Comparing different indexes to quantify occupational heat exposure

Introduction:  Occupational heat stress is a new concern in relation to local climate change linked to global change. The potential health and productivity impacts are well known, but quantitative analysis of impacts at different heat levels and the potential result of global heating is rare.    

Methods:  We calculated different heat indexes from a series of climate input data and compared the interpretation that emerged from standards and regulations for each index. Real climate conditions in 20 highly populated hot places were also used in the comparison. The aim was to assess the variability in impact assessment outcomes depending on the index used.    

Results:  We found that the different indexes produced different output numbers, but the risk assessments would create similar interpretation for many of these indexes. As an example, the comparison of calculated WBGT and UTCI shows that the four levels of assessed heat stress according to UTCI coincide closely with the rest break recommendations by ISO for WBGT.    

Discussion:  We compared more than 10 heat indexes applied to the climate conditions in 20 hot places, and we concluded that at the extreme heat exposure end it matters little which index one uses. The most important issue is to define the aim of interpretation guidelines: do the guidelines include safety margins? Do they cover all ages, genders, and other individual characteristics? Etc. Our recommendations will be fed into the discussions at ICOH about recommended heat hazard indicators.