Thermal work limit (TWL) is an index defined as the 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).[1] The index is designed for self-paced workers and does not rely on estimation of actual metabolic rates. The index has been introduced into the United Arab Emirates[2] and Australia, resulting in a substantial fall in the incidence of heat illness in the latter.[3]