Volume 31, Issue 2 (March 2003)
Evaluation of a Boron-Nitrogen, Phosphate-Free Fire-Retardant Treatment. Part III. Evaluation of Full-Size 2 by 4 Lumber per ASTM Standard D 5664-95 Method C
The purpose of this work was to evaluate the effects of a new boron-nitrogen, phosphate-free fire-retardant (FR) formulation on the initial strength of No. 1 southern pine 2 by 4 lumber and its potential for in-service thermal degradation. The lumber was evaluated according to Method C of the D 5664 standard test method. The results indicated that for lumber exposed at 150°F (66°C) for 108 days, FR treatment and redrying significantly (α ≤ 0.10) decreased initial bending strength by about 13% compared to that of untreated controls. No significant difference occurred in the rate of strength loss over time of exposure. This infers that, after accounting for the initial reduction in strength, the field performance of FR-treated lumber should be comparable to that of untreated lumber. From a practical standpoint, the effect of FR treatment on maximum load capacity was similar to that on bending strength. Treatment significantly reduced work to a maximum load by 29%, but it had no differential effect on the rate of change in this property when the lumber was exposed to elevated temperatures. Although modulus of elasticity was not significantly changed by treatment, this property was significantly increased by extended exposure at high temperature. In summary, the reduction in mechanical properties for FR-treated 2 by 4 lumber occurred at a rate no different than that for matched untreated lumber when exposed to elevated temperature.