Engineering & Mining Journal

JUN 2014

Engineering and Mining Journal - Whether the market is copper, gold, nickel, iron ore, lead/zinc, PGM, diamonds or other commodities, E&MJ takes the lead in projecting trends, following development and reporting on the most efficient operating pr

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(>90%) in protecting miners from DPM exposures. However, over time, factors such as a loss in cab integrity or cab filter degra- dation can cause higher concentrations of DPM to penetrate into the cab. Periodically, researchers and operators evaluate cabs to determine their effectiveness at reducing DPM concentrations. In addition, cabs are evaluated to determine the effectiveness of alterations to the cab system and the use of different types of filters. The problem with using the NIOSH method 5040 for evalu- ating cabs is that the results include effects from work practices such as opening and closing doors. This could result in inaccu- rate data about the cab system itself. Because it is a real-time monitor, the Airtec allows researchers and operators to account for these work practices. To demonstrate, when using the standard method (NIOSH method 5040) for evaluat- ing the effectiveness of some cabs for reduc- ing DPM over a number of days at a lime- stone mine, the DPM reduction efficiencies ranged from 46% to above 95% (Noll et al. 2014). This large range of efficiencies was probably because under real-time operating conditions, operators periodically need to open their cabs (for example, to communi- cate with other miners or to perform duties outside of the cab). When a door or window is open, the cab compartment becomes con- taminated. Therefore, it can be deduced that the efficiency for each day was probably influenced by how often and how long the door and windows in the cab were opened. At the same limestone mine, the real- time information from the Airtec took into account the work practices and provided the efficiency of the cab system itself. Airtecs were used to take samples inside and outside of the cab, and a pressure mon- itor inside the cab was used to determine when the door or window was open. A pos- itive pressure indicated that the cab was sealed, while a pressure of zero revealed that a door or window was open. The real- time concentrations of the Airtecs were averaged only at the times of the day when the cab door and window were closed (as revealed by the pressure data), and these concentrations were used to determine the reduction efficiency. This procedure result- ed in the determination of reduction effi- ciencies (consistently above 90%) only when the cab was sealed (Noll et al. 2014). Slightly modifying this procedure, another mine had the cab operator take notes indi- cating when the cab door or window was open instead of using a pressure monitor. The real-time DPM measurements can also be utilized to provide a "quick and dirty" evaluation of the cab system. After the inside of the cab is measured for an entire shift with the Airtec, both the eight- hour time-weighted average (TWA) and the real-time graph should be assessed. When the eight-hour TWA concentration is above the final MSHA-permissible exposure limit (PEL) (about 120 µg/m 3 EC or 160 µg/ m 3 TC), the real-time graph helps differen- tiate whether an inefficient cab or work practice is the cause. If elevated concen- trations of DPM are due to an open door or window, peaks in the graph should be observed (see Figure 2a), because the con- centration of DPM should increase when the door is open and then decrease once JUNE 2014 • E&MJ; 79 www.e-mj.com D P M M O N I T O R I N G Figure 3—A still picture of the merged video footage and DPM concentration graph from the Helmet-CAM Figure 2a—(left) A chart representing peaks in DPM concentrations due to an open cab door. Figure 2b (right) a chart representing real-time DPM concentrations being continuously above the final PEL inside a cab. EMJ_pg78-81_EMJ_pg78-81 6/3/14 3:23 PM Page 79

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