Floor finish is a different test
Interior floor finish is not rated by flame spread. Under IBC Section 804.2 it is tested per ASTM E648 or NFPA 253 to find its critical radiant flux. Keep the standards straight:
- ASTM E648 or NFPA 253: floor finish radiant flux
- ASTM E84 or UL 723: the tunnel test for wall and ceiling flame spread classes
- NFPA 286: the room corner test that can qualify a wall finish for Class A locations
- ASTM C840 or GA-216: gypsum panel installation, not a fire test
Class I and Class II
Section 804.2 sets two classes:
- Class I: critical radiant flux of 0.45 W/cm2 or greater
- Class II: critical radiant flux of 0.22 W/cm2 or greater
The trap is direction. For radiant flux a higher value is better, the opposite of the flame spread index for walls, where lower is better. Writing "0.45 or less" or "0.22 or less" reverses it. Class I, the higher number, is the more restrictive class.
Also do not mix the letters and numerals. Classes A, B and C are wall and ceiling flame spread classes. Floors use Class I and Class II only.
Where Class I is required
IBC Section 804.4.2 requires at least Class I in Groups I-1, I-2 and I-3. At least Class II is the minimum for groups such as A, B, E, M and R-2. The minimums apply in corridors, exits and rooms not separated from corridors by full-height partitions. So a nonsprinklered Group I-2 hospital needs Class I in its corridors; corridors are expressly a covered location.
The sprinkler exception
Under the exception to Section 804.4.2, in a building sprinklered throughout per 903.3.1.1 or 903.3.1.2, Class II may be used where Class I is required. That is a one-step relaxation, not an exemption: sprinklers do not free floor finish from the rule altogether. The exception applies wherever Class I is required, including Group I occupancies, so the sprinklered hospital corridor may use Class II.