Cracking quantification of wood exposed to constant heat fluxes

Surface cracking of wood when exposed to a heat source is one of the factors understudied by the fire community despite the fact that the cracks may guide the release of pyrolysis gases, inducing heterogeneity in the effusion of gas and therefore may affect ignition and extinction of flame at the material surface. This study aimed to develop a dynamic detection method for characterizing wood cracking during fire tests by providing quantities such as surface area, length, and number of cracks. Spruce samples were exposed to a wide range of heat fluxes during for at least 40 min using a vertical cone calorimeter. An infrared camera with a specific filter wavelength was used to track crack formation. A total of 74 experiments were carried out in air, and seven were carried out in an oxygen-free atmosphere to determine the cracking dynamics of the wood. The results show that the cracking rate and the number of cracks quickly reach to a constant value. The heat flux and the presence of oxygen are not dominant factors in wood's dynamic cracking. This work provides quantitative data for readers interested in accounting for cracking and heterogeneous pyrolysis gas release on the surface of a sample.