Considerable study has been made over the past few years of the conditions under which damage can be sustained by living tissue due to laser light. This has led to limits of power density which should not be exceeded without caution. However, many applications have to be carried on where it is not possible to exclude all possibility of hazard. In such cases it is necessary to assess the probability of the hazard and to decide whether the event is sufficiently improbable to be acceptable or not. This paper deals with some of the factors useful in making this type of assessment.
