Air locks were originally designed for use in pressurised environments such as submarines to allow someone to enter to leave the vessel without it flooding. This is achieved by two independent doors that do not open at the same time, allowing the inner chamber to flood with water before the diver leaves the submarine.
This same concept has been adopted in security to prevent people escaping, or to ensure that only one person can enter at a time.
How airlocks work
Each door in an airlock pair has its own status and will report to the access control system if the door is open, closed or if the door is busy (I.e. in use).The most basic form of air-locking is physical inputs and outputs are wired between the access controllers.
The system will then inhibit door 2 from opening if door 1 is open or busy.
When door 1 is then reported as closed, door 2 is able to open, which will inhibit door 1 from opening.
How airlocks are setup
This wiring of different doors can get very complex when more than two sets of doors need to be airlocked together.
This problem is eased with some systems which allow doors to be synchronised and air locked using software within the controller.
Configuration of software airlocking is fast and easy to understand and deploy.
Care should be taken in design to ensure that both sets of doors on an airlock will not fail if a single controller fails.
Likewise, systems which rely on the server to maintain an airlock should be avoided as this creates reliance on a communications network and server in addition to the controller.
Where are airlocks used?
Airlocks tend to be used in custodial environments and higher security sites like data centres.
Data centres commonly also use tube lock devices to ensure that only one person can gain access at any time.
This also reduces the risk of people trying to remove servers or other large devices without authorisation.
This also provides the option to trap the person in the tubelock if multiple people try to gain access.
Rudimentary airlocks are also commonly used in wildlife parks in walk-through aviaries to prevent birds from escaping.
Many thanks to Meesons for allowing me to use an image of their product in this post. I have no affiliation to Meesons and was not paid to feature their product.