By: Thomas H. Welby Geoffrey S. Pope Published: May 2013

Safety Policy: Limiting Employee Exposure to Diesel Particulate Matter

OSHA (the federal agency within the U.S. Department of Labor) is the largest, but by no means the only, government agency dedicated to occupational safety and health. Under the federal OSH Act, individual states are permitted to "opt out" of federal OSHA. New York, New Jersey and Connecticut have chosen not to opt out, and so are governed by federal OSHA as to those private-sector employees that fall within the statute. Each of these three states, however, has its own agency, within its (state) Department of Labor that covers public-sector employees. Approximately half the states do have their own "little OSHAs," as authorized by the federal statute. The standards promulgated and enforced by "little OHSAs" generally differ but slightly from the federal standards, as the nationwide statute requires states' "little OSHAs" to afford no less protection to employees.

Excluded from OSHA coverage are mining operations, for which there is a separate Mine Safety & Health Administration (MSHA). From 1891 until 1977, mine safety was under the U.S. Department of the Interior. Under the current statute, which moved enforcement from Interior to Labor, enforcement is under the MSHA, and adjudication under a separate MSH Review Commission. This organizational setup is borrowed from the OSH Act.

Recently, OSHA and MSHA issued a joint "Hazard Alert" concerning Diesel Exhaust and Diesel Particulate Matter. This is a major hazard in underground mines, in which diesel-powered equipment is ubiquitous, and ventilation must be mechanically supplied. However, most heavy equipment, medium and heavy-duty trucks, bucket lifts and generators found on construction sites have diesel engines, and so construction workers are at considerable risk from this hazard, too.

Diesel exhaust (DE) is a complex and unwholesome mixture of chemicals and particulates. It includes both a gas/vapor phase and a particulate phase, each of which includes both organic and inorganic components.

The major constituents of the gas/vapor phase of DE include carbon monoxide, oxides of nitrogen, sulfur dioxide, formaldehyde and other aldehydes, benzene, 1,3-butadiene, and a number of polycyclic aromatic hydrocarbons.

The particulate phase includes clusters of respirable particles, composed mainly of carbon. A variety of chemicals are contained within, or adsorbed onto, the DPM, affecting the toxicity of the particulate. The particles are classified according to size as well as composition.

Of particular health concern are fine or ultrafine particles, as these can get inhaled deep into the lungs. The composition of these particles is, typically, elemental carbon, with adsorbed compounds such as various organic compounds, sulfates, nitrate, metals (including metallic abrasion particles) silicates, ash, and a variety of trace elements.

Short-term exposure to high concentrations of diesel exhaust can cause irritation to the eyes, nose, throat and lungs, as well as lightheadedness, coughing and nausea. DE can exacerbate asthma and cause allergies. Long-term exposure has shown in laboratory studies a range of dose-dependent inflammation and cell changes in lung tissue. In June 2012, the International Agency for Cancer Research classified diesel exhaust as a Group 1 human carcinogen.

Miners in underground metal/nonmetal mines have, under the MSH Act, a permissible exposure limit (PEL) of 160 µg/m3 when measured as an 8-hour time-weighted average. If engineering and administrative controls do not reduce exposures below the PEL, respiratory protection, a high-efficiency air-purifying respirator must be worn.

OSHA does not presently have a PEL for DPM. However, there do exist PELs for other components of diesel exhaust (e.g., carbon monoxide, nitric oxide, and nitrogen dioxide) and monitoring for these can give some indication of the presence of diesel exhaust, as well as the effectiveness of engineering and administrative controls aimed at minimizing employee exposure to such exhaust, when working with or around diesel-powered equipment.

Because, usually, the health impacts of exposure to toxins such as DPM and other toxins are not so sudden or dramatic as when a trench caves in, or a worker falls to his death from an elevated surface, there is some danger of these hazards being overlooked in developing and implementing a health and safety program.

Don't think that, because OSHA's standards don't have a prescribed PEL for diesel exhaust that you can't be cited for employee exposure. Since it's a recognized hazard, it likely falls under the General Duty Clause. Another consideration to keep in mind is that, under OSHA's "multi-employer policy," you can be cited if your employees are exposed to unhealthful levels of DE, even if the source is diesel equipment operated by another employer or employers.

While monitoring for air quality and employing an industrial hygienist are seldom if ever bad ideas, these are definitely steps you should take, if you utilize diesel-powered equipment indoors, or in semi-enclosed spaces (such as parking garages). Likewise, if your employees must work where other employers' activities are creating a potential DE hazard, having an industrial hygienist monitor the air provides you with a stronger basis to negotiate abatement, if needed, with the trade creating the hazard, the GC, and/or the owner.

Assuming only open-air use of diesel-powered equipment, except in unusual circumstances the primary strategy in keeping employee exposure to DE at tolerable levels will be a combination of engineering controls. Examples of these include:

  • Routine preventive maintenance of diesel engines to minimize emissions;
  • Installing cleaner-burning engines;
  • Installing diesel oxidation catalysts;
  • Using engine exhaust filters;
  • Using special fuels or additives;
  • Installing or upgrading main or auxiliary ventilation systems, e.g., tailpipe or stack exhaust vents to capture and remove emissions in maintenance shops or other indoor locations; and
  • Providing equipment cabs with filtered air.

Administrative controls (changing procedures to reduce or eliminate the hazard) should also be employed. A few you should consider are these:

  • Limiting speeds and using one-way travel routes to reduce traffic congestion;
  • Limiting or prohibiting unnecessary idling or lugging of engines;
  • Limiting the total amount of diesel-powered equipment or total engine horsepower operating in a given area;
  • Employing an industrial hygienist to confirm that DE output does not exceed the capacity of the ventilation system; and
  • Restricting unnecessary employee access to areas in which diesel equipment is being used, and keeping diesel equipment, insofar as it is practicable to do so, away from employees not involved in its use.

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