The evolution law of combustion characteristic parameters of Chinese fir with the degree of biological aging
摘要
Ancient wooden structures, long-term exposed to natural environments, are susceptible to microbial invasion leading to biological aging. To investigate the combustion characteristics of such structures, a cone calorimeter was employed to test Chinese fir samples subjected to seven different biological aging cycles (0–12 weeks) under four radiation intensities (25–40 kW m−2). The results demonstrate that progressive biological aging noteworthily alters the wood’s composition and structure: The lignin content increased by up to 15% (from week 0 to 12), while cellulose and hemicellulose decomposed, resulting in a mass loss coefficient decrease of approximately 20% in severely aged samples. Consequently, the ignition time was notably abated, e.g., from 45 ± 3 s for unaged wood to 28 ± 2 s for 12-week aged wood at 35 kW m−2. The peak heat release rate (pHRR) initially increased with aging up to 10 weeks (e.g., 180 ± 10 kW m−2 at 35 kW m−2) before declining. Furthermore, the total smoke production was the highest at moderate aging stages (6–8 weeks), while severely aged wood exhibited more intense combustion, promoting the conversion of CO – CO₂ and leading to a 25% lower CO release rate compared with mildly aged wood. The fire performance index (FPI) reached a minimum at 10 weeks of aging, indicating the highest fire risk at this stage. These findings provide a crucial theoretical basis for enhancing fire prevention and suppression strategies in ancient timber buildings.