As part of this project, we examined the degradation of carbon fibers in fiber-reinforced plastics (CFRP) under thermal stress, such as that experienced during a fire. Commercial CFRP was exposed to high temperatures, and fire-damaged components were analyzed. The results showed that at 550°C in air, oxidation of the carbon fibers begins, thinning them to less than 3 μm. Using an Arrhenius model, we were able to estimate the thermal exposure of critical fibers during damage, including fire duration and temperature.