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Diesel Particulate Matter and the Underground Workforce

Published 27 June 2026 • By Dr. Megan Tranter

Diesel particulate matter (DPM) is among the most significant chemical carcinogens encountered in the modern workplace, and nowhere is the hazard more concentrated than in underground mining, where enclosed workings, limited natural ventilation, and intensive use of diesel-powered equipment combine to produce some of the highest occupational DPM exposures ever documented. In 2012 the International Agency for Research on Cancer classified diesel engine exhaust as a Group 1 human carcinogen, its highest category, based substantially on the cohort and case-control evidence from underground miners. For the industrial hygienist, DPM exemplifies the challenge of controlling a complex, sub-micron aerosol within the constrained environment of an underground operation.

What You’ll Learn

  • What diesel particulate matter is made of and why it is so hazardous.
  • Why elemental carbon is used as the marker for diesel exposure.
  • The MSHA permissible exposure limit for underground miners.
  • Which engineering controls reduce DPM at the source.
  • How to build a defensible underground DPM exposure-assessment program.

Introduction

Because diesel exhaust is a mixture rather than a single compound, both its toxicology and its measurement demand a surrogate-based approach centered on elemental carbon. Underground mining concentrates the hazard, but the same principles apply wherever diesel equipment runs in enclosed spaces. This post explains the composition and toxicology of DPM, the elemental-carbon marker, the regulatory limit underground, and the layered engineering controls that bring exposures down.

Composition and Toxicology

Diesel exhaust is a heterogeneous mixture of gases and fine particulate matter. The particulate fraction consists of an elemental carbon core onto which organic compounds, including polycyclic aromatic hydrocarbons, are adsorbed, together with sulfates, metals, and other combustion byproducts. The particles are overwhelmingly in the respirable and ultrafine size range, enabling deep alveolar deposition. The gaseous fraction adds carbon monoxide, nitrogen oxides, and other irritant gases and vapors. Health effects span acute mucous-membrane and respiratory irritation, exacerbation of asthma and cardiovascular disease, and, most consequentially, an established excess risk of lung cancer demonstrated in the Diesel Exhaust in Miners Study.

The Elemental Carbon Marker

Because diesel exhaust is a mixture rather than a single compound, exposure is quantified using a surrogate. Elemental carbon (EC) has become the marker of choice because it is reasonably specific to diesel combustion in most workplaces and can be measured reliably by NIOSH Method 5040, a thermal-optical analysis of respirable samples. Total carbon and respirable EC underpin both epidemiological exposure reconstruction and regulatory compliance sampling. Distinguishing diesel-derived carbon from other sources of industrial dust, such as carbonaceous mineral dusts or tobacco smoke, is an important interpretive consideration in mixed environments. Job-exposure matrices built on elemental carbon now allow historical diesel exposures to be reconstructed for long-latency epidemiology.

Regulatory Limits Underground

The Mine Safety and Health Administration regulates DPM in underground metal and nonmetal mines under 30 CFR Part 57, establishing a permissible exposure limit of 160 micrograms per cubic meter of total carbon as a personal full-shift average, a limit reached through a phased reduction from an earlier total-carbon standard. There is no separate OSHA PEL specific to DPM for general industry, and ACGIH has historically deliberated a low EC-based TLV. The MSHA standard remains the most stringent enforceable benchmark and is the operative limit for the underground workforce.

Engineering Controls Underground

Controlling DPM underground rests on a multi-layered strategy: low-emission and tier-compliant engines, diesel particulate filters and oxidation catalysts on equipment, ultra-low-sulfur fuel, and, most fundamentally, adequate mine ventilation to dilute and remove exhaust at the source. Enclosed, filtered operator cabs provide a critical barrier against exposure for equipment operators. Fleet management, idling restrictions, and rigorous engine maintenance further reduce emissions. Studies in modern mines using renewable fuels and tighter emission standards have documented substantially lower elemental carbon exposures than older operations, confirming that source controls work. Respiratory protection serves as a supplement where engineering controls cannot achieve compliance, not as a substitute for them.

What Industrial Hygienists Should Do

The industrial hygienist supporting an underground operation should build an exposure assessment program around NIOSH 5040 respirable elemental carbon sampling, with representative personal monitoring across job categories and ventilation zones. Verify that DPM exposures remain below the MSHA total-carbon limit, and treat the IARC Group 1 classification as justification for driving exposures as low as reasonably achievable rather than merely to the limit. Prioritize source controls, cleaner engines, filters, low-sulfur fuel, and ventilation over reliance on respirators, and validate the integrity of enclosed cabs for operators. Integrate DPM surveillance with medical monitoring for respiratory and cardiovascular endpoints, and document ventilation adequacy as the primary engineering control on which all underground DPM management depends. Related reactive contaminants, such as isocyanates and hydrogen sulfide, reinforce how strongly the choice of marker and sampling method shapes an exposure assessment.

Summary

Diesel particulate matter is a Group 1 carcinogen, with the greatest occupational burden falling on the underground workforce. It is measured using the elemental-carbon surrogate per NIOSH Method 5040 and calibrated against the MSHA total-carbon limit, but the IARC classification justifies driving exposures as low as reasonably achievable. Source controls, cleaner engines, particulate filters, low-sulfur fuel, and ventilation are the foundation, with respirators reserved as a supplement.

Helpful Resources

Bibliography

American Conference of Governmental Industrial Hygienists. (2026). TLVs and BEIs: Threshold limit values for chemical substances and physical agents and biological exposure indices. ACGIH.

Attfield, M. D., Schleiff, P. L., Lubin, J. H., Blair, A., Stewart, P. A., Vermeulen, R., Coble, J. B., & Silverman, D. T. (2012). The Diesel Exhaust in Miners Study: A cohort mortality study with emphasis on lung cancer. Journal of the National Cancer Institute, 104(11), 869-883. https://doi.org/10.1093/jnci/djs035

Gren, L., Krais, A. M., Assarsson, E., Broberg, K., Engfeldt, M., Lindh, C., Strandberg, B., Pagels, J., & Hedmer, M. (2022). Underground emissions and miners’ personal exposure to diesel and renewable diesel exhaust in a Swedish iron ore mine. International Archives of Occupational and Environmental Health, 95(6), 1369-1388. https://doi.org/10.1007/s00420-022-01843-x

International Agency for Research on Cancer. (2014). Diesel and gasoline engine exhausts and some nitroarenes (IARC Monographs on the Evaluation of Carcinogenic Risks to Humans, Vol. 105). IARC.

Mine Safety and Health Administration. (n.d.). Diesel particulate matter exposure of underground metal and nonmetal miners (30 CFR Part 57, Subpart D). U.S. Department of Labor.

National Institute for Occupational Safety and Health. (n.d.). Elemental carbon (diesel particulate): Method 5040. In NIOSH manual of analytical methods (4th ed.). U.S. Department of Health and Human Services.

Plato, N., Lewne, M., & Gustavsson, P. (2020). A historical job-exposure matrix for occupational exposure to diesel exhaust using elemental carbon as an indicator of exposure. Archives of Environmental & Occupational Health, 75(6), 321-332. https://doi.org/10.1080/19338244.2019.1644277

Plog, B. A., & Quinlan, P. J. (Eds.). (2012). Fundamentals of industrial hygiene (6th ed.). National Safety Council.

Pronk, A., Coble, J., & Stewart, P. A. (2009). Occupational exposure to diesel engine exhaust: A literature review. Journal of Exposure Science & Environmental Epidemiology, 19(5), 443-457. https://doi.org/10.1038/jes.2009.21

Silverman, D. T., Samanic, C. M., Lubin, J. H., Blair, A. E., Stewart, P. A., Vermeulen, R., Coble, J. B., Rothman, N., Schleiff, P. L., Travis, W. D., Ziegler, R. G., Wacholder, S., & Attfield, M. D. (2012). The Diesel Exhaust in Miners Study: A nested case-control study of lung cancer and diesel exhaust. Journal of the National Cancer Institute, 104(11), 855-868. https://doi.org/10.1093/jnci/djs034

Vermeulen, R., Silverman, D. T., Garshick, E., Vlaanderen, J., Portengen, L., & Steenland, K. (2014). Exposure-response estimates for diesel engine exhaust and lung cancer mortality based on data from three occupational cohorts. Environmental Health Perspectives, 122(2), 172-177. https://doi.org/10.1289/ehp.1306880

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