Compliant firestopping depends on the correct products being installed by competent installers, as per the test evidence. What supports this is a good understanding of the building design and engaging early with manufacturers to ensure the correct system is specified and thereby installed.
In this Knowledge Hub article, we cover key aspects of partial penetrations, from what they are and why they’re often misunderstood to available tested solutions and relevant UK standards.
What is a partial penetration in firestopping?
Partial penetrations explained
The phrase ‘partial penetration’ refers to an area where services penetrate only one side of the wall or the supporting construction and do not extend completely through.
Partial penetrations are often associated with walls; however, some floor constructions may also have partial penetrations for applications like ceiling fans and lights.
When the supporting construction is deemed a compartmentation line, partial penetrations, like all service penetrations, must be adequately firestopped to reinstate the supporting construction’s required fire resistance.
They are occasionally referred to as ‘single-side applications’, but this term can cause confusion with single-side access details used in full penetration applications. Therefore, it's better to consistently use the term ‘partial penetration’.
Common scenarios where partial penetrations occur
The term ‘partial penetration’ may seem vague at first, but it really means what it says – let's take a look at some examples.
Partial penetrations include socket boxes installed on one side of a plasterboard wall, radiator pipes that enter a wall to connect to plumbing but don’t pass through to the next room, and conduits or cables that enter a stud wall and stop inside.
Why they are often misunderstood on site
These types of penetrations are often overlooked and not considered at the design stage because they are very small. But they can cause serious compliance issues if installed incorrectly in compartmentation lines.
Simple things, such as being too close to fire doors, penetrating the wall’s deflection head area, and even choosing the wrong service material type, could all have a major impact on reinstating the supporting construction’s fire-resistance rating.
Why are partial penetrations critical to fire performance?
How fire can travel through incomplete seals
Fire will always follow the path of least resistance. Without passive fire protection measures, even small gaps will allow the rapid spread of fire across compartment lines. This allows the fire to spread beyond the compartment of origin, posing an immeasurable danger to those inside the building.
The role of compartmentation in these scenarios
That’s where effective fire compartmentation plays a vital role. It divides a building into areas of manageable risk through using fire-resistant walls and floors.
When the correct (and tested!) products are installed properly, the product’s intumescent material will expand in response to heat and essentially plug the hole formed by the melting, combustible service. This prevents the spread of fire.
Furthermore, the correct installation of non-combustible service details ensures that heat generated by the service remains below the required insulation fire-resistance thresholds, preventing secondary combustion from essentially ‘leapfrogging’ the compartmentation line.
This allows the fire and rescue service time to arrive, help residents, and tackle the fire while limiting damage to the property.
Consequences of getting it wrong
When a building’s design incorporates only larger services and excludes applications such as partial penetrations, the likelihood of non-compliance with building regulations is much higher.
MEP (Mechanical, Electrical & Plumbing) installers may be unaware of how their work affects fire-resistance requirements, and, inevitably, the remedial fallout from this can be very costly.
That is why it’s absolutely critical to understand the full building design picture, especially for HRB (higher-risk buildings) projects going through the Gateway process, where it is a legal requirement to provide a thorough design before a spade even hits the ground.
It’s understandable that contractors may feel frustrated by pushbacks at Gateway 2 and unexpected costs. But the consequences of getting firestopping wrong far outweigh the extra time and consideration needed to incorporate tested solutions at the design stage.
Ultimately, it’s about protecting people and property: every project should be approached with the end user in mind – something that can be successfully achieved through early engagement in fire stopping.
What regulations and guidance apply to partial penetrations?
Relevant UK standards and fire test requirements
There is no official fire-resistance test standard for partial penetrations in the UK or in Europe.
BS EN 1366-14 is being developed to add partial penetrations to the BS EN 1366 series, but it is currently in draft form with no definitive release date at the time of this article’s publication.
However, approved methods have been established to assist in providing tested fire stopping solutions. For example, for partial wall penetrations, we use the principles of BS EN 1366-3 with guidance from the BS EN 1366-14 draft.
Discussions around partial penetrations must take place during the design stages to ensure that what is intended to be built is backed up by fire test evidence.
The importance of service penetration sealing evidence
Ultimately, fire stopping solutions are the only way to ensure that, in the event of a fire, the systems will work exactly as intended and prevent the fire from spreading. Systems must be installed as tested.
There are many considerations when selecting product details, including fire rating requirements, wall or floor build-up, and service type and size. 
With manufacturers understanding their systems and test evidence best, they can offer support where needed, so always reach out if in doubt.
What tested solutions are available for partial penetrations?
Quelfire has tested a full range of partial penetration applications. Take a look at some examples below:
|
Service |
Detail Codes |
||||
|
Metal Socket Boxes |
PP-FW75-01 |
PP-FW95-01 |
PP-FW100-01 |
PP-FW119-01 |
PP-FW130-01 |
|
Plastic Socket Boxes |
PP-FW75-02 |
PP-FW100-02 |
— |
— |
— |
|
Metal Media Panels |
PP-FW75-03 |
PP-FW95-03 |
PP-FW100-03 |
PP-FW130-03 |
— |
|
Plastic Conduits |
HPE-FW75-PP-10 |
HPE-FW100-PP-10 |
QB-FW100-P-PP-14 |
— |
— |
|
Metal Conduits |
QSS-FW75-PP-05 |
QSS-FW100-PP-05 |
QB-FW100-P-PP-17 |
— |
— |
|
Cables |
QSS-FW75-PP-01 |
QSS-FW100-PP-01 |
— |
— |
— |
|
Plastic Pipes |
HPE-FW75-PP-01 |
HPE-FW100-PP-01 |
— |
— |
— |
|
Metal Pipes |
QSS-FW75-PP-03 |
— |
— |
— |
— |
View the solutions above in our Tested Detail Library.
FAQs about partial penetrations in firestopping
What is the difference between a partial and a full penetration?
A full penetration passes all the way through the wall or floor (from one side to the other), whereas a partial penetration passes through the substrate but stops before reaching the other side. Full penetrations must typically be firestopped on both sides!
Can partial penetrations be retrospectively firestopped in existing buildings?
The answer to this question depends on the quality of the service installation in the first instance. Often, partial penetration applications use direct-seal solutions with passive fire products, such as firestop sealants, installed directly into the plasterboard substrate.
However, with existing applications, it is unlikely that the opening will be correctly sized to accommodate the required annulus and depth of the fire stopping product. 
A pattress fire batt solution is likely the most suitable partial penetration method for existing applications being retrospectively firestopped.
Nevertheless, this approach does involve considerations such as the spacing around the seal and the placement of the service that must be accommodated during installation.
In many existing applications, remedial work on the service and substrate must be completed before achieving a compliant firestop seal.
Are partial penetrations suitable for all substrates?
The short answer is no. Generally, partial penetration solutions are limited to substrates that have a cavity, such as a double-sided flexible wall construction, or a double-skin blockwork wall.
What we mean by a cavity is a type of wall with a gap between its exterior and interior faces.
In these cases, the cavity creates a defined separation between the two sides of the wall and a clear area for the service to enter and bend to distribute within the substrate.
Whereas with a solid substrate, the depth the service penetrates before bending to distribute within the wall or floor may vary from application to application; therefore, it does not allow a defined performance to be determined.
Can I use the same product for both partial and full penetrations?
Yes, in many cases, a product and solution tested for a full penetration can be applied to a partial penetration application.
Quelfire has a Technical Guidance Note that outlines this in more detail (available on request from technical@quelfire.co.uk).
In summary, due to the extent of testing we have conducted, we have been able to compare data for services tested in the same application under both partial and full penetrations, and can apply full penetration details to a partial penetration application where practical.
If you have a specific application you would like assistance with, please contact Quelfire's Technical Team.
How do I prove compliance for a partial penetration?
Demonstrating compliance with building regulations depends on multiple factors, such as installing tested systems in line with guidance and evidence, implementing the golden thread of information, for example, taking before, during, and after photos of every penetration, and ensuring competence across all project teams. Third-party accreditation is one way to support this.
