Exposure monitoring in mines using diesel equipment

Introduction:    Occupational exposure to diesel particulate matter (DPM) has been suspected of causing cancer. DPM has a complex chemical structure. Identifying the potentially harmful constituents of DPM has been the subject of much research. Measuring those constituents in an underground mining environment has been challenging.    

Methods:    The first cut at measuring the inhaled constituents of DPM is to sample for Respirable Combustible Dust (RCD). Following on from RCD, researchers at the National Institute of Occupational Health (NIOSH) developed the NIOSH 5040 Method. This utilizes a submicron filter to cut the sampled material at 0.8 microns, and is mandated for compliance sampling by the US Mine Safety and Health Administration (MSHA). The analysis of DPM is complex and determines organic and elemental carbon components; there are also confounding factors that might affect the results. A recently-developed device monitors for elemental carbon levels in real time. It may also be possible to derive qualitative estimates of DPM for specific engines from exhaust gas testing.    

Results:    In May 2008 the DPM exposure limit in underground non-metal mines in the US was reduced to 160 ug/m3 total carbon. Sampling with the NIOSH 5040 is used extensively to verify compliance. Early problems with over-exposures have essentially been resolved, as mines improve ventilation and equipment maintenance, upgrade to cleaner engines, and/or convert to bio-diesel fuel.    

Discussion:    Concerns about inaccuracies and confounding factors with the NIOSH 5040 method have been addressed in the way the samples are taken and analyzed. Lab results delays have prevented it from being used in operational settings. However, DPM monitoring using the Airtec unit for FLIR has allowed operators to adjust for likely DPM exposure in real-time. The use of surrogates, such as carbon monoxide, for DPM is specific to the engines in use and the ventilation conditions in a section.