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Industrial Hygiene Success Story


Case 5: Control of Wood Dust During Manual Sanding

Michelle L. Dunham, MSPH
Art Wickman, CIH

Georgia Institute of Technology Atlanta, Georgia

Abstract
Wood dust images

Woodworkers are routinely overexposed to wood dust when they use powered hand-sanding tools for the surface preparation of wood furniture. Exposure to wood dust causes nasal cancer in human, and other health effects including bronchial asthma, chronic bronchitis, hypersensitivity pneumonitis, and allergic contact dermatitis. Certain hardwoods, including those which are preferred in furniture manufacturing, appear to be associated with higher toxicity. In response to the research linking wood dust to adverse health outcomes, occupational exposure limits have been lowered. The current ACGIH TLV is 5 mg/m3 for soft wood dust, and 1 mg/m3 for certain hardwoods.

The current study documents reductions of exposures in two cabinet shops, which were surveyed to evaluate employee exposure to wood dust during the use of non-ventilated palm sanders. At one facility, two face frame sanders were evaluated and at the second facility three case sanders were evaluated. Samples were collected in aluminum-shielded cassettes on 5-micron PVC filters, using Gilair 5 sampling pumps at 2.0 LPM. Analysis was done at the Wisconsin Occupational Health Laboratory (WOHL) per NIOSH methods 0500/0600. Breathing zone concentrations for the face frame sanders and case sanders ranged from 16 to 107 mg/m3 and both the OSHA PEL (15 mg/m3) and ACGIH TLVs were exceeded. Both facilities changed to sanders with dust collection systems to reduce wood dust exposure. The follow-up exposure monitoring ranged from 1.4 to 10.7 mg/m3, a reduction of greater than 80%. Employee exposure to wood dust during hand sanding operations was substantially reduced. The controls used are readily available, and economically feasible. However, these effective controls are not in wide spread use.

Background

According to the 1999 US Bureau of Labor Statistics, an estimated 225,000 U.S. workers are employed in the manufacture of wooden cabinets and furniture. Among these workers, the highest exposures often occur when powered palm sanders are used for the final preparation of the wood surface.

Workers in furniture and cabinet shops often use palm sanders that lack dust control. For this type of sander, two forms of dust control are commercially available. For pneumatically driven units, models are available with a venturi fitting in the exhaust stream. As exhaust air passes through the venturi, a vacuum is created which is used to pull dust particles through holes in the face of the sanding pad and into an external filter bag. A second form of control, available for both pneumatic and electric tools, is a hood with an exhaust fitting which connects to an external vacuum source. The current study compares pneumatic sanders which were unventilated to pneumatic sanders which had an internal venturi-driven exhaust system. The wood species used in the study were a combination of both soft and hard woods.

Methods
  Pre Ventilation mg/m3 Post Ventilation mg/m3 Percent Reduction
Face Frame Sander 1 73 11 85%
Face Frame Sander 2 50 5 90%
Case Sander 1 107 3 97%
Case Sander 2 21 2 90%
Case Sander 3 16 1 94%

Full-shift personal monitoring was conducted at two cabinet shops. At cabinet shop A, two face sanders were monitored and at cabinet shop B three case sanders were monitored. Samples were collected in aluminum-shielded cassettes on 5-micron PVC filters, using Gilair 5 sampling pumps at 2.0 LPM. Analysis was done at the Wisconsin Occupational Health Laboratory (WOHL) per NIOSH methods 0500/0600. All five employees were monitored using non-ventilated palm sanders and then using ventilated sanders. Cabinet shop A used basic sanders and cabinet shop B used deluxe sanders.

Results and Discussion

Both cabinet shops A and B reduced wood dust exposure by 85 to 97% after they replaced unventilated sanders with models which contained venturi-driven local exhaust systems. While these reductions were substantial, neither company achieved levels which met either the NIOSH REL or the ACGIH TLV of 1 mg/m3 for hard woods. This may be due to the weak vacuum induced by the venturi system. In a 1992 study, NIOSH measured this vacuum to be approximately 2 inches water gauge. (1) Since the sanders are spinning, they forcibly eject dust particles, and these particles likely escape capture by the weak vacuum of the venturi system. Thus, NIOSH recommended the use of a vacuum at 8 inches water gauge. In order to achieve higher vacuum pressure and lower exposure levels, an external central vacuum was required in the NIOSH study.

Conclusion

Palm sanders with internal, venturi-driven vacuum systems substantially reduced the exposures of employees to wood dust. Exposures were reduced below the OSHA PEL for nuisance dust of 15 mg/m3. These sanders are commercially available, economically feasible, and should be used to prevent overexposure to wood dust in cabinet shops. However, to achieve reductions to below the NIOSH REL or the ACGIH TLVĀ¬ of 1 mg/m3 for hard woods, a larger vacuum source is needed.

Reference

1. Hampl, Vladimir; Topmiller, Jennifer L.; Watkins, Daniel S.; and Murdock, Donald J.: "Control of Wood Dust from Rotational Hand-Held Sanders". Applied Occupational and Environmental Hygiene. 7(4): 263-270, (1992).