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>> Plant-Wide Hazards |
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Health Hazards > Wood Dust
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| 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.
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Potential Hazards:
- 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.
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Wood dust on a worker.
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- 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.
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Possible Solutions:
Engineering Controls
- Wood dust is emitted at a 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. 31 a&b). LEV systems often 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.
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Fig. 31a Local exhaust hood
for table saws with arrow pointing to moving table and fence
Fig. 31b Local exhaust hood
for table saws
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- 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.
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Improved hood configuration for shapers |
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Blower collecting, and exhaust
systems must be designed, constructed, and maintained in accordance
with American National Standards Z33.1-1961 and Z12.2-1962 (R1969).
1910.265(c)(20)(i)
All mills containing one or more machines that
create dust, shavings, chips, or slivers during a period of time equal
to or greater than one-fourth of the working day, need to be equipped with
a collecting system. It may be either continuous or automatic, and must remove such
refuse from points of operation and immediate vicinities. 1910.265(c)(20)(ii)
Each woodworking machine that creates
dust, shavings, chips, or slivers must be equipped with an exhaust or
conveyor system. 1910.265(c)(20)(iii)
Exhaust pipes may not discharge into an unconfined
outside pile if uncontrolled fire or explosion hazards are created. They
may empty into settling or dust chambers, designed to prevent the dust
or refuse from entering any work area.
1910.265(c)(20)(v)
Operations not required to have an exhaust system
or having refuse too heavy, bulky, or otherwise unsuitable to be handled
by the exhaust system may remove the refuse daily by hand. 1910.265(c)(20)(vi)
The following
machines all have wet systems and liquid catch basins to
recycle liquid for dust control:
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Saw blade sharpener
Chipper knife sharpener
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Modern saw blade sharpener
Planer knife sharpener
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Circular Saws
- 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 more information on control of wood dust
from circular and other kinds of table saws,
please consult the NIOSH Hazard Controls
HC10.
Band Saws
- 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.
Jointers
- Place a hood under the machine head.
Shapers
- 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 more information consult the NIOSH Hazard Controls
HC5: Wood Dust from Shapers.
Planers/Moulders
- 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 controlled separately.
- For increased dust control, add a small open-faced
hood along the side of the moulder
between the main head and the worker.
Lathes
- Place an open-faced hood attached to a movable
mechanical arm at the point of operation.
Sanders
- 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
(See Appendix B). 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.
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- 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. 30 a&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.
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Fig. 30a
Orbital sander with labeled parts
Fig. 30b
Dust control plenum for orbital sanders
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Routers
- 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.
Other Sources of Information on Wood Dust Control
NIOSH has published a series of “Hazard
Controls” concerning wood dust control
techniques. For details see the Additional
References section of this eTool.
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Click
here for more pictures related to wood dust housekeeping.
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Excessive buildup of sawdust
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