The Development of a Practical Heat Stress Assessment Methodology for Use in UK Industry

A series of ten experiments were conducted at the Human Thermal Environments Laboratory at Loughborough University to compare the validity of ISO 7933 Required Sweat Rate (SWreq) and Predicted Heat Strain (PHS) index predictions with observed physiological data.

Comparisons were made between the predicted and observed sweat rates and the time it took core temperature to reach 38 C (Duration Limit Exposures). The results showed that neither the SWreq nor the modified SWreq model were valid predictors of Duration Limit Exposures (DLE) and predicted sweat rate for people wearing protective clothing in warm humid environments.

The PHS DLE predictions were more representative of the ISO predictions that the observed DLEs in all but one experiment.

Although the PHS model predictions of sweat rate were an improvement on the ISO predictions.

The model also significantly underestimated the observed sweat rates.

Following the validity study, a heuristic evaluation of the usability of ISO 7933 was also performed.

This found that the standard is unnecessarily scientific and may not encourage users to use it.