Interior wall and ceiling finish classifications are based
mainly on flame spread index with a single smoke developed
index limit value of 450, which is common to all
classifications.
Flame spread indices are used to provide information on
the rate of flame spread across the surface of a material. Heat
transfer would be the principal hazard associated with flame
spread and would only affect a person who was in close proximity
to the fire. As a consequence, different classes of interior
finish materials are specified within a building, depending on
location. For example, exit enclosures in which travel paths are
severely restricted have the most severe flame spread index limitations,
since individuals in such a location would be restricted
in their travel paths and, therefore, might not be able to avoid
the heat from the flame