When doors and gates in the guard fencing around a machinery system are locked during operation, this results in a secondary risk which is easily overlooked.
This can pose significant risk to the person attending to a maintenance or fault issue within the machine who can easily be locked inside. That is bad enough but imagine a colleague outside would not notice them and restart the machine. This might result in a very dangerous situation. In such case, an escape release lock is necessary to allow the person inside the door to escape and stop the machine from continuing to run.
The escape release is triggered by hitting a button or pressing down a door handle on the inside of the door. It will then open, and the machine is stopped immediately. Of course, it must not be possible to use the escape release from outside the protected area, to prevent misuse. From outside a door lock can be released by resetting the safety circuit or by an emergency release, which is standard on most guard locking switches.
Emergency release is achieved by using a special tool to forcibly open the guard locking switch. Of course, this will also stop the machine immediately.