What type of fuel ignites slowly because it has a large diameter, such as large brush or branches?

• A. Heavy fuel
• B. Live fuel
• C. Ground fuel
• D. Dead fuel

Answer: (A)

Ignition speed is influenced by fuel size. Large-diameter fuels, like big brush or branches, have less surface area exposed per unit of volume, so heat must penetrate into the interior to raise the core to ignition temperature. That extra heat input makes ignition happen more slowly. This is why materials described as heavy fuels—large pieces of fuel—ignite slowly but can burn hot and for a long time once they catch. In contrast, live fuels (living vegetation) often resist ignition due to moisture, ground fuels are near or within the soil layer, and dead fuels are dry plant material, which can ignite differently but don’t describe the large-diameter ignition delay as directly as heavy fuels do.