Insight · 4 min read
Fail-safe or fail-secure? Deciding door by door
What a door does when the power goes out is a design decision. Make it per door, in writing.
Two ways a lock can fail
Every electrically controlled door must do something when power is lost. A fail-safe lock releases. A fail-secure lock stays locked. Neither is better in general; each is right for different doors.
| Lock type | Usual fail mode | Typical use |
|---|---|---|
| Magnetic lock | Fail-safe (always) | Glass doors and escape routes, with egress devices |
| Electric strike | Either, chosen at order | Office doors, store rooms |
| Motorised or solenoid mortice lock | Either, chosen at order | Perimeter and high-security doors |
Escape routes come first
On an escape route, people must be able to leave without a key, card or knowledge of the system. That usually means a fail-safe lock, a request-to-exit device, an emergency break-glass or release unit, and release on a fire alarm signal. Many fail-secure locks can still open mechanically from the inside with a handle, which also allows free exit. The approving authority's requirements for each door take precedence over convenience or security preferences.
We don't design or install fire alarm systems. On escape routes we design the release interface and witness the release test together with the fire-alarm contractor.
Where fail-secure is right
Server rooms, cash offices, drug stores and perimeter doors often need to stay secure during an outage, provided people can still leave mechanically from inside. Here a fail-secure lock with a battery-backed controller keeps the door secure and still allows authorised entry for as long as the battery lasts.
Write a door schedule
The way to get this right is a door schedule: one line per door, with lock type, fail mode, egress method, fire release requirement, door contact, request-to-exit, and any interlock. It is agreed with the client, consultant and fire-alarm contractor before ordering hardware, then tested door by door at commissioning. A door schedule takes a day to prepare and prevents the most serious failures an access control system can have.