Dust Hazards

Dust is hazardous!  Here are a few articles regarding combustible dust and how to deal with it.
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Vacuuming Wood Dust Can be Hazardous

Environmental-Expert 

Courtesy of SafetySmart

“It’s well known that wood dust is highly combustible, but the practice of removing it with vacuum trucks can also be dangerous, because of the potential buildup of static electricity.

WorkSafeBC has issued a bulletin stating that “static electricity discharges can ignite wood dust and therefore must be eliminated or adequately controlled during vacuuming.”

When wood dust or other fine, dry materials are vacuumed through a hose or pipe, the friction between the dust and the hose can generate static electricity. If the hose is made of a material that conducts electricity and is properly grounded, the static charge will safely dissipate into the earth.

However, WorkSafeBC notes that if the hose is non-conductive, a static charge will build up on its interior surface and could discharge with enough energy to ignite wood dust or other combustibles. Since plastic does not conduct electricity, plastic hoses are not safe to use for vacuuming wood dust unless they are embedded with a static wire.

Also, hoses that have ridged or corrugated interior surfaces should not be used for vacuuming wood dust. Using hoses with ridged interior surfaces results in more physical interaction between the dust particles—and between the dust particles and the hose—than using hoses with smooth interior surfaces. This increased interaction results in a static charge with higher amounts of static energy, making static discharge more likely.

WorkSafeBC says when vacuuming wood dust or other dry combustible materials, use only conductive hoses, nozzles and connectors that are designed to be used with those types of materials. If you are unsure whether a hose or other equipment is safe to use for vacuuming wood dust, check the manufacturer’s instructions.

Following are some additional wood dust vacuuming safety tips from WorkSafeBC:

Ensure that trucks are grounded directly to the earth or another verified ground before vacuuming starts. Also, hoses and all other parts of the truck and vacuum system should be properly bonded to each other.
Pay particular attention to ensuring proper bonding in baghouses (air pollution control devices), where the risk of dust ignition is high because of high volumes of dust and air that flow through them.

Ensure that vacuum trucks are regularly inspected and properly maintained. Pay particular attention to potential problem areas such as hoses, baghouses, vacuum pumps, collection boxes and filtration systems. Conductive hoses should be tested regularly and removed from services if they have lost their conductivity.

Ensure that wood dust is safely removed before buildup of the dust could cause a fire or combustible dust explosion.

Ensure that workers follow manufacturers’ instructions, safe work procedures and occupational health and safety regulations, and are properly trained and supervised.”

Dust Hazards

Combustible Dust: It Doesn’t Take Much

Environmental Expert

Courtesy of SafetySmart

“A dust accumulation of 1/32 of an inch deep—about the thickness of a dime—covering just five percent of a room’s surface area doesn’t sound like much, but it’s enough to cause a catastrophic explosion, according to the National Fire Protection Association (NFPA).

Although good engineering and safety practices to prevent dust explosions have existed for decades, there are no government standards for general industry requiring and enforcing policies aimed at preventing combustible dust explosions, according to the US Chemical Safety and Hazard Investigation Board (CSB).

The CSB adds that many companies are not taking effective action to control dust hazards. Industries at risk for combustible dust explosions include food production, metal processing, wood products, pharmaceutical, chemical manufacturing, rubber and plastic manufacturing and coal-fired power plant operations.

Angela Blair, a former CSB investigator, says most solid organic materials will explode if the particles are small enough and they are disbursed in a sufficient concentration.

“What is so frustrating about dust explosions is that they are so preventable and I believe one of the reasons that dust explosions continue to occur may simply be a lack of understanding about the materials,” says Blair. “Some of the materials that could form combustible dust, and there are lots of them, could include coal, food products like sugar and flour, pharmaceuticals, many chemicals and even many metals.”

Like all fires, a dust fire requires fuel, oxygen and an ignition sources. A dust explosion requires two additional elements—dispersion and confinement. When the dust is confined within a structure or a piece of equipment, a powerful explosion can occur.

Dust may accumulate on surfaces such as floors, beams, rafters and lights and lie undisturbed for years. If a fire or explosion occurs, this accumulated dust can ignite in a series of explosions, with devastating results.

The chances of a combustible dust explosion occurring are greater during cold-weather months, because low humidity levels can make dust particularly easy to disburse and ignite.

The NFPA says preventing dust explosions involves designing facilities in such a way that combustible dusts cannot accumulate and migrate and performing rigorous housekeeping on a continuing basis to remove any dust that does build up.

The NFPA also recommends:

Vacuuming dust using specialized equipment designed for that purpose. Never use compressed air to clear dust accumulations because doing so can create a dust cloud that could easily explode in the presence of an ignition source.

Paying particular attention to out-of-the-way areas that might not be visible from the floor yet could contain dangerous buildups of combustible dust.

Having a laboratory test the potential for explosion of any materials in dust (powder) form that are present in your workplace.

In addition, your workers need to be trained to recognize and report combustible dust hazards so that they can be addressed before a disaster occurs.”

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