What is a fire resistance rating?
A fire resistance rating is the period, in minutes, for which an element of a building has been tested to hold back fire. It describes tested performance, not a guarantee for any particular installation.
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<a href="https://fireoptix.co.uk/glossary/fire-resistance-rating">What is a fire resistance rating?</a> — diagram by
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</figure>The rating comes from a standard test, and it belongs to the tested arrangement. The same rating in a real building depends on the element being installed and maintained as it was tested — which is why an inspection is interested in gaps, fixings and alterations rather than in the certificate alone.
Different elements carry ratings for different reasons: a compartment wall to contain a fire, a door to protect an escape route, a duct or damper to stop a fire travelling through a service route.
Because the rating is a period and not a state, it is only meaningful alongside the fire strategy it serves. Thirty minutes is ample in one building and insufficient in another.
In practice
A door assumed to be rated because it is heavy.
It is solid, it has a closer, and somebody has painted a sign on it. Nothing evidences any rating at all.
A rating is established by what a door assembly was tested and certificated to, not by weight, appearance or the presence of ironmongery.
Where no evidence survives, the honest entry on a register is that the rating is unknown rather than assumed.
What goes wrong in practice
- Treating a certificate for a product as evidence about the assembly actually installed.
- Alterations that pierce or weaken a rated element with no record and no reinstatement.