NIOSH 5040: A LABORATORY METHOD FOR MEASURING OCCUPATIONAL EXPOSURES TO DIESEL PARTICULATE MATTER

摘要

The analysis for elemental carbon (diesel exhaust) as determined by Method 5040 is a precise process (1.85%RPD) and, for organic carbon, is an accurate (99.97% average) process as shown by our spike and duplicate data. Based on interlaboratory comparison data, the results generated in our laboratory are statistically indistinguishable from results generated by other laboratories using this technique. Although our experience with NIOSH 5040 has been good, we have some concerns that in certain cases the results need additional care in their interpretation. We have encountered many samples that contain carbonate. Samples from a limestone (calcium carbonate) or trona (sodium carbonate) mine will usually have carbonate present on the sample. If the thermogram indicates the presence of carbonate in the sample (a large fourth peak eluting in the anerobic heating zone - >900℃), we confirm the presence of carbonate by exposing the sample to HCl fumes and then rerunning it. This exposure is accomplished by setting the filter punch on a stainless steel screen suspended over a beaker of hydrochloric acid for thirty minutes. We report the results from the acid-treated sample, and can determine the amount of carbonate carbon by difference. We have, however, encountered samples that were acid treated and still had a measurable carbonate peak present. Such a case would be an interference for the determination of diesel particulate matter using the total carbon measurement as the surrogate. The large range of values (-3.5 - 35.3) encountered in the organic carbon blanks causes some additional concern. This range may be the result of different levels of expertise in the handling of the samplers in the field. There is a potential for a significant contribution from the blank to the reported total carbon determination. We have analyzed bulk ore samples by dusting some of the finely pulverized ore onto a filter and performing the analysis. We have found that some materials from halite ore samples with small amounts of oil shale present will contribute to the elemental (and consequently the total) carbon determination. Additional studies are needed prior to utilizing the Method 5040 for compliance sampling as proposed by MSHA.