Fire retardant-treated wood

Building code requirements for fire performance are mainly concerned with noncombustibiUty (41), fire endurance (42,43), and surface burning characteristics (44). Wood, even in its treated form, does not meet the building code requirements for a noncombustible material. However, for some specific apphcations where noncombustible materials are required, the codes permit the substitution of fire retardant treated wood. 

During the initial stages of a fire, fire-retardant-treated wood contributes less heat than does untreated wood, especially from the flammable volatiles (8,26). This means that the spread of fire to nearby combustibles is slow. The fire tends to be confined to the primary source. In the ASTM E84 test for building materials, treated specimens produce about 75 percent less heat than untreated red oak. In a total combustion test, however, such as the National Bureau of Standards potential heat method (54), both treated and untreated wood release about the same total heat. 

Treatment-Related Properties of Fire-Retardant-Treated Wood... 

Gerhards (57) reviewed the results of 12 separate studies on strength properties of fire-retardant-treated wood conducted at the FPL and other laboratories. He concluded that modulus of rupture (MOR) is consistently lower and modulus of elasticity (MOE) and work to maximum load are generally lower for fire-retardant-treated wood than for untreated wood if fire-retardant treatment is followed by kiln drying. The effect may be less or negligible if the fire-retardant-treated wood is air dried instead of kiln dried. The most significant loss was in work to maximum load, a measure of shock resistance or brashness, which averaged 34 percent reduction. 

Generally, the bonding obtainable with fire-retardant-treated wood is satisfactory for decorative purposes. Treated wood members can be bonded into structural assemblies with specially formulated adhesives under optimum bonding conditions (8). 

Fire-retardant-treated wood is durable and stable under normal exposure conditions. Treatments using inorganic water-soluble salts, however, are not recommended for exterior exposures to rain and weathering unless the treatment can be adequately protected by water-repellent coating. Exterior-type treatments in which the chemicals are "fixed" in the wood in some manner are leach resistant and nonhygroscopic. 

At the U.S. Forest Products Laboratory, many of the research programs involve fire-retardant-treated wood. This has included extensive basic study of pyrolysis and combustion reactions of wood and its components and the effects of chemical additives on these reactions (15,24-26,28,29,66). A cooperative study (9) with the Division of Chemical Development of the Tennessee Valley Authority, showed the effectiveness of liquid ammonium polyphosphate fertilizers as fire retardants for wood. The commercial use of these products, made from electric furnace superphosphoric acid, has been shown to be economically feasible. Work has been completed by Schaffer (33) on the rate of fire penetration in wood treated with different types of chemicals. Some results of this study are reported elsewhere in this paper. 

Using full-scale fire test facilities of the Illinois Institute of Technology-Research Institute (IITRI), Christian and Waterman (69) studied fire and smoke behavior of interior finish materials including fire-retardant-treated wood products. The authors found that the materials performed according to a... 

Continuing research must yield information on the treatment-related properties of fire-retardant-treated wood and methods for their improvement. The properties of the conventional salt treatments which need improvement especially are hygroscopicity, strength properties, gluing, and finishing. 

Chapter 23 Wood (including fire retardant-treated wood). 

The National Bureau of Standards smoke density chamber (Figure 7) is a more recent technique used to evaluate smoke. This chamber can be used to measure adequately the smoke produced from untreated and fire-retardant-treated wood (27, 28). This method has three advantages over the tunnel method (1) application to a variety of room situations, burning areas, and light-path lengths, (2)... 

Smoke from treated wood.—Fire-retardant-treated wood also... 

Type IIL Type 111 constraction is that type of construction in which the exterior walls are of noncombustible materials and the interior bnilding elements are of any material permitted by this code. Fire-retardant-treated wood framing complying with Section 2303.2 shall be permitted within exterior wall assemblies of a 2-hour rating or less. 

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