Scanning laser beams across the faces of the audience at a laser light show is an accepted practice in many countries. Guidance generally requires the exposure levels to be below the internationally agreed maximum permissible exposure (MPE) levels. Laser shows consist of a large number of sophisticated scan patterns that appear to require considerable time and effort to analyse and therefore demonstrate that exposure levels are below the MPE. In short, the risk assessment is complex.
A method for analysing some scan patterns used in a laser light show is presented which shows that the practice, as currently carried out, will invariably exceed the MPE. Some laser light show installations include scan failure detection systems but these may not be making the correct assumptions about the applicable MPE.
A simplified risk assessment approach is presented which leads to proposals for audience scanning which is below the MPE. A full understanding of the MPE boundaries for audience scanning allows the laser light show designer to develop shows which should stand up to the risk assessment process, including reasonably foreseeable failure modes.