What is the most common way fire spreads in a building?

The most common way fire spreads in a building is through lapping out of windows. This phenomenon occurs when flames escape from a window and ignite combustible materials outside or nearby, creating a dangerous condition known as "window lapping" or "flame impingement." Once the fire breaches the window, the hot gases and flames can move rapidly, affecting adjacent areas and potentially leading to greater fire spread.

This method of fire spread is significant because it highlights the importance of window placement and construction materials. Additionally, when flames lap out of windows, they can create a thermal draft that pulls more air into the building, promoting further combustion and intensifying the fire. Understanding this mechanism is crucial for firefighters, as it influences fire behavior and the necessary strategies for containment.

In contrast, while electrical wiring, ventilation systems, and roof areas can all contribute to fire spread, they are less common pathways compared to the immediate and direct propagation observed with fire lapping out of windows. This makes the phenomenon particularly critical for fire response and prevention strategies in buildings.