Fail-Safe vs Fail-Secure Locks: The Difference That Matters in a Fire

The two behaviours, precisely

Fail-safe: energised to lock — cut power (deliberately via fire alarm/break-glass, or accidentally via outage) and the door releases. Maglocks are inherently fail-safe; solenoid locks and strikes come in fail-safe variants. Fail-secure: energised to unlock — unpowered, the door stays locked, and exit depends on the mechanical hardware (a handle or push bar still works from inside on a properly specified door). The names confuse buyers annually: 'safe' refers to people, 'secure' to property.

Where each belongs

• Final exits, corridors, stair doors, communal entrance doors used for escape: fail-safe, interfaced to the fire alarm, with a green break-glass override beside the door
• Server rooms, comms cupboards, stock and cash rooms (not escape routes): fail-secure — a power cut shouldn't open your valuables to the building
• Plant rooms and roof access: usually fail-secure with mechanical escape from inside
• External gates on escape routes: fail-safe or panic hardware — gates get forgotten in fire strategies
• Anywhere in doubt: the fire risk assessment and escape strategy decide, not preference

The fire alarm interface, and how it's tested

Fail-safe locking on escape routes is wired through the fire alarm's cause-and-effect: alarm activation drops lock power across the escape doors so evacuation never meets a locked leaf. The green break-glass beside each door provides local manual release independent of everything else. Both must be proven — at commissioning and at service visits — by actually triggering the interface and walking the doors. An unlabelled relay added years later by another trade is how buildings end up secure and unsafe; it's a standing item in our access control maintenance checks.