Understanding Heat Stress Measurement & Exposure Guidelines

Cheryl Allen,
Abstract Management of heat exposure in mining is becoming an important issue in increasingly deep and mechanized mines due to the potential of reduced productivity and increased risk of accidents. Currently heat stress management is based on providing a specific temperature/humidity (wet-bulb) environment to accommodate a certain level of continuous or intermittent physical activity. However to apply such a procedure, a better understanding of the instrumentation available to measure thermal parameters and the regulatory framework within which they are used is required.

An assessment of “heat stress” instruments funded by the DMRC, has found that traditional Wet Bulb Globe Temperature (WBGT) devices, as specified in many Provincial guidelines, may be of limited value in today’s instrumented mine, and furthermore that some of the basic measurements of these traditional instrument’s can not be substantiated. Consequently, a standard for temperature and relative humidity traceable measurements is proposed.

In Canada, the most extensively cited guideline of exposure limits is the ACGIH’s WBGT TLVs®, however there are three different versions in place depending on the Province. In a review of these guidelines, it was found that the actual temperature limits listed in the standard TLV® table are purely a function of how the work intensity has been categorized, they all use the same original data set so which might is correct or better is irrelevant. However, what is often omitted, even in earlier versions of the TLV’s®, is the importance of the weight/size of the individual in determining the metabolic work rate required for a specific activity. Currently, only one province recognizes the need to correct the TLV’s® in respect to weight.

Together, the potential limitations of instruments and the misinterpretation of the TLV’s® are just two aspects showing the need for a far greater understanding of the management of heat exposure.
Keywords: Heat Stress, Regulations, TLVs, Ambient Measurements, safety management, WBGT, Relative Humidity, Mining Health & Safety, Exposure Limits, mine environment
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