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What is Combustible Dust? Part 1

The Occupational Safety and Health Administration (OSHA) defines combustible dust as a “combustible particulate solid that presents a fire or deflagration hazard when suspended in air or some other oxidizing medium over a range of concentrations, regardless of particle size or shape.” This dangerous substance can be found at “Class II locations” and is largely defined by National Fire Protection Association (NFPA) standards and 29 CFR 1910.399.

In this two-part article, the OSHA defense attorneys at Cotney Construction Law will discuss everything contractors should know about combustible dust. Protecting your workers from the dangers of combustible dust can help you avoid a potential OSHA citation and ensure that your projects meet their deadlines.

Class II Locations

Class II locations are designated as “hazardous” because these areas contain combustible dust. Some examples include Group E, Group F, and Group G.

Group E: atmospheres that contain combustible metal dusts such as aluminum, magnesium, and their commercial alloys, as well as other combustible dusts that can present a hazard in the presence of electrical equipment due to their particle size, abrasiveness, and conductivity.

Group F: atmospheres that contain combustible carbonaceous dusts with over 8 percent total entrapped volatiles. Contractors can reference ASTM D 3175, Standard Test Method for Volatile Matter in the Analysis Sample of Coal and Coke, for more information. Group F also includes various types of dust that present a risk of explosion, including coal, carbon black, charcoal, and coke dust.

Group G: atmospheres that contain flour, grain, wood flour, plastic, and chemicals.

Important Definitions

Even the most seasoned contractor may be unaware of the dangers of combustible dust. To develop a more comprehensive understanding of combustible dust, it’s important that contractors are familiar with the following terms:

  • Combustible Particulate Solid: combustible solid materials composed of clear-cut particles or pieces. The size, shape, and chemical composition is irrelevant.
  • Deflagration: propagation of a combustible substance at subsonic speeds.
  • Deflagration Isolation: a method wherein propagation of a deflagration of a flame front is interrupted.
  • Deflagration Suppression: a specialized technique in which an incipient combustion is detected and arrested in order to stifle the development of pressure and thus the explosion that would otherwise occur.
  • Detonation: combustion of a substance at a rapid speed that creates a shock wave.
  • Dust-Ignitionproof: protecting equipment in a way that mitigates exposure to dust and prevents arcs, sparks, or heat from being generated.
  • Dusttight: constructed in a way that prevents dust from entering under specific testing conditions.
  • Explosion: the resulting burst of energy that occurs when a container is subjected to extensive internal pressure from deflagration.
  • Hybrid Mixture: a mixture containing flammable gas and combustible dust or combustible mist
  • Minimum Explosible Concentration (MEC): a measurement in mass per unit volume that depicts the minimum concentration of a combustible dust suspended in the air and that can experience deflagration.

In part two, an OSHA attorney will continue to discuss everything contractors should know about combustible dust. 

If you would like to speak with an OSHA defense attorney, please contact us today.

Disclaimer: The information contained in this article is for general educational information only. This information does not constitute legal advice, is not intended to constitute legal advice, nor should it be relied upon as legal advice for your specific factual pattern or situation.