Impact of Fan Use on Physical Work Capacity in Extreme Heat

Abstract

Emerging evidence suggests that electric fan use can reduce thermoregulatory and cardiovascular strain at air temperatures as high as 42°C during rest. However, there is a dearth of empirical evidence relating to the safety limits for fan use at various combinations of air temperatures and humidity, and how their use impacts physical work capacity (PWC). PURPOSE: The aim of the current study is to provide new threshold limit values for electric fan use during physical work. METHODS: Sixteen young adult males (heterogenous in fitness and anthropological characteristics) performed ~20 trials, consisting of 1 hour of treadmill walking at a fixed heart rate of 130 beats·min-1. The first experimental trial was conducted in a reference environment with no heat-stress (15°C, 50% rh). The remaining trials were conducted at the same fixed heart rate for a maximum of 1 hour at 30-50°C at various humidities. Each experimental trial was conducted with and without electric fans. The PWC in each heat-stress trial was defined as the total energy expended during 1 hour of treadmill walking and was expressed relative (%) to that expended during the reference condition. The study cohort was split into two subgroups with one group performing trials in minimal clothing (shorts only) whilst the second group undertook trials wearing protective clothing covering the legs, torso and arms (e.g. coveralls). RESULTS: Based on individual responses to fan exposure during moderate to heavy work undertaken wearing minimal clothing, forced convection was always beneficial at air temperatures ≤34°C. Between 34 and 43°C, a consistent fan benefit was only observed between 40 and 60% relative humidity, with lowered PWC above and below. In contrast, when protective clothing was worn, the beneficial impact of fans between 34 and 43°C was eroded with negligible effects on PWC observed. PWC was consistently impaired by fan use at air temperatures >43°C. CONCLUSION: These empirical data will facilitate the formulation of comprehensive threshold limit values for fan use during physical work based on biophysical parameters. Funding was provided by ‘Heat-Shield’, European Union's Horizon 2020 research and innovation programme under the Grant agreement no. 668786.