Optical radiation hazards associated with the use of neodymium yttrium aluminum garnet lasers were investigated. Several Class IV laser systems operating at a pulse repetition frequency of 20 hertz were tested for scattered laser radiation and plume radiation during typical enclosed metal welding operations. Continuous power and integrated energy measurements were made with a radiometer equipped with a calibrated silicon photodiode detector. Spectral irradiance was measured with a spectroradiometer, and ultraviolet radiation was measured with a radiometer fitted with special ultraviolet sensitive detectors. Normalized scattered radiation at 1 meter varied markedly with the base material, with platinum giving the highest value. Radiation level also was influenced by the viewing angle and direction of the weld. The highest spectral irradiance value measured was 0.11 microWatts per square centimeter per nanometer at 350 nanometers. Very low levels of ultraviolet radiation were found. The total average irradiance of the plume radiation slightly exceeded the American National Standards Institute Maximum Permissible Exposure Limit of 0.000001 Watts per square centimeter. The authors conclude that Class IV lasers can present radiation hazards to the eyes and skin of unprotected operators. Protective eyewear with the appropriate optical density will prevent ocular damage.
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