The basic concept of laser hazard classification with four fundamental risk groups and several subclasses is well understood by most laser users. However, many readers of laser safety standards are frequently puzzled by the rigid measurement conditions applied for hazard classification, even if this is normally a task performed by the laser manufacturer and not by a laser user or a Laser Safety Officer. The historical rationale for the measurement conditions is provided and it is emphasized that the aim of each measurement is to simulate a wide range of ocular exposure conditions that would be reasonably foreseeable worst-case viewing conditions during the use of the laser product. Measurements, if needed to compare human exposures with the maximum permissible exposure limits, emphasize actual exposure conditions and generally do not match the measurement used for hazard classification.

Magnifying optics can increase the hazards for intrabeam viewing of lasers. Although it is rather straightforward to evaluate these increased hazards for point-source lasers at distance, limited information is available for determining the hazards from viewing extended-source lasers from within the beam when magnifying optics are used. Since intrabeam viewing of nearly all lasers results in an extremely small retinal image, commonly known as a “point source,” extended-source maximum permissible exposures (MPEs) are seldom applicable; however, a substantial correction factor is allowed for extended-source lasers in the determination of the MPE. In those rare cases where an extended-source laser is viewed by an optical aid, it is important to avoid applying an incorrect and sometimes very large extended-source correction factor. Extended-source lasers were constructed and then measured to determine if standard hazard classification techniques, mainly developed for point-source lasers, would adequately assess the true optical viewing hazards from viewing extended-source lasers with telescopes. It was found that current techniques are adequate since telescopes would normally be expected to be used at tens or hundreds of meters from the laser source, although purposeful exposure at close distance would require specialized hazard evaluation techniques.

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