Which of the following is an example of heavy fuels?

Heavy fuels are characterized by their density, size, and the amount of energy they release when combusted. Large logs and timber fit this definition well, as they are substantial natural materials that provide a significant amount of fuel for a fire. Their larger mass and higher moisture content compared to lighter fuels mean that they can burn for an extended period, offering a sustained source of heat and flames.

In contrast, lighter fuels, such as grass, leaves, small twigs, and pine needles, tend to ignite and burn quickly. These materials burn off rapidly because of their smaller size and lower moisture content, which allows them to ignite more easily but does not sustain a fire in the same way that heavy fuels do. Thus, large logs and timber are the prime example when discussing heavy fuels in the context of fire behavior and firefighting operations.