Fire Stopping Calculator — Service Penetration Fire Seals

Fire stopping is the sealing of openings and gaps in fire-rated walls and floors to maintain their fire resistance. It is required wherever services (pipes, cables, ducts) penetrate fire-rated construction, and at junctions between fire-resisting elements. Approved Document B requires all penetrations through compartment walls, compartment floors and protected shafts to be fire-stopped to maintain the full fire resistance period of the element being penetrated.

Yes, plastic pipes (PVC, ABS, PP, PE) passing through fire-rated walls and floors require intumescent collars or wraps. During a fire, the plastic pipe melts and the intumescent material expands to close the hole, preventing fire and smoke spread. For pipes up to 110mm diameter, a proprietary intumescent collar is standard; larger pipes generally use an intumescent wrap and fire batt instead. Wall penetrations typically need a collar on both sides, while floor penetrations need one collar on the soffit (underside). All collars and wraps must be from a system tested to BS EN 1366-3 and classified to BS EN 13501-2.

Cable penetrations through fire-rated construction must be sealed with tested fire stopping systems. For small cable bundles, intumescent mastic or sealant packed over mineral wool backing is standard. For larger openings such as cable trays, intumescent pillows or fire batt systems with coated sealant are used. Cable fill ratio must not exceed 60 percent of the opening area. All systems must be tested to BS EN 1366-3, classified to BS EN 13501-2, and installed per the manufacturer tested specification.

The minimum depth of a fire seal depends on the product, fire rating and penetration type. Typical minimum depths are: intumescent sealant around metal pipes, 15-30mm; fire batt and sealant for larger openings, 50-100mm; intumescent pillows for cable trays, 100-200mm. The seal depth must match the manufacturer tested detail and is typically the full wall or floor thickness. Always follow the specific product installation guide as tested seal depths vary between manufacturers.

Under the Regulatory Reform (Fire Safety) Order 2005, records must be maintained for all fire stopping installations, following the ASFP / BESA / BSRIA / FIS / GPDA Best Practice Guide for Firestopping of Service Penetrations and the ASFP Red Book. This includes: the product used and its reference number, the tested detail being replicated, the installer name and competency certification, date of installation, location within the building, and photographic evidence before concealment. Fire stopping should be inspected before being covered up. Many building control bodies and warranty providers require independent third-party inspection.