Combustible dust generation and accumulation should be considered a potentially serious hazard and a very significant threat to a great many industries and facilities. Excessive, improperly managed dust accumulations are literal powder kegs – readily capable of exploding and causing large-scale loss of life and catastrophic damages, including the destruction of entire buildings. According to a 2018 report by the U.S. Chemical Safety Board, there were 105 combustible dust explosion incidents throughout the United States between 2006 and 2017 – resulting in 59 fatalities and 303 injuries along with extensive damage. In fact, there was a reported annual average of 28 dust explosion incidents, with 24 injuries and four fatalities over the past two years. In most of these incidents, employers and employees were unaware that a hazard even existed.

The Occupational Safety & Heath Administration (OSHA) Office of General Industry Enforcement initiated a Combustible Dust National Emphasis Program (NEP) in October 2007 to inspect facilities that generate or handle combustible dusts that pose a fire or explosion hazard. A 2009 NEP status report of more than 1,000 inspections found more than 4,900 combustible dust-related OSHA violations – with a total penalty of about $15 million. Only some 20% of the inspected facilities were found to be in compliance with applicable regulatory standards.

Causes of Dust Explosions

Most solid organic materials, as well as many metals such as such as sodium, lithium and zirconium, can cause a flash-fire and explode if finely divided and dispersed in sufficient concentrations. Combustible dusts can be intentionally manufactured powders, such as corn starch or aluminum powder coatings, or they could be generated when materials are transported, handled, or processed. For example, polishing, grinding, and shaping many materials can produce very small particles that can easily become airborne and settle on     surfaces, crevices and equipment. As little as 1/32 of an inch of accumulated dust can cause a catastrophic explosion.

Five elements – illustrated in what is known as the Dust Combustion Pentagon – must be present for a dust explosion to occur. If any of the following is missing, an explosion will not occur:

1. Combustible dust sufficiently fine to become airborne
2. An ignition source such as a hot surface, flame, spark or static electricity
3. Oxygen in the atmosphere sufficient to support and sustain combustion
4. Dispersion of the dust particles within explosion concentration values
5. Confinement of the dust cloud in a closed room, inside equipment, ducts, etc.

When airborne dust particles are ignited, their resultant combustion and heat release are extremely rapid – with combustion gases generating a sudden, rapid pressure increase, having explosive force on the walls of the vessel containing the dust cloud. The effect of this explosive pressure wave, or shock wave, can rupture vessel walls and allow burning dust and gases from the explosion to be expelled into the surrounding areas – causing deaths and injuries to nearby persons. The shock wave also typically causes dusts that have accumulated on surfaces elsewhere in the building to be dislodged, thrown into suspension, and become ignited – thereby resulting in a far more disastrous, large-scale secondary explosion. In most cases, the greatest hazard associated with combustible dust comes from the threat of secondary explosions.

Regulations Oversight & Requirements

Measures and recommendations for preventing combustible dust fire and explosion hazards are specified in National Fire Protection Association (NFPA) and OSHA standards and guidelines. The NFPA is a non-profit, standard-making industry association with no ability to make or enforce laws or codes; however, OSHA incorporates NFPA standards under the General Duty Clause [Section 5(a)(1)] of the Occupational Safety and Health Act of 1970, and companies found in violation of the NFPA standards can be cited under federal OSHA jurisdiction.

Dust Hazard Analysis

Prior to 2016, the NFPA had multiple industry-specific combustible dust standards with varying, and sometimes confusing, requirements. However, in 2016 the NFPA revised NFPA 652 – Standard on the Fundamentals of Combustible Dust to create commonality among the other standards. One of the new requirements of NFPA 652 was the need for every facility that processes, handles or generates dust to complete a Dust Hazard Analysis (DHA) by September 7, 2020.

A DHA is a systematic analytical review of a facility to determine if dust being generated, handled or stored poses a fire or explosion hazard. A DHA report is also required to evaluate all aspects of a facility’s operation to determine administrative and engineering safeguards that should be implemented to mitigate such hazards. Additionally, all affected employees are required to be trained about the hazards and dangers posed by combustible dust, where dust explosions might occur,  and control and management programs being implemented to minimize or eliminate such hazards. Furthermore, the NFPA specifies that a DHA be performed or led by a “qualified” person having “a recognized degree, certificate, professional standing, skill, training, and            experience” to deal with such matters.

Combustible Dust Explosion Prevention Measures

Administrative & Engineering Controls – According to OSHA, there are two categories of dust explosion preventive measures: (1) administrative controls which comprise such measures as housekeeping, hot work, and lockout/tagout procedures that address the hazards of performing work in areas where combustible dusts are present; and (2) engineering controls that comprise mechanical measures to prevent an explosion from spreading to occupied areas and/or to safely extinguish or vent an explosion, as a means to prevent structural failures of equipment or buildings.

Recommended Prevention Measures – Below are some of the combustible dust explosion prevention measures recommended by OSHA and included in NFPA 654 – Standard for the Prevention of Fire and Dust Explosions from the Manufacturing, Processing, and Handling of Combustible Particulate Solids:

Dust Control Recommendations

• Implement a dust inspection, housekeeping and control program
• Use proper dust collection systems and filters
• Minimize the escape of dust from process equipment or ventilation systems
• If ignition sources are present, use cleaning methods that do not generate dust clouds
• Use only vacuum cleaners approved for dust collection

Ignition Control Recommendations

• Use appropriate electrical equipment and wiring methods
• Control static electricity, including bonding of equipment to ground
• Control smoking, open flames and sparks
• Separate heated surfaces and heating systems from dusts

Injury and Damage Control Methods

• Separation of the hazard -– isolate with distance
• Segregation of the hazard – isolate with a barrier
• Pressure relief venting for equipment
• Specialized fire suppression systems
• Explosion protection systems

HETI: Helping Minimize Combustible Dust Hazards

Combustible dusts pose imminent hazards to a great many facilities and industries throughout the country because of their ready potential to explode with catastrophic consequences. OSHA has imposed a deadline of September 7, 2020, by when all companies that generate or handle dusts must conduct a Dust Hazard Analysis leading to the implementation of measures to safeguard against such explosions. According to the NFPA, a DHA must be performed or led by a “qualified” and experienced individual. HETI staff have such qualifications and experience…and are available to assist our clients minimize their exposures.