Flame Spread Performance of Wood Products


Wood and wood-based products are widely used in interior wall, ceiling, and floor surfaces in all types of buildings.

Appearance, acoustical qualities, and interior design versatility have made wood surfaces highly desired by architects, designers, and building occupants. This publication briefly describes building code flame spread regulations on products used in interior finish and presents performance data on a range of wood products.

Flame Spread Requirements
Most code requirements for wood interior finish materials are expressed in terms of flame spread index numbers. These values are determined in a standard fire test which evaluates the surface burning characteristics of a material. Different maximum flame spread indices are permitted depending upon building occupancy, location of the material in the building, and the presence of sprinklers. Flame spread indices in this publication are provided for wood materials that qualify for various building design requirements.

Test Method
The standard fire test used to evaluate flame spread characteristics of wood building materials in the United States is ASTM E-84, Standard Test Method for Surface Burning Characteristics of Building Materials. 

Classification in Codes are:

Class 
Flame Spread Range
Example Locations 
I or A 
0-25
Enclosed vertical exits
II or B 
26-75 
Exit access corridors 
III or C 
76-200 
Other rooms and areas 

The test procedure exposes candidate materials in a horizontal, rectangular tunnel 17 3/4" wide by 12" in height and 25 feet long. The tunnel is equipped with two gas burners at one end that direct a flame onto the surface of the test material under a controlled air flow. Flame spreads along the surface of the material as the test progresses. Distance of the flame travel and the rate at which the flame front advances during a 10 minute exposure determine the calculated flame spread index.

To provide standard conditions for each test, the tunnel is calibrated to an index of 0 for noncombustible materials and 100 for 23/32" red oak flooring. Indices for tested materials can range from 0 to over 1000.

Wood Products
Lumber, plywood, and other wood-based materials exhibit a relatively narrow range of flame spread. Differences result from factors such as density, thickness, surface characteristics and chemical constituents. If the material is homogeneous, flame spread may be considered nearly independent of material thickness at thicknesses greater than 1/4".

Flame spread indices for a number of species of lumber, plywood, particleboard, shakes and shingles are listed in Table 1. In products such as softwood and hardwood plywood, the arrangement and type of components may also influence surface flame spread. Some such products are described by face species and core composition in Table 1. All ratings are based on the ASTM E-84 test method.
 


Flame spread indices for a number of commercially available wood products with factory applied overlay finishes are listed in Table 2. Factory finished wall panels are typically tested and labeled to identify the flame spread classification of the finished product. Finish composition, adhesive, and finish thickness may, however, affect flame spread.

As can be seen from the listed indices, most tested wood products have a flame spread index less than 200, making them acceptable under current building codes for a wide range of interior finish uses. Flame spread indices for a range of proprietary wood-based interior finish materials are also available from their manufacturers. Commercially available fire retardant treatments for wood and panel products can reduce flame spread performance to an index of 25 or less. Check with the manufacturer for flame spread index.
 

 A smoke-developed index was also measured for some of the wood products listed in Table 1 and Table 2. This index also has a value of 100 for red oak. None of the products tested exceeded 450, a limiting value commonly used in building code regulations.
 
 
 
 
 
While effort has been made to ensure the accuracy of the information in this publication, the American Forest & Paper Association, and the Companies and Associations identified, do not assume responsibility for the accuracy of the indices reported, the applicability or extension of the reported flame spread values to specific products, or their acceptance for use in particular applications.

Copyright © 1997- 2007
American Forest & Paper Association, Inc.
 
September 2007 Revisions