Sweat loss (litres) = body weight before exercise (kg) – body weight after exercise (kg) + fluid consumed during exercise.

If sweating rate is adequate, evaporative cooling is determined ultimately by the water vapour pressure gradient between the wet skin and the air surrounding it.

The volume of sweat produced by each gland is dependent upon both the structure and the function of the gland, and total sweating rate in turn depends on both the recruitment of glands (active sweat gland density) and sweat gland output.

If sweating rate is adequate, evaporative cooling is determined ultimately by the water vapour pressure gradient between the wet skin and the air surrounding it.

If required sweat rate can be achieved by persons and it will not cause unacceptable water loss, then there is no limit due to heat exposure over an 8-hour shift.

An important improvement is the recognition that not all sweat evaporates (e.g., some drips) hence required sweat rate is related to required evaporation rate by:

If required sweat rate can be achieved by persons and it will not cause unacceptable water loss, then there is no limit due to heat exposure over an 8-hour shift.

Further investigation, however, showed that ET had serious disadvantages for use as a heat stress index, which led to the Predicted Four Hour Sweat Rate (P4SR) index.

Further investigation, however, showed that ET had serious disadvantages for use as a heat stress index, which led to the Predicted Four Hour Sweat Rate (P4SR) index.