Pro Tip: Preventing dust explosions in a bakery

Pro Tip: Implementing the correct policies, practices and procedures can mitigate dust explosions in bakeries.

According to a study by the Chemical Safety Board, dust explosions are a serious problem in American industry.

The US Chemical Safety and Hazard Investigation Board (CSB), for example, identified 281 combustible dust incidents between 1980 and 2005 that led to the deaths of 119 workers, injured 718 and extensively damaged numerous industrial facilities.

In addition, there were 13 reported agricultural dust explosions in the United States in 2005 resulting in two fatalities and 11 injuries.

For a dust explosion to take place, the concentration must be between 40 and 4,000 grams per cubic meter.

The optimum explosive concentration (OEC) value of 0.5 to 1.0 ounces of wheat flour per cubic foot equates to about 1.5 to 3.0 cubic inches of grain dust per cubic foot of volume.

The minimum explosive concentration (MEC) would be about 0.15 to 0.30 cubic inches per cubic foot. In a 1.0-cubic-foot chamber, the bottom would be covered to a depth of 0.01 inches to 0.02 inches at the OEC level. As the size of the particle decreases, the risk of deflagration or explosion increases.

Source: Rowdy Brixey

In a bakery, the risk can increase during a down day if compressed air is used to sweep dust —typically flour — from overhead pipes and structural supports. Conditions also increase when vent bags blow off or dust handling equipment has any type of leak.

Often the initial explosion is followed by a much more severe secondary explosion that is triggered by the dust displaced from overhead during the first shockwave. This is why good housekeeping is so important.

Bakeries should use either intrinsically safe vacuums or vacuums that use compressed air. Cheap, open electrical “shop-vacs” can be an ignition source and should not be used in dusty environments.

Open electrical cabinets can also provide a trigger as contactors open and close. Only intrinsically safe electrical components should be used in dusty areas. For example, flour rooms typically have Class 2 Division 2 devices for this reason.

The policies, practices and procedures designed to keep conditions necessary to prevent a fire (explosive pentagon) include:

Implement an effective housekeeping program. The most crucial key to the reduction of fires and explosions is good housekeeping. Research has shown that facilities that are well maintained experience fewer fires, explosions and other accidents.
Follow National Fire Protection Association (NFPA) standard 654.
Ensure operations involving dust have proper engineering design and controls.
Establish and maintain a preventative maintenance program.
Issue Hot Work Permits when required or needed.
Establish severity reduction policies, practices and procedures designed to minimize the spread of fire.
Implement standard operating procedures and specifications for storage of flammable materials.

The most common ignition source of dust explosions include: