or contained.
—The working surfaces should be designed in a manner to minimize dust accumulation and facilitate cleaning.
—Electrically powered cleaning devices, such as vacuum cleaners, and electrical equipment should be approved for Class II hazardous locations.
The following OSHA publications contain voluntary guidelines for employers and employees. The first is a short hazard alert with basic information. The second is a bulletin that is more comprehensive in nature. The third gives specific guidance on hazard communication. The final item is a poster listing some of the more common materials that can form combustible dust
- Precautions for Firefighters to Prevent Dust Explosions [PDF*]. OSHA QuickCard, Publication 3674-08 2013 (2013, August).
- Firefighting Precautions at Facilities with Combustible Dust [PDF*]. OSHA Publication 3644-04-2013 (2013, April).
- Hazard Alert: Combustible Dust Explosions [PDF*]. OSHA Fact Sheet, (2008, March), 2 pages.
- Combustible Dust in Industry: Preventing and Mitigating the Effects of Fire and Explosion [PDF*]. OSHA Safety and Health Information Bulletin (SHIB) 07-31-2005, (2005, July 31).
- Hazard Communication Guidance for Combustible Dusts [PDF*]. OSHA Publication 3371-08, (2009).
- Combustible Dust — Does your company or firm process any of these products or materials in powdered form? [PDF*] OSHA Poster, (2008), 1 page.
- Combustible Dust. Safety and Health material produced through OSHA Susan Harwood Training Grant Program.
If your company or firm processes any of these products or materials, there is potential for a “Combustible Dust” explosion. Agricultural Products. Egg white.
Combustible dust explosion hazards exist in a variety of industries, including: agriculture, chemicals, food (e.g., candy, sugar, spice, starch, flour, feed), grain,