Which component is essential for sustaining a fire once it has started?

Oxygen is crucial for sustaining a fire because it is a key component of the fire triangle, which includes heat, fuel, and oxygen. When a fire ignites, it requires a sufficient supply of oxygen to continue burning. The chemical reaction that occurs during combustion involves the fuel reacting with oxygen to produce heat, light, and various combustion products.

Water is commonly used to extinguish fires by cooling the flames and displacing oxygen, but it does not play a role in sustaining a fire. Chlorine and sodium are not involved in the basic combustion process and do not contribute to maintaining the fire's reaction. Thus, without oxygen, a fire cannot sustain itself, making it the essential component for continuing the fire once it has started.