Compartmentation

Compartmentation is the part of a building's passive fire protection that buys time. By dividing the building into fire-resisting cells, it holds fire and smoke within the compartment where they started for a rated period, protecting escape routes and giving occupants time to leave and the fire service time to respond.

Where it usually fails

Compartmentation rarely fails because a wall was built badly. It fails because it was breached afterwards. Cables, pipes and ducts run through compartment walls and floors and are not always fire-stopped correctly. Ceiling voids and riser cupboards are opened for maintenance and not made good. A doorset is replaced with one that looks similar but carries no rating.

Each of those is invisible from the occupied side of the wall, which is why compartmentation is assessed by opening up and inspecting rather than by walking the corridors.

Assessing it

A compartmentation survey samples the concealed spaces — above ceilings, inside risers, within roof voids — and traces the compartment lines against the building's design. Findings are usually recorded with photographs and locations, because remediation is carried out by someone who was not present at the survey and needs to find the defect again.

Where a building relies on a stay put strategy, the integrity of its compartmentation is not one finding among many: it is the assumption the whole strategy rests on.