An advanced empirical model for quantifying the impact of heat and climate change on human physical work capacity

Abstract

Occupational heat stress directly hampers physical work capacity (PWC), with large economic consequences for industries and regions vulnerable to global warming. Accurately quantifying PWC is essential for forecasting impacts of different climate change scenarios, but the current state of knowledge is limited, leading to potential underestimations in mild heat, and overestimations in extreme heat. We therefore developed advanced empirical equations for PWC based on 338 work sessions in climatic chambers (low air movement, no solar radiation) spanning mild to extreme heat stress. Equations for PWC are available based on air temperature and humidity, for a suite of heat stress assessment metrics, and mean skin temperature. Our models are highly sensitive to mild heat and to our knowledge are the first to include empirical data across the full range of warm and hot environments possible with future climate change across the world. Using wet bulb globe temperature (WBGT) as an example, we noted 10% reductions in PWC at mild heat stress (WBGT = 18°C) and reductions of 78% in the most extreme conditions (WBGT = 40°C). Of the different heat stress indices available, the heat index was the best predictor of group level PWC (R2 = 0.96) but can only be applied in shaded conditions. The skin temperature, but not internal/core temperature, was a strong predictor of PWC (R2 = 0.88), thermal sensation (R2 = 0.84), and thermal comfort (R2 = 0.73). The models presented apply to occupational workloads and can be used in climate projection models to predict economic and social consequences of climate change.

The impact of heat on human physical work capacity; part III: the impact of solar radiation varies with air temperature, humidity, and clothing coverage

“…The secondary aim was to generate correction factors so PWC can be modelled outdoors using heat stress indices that do not ordinarily account for SOLAR in their calculation (namely T wb , Humidex, and Heat Index). The final aim was to test the sensitivity of WBGT and UTCI to added solar heat loads, confirming whether our earlier published functions (Foster et al, 2021b) can be used for indoor and outdoor work settings.…”

“…Environmental heat exposure has a negative impact on human health and physical working capacity (PWC) (Flouris et al, 2018;Foster et al, 2021bFoster et al, , 2021aIoannou et al, 2021), incurring significant economic damage through its impact on workplace productivity (Hsiang et al, 2017;Hübler et al, 2008;Zander et al, 2015). Understanding the full effect of heat on PWC is required for economic cost and general impact analysis associated with climate change and hot weather events in general (Hsiang et al, 2017).…”

“…Understanding the full effect of heat on PWC is required for economic cost and general impact analysis associated with climate change and hot weather events in general (Hsiang et al, 2017). While models of PWC based on various climate indices have recently been developed (Dunne et al, 2013;Foster et al, 2021b;Kjellstrom et al, 2018), at present, none account for the effect of solar or general thermal radiation. Given that many occupational tasks involve outdoor exposure, not accounting for thermal radiation is presently a significant limitation.…”

“…In 338 trials with work paced based on heart rate (limit of 130 b•min -1 , [moderate to heavy work]) our group recently developed empirical models for PWC based on a suite of heat stress indices (Foster et al, 2021b). However, those trials were conducted without added solar radiation (SOLAR).…”

“…Hence, to use the equations for both conditions with and without SOLAR, correction factors may be needed, especially for heat stress indices that do not intrinsically account for this parameter. For example, although wet bulb temperature (T wb ), Humidex, and Heat Index strongly predict PWC in shaded environments (Foster et al, 2021b), they are calculated from T a and Rh alone, and therefore cannot accommodate conditions in which there is additional SOLAR. Moreover, while wet-bulb globe temperature (WBGT) and universal thermal climate index (UTCI) account for radiation in their calculation (Havenith and Fiala, 2015), their correct sensitivity to radiation must also be validated empirically.…”