Combustible Dust

Causes of a Dust Explosion (right, Fire Triangle)

1) Fuel: combustible dust
2) Oxygen: oxidizer
3) Heat: ignition source

Also:

4) Confinement of a dust cloud
5) Sufficient dispersion of dust particles in quantity and concentration

The latter two create an explosion pentagon. If airborne dust is ignited within a confined space, it burns rapidly and could explode. Employee safety is threatened by potential explosions, fires, debris and building collapse.

If one of the elements of the explosion pentagon is missing, a catastrophic explosion cannot occur. Without sufficient heat and oxygen, a fire cannot begin. Without fuel, a fire will stop.

To stop a combustion reaction, one of the three elements has to be removed:

• Suppression of fuel: by closing of the valve fueling the combustion, creating sufficient distance between fire and flame, exhausting hot smoke, etc.
  
  
• Suppression of oxygen (choking): use of a carbon dioxide fire-extinguisher, blanket, or spraying sufficient water on a solid combustible
  
  
• Suppression of heat (cooling down): by spraying water into a mixture of air and combustible particles, net absorbing the heat, removal of hot smoke
  

It is nearly impossible to eliminate two of the elements in the explosion pentagon: oxygen and the space that confines the dust cloud. However, the other three elements of the pentagon can be significantly controlled.

Businesses should identify the following to assess their potential for dust explosions:

• Fine materials that can become airborne and combustible;
• Processes which use, consume, or produce combustible dusts;
• Areas where combustible dusts may accumulate;
• The ways in which dust may become airborne;
  
• Ignition sources in those areas.

Employees are the first line of defense in preventing fires and explosions. If the workers closest to the source of the hazard are trained to recognize and prevent hazards associated with combustible dust in the building, they can be instrumental in recognizing unsafe conditions, taking preventative action, and/or alerting management. While OSHA standards require training for certain employees. All employees should be trained in safe work practices applicable to their job tasks, as well as on the overall plant programs for dust control and ignition source control. They should be trained before they start work, periodically to refresh their knowledge, when reassigned, and when hazards or processes change.

Employers with hazardous chemicals (including combustible dusts) in their workplaces are required to comply with 29 CFR 1910.1200, the Hazard Communication standard. This includes having labels on containers of hazardous chemicals, using material safety data sheets, and providing employee training.

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