Compartmentation and fire-stopping

Compartments and where their lines run

In a block of flats, each dwelling is its own compartment and the common escape route is another. In a converted HMO, each bedroom is usually made fire-resisting to protect the shared stairs. In a commercial building, compartment lines separate plant rooms, boiler rooms, stores, risers and any area of higher risk from the rest of the floor plate. Knowing where those lines run is the first job: if nobody can point at a plan and say "this wall is 60 minutes", the building will be damaged by well-meaning contractors within a year.

How fire resistance is measured

Elements are tested for integrity (holding back flame and hot gases), insulation (limiting heat transfer to the unexposed face) and, for load-bearing elements, stability. A wall described as EI 60 provides 60 minutes of integrity and insulation. Any product used to seal a hole through that wall must be tested to give at least the same performance in that construction.

What fire-stopping actually involves

• Intumescent pipe collars and wraps — for plastic pipes, which melt away and leave an open hole unless the collar crushes it closed.
• Coated fire batt — mineral wool board with an ablative coating, used for large mixed-service openings in risers.
• Fire mastic and acrylic sealants — for linear gaps and small cable penetrations, applied to a tested depth with the correct backing.
• Fire mortar and compound — for larger floor openings carrying heavy services.
• Cavity barriers — mineral wool or intumescent barriers closing voids above ceilings and within external wall constructions.
• Fire dampers — mechanical closures where ductwork crosses a compartment line, which need periodic drop-testing.

The defects surveys find most often

Unsealed cable bundles through riser walls. Waste pipes passing through a compartment floor with a gap you can post a hand through. Loft party walls stopping at ceiling level so the roof void runs the length of the terrace. Downlights and extract fans cutting through a fire-resisting ceiling with no protective hoods. Expanding foam used as a seal, which burns readily and provides no rating whatsoever. Old boarding removed for maintenance and never replaced.

Prioritising remedial work

Not everything can be fixed at once, so triage by consequence. Defects on the sole escape route come first, then anything separating a sleeping area from a risk area such as a boiler room or commercial kitchen, then risers and voids, then lower-consequence internal separations. A good survey report does this ranking for you and gives an indicative cost per item so you can build a programme rather than a panic.

Evidencing the repair

Each completed seal should be recorded with a photograph, a location reference, the product used and its test evidence, the installer's name and the date. Many installers now tag each seal with a barcode label linked to that record. Without it you have no way to prove, two years later, that the sealed penetration behind a plasterboard ceiling was ever done properly.

Keeping it intact

Put fire-stopping into your contractor induction and permit-to-work. Make good with a tested system on the same day the hole is made. Re-survey after major works. And make sure your fire risk assessor is told about any building work since the last assessment — it is the single most useful piece of information you can hand over.