Two Fire Dampers for a "Double" Fire Wall?

10/4/2019

Being told I need two fire dampers to serve a single fire wall. The fire wall is made of a "double wall", essentially two masonry walls next to each other with a very small (less than 2-inch) air gap in-between. The engineer on the project is stating that this "double wall" requires a fire damper in each.

I've never come across this as a requirement before. Do I need two fire dampers?

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8 Comments

Paul Pinigis link

10/4/2019 10:28:29 am

A double fire wall is an assembly of two rated wall, so each wall is required to maintain its rating in the event that the other wall collapses. Therefore, each would have to have its own fire damper. This is also true if there is a door through the wall, each wall would have to have an appropriately-rated door.

efi sher

10/4/2019 11:45:27 am

Why to use double fire wall if you can construct a single fire wall with the required fire rating.The rating of the wall is for the whole element no matter the side.
This concept leads to sigle fire damper depnds on the width of the wall.Fire damper rating is the sme for both sides of the damper.

Cyril McIvor

10/4/2019 11:49:15 am

A double skin masonry wall is very common and only requires a single fire damper constructed to suit the width of the two skins including the gap between. It would be impossible to install two fire dampers as it is not possible to installed the required angles for each damper for each skin. The installation of fire dampers requires the damper to have retaining angles on both sides of the wall.

Whoever came up with the idea that you need two dampers in this situation has no common-sense and does not know how a damper must be installed. Back to kindergarten school for him

Paul Pinigis link

10/4/2019 12:46:31 pm

CYRIL MCIVOR, please define "double skin wall". If you have two 2-hour walls together to make a three hour wall, but only one fire damper, how do you maintain the 2-hour rating of the unprotected opening when the wall with the damper collapses?

Paul Pinigis

10/4/2019 01:53:51 pm

From NFPA 221, 2018:

6.10.3* Double Fire Walls. Openings in double ƒre walls shall
be protected using one ƒre door in each separate wall.

5.10 Ducts and Air Transfer Openings.
5.10.2 HC ƒre walls shall be protected with two ƒre damper
assemblies.

Cyril McIvor

10/4/2019 02:00:23 pm

The sole reason to construct a wall with two skins is to achieve the nominated fire rating level. If a check of a masonry wall construction manual is made it will be seen that this wall is most likely only rated for 2 hours as a combined system (similar to dry wall construction) with brick ties between the two skins of masonry. Otherwise why build to separate wall systems so close together.

A lot depends on the design of the wall to achieve the fire rating. This is a circular discussion until the design of the wall is clearly understood. Certainly adding two 2 hour walls together does not give you a 3 hour wall so much more depends on getting the 3 hour rating

Paul Pinigis

10/4/2019 03:10:14 pm

CYRIL MCIVOR, I don't think that you understand the requirements for firewalls. Please read NFPA 221 before suggesting that anyone else go back to kindergarten.

Two 2-hour walls do, in fact, make one 3-hour fire wall (see table 4.6 of NFPA 221).

We are not talking about two layers of masonry on a single wall, we are talking about a double fire wall (two fire rated walls in close proximity).

There is so much wrong with your responses that I will simply chalk them up to inexperience.

Efi SHER

10/5/2019 12:23:45 am

Why use double wall for 3 hours
Below one example.You can find much more with UL approved

The 3-hour Area Separation Wall System is a 3-hour fire wall consisting of two layers of 1 in. (25.4 mm)
shaftliner panels friction-fit between 2 in. (50.8 mm) light-gauge steel H-Studs and a layer of
5/8" Fire-Shield C gypsum board fastened to each side of the studs.
The steel H-Studs are attached to adjacent framing on each side with heat-softenable, aluminum
break-away clips (ASW clips) that allow for collapse of the fire-exposed unit without collapse of the
Area Separation Wall.

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