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.