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Heart rate and body temperature responses to extreme heat and humidity with and without electric fans

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journal contribution
posted on 2015-02-27, 15:20 authored by Nicholas M. Ravanelli, Simon HodderSimon Hodder, George HavenithGeorge Havenith, Oliver E. Jay
Patz et al1 described the projected effects of more prolonged and severe heat waves on human health. A simple, low-cost cooling device is an electric fan. A Cochrane review2 concluded “no evidence currently exists supporting or refuting the use of electric fans during heat waves” for mortality and morbidity. However, public health guidance typically warns against fan use in hot weather. Recommended upper limits range from 32.3°C (90°F) at 35% relative humidity (RH) to the high 90s (96-99°F; 35.6-37.2°C, no RH stated2). The skin-to-air temperature gradient reverses with rising environmental temperature, causing dry heat transfer toward the body via convection rather than away from it. Fan use would increase this dry heat transfer, potentially accelerating body heating3,4; however, the efficiency of sweat evaporation from the skin would be simultaneously increased. Thus, fans could still improve net heat loss. Sweat evaporation declines with increasing humidity, so in more humid environments fans may not prevent heat-induced elevations in cardiovascular (heart rate, HR) and thermal (core temperature) strain. This study examined the influence of fan use on the critical humidities at which hot environments can no longer be physiologically tolerated without rapid increases in HR and core temperature.


This research was supported by discovery grant 386143-2010 from the Natural Sciences and Engineering Research Council of Canada (held by Dr Jay).



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JAMA: Journal of the American Medical Association






725 - 725 (2)


RAVANELLI, N.M. ... et al., 2015. Heart rate and body temperature responses to extreme heat and humidity with and without electric fans. JAMA: Journal of the American Medical Association, 313 (7), pp. 724 - 725.


© American Medical Association (AMA)


AM (Accepted Manuscript)

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This work is made available according to the conditions of the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0) licence. Full details of this licence are available at: https://creativecommons.org/licenses/by-nc-nd/4.0/

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This article was accepted for publication in the Journal of the American Medical Association [© American Medical Association] and the definitive version is available at: http://dx.doi.org/10.1001/jama.2015.153