The Way They Work

Typically, horizontal accordion-style sliding-door assemblies are custom-designed to be stored in shallow recessed pockets in walls. Pocket door covers are made to be consistent with the interior finish of the adjacent space and stay in the closed position with the use of simple magnetic latches. The fire door is installed to ignore obstructions during the first few feet of closing to allow the pocket cover door to be pushed out of the way.

Some of the most important features concern electronic surveillance and power issues.

The door assemblies incorporate the use of a back-up battery system, direct current (DC) motor and an integrated microprocessor to control the operation of the door during fire emergencies.

In a typical system, the 12-volt battery is continuously charged by the in-house 120-volt electrical system, and the microprocessor and logic board regularly supervise all critical operating functions of the door system, multiple times per second. In addition, the system replicates a "loaded stress test" designed to simulate the voltage required to actually close the door during a real-life emergency. All fault signals are sounded audibly at the door location and can be communicated to a remote location in the building or to an off-site central monitoring station.

The vertical "fire-exit-type hardware" is attached at or near the leading edge of the door assembly and is programmed to respond to light pressure applied in the direction of exit travel. Most manufacturers set the force to open at 5 pounds or less to comply with ADA requirements for fire doors in egress applications. Upon activation the door assembly is programmed to retract a preset distance, typically 36 inches, pause for a moment, and then recycle close. If the door encounters an obstruction during the closing cycle it will stop, pause for three seconds and then continue the closing cycle. At all times a door serving as a means of egress can be opened manually.

The horizontal sliding accordion-type fire door is designed to respond to smoke detector activation, a fire alarm system, a manual pull station or in some instances even the activation of a sprinkler flow valve. Upon activation the door assembly will automatically begin closing. The building code permits a rate of closing speed not less than six inches and no more than 24 inches per second.

The Underwriters' Laboratories (UL) listing contains no limitations on the size of opening width and heights can be designed up to 28 feet. The typical assembly has a separate listing from UL as a rated fire door assembly for 20 minutes, one hour, one-and-a-half hours, and three hours. It also meets the UL 864 standard for electrical safety as a releasing device and as an IBC air leakage (smoke control) assembly when tested to UL 1784.

In terms of installation, the assembly can be designed in radial configurations and never needs a floor track, both features increasing design flexibility.