Original article

Scand J Work Environ Health 1979;5(1):23-30    pdf


Evaluation of heat stress during sedentary work.

by Ljungberg A-S, Enander A, Holmer I

The aim of the investigation was to study physiological effects and subjective experience during sedentary work in two different climates (air temperature 40°C and relative humidity 40%, and 32°C and 80%, respectively). Four men and four women, all unacclimatized and of normal body weight and height, participated in the study. Earh subject was exposed to both climate conditions for 90 min. Body temperature, skin temperature, heart rate, and body weight loss were measured continuously. At certain intervals during exposure subjects rated perceived temperature and comfort. Significant differences in the physiological reactions to the two conditions were observed. Heart rate, mean skin temperature and sweat rate were higher under the 40°C temperature conditions than at 32°C. The mean rise in body temperature was approximately O.2-0.3°C. All subjects rated the climate at 40°C as warmer and more uncomfortable than at 32°C. During the last half hour of exposure, air velocity was increased with the aid of a fan. This action increased the heat loss at 32°C and resulted in a decrease in mean skin temperature although body temperature mainly remained unchanged. The increased air velocity had a positive effect on perceived comfort. The men had a higher sweat rate and reported more discomfort than the women. Indices such as the Swedish wet-bulb globe temperature and corrected effective temperature did not discriminate between the two climates, but they yielded lower values with decreased air velocity. On the other hand, indices based on heat balance analysis or calculations of sweat rate (heat stress index, predicted 4-h sweat rate and effective temperature) could more accurately predict the physiological and psychological strain.