Substantial evidence has shown that underground miners are routinely exposed to very high concentrations of diesel particulate matter (DPM), much higher than for any other occupation. In 1998, the Mine Safety and Health Administration (MSHA) proposed two diesel rules - one for coal mining, the other for metal/nonmetal mining. The coal rule set a staged implementation limit on DPM emission ending at 2.5 g/hr for heavy-duty equipment and can be met by the use of MSHA-approved filters based on the diesel emission characteristics of the engines involved. The metal rule set an interim concentration limit of 400 µg/m3 of total carbon and a final concentration limit of 160 µg/m3 of total carbon scheduled to go into effect in January 2006.

In early 1999, with both MSHA and the American Conference of Governmental Industrial Hygienists setting limits on DPM, NIOSH convened a committee with the intent of determining a realistic exposure limit for DPM in mining. Although it was decided that an exposure limit for DPM was premature, NIOSH was, however, able to estimate a minimum DPM level achievable by using clean engines and ceramic filter technologies. This analysis was placed into the MSHA rule hearing record and published in Mining Engineering magazine in 2001.

Later in 1999, a coal diesel partnership was formally established among union, industry, and NIOSH. Its goal is to work together to address technology to control diesel emissions in coal mines. The partners requested that NIOSH provide a review of available technology. This was presented to the partnership in 2000 and published as NIOSH Information Circular 9462 in 2002. That same year, the metal/nonmetal industry, observing the coal partnership successes, requested that NIOSH establish a similar metal/nonmetal partnership to address diesel issues of concern in its own industry.

NIOSH researchers have greatly facilitated the implementation of diesel control technologies into both coal and metal/nonmetal mines:

• NIOSH researchers worked in conjunction with the Canadian Diesel Emissions Evaluation Program (DEEP), a consortium of Canadian industry, academics, government, and labor. NIOSH participated in an isolated zone study to determine exhaust particulate filter performance and took the initiative to conduct the world's first examination of the size distribution of diesel exhaust particles downwind of an operating vehicle. NIOSH found that the nanoparticle concentration actually increased with the use of filters, many of which were 98% efficient in removing larger particles. Based on this experience, NIOSH was able to suggest and conduct isolated zone experiments in coal and metal mines that obtained definitive assessments of the effects of engine tuning for altitude, pleated-element filters, ceramic filters, and fuels. Findings from these efforts were transferred to the U.S. mining industry through reports, conference presentations, and workshops.
• The metal/nonmetal industry contested the metal rule. In an agreement with MSHA, it demanded that NIOSH be involved in determining the proper compliance surrogate for DPM exposures in metal mines. The contested rule had incorporated the commercial version of the U.S. Bureau of Mines (USBM) diesel sampler to separate out carbon-bearing dusts from diesel soot and used total carbon (TC) as the DPM surrogate. NIOSH worked with MSHA and the manufacturer to improve the reliability and accuracy of the commercialized version of the USBM diesel sampler. It is now the MSHA-required sampler for sampling DPM in metal/nonmetal mines. NIOSH research was instrumental in changing the surrogate from TC to elemental carbon (EC). Using EC overcame the problem of sampling interference from oil mist, carbonaceous ores, or tobacco smoke, all of which can be present in metal/nonmetal mines. NIOSH was tasked with reviewing the results of a study at 31 mines, which was agreed to under a litigation agreement between MSHA, industry, and labor. NIOSH analyzed all samples from the study, and reviewed and commented on the study results.
• Uncertainty from the metal/nonmetal industry over the real-world performance of diesel control technology resulted in two NIOSH studies in a western metal mine in 2003 and 2004. The studies verified that ceramic filters could reduce EC by 98% under actual production scenarios, biodiesel blends could reduce EC by over 40%, water fuel emulsions reduced EC by more than 80%, and differences among No. 1, No. 2, and ultralow sulfur fuels were negligible. Also, excess NO2 was observed when platinum-catalyzed systems were used.
• In late 2002, MSHA requested NIOSH assistance in producing an industry guideline for the selection of diesel filters. NIOSH took the lead and produced a highly acclaimed Diesel Particulate Filter Selection Guide in early 2003. The guide is Web-based and leads a novice through the process of selecting the proper system for equipment requiring filters. It starts with organizational and engine maintenance/condition prerequisites and continues all the way through filter selection criteria and operational limitations. It is posted on both the MSHA and NIOSH websites.
• In 2003, NIOSH, working through the abovementioned partnerships, hosted workshops for control of diesel emissions at coal and metal/nonmetal mines. The workshops were held at several locations and transferred the latest diesel emission control technologies, Canadian experiences, and engine maintenance practices to the U.S. mining industry.
• NIOSH, working together with a private company, has developed an exhaust cooling system that reduces the diesel exhaust temperature entering high-temperature pleated-element filters, which are widely used in the coal mining industry. The cooler exhaust from this device prevents unintended ignition of the diesel soot accumulations in the filter (filter fires) that can result from uncooled exhaust.
• NIOSH is working with a diesel ceramic filter manufacturer to develop a passive (self-regenerating) filter that will regenerate at lower-duty cycle temperatures without creating an increase in tailpipe emissions and workplace concentrations of NO2 in the mines. Successful curtailment of excessive NO2 of this system would allow the application of passive filter technology on a wider range of underground equipment in underground mines.

As a result of NIOSH efforts, the coal and metal/nonmetal industries, labor, and MSHA have pertinent and useful results based on solid research and have a continuing resource for unbiased and factual information about technology to control diesel emissions. Better and more technology is now being implemented that will reduce miners’ exposures to diesel exhaust contaminants.