There are two primary types of removable mullions used in door openings – one that is considered a piece of hardware, and one that is part of the frame. The more common removable mullion (the hardware type) sits behind the meeting stiles of a pair of doors, and allows two rim panic devices to latch into it.
Less common is a mullion made from hollow metal frame material, with brackets that allow it to be removed when the entire width of the door opening is needed. This type of mullion sits between the doors, rather than behind them.
Hardware removable mullions are popular because they allow rim panic hardware to be used on pairs of doors, rather than vertical rod panic hardware. Panic hardware that incorporates vertical rods or vertical cables can be more challenging to keep adjusted properly, and the tolerances at the sill need to be fairly tight, so doors with this hardware require periodic attention. The rim x rim x removable mullion application is typically easier to maintain, and the panic hardware may latch more reliably.
Pairs of doors with locksets and flush bolts can result in some of the same challenges seen with vertical rod panic hardware, so my question is this…would a hollow metal removable mullion be a good application for pairs of doors where the inactive leaf is rarely used?
For example, on mechanical rooms, the inactive leaf may only be needed when new equipment is moved through the opening. In health care facilities, corridor doors – including the inactive leaf of a pair – require positive latching hardware; this means automatic/constant-latching flush bolts and sometimes a coordinator. This question actually came to me from a health care facility trying to overcome problems with flush bolts.
Would a pair of doors with a hollow metal removable mullion and locksets on both door leaves be more reliable and require less maintenance than the alternative?
Other than the extra 2 inches of door opening width needed, what are the challenges with this application?