Interior finish materials are broken into three classes based on which property?

• A. Fire-resistivity ratings
• B. Critical radiant flux ratings
• C. Potential for flashback
• D. Flame-spread and smoke development index

Answer: (D)

Interior finish materials are grouped by how they behave when exposed to fire, specifically through flame-spread and smoke-development. The flame-spread index tells you how quickly flames can travel across a material’s surface, while the smoke-developed index measures how much smoke is produced as it burns. Codes use these two measurements to sort finishes into three classes, reflecting their contribution to fire growth and visibility/toxicity in a fire scenario. The other properties mentioned aren’t used to classify interior finishes in this way: fire-resistivity ratings pertain to the overall fire resistance of assemblies, critical radiant flux is a metric tied to certain textile tests, and a general “flashback potential” isn’t a formal classification used for interior finishes.