Second order PRA model for ocular laser damage

Abstract

Dose-response curves characterize the variability of damage thresholds within the population under consideration. In probabilistic risk analysis (PRA) for laser injury, a log-normal cumulative distribution is usually used as dose-response curve to calculate the probability for injury as function of radiant exposure. However, experimental uncertainty as well as a different variability within the group under consideration can influence the shape of the dose-response curve. Previously, to our knowledge, dose response curves were used in PRA for laser injury without considering uncertainties. We have developed a second order probabilistic risk analysis model, which accounts for uncertainties of the dose response curve by defining distributions for the slope and ED-50 values of the dose response curve and using Monte-Carlo simulation.

Risk analysis relevant for laser products under IEC 60825-1

“…For a general characterization of what risk is usually seen as acceptable (or "tolerable"), the autor has identified relevant numbers in the literature for a PRA project on laser satellite missions of the European Space Agency [9]. In risk analysis, individual risk and global risk is distinguished.…”

“…has an acceptable low level of risk (see EC guidance [7]). Another example is a laser beam emitted from a satellite for instance to measure atmospheric properties; here, the design would usually be such that the MPE for the naked eye is not exceeded, but a risk analysis is needed to characterize if the risk for exposure through telescopes is acceptable (even large telescopes are sometimes used to track satellites); such a risk analysis was developed by the author for the European Space Agency and not only included the estimated probability for ocular injury per mission duration, but also the uncertainty of that figure calculated with Monte Carlo analysis for what is referred a second level PRA [23,24]. A third example is a consumer product with a highly divergent infrared beam, which is Class 1 but at contact significantly exceeds the exposure limits of the skin.…”