Practical Pre-cooling Methods for Occupational Heat Exposure
Summary of Report
Miss Emily Watkins, Dr Mark Hayes, Dr Peter Watt, Dr Alan Richardson
Pre-cooling is a method used to reduce core temperature, heart rate, and the sensation of being hot when individuals are exposed to hot environments. The aim is to reduce core temperature before the heat exposure, meaning an individual will stay at a safe core temperature for longer. In our previous study “Fire Service Instructors’ Working Practices: A UK Survey” it was indicated that few instructors used pre-cooling and those that did were using a variety of methods. This study aimed to assess 3 practical pre-cooling methods currently being used by instructors, to identify which method is the most beneficial in terms of reducing physiological and perceptual strain experienced from a heat exposure. Inflammatory responses were also investigated, as they can be markers of an increased risk of a cardiovascular event. The pre-cooling methods used were ice slurry consumption, phase change vest, and forearm cooling.
The study was conducted in a laboratory at the University of Brighton, so that exercise intensity and heat exposure could be controlled. Eleven male participants took part. Participants donned firefighter protective clothing, then pre-cooled for 15min. Ice slurry pre-cooling consisted of consuming 500ml of slurry made with orange squash. Forearm cooling involved the immersion of both forearms in a bucket of cold tap water. Phase change vest cooling involved donning the Dräger Comfort Vest CVP 5220. A control session also occurred where no cooling intervention was used. After 15min participants entered a heat chamber (49.6 ± 0.8°C and 15.4 ± 1.2% relative humidity) where they alternated between 5min of treadmill walking (4km.h-1 with a 1% gradient) and 5min resting for 45min. The exercise was designed to cause similar core temperature and heart rate responses as previously recorded in instructors.
The only cooling method to successfully reduce core temperature prior to heat exposure was the ice slurry. Core temperature was 0.24 ± 0.09ºC lower following the 15min ice slurry cooling, whilst core temperature remained the same during the other methods. The ice slurry continued to have an effect on core temperature for up to 20min into the heat exposure, with core temperature being 0.18 ± 0.14ºC lower than resting temperature. Core temperature in the ice slurry trial did not rise above resting levels until 30min into the heat exposure. In comparison, the forearm and phase change vest trial had no impact on core temperature, with changes being similar to that recorded in the control trial.
Participants reported feeling cooler in the forearm cooling trial and in the ice slurry trial. This was reported for around 30min of the heat exposure. However, as the forearm cooling did not change core temperature, this could potentially be dangerous, as individuals may think they are cooler so work harder or for longer, putting themselves at a greater risk of a heat illness.
Heart rate, inflammatory markers, perceptions of effort, and overall skin temperature during heat exposure were all not effected by cooling types.
In conclusion, 500ml of ice slurry should be consumed 15min prior to a wear to reduce core temperature and thermal sensation. Forearm cooling and the phase change vest tested in this study are not recommended, as they do not reduce physiological strain. In addition forearm cooling may be dangerous as feeling cooler may mask increasing core temperatures.