To be quite honest, its a "technicality" thing.
1) According to 21 CFR 1040 (our laser regs). Class 4 Lasers need to have case interlocks to protect users from opening system and being exposed to hazardous radiation. However- when one certifies a laser product over here (as i did with the Luminance projectors) If the system is certified to NOT have any user serviceable parts inside and have NO removeable panels, than system does not require case interlock system. In addition, it is certified that any and all "servicing" and/or maintenance is performed by CT. Lasers ONLY. If a panel is removed, this is considered maintenance or service and therefore voids the no user serviceable components inside and the user has disregarded all warnings (clearly labeled).
2) You may say, "whats the big deal about having a case interlock?" OK, fair enough- HOWEVER- CDRH loves to make sure that if something *IS* included, it is absolutely IMPOSSIBLE for it to fail. So therefore, if an interlock is needed, it cant just be some sort of "microswitch" or something on a panel. It has to be undefeatable (indefeatable? non-defeatable? lol...) and redundant. So i would need to have 4 redundant switches with fail safes on all panels. A little silly IMO and 99% of my clients opinions.
3) Without aperture glass, this allows users to clean optics WITHOUT having to remove any panels. Therefore does not violate the "no opening of unit" clause.
It gets a little deepr than this. But that is the premise of it. you would be surprised to see that most pro systems over here do not have aperture windows.
What users do on their own and disregard my warnings is their call.
-Marc