How sealing gaps, joints and service penetrations keeps your passive fire protection strategy intact

This article provides general information on fire stopping and compartmentation. It is not legal advice. Building owners and managers should confirm their specific fire safety requirements with a competent fire risk assessor or fire engineer.

What Is Fire Stopping?

Fire stopping (often written as firestopping) is the sealing of gaps, joints and service penetrations in fire resisting walls and floors, so that the fire resistance of that element is not reduced by the openings made through it.

Every time a pipe, cable, duct or conduit passes through a compartment wall or floor, it creates a hole in what is otherwise a continuous fire resisting barrier. Fire stopping closes that hole with a tested product or system, designed to maintain the fire resistance of the wall or floor around it: its integrity (stopping flames and hot gases getting through) and, where required, its insulation (limiting heat transfer to the other side). Without it, a well-built compartment wall can be rendered almost useless by a handful of unsealed penetrations.

How Fire Stopping Fits into Fire Compartmentation

Compartmentation is the strategy of dividing a building into sections, so that a fire starting in one area is contained there for a defined period rather than spreading freely. It relies on four elements working together as a complete system: fire resisting walls and floors, fire doors, cavity barriers and fire stopping.

Fire stopping is what holds that system together at its weakest points. A compartment wall can be built to the correct specification and still fail in a real fire if the penetrations through it were never properly sealed, or were sealed with an unsuitable product. Fire stopping is not an add-on to compartmentation. It is one of the elements that makes compartmentation work in practice.

Why Fire Stopping Matters More Than It Looks

Fire stopping rarely gets noticed when it is done properly, because once the surface is made good a sealed penetration looks much like any other finish. That is part of the problem. It is one of the few elements of passive fire protection that becomes almost invisible once the job is finished, which makes it easy to overlook during construction and during later refurbishment.

The consequences of poor fire stopping are serious. Unsealed or incorrectly sealed penetrations let fire and smoke bypass compartment lines, eating into the evacuation time a building's fire strategy depends on and compromising escape routes, stairwells and neighbouring compartments. It is exactly the kind of hidden defect a fire risk assessment is meant to pick up, and exactly the kind that is easiest to miss if nobody is specifically looking for it.

On a recent riser survey in an occupied block, our team found 4 penetrations that had been correctly sealed at handover but later cut open for new data cabling and a pipework alteration and never reinstated. Nothing looked wrong from the corridor. Behind the riser door, the compartment line was effectively open.

Where Fire Stopping Is Needed

Fire stopping is needed wherever a service passes through a fire resisting element, and wherever there is a joint or gap in that element that could otherwise let fire or smoke through.

Typical locations include pipework and cabling through compartment walls and floors, service risers, ductwork penetrations, the head of compartment walls where they meet the floor slab above, structural movement joints, and the perimeter gaps around fire door frames and glazed screens. Approved Document B is clear that openings for pipes, ducts, conduits and cables through a fire resisting element should be kept as few and as small as practicable, and properly fire stopped where they do occur.

Common Types of Fire Stopping and Related Systems

Fire stopping covers a range of products and systems, each suited to a different type of opening. Cavity barriers are a separate element of compartmentation, but they are usually inspected and installed alongside fire stopping, so we cover them here too.

Penetration Seals

These seal the gap around services such as pipes, cables and ducts passing through a wall or floor. The correct system depends on the type of service, its material and diameter, the surrounding construction and the fire resistance period required.

The material of the service matters as much as its size. Metal pipes conduct heat and are typically sealed with intumescent or ablative mastics, sleeves or wraps. Plastic pipes soften and collapse in a fire, so they need an intumescent collar or wrap that expands to close the opening as the pipe burns away. Insulated pipework needs a tested detail that suits the insulation, which often means keeping the lagging in place rather than cutting it back. Larger openings carrying several services are commonly sealed with coated mineral wool batt systems.

Fire-rated foam has its place, but only within its tested scope. It is one of the most commonly misused products we find on site, often used to fill openings far larger, or around services far different, from anything it was tested for.

Linear Gap and Joint Seals

These seal continuous gaps and joints, such as the head of a compartment wall where it meets the slab above, or a movement joint built into the structure. They need to accommodate movement without losing their fire performance, which makes product selection and installation detail particularly important.

Cavity Barriers

Cavity barriers close off concealed spaces, such as voids above suspended ceilings, within raised floors or inside partition walls, to stop fire and smoke travelling unseen through the building. Because they sit inside a cavity, they are often the hardest element of passive fire protection to inspect once construction is complete, which makes getting the installation right first time especially important.

Why a Tube of Sealant Is Not a Fire Stopping System

One of the most common misunderstandings in the industry is treating any fire-rated sealant as an adequate fire stopping solution on its own.

A genuine fire stopping system is a tested combination of products, installed in a specific configuration, for a specific service, penetration size and surrounding construction. A product that performs well in one scenario may be completely unsuitable in another. Applying a generic fire-rated sealant around a penetration, without reference to a tested system or the manufacturer's field of application, does not reliably achieve the fire resistance the compartment line depends on, even if the product itself carries a fire rating. Fire resistance is a property of the whole installed system, not of the tube.

Standards and Certification for Fire Stopping

Penetration seals are tested to BS EN 1366-3 and linear joint seals to BS EN 1366-4, with performance classified under BS EN 13501-2. Many existing installations were tested under the older British Standard BS 476 series, and you will still see both in product data. The Association for Specialist Fire Protection publishes further guidance on good practice for design, installation and inspection.

Third-party certification through a UKAS-accredited scheme provides an added layer of independent assurance. It typically covers the competence of the installing company, the training of individual operatives, and ongoing surveillance audits of completed work. Certification is not a legal requirement on every project, but it is one of the clearest ways a specialist contractor can show that its work is carried out and checked under an independently assessed system, rather than relying on self-certification.

Crown Fire Systems is a 3rd party accredited certified installer for firestopping and fire door installation, under an UKAS-accredited scheme. Every certified seal we install is uniquely labelled and recorded, so building owners have the evidence they need for their fire safety information.

Common Fire Stopping Failures Found on Inspection

Fire stopping is one of the areas most often found defective during passive fire protection surveys, and the reasons follow a familiar pattern.

Typical issues include penetrations sealed with an unsuitable or untested product, foam used well outside its tested scope, plastic pipes sealed with mastic alone instead of a collar or wrap, gaps left entirely unsealed after a service was added or altered, and cavity barriers missing or displaced by other trades. Many of these defects are introduced after the original installation, during refurbishment, maintenance or the fitting of new services, rather than at the point of construction.

Who Is Responsible for Maintaining Fire Stopping?

Installing fire stopping does not transfer responsibility for fire safety away from the building's Responsible Person. Under the Regulatory Reform (Fire Safety) Order 2005, the Responsible Person must manage fire safety across the premises, including making sure compartmentation is maintained and acting on defects identified by the fire risk assessment. In multi-occupied residential buildings, the Fire Safety (England) Regulations 2022 add further duties. In higher-risk buildings, the Building Safety Act 2022 places duties on the Accountable Person, including keeping accurate fire safety information as part of the golden thread.

This matters because fire stopping is disturbed so often after handover. Every time a new cable, pipe or duct goes through a compartment line, the fire stopping around it is at risk unless the work is carried out, or checked, by someone competent to do so.

A Simple Fire Stopping Checklist for Facilities Managers

1. Identify where services pass through compartment walls, floors and cavities across the building
2. Look for identification labels on existing seals, and check your O&M manuals or fire safety information for installation records and product data
3. Check for gaps introduced by later cabling, pipework or refurbishment work, particularly in risers and above ceilings
4. Inspect cavity barriers above suspended ceilings and within partitions where access allows
5. Require a permit or sign-off for any contractor who cuts through a compartment wall or floor, and make reinstating the fire stopping part of their scope
6. Keep schedules, product data and certification for all fire stopping work carried out
7. Arrange a professional inspection where the condition or extent of existing fire stopping is unclear

Frequently Asked Questions

Is fire stopping a legal requirement?

Yes. For new building work, the Building Regulations require fire resisting walls and floors to keep their fire resistance where services pass through them. For existing, occupied buildings, the Responsible Person has an ongoing duty under fire safety legislation to make sure compartmentation, including fire stopping, is maintained.

Can any fire-rated sealant be used for fire stopping?

Not reliably. The product needs to form part of a tested system suited to the specific service, penetration and construction, rather than being assumed suitable because it carries a general fire rating.

Is fire-rated foam acceptable?

Only where it is used within its tested scope, for the opening size, service type and construction it was tested with. Used outside that scope, which is common, it should not be relied on.

How do I know if my building's fire stopping is still intact?

Because much of it is hidden in risers, ceiling voids and behind walls, this usually needs a professional inspection, particularly if services have been added or altered since the original installation.

Does fire stopping need to be replaced if it's disturbed?

Generally, yes. Fire stopping that has been cut into, removed or displaced to let new services through should be reinstated using an appropriate tested system, not left open or patched with an unsuitable product.

Where This Fits with Our Services

Fire stopping is one of the easiest elements of passive fire protection to get wrong, and one of the hardest to check once it is hidden behind a finished wall or ceiling. Getting it right depends on the right tested system, properly installed and properly recorded.

Crown Fire Systems surveys, selects and installs tested fire stopping systems and cavity barriers as part of a complete passive fire protection approach, alongside our fire safety inspections and surveys, fire door installation and certification and fire-resistant boarding. Take a look at our full range of services, or get in touch if you would like to discuss the condition of your building's compartmentation.

About the Author: Alex Orza is Head of Fire Stopping at Crown Fire Systems, with 8 years in passive fire protection across estimating, contracts and site delivery.