Federal regulations require refuge alternatives (RAs) in United States underground coal mines. The thermal environment of RAs is a concern because, if the thermal environment in an RA becomes severe, trapped miners could experience heat exhaustion or heat stroke, which is deadly. To prevent exposing RA occupants to heat stress, regulations for underground coal mine RAs mandate an apparent temperature (AT) limit of 35°C (95°F). To examine occupancy derating to meet the AT limit, NIOSH conducted RA thermal simulations with actual mine strata and temperature data using validated thermal simulation models. NIOSH examined occupancy derating for a portable 23-person tent-type RA and a portable 6-person rigid RA across a range of initial temperatures for the mine strata of its Experimental Mine. For these RAs, occupancy derating was necessary for mine temperatures as low as 60°F. NIOSH also examined occupancy derating for each of the RAs for five mines across the United States using measured worst-case temperatures and the mine strata of each mine. The results showed occupancy derating would be necessary for the mines with relatively warm initial temperatures. RA manufacturers and mines can use this information to ensure RAs do not exceed the AT limit.
