Inhalable dust exposures, tasks, and use of ventilation in small woodworking shops: a pilot study

Wood dust particle and mass concentrations and filtration efficiency in sanding of wood materials

The importance of fine particles has become apparent as the knowledge of their effects on health has increased. Fine particle concentrations have been published for outside air, plasma arc cutting, welding, and grinding, but little data exists for the woodworking industry. Sanding was evaluated as the producer of the woodworking industry's finest particles, and was selected as the target study. The number of dust particles in different particle size classes and the mass concentrations were measured in the following environments: workplace air during sanding in plywood production and in the inlet and return air; in the dust emission chamber; and in filter testing. The numbers of fine particles were low, less than 10(4) particles/cm(3) (10(7) particles/L). They were much lower than typical number concentrations near 10(6) particles/cm(3) measured in plasma arc cutting, grinding, and welding. Ultrafine particles in the size class less than 100 nm were found during sanding of MDF (medium density fiberboard) sheets. When the cleaned air is returned to the working areas, the dust content in extraction systems must be monitored continuously. One way to monitor the dust content in the return air is to use an after-filter and measure pressure drop across the filter to indicate leaks in the air-cleaning system. The best after-filtration materials provided a clear increase in pressure drop across the filter in the loading of the filter. The best after-filtration materials proved to be quite effective also for fine particles. The best mass removal efficiencies for fine particles around 0.3 mum were over 80% for some filter materials loaded with sanding wood dust.

The effects of wood dusts on the redox status and cell death in mouse macrophages (RAW 264.7) and human leukocytes in vitro

Wood dusts are classified as carcinogenic to humans and also produce other toxic, allergic, and acute effects in woodworkers. However, little is known about causative agents in wood dusts and their mechanisms of action. The effects of different tree species and particle size for biological activity were studied. The differences in the production of reactive oxygen species (ROS) and cell death (necrotic and apoptotic) between mouse macrophage (RAW 264.7) cells and human polymorphonuclear leukocytes (PMNL) for pine, birch, and beech dust exposures were investigated in vitro. The pine and birch dust exposure (1-100 microg/ml) produced concentration-dependent ROS production in both the cells, which was one order of magnitude higher with pine dust. The ROS production was faster in human PNML than murine RAW cells. The higher concentrations (500 and/or 1000 microg/ml) decreased ROS formation. With pine and birch dust exposure, this was probably due to the necrotic cell death. The pine dust concentrations of 500 and 1000 microg/ml were cytotoxic to human PMNL. The beech dust exposure activated the ROS production and decreased the cell viability only at the highest concentrations, being least potent of the three dusts. A sign of the apoptotic cell death in the murine RAW cells was observed at the pine dust concentration of 100 microg/ml. The exposure to the birch and beech dusts with a smaller particle size (<5 microm) produced greater ROS production than exposure to the corresponding dust with a wide range of particle sizes. However, changing the particle size did not affect the cell viability. The results indicate that the type of wood dust (tree species and possibly particle size) has a significant impact on the function and viability of phagocytic cells.

An exposure prevention rating method for intervention needs assessment and effectiveness evaluation

This article describes a new method for (1) systematically prioritizing needs for intervention on hazardous substance exposures in manufacturing work sites, and (2) evaluating intervention effectiveness. We developed a checklist containing six unique sets of yes/no variables organized in a 2 x 3 matrix of exposure potential versus protection (two columns) at the levels of materials, processes, and human interface (three rows). The three levels correspond to a simplified hierarchy of controls. Each of the six sets of indicator variables was reduced to a high/moderate/low rating. Ratings from the matrix were then combined to generate a single overall exposure prevention rating for each area. Reflecting the hierarchy of controls, material factors were weighted highest, followed by process, and then human interface. The checklist was filled out by an industrial hygienist while conducting a walk-through inspection (N = 131 manufacturing processes/areas in 17 large work sites). One area or process per manufacturing department was assessed and rated. Based on the resulting Exposure Prevention ratings, we concluded that exposures were well controlled in the majority of areas assessed (64% with rating of 1 or 2 on a 6-point scale), that there is some room for improvement in 26 percent of areas (rating of 3 or 4), and that roughly 10 percent of the areas assessed are urgently in need of intervention (rated as 5 or 6). A second hygienist independently assessed a subset of areas to evaluate inter-rater reliability. The reliability of the overall exposure prevention ratings was excellent (weighted kappa = 0.84). The rating scheme has good discriminatory power and reliability and shows promise as a broadly applicable and inexpensive tool for intervention needs assessment and effectiveness evaluation. Validation studies are needed as a next step. This assessment method complements quantitative exposure assessment with an upstream prevention focus.

Effectiveness of a worksite intervention to reduce an occupational exposure: the Minnesota wood dust study

OBJECTIVES

This study assessed the effectiveness of an intervention to reduce wood dust, a carcinogen, by approximately 26% in small woodworking businesses.

METHODS

We randomized 48 businesses to an intervention (written recommendations, technical assistance, and worker training) or comparison (written recommendations alone) condition. Changes from baseline in dust concentration, dust control methods, and worker behavior were compared between the groups 1 year later.

RESULTS

At follow-up, workers in intervention relative to comparison businesses reported greater awareness, increases in stage of readiness, and behavioral changes consistent with dust control. The median dust concentration change in the intervention group from baseline to follow-up was 10.4% (95% confidence interval = -28.8%, 12.7%) lower than the change in comparison businesses.

CONCLUSIONS

We attribute the smaller-than-expected reduction in wood dust to the challenge of conducting rigorous intervention effectiveness research in occupational settings.