Establishing heat stress indicators for work in a warming world: multi-country field evaluation and consensus recommendations

Abstract

BACKGROUND AND AIM: One third of the world labour force is frequently exposed to high heat stress at work, leading to significant health and labour implications. In a series of studies, we identified and validated the available thermal stress indicators (TSIs) for their capacity to protect individuals who work in the heat. METHODS: We conducted a systematic review to identify all TSIs and provide reliable information regarding their use. Then, we identified the criteria to consider when adopting a TSI and we weighed their relative importance using a Delphi exercise with 20 experts from 12 countries. Finally, we conducted field experiments across nine countries (372 workers during 893 full work shifts) to evaluate the efficacy of the meteorology-based TSIs for protecting individuals working in the heat. RESULTS: Our search identified 340 instruments and indicators developed between 200 BC and 2019 AD. Of these, 187 can be mathematically calculated utilizing only meteorological data. Of these meteorology-based TSIs, 127 were developed for people who are physically active, and 61 of those are eligible for use in occupational settings. Two Delphi iterations were adequate to reach consensus within the expert panel (Cronbach’s α=0.86) for 17 criteria with varying weights to be considered when adopting a TSI. These criteria considered physiological parameters such as core/skin/mean body temperature, heart rate, and hydration status, as well as practicality, cost effectiveness, and health guidance issues. In the third study, when evaluated against the 17 Delphi criteria, the 61 meteorology-based TSIs for occupational settings scored from 4.7 to 55.4%. The indoor (55.4%) and outdoor (55.1%) Wet-Bulb Globe Temperature and the Universal Thermal Climate Index (51.7%) scored higher compared to other TSIs (4.7-42.0%). CONCLUSIONS: We found that three TSIs are more efficacious and should be adopted to support evidence-based decision making and protect individuals who work in the heat.