Combustion is the chemical reaction that feeds a fire more heat and allows it to continue. When the fire involves burning metals like lithium, magnesium, titanium, etc. (known as a class-D fire), it becomes even more important to consider the energy release. The metals react faster with water than with oxygen and thereby more energy is released. Putting water on such a fire results in the fire getting hotter or even exploding. Carbon dioxide extinguishers are ineffective against certain metals such as titanium. Therefore, inert agents (e.g. dry sand) must be used to break the chain reaction of metallic combustion.
In the same way, as soon as one of the four elements of the tetrahedron is removed, combustion stops.
The oxidizer is the other reactant of the chemical reaction. In most cases, it is the ambient air, and in particular one of its components, oxygen (O2). By depriving a fire of air, it can be extinguished; for example, when covering the flame of a small candle with an empty glass, fire stops; to the contrary, if air is blown over a wood fire with bellows, the fire is activated by the