How does the size of a wooden structural member affect its reaction to fire?

The size of a wooden structural member plays a significant role in its reaction to fire due to the principles of heat transfer and combustion. Larger wooden members, also known as heavy timbers, benefit from a greater mass, which means they can absorb more heat without reaching their combustion temperature immediately. This property allows heavy timbers to maintain structural integrity even under direct flame exposure for an extended period.

Heavier timbers will char on the surface when exposed to fire; this char layer acts as an insulator that slows the progression of heat to the inner material, helping to preserve its overall strength and stability for a longer duration compared to smaller members. This characteristic is particularly important in construction and fire safety, as it can provide additional time for occupants to evacuate and for firefighters to extinguish the fire.

In contrast, smaller wooden members are more prone to ignition and can burn through relatively quickly. This underscores the importance of understanding how the dimensions of structural elements affect their behavior in a fire scenario, thereby influencing design choices in fire-resistance building practices.