Dust explosions have been linked to numerous fatal accidents in the United States. Between 1980 and 2012, the U.S. Chemical Safety Board investigated more than 280 combustible dust incidents that was responsible for killing 141 people and injuring 767 others.
Food manufacturing plants are among the most susceptible to these incidents, especially plants in the baking segment that use a lot of flour and sugar. It can be difficult to protect a facility and employees when risk factors aren’t always obvious.
How does dust explode?
Combustible dust is a risk factor for manufacturing plants that occupy the food product segments, such as: Confectionary Bakery Cookie and cracker Snack food Blends/mixes Cereal Spices.
According to the National Fire Protection Association (NFPA), a room with at least 5% of its surface area covered with more than 1/32-in presents an explosion hazard. That thin layer of dust in a closed room is enough to trigger an explosion if the dust becomes airborne and ignited.
Potential ignition sources include:
- Sparks from electrical or mechanical processes
- Open flames
- Electrostatic discharge (ESD).
Just because a work area looks clean, doesn’t necessarily mean it is safe. Combustible dust can accumulate inside equipment, and it can settle in hidden spaces like air ducts. [subhead]
The 5 elements of a dust explosion
Five elements are necessary to trigger a dust explosion. This combination is often referred to as the dust explosion pentagon. The first three elements are those needed for a fire, and the second two elements must be present for an explosion:
- Combustible dust (fuel)
- Ignition source (heat)
- Oxygen in air (oxidizer)
- Dispersion of dust particles in sufficient quantity and concentration
- Confinement of the dust cloud.
Dust explosions are particularly dangerous because they often trigger a domino effect. An initial dust explosion in processing equipment may shake loose accumulated dust or damage a containment system (such as a duct, vessel, or collector). This causes more dust to become airborne and could trigger secondary explosions if ignited. These secondary explosions are often more destructive, due to the increased quantity and concentration of flammable dust.
Preventing a combustible dust explosion
These explosions are a major risk for employees and the structural safety of a facility. That being said, how can explosions be avoided? The Occupational Safety and Health Administration (OSHA) and the NFPA recommend several steps to maintain work environments that are not conducive to dust explosions.
First, ensure the travel and amount of dust in facility is controlled by:
- Implementing a program for hazardous dust inspection, testing, housekeeping, and control
- Using proper filters and collection systems
- Minimizing the escape of dust from equipment and ventilation systems
- Using surfaces that are easy to clean and don’t easily accumulate dust
- Inspecting for dust residue in hidden and open areas regularly
- Using cleaning methods that don’t generate dust clouds if ignition sources are present
- Using specialized vacuum cleaners approved for dust collection
- Locating relief valves away from dust deposits.
By managing dust collection, the available "fuel" for potential explosions is minimized.
Even if some dust is present, an explosion can’t be triggered without something to ignite it. Ignition sources can be controlled within a plant by:
- Using appropriate electrical equipment and wiring methods
- Controlling static electricity, including bonding of equipment to ground Controlling smoking, open flames, and sparks
- Controlling mechanical sparks and friction
- Using separator devices to remove foreign materials capable of igniting combustibles from process materials
- Separating heated surfaces and systems from dusts
- Utilizing the proper type of industrial trucks
- Properly using cartridge-activated tools
- Maintaining all above equipment adequately.
There are so many variables that can contribute to a dust explosion – the size of the dust particles, how they’re dispersed, the ventilation system, physical barriers, and the size of work areas. Therefore, there’s no one-size-fits-all rule of thumb to measure whether there is too much accumulation or if a plant is truly at its safest.
A tailored hazard analysis is the best way to ensure a facility is as safe as possible. When it comes to the safety of workers and the future of a business, cutting corners is not an option.