Preventing Combustible Dust Explosions and Fires

OSHA has not promulgated a regulation for combustible dust hazards, yet facilities can still be held accountable for safety violations related to this hazard and can receive stiff penalties based on OSHA inspections. As a guideline for evaluating combustible dust hazards and issuing citations, OSHA inspectors are trained to use the Combustible Dust National Emphasis Program. (A National Emphasis Program is a set of policies and procedures for OSHA to respond to situations they believe may risk the health and safety of workers.)

OSHA's Combustible Dust NEP lists 18 different standards that can be used to inspect and cite workplaces that create or handle combustible dusts. These standards cover everything from ventilation and electrical systems to housekeeping regimens. Facilities even can be cited when inspectors find hazards not addressed by the NEP. In those cases, OSHA relies on the General Duty Clause of the Occupational Health and Safety Act of 1970, the clause that requires employers to provide a workplace free from recognized hazards that are likely to cause death or serious physical harm.

If combustible dust hazards are present at a facility and not properly mitigated, the inspector can assume risk and serve a citation. OSHA regularly hands out hefty fines for housekeeping violations related to the handling of combustible dust. As recently as Aug. 31, 2015, OSHA cited a Mississippi lumber mill, issuing one willful, 22 serious, and four other-than-serious citations, after investigators found combustible dust accumulations and other hazards. OSHA issued $78,800 in proposed penalties in the case.

The NEP details policies and procedures for inspecting workplaces that create or handle combustible dusts that include, but are not limited to:

  • Metal dust, such as aluminum and magnesium
  • Wood dust
  • Coal and other carbon dusts
  • Plastic dust and additives
  • Biosolids
  • Other organic dusts, such as sugar, flour, paper, soap, and dried blood
  • Certain textile materials

According to the document, industries that handle combustible dusts include, but are not limited to:

  • Agriculture
  • Food products
  • Chemicals
  • Textiles
  • Forest and furniture products
  • Metal processing
  • Tire and rubber manufacturing plants
  • Paper products
  • Pharmaceuticals
  • Wastewater treatment
  • Recycling operations (metal, paper, and plastic)
  • Coal dust in coal handling and processing facilities

The U.S. Chemical Safety Board has issued recommendations following its investigations of several major dust explosions, with CSB's final reports available here.

Guy Colonna, manager of NFPA's Industrial and Chemical Engineering Division, wrote an article about the process of developing the new standard for the March/April 2015 issue of the NFPA Journal. Titled "Credible Risk," his article discusses the requirements in the new standard that are retroactive in nature, including the requirement to perform a dust hazards analysis. He noted in the article that existing facilities will have to complete a DHA within three years after the effective date of the standard.

Preventing Dangerous Dust Accumulations
To prevent dangerous accumulations and fines based on them, housekeeping standards call for the use of industrial vacuum cleaners designed for Class II Division 2 environments. According to OSHA, these are locations in which combustible dust is or may be in suspension in the air under normal operating conditions, in quantities sufficient to produce explosive or ignitable mixtures; or where mechanical failure or abnormal operation of machinery or equipment might cause such explosive or ignitable mixtures to be produced and might also provide a source of ignition through simultaneous failure of electric equipment, operation of protection devices, or from other causes; or in which combustible dusts of an electrically conductive nature may be present.

Vacuum cleaners and other electrical equipment must meet very specific requirements and go through a careful testing process to be certified "explosion proof." This is one of the most misunderstood concepts in the vacuum cleaner industry.

To be certified as explosion proof, a vacuum must be tested by one of OSHA's Nationally Recognized Testing Laboratory – or NRTLs. The NRTL will confirm that the vacuum complies with the standards outlined in article 500 of the 2014 National Electrical Code. NRTLs are the only organizations that can provide certification for electrical equipment for hazardous locations in the United States. In fact, OSHA states that in order to be truly considered certified, each vacuum must bear the specific approval marks of one of the NRTLs. Facility managers should look for an NRTL mark on any vacuum that claims to be explosion-proof; it can be found next to the listing of approved environments for that vacuum.

The features that make vacuums explosion-proof and dust-ignition proof are features that prevent them from creating sparks and arcs, whether they be electrical, percussion, or static discharge arcs. Sealed motors prevent electrical arcs. Stainless steel construction prevents percussion arcs caused by metal-to-metal contact. And continuity through the tool, hose, and other vacuum parts prevents static discharge arcs caused by high levels of static electricity buildup.

Overall, the "explosion-proof" label carries a lot of meaning and should be taken very seriously. Facilities can require National Fire Protection Association-compliant vacuums even when they are not classified as hazardous or classified environments. Vacuum requirements are dictated by the type and amount of dust collected and not by the environment being cleaning. If a facility is collecting any amount of dust, electric-powered vacuums must meet certain safety requirements set by NFPA.

NFPA 652 and Other Dust Standards
NFPA standards outline the requirements for identifying and managing combustible dust fire and explosion hazards. Originally, there were five industry-specific standards. Then, in September 2015, NFPA 652, Standard on the Fundamentals of Combustible Dust, was added. It serves as the unifying standard to make sure that fundamental requirements are addressed consistently across industries, processes, and dust types.

These NFPA standards apply to all facilities and operations that manufacture, process, blend, convey, repackage, generate, or handle combustible dusts. It is the facility manager's responsibility to assess the risk and have the dust tested, even if there has never been an incident. That risk assessment must be documented, specifying cleaning methods and equipment.

Vacuuming is the preferred cleaning method to reduce the risks of combustible dust. Section 8.4.2.2 of NFPA 652 provides a list of seven specific requirements for all portable vacuum cleaners that will be used to collect combustible dust in any unclassified (non-hazardous) area. These requirements cover the construction and operation of the vacuum, including its motor, filters, hoses, and accessories.

NFPA 652 is not a law, but it should be taken very seriously. It is a set of guidelines that OSHA will use to evaluate risk and cite safety violations. Failure to comply can lead to hefty fines and penalties. Violations of NFPA 652 guidelines also may also lead other authorities having jurisdiction – including fire marshals, OSHA, and insurance companies – to withhold permits or insurance coverage.

Worst of all, failure to comply with NFPA 652 will put facilities and people at risk for devastating combustible dust fires and explosions.

Posted by Jerry Laws on Jan 20, 2016


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