Have you ever worked on a project that used hollow-core concrete floor panels? I have a scary bit of news to share with you: I have never seen a hollow-core concrete project that was firestopped properly…without some solid guidance. In fact, on the last hollow-core concrete project I participated in, the general contractor went bankrupt because they went too far through the project before they started thinking about firestop—they went so far along that there was no cost-effective remediation.
I want to save you from this headache. If you have a hollow-core project coming in your lineup, please read this closely and share it with your entire build team, because while we address what plumbing engineers need to know, all of the trades need to be aware of these issues.
The Code Riddle
You can scour the building codes and you will never find this information, but it is still a code requirement. That sounds like a riddle, but it’s a serious life-safety issue. The codes say you have to install your pipes to a system tested to ASTM E814 or UL 2179; that is the code section you have to reference in chapter 7. To better understand that, you need to go here and view the XHEZ document (free signup is required). If you deal with firestop a lot, you might want to read through the whole document. It’s a great resource for an array of topics.
Breaking Down the Listing Requirement
In this discussion we are going to deal with the section extracted below:
Some firestop systems specify the use of hollow-core precast concrete unit floor assemblies. Where not specified, firestop systems utilizing caulk, sealant, putty, or spray materials installed over a mineral wool or ceramic blanket may be installed in hollow-core floors, provided that:
- The thickness of the hollow-core floor is equal to or greater than the minimum concrete thickness specified in the system,
- The maximum size of the opening is 7 in. diameter or 7 in. by 7 in., and
- Any cores of the precast concrete units penetrated as a result of the firestop system are sealed with a minimum 4 in. depth of either firmly packed minimum 4-pcf mineral wool or ceramic fiber blanket, or concrete, grout, or mortar. Additionally, firestop systems utilizing a firestop device or wrap strips/steel collar installed around the penetrant beneath the floor may be installed in hollow-core floors, provided that (1) the thickness of the hollow-core floor is equal to or greater than the minimum concrete thickness specified in the system, and (2) the maximum size of the opening is 7 in. diameter or 7 in. by 7 in.
A plumbing engineer can’t do much with the first item, but you sure can with the second item. Let’s imagine you have a 6-inch roof drain. How are you going to make a hole that can accommodate the pipe and the required firestop material? Let’s look at the first detail in the UL directory that could work. This is a Tremco product, and the detail is CAJ 1205. If you want to look it up, go here.
The detail says the maximum pipe size is 12 inches, but if the maximum opening is 7 inches, then clearly there are restrictions in hollow-core projects. Keep going to the third item in the listing, where it requires 4 inches of mineral wool and ½ inch of sealant. If the top section of the hollow core is only 2 inches or even 3½ inches, how can you fit in 4 inches of mineral wool along with the ½ inch of firestop sealant? As you can see, if you have a hollow-core project, you have to be able to filter the information to specifically what you need.
What Happens if You Don’t Meet the Requirement?
Let’s talk about what happens if you don’t fill these cores before the trades run their services. Well, it becomes close to impossible to complete this required task—that’s what happens.
It’s one thing for me to tell you, “YOU MUST DO THIS!” It’s another thing for you to actually understand why it’s important, so let’s take care of that as well.
Let’s say this is a 15-story apartment complex. A resident gets home after working a night shift and is hungry, so they start cooking pasta. They doze off while it’s cooking, and a fire starts in the kitchen. The firestop in a solid concrete floor could be expected to perform and prevent the transfer of fire and smoke to other areas of the building, but in a hollow-core concrete project where the cores are not properly closed, the pressure buildup in one room will be high: Close to the ceiling end it will begin to force smoke into every other room. However, the heat keeps the smoke tight to the ceiling, which means anyone trying to evacuate from that room can get on their hands and knees since they’re likely to find cleaner air close to the floor.
On the other hand, people in adjacent rooms will find that toxic smoke fills the room from floor to ceiling since the buoyancy will be gone because the smoke will mix with the cool air in the room. Carbon monoxide is a colorless, odorless gas that will be the predominant deadly factor. What does that mean? While other building residents sleep, we hope that the toxic elements in the smoke will irritate their lungs and cause them to cough and wake up. This is the only chance they have of escaping this toxic, smoke-filled environment.
Maybe it wasn’t a kitchen fire. Maybe it was an overloaded extension cord. Maybe it was an overheated electric bike or scooter. Regardless of the cause, the importance of this article for those of you working on hollow-core concrete projects is that you remember to fill these cores. This is a critical element of life safety. Plan your project so you get this right.
With that, I want to wish you all the best during this holiday season. Be careful with candles and power strips. Since I won’t share with you again for the rest of 2022, I want to wish you a safe and Happy New Year! Thank you for reading about my favorite construction topic. I hope you find it valuable; if you do, I would love to hear from you so I know what you like, what you want to hear more about, and how this has helped you build better.
With that, I will see you all again in 2023!
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.