Exterior Design: Using the onion peeling metaphor, we will start from the outside of the lab and work our way inward. Therefore, this section details items to consider when setting up your lab that are on or related to the exterior of your lab. Remembering your lab is not just the inside.
1.1 Access control/controlled entry
Class 3B and class 4 laser labs require access control. The laser American National Standards Institute (ANSI) standards (Z136.1 and Z136.8) allow for a wide range of access controls. The three most common are: door interlock systems, an electronic lock, and posting. The system that should be chosen depends on how well the laser beams are contained. Your laser safety officer (LSO) should be consulted to help make this determination. If a laser interlock system is required, it must be such that the interlock must be armed first to allow the laser to be turned on. An interlocked system is not always the best solution. Most importantly, it does not protect the users, only those who should not be entering. Interlock systems only must cause the laser beam to revert to safe status when tripped. This is often achieved by dropping a shutter or causing the laser to lose power (least favored approach).
1.1.1 Door interlock system
Commercial or home-made systems are options, though home-made systems have issues with long-term maintenance.
The interlock must be armed to allow the laser to be turned on. Otherwise, it is too easy to forget to arm the system.
A nondefeatable door interlock is not a viable option. This type of system is designed to block the beam or drop power every time the door is opened. This means you are trapped in the lab once you enter and arm the system.
A defeatable door interlock is set with an access device on the outside (i.e., key pad or card key reader) that allows authorized staff to enter and exit. Triggering the device sets a predetermined (15 to 30 s) bypass where the door can be open and the laser will stay on. Exiting is best controlled by a crash bar which triggers a pretimed bypass. If the system is magnetically locked to meet Life Safety Codes, one has to be able to exit in one motion, not requiring any preknowledge, such as pushing a button (exit bypass) and then opening the door. That is why having the bypass wired into a crash bar is your best option.
Note: Making holes in your doors can change the fire rating of the door, which might require putting in a new door (which can be costly).