Measurement of Heating of the Skin During Exposure to Infrared Radiation

¹ From the Air Crew Equipment Laboratory, U.S. Naval Air Material Center, Philadelphia, the Aviation Medical Acceleration Laboratory, U.S. Naval Air Development Center, Johnsville and the University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania

For the case of nonpenetrating radiation, it is shown that the change in surface temperature depends upon the intensity of effective heat supplied, duration of heating and thermal inertia for surface heating. The latter is expressed as the product of , the thermal conductivity, , the density, and c, the specific heat. An equation relating the factors mentioned above is derived and the limitations of its application with respect to duration of of heating and other factors are shown. A sensitive apparatus is described by means of which a test surface can be heated or cooled while its temperature is accurately measured without contact with the surface. Using this apparatus, values of c were determined for the unblackened surface of an inert substance, masonite and for the unblackened surface of intact, living, human skin. Relatively constant c values were obtained during periods of heating lasting over 2 minutes. The mean value and its standard deviation of the c product for dry skin of rested subjects in thermal equilibrium at normal room temperatures was calculated to be 108 ± 8 x 10^–5 cal²/cm⁴/°C²/ sec. Because of the mild heating involved in the method employed, its further use for cutaneous blood flow studies is suggested. The apparatus may also be used to study the relationships between temperature sensation and temperature, and the derivatives of the latter with respect to time.