Fire door ratings, decoded: how to spec the right one

What the rating actually measures

When a door is described as 60-, 90- or 120-minute, the number is how long the complete door assembly resists fire in a standardised furnace test. The clock measures integrity — keeping flames and hot gases from passing through — and, for many ratings, insulation, meaning the unexposed side stays cool enough to slow fire spread. Crucially, the rating belongs to the tested assembly as a whole: leaf, frame, glazing, intumescent seals and hardware. Change a component and the certified performance no longer strictly applies.

Match the rating to the opening

The right duration comes from the building's fire strategy and the applicable code, which classify openings by the compartment they protect and the escape routes they serve. Corridors, stairwells, service shafts and equipment rooms can each demand something different. Over-specifying wastes budget; under-specifying creates a life-safety and compliance risk. Confirm the requirement for each opening before you procure anything.

The mistakes that quietly void a rating

Most failures aren't the door itself — they're the details around it:

• Gaps and clearances outside the tested tolerance, so seals and intumescent strips can't close the opening.
• Site modifications — extra cut-outs, vision panels or hardware the certification never covered.
• Hardware substitutions: hinges, closers and locks must be rated and compatible.
• Installation into the wrong wall type, or with fixings that differ from the tested setup.
• A disabled or missing self-closer, which defeats the door the moment it's propped open.

What to ask for

Insist on documentation linking the door to a test or certification, a hardware schedule listing rated components, and an installation method that matches the tested configuration. Then protect the rating in use: keep doors unobstructed, closers working and seals intact. A correctly specified fire door asks for almost nothing — until the day it has to perform.