Fail-safe and fail-secure locks
Fail-safe and fail-secure
| Fail-safe | Fail-secure | |
|---|---|---|
| When the power is removed | The lock releases. The door can be opened. | The lock stays locked. |
| Usually | Magnetic locks | Electric strikes |
| Often used on | Escape routes and stairwells | Server rooms and stores |
| The trade-off | The door is open in a power cut, so the room is not secure. | The door stays locked in a power cut, so people need another way out. |
People must always be able to leave. On an escape route that decides which type you can use, and the fire risk assessment has the final say.
BS 7273-4: doors that release when the fire alarm sounds
BS 7273-4 sets how the fire alarm releases doors held shut by locks. It has three categories. This is a summary of BS 7273-4:2015+A2:2023, from a fire and rescue service advice note and FIA guidance.
| Category | What it means |
|---|---|
| A (critical) | Fail-safe for any fault that affects the ability to release in a fire, including any fault on the critical signal path and a power failure. It releases 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. |
| B (standard) | Fail-safe for any fault on the critical signal path and for a power failure. Radio is allowed, with release within 120 minutes. Release triggered by sound might be suitable. |
| C (indirect) | Fail-safe for any fault on the critical signal path up to the interface with the access controller. There is no direct link between the fire alarm panel and the release: the signal goes through other equipment, such as the access control system. Radio is allowed, with release within 120 minutes. Release triggered by sound might be suitable. |