October 2022 Lessons in Firestop: Mickey Mouse Ears in Wood-Framed Assemblies

Lessons in Firestop by Sharron HalpertWelcome back to our Lessons in Firestop! In our last discussion I told you that firestop is lazy. Well, it’s not so much lazy as it simply acts like most things in nature: It operates in the area of least resistance—the annular space, which is the distance from the inside edge of the opening to the outside edge of your pipe or the pipe insulation, is what provides the resistance for the firestop.

If you are responsible for QAQC and all you do is walk around after the firestop is complete to make sure that you see red stuff around all of the pipes, then you are missing a critical piece because you can’t see the annular space. I suggest to all inspectors and installers that you walk an area before the firestop is installed so you can easily see what is going on beneath the firestop.

Mickey Mouse Ears

For those of you working with plastic pipe brackets, this next discussion is going to be important. I see it predominantly on wood-framed construction and in drywall, but I have seen it on Hambro-style floor-ceiling assemblies as well. Plumbers in the field call them Mickey Mouse Ears. They are made by various different companies.

The picture to the right is an example of what I see in the field. Firestop was piled on top of the PEX pipe and the bracket, so if you were looking closely it would be easy to assume that this was firestopped and you wouldn’t even know there was a problem. As you can see now that the firestop has been removed, the bracket fills the annular space and the firestop is just piled on top.

If you have been following this Lessons in Firestop series, you know what is going to happen in a fire scenario: The  firestop will mushroom away from the opening, and you will potentially have a hole in your fire-rated floor.

You might think, “It’s just a small pipe—it will only leave a small hole so it’s not a big deal.” Well, if you listen to Bruce Johnson of UL in this video, he says, “When a fire is actively burning, it will create a lot of heat and pressure. Even the smallest void that is not protected with proper firestop almost acts like a blowtorch. You will have really hot flames, gas, and smoke going through that opening under pressure, so it rapidly spreads the fire beyond that original compartment.” Hopefully that helps you rethink the level of importance of this small pipe.

Some applications might be easier to notice as problematic, such as the one in the picture to the right.

In this case it’s much easier to see the ear bits that receive the screws and the body of the bracket that is seated into the wood framing member. You probably already know that is where the firestop is supposed to be, but since the bracket and the firestop sealant can’t both occupy the same space at the same time, there is a problem. Since the firestop sealant sitting on top of everything is going to act in the area of least resistance, it will mushroom away from the center of the opening because the firestop doesn’t have the guidance and direction it would have from the straight-cut edge of the wood opening.

If you are using these, please be sure that when the crews are installing them on gypsum walls, the body of the bracket does not lay in the same plane as the gypsum wall or the wood framing. If this is what your crews are doing, then the bracket is going to be located right where you need the firestop to sit.

What I see happen in the field is that the firestop will be installed on top of the clamp. In a fire scenario, the firestop, being lazy, will expand in the area of least resistance, which in this case means it will mushroom out, away from the pipe, and when the plastic pipe melts away, your fire-rated floor or wall will have a hole in it. You might think, “It’s a small hole.” If you didn’t take the time to watch the video mentioned above, I want you to think about steam in a pot of pasta. When you are cooking, the steam comes out of a small opening with a lot of force, so much that it can cause the lid to jump up and down. Smoke and fire are going to be powered by the same pressure, and according to Bruce Johnson of UL, that small opening can behave like a blowtorch.

How to Fix This Problem

It’s important that you don’t let this happen on your projects. If you need to have a clamp, please think about how you are going to fix this problem.

If you are working in a gypsum wall, you can simply place the clamp so it is inside the wall cavity and not inside the gypsum board itself.

If you are working in the wood-framed assembly, you can do one of two things:

  1. You can work really hard to get the firestop deeper into the floor assembly, but the system is going to call for ¾ inch of sealant. You will have to really work to achieve this.
  2. Alternately, you might be able to install it upside down. Please check with the bracket manufacturer to see what they think of this.

If you are working in a Hambro-style floor-ceiling assembly, that would be a G500 floor ceiling assembly, so join us for the next Lesson in Firestop when we will tackle that.

If you have anything else you’d like me to cover, just email me at [email protected]. We will dive into this T rating topic more maybe next year, but in our next lesson we are going to tackle Hambro/G500 assemblies. See you there.

Connect with Sharron

A former kindergarten teacher turned firestop expert, Sharron is President of Halpert Life Safety Consulting LLC, a leading provider of firestop-related life-safety and passive fire protection solutions.

If you like what you read here and want to know more, email [email protected] or connect with her on LinkedIn or Twitter to tell her what else you want her to cover in this column. You can also follow her on Instagram. If you find this information valuable, please like, share, comment, repost, retweet, and throw it on IG to help people build better.

The opinions expressed in this article are those of the author and not the American Society of Plumbing Engineers.

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