Since 2000, MSHA has made detailed information regarding the occupational health exposure assessments performed during inspections available to the public. These data cover a range of exposure types found in the industry. According to data since the new diesel exhaust standard, DPM had a higher median exposure concentration-to-PEL (ECP) ratio (0.47) than any other airborne contaminant (for which 100 or more samples were taken) except silver fumes (0.88).

Median DPM ECP ratios vary widely by state. The state of Washington has the only median ECP ratio above 1.0 (1.22, based on 27 samples), followed by Virginia (0.98, 37 samples). Oklahoma (0.13, 24 samples) and Arkansas (0.15, 34 samples) had the lowest median ECP ratios. Of those counties with more than 10 samples, Okanogan County in Washington state (1.92, 20 samples) and Shasta County of California (1.56, 16 samples) had the highest median ECP ratios, while Sequoyah County in Oklahoma (0.13, 24 samples) and Rock Castle of Kentucky (0.14, 10 samples) had the lowest.

DPM exposures differ among mine type, mine size, and commodity sector as well. The worst median ECP ratios were observed at underground mines for copper ore (1.03, 71 samples, 207.6 million hours worked) and zinc (0.91, 170 samples, 610.5 million hours worked) mines. Where there were at least ten samples taken, underground stone (0.15, 47 samples, 84.6 million hours worked) and underground common clay (0.28, 18 samples, 6.2 million hours worked) mines had the lowest median ECP ratios for DPM. The data clearly indicate a huge disparity in DPM compliance based on geography, mine type, mine size, and commodity sector, among several other factors. It is also obvious that much work remains to be done in controlling DPM exposures, given that nearly 50 percent of all DPM samples collected by MSHA are over 50 percent of the DPM PEL. While the MWG recognizes these issues, the unique nature of each mine and the factors that affect its safety and health have led some to question whether a “one-size-fits-all” approach is most appropriate or cost-effective at reducing injury and illness.

In the complex American regulatory system, the U.S. Department of Labor, through MSHA, publishes new regulations, standards, and operating requirements based on mandates from Congress and executive authority. Compliance with new safety and health regulations is mandatory for all mining facilities under MSHA’s jurisdiction. They represent the “do’s and don’ts” that mining companies must follow to legally operate and avoid civil and criminal penalties. This contrasts with Australia’s risk-based, “duty of care” regulatory structure implemented in New South Wales and Queensland in 2002 and 1999, respectively. The approach consists of three steps: a scoping assessment in which risks associated with specific operations are identified; a qualitative or semi-quantitative risk assessment that characterizes the magnitude of potential consequences and their likelihood, and outlines recommended controls; and a review of the recommended corrective actions, including an assessment of control efficiencies. Australia’s regulatory agency works with each mine site on all three steps.

It is conceivable that an approach targeting those mine sites with greatest risk of DPM overexposure may more efficiently utilize MSHA’s limited time and resources. A study published in in 2008 found that, after implementing the risk-based approach, incident rate ratios of coal mining lost-time injuries fell by 52 and 72 percent in New South and Queensland, respectively, compared to an 11 percent reduction in the U.S. over the same period. Making such a change in a country as large as the U.S. and in an industry as well-established as mining would require monumental efforts, resources, and data. While this is just one study evaluating a highly complex issue, a risk-based regulatory approach should be investigated and considered for the U.S. mining industry. To control diesel exhaust exposures, options currently exist for every portion of the IH control hierarchy. Electrical equipment is becoming more common and may soon present a feasible, cost-effective solution for mining and other industrial settings. While newer diesel equipment doesn’t eliminate the risk of diesel exhaust exposure, it can result in exhaust reductions. Substitutions for diesel fuel, such as biodiesel or a natural gas/diesel blend called GDiesel, are being evaluated for their effect on diesel exhaust emissions. Generally, biodiesel has the potential to reduce DPM exposures but can actually increase others, as noted by a study published in the in 2010. While less is known about GDiesel, a paper in the March 2015 suggests that it, too, has the potential to significantly reduce diesel exhaust exposures. Fuel additives can also improve fuel delivery and combustion, resulting in lower emissions, as shown by research published in the journal .

Engineering controls include improved ventilation, as well as installation of exhaust after-treatment (EAT) systems, diesel oxidation catalysts, and diesel particulate filters. In addition, enclosed cabs with regularly changed particle filters can protect equipment operators from overexposure. Administrative controls consist of proper maintenance of engineering controls, such as EATs, as well as ensuring that the equipment’s fuel injection pressure is sufficiently high, fuel injector angles and timing are correct, and a sufficient amount of air is entering the engine chamber. While personal controls, such as air-purifying respirators, are an option, industrial hygienists should make every reasonable effort to maintain low diesel exposure concentrations. Despite the dangerous nature of mining, significant strides have been made since passage of the Coal Mine Health and Safety Act of 1969 thanks, in part, to the tireless efforts of mining health and safety professionals. According to MSHA, averaged 426 per year from 1966 to 1970. Those numbers have dropped to an average of 38 per year during 2011–2016.

Mine safety and health is improving not only in comparison to historic data, but to other industries as well. According to the U.S. Bureau of Labor Statistics, the injury incidence rate for all of mining was 2.6 in 2014. This is lower than the incidence rates for the construction (11.7); educational and health services (11.6); public administration (10.4); trade, transportation, and utilities (9.3); agriculture, forestry, fishing and hunting (5.2); state government (3.8); manufacturing (3.6); and leisure, entertainment, and hospitality (3.5) industries for the same year. Though these data do not speak to the severity of injury, we are confident that mine safety and health is progressing—and the AIHA Mining Working Group is poised to help take it to the next level.

NIOSH: “” (January 2004).

: “” (June 2012).

: “” (2012).

: “Occupational Exposures to Emissions from Combustion of Diesel and Alternative Fuels in Underground Mining-A Simulated Pilot Study” (March 2015).

: “International Evaluation of Injury Rates in Coal Mining: A Comparison of Risk and Compliance-Based Regulatory Approaches” (October 2008).

Society for Mining, Metallurgy, and Exploration: (2001).

“Ultra Low Dosage of Platinum and Cerium Fuel Additives in Diesel Particulate Control” (September 2001).