Prediction of the average skin temperature in warm and hot environments

The prediction of the mean skin temperature used for the Required Sweat Rat e index was criticised for not being valid in conditions with high radiatio n and high humidity. Based on a large database provided by 9 institutes, 19 99 data points obtained using steady-state conditions, from 1399 experiment s and involving 377 male subjects, were used for the development of a new p rediction model. The observed mean skin temperatures ranged from 30.7 degre es C to 38.6 degrees C. Experimental conditions included air temperatures ( T-a) between 20 and 55 degrees C, mean radiant temperatures (T-r) up to 145 degrees C, partial vapour pressures (P-a) from 0.2 to 5.3 kPa, air velocit ies (v(a)) between 0.1 and 2 m/s, and metabolic rates (M) from 102 to 620 W . Rectal temperature (T-re) was included in the models to increase the accu racy of prediction. Separate models were derived for nude (clothing insulat ion, I-cl, less than or equal to 0.2 do. where 1 do = 0.155 m(2) . degrees C . W-1, which is equivalent to the thermal insulation of clothing necessar y to maintain a resting subject in comfort in a normally ventilated room, a ir movement = 10 cm/s, at a temperature of 21 degrees C and a humidity of l ess than 50%) and clothed (0.6 less than or equal to I-cl less than or equa l to 1.0 clo) subjects using a multiple linear regression technique with re -sampling (non-parametric bootstrap). The following expressions were obtain ed for nude and clothed subjects, respectively: T-sk = 7.19 + 0.64T(a) + 0. 061T(r) + 0.198P(a) - 0.3481v(a) + 0.616T(re) and T-sk =12.17 + 0.020T(a) 0.044T(r) + 0.194P(a) - 0.253v(a) + 0.0029M + 0.513T(re). For the nude and clothed subjects, 83.3% and 81.8%, respectively, of the predicted skill te mperatures were within the range of +/-1 degrees C of the observed skin tem peratures. It is concluded that the proposed models for the prediction of t he mean skin temperature are valid for a wide range of warm and hot ambient conditions in steady-state conditions, including those of high radiation a nd high humidity.