Solid wood resists fire. Contrary to popular thinking it burns at a slow rate and does not melt and suddenly collapse as steel can when heated. It can also often be sanded and reused after less severe fires.
When wood is exposed to high temperature it will burn and decompose to provide an insulating surface layer of char that retards further degradation of the wood. The rate of char is initially fast but as the depth of char increases the rate of char slows because of the increasing insulation provided.
Although wood is a combustible material, when it burns, a surface layer of char is created which helps to protect and maintain the strength and structural integrity of the remaining unburned wood beneath. Engineered pine solid wood walls have a char rate of 0.6mm per minute.
Most building fires are started by heat sources that ignite materials such as furnishings and items that are introduced into the building and it is these materials that emit toxic fumes that most often threaten life and limb. The building structure is usually not the first material ignited.