Why is 90-Minute Door Allowed in 2-Hr Barrier?

10/21/2024

Does anyone know the historical context of why a 90-minute door is permitted on a 2-hour barrier?

Why the 30-minute difference?

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7 Comments

Todd E Wyatt

10/21/2024 08:16:47 am

From idighardware.com :

The rating of the door assembly is often less than the required rating of the wall, because it is assumed the door will have a lower fuel load since no combustibles (e.g. furniture, storage, etc.) will be piled in front of the door.

Todd E Wyatt

10/21/2024 09:22:01 am

That being said, some users (after the Certificate of Occupancy has been issued) of a room with (2) fire doors (FD) will sometimes place storage (e.g. file cabinets) in front of the "unused" FD which "voids" its fire-resistance rating (FRR) since it now has a higher fuel load in front of it.

Dan Wilder

10/21/2024 08:19:36 am

Can't speak to the history but when tested to NFPA 252

Annex B - B.4.4

It is common for a fire door to have a fire protection rating lower than the wall fire resistance rating in which it is installed. For example, a 11⁄2-hour fire protection–rated door can be required in a wall having a fire resistance rating of 2 hours. This is justified in part by the fact that, under normal conditions of use, the potential fire exposure in the vicinity of a door opening is decreased, since there will usually be a clear space on both sides of the opening for traffic purposes. Since wall assemblies are put together at the site, their uniformity is not as certain as a fire door assembly that is factory assembled (e.g., undesigned penetrations tend to show up in wall assemblies). For this reason, any factor of safety that is tacitly called for in a wall assembly requirement should exceed that of a door assembly. If the opening is not used, combustibles could be piled against the door, and the assumed enclosure protection might not be maintained. In these instances, ratings for the openings should be equivalent to the rating of the wall, or precautions should be taken to prevent storage of combustibles against the doors [2, 6].

Greg

10/21/2024 08:21:43 am

....Could it be the hose stream portion of the Fire Door Test is included in the total duration of time and therefore the hourly rating is rounded up?

Chris Nelson

10/21/2024 08:56:11 am

This was my question. Thank you all! The limited fuel load makes sense!

Jack G

10/21/2024 10:21:12 pm

I agree with the above comments. Unless the fire door is unused, and allowed to be blocked off for storage —- as long as egress allows the reduction of exits—- 90 minutes is fine.

Mike Morey

10/24/2024 08:21:24 am

IBC Table 716.1(2) lists the door requirements relative to wall requirements, for what it's worth, including allowable glass sizes etc.

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Why is 90-Minute Door Allowed in 2-Hr Barrier?

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