March 2023 Lessons in Firestop: Deciphering Firestop Details for Metal Pipes

Sharron Halpert's Lessons in FirestopFirestop on metal pipes is likely the easiest thing to get right, but let me tell you about a few critical things to which you must pay attention. First, you can’t tell me how to firestop a standard application unless you have a listed firestop detail. You probably hear people talk about UL details. Well, UL is not the only fire test lab—there are several others around the U.S.—but UL has the lion’s share of listed details, which explains why UL is what you hear most of the time.

You Have to Identify Two Things to Firestop Metal Pipes

First: what is the fire resistance-rated assembly? Is it a floor or a wall? If it’s a wall, is it block or gypsum? Is it a wall that you can access from both sides or just one? A shaft, for example, is a wall that may offer access to only one side, which means you have to firestop it differently, but we will get into that discussion another time. If your pipe is running through a floor assembly, is it a wood-framed assembly or a G500 such as a Hambro floor ceiling assembly? Those are firestopped very differently than a solid concrete floor or hollow-core concrete. (Be sure to go back and review our article on hollow-core concrete.) You get the picture: you have to know your fire-rated assembly.

Second: what detail to firestop metal pipes will work for that assembly and your pipe? If your pipe is steel, cast iron, or copper, you won’t have a hard time finding a firestop detail. If you are working with metal pipes that are made of  aluminum, brass, or bronze, it is important to understand that the fire dynamics are very different, and, as you might expect, you will have to use a different firestop detail.

Now You Can Start

Once you have a firestop detail that matches your rated assembly and your pipe (type and size), then you are ready to start.

Oh, first I should clarify that we are talking about bare pipes (pipes that are not insulated). If they are insulated, you will need a different detail—that is unless the insulation stops before the pipe runs through the rated assembly.

It’s easier to work with examples for this next step, so let’s say you are running a cast iron pipe through a gypsum wall. Before you make your hole, you need to be able to look at the firestop detail and clarify what the annular space is. Let’s say you are running a 4-inch cast iron pipe; you need to have a hole a bit larger than the outside diameter of the pipe. The obvious reason is so you have space to work, but if you read the firestop detail, you will see that most of them will list a minimum and a maximum allowable annular space.

Here Is Where Firestop for Metal Pipes Gets a Little Confusing

Let’s say the firestop detail says you can have an annular space of 0 to 1 inch. Let’s talk about this a little bit. You are allowed to have 1 inch of annular space all the way around the pipe, but here is where it can get confusing: You cannot have 0 inch all the way around the pipe. The exception to this would be if your firestop detail allows continual annular space. You should know that not many details have this called out, which means there are not many scenarios where you are allowed to have the pipe tight all the way around the opening.

So Why Does This Matter in the First Place?

Firestop is designed to be installed in the space between the fire-rated assembly and the penetrating item—in our case, a 4-inch cast iron pipe that is running through a gypsum wall. If there is a fire, the chemically bound water in the drywall will dissipate, and when that happens, the gap between the pipe and the drywall will grow. If the firestop is simply laying on the surface, there is a risk that the fire can come through the wall prematurely. When firestop is properly installed into space between the metal pipe and a gypsum wall, it will be installed the full depth of the drywall, and the fire dynamics will be very different.

The exception, of course, is if you are allowed to have point contact, then obviously you won’t be able to achieve the sealant depth where the pipe is touching, but the firestop detail will require a “bead of sealant,” or a buildup at that area where you can’t get the proper sealant depth. This is universal in all firestop details I’ve ever seen. So if you are responsible for QAQC or inspection of any kind, it’s useful to walk the project after the pipes are installed and before the firestop is in place so you can confirm that the annular space meets the requirements of the firestop detail. If you look at it after it is firestopped, you can’t tell if the annular space conforms with the requirements of the firestop system without destructive testing.

What About Angled Pipes?

Most of the time, your pipe will run through a rated assembly at a 90-degree angle. When this happens,  the annular space is pretty easy to understand, but if the pipe runs at an angle through the wall, several things change. The annular space is going to be different on one side of the wall than it is on the other side, so how do you address that when it happens? Join us for our next Lessons in Firestop to find out.

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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