LABORATORY AND FIELD EXPOSURES OF FRT PLYWOOD: PART 2—MECHANICAL PROPERTIES1

Abstract. Our understanding of how to interpret the laboratory-induced degradation data to real-world in-service performance of fire-retardant (FR) systems is currently limited because we are unable to correlate laboratory steady-state experiments with actual in-service field performance. Current model studies have generally been limited to isothermal rate studies with selected model FR chemicals. Other factors also play a major role in the degradation of FR-treated wood. These factors, which have not been studied in any detail, include RH/MC cycles and thermally induced evolution of ammonia from ammoni-um phosphates to provide phosphoric acid. Because there exists no known direct comparison of matched samples with one exposed to high-temperature laboratory conditions and the other exposed for an extended period of time as traditionally used in North American light-framed construction, the objective of this study was to determine the relationship for FR model compounds between laboratory and field results based on strength–temperature–RH (MC)–FR chemical interactions. The impact of the variables was evaluated by measuring bending strength properties and comparing matched laboratory and field exposure samples. The physical test data show the positive effects of adding a buffering system to model FR compounds when exposed to high moisture environments and the negative effects of increasing the moisture in the in-service environment during exposure