CONVECTIVE HEAT LOSS THROUGH CLOTHING I. Holm6r1, H. Nilssonl, G. Havenith2 and K. Parsons2 INational Institute for Working Life, Solna, Sweden 2Department of Human Sciences, Loughborough University, UK P INTRODUCTION Convection and evaporation comprise the most significant ways of heat exchange between the human body and the environment. Both convection and evaporation are sensitive to air motion and, consequently, are modified by work- er movements, external wind and their interaction. However, it seems that most of the methods for calculation of convective and evaporative heat losses in use do not accurately account for such dynamic effects, leading to errors in the heat balance calculations and, eventually, inaccurate risk assessments. Criticism of the IS0 7933 method has been raised on these grounds. Within the Biomed 2 research project “Assessment of the risk of heat disorders encountered during work in hot conditions (Heat Stress),” the problem has been analyzed and the result is presented in three papers. This frrst paper analyzes convective heat exchange through clothing and proposes ways of improving the consideration of dynamic effects. Bodv Surface Convection Convective heat loss at the surface of the human body has been studied for many years . The presently used formulas in international standards are It is observed that convective heat loss by equation 1 is 42 % higher than 2 and 3 at an air velocity of 1 m/s. Yet equations 2 and 3 give values in the upper range of a large number of reported formulas . h, = 12.1-v05 (3) IS07730 (1) hc = 3.5t3.2~~ for vu< 1 ms-’ (6) IS09233 (2) hc = S.~.V,O.~ for var > I mas-’ (6) IS0 9233 (3) I I In general, most of the studies only dealt with the effect of external wind on stationary subjects. The concept of net or relative air velocity was introduced to account also for the effects on convective heat exchange by body movements. This factor is described below. ClothinP Heat Transfer ~ I I The effect of clothing on dry heat exchange is defined and determined by the I 1 I insulation value (I). Burton proposed I At I= - DRY 293