The ADS's effect of repelling humans occurs at slightly higher than 44 °C (111 °F), though first-degree burns occur at about 51 °C (124 °F), and second-degree burns occur at about 58 °C (136 °F). In testing, pea-sized blisters have been observed in less than 0.1% of ADS exposures, indicating that second degree surface burns have been caused by the device. The radiation burns caused are similar to microwave burns, but only on the skin surface due to the decreased penetration of shorter millimeter waves. The surface temperature of a target will continue to rise so long as the beam is applied, at a rate dictated by the target's material and distance from the transmitter, along with the beam's frequency and power level set by the operator. Most human test subjects reached their pain threshold within 3 seconds, and none could endure more than 5 seconds.