Which is an element of the fire triangle?

The fire triangle is a fundamental concept in fire science that identifies the three essential elements needed for combustion to occur: heat, fuel, and oxygen. Oxygen is a critical element because it is necessary for the chemical reactions that take place during a fire. Without sufficient oxygen, a fire cannot ignite or sustain itself.

In this context, while foam and water are utilized as firefighting agents to extinguish flames, they do not form part of the fire triangle itself. Foam can smother a fire by cutting off its oxygen supply, and water cools down the heat, but neither of these materials is required for the fire to exist. Chemical substances may contribute to combustion or fire behavior, but they do not represent a separate element in the fundamental concept of the fire triangle. Therefore, oxygen stands out as a pivotal element necessary for the fire to start and continue burning, making it the correct answer.