Rules for maximum permissible exposure for pulses in a train of multiple pulses

Purpose: This paper analyzes the performance of the three rules given in ANSI Z136.1-2022—American National Standard for the Safe Use of Lasers—to set radiant exposure limits on pulses comprising a train of pulses on five example pulse trains to see whether the third rule, rule 3, is actually needed to ensure ocular safety. Method: A thermal eye model is used to calculate the temperature versus exposure time and the thermal damage integral for each of the five pulse trains using the pulse limit set using only rules 1 and 2 and then using the limit set by using rule 3. In addition, the temperature versus exposure time and the thermal damage integral are calculated for continuous exposure for the duration of the pulse train at the maximum permissible exposure, MPE. Conclusion: For cases where the limit was set using rule 1, the total radiant exposure for the pulse train was always less than the safe radiant exposure of the continuous exposure for the duration of the pulse train. For cases where the radiant exposure limit found using rule 2 was smaller than the MPE for a single pulse (the rule 1 limit), the total radiant exposure for the pulse train is always equal to that of the continuous exposure, a radiant exposure that is known to provide retinal thermal safety. The conclusion is that rule 3 is never needed to ensure retinal thermal safety and should be removed from the standard.