An expert offers an introductory guide to passive fire-stopping and outlines when advanced preformed materials and devices are useful.
Recent events, including the Grenfell Tower tragedy and the Lacrosse tower fire in Melbourne, show that fire-conscious construction is as essential as it’s ever been. This involves three interconnected goals: preventing fires from starting, preventing them from spreading, and ensuring people have a means of escape during a fire incident.
Hani Adnan, Codes and Approvals Manager (Fire Protection) at Hilti, specialises in the second of these. He has a particular focus on passive fire-stopping – the use of materials and devices to close service penetrations or construction joint gaps in fire-rated walls and floors.
He is talking ahead of a webinar Hilti is hosting in partnership with Engineers Australia later in the year regarding the history and future of fire protection.
“One thing I heard when I started in this industry that I still really believe is this: Fire-stopping, unlike perhaps other fire measures, is either 100 per cent effective or entirely ineffective. There is nothing in between,” he says.
Adnan is enthusiastic about the potential of preformed fire-stopping materials and devices to assist designers and engineers in improving their work productivity and the fire resistance efficiency of their projects. Compared to traditional solutions, he says, they provide easier installation, inspection and maintenance, which leads to higher levels of safety.
Of course, says Adnan, understanding the needs of your project is key. To determine when preformed materials are best used, there are a few concepts you need to understand.
Where fire-stopping products are used
There are three passive fire-stopping categories:
- Through penetrations: openings in fire-rated assemblies where penetrants (pipes, cables, etc) pass through a fire-rated element and where the integrity of the wall or floor must be maintained.
- Fire resistive joints: any gap, joint, or opening between two fire-rated barriers including top of the wall to floor, wall edge to wall edge, floor edge to floor edge, and so on.
- Perimeter fire barriers: sealing any gap, joint or opening between a fire-rated floor assembly and the exterior wall assembly (for example, cladding).
Mastic vs intumescent materials
Mastic (or non-intumescent) materials such as silicone or acrylic sealants tend to be cheaper and used when penetrations have a higher melting point. A mastic works through an ablative reaction. It prevents heat transfer by ‘sacrificing’ itself, protecting the unexposed side of a compartmentalisation zone until the material is spent.
Intumescent materials are those that increase in volume when exposed to heat. A rigid char layer formed in the reaction insulates and prevents flame passage.
Some intumescent material formulations will also cause significant pressure while expanding. This pressure can be useful in applications such as the fire-stopping of plastic pipes, where the pressure can compress and seal the softening pipe during a fire.
Testing and the importance of compliance
All fire-stopping products must be tested as a full system including the penetrating item (such as a pipe), the opening size, the main structure, and (for dynamic joints) movement capability. This last factor is frequently overlooked.
“I sometimes get asked why fire-stopping applications on construction joints have torn after a few years,” says Adnan. “It could be the wrong installation – basically, if you apply the wrong sealant thickness it will crack over the years. It could also be that your joint’s movement capability – its ability to accommodate your building materials’ normal cycles of thermal movement – is more than your sealant’s movement capability.”
Adnan says when you test fire-stopping products in the lab, it is relatively easy to install them and get optimal results. When installing on site it is not as easy. One of the advantages of preformed products is the simplicity of their installation.
Traditional products vs preformed products
Traditional fire-stopping products include sprays, caulks, foams and sealants. They have many advantages. They’re cheaper up-front, they’re versatile, and there are lots of options to choose from as they’re a standard for most manufacturers.
Compared to preformed products, a major drawback is installation is harder to get right and more prone to human error.
Say you’re using a mastic sealant. You have to ensure you apply the correct thickness, take into account the spacing between the surface and the edge of the wall or floor, and sometimes the spacing between different services (eg: cables and a pipe), which can have different fire ratings. If you’re using it on a joint, you need to know the movement capability too.
“If you don’t pay attention to details, what you install might not be enough to get you the required resistance,” says Adnan. “You need to install it to the same configuration and specifications as the materials have been tested in. If you don’t, nobody could guarantee that you can achieve the same fire resistance level as in the lab.”
This is why preformed materials can end up saving money, even though they cost more up-front.
Also coming in intumescent and mastic variations, preformed materials are built to the required thickness of the application and often remove the need for other back-filling materials.
Another advantage of preformed materials is re-penetrability. If you need to verify the fire resistance of traditional sealants, you have to do a destructive check to inspect the whole system. Similarly, if you need to change the wires penetrating between two zones in a building, you will frequently have to re-assess and apply new fire-stopping foam or sealant.
One example of a preformed product that doesn’t require this is intumescent fire blocks. They can be cut into relatively easily without compromising fire resistance, and may also be removed and cut to size when additional services need to be accommodated. No electric tools are necessary.
These fire blocks are dust and fibre free and are recommended for big, multi-penetration openings. They’re also relatively easy to install, says Adnan, though you still need skilled installers because the orientation of the block can change the thickness.
A preformed device can be especially helpful for situations where changes are frequently required, such as data centres. Fire-stop sleeves can have a twist mechanism that opens and closes the inside of the sleeve, allowing for quick and easy re-cabling. They’re also very easy to install, maintain and inspect while offering superior smoke tightness and airflow control performance.
For the trade-off between higher up-front costs and higher productivity and efficiency to be worth it, any project using preformed materials needs to be properly planned and managed.
“I highly recommend excellent coordination between all the parties all the way down to the subcontactor. If that happens, you can save a lot of time, effort and cost,” says Adnan.
“Preformed devices simplify compliance with legislation and construction codes during and after construction, they’re easier to design for and they’re compatible with many other great building solutions such as BIM. They’re especially ideal in specific circumstances, including retrofitting, or when you need additional attributes such as greater movement capability, acoustic dampening and resistance to mould and mildew.”
To find out more about Hilti’s own preformed and more traditional fire-stop products, check out this page. If you are interested in a more detailed discussion, you can also reach out to Hani Adnan on LinkedIn.