Estimated work ability in warm outdoor environments depends on the chosen heat stress assessment metric

Abstract

With a view to occupational effects of climate change, we performed a simulation study on the influence of different heat stress assessment metrics on estimated workability (WA) of labour in warm outdoor environments. Whole-day shifts with varying workloads were simulated using as input meteorological records for the hottest month from four cities with prevailing hot (Dallas, New Delhi) or warm-humid conditions (Managua, Osaka), respectively. In addition, we considered the effects of adaptive strategies like shielding against solar radiation and different work-rest schedules assuming an acclimated person wearing light work clothes (0.6 clo). We assessed WA according to Wet Bulb Globe Temperature (WBGT) by means of an empirical relation of worker performance from field studies (Hothaps), and as allowed work hours using safety threshold limits proposed by the corresponding standards. Using the physiological models Predicted Heat Strain (PHS) and Universal Thermal Climate Index (UTCI)-Fiala, we calculated WA as the percentage of working hours with body core temperature and cumulated sweat loss below standard limits (38 °C and 7.5% of body weight, respectively) recommended by ISO 7933 and below conservative (38 °C; 3%) and liberal (38.2 °C; 7.5%) limits in comparison. ANOVA results showed that the different metrics, workload, time of day and climate type determined the largest part of WA variance. WBGT-based metrics were highly correlated and indicated slightly more constrained WA for moderate workload, but were less restrictive with high workload and for afternoon work hours compared to PHS and UTCI-Fiala. Though PHS showed unrealistic dynamic responses to rest from work compared to UTCI-Fiala, differences in WA assessed by the physiological models largely depended on the applied limit criteria. In conclusion, our study showed that the choice of the heat stress assessment metric impacts notably on the estimated WA. Whereas PHS and UTCI-Fiala can account for cumulative physiological strain imposed by extended work hours when working heavily under high heat stress, the current WBGT standards do not include this. Advanced thermophysiological models might help developing alternatives, where not only modelling details but also the choice of physiological limit criteria will require attention. There is also an urgent need for suitable empirical data relating workplace heat exposure to workability.

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Acknowledgements

Initial ideas to this study were developed during the “International Workshop On Occupational Heat Exposure Indicators For Use In Climate Change Impact Assessments” held at Lund University from 13 to 15 August 2012 with support from the Swedish Council for Working Life and Social Research (FAS), the Centre for Medicine and Technology for Working Life and Society (Metalund), the Strategic Research Area Epidemiology for Health (Epihealth) and the Swedish International Development Cooperation Agency (Sida). Bruno Lemke’s input was supported by the internal research funds of the Nelson-Marlborough Institute of Technology. Tord Kjellstrom’s contribution was supported by the HEAT-SHIELD project under EU framework programme Horizon 2020 (grant no. 668786). The authors are particularly grateful to Ms. Mina Sandusky for thorough and excellent language editing of this manuscript.

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Bröde, P., Fiala, D., Lemke, B. et al. Estimated work ability in warm outdoor environments depends on the chosen heat stress assessment metric. Int J Biometeorol 62, 331–345 (2018). https://doi.org/10.1007/s00484-017-1346-9

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Keywords

  • Climate change
  • Heat stress
  • Productivity
  • Work capacity
  • Model
  • Index