What is the most critical factor determining the risk of fire spread?

The most critical factor determining the risk of fire spread is the presence of ignition sources and combustible materials. This is because fire requires three elements to ignite and sustain: heat, fuel, and oxygen. When ignition sources, such as sparks or open flames, are introduced to combustible materials, which may include wood, fabrics, or chemicals, the fire can easily start and rapidly spread.

While wind speed can accelerate fire spread and impact the direction of flames, it is ultimately the combination of available fuel and potential ignition sources that sets the stage for a fire to ignite in the first place. Fire department response time is crucial for controlling and extinguishing a fire once it has started, but it does not directly influence the initial risk of fire spread. Similarly, temperature can influence the rate of combustion and the likelihood of ignition, but without combustible materials or ignition sources, a fire cannot spread. Hence, the presence of these elements is fundamental in assessing the overall risk of fire spread.