Which fire extinguishment method involves CO2?

The use of carbon dioxide (CO2) as a fire extinguishment method is primarily based on its ability to displace oxygen in the environment of a fire. Fires need three elements to sustain combustion: heat, fuel, and oxygen (the fire triangle). By introducing CO2, which is an inert gas, it effectively reduces the concentration of oxygen available to the fire, thereby suffocating it and stopping the combustion process. This method is particularly effective for certain types of fires, especially those involving flammable liquids and electrical equipment, where water application could be hazardous.

In contrast, the other methods listed do not specifically involve the use of CO2 in their extinguishing processes. Nitrogen dilution, for instance, focuses on lowering oxygen levels but does not use CO2 as the primary agent. Water application cools the burning material and removes heat, which is not related to the action of CO2. Fixed foam systems work by creating a barrier that separates the fire from the atmosphere, primarily using foam to smother the flames rather than displacing oxygen with CO2. Hence, the role of CO2 in extinguishing fires through oxygen dilution stands out as the primary means of suppression in this context.