Rock Products

OCT 2014

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www.rockproducts.com ROCK products • OCTOBER 2014 27 to this sampling setup is in the sam‐ pling pumps; they have become smaller, lighter, have better battery‐life, and are constant flow devices whereby the flow rate is maintained at the required 1.7 lpm flow rate. Once sampling is complete, filters are submitted for analysis to an American Industrial Hygiene Association (AIHA) accredited laboratory. The miners' res‐ pirable dust concentration is deter‐ mined by dividing the weight of respirable dust by the volume of air col‐ lected over the period of sampling. The weight of respirable dust, reported in micrograms or milligrams, is deter‐ mined by pre‐ and post‐weighing the filter on a microbalance. The volume of air, reported in cubic meters, is deter‐ mined via multiplication of the total sample time (obtained in one‐minute measurements on the sampling pump) by the flow rate. If silica dust is believed to be present, further analysis of the sample is per‐ formed, typically via the National Insti‐ tute for Occupational Safety and Health (NIOSH) 7500 method "Silica, Crys‐ talline, by XRD (filter redeposition)." This analytical method permits deter‐ mination of the weight (and therefore, percentage) of respirable crystalline sil‐ ica (RCS) within the sample. Ultimately, the worker's respirable dust concentration is compared to the permis‐ sible exposure limit (PEL) to determine whether the miners' exposure was in ex‐ cess of the PEL. If worker exposure exceeds the PEL, operators should investigate the causes of the excessive exposure, make cor‐ rections, and resample to confirm effec‐ tiveness of the corrective interventions. Special Challenges For exposures that exceed the PEL, identification of root causes can be challenging, particularly if detailed op‐ erational or operator notes were not kept. The challenges associated with root cause identification can be espe‐ cially difficult for workers who are mo‐ bile during their shift because they may be constantly moving to different work areas while performing multiple duties and job tasks throughout the workday. In the metal/nonmetal mining industry, mobile workers have some of the highest overexposure rates for RCS for all the various job occupation classifications. Table 1 lists the overexposure rates of a few mobile worker job categories for a 10‐year period (2003‐2012) based upon MSHA's respirable dust compliance sam‐ pling results. In evaluating this data, a dif‐ ficult challenge is determining the primary contributors (i.e., tasks or processes) to the respirable dust expo‐ sures exceeding the PEL. Over the years, video technology has been used to evaluate worker exposure to different types of contaminants, but these evaluations were always per‐ formed with the camera in a stationary position (Gressel et al., 1992; Rosen et al., 2005). Unfortunately, these tech‐ niques were not applicable for mobile workers in the mining industry because of their need to move to various loca‐ tions throughout the mining operation to perform their work. Helmet-CAM Technology The newly developed Helmet‐CAM technology provides a first‐person video display of the job tasks per‐ formed by miners along with data on their respirable dust exposure. In con‐ sidering both sources of information si‐ multaneously, immediate insight is gained into work areas and/or tasks that contributed to elevated respirable dust exposures (Cecala et al., 2013). Helmet‐CAM was developed under a cooperative relationship between Unimin and NIOSH. The original goal was to be able to evaluate a workers' respirable dust exposure without the need to closely follow a worker and ob‐ serve or monitor the worker to deter‐ mine his or her exposure. The possibility of combining a small video camera with an instantaneous dust monitor to determine a worker's respirable dust exposure seemed like a viable methodology. The next step was finding a means to compare the video and dust data simultaneously. This led to the development of the EVADE software, which merges these two pieces of infor‐ Table 1. Silica overexposure rates for mobile workers in the metal/nonmetal industry from MSHA data from 2003 to 2012. Sand and Gravel Mines Stone Quarries Metal Mining Mines Occupation % > PEL Total % > PEL Total % > PEL Total Samples Samples Samples Laborer 15 1187 10 1864 16 120 Mechanic 4 240 5 365 13 174 Utility Man 10 435 10 1246 22 72 Cleanup Man 16 633 11 793 21 80

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