Verification of a Kinetics-based Model for Long-term Effects of Fire Retardants on Bending Strength at Elevated Temperatures

This study verifies a single-stage reaction-rate model for the long-term effects of various fire retardants. The adequacy of predictions from our previously reported models was tested using data from fire-retardant-treated wood exposed at 66°C (150°F) and 75% relative humidity for 3 or 4 years. Our analysis showed that if the treated wood experienced significant thermal degradation early during exposure to high temperature, then the previously reported model parameters adequately predicted thermal degradation for up to 4 years of steady-state exposure. However, if the treated wood did not experience significant thermal degradation early during high-temperature exposure, then the previous parameter estimates tended to underpredict degrade. Modified parameter estimates are presented where appropriate. This report also describes the practical implications of running the verified models for up to 10 annual iterations of an actual year of measured roof sheathing temperatures derived from structures exposed in the field. Our results predict that monoammonium phosphate, a generic fire-retardant formulation, can be expected to cause an additional 15% loss in original strength capacity in 10 years if used for roof sheathing under similar conditions.