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 the more relevant facets of workplace assessment. Based on the predicted heat strain (PHS) 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 subjective (metabolic rate and thermal clothing insulation) parameters. As far as the measurement of microclimatic parameters is concerned, ISO 7726 Standard suggests minimum and maximum accuracy values. On the other hand, for subjective measurements the situation does not appear so clear since the metabolic rate accuracy requirements are strictly related to the calculation method, whereas any accuracy 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 assessment, this work reports a sensitivity analysis of the PHS model to its independent variables. The results obtained 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.