Intumescent Seals & Collars: Door Seals, Pipe Penetrations & BS 476 Testing

Summary

Intumescent products are passive fire protection. They do nothing until a fire occurs, at which point they expand to seal gaps that combustion gases and heat would otherwise exploit to spread the fire. Because they must perform reliably in an emergency, third-party certification is not optional — it provides evidence that the product will perform as intended in the specific application.

For builders, joiners, and mechanical services contractors, the most common intumescent applications are: fire door seals (edge seals that expand to seal the smoke gap in a fire), pipe penetration collars (around plastic waste pipes through concrete floors), and duct and cable management penetrations. This article covers each application, the certification requirements, and the installation details that affect performance.

Key Facts

• Intumescent material — typically graphite-based; expands 5–10× original volume when heated to activation temperature (150–250°C depending on product); the expanded material is a rigid foam that seals the gap
• Fire door seals — intumescent strips and smoke seals fitted around the edge of a fire door; the intumescent expands and seals the gap between door and frame, preventing passage of hot gases; smoke seals (brush or rubber) are separate and seal against cold smoke; many modern products combine both functions (intumescent + smoke seal)
• FD30 and FD60 — fire door ratings; FD30: 30 minutes fire resistance; FD60: 60 minutes; the door, frame, seals, hinges, closer, and any vision panel must all be certified to the same rating as a complete system
• BS 476: Part 22 — fire test for fire doors (closure elements); tests resistance to fire on one face; used for door sets tested in the UK
• BS EN 1634-1 — European fire test for door sets; increasingly used alongside or instead of BS 476
• Certificate of Conformity — fire door seals and intumescent products should be supplied with a certificate confirming compliance with BS 476 or BS EN 1634 test data for the specific application; keep this on file
• Pipe penetration collars — plastic waste pipes (uPVC, MDPE, polypropylene) cannot pass through a fire-resistant floor or wall without a fire stop; when the pipe melts in a fire, the collar compresses and seals the hole; collar must be size-matched to the pipe and the construction (concrete floor, plasterboard wall, etc.)
• Metal pipes — cast iron and copper pipes do not require collars; they do not melt; the penetration is sealed with fire-rated sealant or mortar around the pipe
• Ductwork penetrations — HVAC ductwork through fire barriers requires either a fire damper (intumescent or motorised, closes in a fire) or intumescent wrapping/fire pillows around the duct; the method depends on the duct material and the fire resistance required
• Electrical cable management — multiple cables through a fire barrier can be sealed with intumescent pillows, putty pads, or expanding sealant rated for the specific cable bundle density
• Fire-rated sealant — around the collar, services, and frame joints; BS EN 1366-4 tested; do not substitute standard mastic sealant for fire-rated sealant at fire barrier joints
• Third-party certification — CERTIFIRE (Exova/Element), UKAS-accredited testing; Product Approvals Limited (PAL); Warringtonfire; ensure the certificate matches the exact product and application

Quick Reference Table

Detailed Guidance

Fire Door Seals — Selection and Installation

Fire doors are only as effective as their seals. The most common failures are:

• Seals missing (not fitted after replacement of door or frame)
• Seals of the wrong type (smoke seal only, no intumescent — or vice versa)
• Seals not correctly fitted (not continuous; not in the groove; damaged)
• Gap between door and frame exceeds 3–4mm (seals cannot bridge large gaps)

Gap requirements for fire doors: BS 8214 (Code of practice for fire door assemblies) specifies: the gap between door and frame should be 2–4mm on the latch and hinge sides; 3–4mm on the top; the threshold can be 0–8mm (with compliant threshold strip). Seals must be sized for the gap.

Intumescent strip installation:

1. Clean the rebate groove (in the door edge) or the face of the door/frame (if surface-mounted) — must be clean and free of paint or debris
2. Insert the intumescent strip into the groove; press firmly along the full length; the strip should be continuous with no gaps
3. Do not cut at mitred corners — butt joints at corners are acceptable and do not compromise performance
4. On the hinge side, the strip must not be obstructed by the hinges — the strip passes behind or around the hinge plate (depends on hinge type)

Smoke seal (brush seal): The brush or rubber smoke seal prevents cold smoke passage under and around the door. Fitted separately from (or combined with) the intumescent strip. For FD30+ rated doors, both are generally required. For FD30S (smoke control door), the smoke seal is the primary function.

Vision panels: Any glazed panel in a fire door must be fire-resistant glazed to the same rating as the door (FD30 or FD60). Standard float glass is not fire-resistant and must not be used. Fire-rated glass is expensive; the size of the panel affects the door's rated performance — use only panels that are part of the certified door assembly.

Pipe Penetration Collars

Plastic pipes (uPVC soil and waste, polypropylene, MDPE) melt in a fire. Without a collar, the hole left by the melted pipe allows fire to pass through a fire-resistant floor or wall.

How a collar works: The collar is wrapped around the pipe at the face of the floor or wall (or embedded in the structure). In a fire, the intumescent material within the collar expands and compresses the pipe from outside as it melts, sealing the penetration.

Specifying the correct collar:

1. Pipe outside diameter (OD): measured in mm; must match collar specification exactly (collars are sized for specific pipe ODs)
2. Construction type: concrete floor (thickness matters), blockwork wall, plasterboard stud wall — each has a different certificate
3. Fire resistance required: typically FRR 30/60 for floors; the floor's fire resistance determines the collar requirement
4. Is the collar on one or both sides? For a floor, one collar at the top (fire coming from below) is standard; some products require collar both sides for higher fire resistance

Installation method: For a concrete floor:

1. The pipe must be centred in the penetration hole; hole should be slightly larger than the pipe to allow collar to fit
2. Fit the collar around the pipe at the top face of the floor; secure with appropriate fixings per manufacturer's instructions (typically masonry anchors)
3. Seal around the collar with fire-rated sealant to BS EN 1366-4
4. Label the penetration: "INTUMESCENT COLLAR FITTED — DO NOT MODIFY" on both sides

Electrical Penetrations

Cables and cable trays through fire-resistant floors and walls must be sealed. The seal must:

• Fill the entire void, not just the area around the cables
• Be rated for the density and type of cables present
• Be accessible for future cable additions (most systems allow this with additional fire pillows or putty)

Typical solutions:

• Fire pillows: compressed against cables in the opening; expand to fill gaps; stackable; suitable for maintenance access
• Intumescent putty pads: wraps around individual cables; moulds around irregularities; pliable; no-drip in fire
• Expanding foam (fire-rated): do not use standard expanding foam (highly combustible); use only fire-rated expanding foam tested to BS EN 1366-3; this is a specialist product, not standard DIY foam

Frequently Asked Questions

My customer has replaced a fire door but the old intumescent seals are still in the frame. Do they need to be replaced?

Yes, if the new door is a different size or specification. Intumescent strips in the frame must match the door edge specification — if the new door has the strip in the door edge groove (which is common for modern factory-fitted strips), the old frame strips should be removed or will be covered by the new door edge strips. If the new door has a different gap to the old door, re-seal with correctly specified strips for the new gap dimensions. Document the seal specification.

I'm plumbing a bathroom over a concrete floor. Do I need a collar on the waste pipe?

Only if the floor is a fire-separating element — i.e., between two storeys (or between a dwelling and a common area in an HMO or apartment block). In a detached house, a ground floor concrete slab to a suspended floor is not typically a fire-separating element between occupied storeys; above a basement or between flats it would be. If in doubt, confirm with Building Control or the fire risk assessor.

Where do I source fire-rated collars and seals?

Specialist fire protection suppliers (Envirograf, Nullifire, HoldRite, FRS Ltd) stock BS EN 1366-3 tested collars and BS 476 tested door seals. Do not buy these from general plumbing or DIY merchants who may not carry certified products — the packaging must state the certificate number and the test conditions.

Regulations & Standards

• BS 476: Part 22:1987 — Fire tests on building materials and structures; fire resistance of closures (fire doors)

• BS EN 1634-1:2014 — Fire resistance and smoke control tests for door and shutter assemblies

• BS EN 1366-3:2009 — Fire resistance tests for service installations; seals

• BS EN 1366-2:2015 — Fire resistance tests for service installations; fire dampers

• BS 8214:2016 — Code of practice for fire door assemblies

• Building Regulations Approved Document B (2019) — Fire safety; compartmentation; protected routes

• Association for Specialist Fire Protection (ASFP) — Technical guidance on passive fire protection

• CERTIFIRE Scheme — Warringtonfire product certification scheme

• Fire Door Safety Week — Inspection guidance for fire doors

• fire extinguishers — Active fire protection; extinguisher selection

• part b fire — Building Regulations Part B fire safety requirements

• drain testing — Drainage through floor slabs

• testing commissioning — Cable management through fire barriers