Dust explosions caused by combustible particles in a workplace are a serious hazard that can cause not only destruction of buildings and property, but also injuries and deaths of employees. Awareness of the conditions that can lead to these explosions can help to prevent them.
While fire requires the three elements of oxygen, heat, and fuel known as the “fire triangle”, there are five factors, known as the “dust explosion pentagon,” that can cause a dust explosion. Without all five, an explosion cannot occur. The five factors are oxygen, heat, fuel, dispersion, and confinement. These can cause an initial explosion or secondary explosions when dust is dispersed through the air near a primary explosion. Often secondary explosions cause more damage than the initial explosion resulting in serious damage and deaths.
There are a number of industries where combustible dust exists. These include: chemicals, pharmaceuticals, pesticides, fertilizer, tire and rubber manufacturing, plastics, recycling operations, fossil fuel (coal) power generation, agriculture, food manufacturing (feed, flour, starch, spice, sugar, and candy) grain, tobacco, wood, paper, pulp, forest, rubber, furniture, textiles, dyes, coal, and metal processing (aluminum, iron, magnesium, chromium, and zinc).
OSHA recommends identifying and assessing the following factors that can contribute to dust explosions:
• All materials handled
• All operations conducted, including by-products
• All spaces (including hidden ones)
• All potential ignition sources
OSHA recommends the following steps to control dust:
• Implement a hazardous dust inspection, testing, housekeeping and control program
• Use proper filters and collection systems
• Minimize the escape of dust from equipment and ventilation systems
• Use surfaces that facilitate cleaning and minimize dust accumulation
• Inspect all hidden areas
• Inspect for dust residue in all areas, both hidden and open, at regular intervals
• Use cleaning methods that do not generate dust clouds if ignition sources are present
• Use specialized vacuum cleaners that are approved for dust collection
• Locate relief valves away from dust deposits
To avoid ignition near dusty areas OSHA recommends:
• Using appropriate wiring methods and electrical equipment
• Controlling static electricity
• Controlling smoking, open flames, and sparks
• Controlling friction and sparks from equipment
• Using separator devices to remove combustible foreign materials from process materials
• Separating heated surfaces from dusty areas
• Separating heat systems from dusty areas
• Selecting and using industrial trucks properly
• Using cartridge activated tools properly
• Using a preventive equipment maintenance program
For information on combustible dust hazards visit the OSHA website at http://www.osha.gov .