What is compartmentation?
Compartmentation is the division of a building into fire-resisting sections so that a fire is contained where it starts, protecting escape routes and limiting spread for a period.
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<img src="https://fireoptix.co.uk/glossary/compartmentation/diagram.svg" alt="compartmentation — diagram from FireOptix" width="880" height="620" loading="lazy">
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<a href="https://fireoptix.co.uk/glossary/compartmentation">What is compartmentation?</a> — diagram by
<a href="https://fireoptix.co.uk">FireOptix</a>
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</figure>It works by making walls, floors and doors resist fire for a defined period. Its weakness is always the penetrations: every cable, pipe and duct passing through a compartment wall is a route for fire and smoke unless it is sealed with a system tested for that purpose.
Compartmentation degrades invisibly. It is installed correctly, then a contractor drills through it for a new cable and makes good with the wrong material, and the wall keeps its appearance while losing its function.
It underpins several other measures. A stay put policy in a residential block, for example, depends on compartmentation performing as designed — which is why breaches in those buildings are treated as urgent rather than routine.
In practice
A building where the compartment walls are sound and the ceiling void is not.
Below the ceiling tiles every wall runs correctly. Above them, cabling contractors have been through the line of the wall for twenty years and nobody has looked.
Compartmentation is a three-dimensional line, and the parts of it that fail are the parts nobody can see without a ladder and a tile lifted.
A survey that stops at head height has surveyed the half that was never the problem.
What goes wrong in practice
- Service penetrations sealed with ordinary filler or foam rather than a tested fire-stopping system.
- Voids above suspended ceilings where the compartment wall stops at ceiling level and was never continued to the slab.
- Breaches created by a contractor with no record that the work happened, so nobody knows to check it.