What is flame spread and smoke developed?

Surface Burning Characteristics Rating (Formerly Flame Spread Rating)

The surface Burning Characteristics Rating of a material is a number, calculated from the results of a test, which indicates the relative rate at which flame will spread over the surface of the material as compared with flame spread on asbestos-cement board, which is rated 0, and on red oak, which is rated 100. Note that this rating is not the rate at which the flame actually spreads along the surface and is not at all an indication of the fire resistance of the material.

Test Method
The test used to obtain results from which a rating is calculated is called “Method of Test of Surface Burning Characteristics of Building Materials” (NFPA No. 255, ASTM E 84, UL No. 723). It is commonly known as the tunnel test; the test equipment is referred to as the 25′ tunnel. Although several small-scale tests have been developed to predict flame spread ratings based on the tunnel test, these are primarily bench tests for product development. The National Fire Protection Association has not accepted any alternate methods for determining the flame spread characteristics of materials to be used in buildings; for this purpose, NFPA recommends only the tunnel test.

The sample of material to be tested (minimum 18 in. wide, 25′ long) is installed beneath the removable top panel. A gas flame is applied at one end and a regulated constant draft is directed through the tunnel from the flame end. The progress of the flame front along the sample is observed through side windows.

A flame spread rating is a relative number. It has no direct relationship to a fire resistance rating, which is a rating in hours determined by an entirely different test, known as “Standard Methods of Fire Tests of Building Construction and Materials” NFPA No. 251, ASTM E 119, UL No. 263). The exposed surface (ceiling) of an assembly with a high (good) fire resistance rating; and, conversely, the exposed surface of an assembly possessing very little fire resistance could both have a very low flame spread. There is not necessarily any correlation between the two ratings.

There are numerous laboratories with 25 foot tunnels that do commercial testing.

Applying The Ratings
Relative figures on how fast fire will spread over the surface of the material allow fire protection engineers to deal with problems involving possibilities of (1) people being trapped within a building before orderly evacuation can be accomplished, and (2) rapid spread of fire through an entire building or area of a building before the usual fire protection measures can be put into effect to control or extinguish the fire. Building codes generally group flame spread ratings into classifications as follows:

Class 25 or Class I or Class A = Flame Spread Ratings 0-25 Class 75 or Class II or Class B – Flame Spread Rating 26-75 Class 200 or Class III or Class C – Flame Spread Rating 76-200 Class IV or Class D = Flame Spread Rating 201-

ASTM E-119 and Fire Guard Products
ASTM E-119 is an assembly test, not a product test. This is the test method (UL) used for fire resistance rated assemblies. UL does make note of this in the 2000 UL Fire Resistance Directory under INTRODUCTION. Therefore, any of our Fire Guard products have been tested according to this method.


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