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Flame Spread and Smoke Development
Model building codes require a flame spread rating of 25 or less and a smoke developed rating of 450 or less, when the standard surface burning test is extended to 30 minutes and after weathering, to qualify as a Class A material. FRX® fire retardant treated wood maintains ratings less than both those levels for all species listed. See accompanying table for specific ratings by species.
The ASTM E 84 tunnel test compares surface burning characteristics of tested materials to those of asbestos cement board and untreated red oak lumber. A rating of 0 is assigned to asbestos cement board and a rating of 100 is assigned to untreated red oak flooring. Flame spread ratings of various species of untreated lumber range from 60 to 230. During this test, smoke emissions are also measured and ratings are assigned on the same scale. The ratings are established during the first 10 minutes. Furthermore, unlike the less stringent requirements for fire retardant coatings, building codes required that the test be extended from 10 minutes to 30 minutes and the flame spread not progress more than 10 ½ feet beyond the burners and show no evidence of progressive combustion.
For exterior use, FRT wood must undergo further ASTM E 84 testing, which is conducted on material that has been through the ASTM D 2898 accelerated weathering test, also referred to as the "800-inch rain test."
*Test extended to 30 minutes and after completion of ASTM D 2898 weathering.
Standard tests for surface burning characteristics of materials referenced in the model codes as a basis of acceptance are all essentially the same:
|• ASTM E 84 Standard Test Method for Surface Burning Characteristics of Building Material.|
|• NFPA 255 - Method of Test Surface Burning Characteristics of Building Materials.|
|• UBC Standard 8-1 Test Method for Surface-Burning Characteristics of Building Materials.|