The effect of pulse-modulated thermal radiation on the time-intensity relationship for dermal pain

A simple experimental model was used to examine the relationship between modulation and hazard for thermal bioelectromagnetic effects. The inner forearms of 11 human volunteers were exposed to continuous and pulse-modulated thermal radiation from an incandescent light source. The time of irradiation required to produce threshold pain sensation was measured as a function of the average power density (450-2500 m W cm-2), pulse repetition frequency (continuous, 0.4 Hz, 8.0 Hz) and duty cycle (continuous, 0.33, 0.50). The resulting 32 sets of data could be described by a single power function expression which relates time and power density through a regression slope. The slope was found to depend on the modulation of the radiation, but not on the age of the subject or wet bulb globe temperature (WBGT). The minimum average power density which could elicit pain within 200 sec (an effective threshold intensity) was determined to be independent of modulation, regression slope, subject age and WBGT.