In case of fire wood as a construction component turns out to be safer than unprotected steel.
The burning components form a layer of charcoal, which conducts heat poorly and protects the core of the cross section. On average, one expects a burnup of 0.7 mm / min.
In 30 minutes, the cross-section reduces at all sides by about 20 mm, in 60 minutes to 40 mm. The remaining cross-section then carries the loads.
Wood alone with its natural properties, without any coating or other preventive measures, reaches a fire resistance class F 30 or F 60.