What is the rating for an interior finish material with a flame spread index of 100?

According to NFPA 101, Life Safety Code, interior wall and ceiling finish materials are classified based on their flame spread index (FSI) and smoke developed index as determined by the ASTM E84 or UL 723 Steiner Tunnel Test. The classification system is as follows: Class A (FSI 0-25), Class B (FSI 26-75), and Class C (FSI 76-200). A material with a flame spread index of 100 falls squarely within the range specified for a Class C interior finish.

A. Class A: This classification is for materials with a flame spread index between 0 and 25, which is a much lower and safer rating.

B. Class B: This classification applies to materials with a flame spread index in the range of 26 to 75.

D. Class D: This is not a standard classification for interior wall and ceiling finish materials under the NFPA 101 classification scheme.

1. NFPA 101®, Life Safety Code®, 2021 Edition. Chapter 10, Section 10.2.3.4, "Interior Wall or Ceiling Finish Classification."

10.2.3.4(1) Class A Interior Wall and Ceiling Finish. Flame spread index 0–25; smoke developed index 0–450.

10.2.3.4(2) Class B Interior Wall and Ceiling Finish. Flame spread index 26–75; smoke developed index 0–450.

10.2.3.4(3) Class C Interior Wall and Ceiling Finish. Flame spread index 76–200; smoke developed index 0–450.

2. Hurley, M. J., et al. (Eds.). (2016). SFPE Handbook of Fire Protection Engineering (5th ed.). Springer. Section 2, Chapter 29, "Surface Fire Spread," Page 911. The handbook discusses the Steiner Tunnel Test (ASTM E84) and references the NFPA 101 classification system for interior finishes.

3. University of Maryland, Department of Fire Protection Engineering. ENFP 429 - Fire Dynamics Laboratory Courseware. The course materials on surface flame spread cover the ASTM E84 test and the resulting A-B-C classification system as defined in building and life safety codes.