Thermal work limit
From Wikipedia, the free encyclopedia
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] TWL recommends a maximum metabolic rate based on environment, clothing, and acclimatization to achieve thermal equilibrium within acceptable limits of the metabolic rate.[2] The index is designed for self-paced workers and does not rely on estimation of actual metabolic rates. Self-paced workers are defined as those not subjected to excessive external pressure from other individuals or those offering financial incentives and are well informed of issues when working in the heat.[1] The index has been introduced into the United Arab Emirates[3] and Australia, resulting in a substantial fall in the incidence of heat illness in the latter.[4]
The idea of a thermal work limit (TWL) was developed by Graham Bates and Derrick Brake in 1997 to address limitations in earlier occupational heat-stress assessment methods, such as Wet-Bulb Globe Temperature (WBGT), that relied on metabolic approximations and fixed work-rest guidelines.[5] TWL was presented in response to these limitations as a rational, more direct method in comparison to existing indices that were either overly conservative or insufficiently adaptive to work environments. Building onto the heat indices such as Wet-Bulb Globe Temperature and Predicted Heat-Stress (PHS), thermal work limit incorporates earlier research into human heat balance and adds factors such as moisture transfer between the body, clothing, and environment. TWL and its management protocols have been introduced into several industrial operations where workers are subject to thermal stress including mining and labor intense industries, like construction.[2][6] TWL was first implemented into Australia and the UAE in the early 2010's after field testing in Abu Dhabi and Dubai demonstrated it's effectiveness in reducing thermal stress while maintaining work productivity, which led to its adoption in various work safety and health policies.[2][7] Since the introduction of TWL-based policies in the Australian mining industry, the amount of man-hours lost due to serious heat illness has fallen from 12 million to 6 million, and the amount lost due to all heat illness incidences has fallen from 31 million to 18 million.[8]
