Which of the following is NOT part of the fire triangle?

The fire triangle is a fundamental concept that describes the three essential components required for fire to ignite and sustain. These components are fuel, oxygen, and heat. Fuel refers to any combustible material, oxygen is necessary for combustion, and heat is required to raise the material to its ignition temperature.

Water, while critically important in firefighting to extinguish fires, does not fall within the basic elements that constitute the fire triangle. Instead, water acts as a cooling agent and can help remove heat from the fire, thus impacting the triangle indirectly. By removing heat, water can effectively disrupt the combustion process. Therefore, water is not one of the core components necessary for fire itself to start or continue burning, making it the correct answer to this question.