Why North America needs them
A fire door sold into the US or Canada normally needs a UL (or equivalent) label, and the label rests on a UL 10B or UL 10C test. Fire door ratings range from 20 minutes to 3 hours, depending on where the door sits in the building — stair enclosures, shafts, corridors or fire walls.
How the test works
The door assembly — leaf, frame, hardware and seals — is installed in a supporting wall and mounted on a vertical furnace. It is exposed to the same standard time–temperature curve as UL 263, then, within a few minutes of the end of the fire exposure, to a hose stream that tests the assembly's resistance to impact, erosion and cooling.
- UL 10C (positive pressure): the neutral pressure plane is set no higher than 1016 mm (40 in) above the sill, so most of the door is under positive furnace pressure and hot gas is pushed outward through gaps — the way a real fire behaves.
- UL 10B (neutral pressure): the furnace is run close to neutral pressure at the top of the door, so less hot gas is driven through the gaps.
Observations include flaming on the unexposed side, through-openings, the leaf's movement relative to the frame, and whether the door stays latched.
Common causes of failure
From our own test experience:
- Infill and core materials that decompose quickly at high temperature.
- Weak frames and fixings. Distortion opens the edge gap; hinges or locks loosen under heat and the hose stream.
- Poor sealing design. Even a good core fails if the perimeter seal does not close the gap under positive pressure.
Because the test magnifies small weaknesses, we recommend an indicative test before the certification test.
Frequently asked questions
Do I need UL 10B or UL 10C?
For side-hinged and pivoted swinging doors sold into the US, the International Building Code requires positive pressure testing — UL 10C. UL 10B (neutral pressure) is still used for other door types and some markets. Your certifier will confirm which applies to your product and listing.
Why do fire doors fail UL 10C?
Under positive pressure hot gas is pushed through every gap. Typical failures: flaming at the latch edge and head because intumescent seals are missing or too small, hardware softening, leaf distortion that opens the gap, and frames pulling away from the wall. The hose stream test then exposes weak hinges and fixings.
Do you offer pre-tests before certification?
Yes. Most of our door clients run an indicative test first. It costs far less than failing a witnessed certification test.