Dust Explosions
When combustible or non-combustible materials are broken down into fine dusts or powders, they create a fire and explosion hazard affecting many operations and materials: sugar, flour, animal feed, plastics, paper, wood, rubber, furniture, textiles, pesticides, pharmaceuticals, paints and resins, dyes, coal, and metals.
To prevent fires from dust explosions, control the “dust explosion pentagon.” This includes the traditional fire triangle: fuel, heat, and oxygen along with a dust cloud and enclosed space. Keep dust levels (fuel) in the workplace to a minimum with dust control and housekeeping. Control flame and ignition sources (heat) such as pilot lights, open flames, hot equipment, and static electricity. Never allow smoking in the worksite.
Due to the hazard of dust explosions, CalOSHA Title 8, Section 5174 limits combustible dust to a concentration of 25% of its lower explosive limit (LEL) “unless all sources of ignition are eliminated or identified and specifically controlled.” (See CalOSHA’s website at http://www.dir.ca.gov/Title8/5174.html).
Static electricity is a serious explosion and fire ignition source, but grounding prevents this. CalOSHA defines effective grounding as linking equipment to earth through a connection that has “low impedance” and enough current-carrying capacity to prevent hazardous voltages.
When you operate, service, and maintain equipment, ensure that the proper grounding is in place. Review facility machines, conveyors, housings, and conductive surfaces for proper ground. Hoses and nozzles used to collect or blow dust should be grounded along their entire lengths. Belts can be grounded through metal combs or other devices.
Dust collection, filtering, and treatment prevent explosions by removing dust from the air. Dust collectors should be hooked up outdoors or in a separate room. Wet spray dust collectors can be located inside the building. For grinding, shredding, or pulverizing equipment, use pneumatic or magnetic separators to remove metal and debris that could ignite a fire. Lay out your facility so that machines with dust explosion hazards are enclosed or facing away from populated work areas to minimize the fire and energy impact if there is an explosion.
Establish a routine cleaning schedule to remove dust from floors, ledges, beams, equipment, or other surfaces. Clean often enough to prevent dust buildup. If production changes and dust piles up faster than your schedule, clean more often. Create a checklist that identifies all areas to be cleaned so you don’t miss any. Use the proper tools, equipment, and safety procedures to clean dust from heights.
Before you begin cleaning, shut down all flame and ignition sources. Allow dust to settle out of the air. Permanent, grounded vacuum systems or wet methods are ideal for dust cleanup. Use caution with push brooms or brushes that can make dust airborne. Choose natural bristle brushes; some synthetic fiber brushes can build up static. Using compressed air to blow and clean up dust is not recommended because of the potential to make a dust cloud. If there is no other alternative to compressed air, extinguish all flame and ignition sources and ground the hose and nozzle before use.
Attention to housekeeping and cleaning can prevent secondary explosions, which occur when an initial dust cloud ignites, explodes, and topples a duct, pipe, or other accumulation of dust. The newly airborne dust can then form a second explosive dust cloud, often larger and more deadly than the first.
The above evaluations and/or recommendations are for general guidance only and should not be relied upon for legal compliance purposes. They are based solely on the information provided to us and relate only to those conditions specifically discussed. We do not make any warranty, expressed or implied, that your workplace is safe or healthful or that it complies with all laws, regulations or standards.