Hazard Alert: Combustible Dust Explosions

Combustible dusts are fine particles that present an explosion hazard when suspended in air in certain conditions. A dust explosion can be catastrophic and cause employee deaths, injuries, and destruction of entire buildings. In many combustible dust accidents, employers and employees were unaware that a hazard even existed. It is important to determine if your company has this hazard, and if you do, you must take action now to prevent tragic consequences.

How Dust Explosions Occur

In addition to the familiar fire triangle of oxygen, heat, and fuel (the dust), dispersion of dust particles in sufficient quantity and concentration can cause rapid combustion known as a deflagration. If the event is confined by an enclosure such as a building, room, vessel, or process equipment, the resulting pressure rise may cause an explosion. These five factors (oxygen, heat, fuel, dispersion, and confinement) are known as the “Dust Explosion Pentagon”. If one element of the pentagon is missing, an explosion cannot occur.

A pharmaceutical plant after a dust explosion.

Catastrophic Secondary Explosions

An initial (primary) explosion in processing equipment or in an area where fugitive dust has accumulated may dislodge more accumulated dust into the air, or damage a containment system (such as a duct, vessel, or collector). As a result, if ignited, the additional dust dispersed into the air may cause one or more secondary explosions. These can be far more destructive than a primary explosion due to the increased quantity and concentration of dispersed combustible dust. Many deaths in past accidents, as well as other damage, have been caused by secondary explosions.

Industries at Risk

Combustible dust explosion hazards exist in a variety of industries, including: agriculture, chemicals, food (e.g., candy, sugar, spice, starch, flour, feed), grain, fertilizer, tobacco, plastics, wood, forest, paper, pulp, rubber, furniture, textiles, pesticides, pharmaceuticals, tire and rubber manufacturing, dyes, coal, metal processing (e.g., aluminum, chromium, iron, magnesium, and zinc), recycling operations, and fossil fuel power generation (coal).

Prevention of Dust Explosions

To identify factors that may contribute to a explosion, OSHA recommends a thorough hazard assessment of:

• All materials handled;
• All operations conducted, including by-products;
• All spaces (including hidden ones); and
• All potential ignition sources.

Dust Control Recommendations

• Implement a hazardous dust inspection, testing, housekeeping, and control program;
• Use proper dust collection systems and filters;
• Minimize the escape of dust from process equipment or ventilation systems;
• Use surfaces that minimize dust accumulation and facilitate cleaning;
• Provide access to all hidden areas to permit inspection;
• Inspect for dust residues in open and hidden areas at regular intervals;
• If ignition sources are present, use cleaning methods that do not generate dust clouds;
• Use only vacuum cleaners approved for dust collection; and
• Locate relief valves away from dust deposits.

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;
• Control mechanical sparks and friction;
• Use separator devices to remove foreign materials capable of igniting combustibles from process materials;
• Separate heated surfaces from dusts;
• Separate heating systems from dusts;
• Select and use industrial trucks properly;
• Use cartridge activated tools properly; and
• Use an equipment preventive maintenance program.

Injury and Damage Control Methods

• Separation of the hazard (isolate with distance);
• Segregation of the hazard (isolate with a barrier);
• Deflagration isolation/venting;
• Pressure relief venting for equipment;
• Direct vents away from work areas;
• Specialized fire suppression systems;
• Explosion protection systems;
• Spark/ember detection for suppression activation;
• Develop an emergency action plan; and
• Maintain emergency exit routes.

Applicable OSHA Requirements Include:

• §1910.22 Housekeeping
• §1910.307 Hazardous Locations
• §1910.1200 Hazard Communication
• §1910.269 Electric Power Generation, Transmission and Distribution (coal handling)
• §1910.272 Grain Handling Facilities
• General Duty Clause, Section 5(a)(1) of the Occupational Safety and Health Act (Employers must keep workplaces free from recognized hazards likely to cause death or serious physical harm).

Resources

Readily available from www.osha.gov are:

• Combustible Dust National Emphasis Program
• Safety and Health Information Bulletin (SHIB) (07- 31-2005) Combustible Dust in Industry: Preventing and Mitigating the Effects of Fires and Explosions

See the SHIB or www.osha.gov for other applicable standards.

The primary National Fire Protection Association (NFPA) consensus standards related to this hazard are:

• NFPA 654, Standard for the Prevention of Fire and Dust Explosions from the Manufacturing, Processing, and Handling of Combustible Particulate Solids
• NFPA 61, Standard for the Prevention of Fires and Dust Explosions in Agricultural and Food Processing Facilities
• NFPA 484, Standard for Combustible Metals
• NFPA 664, Standard for the Prevention of Fires and Explosions in Wood Processing and Woodworking Facilities
• NFPA 655, Standard for the Prevention of Sulfur Fires and Explosions
• See www.nfpa.org to view NFPA standards.

This is one in a series of informational fact sheets highlighting OSHA programs, policies or standards. It does not impose any new compliance requirements. For a comprehensive list of compliance requirements of OSHA standards or regulations, refer to Title 29 of the Code of Federal Regulations. This information will be made available to sensory impaired individuals upon request. The voice phone is (202) 693-1999; teletypewriter (TTY) number: (877) 889-5627.

For more complete information:

OSHA Occupational Safety and Health Administration
U.S. Department of Labor
www.osha.gov
(800) 321-OSHA