I have one more draft script coming – this is my fourth script for an upcoming whiteboard animation video. If you haven’t had a chance to add your input on the previously-posted scripts (panic hardware, classroom lock options, door closer arms), there’s still time! I really appreciate your comments on these drafts…I think the whiteboard animations will be really helpful for people who are new to the industry, or those who need to review the basics.
If you’re looking for today’s Wordless Wednesday post, it’s here!
Flush Bolts and Coordinators [Draft Script]
Flush bolts are used on pairs of doors to secure the inactive leaf, projecting into the frame head and into a floor strike. In this application, the active leaf would typically have a lockset which latches into a strike mounted on the edge of the inactive leaf.
Manual flush bolts and surface bolts are projected and retracted manually. Because manual bolts do not provide a positive latch and could be left in the retracted position, they are not typically allowed for use on fire doors. One exception is when the pair of fire doors leads into a room that is not normally occupied by humans, like a storage room or electrical room. If allowed by the Authority Having Jurisdiction – the AHJ, manual flush bolts can be used on these rooms.
Two types of flush bolts are available – the extension rod type, traditionally used on hollow metal doors, or the corner wrap type, designed for wood doors. Corner wrap flush bolts can sometimes weaken the top corner of a wood door because of the volume of material that is removed in preparing the door for the flush bolts, so some specifiers and suppliers use extension rod flush bolts for wood doors as well as hollow metal doors.
An automatic flush bolt is projected when the active leaf closes and depresses a trigger on the edge of the door. When the active leaf is opened, the automatic flush bolt retracts. Constant latching flush bolts are a type of automatic bolt – the bottom bolt is a regular automatic flush bolt, but the top bolt latches when the inactive leaf closes, and stays latched until it is retracted manually. Either type may be used on fire door assemblies.
Automatic and constant latching flush bolts are both available with a top bolt only, and a fire pin in place of the bottom bolt. These sets are called “LBB” or “less bottom bolt.” The top bolt functions normally – an automatic bolt is projected by the active leaf and the constant latching bolt is always latched, but the fire pin remains retracted until there is a fire. When the pin is heated to a certain temperature, it projects into a hole in the edge of the active leaf, securing the doors to compartmentalize the building. The benefit of omitting the bottom bolt is that there is no need for a strike in the floor.
In order to ensure that the inactive leaf closes first, pairs of doors with automatic flush bolts must also have a coordinator. If both leaves of a pair are opened, the coordinator will hold the active leaf open slightly during its closing cycle. This allows the inactive leaf to close fully and be in the proper position for the active leaf to then close and project the bolts. A coordinator may also be used when a door has an astragal that could inhibit a pair from closing if not sequenced properly. A carry bar may be needed if the inactive leaf can be opened before the active leaf, but carry bars are not common.
Two types of coordinators are available – the gravity type which mounts on the face of the door frame, and the bar type which mounts on the underside of the frame head. The bar type is preferred because it is less visible than the gravity type, and less prone to vandalism. When a bar type coordinator is used, a filler bar is required to extend the coordinator the full width of the door opening. Mounting brackets may also be needed if parallel arm door closers or surface-mounted vertical rod panic hardware or fire exit hardware is used. The mounting brackets are installed after the coordinator, so other hardware can be attached without damaging the coordinator.
Egress is an important consideration when using flush bolts. Manual flush bolts are allowed in limited locations in a means of egress, because the operation required to retract the flush bolts does not meet the egress requirements. When automatic flush bolts are used on a door in a means of egress, no hardware may be installed on the inactive leaf that could confuse building occupants about which door to open for egress. For example, a dummy lever or push rail cannot be installed on the egress side of the inactive leaf so it’s obvious that the active leaf is the one that can be opened.
A 2-point latch, like the Schlage LM9200, is a good solution for pairs of doors, and can be used in place of flush bolts. Lever handles retract the latches at the head and at the floor, and the doors operate independently with no need for a coordinator. This product is also available with a latch at the head only. The LM9200 meets model code requirements for egress and accessibility, and can be used on fire door assemblies. Check the listings for the fire door and the latch, to verify the maximum allowable fire rating.