Safety interlocks to protect from C

Safety interlocks to protect from Class IIIb or IV levels must also be redundant or fail-safe; if fail-safe, they must either prevent opening the housing in case they fail or they must be incapable of failing in a mode that would permit access. Defeatable safety interlocks must provide a visible or audible indication of defeat; further, it must not be possible to close the housing with the interlock remaining defeated. A redundant or fail-safe safety interlock is also required if failure of a single interlock would allow access to laser radiation in excess of the accessible emission limits of Class II to be emitted directly through the opening created by removal or displacement of the interlocked portion of the protective housing.