Predicting increases in skin temperature using heat stress indices and relative humidity in helicopter pilots

We used measurements of heat stress in the cockpit of Bell 206 and 212 helicopters manned by a crew of two to predict changes in the skin temperatures of 50 pilots over a 1-h ground standby period. Cockpit wet bulb globe temperatures increased from 28.1 +/- 5.6 degrees C to 32.9 +/- 3.9 degrees C over the 1-h ground standby period. Skin temperatures increased from 34.7 +/- 1.1 to 35.4 +/- 1.1 degrees C, while heart rate increased from 79.4 +/- 9.6 to 82.6 +/- 9.8 bpm. Cockpit wet bulb temperatures explained 26.9% of the variance of the increase in skin temperature (P = 0.0002). Wet bulb globe temperatures, discomfort index and dry bulb temperatures did not improve the predictive value of wet bulb temperatures alone. Relative humidity was not significantly associated with the increase in skin temperature. We conclude that wet bulb temperatures predict changes in skin temperature as well as other heat stress indices. Furthermore, despite high cockpit temperatures, pilots experienced only minimal strain during the 1-h ground standby period. Extrapolation of our results to the effects on body temperature of higher degrees of heat stress and physical activity is unwarranted and deserves further study.