Exposure to wood dust has long been associated with a variety of adverse health effects, including dermatitis, allergic respiratory effects, mucosal and nonallergic respiratory effects, and cancer. Contact with the irritant compounds in wood sap can cause dermatitis and other allergic reactions. The respiratory effects of wood dust exposure include asthma, hypersensitivity pneumonitis, and chronic bronchitis.
Both the skin and respiratory system can become sensitized to wood dust. When a worker becomes sensitized to wood dust, he or she can suffer severe allergic reactions (such as asthma or dermatitis) after repeated exposure or exposure to lower concentrations of the dust.
Other common symptoms associated with wood dust exposure include skin and eye irritation; nasal dryness and obstruction; and prolonged colds.
The OSHA permissible exposure limit for nuisance dust is 15 mg/m3 , total dust (5 mg/m3 , respirable fraction) 8 hour time weighted average. NIOSH has set a recommended exposure level of 1 mg/m3 total dust. The ACGIH has recommended a 0.5 mg/m3 Threshold Limit Value for western red cedar based on its asthma effects. Certain species of hardwood—such as oak, mahogany, beech, walnut, birch, elm, and ash— have been reported to cause nasal cancer in woodworkers. This is particularly true when exposures are high.
Possible Solutions: Engineering Controls
Wood dust is emitted at high velocity by moving or spinning machine components. The primary method of controlling wood dust is with local exhaust ventilation (LEV), which removes dust at or near its source (Fig. 31a&b). LEV systems can often be integrated with machine guards. Exhaust hoods should be located as close as possible to the emission source, either on the woodworking machinery itself or near to the machine. The local exhaust systems should have an efficient air cleaning device.
For LEV systems to provide maximum protection, they should be properly maintained. Check and clean ducts and dust collectors at regular intervals. Inspect ducts to ensure that they are not loose, broken, or damaged. Check the V-belts on the drive units of belt-driven exhaust fans for slippage or breakage. Make sure the duct velocity is maintained at a minimum of 2,500 to 4,000 feet per minute to effectively remove light, dry saw dust, heavy wood chips, and green shavings, and to prevent these from plugging the system.
Sanders, shapers, and routers generally produce the greatest amount of dust. Conventional means for exhausting these machines are not very effective. NIOSH has developed new, innovative means for controlling dust exposure from these machines, but these methods are not yet commercially available. These methods either increase the exhaust volume or velocity, or supply pressurized air to help blow dust particles from the machine into an exhaust hood.
LEV Recommendations for Individual Machines
Exhaust the saw through the bottom of the table. Provide LEV under the blade slot. To decrease the open area between the table and the lower hood, attach a strip of flexible material to the machinery that will cover this area when the hood operates.
For increased dust control, add a local exhaust hood above the top of the saw blade. The hood should be integrated with the guard on the upper part of the blade.
For further information on control of wood dust from circular and other kinds of table saws, please consult the NIOSH Hazard Controls HC10.
Provide LEV under the blade slot. To increase the collection area of the hood, add holes (1/8 inch in diameter) in the table around the slot area.
To collect wood dust from the saw teeth, place a suction nozzle above the table, at the rear of the saw blade.
Place a hood underneath the machine head.
Control each head with an open-faced hood, located on the table behind the head. For additional protection, use a combination of fixed and adjustable hoods. A fixed open-faced hood can be attached to the rear of the table between the shaper heads. Movable open-faced hoods also can be used on the table. For further information please consult the NIOSH Hazard Controls HC5: Wood Dust from Shapers.
Place open-faced hoods above the spinning heads of planers. Each head can be ventilated separately, or one hood can be used to control several heads.
Place open-faced hoods around the spinning components of moulders. Each head should be separately controlled.
For increased dust control, add a small open-faced hood along the side of the moulder between the main head and the worker.
Place an open-faced hood attached to a movable mechanical arm at the point of operation.
Sanders produce a considerable amount of dust and are difficult to control. Conventional methods do not effectively remove dust. New innovative systems have been developed for controlling dust emissions from horizontal belt sanders, large-diameter disc sanders, random orbital hand sanders, and orbital hand sanders. Although these systems are not yet commercially available, more information can be obtained from the National Institute for Occupational Safety and Health (NIOSH). The following NIOSH Hazard Controls deal with horizontal belt sanders, large diameter disc sanders, random orbital hand sanders and orbital hand sanders respectively: HC4, HC 7, HC 8 and HC 9. Some of these systems are discussed below.
Enclose disc sanders with an exhaust hood, installed below the table; cover the back of the sanding disc at points above the worktable. A system has been developed that supplies pressurized air to the disc inside the hood. The jet of high speed air blows dust particles out of the disc air layer so that they can be captured by the exhaust hood.
On random orbital sanders, use an aspirator in combination with a perforated sanding pad. The aspirator creates a vacuum that draws wood dust up through the holes of the sanding pad. An innovative dust control system has been developed that uses additional exhaust and a slotted sanding pad.
A new dust control plenum has been designed for orbital sanders (Fig. 30a&b). The plenum fits between the sanding pad and the sander body and has a series of exhaust slots along its edges.
Enclose horizontal belt sanders with exhaust hoods covering each end of the belt. These hoods control the dust carried by the belt. To further control dust emissions, install an additional hood above the area where the wood is processed. To increase the effectiveness of this system, add a narrow hood and a stripper.
Place two open-faced hoods behind the heads of the router table. Connect the hoods to the exhaust ductwork via a flexible hose.
Locate an open-faced or slot hood at the rear end of the router table.