What factor is critical in determining if a fire continues to burn?

The presence of a heat source and the availability of a fuel source are both essential for a fire to sustain itself. According to the fire triangle, which consists of heat, fuel, and oxygen, all three elements must be present for combustion to occur.

A heat source provides the energy needed to ignite and maintain the fire. This could be anything that generates enough heat to raise the fuel to its ignition temperature. Conversely, the fuel source is the material that burns, providing the necessary substance for the fire to consume. Without adequate fuel, even with heat present, a fire will eventually extinguish as it runs out of material to burn.

While humidity levels can influence the burning characteristics of certain fuels by affecting their moisture content, it is not a core factor in determining whether a fire can continue to burn. Therefore, the correct answer encompasses both the necessity of having a heat source and a fuel source, showcasing their combined role in sustaining combustion.