WHAT 25 FLAME SPREAD REALLY MEANS

What does 25 Flame Spread mean?
The Flame Spread rating is a result of a test procedure developed by Underwriters’ Laboratories, Inc. to measure the surface burning characteristics of materials. Commonly known as the "tunnel test", or more technically UL 723, NFPA 255 or ASTM E 84, it is conducted in tunnel-like equipment approximately 1’ x 1-1/2’ square and 25’ long. A damper and burners are located at one end and a set of dampers and a flu at the opposite end. Sealed observation windows are along the sides. Materials to be tested are affixed to the top of the tunnel.

Asbestos cement board is initially tested to calibrate the tunnel. The distance the flame travels down the test sample is used in a formula and the result is established as zero flame spread. Red oak flooring is then tested. The time required for the flame to travel the length of the sample is used in the formula and the result is posted as 100 flame spread.

The material to be rated is then tested in the same manner and the result is compared to the calibrations for asbestos cement board and red oak. This comparison determines the flame spread rating.

Metal building insulation must be tested as a combined, laminated product-fiberglas insulation, adhesive and facing. Results of tests on the separate components would not constitute a realistic basis for rating the complete product.
 
Why is 25 Flame Spread important?
The National building code of the National Board of Fire Underwriters (now American Insurance Association) contains a definition of the term "noncombustible", which in essence states that a building construction material, such as metal building insulation, having an Underwriters’ Laboratories Flame Spread rating no higher than 25 is classified as noncombustible. A rating higher than 25 is classified as combustible.
 
What does this 25 Flame Spread rating mean to you?
Most stock insurance companies use insurance rates set by the State Rating Bureaus. These rates vary from state to state but, in general, basic metal buildings are given a noncombustible classification such as Fire-Resistive", "Brick or Iron Clad". However, if a combustible material is added, the building must then be in a combustible category and a severe penalty will be imposed in the insurance rate. Therefore, it is important not to use any combustibles in the building construction. Don’t make the building lose its favorable insurance rate just because a combustible insulation was used!

How do the rating bureaus define "non-combustible"? Most of them use the National Building Code definition of "25 Flame Spread or less."

As you can see, the use of insulation with a UL Flame Spread of 25 or less (on the combined product) can mean big dollar savings to the owner of the building. Also, remember that this saving applies to the contents as well as the building itself, and continues for the life of the building.