Objectives In order to make recommendations to protect wildland firefighters (WLFFs) from heat-related illness, the role physical exertion plays on core body temperature (Tc) in the work environment needs to be considered. We aimed to estimate the association of time-varying job tasks with differing exertion levels on change in Tc, among WLFFs engaged in fire management activities, while controlling for ambient conditions and individual characteristics. In addition, we examined whether duration of tasks modified the relationship between task and change in Tc.
Methods We used data from The Wildland Firefighter Heat Related Illness study, a repeated measures study with individual-level data on 301 WLFFs from 2013 to 2016. Job tasks over one full shift were recorded and categorised into four levels (sedentary, light, moderate and high) based on estimated exertion levels. Tc was measured every 15 s using an ingestible sensor and personal monitors measured ambient conditions. The analysis used generalised estimating equations with an autoregressive correlation structure.
Results We found statistically significant associations between job tasks with increased physical demand and increases in Tc. When compared with sedentary tasks, the estimated increases in Tc for light, moderate and high activity tasks of average duration were 0.07°C (95% CI 0.02 to 0.11°C), 0.19°C (95% CI 0.15 to 0.23) and 0.44°C (95% CI 0.39 to 0.49°C), respectively. In addition, we found evidence of interaction between task type and duration.
Conclusions This study supports the hypothesis that occupational exposure to physical exertion increases Tc, highlighting the need to update recommendations to protect WLFFs from heat-related illness.
- health and safety
- fire fighters
- physical work
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Contributors MRW participated in the study design, data acquisition, data analysis, interpretation of data and wrote the manuscript. SC participated in the study design, data analysis, interpretation of data, drafting and revising of the manuscript, and overall advising for MRW. JAS participated in conception, design, data acquisition, interpretation of data and aided in revising the manuscript. JWD participated in the conception, design, data acquisition, interpretation of data and aided in revising the manuscript.
Funding This study was supported by funding from the United States Department of Agriculture and Forest Service Fire and Aviation Management Group in addition to the National Wildfire Coordination Group, Department of Interior, Bureau of Land Management, National Park Service, Fish and Wildlife Service, and Bureau of Indian Affairs.
Disclaimer The views and conclusions contained herein are those of the authors and should not be interpreted as necessarily representing the official policies or endorsements, either expressed or implied, of the United States Department of Agriculture, Forest Service, National Wildfire Coordination Group or the Department of Interior.
Competing interests None declared.
Patient consent for publication Obtained.
Ethics approval This study was approved by The University of Montana–Missoula Institutional Review Board. Title: Quantification of physiological heat stress in wildland firefighters. IRB Protocol No. 111-14.
Provenance and peer review Not commissioned; externally peer reviewed.
Data availability statement Data are available on reasonable request for up to 7 years.