Standard Test Method for Monitoring Diesel Particulate Exhaust in the Workplace
5.1 The test method supports previously proposed occupational exposure standards (7, 8) for DPM. A DPM exposure limit has since been promulgated for metal.nonmetal mines, but there currently are no limits for general occupational settings (a proposed limit (7) was withdrawn from the ACGIH Notice of Intended Changes (NIC) list in 2003). In the United States alone, over a million workers are occupationally exposed (9). An exposure standard for mines is especially important because miners' exposures are often quite high. NIOSH (9), the International Agency for Research on Cancer (10) (IARC), the World Health Organization (11) (WHO), the California Environmental Protection Agency (12), the U.S. Environmental Protection Agency (13) (EPA), and the National Toxicology Program (14) reviewed the animal and human evidence on DPM and all classified diesel exhaust as a probable human carcinogen or similar designation. In 2012, the WHO reclassified diesel exhaust as carcinogenic to humans (Group 1) (15). In addition, in a study of miners, the National Cancer Institute (NCI) and NIOSH reported increased risk of death from lung cancer in exposed workers (16 and 17).
5.2 The test method provides a measure of occupational exposure to DPM. Given the economic and public health impact of epidemiological studies, accurate risk assessment is critical. The NIOSH/NCI study of miners exposed to diesel exhaust provides quantitative estimates of lung cancer risk (16 and 17). The test method was used for exposure monitoring. Since publication (in 1996) as NMAM 5040, the method has been routinely used for occupational monitoring (5).
5.3 Studies indicate a positive association between airborne levels of fine particles and respiratory illness and mortality (18-26). The test method and others have been used for EPA air monitoring networks and air pollution studies. Because different methods produce different results, method standardization is essential for regulatory compliance determinations and valid comparisons of interlaboratory data.
5.4 The test method is being applied for emission-control testing.
1.1 This test method covers determination of organic and elemental carbon (OC and EC) in the particulate fraction of diesel engine exhaust, hereafter referred to as diesel particulate matter (DPM ). Samples of workplace atmospheres are collected on quartz-fiber filters. The method also is suitable for other types of carbonaceous aerosols and has been widely applied to environmental monitoring. It is not appropriate for sampling volatile or semi-volatile components. These components require sorbents for efficient collection.
1.2 The method is based on a thermal-optical technique (1, 2)2. Speciation of OC and EC is achieved through temperature and atmosphere control, and an optical feature that corrects for sample charring (carbonization).
1.3 A portion of a 37-mm, quartz-fiber filter sample is analyzed. Results for the portion are used to calculate the total mass of OC and EC on the filter. The portion must be representative of the entire filter deposit. If the deposit is uneven, two or more representative portions should be analyzed for an average. Alternatively, the entire filter can be analyzed, in multiple portions, to determine the total mass. Open-faced cassettes give even deposits but may not be practical. At 2 L/min, closed-face cassettes generally give results equivalent to open-face cassettes if other dusts are absent. Higher flow rates may be employed, but closed-faced cassettes operated at higher flow rates (for example, 5 L/min) sometimes have uneven deposits due to particle impaction at the center of the filter. Other samplers may be required, depending on the sampling environment (2-5).
1.4 The calculated limit of detection ( LOD) depends on the level of contamination of the media blanks (5). A LOD of approximately 0.2 µg carbon per cm2 of filter was estimated when analyzing a sucrose standard solution applied to filter portions cleaned immediately before analysis. LODs based on media blanks stored after cleaning are usually higher. LODs based on a set of media blanks analyzed over a six month period at a commercial laboratory were OC = 1.2 µg/cm2, EC = 0.4 µg/cm2, and TC = 1.3 µg/cm 2, where TC refers to total carbon (TC = OC + EC). In practice, the LOD estimate provided by a laboratory is based on results for a set of media blanks submitted with the samples. To reduce blank variability (due to lack of loading), a manual OC-EC split is assigned at the time when oxygen is introduced. With manual splits, the SD for media blanks is typically about 0.02-0.03 µg EC/cm2, giving LODs (3 × SD blank) from about 0.06-0.09 µg EC/cm2. The corresponding air concentration depends on the deposit area (filter size) and air volume.
1.5 OC-EC methods are operational, which means the analytical procedure defines the analyte. The test method offers greater selectivity and precision than thermal techniques that do not correct for charring of organic components. The analysis method is simple and relatively quick (about 15 min). The analysis and data reduction are automated, and the instrument is programmable (different methods can be saved as methods for other applications).
1.6 A method (5040) for DPM based on thermal-optical analysis has been published by the National Institute for Occupational Safety and Health (NIOSH). Method updates (3, 4) have been published since its initial (1996) publication in the NIOSH Manual of Analytical Methods (NMAM). Both OC and EC are determined by NMAM 5040. An EC exposure marker (for DPM) was recommended because EC is a more selective measure of exposure. A comprehensive review of the method and rationale for selection of an EC marker are provided in a Chapter of NMAM (5).
1.7 The thermal-optical instrument required for the analysis is manufactured by a private laboratory.3 As with most instrumentation, design improvements continue to be made. Different laboratories may be using different instrument models.
1.8 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.9 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. Specific precautionary statements are given in 7.1.5, 8.3, and 12.12.2.
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