Kestrel instruments which measure Thermal Work Limit (TWL)
Thermal Work Limit:
(TWL) is defined as the limiting (or maximum) sustainable metabolic rate that well-hydrated, acclimatized individuals can maintain in a specific thermal environment, within a safe deep body core temperature (< 38.2 °C or 100.8 °F) and sweat rate (< 1.2 kg or 2.6 lb per hour). The index is designed for self-paced workers and does not rely on estimation of actual metabolic rates, a process that is difficult and subject to considerable error.