13 Feb Dust Explosion Prevention

Dust Explosion Prevention

Combustible dust can create a serious fire, flash-fire, and explosion hazard when fine particles become suspended in air and encounter an ignition source. Materials that may create combustible dust include wood, paper, plastics, rubber, textiles, grain, flour, sugar, animal feed, coal, pharmaceuticals, chemicals, and certain metals.

Not every type of dust is combustible. The hazard depends on the material’s properties, particle size, concentration, and workplace conditions. Employees should know whether the dust generated by their work is combustible and follow the facility’s established controls.

The Dust Explosion Pentagon

A combustible dust explosion generally requires five elements, often referred to as the Dust Explosion Pentagon:

1. Combustible dust (fuel)
2. Oxygen
3. Ignition source
4. Dispersion of the dust into the air
5. Confinement of the dust cloud

Removing or adequately controlling one or more of these elements can prevent an explosion.

Control Dust Accumulation

Good housekeeping is one of the most important defenses against combustible dust hazards. Dust should not be allowed to accumulate on floors, equipment, structural members, ducts, pipes, beams, ledges, or other surfaces.

• Establish and follow a routine dust-cleaning schedule.
• Inspect overhead and difficult-to-reach surfaces for accumulated dust.
• Increase cleaning frequency when operations generate more dust than normal.
• Clean spills and accumulations promptly.
• Keep dust-producing equipment and dust-control systems properly maintained.
• Use cleaning methods that minimize the creation of airborne dust clouds.
• Pay particular attention to hidden or elevated areas where dust can accumulate unnoticed.

Even relatively thin layers of accumulated combustible dust can become dangerous if disturbed and dispersed into the air.

Control Ignition Sources

Potential ignition sources must be identified and controlled wherever combustible dust may be present.

Possible ignition sources include:

• Open flames.
• Smoking materials.
• Welding, cutting, grinding, and other hot work.
• Hot bearings and equipment surfaces.
• Electrical equipment and sparks.
• Static electricity.
• Friction and mechanical sparks.
• Improperly maintained machinery.

Smoking and unauthorized open flames must be prohibited in combustible-dust hazard areas. Hot work must be controlled through the company’s established hot-work procedures and permit system.

Static Electricity and Bonding/Grounding

Static electricity can provide enough energy to ignite certain combustible dust clouds.

Where required by the process and equipment:

• Properly bond and ground conductive equipment.
• Inspect bonding and grounding connections regularly.
• Do not remove or bypass grounding components.
• Maintain conductive hoses, ducts, containers, and other equipment according to manufacturer and facility requirements.
• Report damaged or missing bonding and grounding equipment immediately.

Bonding and grounding help control static ignition hazards but do not eliminate the need for other combustible-dust controls.

Dust Collection and Ventilation

Dust should be captured as close as practical to the point where it is generated.

• Operate required local exhaust and dust-collection systems whenever dust-producing equipment is operating.
• Inspect ducts, collectors, filters, and associated equipment as required.
• Never disable, bypass, or modify dust-control equipment without authorization.
• Report leaks, damaged ductwork, poor suction, or unusual dust accumulation.
• Keep dust collectors and associated systems maintained according to their design and manufacturer requirements.

Dust-collection systems handling combustible dust may require specialized explosion protection, isolation, suppression, or venting systems. These systems must not be altered or defeated.

Safe Dust Cleanup

Improper cleaning can turn settled combustible dust into a dangerous airborne cloud.

Preferred cleaning methods include:

• Approved vacuum systems designed for the specific combustible dust hazard.
• Wet cleaning methods where appropriate for the material and process.
• Other methods specifically approved by the employer for the material involved.

Avoid dry sweeping or brushing when it could create a hazardous dust cloud.

Do not use compressed air to clean combustible dust from surfaces or clothing unless the method has been specifically evaluated and authorized and appropriate controls are in place. Blowing accumulated dust into the air can create the exact conditions necessary for a flash fire or explosion.

Never use ordinary shop vacuums or other electrical equipment in a combustible-dust hazard area unless the equipment is approved and suitable for the location and material.

Equipment and Machinery

Grinding, cutting, sanding, pulverizing, conveying, and other material-processing operations can generate combustible dust and potential ignition sources.

Employees should:

• Inspect equipment before use.
• Keep guards and safety devices in place.
• Maintain bearings, belts, and moving components to prevent overheating or friction.
• Report unusual noises, vibration, overheating, sparks, or burning odors immediately.
• Use required separators or other systems designed to remove tramp metal or foreign material where applicable.
• Follow lockout/tagout procedures before servicing or maintaining equipment.
• Never modify dust-producing or dust-collection equipment without authorization.

Secondary Explosions

One of the greatest dangers associated with combustible dust is a secondary explosion.

An initial fire or explosion can disturb accumulated dust on floors, beams, equipment, pipes, and overhead surfaces. Once this dust becomes airborne, it can ignite and produce a much larger explosion that travels through the facility.

Preventing accumulated dust from developing in the first place is therefore critical. Good housekeeping is an explosion-prevention measure, not simply a cleanliness issue.

Employee Responsibilities

Employees working around combustible dust should:

• Understand the combustible-dust hazards associated with their work.
• Follow established operating and housekeeping procedures.
• Keep ignition sources away from dust-producing operations.
• Use required PPE.
• Operate dust-collection systems as instructed.
• Never bypass explosion-protection or safety devices.
• Report excessive dust accumulation, leaks, sparks, overheating, or other unsafe conditions immediately.
• Follow emergency procedures and evacuate when directed.

Remember

A dust that appears harmless while lying on a surface may become extremely dangerous when dispersed into the air. Control the dust, control ignition sources, maintain dust-collection systems, and practice effective housekeeping. Preventing dust accumulation can prevent both the initial event and a potentially devastating secondary explosion.