classifications. The smoke developed indices assess product
behavior in terms of obscuration of exit paths and loss of visibility
by smoke. Smoke interferes with visibility on the basis of the
accumulated soot and other particles within a given volume. The
smoke level will depend on both time and rate of smoke production.
A product that has a low smoke developed index would be
expected to maintain visibility in egress paths for a longer period
of time than a material with a high smoke developed index.
The same smoke developed index criterion is used for all three
classifications (i.e., classes A, B, and C). The recommended 450
limit acknowledges that smoke affects visibility both in the immediate
vicinity of the fire and in remote areas as well. Large
buildings can be quickly filled with smoke as the result of a fire.
An upper limit has been established that is applicable to interior
finishes, regardless of where the materials are installed.