I haven’t written much about interlocks on this site because the International Building Code (IBC) doesn’t include requirements for interlocks except for sallyports used in I-3 occupancies (usually detention facilities).  NFPA 101 – The Life Safety Code doesn’t address interlocks either.  A proposal submitted for the 2021 IBC could change that.

If you’re not familiar with interlocks, I wrote about them back in 2010 – there’s even a video to illustrate how they work.  Imagine a vestibule with 2 doors.  When someone opens one door of the vestibule, the other door can not be opened until the first door is closed.  This operation controls traffic or the transfer of air and contaminants; interlocks are sometimes used in clean rooms, data centers, cash rooms, and other secure environments.

Because of the potential for interlocks to inhibit egress, it’s important for the model codes to include some requirements.  Currently, each interlock must be approved by the Authority Having Jurisdiction, but there are no standardized guidelines for what a code official should require when evaluating a proposed interlock.

BHMA has proposed a change to the 2021 IBC, to create some guidelines for interlocks – called “control vestibules” in the proposed code language.  At the recent hearings, there was discussion among the technical committee about limiting the use groups where an interlock/control vestibule may be used.

We need your help to get this right!  We want to make sure that the code allows control vestibules where they are needed.  I have seen them in business, factory, institutional, and storage occupancies.  The other IBC use groups are assembly, educational, high-hazard, mercantile, residential, and utility.  Do you see a need for control vestibules in these occupancies?  Where have you specified/installed control vestibules?  WWYD?

And in case you’re curious, here is the current proposed language for the code change:

1010.1.4.6 Control vestibule. Where doors in the means of egress are configured as a control vestibule, the door locking system shall provide for emergency egress.  The control vestibule shall comply with all of the following unless otherwise approved.

1. An approved override shall be provided on the egress side of each door of a control vestibule.

2. An approved override shall be provided on the ingress side of the outer door of a control vestibule.

3. Upon activation of the automatic sprinkler system or automatic fire detection system, the interlock function of the door locking system shall deactivate.

4. Upon loss of power to the interlock function of the doors, the interlock function of the door locking system shall deactivate.

5. The egress path from any point shall not pass through more than one control vestibule unless approved by the code official.

6. The door locking system units shall be listed in accordance with UL 294.


I can’t find a good photo or graphic of an interlock, so if you have one that I can add to this post, send it along!



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