Fire Stopping Around Structural Steel: Methods and Ratings

There’s no specific fire-test standard for penetrations by structural steel beams and purlins. Fire stopping around structural steel penetrations must therefore be assessed against the actual construction and the evidence for the proposed system. Because steel is load-bearing, its behaviour under heat and any movement or deflection matter alongside the seal around the opening. Service penetrations through walls and floors are assessed differently.

It’s understandable to focus on the fire-resistance rating, but a rating is useful only when it applies to the arrangement being installed. This article explains how beams and purlins affect fire stopping, what spray applications and ratings can tell you, and why coatings, sealants and other components must work together. It also explains how tested systems for pipes and other services through walls and floors are assessed, helping you distinguish a suitable penetration detail from one that merely looks complete.

Fire stopping spray materials and application

Suitable products depend on the steel detail and the tested system. Options include fire-rated boards, intumescent coatings, cementitious sprays, and, around beams or columns, intumescent pillows or ablative mineral wool batts, according to the Scottish Government. These materials protect steel or close openings, but they are not interchangeable. The selection must match the construction and required fire performance.

Measure the width and depth of each gap, then compare both with the tested system’s permitted installation details. Fill the annular space using the specified materials and arrangement, including any backing material or sealant. Don’t assume a larger gap can be filled by applying extra spray: the system evidence must cover the actual opening and steel configuration.

Thin-film intumescent paint reacts at about 200-250°C and expands to insulate steel. Thin-film systems are mainly used for 30, 60 or 90 minutes of fire resistance; some products reach 120 minutes. Dry-film thickness can range from 100 to 5,000 microns, so the project specification determines the required application. Steel needs a compatible anti-corrosion primer, and intermediate drying between paint layers usually takes 24 hours.

Cementitious spray-applied coatings provide fire and thermal insulation. Fire-stopping sprays are applied in layers 10 to 70 mm thick; reinforcing mesh can support a thicker layer. Intumescent fire-protection paints should be tested to EN 13381-8. For a complex beam or purlin penetration, a technical assessment will almost always be required. Bespoke details need evidence that addresses the specific application, not just a similar-looking assembly.

Coatings can be applied on-site or off-site. Off-site application allows the coating to be applied before steel erection; on-site work accommodates installed members and site conditions. Both require checks of preparation, coverage and thickness. A qualified, competent fire engineer can support the technical assessment, while an experienced third-party-approved contractor can inspect the installation. The system evidence and inspection records support assurance, but no single certificate should be assumed to cover every bespoke detail.

Fire resistance ratings and testing standards

A fire-resistance period describes how long an element maintains its relevant performance under fire conditions. For structural steel, the rating must address load-bearing capacity as well as the protection system.

Fire Resistance Ratings

A rating classifies an element’s performance for a stated period and criteria. It is not a universal guarantee for every installation. Structural-steel testing considers whether the member retains its capacity under heat and applied load. That distinction matters: a seal around an opening and the steel supporting the building perform different functions. Passive fire protection must address the required performance of each part.

For example, full concrete encasement of structural steelwork can achieve up to 240 minutes of fire resistance. Reinforced concrete between steel-member flanges can provide up to 120 minutes for columns and 180 minutes for beams. These examples show why the period depends on the tested construction, rather than the material name alone. Match the evidence to the actual member, protection arrangement and intended fire-safety function.

Testing Standards

Testing standards define how protection systems are assessed and what their classifications demonstrate. Fire-protection boards should be tested to EN 13381-4, while a horizontal fire-protection membrane should be tested to EN 13381-1 to classify load-bearing capacity. A horizontal fire-stopping membrane may also be tested to EN 1365-2 for load-bearing capacity and fire resistance.

By contrast, membrane systems tested to EN 1364- 2 provide EI fire resistance, but do not establish structural load-bearing capacity. That difference is critical when reading test evidence: an EI result cannot, by itself, demonstrate that a steel structure retains its capacity. Structural-steel fire tests are often conducted in floor furnaces, where a load is applied and sections may bend or deflect as they weaken.

There is no specific fire-test standard for penetrations by structural steel beams and purlins. Steel pipes follow service-penetration testing, but load-bearing steel requires different methods. For a project-specific assessment, fire stopping support can help address the protection details alongside the relevant evidence.

Compatibility of coatings, sealants and other systems

Compatibility means each component works with adjoining materials as part of one tested arrangement. Around steel, the coating, sealant and supporting wall must not undermine one another’s performance.

System Compatibility

Start by identifying the steel’s coating, the opening’s construction and the proposed firestop. An intumescent coating needs room to expand when heated, so brackets, boards or sealants must not obstruct it. Consider whether steel movement or deflection during a fire could damage the seal or compartment wall. These interactions affect both the coating’s protective function and the wall’s ability to maintain separation.

At the penetration, compare the installed detail with the evidence for the complete system. If a pipe collar or wrap leaves a gap, fire-stop that space with a tested system compatible with the collar or wrap. Separate product test results do not prove that the combined arrangement will perform as intended.

Comparing Sealants, Batts and Collars

Intumescent sealants, fire batts and collars have different roles, so selection depends on the opening and the service passing through it. Sealant can close gaps within a tested arrangement; mineral wool batts can form part of fire stopping around beams or columns. A collar or wrap is used around a compatible pipe system, with any surrounding gap filled using a tested, compatible detail.

According to the Scottish Government, intumescent pillows and ablative mineral wool batts are useful for fire stopping around columns and beams. Neither material substitutes for protecting the steel’s load-bearing capacity. A collar addresses a pipe penetration, not the steel member itself. Keep these functions distinct when assessing the detail.

Before installation, record the coating type and condition, the sealant or batt arrangement, and the service passing through the opening. Check the stated thickness and backing arrangement against the tested system. For example, a pipe wrap beside an intumescent coating needs a compatible gap seal, while a beam opening needs a detail that addresses both the penetration and steel protection. Sprays, coatings and sealants must not conceal damage or interfere with the system’s bearing and stability. A change to one component can alter the tested arrangement, so assess the revised detail as a whole.

Testing service penetrations through walls and floors

A service penetration is an opening for pipes or other services through a separating wall or floor. Its tested fire-stopping arrangement must suit both the service and the element it passes through.

Testing differs from structural-steel assessment. Steel pipes are tested as service penetrations, while beams and columns require methods that consider load-bearing capacity and possible deflection at high temperatures. Don’t treat evidence for a pipe as proof that a structural member is protected, or vice versa.

In the UK, evidence that a fire-stopping product suits a particular use may include a fire classification report to EN 13501-2. That report can be based on testing to EN 1366 Parts 3 or 4, as appropriate. The key is whether the evidence covers the application or a defined range of applications. A tested result applies to its assessed arrangement, not every opening that looks similar.

For combustible soil pipes passing through floors, tested intumescent collars and/or wraps at the floor penetration help prevent fire passing through. Around uPVC branch pipes penetrating walls separating dwellinghouses, use fire-tested pipe-closing devices. An alternative arrangement for uPVC pipes uses a non-combustible sleeve at least 1000 mm long on both faces of the separating element. These methods address different details, so match the evidence to the pipe type and wall or floor construction.

For a practical review, record the service type, the separating element, and the installed firestop. Compare those details with the classification evidence, including any stated limitations. This gives the project team a clearer record of which tested method applies to each location, rather than relying on appearance alone. Accurate floor plan generation can help identify and document service locations for that review.

National Fire: Fire Stopping

National Fire provides Fire Stopping for projects where steel penetrations, service openings or compartment details need a coordinated passive fire protection approach. Use the service when planning new penetrations, reviewing existing fire stopping or addressing changes that may affect a tested arrangement. The system must suit the opening, adjoining materials and required performance, with installation details documented for future review.

Where a wider building review identifies other passive fire protection needs, National Fire also provides Fire Door Installation, Fire Door Maintenance and Injectable Cavity Barriers. These services address different parts of a building’s fire protection strategy, while fire stopping focuses on openings and joints that could allow fire and smoke to pass.

For support with a fire-stopping project, contact National Fire.

Make the next project decision clear

Plan steel penetrations as part of the building’s wider fire strategy, rather than treating each opening as an isolated detail. Clear records of the intended arrangement and later changes help project teams maintain a consistent approach as work progresses. This is especially valuable when alterations affect the relationship between structural protection and compartmentation.

National Fire provides Fire Stopping, Fire Door Installation and Injectable Cavity Barriers to support different parts of a building’s passive fire protection. If your project needs a fire-stopping assessment or installation, discuss your fire-stopping requirements with National Fire. A considered approach to fire stopping around structural steel penetrations helps keep the project focused on appropriate system selection and reliable documentation.

Take the next step with a clear understanding of the building’s requirements and strengthen confidence in its fire protection strategy.

Frequently Asked Questions

How should steel beams and purlins be firestopped, and what are the challenges?

Use a project-specific detail that addresses both the opening and the steel member’s structural fire protection. Beams and purlins can move or deflect as temperatures rise, potentially stressing the seal or adjoining wall. Early coordination can also avoid unnecessary penetrations. For complex steel details, a technical assessment should consider the member, compartment construction and likely movement together.

What data or documentation should I ask for to demonstrate that product X is suitable for use?

Ask for evidence covering the proposed application, not just the product in isolation. This may include a fire classification report to EN 13501-2, based on testing to EN 1366 Part 3 or Part 4 as appropriate. Compare the report’s scope with the actual service, opening and separating element. Installation instructions and records showing the installed arrangement can help connect the evidence to the completed work.

What UK building regulations apply to fire stopping around structural steel penetrations?

Applicable fire-safety requirements depend on the building’s design and the functions of the wall, floor and steel member. The project fire strategy identifies the intended compartmentation and structural fire performance. The Building Safety Act places significant responsibility on Principal Designers to ensure fire safety. For a particular penetration, assess the design evidence and tested system against the actual construction rather than relying on a generic detail.

How should fire stopping be detailed where steel beams or columns pass through fire-resisting walls and floors?

Detail the wall or floor interface so the penetration does not compromise the required separation, and account for movement of the steel member. ASFP Advisory Note 21 recommends limiting penetrations of fire-protective encasement and aligning bracket connections with board joints to minimise gaps. For a beam passing through a wall, coordinate the encasement, brackets and firestop as one interface, with records of the installed arrangement.

How is the required fire-resistance period for a steel penetration determined in the UK?

The required period comes from the building’s fire-safety design and the performance expected of the structural element and separating construction. A penetration does not determine the period by itself. The assessment considers the member’s role, the surrounding wall or floor, and how the proposed protection addresses structural stability and fire separation. The project specification and supporting evidence should describe these requirements for the actual detail.

Do structural steel members need fire protection where they pass through compartment walls?

Assess the steel member and compartment wall separately, then coordinate their interface. The wall’s fire-resisting function does not demonstrate that the beam or column retains its load-bearing capacity during fire exposure. Equally, protecting the member does not close gaps around it. The fire strategy and detail should show how structural protection and the compartment boundary work together at the crossing.