Patterns of Heat Strain Among a Sample of US Underground Miners

Abstract

Objective-This study characterizes physiological measures of heat exposure among US underground miners.Methods-Core body temperature measured by using ingestible sensors during subjects' normal work shifts was categorized into four temperature zones: less than 37.5 °C, 37.5 °C to less than 38 °C, 38 °C to less than 38.5 °C, and more than or equal to 38.5 °C.Results-On average, subjects changed temperature zones 13.8 times per shift. Temperatures increased above the recommended limit of 38 °C nearly 5 times per shift for an average of 26minutes each episode.Conclusions-Unlike previous heat stress research that reported only maximum and mean temperature measurements, this analysis demonstrates a dynamic pattern of physiologic heat strain, with core body temperatures changing frequently and exceeding the 38 °C limit multiple times per shift. Further research is needed on the impact of multiple short-term, intermittent heat exposures on miners. Keywords core body temperature; heat stress; mining Heat stress is a growing issue in US mining. Heat stress, which refers to the total heat load placed on the body, can lead to heat strain, which is the physiologic effect of heat exposure. Because of increasing mineral consumption worldwide and the use of new technologies, underground mines are expanding to greater depths; globally, coal and metal mines have reached depths of 1500 and 4500 m, respectively. 1 As mines expand to deeper, hotter levels, the risk of heat strain and subsequent heat-related illness among miners will likely increase. Differences in heat exhaustion incidence by depth of mine have been reported.

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