The thermal work limit is a simple reliable heat index for the protection of workers in thermally stressful environments.

BACKGROUND Workers in many industries are exposed to thermally stressful work environments. Protection of the health of workers without unnecessarily compromising productivity requires the adoption of a heat index that is both reliable and easy to use. OBJECTIVES To evaluate the Thermal Work Limit (TWL), in a controlled environment and under field conditions, against these criteria. METHODS Volunteers performed graded work in a controlled thermal environment to determine the limiting workload for the conditions. Core temperature and heart rate were monitored as indicators of thermoregulation. In the field study, outdoor workers were monitored for signs of physiological strain in thermal environments which were characterized using both the traditional Wet Bulb Globe Temperature (WBGT) and the TWL. Abilities of each of these indices to accurately reflect the thermal stress on workers were evaluated. RESULTS In the controlled environment, the TWL was found to reliably predict the limiting workload. In the field study, TWL was a more appropriate and realistic index than WBGT, which was found to be excessively conservative. CONCLUSIONS The results confirm previously published studies evaluating TWL in underground environments, which have led to its widespread adoption in the Australian mining industry. The study extends the applicability of TWL to outdoor environments and generates management guidelines for its implementation.