When a fire alarm activates, what must stair enclosure doors do?

When a fire alarm activates, stair enclosure doors must unlock. The purpose of stair enclosure doors is to provide a safe exit route for occupants during a fire or emergency situation. If these doors were to remain locked when an alarm is activated, it could trap or impede individuals attempting to evacuate the building, thereby compromising their safety.

Unlocking the doors allows for free and immediate access to the stair enclosure, which is typically a protected area designed to lead to an exit. This functionality is crucial for effective emergency egress in a fire situation, where quick and unimpeded access to a safe route is necessary.

While the other options may seem logical in considering safety protocols, they would not adhere to the requirements for life safety during emergencies. For instance, closing the doors may be necessary to contain smoke in a typical situation, but they need to be unlocked and readily accessible at the time of a fire alarm to facilitate evacuation.