Coal Age

DEC 2017

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34 December 2017 refuge alternatives continued To ensure that NIOSH heat and hu- midity research on refuge alternatives was as complete as possible, NIOSH wanted to examine the resulting internal thermal environment of refuge alterna- tives across a wide variety of actual pro- duction U.S. coal mines with different mine temperatures, mine strata compo- sitions (thermal properties), and mine entry sizes. In support of this effort, five mines across the U.S. worked with NIOSH to measure the fluctuating mine air and mine strata temperatures near existing refuge alternatives for a time period of at least one year to determine the worst- case thermal conditions at each mine. The mines were located in the Eastern, Midwestern, Western, Southern, and Southwestern regions of the U.S. Based on the thermal simulation models described above, NIOSH and TAI used the mine temperature data, mine strata thermal properties, and mine sizes of each of the five mines to carry out sim- ulations to determine the final tempera- ture, relative humidity, and apparent tem- perature of the 23-person tent-type and six-person rigid-type refuge alternatives tested by NIOSH. Simulations used the worst-case temperatures for the mines to determine if the apparent temperature limit would be reached. If the apparent temperature limit was reached, the occu- pancy of the unit(s) was reduced and the simulation was rerun to determine the maximum number of miners that could occupy the refuge alternative for the mine in question without exceeding the appar- ent temperature limit. In these simulations, based on data gathered from the five participating mines, the 95°F apparent temperature limit was exceeded in some cases and derating was therefore necessary. The following obser- vations were made: • For the Eastern, Western, and South- western mines, derating was not nec- essary for either refuge alternative. • For the Midwestern mine, which had a worst-case mine temperature of 69°F, the 23-person tent-type RA would have to be derated by two, to 21 miners. The six-person rigid-type RA would not have to be derated. • For the Southern mine, which had a worst-case mine temperature of 81°F, the 23-person tent-type RA would have to be derated by 22, to only one miner. The six-person rigid-type RA would exceed the apparent tem- perature limit with even just 1 min- er. These more extreme cases for the Southern mine underscore how crit- ical the initial mine temperature is with respect to occupancy derating. As these results show, derating a refuge alternative's occupancy is not a "one-size- fits-all" proposition. By definition, each unit to be derated must be considered as an individual case based on the refuge al- ternative type and mine. Applying Occupancy Derating Results from NIOSH testing and bench- marked thermal simulation models show that the MSHA-mandated appar- ent temperature limit of 95°F may be reached in refuge alternatives depend- ing on initial mine strata temperature, mine thermal conductivity, and, to a lesser degree, mine entry size. If the apparent temperature limit is reached, it would be necessary to derate the oc- cupancy of a refuge alternative or to use some type of cooling system. Obviously, the necessary derating discussed here depends on the mine- specific refuge alternative installation. The most critical parameter to consider is the initial mine strata temperature, which, in many cases, is approximately equal to the mine air temperature. Table 1 shows an approximate occupancy derating based on mine temperature. Importantly, this ta- ble was derived from the specific condi- tions and locations described here — i.e., NIOSH's Safety Research Coal Mine and Experimental Mine, and the refuge alter- natives used for NIOSH tests and simu- lations. Derating percentages for refuge alternatives in actual mines should be based on a combination of mine tempera- tures, thermal conductivity values, entry sizes, and the specific refuge alternative used in the installation. With the concept of occupancy der- ating to reduce a refuge alternative's ap- parent temperature now thoroughly ex- plored, NIOSH is conducting research on the use of cooling systems to reduce the temperature and relative humidity. Use of cooling systems might be more desir- able, especially considering the high ini- tial temperatures in some mines, where solutions other than derating could be necessary. Cooling strategies such as bat- tery-powered air conditioners, cryogenic air supplies, and carbon-dioxide-based cooling systems may be possible solutions in these cases. To that end, through exter- nal research contracts, NIOSH is currently working on developing a battery-powered air conditioner and a cryogenic air supply for refuge alternatives. Dave Yantek is a lead research engineer for the Electrical and Mechanical Systems Safety Branch of NIOSH's Pittsburgh Min- ing Research Division. He can be reached at: Joseph Schall is a health communications specialist for the Health Communications, Surveillance, and Research Support Branch of NIOSH's Pittsburgh Mining Research Division. For further information on NIOSH's refuge alternative research, go to: niosh/mining/researchprogram/projects/ project_RefugeAlternatives.html. Disclaimer The findings and conclusions in this paper are those of the authors and do not nec- essarily represent the views of the Nation- al Institute for Occupational Safety and Health (NIOSH). Mention of any company or product does not constitute endorse- ment by NIOSH. Table 1—Example of derating percentages for refuge alternatives in the NIOSH Safety Research Coal Mine and Experimental Mine based on heat and humidity testing and thermal simulations. Mine Temperature % Derating Needed to Prevent Apparent Range Temperature From Exceeding 95°F 60°F to 65°F 0% to 30% 65°F to 70°F 20% to 50% 70°F to 75°F 25% to 70% 75°F to 80°F 60% to 90%

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