EFFECTS OF THERMAL, PERSONAL AND BEHAVIORAL-FACTORS ON THE PHYSIOLOGICAL STRAIN, THERMAL COMFORT AND PRODUCTIVITY OF AUSTRALIAN SHEARERS INHOT WEATHER

Multiple-regression analyses were used to evaluate the separate and co mbined effects of factors that are commonly expected to influence stra in and productivity in a hot workplace. Forty-three men were studied t hroughout 54 man-days of shearing sheep and pressing wool bales, in ai r temperatures 19-41 degrees C and Wet-bulb Globe Temperature index (W BGT) 16-29 degrees C; 43% of the observations of WBGT exceeded 26.7 de grees C, the Threshold Limit Value (TLV) for the subjects' work rate o f 400 W. Subjects were men of age 18-59 years, fat-free mass 44-77 kg, and body fat content 11-26%, who had drunk an estimated 0-207g alcoho l the previous evening. Afternoon mean values of rectal temperature (T -re) exceeded 38.0 degrees C (maximum 38.4 degrees C) in 4 of the 15 o bservations made when WBGT > TLV, and in none of those made when WBGT < TLV. Over the 10h work day the subjects sweated 2.4-9.9 kg, but they replaced their sweat losses so successfully that warmer weather and h eavier sweating were not accompanied by significantly greater dehydrat ion. Surprisingly, the fatter men felt cooler, and those who had drunk more alcohol the previous evening had lower T-re and tended to be mor e productive. Age was not associated with any measured response. All f actors together explained barely half the observed variation in T-re a nd thermal comfort, and almost none of the variation in productivity. The findings highlight the uncertainty inherent in attempts to define safe limits for occupational heat stress; they show how such uncertain ty could restrict the usefulness in the shearing industry of current h eat-stress guidelines; and they demonstrate the effectiveness of the b ehavioural responses that permit shearers to perform sustained strenuo us work in a hot environment without excessive physiological strain.