PlantFlow 3D › Guides › Access control: fail-safe and fail-secure locks
Access control: fail-safe and fail-secure locks
How an access controller decides to open a door, the difference between fail-safe and fail-secure locks, and why fire release matters.
How a card decision is made
When a card is presented, the controller checks whether the card is known, whether it is still valid, whether its access level includes this door, and whether the current time is inside the level's schedule. Only if all four pass does it release the lock for a set time and log the event.
Fail-safe and fail-secure
A fail-safe lock, such as a magnetic lock, needs power to stay locked. If power is lost, or the fire alarm removes it, the door opens. That is what escape routes need.
A fail-secure lock, such as many electric strikes, stays locked without power and only opens when powered. It protects rooms like server rooms or stores, but such doors must still allow free mechanical exit from the protected side where escape is needed.
Door supervision
A door contact tells the controller whether the door is actually closed. If it opens without a valid card or exit request, the controller raises a "forced" alarm. If it stays open longer than allowed after a valid opening, it raises a "held open" alarm. Cameras can record a clip linked to these events.
Fire release
Doors on escape routes are released by the fire alarm system, usually by removing power from fail-safe locks through a fire-alarm relay, often backed by a green break-glass unit at the door. Local regulations decide which doors must be released.
Try it yourself
Open the Security tab, present different cards, cut the access control power and switch on the test fire signal. Watch which doors open.
Open the PlantFlow 3D simulator →Safety: this guide explains principles for learning. Real installations must follow the applicable codes, the equipment manufacturer's instructions and the approval of a competent, qualified person. Isolate, lock off and prove dead before touching any circuit.