What Is Passive Fire Protection and What Products Are Used?

Summary

Fire protection is divided into two broad categories: active and passive. Active fire protection systems respond when a fire starts — sprinklers discharge water, alarm systems sound, dampers close. Passive fire protection is built into the fabric of the building itself and provides continuous, maintenance-free resistance to fire spread, regardless of whether any detection or suppression systems have activated.

Passive fire protection buys time. A compartment wall rated to 60 minutes means occupants and firefighters have at least 60 minutes from the point of fire exposure before that barrier is breached. During that time, people can escape, the fire service can arrive, and suppression can begin. The entire passive fire protection system — from the structural steel casing to the door seals — must work together; a single weak point (an unsealed penetration, a failed self-closer, an unprotected beam) can negate the benefit of everything else.

Third-party certification is the cornerstone of credible PFP specification. Products must be tested and classified, and ideally certified by an independent body such as the LPCB or BBA. Installers should ideally hold FIRAS or IFC accreditation. The Building Safety Act 2022 has increased scrutiny on PFP specification and installation competency, particularly for higher-risk residential buildings.

Key Facts

• Active fire protection (AFP) — Systems that respond to fire: sprinklers, fire alarms, smoke ventilation, fire suppression
• Passive fire protection (PFP) — Built-in resistance: compartment walls/floors, structural protection, fire doors, fire stopping, cavity barriers
• BS EN 1363 — Current European test standard for fire resistance of building elements
• BS 476 — Older UK test standard; still referenced for many products and historical installations
• Fire resistance rating (FRL) — Combination of three performance criteria: load-bearing capacity (R), integrity (E), and insulation (I)
• R rating — Resistance to collapse under load for the rated period
• E rating — Resistance to passage of flame and hot gases (integrity)
• I rating — Resistance to heat transfer (insulation); temperature rise limited on unexposed face
• Typical ratings — REI 30, REI 60, REI 90, REI 120; expressed in minutes
• Intumescent products — Materials that expand dramatically when exposed to heat; used in seals, mastics, pipe collars, and structural coatings
• Structural fire protection — Casing, boarding, or intumescent coatings applied to structural steelwork
• Third-party certification — LPCB, BBA, CERTIFIRE, UL; essential for credible product specification
• Installer accreditation — FIRAS (passive fire protection); IFC Certification
• Architect/specifier responsibility — Selection of fire-rated products must match tested configurations
• Specification error risk — A product installed outside its tested application provides no guaranteed performance

Quick Reference Table

Detailed Guidance

Structural Fire Protection

Steel structures are non-combustible — they will not catch fire. However, structural steel loses its load-bearing strength rapidly at elevated temperatures. At approximately 550°C, steel strength is reduced to around 60% of its cold value; failure can occur. In an unprotected building fire, structural steel can reach failure temperatures within 15–30 minutes.

Structural fire protection (SFP) keeps the steel temperature below its critical temperature for the required fire resistance period. The required period (typically R30, R60, or R90) is determined by Approved Document B based on the building's purpose group and height.

Methods of structural fire protection:

Board protection: Fire protection boards (calcium silicate, vermiculite-based, or other mineral boards) are fixed around columns and beams. Highly reliable and durable. More labour-intensive than spray or paint methods. Preferred in high-traffic areas and where the protection may be physically damaged.

Intumescent coating (paint): Applied as a liquid coating similar to paint (though it may be several millimetres thick when fully built up). On fire exposure, the coating intumesces — expanding to 20 to 50 times its original thickness — forming an insulating char layer that slows heat transfer to the steel. Available in thin-film and thick-film variants. Thin-film intumescent coatings are commonly used in commercial buildings where the steel is exposed architecturally. Thick-film coatings provide longer rated periods.

Intumescent coatings must be applied to the correct specified thickness, confirmed by wet film gauge measurement during application and dry film gauge on the cured product. Over-application or under-application will affect performance.

Spray protection: Mineral fibre or cementitious spray applied by specialist subcontractors. Provides effective fire protection and can achieve complex profiles, but produces a rough, grey appearance that is unsuitable where aesthetics matter. Most commonly used in car parks, plant rooms, and industrial buildings.

Concrete encasement: Traditional method using concrete formed or cast around the steel. Very robust and permanent. Less common in modern construction due to the weight and formwork required.

Intumescent Products for Penetrations

Where pipes, cables, ducts, and other services pass through fire-resisting walls and floors, the penetration must be sealed to maintain fire resistance. Intumescent products are the primary technology:

Intumescent pipe collars (for plastic pipes): A collar of intumescent material is fitted around the plastic pipe where it passes through the compartment wall or floor. On fire exposure, the plastic pipe melts and the intumescent material expands, crushing the void left by the pipe and restoring the fire resistance of the wall or floor. Must be fitted on both sides of the penetration or through the full thickness of the wall, depending on the tested configuration. Collar size, pipe material, wall construction, and fixing method must all match the tested system.

Intumescent mastic: A flexible, paste-like material that swells significantly when exposed to heat. Used to seal gaps around cables, pipes, and at junctions between fire-rated elements. Applied from a cartridge into the annular gap. Not suitable as the sole protection for plastic pipe penetrations (the pipe void remains when the pipe melts); typically used in combination with other products for pipes, and as the primary product for cable penetrations in combination with fire batts.

Fire batts (mineral wool or intumescent): Preformed slabs cut to fill the annular space around a penetration. Used for cable trays, bunched cables, and large service penetrations. Must be the correct density and compressed correctly within the penetration. Often used with intumescent mastic on the exposed faces.

Ablative coatings: Applied to the outside of ductwork passing through compartment walls. The coating burns away slowly, insulating the duct for the required period. Used where a fire damper is impractical or for short duct penetrations.

Fire-rated sealants (joints and junctions): For sealing the junction between a fire-rated wall and the structure above (where a fire-rated partition meets the underside of a concrete slab, for example), fire-rated acoustic and fire sealants are used. These must achieve the required fire resistance period under the test evidence for the specific joint configuration.

Fire Doors

Fire doors are a critical PFP element — they form the openable portion of compartment walls and protect escape routes. A fire door is a complete doorset system: the door leaf, frame, seals, ironmongery, and glazing must all be specified and installed as a tested assembly.

• FD30: 30 minutes integrity; most common in residential and commercial buildings
• FD60: 60 minutes integrity; required for certain higher-risk areas, stair enclosures in taller buildings, and high-risk occupancies

Fire doors are covered in detail in the related article fire door installation.

Cavity Barriers

Concealed voids in buildings — wall cavities, ceiling voids above suspended ceilings, floor voids — allow fire and smoke to bypass compartment barriers. Cavity barriers are fire-resisting closures installed within these voids to restrict this spread.

Types of cavity barrier:

Mineral wool cavity barriers: Rigid or semi-rigid mineral fibre (stone wool or glass wool) sections fixed within the cavity. Must be mechanically fixed (not simply laid in position) and must butt tightly to all surrounding construction elements. Must achieve at least 30 minutes' integrity under BS EN 1364 conditions.

Intumescent cavity barriers: Strip or section products incorporating intumescent material. Used where the void width varies or where gaps around the barrier must be self-sealing. The intumescent element expands on fire exposure to seal any gaps.

Flexible barriers: For cavities that experience movement (e.g., around window frames in curtain wall systems), flexible mineral fibre barriers with intumescent strips allow movement while maintaining fire resistance.

Critical installation requirements:

• Cavity barriers must be continuous — no gaps at junctions
• Must close on all four sides: top, bottom, and both edges
• Service penetrations through cavity barriers must be sealed with appropriate fire-stopping products
• Must not be compressed excessively (compression reduces performance)

Certification and Third-Party Approval

The chain of evidence for PFP must be robust:

1. Test evidence: Products must have been tested to the relevant BS EN or BS standard. Test reports from accredited test houses (Warrington Fire, BRE, etc.)
2. Third-party certification: Products assessed and listed by independent bodies such as LPCB (LPS 1181 for passive fire protection products), BBA (Agrément certificates), or CERTIFIRE
3. Installer competency: Installation by FIRAS or IFC-accredited contractors provides documented evidence that the product was installed in accordance with its test evidence
4. As-installed records: Photographs, schedules of products installed, test evidence retained — particularly important for hidden elements such as pipe collars above suspended ceilings

The Building Safety Act 2022 gateway process for higher-risk residential buildings now requires demonstration of PFP product selection and installation competency at each stage of design and construction.

BS 476 vs BS EN 1363

There are two generations of fire resistance test standards relevant to UK buildings:

BS 476 series (British Standard, pre-harmonisation):

• Part 20: Determination of fire resistance of elements of building construction
• Part 21: Methods for determination of fire resistance of loadbearing elements
• Part 22: Methods for determination of fire resistance of non-loadbearing elements
• Part 23: Contribution of components to fire resistance of assemblies

Products tested only to BS 476 remain in use and in specifications. BS 476 ratings are expressed as minutes only (e.g., "60 minutes") without the REI classification notation.

BS EN 1363 series (European harmonised, current):

• Harmonised test standard across EU/UK
• Produces results expressed as R, E, I with time in minutes (e.g., REI 60)
• More detailed classification allows distinction between load-bearing, integrity, and insulation performance

Both generations of test evidence remain valid for products on the market. When comparing products or updating specifications, ensure like-for-like comparisons — a BS 476 Part 22 60-minute result (integrity only) is not the same as an REI 60 result (which includes load-bearing capacity and insulation).

Frequently Asked Questions

Does PFP replace the need for sprinklers?

No. PFP and active fire protection are complementary, not alternatives. In some circumstances, Approved Document B allows increased compartment sizes or relaxation of other requirements in sprinklered buildings — so the presence of sprinklers can inform the level of passive protection required. But passive compartmentation, fire doors, and structural protection remain essential even in sprinklered buildings.

How long do intumescent coatings last?

Properly applied and protected intumescent coatings on structural steel have an expected service life of 10–25 years, depending on the product, environment, and any mechanical damage. They must be periodically inspected for adhesion failure, cracks, impact damage, and evidence of moisture ingress. An inspection programme should be in place, with records maintained. Where damage is found, repair or replacement must be carried out using the same product to the same specified thickness, with new dry film gauge checks.

Can I install passive fire protection products myself?

Some products (such as intumescent mastic around cable penetrations in a simple configuration) can be installed by a competent tradesperson following the manufacturer's instructions. However, more complex applications — structural intumescent coatings, fire damper installations, large penetration sealing — require specialist knowledge. For higher-risk buildings, the Building Safety Act now effectively mandates that PFP installers demonstrate competency, and FIRAS or IFC accreditation is the recognised route. Wherever liability and regulatory compliance matter, using accredited installers is strongly recommended.

How do I know which product to specify for a particular penetration?

Consult the manufacturer's product data and test evidence (often called application data or system data sheets). The data will specify:

• What substrates the product has been tested in (e.g., 100mm blockwork, 150mm concrete, 100mm metal stud drywall)
• What pipe materials and diameters are covered
• The maximum annular gap that can be sealed
• The fire resistance period achieved
• The fixing or application method required

If the specific application is not covered by the test evidence, contact the manufacturer's technical support. Do not substitute a similar-looking product from a different manufacturer or use the product in an untested configuration.

Regulations & Standards

• Approved Document B (ADB) Volumes 1 and 2 (2019) — Fire resistance requirements for elements of structure and compartmentation

• BS EN 1363-1 and -2 — Fire resistance tests; general and alternative methods

• BS EN 13381 series — Test methods for determining the contribution to the fire resistance of structural members; Part 8 covers intumescent coatings

• BS 476 Part 20, 21, 22, 23 — Legacy UK fire resistance test standards; still valid for products tested to these standards

• BS EN 1366 series — Fire resistance of service installations (Part 2: fire dampers; Part 3: penetration seals; Part 4: linear joint seals)

• BS EN 1634-1 — Fire resistance and smoke control tests for door and shutter assemblies

• LPS 1181 — LPCB scheme for passive fire protection products

• Regulatory Reform (Fire Safety) Order 2005 — Duty to maintain fire precautions; application of PFP in occupied buildings

• Building Safety Act 2022 — Gateway process requiring demonstration of PFP competency

• ASFP (Association for Specialist Fire Protection) — Technical guidance, product directories, good practice guides

• LPCB Red Book — Directory of third-party certified PFP products and installers

• FIRAS installer scheme — Accreditation for passive fire protection installers

• BBA (British Board of Agrément) — Agrément certificates for PFP products

• Approved Document B — Fire Safety — DLUHC guidance

• compartmentation — Compartmentation principles and maintaining fire-stopping

• fire door installation — Fire door specification, installation, and maintenance

• sprinkler systems — Active fire suppression systems and their interaction with passive protection

• fire risk assessment — Identifying PFP deficiencies as part of a fire risk assessment