Comparative Flammability and SEM–EDS Characterization of Contemporary, Aged and Charred Oak Wood from Historic Timber Structures

Historic timber combines structural function with heritage value, yet its fire behaviour is inferred from contemporary wood data. This study provides an integrated, condition-based assessment of contemporary oak (Quercus robur L.) and historic oak from a nineteenth-century half-timbered building in Swołowo, Poland. Mass loss calorimetry (MLC) at 35 and 50 kW/m2 was combined with scanning electron microscopy (SEM) and SEM coupled with energy-dispersive X-ray spectroscopy (SEM–EDS). The aim was to determine whether surface preservation state explains differences between ignition sensitivity and cumulative heat release. Historic oak ignited earlier than contemporary oak, especially when the tested surface was degraded; at 50 kW/m2, time to ignition decreased from 25.33 s for contemporary oak to 18 s for non-degraded historic oak and 5.33 s for degraded historic oak. However, total heat release was lower for historic variants and final mass loss remained comparable. SEM showed roughness, fibrillation, delamination, fractured cell-wall edges and secondary porosity in aged and charred zones. SEM–EDS indicated C- and O-dominated preserved areas, whereas degraded and charred surfaces were enriched in inorganic elements. The results show that ignition propensity and total fire contribution should be evaluated separately, and that condition rather than age alone is critical for historic oak assessment.