WOODWORKING DUST COLLECTION
INDUSTRIAL WOOD DUST COLLECTION
Wood dust is a health, safety, and process hazard if not properly addressed. Learn how to deal with it safely with industrial wood dust collection systems.
Wood dust is produced by everything from small hand-held tools to CNC machines by a variety of industrial processes.
Wood dust is a health and safety hazard if not properly addressed in the workplace. Exposure to excessive amounts of wood dust can cause eye, nose and throat irritation, in addition to pulmonary function impairment.
For these reasons, The United States Occupational Safety and Health Administration (OSHA) has set a standard at 5 mg/m3 for respirable dust and 15 mg/m3 for total dust. The US National Institute for Occupational Safety and Health (NIOSH) has a lower recommended exposure limit of 1 mg/m3.
In addition, wood dust is a fire and explosion hazard if not properly handled. Dust can settle almost anywhere - on and around machines, but also on ducting, rafters, and other areas. Once it settles in these places, anything can shake the settled dust loose - cleaning by compressed air, an earthquake, or any other shock. Once suspended in the air, this dust becomes fuel primed for a fire or explosion.
The National Fire Protection Association (NFPA) is a global organization that delivers information, knowledge, and standards. Two of these are particularly important for woodworking dust collection:
In particular, NFPA 652 introduces the Dust Hazard Analysis (DHA) process. The DHA will identify conditions that may contribute to a fire, deflagration, or explosion: fuel, the presence of an oxidant, ignition, dispersion, and containment. A DHA is now required for new installations and upgrades to existing installations, and should be completed by October 2018.
HOW TO HANDLE WOOD DUST SAFELY
Handling wood dust safely can be thought of as a three-step process:
1. Capture It
The first step towards handling wood dust safely is to capture it at the source.
This is accomplished by the means of designing a good hood at each source of dust. Each machine has specific requirements in terms of the amount of suction, typically given as a combination of drop diameter and air velocity that must be maintained. Maintaining these air velocities while the machine is producing dust is absolutely critical.
Note that not all woodworking machine manufacturers thoroughly test their hood designs, and as a result, not all dust is collected even at the recommended air velocity in some machines. In these instances, it may be necessary to redesign and adjust the machine hoods.
How do you know if you should do this? It's easy: if the machine-manufacturer's specifications are being met at the hood and dust is still not captured reliably, changes are necessary.
2. Move It
Once dust is captured at the source, it must be reliably transported to the dust collector. The air velocities required to reliably transport the contaminant vary depending on the contaminant type.
The American Conference of Governmental Industrial Hygienists provides recommended design velocities for different types of contaminants:
Minimum Transport Velocities for wood dust and other materials.
(source: Industrial Ventilation by The American Conference of Governmental Industrial Hygienists)
Depending on the specifics of the materials and processes used in each facility, the minimum transport velocity can be from 2000 feet per minute up to 4000 feet per minute.
One key element of maintaining transport velocities in the ducting is the design of the ducting system. In general, a good design should have the following characteristics:
As simple as possible and as short as possible, in order to minimize pressure losses
Suitable hoods for all machines
Minimize the number of elbows
Elbows no greater than 45 degrees
Flexible ducts should be avoided or used as minimally as possible
3. Deal With It
Finally, you need the right fan, motor, and dust collector. Factors that influence which fan, motor, and dust collector is right for your application include:
Total air volume requirements
Type of dust
Production processes used
The fan should always be installed without system error - meaning the first elbow at the fan inlet should be at least 3 times the diameter away from the fan inlet (and ideally 5 times away). This significantly improves the fan efficiency. A stack should be used on the fan outlet.
A direct-driven fan motor should be used; this provides better energy-efficiency.
Optionally, wood dust can later recycled into new material (such as MDF board) or used to generate energy as a bio-fuel.
Ultimately, each situation is unique, and should be prepared for each individual project together with a domain expert.
A good dust collection system will provide a reliably clean and safe working environment that is conducive to high productivity.
Well-maintained industrial dust collection systems should have a lifecycle of 20 years. It is critical to consider this when deciding what dust collection solution to deploy - money spent today on a superior solution can be recouped many times over the system's life-cycle.