A fire-door contains a fire, at least for a little while. Containing a fire delays the fire's progression, hopefully until the fire department arrives.
A fire-door also contains smoke so it doesn't travel from one part of a building to another part. Smoke progresses much faster than fire does. Smoke inside any building is also poisonous (toxic). Just a few breaths of the smoke can easily disable a person, and if that person isn't helped really soon, that person can easily die.
By automatically closing, when just a little smoke is building up near the doorway, the fire-door slows down the fire's progression, and slows down the spread of smoke.
Automatic Closing of the Fire-Door
When a fire starts in a building like a restaurant, no one is going to go around closing doors. Any occupants of the building should leave, so the doors have to close without human intervention. Besides, even most restaurants aren't occupied 24/7. When no one's in the building when a fire starts, no one is even in the building to close the doors.
When considering a fire-door, the greatest concern is that, unless the door is held open by a person standing there, the door just automatically closes when there's smoke in the area.
Holding Open the Fire-Door
The best way of holding a door open is with a powered-on electromagnet. As long as the electromagnet is powered-on, the electromagnet holds the door open. Turn off the power to the electromagnet, the magnet deenergizes, and the door automatically closes.
Google the words "electromagnetic door holder" to see a whole bunch of door holders.
Smoke Detection
Smoke almost always arrives before the fire arrives; for fire-doors, smoke detection is about the only reliable method of detecting smoke or fire.
Because it's the fire-door that's supposed to close when there's smoke or a fire, there has to be smoke detectors within a few feet or a couple of meters of the fire-door. Often, the smoke detectors have to be on both sides of the fire-door.
Sequence to Close a Fire-Door
In order for a fire-door to close when there's a fire, the first thing that happens is the fire alarm system detects the fire (or smoke).
The fire alarm control panel then sounds the alarm in the building, calls the central station (so they can dispatch the fire department), and turns off the power to the door holder.
Because the door holder loses power, the door holder can no longer hold-open the fire-door, and the fire-door just closes.
Sometimes the alarm shutting the fire-door can be any fire alarm in the building, sometimes the alarm shutting the fire-door is only from the smoke detectors next to the fire-door. Mostly, what triggers the doors to shut depends on what the fire marshal wants.
Issues
Adding smoke detectors and an electromagnetic door holder to an existing fire alarm panel may be easily done, or special wiring may be required, or a whole new fire alarm control panel may be required.
At this point, I recommend that you hire a fire alarm installation company to install the door holder.
Keep in mind that the city is involved, and the city is probably is looking for documentation that the door holder is installed correctly. The only place that the proper documentation is available is from the fire alarm installation company. There's also a good possibility that the city just won't just accept your word on this.
There are also long-term liability issues involved when there isn't the proper documentation. According to the state fire marshal in my state, "If it aint on paper, it didn't happen". Make sure you have good CYA Paperwork.
Douglas Krantz
