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NIOSH Respiratory Diseases Research Program

Evidence Package for the National Academies' Review 2006-2007

NIOSH Programs > Respiratory Diseases > Evidence Package > 5. Respiratory Malignancies > 5.4 Lung Cancer Induced by Diesel Engine Exhaust

5.4b) Size-Selective Sampler for Compliance with Diesel Exhaust PEL

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Issue

 NIOSH and others have concluded that diesel exhaust particulate matter is probably a human carcinogen (IARC Group 2A), yet more than 30,000 underground mine workers are estimated to be exposed at levels in excess of 0.5 mg/m3. Based in part on RDRP research, MSHA proposed a new rule to regulate the exposure of underground metal/nonmetal miners to diesel particulate matter in 1998. MSHA proposed using measurements of total carbon (the sum of organic carbon and elemental carbon) as a surrogate for diesel particulate matter.

Before the MSHA rule could be finalized, a problem needed to be solved, namely that of total carbon interference from carbon-containing ore dust. MSHA asked RDRP scientists to verify that a size-selective sampler developed by the U.S. Bureau of Mines to separate coal mine dust from diesel particulate matter would also work for metal/nonmetal mine dusts.

In January 2001, MSHA promulgated a final rule regulating underground metal/nonmetal miners' exposure to diesel exhaust particulate matter. Compliance would be determined by sampling concentration of total carbon collected by a size-selective impactor. Mining industry officials challenged the rule, claiming that sources of organic carbon in the mine other than diesel particulate matter (e.g. carbonaceous ore dust, tobacco smoke, and oil mist from drills) would falsely elevate total carbon above that attributable to diesel exhaust particulate matter. The resulting settlement agreement among industry, labor, and MSHA specified that a metal/nonmetal mine study would be conducted in a variety of mines around the country. RDRP staff were to be involved in the study, evaluate the data, and review and comment on the final report of the study.

Approach

RDRP scientists contracted with SKC Inc. to develop a commercial version of the U.S. Bureau of Mines sampler and with the University of Minnesota to test it. In-mine and laboratory testing of the sampler verified that it eliminated metal/nonmetal mine dusts as desired. Subsequently, RDRP scientists worked with MSHA to conduct additional laboratory and field tests. These activities revealed that the samplers produced irregularly shaped deposit areas on the filters. RDRP scientists found a solution to the problem. Upon recommendations from RDRP scientists and MSHA, SKC replaced the crimped aluminum shield holding the filter media with a flat gasket. This resulted in precise circular deposit areas. SKC also incorporated a RDRP recommendation to increase the filter diameter for a better fit and to include a second filter to serve as a field blank. RDRP scientists tested the new commercial version extensively to ensure its reliability and the reproducibility of sampling results.

Working together, RDRP, MSHA, labor, and industry developed a protocol to identify possible non-diesel particulate matter sources of organic carbon in underground metal/nonmetal mines and to evaluate the impact of those interferences on total carbon measurement. The study verified that drill-oil mist and cigarette smoke could be significant sources of organic carbon. Some sources of organic carbon could be eliminated or corrected out. The impactor sampler eliminated mineral dust from the filter sample, and vapor-phase organic carbon could be corrected for by applying a second filter. However, the study concluded that the non-diesel particulate matter contributions to organic carbon from oil mist and cigarette smoke could not be avoided, nor could an appropriate correction factor be applied to account for these organic carbon sources. These RDRP findings verified the earlier (1997) position of NIOSH, namely, that elemental carbon was a better surrogate for diesel particulate matter than total carbon because the only source of elemental carbon was diesel particulate matter.152

Outputs and Transfer

RDRP, MSHA, and SKC worked as a team on this research, which facilitated the transfer of the technology. Industry and labor groups were kept informed of progress. Stakeholder interaction increased acceptance of this technology. The results of this research were also published as six peer-reviewed journal reports and have been presented at a number of technical conferences (A5-33).

RDRP research on this diesel exhaust sampler was cited by MSHA in support of its Final Rule on diesel particulate matter published in January 2001.

Findings have been presented at workshops and partnership meetings attended by personnel from MSHA, industry, and labor. They have also been noted in the Federal Register (A5-34) and published in peer-reviewed journals (15, A5-35, A5-36).

Intermediate Outcomes

The modified sampler is now a commercial product manufactured by SKC Inc. It represents the state of the art in measuring diesel particulate matter in underground metal/nonmetal mines and has become the MSHA-required sampler for measuring diesel particulate matter in metal/nonmetal mines (16, A5-37).

 As a result of this work, MSHA (with industry and labor concurrence) changed the interim standard’s surrogate for measurement of diesel exhaust particulate matter in metal/nonmetal mines from total carbon to elemental carbon (17, A5-38). Subsequently, MSHA included the elemental carbon standard in its final rule on diesel exhaust exposure in metal and non-metal mines (A5-39).

What’s Ahead

RDRP will continue to address issues related to the regulations established by the MSHA final rule.153 For example, MSHA's new diesel rule for metal/nonmetal mines lowers the allowable Total Carbon (TC) limit to 160 μg/m3 by May 2008. TC cannot be accurately measured at this lower limit, but EC (elemental carbon) can be measured. RDRP scientists are working on finding a reliable ratio between EC and TC at these measurement levels. This will allow MSHA to establish an EC surrogate for TC at these lower limits and thus enable MSHA to enforce the new exposure limit.