(Received 17 December 2001; accepted 18 September 2002)
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The objective of this work was to evaluate the effects of a new boron-nitrogen, phosphate-free fire-retardant (FR) formulation on several mechanical properties of FR-treated wood and to assess the potential of this treatment for in-service thermal-induced strength loss resulting from exposure to high temperature. Fire-retardant-treated and untreated small clear specimens were cut from three wood species, Douglas-fir, southern pine, and white spruce, according to ASTM D 5664-95 and evaluated in bending and tension, compression, and shear parallel to grain. Evaluations were conducted before and after matched specimens were exposed at elevated temperature (150°F(66°C)) for 36, 72, or 108 days. The results indicate that treatment with FR and redrying followed by long-term exposure at high temperature could significantly affect some mechanical properties when compared to the same properties of untreated and unexposed controls. However, FR treatment and redrying in themselves did not have an across-the-board effect on all properties of specimens or on the rate of strength loss compared to the properties of matched untreated lumber exposed at 150°F (66°C) for up to 108 days. Our analysis indicated that for some species, some engineering properties will require modification, whereas other species-property combinations will not. Our results indicate that the likelihood of FR-treated lumber to experience in-service reduction in mechanical properties when exposed to elevated temperatures is no different than that of matched untreated material.
Supervisory wood scientist, USDA Forest Service, Forest Products Laboratory, One Gifford Pinchot Drive, Madison, WI
Wood Technologist, Osmose Inc., Buffalo, NY
Stock #: JTE12411J