The short answer is no.
Although a hollow core concrete slab might seem similar to a traditional reinforced concrete floor, it's important to note that manufacturers of hollow core slabs have very specific requirements about using mechanical fixings. These requirements can impact the slab's structural strength.
That’s why we’d always advise reaching out to the relevant manufacturer at an early design stage for best practice and to understand what has been fire tested.
What makes hollow core slabs different from traditional concrete floors?
How hollow core slabs are constructed
Hollow-core floors are a modern form of construction: precast concrete slabs with internal tube-like voids. Used across a wide range of construction projects, including multi-storey car parks, apartment buildings, hotels, and offices, they are increasingly popular for their excellent fire resistance and acoustic properties.
You may also hear them referred to as hollowcore planks, voided slabs, concrete slabs, or precast slabs.
Why the internal voids matter in a fire
The simple answer is that they are an unknown factor.
Unlike flexible walls, which have an interchangeable field of application that allows penetrations to be tested in a way that limits the number of tests conducted, there is currently no comparable scope for rigid floor testing. 
This means that evidence from a solid concrete floor test cannot be simply transferred to this different floor type, and therefore, specific testing on hollow core floors must be conducted.
How penetrations affect compartmentation
First, let’s quickly look at what fire compartmentation is. As a critical element of a building’s fire strategy, if done correctly, it contains a fire to its area of origin for a specified time, providing ample time for the fire service to arrive, attend to those in the building, and tackle the fire.
Compartmentation is determined at the design stage of a project; those involved will divide the building into risk zones using fire-resistant walls and floors.
What’s important to understand is that, naturally, a building’s compartmentation won’t remain a solid box. If you take a kitchen, for example, it needs windows, doors, pipes, and cables to be habitable.
That’s where firestopping plays a critical part. Each break in the compartment line will require suitable tested systems to reinstate the necessary fire rating.
And the only way to do this is to engage with system manufacturers as early as RIBA Stages 2/3 to guarantee that proposed elements of the design have available tested solutions.
What should you consider before installing services through a hollow core slab?
Structural considerations
For any supporting construction with structural or load-bearing requirements, the aperture for services needs to be reviewed at the design stage by a qualified structural engineer to ensure it meets structural requirements.
Some floor types may have limits on aperture sizes, spacing between apertures, etc., which could be a critical factor affecting the floor slab.
Firestopping the hollow cores
Because hollowcore planks have internal tubular voids, the penetration design must account for the passive fire protection seal more carefully than for a standard concrete floor slab.
The internal tubular voids often need to be sealed with a rock fibre section, as shown here: 
Coordinating with the slab manufacturer
Some slabs include openings that will require an early design meeting to ensure that any preformed openings meet all requirements, including passive fire protection, which can have specific requirements such as service spacing.
Some hollow core manufacturers can also have solid floor sections installed upon request, which can then be used with standard rigid floor details.
Can you use a fire collar?
Why a standard fire collar installation may not be appropriate
While it is logical to consider a hollow core concrete slab as similar to a traditional reinforced concrete floor, manufacturers of hollow core slabs have very strict requirements regarding the use of mechanical fixings, which can affect the slab's structural integrity.
On this basis, we have carried out specific testing on hollow core slabs using non-mechanical fixing solutions. Therefore, we would not recommend using a fire collar.
The importance of following tested details
Tested fire stopping solutions are the only way to prove an application will perform in the event of a fire – it gives that assurance.
The same applies to manufacturer guidance. Since manufacturers are experts on their products, reaching out to their support can be really helpful in making sure you meet all compliance requirements.
What has Quelfire tested for hollow core slab applications?
Quelfire has tested a variety of service penetration details for hollow core floors, including plastic pipes, metal pipes, cable containment, and even busbars. These can all be found in our QuelSelector Tool under the hollow core floor section.
Frequently asked questions
What are the benefits of hollow core slabs?
Voided slabs are well known for being lightweight and cost-effective. The internal voids reduce the slab’s weight without fully compromising its load-bearing strength, thereby decreasing the load on the building’s foundations and supporting structural elements like support beams. 
Furthermore, their installation is pretty straightforward, with off-site manufacturing and then craning into place. This means that follow-on trades can walk on the construction site without waiting for the concrete to cure.
Do I always need to seal the hollow cores?
Quelfire’s service penetration sealing details have all been tested with the hollow cores sealed. This helps not only with fire resistance but also makes the installation of fire stopping products, such as QF2 Fire Protection Compound, easier by preventing excessive material use.
