A comparison of heat stress indices in a hot-humid environment.

The results of a study of nine physically fit young men performing moderate exercise under various levels of hot-humid conditions are reported. Environmental stress and physiological strain data from the total of 72 test sessions were collected and computed in terms of heat stress and heat strain indices. Single and multiple factor correlation coefficients were calculated on the basis of 11 stress indices versus 4 strain indices. Most of the empirical heat stress indices correlated best with the mean skin temperature, whereas the rational indices correlated best with heart rate and sweat loss. Because of its ease of use, the WGT or the CET index may be the best choice for preliminary industrial surveys in hot-humid environments. A simple and convenient nomogram was developed on the basis of the test data relating increase in heart rate to temperature, humidity, and air velocity.