Your question involves three different classes of doors:
Elevator Doors - Elevator doors cover the opening to the elevator shaft, and they open only when the elevator car is present. They open and close using commands from the elevator control system panel.
Security Doors - Security doors that require key badges are locked shut to prevent unauthorized people from gaining access to certain areas of the building. Sometimes they are held shut using electric door strikes, sometimes they are held shut with strong magnets.
Fire-Doors - The words "Fire-Door" are a technical fire protection term for doors designed to prevent fire or smoke from progressing from one fire/smoke compartment in a building to another.
- The elevator lobby, the small room outside of the elevator doors, is a fire/smoke compartment
- The "First Floor West Wing" of a small apartment building is a fire/smoke compartment
- The 16th floor of a tall office building is often a single fire/smoke compartment. If the 16th floor of the tall office building covers a large area, the 16th floor might even be divided up into smaller firefighting compartments
- A stairway between floors is a fire/smoke compartment
These are all compartments, sometimes referred to Firefighting Zones.
Once is a while, like in the case of elevator lobbies, the fire/smoke compartment can be completely surrounded by another firefighting zone.
If a fire breaks out, what prevents the fire and the smoke from rapidly progressing from one compartment to another compartment are the floors of the building, and any specially designed firewalls.
The firewalls are continuous fire and smoke barriers and, when smoke is detected close to the fire-doors, including the fire-doors, once the fire-doors are closed. Keep in mind that with any firewall, propped open fire-doors let fire and smoke easily pass through them; if the fire-doors are open when there's a fire, the firewalls themselves are useless.
Electromagnet Door Holders
There is a conflict with fire-doors. When there's a fire, in order to prevent the fire or its smoke from passing through from one compartment to another, the fire-doors have to be closed. Then again, like when people come out of the elevator lobby, people want to travel freely between one compartment in a building to another compartment. People just don't want to be required to keep opening the closed fire-doors.
That's when non-fire-prevention trained people (which is most people) take things into their own hands and prop open the fire-doors. The action of propping open the fire-door makes it easier to leave the elevator lobby with a load of groceries, but this action also makes it easier for fire and smoke to pass from one fire/smoke compartment to another. Bad juju.
Taking this conflict into account, a method was devised to allow a normally powered electromagnet to hold the fire-door open. . . That is at least as long as power was applied to the electromagnetic door hold open device.
If there is a power outage, if the wiring to the door holder is broken, if the electromagnet breaks, and especially if there is an approaching smoke belching fire, the smoke detector close by the fire-door disconnects power, and the door closes.
When there's a failure in the fire-door magnet system, the fire-doors default to closing.
Sometimes the fire marshal, the insurance company, or the building owner, or some other Authority Having Jurisdiction (AHJ) adds requirements like "Any fire alarm, anywhere in the building, will close all of the fire-doors in the building."
In the question in the article at:
"How do the Door Holders and Relay Get Their Power?", the questioner MB is wondering about what seems like different rules for different fire-doors. Because I was not present when the building was constructed and the fire alarm system was first installed, I could only show the technical aspects of how the door closing is done.
Door Holders for Fire-Doors
Under normal circumstances, fire-doors can be held open by powered-on door holders. When, for any reason, the power for the electromagnet holding the fire-door opened is turned off, the fire-door automatically, by itself, closes to separate different fire/smoke compartments from each other.
Douglas Krantz
