Some wood species burn slower as wood flooring than previously thought, according to the revised Design for Code Acceptance 1: Flame Spread Performance of Wood Products Used for Interior Finish.
The rate at which flames travel across a surface is called the flame spread rate, and it is split into three classes—from slowest to fastest, A, B and C. Building codes prohibit the use of wood flooring manufactured from species with higher flame spread rates in certain areas, such as an exit stairway or exit corridor.
However, the flame spread indices used by builders were derived from tests conducted in the 1970s, so new tests in accordance with an updated ASTM standard were undertaken.
While the majority of wood species have the same or similar flame spread rate under the new tests, changes to three species were enough to warrant a change in class.
Douglas fir, Eastern white pine and Southern yellow pine are now classified as class B instead of class C.
