Wet-bulb globe temperature (WBGT)—its history and its limitations[1]
Summary
This review traces the history and the limitations of wet-bulb globe temperature (WBGT), described as the most widely used index of heat stress, and observes that many users appear unaware of both. It describes the index's development during the 1950s as a means of reducing heat illness in United States military training, where the innovations were replacing simple temperature and humidity measurements with an index that also accounts for sun and wind, using casualty data to identify hazardous levels, and applying graduated restrictions to vulnerable trainees. The review then sets out the limitations: WBGT gives less accurate assessment where sweat evaporation is restricted by high humidity or low air movement, and interpretation of observed WBGT levels requires careful evaluation of people's activity, clothing and many other factors. It also reports that accuracy has declined through measurement error and calibration problems, and recommends measuring individual elements of the thermal environment separately rather than relying on WBGT alone.
So what
Events that trigger activity restriction or cancellation on a single WBGT number should note this review's claim that the index performs least well in humid or still conditions, which are common in crowded outdoor venues. Recording how WBGT was measured, and logging humidity and air movement separately, makes a threshold decision easier to defend afterwards. The paper is a historical and methodological critique, not a study of event outcomes.
Read the paper
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