Experimental Characterization of Abnormal Heating in Historic Timber Structures Using Low-Temperature Wood Pyrolysis Particles

Fire poses a serious threat to historic timber buildings and cultural heritage. Conventional smoke, carbon monoxide (CO), and flame detectors may respond weakly during the early thermal-degradation stage of wood. This study investigated particles released from wood during low-temperature thermal exposure as potential indicators of abnormal heating. Chinese fir, Masson pine, Korean pine, and Nanmu were tested on a controlled thermal-exposure platform using a particle sensor combining adiabatic-expansion-induced condensational amplification with light-scattering detection. Pyrolysis particle number concentration (PPC) was continuously monitored under uncoated and selected surface-coating conditions. At 180 °C for 30 min, PPC values for Chinese fir, Masson pine, Korean pine, and Nanmu were approximately 114, 125, 135, and 158 particles/cm3, respectively. PPC generally increased with exposure temperature and varied with wood species and coating conditions. Detectable particle responses occurred before visible smoke or open flames appeared, whereas parallel smoke, CO, and flame detectors showed no evident response under the tested conditions. These findings suggest that particles generated during low-temperature wood thermal degradation can characterize early-stage abnormal heating and show potential as indicators for early fire monitoring in historic timber buildings, providing preliminary experimental support for monitoring cultural heritage structures.