Our understanding of the laboratory induced degradation with fire retardant systems is currently limited since we are unable to correlate laboratory steady-state experiments with actual in-service field degradation. 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 relative humidity/moisture content cycles and thermally-induced evolution of ammonia from ammonium phosphates to give phosphoric acid. The objective of this study was to determine the relationship between laboratory and field results based on strength-temperature-relative humidity (moisture content)-FR chemical interactions. The impact of the variables was evaluated by measuring bending strength properties and comparing matched laboratory and field exposure samples. In this first paper, 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.

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