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The Dangers of Combustible Dust

February 16, 2024

Adam Henson, a Chemical Safety Recommendations Specialist at the US Chemical Safety and Hazard Investigation Board, discusses the unseen hazard of combustible dust

The invisible menace of combustible dust looms large over many industries, posing grave risks that often go unnoticed until disaster strikes.

Combustible dust is any solid material that can burn rapidly when in a finely divided form.

Examples of materials capable of generating combustible dust include agricultural products, carbonaceous materials like coal and wood, and other materials like metal, plastic, and various chemicals.

Some dusts are intentionally manufactured powders, others are the result of handling and processing.

What makes these materials so dangerous is that many of them are not considered dangerous by the owner/operators and employees of the facilities who handle and process them.

 To complicate matters further, the explosion hazard posed by these dusts are dependent on several factors including particle size and moisture content.

The severity of incidents involving these materials is contingent on factors such as the competency of the ignition source and the concentration of the material suspended in air.

Underestimating the hazards posed by these materials leads to mismanaging them.

Processes and equipment are often either improperly designed, not maintained appropriately, or just not equipped with necessary safeguards.

Fugitive dust emissions from these processes accumulate over time until conditions are such that a deflagration occurs resulting in loss of life, property damage, and harm to the environment.

A critical safety issue

In 2003, shortly after the Chemical Safety Board (CSB) began operating, there were three catastrophic dust explosions resulting in the death of 14 workers, many injuries, and substantial property and other damage.

Although the incidents occurred in different types of processes and different industry segments they shared many common causes.

Following investigation of these incidents the CSB conducted a hazard study on combust dust.

Through that study it was discovered that from 1980 to 2005 there were at least 281 major combustible dust incidents in the United States resulting in the death of 119 workers, injury to 718 workers, and untold property damage.

Based on these incidents the CSB determined that combustible dust is a significant industrial safety problem.

As a result of the Combustible Dust Hazard Study the CSB issued recommendations to OSHA for them to issue a standard designed to prevent combustible dust fires and explosions in general industry, to revise its Hazard Communication Standard to clarify its applicability to combustible dusts, and to create a special emphasis program on combustible dust hazards in general industry while the standard was being developed amongst other recommendations.

Five common factors

The CSB has investigated several catastrophic incidents in its 25-year history.

These incidents have involved chemical dusts, metal dusts, and dust from agricultural products.

The most substantial incidents in terms of loss of life and destruction of property have involved agricultural dusts.

This is surprising to some considering that chemical dusts and metal dusts are generally considered to pose a greater explosion hazard than agricultural dusts.

Five common causal factors have been identified:

  1. The facilities did not conform to the requirements and/or guidance of consensus and industry best practice standards such as those published by the National Fire Protection Association (NFPA)
  2. Involved parties, such as company personnel, enforcement personnel, and insurance/environmental, health and safety professionals, did not identify dust explosion hazards or recommend appropriate protective measures where such hazards were identified
  3. The dust collectors were inadequately designed or maintained to minimize the effects of primary deflagrations.
  4. The facilities contained unsafe accumulations of fugitive combustible dust.
  5. The facilities had previous fires and other warning events that were accepted as normal and the causes of these fires and events were not determined or resolved.

The most significant single combustible dust incident investigated by the CSB is the sugar dust explosion and fire that occurred at the Imperial Sugar Company facility in Port Wentworth, Georgia on February 7, 2008.

An unknown ignition source caused an explosion in the conveyor equipment beneath the facility’s sugar silos that lofted accumulated sugar dust from floors and elevated horizontal surfaces, propagating more dust explosions throughout the facility.

The most recent incident investigated by the CSB occurred on May 31, 2017 at the Didion Milling Company facility in Cambria, WI.

This incident similarly started within process equipment and propagated throughout the facility as the result of accumulations of fugitive dust.

The report into this incident was released December 6, 2023 and is available on www.csb.gov.

From the very first CSB combustible dust incident investigation to the most recent and every one in between a combination of these same five common factors have been identified as causal.

They played a role in every incident from then to now including in such investigations as the US Ink Fire, the Hoeganaes Corporation Fatal Flash Fires, and the CTA Acoustics Dust Explosion and Fire.

To stop these incidents from occurring it is imperative that owner/operators address these five common factors and in addition to other factors unique to their operations through a comprehensive safety management system.

Setting standards

Prior to the establishment of the Chemical Safety Board (CSB) and workplace safety regulations, combustible dust incidents were an ongoing issue.

In 1922, following a series of devastating incidents in 1919, the National Fire Protection Association (NFPA) formed a committee to address combustible dust hazards.

They developed the first standard in 1923, focusing on grain terminals and flour mills, which laid the foundation for subsequent standards, including NFPA 61.

Over time, the NFPA created various standards for different materials and industries to prevent combustible dust incidents.

Currently, they are consolidating these standards into NFPA 660.

In the past two decades, the NFPA incorporated safety management concepts, like dust hazard analysis and mechanical integrity, into their combustible dust standards.

These standards have been adopted and enforced across the United States but lack a national standard, resulting in varying safety levels by state and city.

Despite the US Occupational Safety and Health Administration’s (OSHA) mandate, they initially didn’t create a comprehensive combustible dust standard.

Instead, they addressed it through specific regulations and the General Duty Clause.

It wasn’t until the 1980s that OSHA introduced the Grain Facilities Standard.

Following CSB recommendations, OSHA updated its Hazard Communication Standard and initiated a special program for combustible dust.

However, CSB’s recommendation for a comprehensive general industry standard remains unaddressed by OSHA.

An updated, all-encompassing standard is essential to build upon the success of the Grain Facilities Standard, even though it’s not currently on OSHA’s rulemaking agenda.

CSB’s efforts to implement this recommendation have faced challenges, but continued dialogue and advocacy may lead to action.

Preventing combustible dust events

The most proactive thing to do is to first recognize the hazard and then acknowledge that an incident such as the catastrophes described above could happen at your facility. Then it is imperative to implement a robust safety management system embodying management leadership and employee engagement focusing on hazard identification and mitigation.

Such a system as applied to combustible dust should ensure the following at a minimum:

  1. That facilities conform to the requirements and/or guidance of consensus and industry best practice standards such as those published by the National Fire Protection Association (NFPA)
  2. That company personnel can identify dust explosion hazards and recommend appropriate protective measures where such hazards are identified
  3. That dust collectors and other equipment are adequately designed and maintained to minimize the effects of primary deflagrations
  4. That facilities do not contain unsafe accumulations of combustible dust. This should be accomplished primarily by preventing fugitive emissions from equipment, and secondarily by housekeeping
  5. That anytime there is a fire or explosion its causes are determined and resolved. These occurrences must not be allowed to be normalized

If your facility isn’t actively managing hazards and risk, especially those associated with combustible dust, now is the time to start.

This article was originally published in the February 2024 issue of Fire & Safety Journal Americas. To read your FREE digital copy, click here.

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