Use of pre-charred surfaces to improve fire performance of wood

Wood is one of the most commonly-used and sustainable construction materials, but it is flammable in nature. Pre-charring is an ancient approach used to protect wooden construction materials against biochemical impacts, but its effectiveness in improving fire performance is still poorly understood. This work proposes a novel method to generate engineered wood with a uniform and robust surface char layer through slow pyrolysis under low thermal irradiation of 20 kW/m2. We found that the flammability of the pre-charred wood can be significantly reduced under higher irradiations up to 50 kW/m2 by increasing the ignition time by up to seven-fold and doubling the ignition temperature to about 670 °C. For the tested wood species (Merbau), we quantify a minimum char-layer thickness of 6 ± 1 mm to achieve effective fire retardancy. The fire hazards of pre-charred wood are also mitigated significantly, where observed flames become weaker, thinner, and bluer than that of the virgin wood. The peak heat release rate of burning pre-charred wood is reduced by over 50%, helping maintain the fire resilience of timber structures. This work quantifies the fire performance of pre-charred wood, highlighting a promising direction toward fire-safe timber construction materials. •Novel engineered woods (Merbau) with robust pre-charred layers are developed.•Minimum char-layer thickness to achieve effective fire retardancy is 6 ± 1 mm.•Thermal inertia (fire-retardant performance) is extraordinarily improved.•Ignition delay time, ignition temperature and ignition heat flux all increase.•Fire hazards of the pre-charred wood are reduced significantly.