California OSHA is in the process of updating permissible exposure limits (PELs) for a number of airborne substances found in the state’s workplaces. Currently under review is wood dust, a byproduct of wood milling, sanding and routing in businesses ranging from small custom cabinetry shops to the largest sawmills and flooring producers. The history of wood dust regulation provides an interesting window into the interaction between researchers, federal and state safety agencies, courts and non-governmental standard setting bodies.
Wood dust first came to the attention of health researchers in connection with nasal adenocarcinoma. In the 1960's, English scientists observed a much higher than expected incidence of tumors in High Wycombe, an area northwest of London that was then a center of the furniture and cabinet industry. Adenocarcinoma cases were several hundred times more common among this group than among comparable industrial workers. When U.S. researchers attempted to replicate these findings, however, they found much lower relative risks associated with occupational wood exposure. In fact, pooled analysis of 220,000 woodworkers studied in North Carolina and Virginia identified only three cases, about what would be expected among the general public.
In light of this ambiguous evidence, U.S. OSHA proposed a fairly reasonable 5 mg /m3 standard for total dust as a time-weighted average (TWA) in 1989. This level, which was supported by key woodworking industry organizations, essentially required older plants to adopt the dust-control technologies such as cyclones and baghouses already being implemented by newer facilities. Unfortunately, OSHA compiled the wood dust standard with proposed PELs for hundreds of unrelated airborne substances. In 1992, a federal court found that not all of these standards were supported by good science and invalidated all of them.
Technically, that left wood dust regulated as a “nuisance dust” at 15 mg/m3. However, state occupational agencies (including Cal OSHA) adopted the 5 mg standard for total dust, and federal OSHA retained the power to cite dusty workplaces under its General Duty Clause. Recent workplace monitoring shows that the vast majority of work stations in woodworking facilities meet the 5 mg level. For example, Glindmeyer (2008) found inhalable dust samples ranging from 0.82 to 2.51 mg/m3 across a group of ten plants, which included furniture, kitchen cabinet, and flooring facilities as well as a sawmill. Geometric standard deviations ranged from 2.1-2.8 mg/m3.
About 15 years ago, researchers began focusing on non-cancer effects of wood dust. The concern was that long-term occupational exposure could compromise pulmonary function. This placed renewed focus on the smallest “respirable” dust particles most likely to reach the lungs. Generally, these measure 2.5 microns or less, the same size as the PM 2.5 particulate matter that have been the subject of ambient air regulation over the last decade.
A concern about the respirable fraction of dust and its impact on pulmonary health has informed analysis and standard setting in recent years. The American Conference of Governmental Industrial Hygienists (ACGIH) has set a recommended threshold limit value (TLV) of 1 mg/m3 for inhalable dust of most wood species. Cal OSHA is evaluating a mandatory PEL of 1 mg/m3 total dust. The agency’s health effects advisory committee wrote earlier this year that “the history of lung disease findings at higher wood dust exposure levels, with recent lower wood dust dose studies showing no or little adverse effect, and the … carcinogenicity of wood dust vis. a vis. sino-nasal cancer [supports] lowering the PEL to 1 mg/m3.” A committee charged with evaluating the technical and economic feasibility of this standard meets this October 6 in Oakland.
Deliberations over wood dust spotlight a complex interaction between researchers, state and federal regulators, industry, and the courts. This is probably not a decision-making apparatus that any of us would design from scratch. However, it has arguably responded effectively to emerging research and technological innovation. Is there a better, time and cost-effective approach?
We welcome your comments.
4 comments:
It seems that environmental and workplace safety limits only move in one direction, becoming more stringent. Maybe it is the better detection that we get from improved instrumentation. Or maybe, as we control larger risks, we become more sensitive to and intolerant of smaller risks.
Great Blog!!!
Probably a little of both. It's only natural that more developed societies can turn their attention to risks that were once considered marginal.
The dust levels measured in modern woodworking facilities are orders of magnitude lower than what was present in plants before and shortly after WWII. Improved work practices, as well as vacuum dust-control equipment must be credited in the U.S. In Europe, the use of enclosed "flatline" operations for sanding, milling and other operations have isolated emissions from employees.
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