Effects of Fire Retardant Treatments on Wood Strength: A Review

Susan L. LeVan, Jerrold E. Winandy


As evidenced by recent structural problems with fire-retardant-treated plywood, fire retardant chemicals and high temperature environments can degrade the strength properties of wood. We do not know to what extent fire retardant chemicals, thermal environment, and moisture content contribute to wood degradation. We suspect that the combination of acidic fire retardant chemicals and elevated temperatures increases the rate of acid hydrolysis in the wood, thereby causing a loss in strength. This paper presents a review of the pertinent literature on the factors influencing strength reduction in treated wood. These factors are the thermal degradation process of wood, the mechanism by which fire retardant chemicals alter wood degradation, the effect of acids on wood strength, the influence of temperature on strength, and the combined effect of fire retardant chemicals and temperature on strength. We also discuss possible long-term effects of in-service conditions on the strength of treated wood; the effects of treatment on the strength of weaker structural members and on species, size, and grade of lumber; and the application of the relationship between treatment and strength to plywood and lumber.


Acid hydrolysis;fire retardants;plywood;strength;thermal degradation

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