The five standard ratings
Commercial door assemblies are rated at 20, 45, 60, 90, or 180 minutes (3 hours). The rating isn't a claim that the door survives exactly that long in a real fire — it means the complete assembly (door, frame, hardware, and any glazing) was tested under controlled conditions and didn't allow flame passage or exceed temperature limits on the unexposed side for that duration.
The required rating for a given opening is derived from the fire-resistance rating of the wall it sits in, not chosen independently. As a general pattern, the door rating is roughly a fraction of the wall rating — a 1-hour wall commonly calls for a 20-minute or 45-minute door depending on the opening's use, and a 2-hour wall commonly calls for a 90-minute door. The specific requirement depends on occupancy classification and the applicable code edition, so it should be confirmed against the approved project documents rather than assumed from the wall rating alone.
Door material limits the achievable rating
Wood doors with standard particleboard-core construction are limited to a 20-minute rating. Getting a 45-, 60-, or 90-minute rating out of a wood door requires mineral-core construction instead — the visual difference is minimal, but the core material determines what rating the door can carry. Beyond 90 minutes, wood isn't an option; a 180-minute (3-hour) assembly requires hollow-metal construction with a masonry frame, since drywall frames top out at 90 minutes.
This is one reason gauge and fire rating get specified together on a hollow-metal takeoff — the frame type and wall condition both have to support the rating the opening requires.
Hardware has its own compliance rules
Every fire-rated door must be self-closing and self-latching, using fire-listed hardware components — a rated door with standard, unlisted hardware doesn't meet the assembly's listing even if the door and frame are correctly rated. Standard panic hardware is listed for non-rated doors only; a fire-rated door that needs panic-style hardware requires fire exit hardware, which is tested to both the standard panic hardware rating and the fire-door standard.
Mechanical dogging (holding the latch retracted) is prohibited on fire exit hardware. Only electric dogging tied into the building's fire alarm panel is compliant, since it has to release automatically on alarm.
Testing standard and smoke ratings
UL 10C, a positive-pressure fire test, is the current U.S. testing standard for fire door assemblies, and replaced the older neutral-pressure UL 10B test. An assembly's label should reference the current standard.
A separate "S" label indicates the assembly was also tested for smoke leakage, not just fire resistance. S-rated assemblies are required at smoke barriers, smoke compartments, and pressurized stairwells — common in healthcare occupancies — and rely on smoke seal gaskets at the door perimeter. A missing or damaged smoke seal on an S-labeled door is a specific, commonly cited compliance gap.
Glazing limits get stricter as the rating goes up
Vision lites (glass panels) are permitted in fire-rated doors, but the allowable size shrinks sharply as the rating increases. A 20-minute or 45-minute door can carry a substantially larger lite than a 60- or 90-minute door, and some of the highest ratings (90-minute with a D label, and all 3-hour A-label doors) don't permit any glazing at all. The exact limit depends on the specific label and rating, so glazing should be confirmed against the door's listing before it's ordered, not assumed from a similar project.
Field modification is a common — and preventable — failure
NFPA 80 prohibits modifying a fire-rated door assembly in the field unless the change is approved by the listing laboratory. The violations that show up repeatedly on inspections are all avoidable: adding surface-mounted hardware that wasn't part of the tested assembly, swapping in non-rated hardware to replace rated hardware, cutting additional holes or mortises for a lock or device that wasn't in the original prep, and painting over or removing the visible fire label.
Any hardware change, added prep, or finish work on a rated opening should be checked against the listing before it happens, not after an inspector flags it.
