Combustible Dust Frequently Asked Questions


What is Combustible Dust?

According to OSHA's Safety & Health Topics Combustible Dust website, combustible material (and some materials normally considered noncombustible) can burn rapidly when in a finely divided form. If such a dust is suspended in air in the right concentration, it can become explosive. Such incidents have killed scores of employees and injured hundreds over the past few decades.

How Does Dust Explode?

Three basic elements are needed for a fire:

      1. Combustible dust (fuel)
      2. Ignition source (heat)
      3. Oxygen (oxidizer)

Two additional elements are needed for a combustible dust explosion:

      4. Dispersion of dust particles in sufficient quantity and concentration
      5. Confinement of the dust cloud

An initial (primary) explosion in processing equipment or in an area were dust has accumulated may shake loose more accumulated dust, or damage a dust containment system and may cause one or more secondary explosions that can be far more destructive than the initial explosion.

What Products/Materials Can Cause a “Combustible Dust” Explosion?

OSHA identifies more than 130 products or materials that pose a threat for combustible dust explosions. Included are many agricultural products and dusts, carbonaceous dusts, chemical dusts, metal dusts, and plastic dusts. OSHA has published a downloadable poster entitled, Combustible Dust: Does your company or firm process any of these products or materials in powdered form?

What Industries are Most at Risk?

Any business that processes or produces materials in finely powdered form have work environments that may present a serious hazard.

In March 2008, 30,000 workplaces received a letter from OSHA and a bulletin titled Combustible Dust in Industry: Preventing and Mitigating the Effects of Fire and Explosions. In this letter employers were urged to review the information and were reminded of their responsibilities to prevent combustible dust hazards to help prevent future tragedies.

In March of 2008, an OSHA-wide directive was issued with instruction, policies and procedures for inspecting workplaces that create or handle combustible dusts. OSHA reissued Combustible Dust National Emphasis Program (CPL 03-00-008) “to increase its enforcement activities and to focus on specific industry groups that have experienced either frequent combustible dust incidents or combustible dust incidents with catastrophic consequences.” Appendix D-1 of this directive entitled, Industries with More Frequent and/or High Consequence Combustible Dust Explosions/Fires, lists 16 industry groups and directs each Area Office to conduct at least three National Emphasis Program (NEP) inspections from the list in each Fiscal Year. Appendix D-2 of the directive lists another 48 industries that may have Potential for Combustible Dust Explosions/Fires, and directs each Area Office to conduct at least one NEP inspection from the list in each Fiscal Year.

What OSHA Directives Relate to Combustible Dust and Flame Resistant clothing?

Section 5(a)(1) of the OSH Act, often referred to as the General Duty Clause, requires employers to “furnish to each of his employees employment and a place of employment which are free from recognized hazards that are causing or are likely to cause death or serious physical harm to his employees.” Section 5(a)(2) requires employers to “comply with occupational safety and health standards promulgated under this Act.”

According to the Combustible Dust National Emphasis Program (CPL 03-00-008), under the section Citations (g) 1910.132(a), the general requirement to provide and assure the use of protective equipment, including protective clothing may be issued, “If an employee exposure to potential burn injuries can be documented. For example, if employees are not wearing protective clothing, such as Flame Resistant clothing, in areas of the plant (e.g., bagging areas) where employees may be exposed to potential combustible dust flash fire hazards, then citations under 1910.132(a) may be issued. Another example where citations under 1910.132(a) may be issued, would be a situation where employees (not wearing Flame Resistant clothing) cleaning out a piece of equipment containing combustible dust may be exposed to a flash fire propagated through the cleanout door. A citation may be issued whether or not an accident precipitated the inspection.”

This 2008 directive also states that NFPA standards “should be consulted to obtain evidence of hazard recognition and feasible abatement methods,” endorsing NFPA standards as part of its compliance strategy and enforcement tools for managing combustible dust hazards. NFPA 652, the Standard on the Fundamentals of Combustible Dust, provides the general requirements for managing combustible dust fire and explosion hazards and states that when FR clothing is required, it must comply with the requirements of NFPA 2112 and be selected, procured, inspected, worn, and maintained in accordance with NFPA 2113.

What are Legislators Doing?

Following a highly publicized combustible dust explosion at a sugar refinery in 2008, legislators drafted H.R. 5522 (110th), the Worker Protection Against Combustible Dust Explosions and Fires Act of 2008, which passed in the House but not the Senate. Legislation was reintroduced on February 4, 2009 (H.R. 849, 111th), February 11, 2011 (H.R. 522, 112th), and February 14, 2013 (H.R. 691, 113th). The Worker Protection Against Combustible Dust Explosions and Fires Act would require the Secretary of Labor to issue an interim occupational safety and health standard regarding worker exposure to combustible dust, and for other purposes.

For additional information about UniFirst Flame Resistant garments or a UniFirst full-service work clothing maintenance program, call us at (800) 455-7654.


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