10. Bottom flush bolts that do not project ½” into the strike
Flush bolts are used on the inactive leaf of pairs of doors when the active leaf has a lockset. There are three types – manual, automatic, and constant-latching. They typically project into the frame head and into the floor, although there are some automatic and constant-latching bolts which have a top bolt only, and incorporate an auxiliary fire pin which projects when a certain temperature is reached and engages into the edge of the other door.
Manual flush bolts are projected and retracted manually, and are only allowed by NFPA 80 on fire doors “where acceptable to the AHJ, provided they do not pose a hazard to safety to life.” Annex A – Explanatory Material states, “This provision limits their use to rooms not normally occupied by humans (e.g., transformer vaults and storage rooms).” The use of manual flush bolts is also limited to certain applications by the egress code requirements, because it requires two motions to unlatch the door when manual flush bolts are installed, and they are not within the allowable reach range for accessibility.
Automatic flush bolts project automatically when the active leaf is closed, via a small trigger on each bolt. When the active leaf is opened, the bolts retract automatically, making them acceptable for use on most egress doors which don’t require panic hardware as long as the inactive leaf is not equipped with “dummy” hardware (lever or bar) which suggests that the inactive leaf can be operated independently. Automatic flush bolts are considered positive-latching and can be used on fire doors. A coordinator is also required to ensure that the inactive leaf closes before the active leaf.
Constant latching flush bolts have an automatic flush bolt on the bottom, and the top is a spring-loaded bolt which is retracted manually to open the door. These bolts provide a higher degree of security than the other two because the inactive leaf is more likely to be closed and latched properly. They can be an egress issue for some doors because the top bolt has to be retracted manually, and it is not within the accessible reach range. A coordinator is also required for this application.
When the bottom bolt doesn’t engage properly, there is no assurance that the fire door will perform as it was designed and tested during a fire. The undercut of the door must be carefully coordinated to ensure the proper engagement of the bottom bolt. Another issue with flush bolts on fire doors is that the coordinator / auto flush bolt combination can be difficult to keep functional in a high-use opening. If the latches don’t retract properly or if the inactive leaf is pulled or pushed without opening the active leaf first, the corners of the door can be susceptible to damage because of the volume of material removed to prepare the door for the flush bolt. This is a particular problem on wood doors.
http://idighardware.com/2012/10/fire-door-inspection-top-10-deficiencies/
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http://www2.mdanderson.org/depts/cpm/standards/supp_stds/ls_lessons/bulletin_10-006.pdf
http://www.steeldoor.org/res/118.pdf