An elemental carbon (7440440) (EC) based technique for monitoring occupational exposure to particulate diesel exhaust was examined. Thermal optical analysis was used for the speciation of organic carbon (OC) and elemental carbon. The efficiency of the oxidation/reduction process occurring within the thermal optical method was near 100% for the different analytes tested. The analytical range and limit of detection (LOD) of the thermal optical method were determined with OC standards. An upper EC loading of 50 micrograms per square centimeter was determined, while the LOD was calculated to be 2 micrograms of carbon per cubic meter, the average minimum background level. The trace amounts of EC detected in carbonaceous aerosols in the workplace were considered negligible. The thermal optical method was considered suitable for use in coal mines, where minor amounts of EC were present in coal dust. When diesel exhaust samples were collected with several different sampler types, no significant differences among the mean concentrations of the various samplers were found. The authors conclude that the EC based, thermal optical method is suitable for routine particulate diesel exhaust exposure monitoring.