By Derek Gunny, Solutions Engineer
Fail safe vs fail secure
Fail safe refers to electronic door lock behavior where a door is unlocked upon loss of power, prioritizing safety by ensuring ease of egress. Fail secure refers to door behavior where a door remains locked when power is lost, usually prioritizing security over ease of passage. Guaranteeing desired fail behavior requires proper electronic lock selection as well as careful integration with an access control unit (ACU).
Background
Electronic locks offer an alternative to traditional mechanical locks for controlling access and support automation with the help of a controller. There are various tactics these locks use to achieve a latching effect, but locks can usually be categorized as either normally open or normally closed.
A normally open electronic lock engages its lock when unpowered (i.e. when a circuit linking the lock with a power source is open). A normally closed electronic lock engages its lock when powered (i.e. when a circuit linking the lock and a power source is closed). Maglocks are often normally closed while magstrikes are usually normally open, though different configurations of both locks exist. The circuit condition of an electronic lock will be specified by the lock manufacturer and the type of lock circuit impacts how a door behaves when power is lost.
Door behavior when power is disrupted is an important building design decision that varies by application and is often subject to regulations. When power to a lock becomes unavailable, the lock can behave as either fail safe or fail secure. A fail safe scenario renders a door unlocked whereas a fail secure scenario renders a door locked. When wired directly to an ACU, a normally closed lock is expected to behave as fail safe while a normally open lock is expected to behave as fail secure. Purely mechanical hardware can help tailor door behavior further during power failure. For example, crash bars on the interior side of fail secure doors can allow for egress.
Frequently asked questions
Does the fail state of the lock matter when using an external power supply?
When using an access power controller (APC) in conjunction with an ACU, ensuring a door’s fail behavior may require further attention. In these scenarios, an ACU will be wired to trigger the input pins of an APC, and the accepted trigger inputs of the APC will influence the wiring schemes to produce the desired door fail behavior. An example of an accepted trigger input is a normally open dry contact from an ACU. A robust access control system should account for the failure of either an ACU or APC.
How does fire alarm integration relate to the default state of a lock?
The integration between a door access control system and a fire alarm system must produce the desired door behavior in the event of an emergency. This integration is directly designed around the fail behavior of the doors’ electronic locks. Access and power controllers can be directly wired to fire alarm systems, and how they respond to a fire alarm signal varies by controller model. Some controllers in a wet configuration may make their power source unavailable to connected door locks upon a fire alarm. In this case, doors would adopt their fail behavior. Other controllers may be configured to flip appropriate relays upon a fire alarm signal so that all doors are unlocked on both inside and outside regardless of lock type.
What is the difference between fail safe and fail secure locks?
Fail safe locks unlock when power is lost, prioritizing safety and ease of egress. Fail secure locks remain locked when power is lost, prioritizing security. The lock type and wiring determine fail behavior.
How do I make my electronic locks fail safe?
Wire a normally closed lock directly to an access control unit. The lock will unlock when power is disrupted.
How do I make my electronic locks fail secure?
Use a normally open lock and wire it directly to an access control unit. The lock will remain locked when power is disrupted.
What happens if an access controller loses power?
Electrified doors will resort to their fail state. Backup batteries can keep access controllers online for a limited time.
What lock should I use for high security areas?
Use fail secure locks for high security areas to keep doors locked during power loss.