Methodologies, limitations and perspectives of the occupational heat stress indeces
DOI:
https://doi.org/10.36125/ijoehy.v17i1.595Keywords:
occupational heat stress indeces, WBGT IndexAbstract
Climate change is intensifying heat exposure, with mounting evidence of adverse health impacts. Heat exposure is associated with both acute illnesses and chronic outcomes. Occupational settings represent a major context of concern, affecting both outdoor and indoor workers, and contributing not only to health effects but also to increased accident risk and reduced productivity.
In Italy, the principal legal framework for occupational health and safety is Legislative Decree No. 81/2008, which includes microclimate among physical agents but does not provide a dedicated section on thermal risk, clear definitions of microclimate-related risk, exposure limit values, or standardised sampling/measurement methods. As a result, risk management relies on general preventive obligations (e.g., employer risk assessment, exposure reduction, protection of vulnerable workers, training, and health surveillance) and on technical guidance and international standards.
Against this background, the overview critically examines two cornerstone approaches within ISO standardisation: the Wet Bulb Globe Temperature (WBGT; ISO 7243) and the Predicted Heat Strain (PHS; ISO 7933). WBGT, developed in the 1950s from military heat-illness prevention efforts, is widely used as a practical screening index. ISO 7243 specifies measurement principles and representative sampling periods and incorporates adjustments for clothing via Clothing Adjustment Values (CAV) and for metabolic rate (ISO 8996), while considering acclimatisation. However, WBGT does not predict individual physiological responses, its reference limits primarily address body temperature rise, and it has recognised constraints in environments with high humidity/low air movement and for vulnerable workers; instrumentation choices can also introduce error.
PHS emerged from revisions to the earlier Required Sweat Rate approach and is presented in ISO 7933 as an iterative heat-balance model estimating physiological strain in “average” healthy workers. It requires environmental inputs, metabolic rate, and clothing characteristics, and outputs a maximum allowable exposure time based on limits for dehydration and core (rectal) temperature, incorporating acclimatisation effects on sweating capacity. Strengths include its analytical, physiologically grounded structure; limitations include reduced applicability with protective clothing (≈1 clo), unsteady conditions, variable workloads, and changing clothing, as well as operational complexity and reliance on specialised software. Several studies have proposed adaptations of PHS for specific populations and sectors.
Overall, WBGT and PHS remain important but non-exhaustive components of heat-risk management. Future tools should be physiologically robust, operationally usable, valid across climates, adaptable to clothing and worker vulnerability, and linked to actionable, hierarchical control measures, while clarifying implications for health, work organisation, productivity, and economic outcomes.
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