Quick reference · Doors that release when the fire alarm sounds
BS 7273-4: quick reference
How the fire alarm releases electrically locked doors on escape routes, and how reliably it must do so.
How doors held shut by electric locks open when the fire alarm goes off, and how dependable that release has to be.
BS 7273-4:2015+A2:2023. Amendment 2 (2023) named the three categories Critical, Standard and Indirect.
Confirmed two or more sources agree, or a source quotes the standard. Check one source, or a detail that could not be confirmed. Check it against the standard.
A (critical) is fail-safe for any fault that affects the release, including a fault on the critical signal path and a power failure. B (standard) is fail-safe for any fault on the critical signal path and for a power failure. C (indirect) is fail-safe for any fault up to the interface with the access controller, where the fire alarm signal goes through other equipment.
A is the strictest, and the door releases even if something in the link fails. B covers faults in the link and power failure. C is used where the alarm reaches the lock through the access control system.
Within 2 minutes of the fire system losing power. Radio is allowed if it releases within 6 minutes of a radio communication failure. Release triggered by sound is not suitable.
In a power failure the door must release within 2 minutes. A radio link is allowed if the door still releases within 6 minutes of the radio failing.
Category A is far quicker than B or C. The bars are drawn to one scale.
A fail-safe lock releases when the power is removed, usually a magnetic lock. A fail-secure lock stays locked when the power is removed, usually an electric strike. People must always be able to leave, which decides what can be used on an escape route.
Fail-safe unlocks when the power goes. Fail-secure stays locked. On an escape route, people must always be able to get out.
Fail-safe unlocks when the power goes, usually a magnetic lock. Fail-secure stays locked, usually an electric strike. People must always be able to get out.