Test Method E-84, commonly known as the tunnel test. The tunnel test measures how far and how fast flames spread across the surface of the test sample. In this test, a sample of the material 20 inches wide and 25 feet long, is installed as ceiling of a test chamber, and exposed to a gas flame at one end. The scale is divided into three classes. In general, inorganic materials such as brick or tile are Class I materials.
Whole wood is defined as wood used in the same form as sawn from the tree.
A few species have a flame-spread index slightly less than 75 and qualify as Class B or II materials. The most widely accepted flame-spread classification system appears in the National Fire Protection Association Life Safety Code, NFPA No. 101. NFPA 101 primarily applies this classification to interior wall and ceiling finish materials. Roof coverings must meet a different set of criteria. Exterior Wall Construction Exterior wall construction can be classified by its fire-resistance.