The need to simplify MPE corrections for repetitive pulse exposures Available to Purchase

The guidance for determining the maximum permissible exposure (MPE) or the accessible emission limit (AEL) in laser safety standards has had a long history of attempts to provide an understandable method. In all cases one guiding principle is accepted (whether explicitly stated or not): At no time t during a train of pulses will the exposure exceed the MPE specified as a radiant exposure for that time period t, nor will the emission exceed the AEL specified as a radiant energy for duration t. This single general principle is actually the rule that applied to repetitive exposures in the 1985 CDRH standard, and presumably technically still applies. All of the other current standards have applied an additional correction factor C_P or C₅ to be applied to single pulses in the train and its value decreases with the number of pulses N. The logic of this type of correction factor is not well justified when one considers that thermal additivity is really dependent upon pulse interval and not on just N. The current guidance for product safety standards has become even more complex and the concern is that with greater complexity there is a greater chance for errors in the application of multiple rules. A guiding principle in establishing limits should really be to minimize complexity. For example, if a repetitive pulse exposure reduces the safety margin, but does not lead to a true risk of injury, should the limits not attempt to track the biological data and thermal injury predictions to the point of adding too much complexity? A fresh look at this issue is warranted.