Fire safety in an office fit-out: compartmentation, fire stopping and sign-off

Fit-outs change a building's fire safety whether anyone intends them to or not. New walls change escape routes, new cables and ducts pass through fire-resisting construction, and new rooms need covering by the alarm. Most of it ends up hidden above a ceiling or under a floor, which is exactly why it needs care.

This is a builder's view of what has to happen. The building's fire strategy, your fire engineer and building control set the actual requirements, and the government's guidance, Approved Document B, is published on GOV.UK.

Compartments, and why the fit-out mustn't breach them

Buildings are divided into compartments by fire-resisting walls and floors, so that a fire is held in one area long enough for people to get out and for the fire service to do its job. In a multi-let office building, the floors between tenancies, the stair cores and the service risers are commonly compartment lines.

A fit-out rarely builds new compartment walls, but it constantly goes through existing ones. Cable trays, pipes and ductwork pass through riser walls and floors, and every hole is a breach until it's properly sealed. Where ductwork crosses a compartment line it usually needs a fire damper. Ceiling voids and raised floors can need cavity barriers, so fire and smoke can't run unseen through the hidden spaces.

Know which walls on your drawings are doing a fire job and which aren't. A glass meeting room is often just a room. The wall between your floor and the stair core is part of the building's life safety, and it should be marked as such on every drawing that goes to site.

Fire stopping: the work nobody sees

Fire stopping is the sealing of gaps and penetrations in fire-resisting construction. It sounds simple, and it's where a lot of buildings go wrong.

• The product has to be tested for that type of wall or floor and that type of service. A sealant that works around a cable may not work around a plastic pipe, which usually needs a collar or wrap that swells shut in a fire.
• It has to be installed exactly as the manufacturer's tested detail shows, by people trained to do it.
• Each penetration should be photographed before it's covered, labelled, and logged in a register with its location, the product used and who installed it.
• It should be inspected before the ceiling closes. Once the tiles are in, nobody looks again until there's a survey or a fire.

Good fire stopping is boring to look at. Bad fire stopping is invisible until the day it matters.

Doors, escape routes, alarms and lighting

Fire doors are tested and certified as a complete doorset: leaf, frame, seals, hinges, closer and any glazing. Swap one part for something uncertified and it's no longer the door that was tested. Gaps around the leaf matter, and a fire door should only be held open by a device that releases it when the alarm sounds.

Escape routes change with a new layout. More walls can lengthen travel distances, and a new room you can only leave by passing through another room, known as an inner room, has its own rules. These are the things building control will check.

Detection and alarm coverage has to follow the new layout, with detectors and sounders in new enclosed rooms as the system design requires. The fit-out usually ties into the base-build alarm, often through the landlord's own alarm contractor, which is one reason the landlord will want to see your drawings under a licence to alter. Emergency lighting has to cover the new layout and escape routes too.

Keeping the building safe while the work goes on

If the building is occupied, the fire strategy has to work every day of the job, not just at handover. I've written about building around a business that cannot close, and fire is the part people underestimate. In practice:

• Hot works only under permit, with a check of the area afterwards
• Detectors in the work zone isolated only under permit, and reinstated before the end of each shift
• Any penetration left open at the end of the day temporarily sealed
• Fire doors kept closed, never wedged for a delivery
• Packaging and combustible waste removed daily
• Escape routes kept clear and signed through or around the works

Whoever is responsible for fire safety in the building needs to know about the works before they start. Their fire risk assessment should be kept under review, and a fit-out is exactly the kind of change that calls for a fresh look.

Sign-off: what you should be handed

At the end you should receive the building control completion certificate, or a final certificate if a registered building control approver was used; commissioning certificates for the fire alarm and emergency lighting; the electrical installation certificate; the fire stopping register with photographs; fire door certification; and as-built drawings showing compartment lines and fire doors. Building regulations also require fire safety information about the work to be passed to the person responsible for the building.

If you're planning a fit-out, send us the floor plan and whatever the landlord has on the base-build fire strategy. We'll tell you what your layout means for it before you commit, and more on how we run fit-outs is on our office fit-out page.