When thinking about dust hazards within your facility, the first thought is typical: “Is my dust an explosible hazard?” Even though that is a great question to investigate, another question to ask should be: “Is my dust a fire hazard?” Depending on the answer to this question, this blog may give u the scenario on combustible dust.
Think about combustible dust explosions and coal dust, grain storage, and flour mills immediately spring to mind because they make primetime news, but essentially any workplace that generates combustible dust is basically coming from “Flammable Solids” and create a risk.
A flammable solid is “any solid, other than an explosive or blasting agent, that can catch fire in the following ways:
- Through friction
- Via absorption of moisture
- A spontaneous chemical change
- Through heat retained from a manufacturing or other process, or
- That which can be ignited easily and, when ignited, burns so vigorously or persistently as to create a serious fire hazard.”
Read More What is Heat Stress or Heat-Stroke?
Many materials can become combustible under specific situations.
- Agriculture, Chemicals, Food (e.g., candy, sugar, spice, starch, flour, feed), Grain elevators, bins, and silos, Fertilizer, Tobacco, Plastics, Woodworking facilities, Paper, Tire and rubber manufacturing, Metal powder processing or storage (especially magnesium and aluminum)
Dust is created when materials are transported, handled, processed, polished, ground and shaped. Dust is also created by abrasive blasting, cutting, crushing, mixing, sifting, or screening dry materials. The buildup of dried residue from the processing of wet materials also can generate dust.
So, what are the conditions that give rise to an explosion? A dust explosion can only occur when the following five factors are present.
- Fuel, in the form of dust particles
- Dispersion of the fuel in the form of a dust cloud
- Oxygen in the form of air
- Confinement of the dust cloud in the form of a container (e.g., a dust collector)
- A source of ignition
PRIMARY AND SECONDARY DUST EXPLOSIONS:
When combustible dust ignites, there are often two explosions known as primary and secondary explosions.
- The primary dust explosion is the first explosion. It occurs when there is a dust suspension in a confined space (such as a container, room, or piece of equipment) that is ignited and explodes.
The figure shows events in a primary dust explosion (Reference from the U.S. Chemical Safety and Hazard Investigation Board).
- Secondary dust explosions are the most severe ones, and occur when the blast wave from a primary explosion entrains dust layers already present in the plant, creating a large dust‐air flammable mixture ignited by the first explosion.
How To Prevent Combustible Dust Explosions
Combustible dust explosions have destroyed workplaces and kill employees.
A comprehensive approach to preventing and controlling combustible dust hazards is