NF EN ISO 7933, X35-204 (08/2023)

This document describes a model [the Predictable Heat Stress (PHS) model] for the analytical determination and interpretation of heat stress (in terms of fluid loss and rectal temperature) experienced by an average person in a hot environment and determines the admissible exposure limit durations during which the physiological stress is acceptable for 95% of the exposed population (the maximum tolerable rectal temperature and the maximum tolerable water loss are not exceeded by 95% of the exposed people). The various terms involved in this predictive model and, in particular, in the heat balance, make it possible to determine the respective shares taken by the various physical parameters of the environment in the thermal stress experienced by the average person. This document thus makes it possible to determine which parameter or set of parameters it is possible to act on, and to what extent, in order to reduce the risk of excessive physiological strain. In its current form, this assessment method cannot be used in the case of wearing special protective clothing (e.g. fully reflective, cooled and ventilated clothing, waterproof suits). This document is not intended to predict the physiological response of any given person, but only concerns an average person who is healthy and able to do their job. It is therefore intended for use, among others, by ergonomists and occupational hygienists, as the results may require interpretation by experts. Recommendations on how and when to use this model are given in ISO 8025.
(Automatic translation from French)