Stairwell interruption gates are those bars or half-size gates that are mounted inside the stairwells on the level of exit discharge. they swing freely allowing exiting in the direction of egress, but they do not swing and prevent people from exiting in the direction away from the stairwell discharge. Section 7.7.3 of the 2000 LSC says stairwell interruption gates are required at the level of exit discharge in stairwells that continue more than one-half story beyond the level of exit discharge. The intent with this standard is to stop people who are egressing down the stairwell before they go beyond the exit discharge door.
Why would this be necessary? Why couldn’t we just post a sign inside the stairwell that says “Exit Here” over the door for the discharge from the stairwell? All good questions, and case histories have proven that people who are exiting under emergency conditions often do not read signs and just run down the stairs to the bottom, where they think the stairwell discharge is located. Then, it is a mess of people who are trying to climb back up to the level of exit discharge. Often, the stairwell interruption gate is on the first floor, preventing exiting to the lower level(s). But, that is not always the case.
Under normal circumstances, if you are on an upper floor, the direction in the stairwell to the exit discharge is downward. Stairs are supposed to be arranged so it is clear as to the direction to the public way. But there may be a situation where you might be on the second floor and the path of egress is upward to the third floor, or something similar. In that situation, a stairwell interruption gate is appropriate on the second floor to direct the direct the path of egress upwards.
Also, please be aware that stairwell interruption gates are not mandatory on the top occupied level of a stairwell, to prevent unauthorized persons from travel upward to a penthouse mechanical room. It is permitted, but it is not a requirement. The Life Safety Code accepts the premise that people will correctly assume that the path of egress is downward in a stairwell when they are on the upper floors. However, if there is an unusual circumstance where people may assume the path of egress is upwards (when it is not), then an interruption gate may be appropriate.
These interruption gates are not optional, but are mandatory where the stairs continue more than one-half story below the level of exit discharge.