The role of Measurement Accuracy on the Heat Stress Assessment according to ISO 7933: 2004.

The thermo-hygrometric risk analysis, regulated by several International Standards, is one of more relevant facets of workplaces assessment. Based on the PHS (Predicted Heat Strain) model, the last version of ISO Standard 7933 devoted to the hot stress evaluation requires the measure of four physical (air temperature, mean radiant temperature, humidity and air velocity) and two sub-jective (metabolic rate and thermal clothing insulation) parameters. As far the measurement of mi-croclimatic parameters is concerned, ISO 7726 Standard suggests minimum and maximum accuracy values. On the contrary hand, for subjective ones the situation does not appear so clear since the metabolic rate accuracy requirements are strictly related to the calculation method, whereas any ac-curacy is actually suggested for the clothing insulation evaluation. In order to evaluate the effect of the measurement accuracy on the reliability of the hot stress as-sessment, this work reports a sensitivity analysis of the PHS model to its independent variables. The obtained results clearly show that the mean radiant temperature measurement appears a tricky matter since only an error within the accuracy range can result in a very strong overestimation (up to 5 hours) of allowable exposure times.