Relationship between pain and tissue damage due to thermal radiation

Sites on the volar surfaces of the forearms of human subjects were blackened with India ink and exposed to thermal irradiances of from 50 to 400 mcal/cm 2 sec. The exposure time and skin temperature at which threshold pain occurred, and which produced minimal blistering within 24 hours, were noted. The thermal inertia (k⍴ c ) of the skin was shown to vary directly with the level of irradiance. The receptors effective in mediating the pain sensation were calculated to be at a depth of approximately 200 μ and to have a threshold of approximately 43.2℃. Tissue damage rates with respect to temperature were derived empirically so that damage integrated over the time for which skin temperature was elevated over the pain threshold was equated to unity. The substitution of the ratio of these rates with respect to temperature for the stimulus ratio, in the prediction of the observed discriminable steps in pain sensation intensity, yielded faithful reproduction of the just noticeable differences observed for pain through the range of this sensation. Submitted on September 17, 1958