Effects of Fire Retardant Treatments After 18 Months of Exposure

In some situations, fire-retardant-treated plywood roof sheathing and roof truss lumber have experienced strength loss from thermal degradation. The combination of elevated tempera-tures on roof systems, fire retardant chemicals, and moisture may prematurely activate the fire retardant. Previous studies examined the physical, mechanical, and chemical properties of fire-retardant-treated wood at various temperatures over a short period. In this study, we ex-amined the rate of strength loss at elevated temperature over a long duration. Small, clear Southern Pine specimens treated with six different fire retardant chemicals were exposed at 150 ° F (66 ° C)/75 percent relative humidity for up to 18 months. The results, consistent with those of previous studies, clearly show that the phenomenon of fire-retardant-related thermal degrade is systematic and potentially quantitative. The results also support the hypothesis that the lower the pH of the fire-retardant-treated wood and/or the dissociation energy of the treatment in the wood, the higher the rate of strength loss over time