Passive fire protection explained

The idea behind it

Fire safety in UK buildings rests on a simple bargain: nobody expects to prevent every fire, so buildings are designed to keep a fire in the room or flat where it starts for long enough that everyone else can get out, or in some designs stay put safely. That containment is passive fire protection. It is built into the fabric, it does not switch on, and it degrades silently — which is exactly why it is the part most often found defective.

What counts as passive protection

• Compartment walls and floors — usually 30 or 60 minutes of fire resistance separating flats, stairs, plant rooms and risers.
• Fire doors — the movable part of a compartment wall, rated FD30 or FD60, with intumescent and smoke seals.
• Fire-stopping — collars, wraps, batt, mastic and mortar sealing the holes made for pipes, cables and ducts.
• Cavity barriers — closing concealed voids above ceilings, in roof spaces and behind cladding, where fire spreads fastest and unseen.
• Structural fire protection — boarding, intumescent coatings and encasement protecting steel and timber from early collapse.
• Fire-resisting glazing — tested glass in a tested frame and bead system, not ordinary toughened glass.
• Fire dampers — closing ductwork where it crosses a compartment line.

Passive versus active

Active protection acts: detectors sense, alarms sound, sprinklers open, extinguishers are used. Passive protection resists. Neither is optional. An alarm buys you warning time; passive protection buys you the escape time to use it. In buildings with a stay-put strategy, compartmentation is not a supporting measure — it is the strategy, and if it is defective the whole evacuation plan has to change to simultaneous evacuation, often with a waking watch.

Where it goes wrong

Almost never in the original build, and almost always afterwards. Every trade that follows the builder makes holes: broadband installers, alarm engineers, heating fitters, kitchen refits. Each unsealed hole is a route for smoke. In older converted HMOs we regularly find riser cupboards with pipework passing straight through a floor into unsealed void, ceilings with downlights cut through a fire-resisting layer, and loft spaces where the party wall stops at the joists.

How defects are found

A standard Type 1 fire risk assessment looks at what is visible in common areas, which catches obvious problems but not concealed ones. Where the building's history, age or alterations suggest concealed defects, a targeted intrusive survey opens up sample locations — riser cupboards, ceiling voids, service penetrations — and reports on what the samples imply for the whole building. That is the point at which Type 2 or Type 4 assessments come in.

Getting remedial work right

Fire-stopping is only compliant when the product used is tested for that exact substrate, service and aperture size, and installed to the manufacturer's instructions. Expanding foam, plasterboard off-cuts and general-purpose silicone are not fire-stopping, however neatly applied. Insist on a photographic record of each seal before it is boarded over, with the product reference recorded. That record is the only evidence you will ever have once the ceiling goes back.

Maintaining it

Add passive protection to your permit-to-work process: any contractor drilling through a wall or ceiling must make good with a tested system and photograph it. Re-inspect after any refurbishment. Keep a plan marked with compartment lines so staff and contractors can see which walls matter — most damage happens simply because nobody knew a wall was fire-resisting.