International standards for the protection of the eyes from the hazards of laser radiation define a Nominal Ocular Hazard Distance (NOHD) beyond which an individual would not be expected to suffer any adverse effects from the laser radiation. The NOHD assumes deliberate viewing of the laser source over an indefinite period of time and takes no account of the probability of the observer’s eye being irradiated. This approach may lead to unrealistically large hazard areas for some laser devices.
An alternative method of hazard assessment without compromising safety is to adopt a probabilistic approach. A probabilistic laser safety scenario can be defined as one in which the chance of optical irradiation is very small and in which the major elements under consideration are inherently probabilistic. Examples of such elements are: i) the probability of irradiation of a given point; ii) atmospheric scintillation; and iii), the resultant risk of ocular damage associated with any ocular irradiation. The ultimate safety criterion is that the expectation of someone receiving ocular damage must be less than some acceptable risk level.
This paper will discuss the concept of probabilistic laser safety, and provide guidelines to be followed for probabilistic laser safety assessments.