Prevention of heat strain by immersing the hands and forearms in water

The effectiveness of hand immersion in water at 10 degrees C, 20 degrees C and 30 degrees C as a technique for reducing heat strain in Royal Navy (RN) personnel has been investigated at the Institute of Naval Medicine (INM). Four subjects exercised at a moderate work rate, whilst wearing fire fighting clothing in an environmental chamber at 40 degrees C. The subjects reached heat strain safety limits within 45 minutes of commencing work at which point they rested in the heat for 30 minutes whilst they underwent one of four experimental conditions: without intervention (control); or with their hands immersed in water at 10 degrees C, 20 degrees C or 30 degrees C. The experiment was repeated on a further three days so that the subjects undertook each experimental condition in a balanced randomised order. During the control condition without hand immersion the subjects were unable to cool. Immersion of the hands in water (at 10 degrees C, 20 degrees C or 30 degrees C) significantly (P < 0.05) lowered body core (auditory canal) temperature within ten minutes. Assessing the effectiveness of this technique by the initial rates of core temperature reduction, revealed that immersion of the hands was more effective the colder the water. Following 20 minutes of hand immersion mean core temperature had dropped from 38.5C to: 36.9(standard deviation 0.19) degrees C, 37.3(0.18) degrees C, and 37.8(0.10) degrees C, in 10 degrees C, 20 degrees C and 30 degrees C water respectively. Cooling powers estimated from changes in mean body temperature were 334, 307 and 113 watts using 10 degrees C, 20 degrees C and 30 degrees C water respectively. These results indicate that hand immersion in water at a temperature of between 10 degrees C and 30 degrees C is an efficient means of cooling heat stressed personnel who have been exercising. This simple and effective technique may be applied to many industrial and military tasks to reduce heat strain, lower the risk of heat injury, and increase safe total work times in the heat. For the RN, hand immersion could be used in fire fighting, damage control and NBC operations where personnel alternately work and rest.