CO2 is great for fire suppression for a number of reasons. CO2 gas is colorless and odorless, which is a bonus for its use. But the big plus about CO2 is that it is a relatively stable gas. It doesn't react with much of anything. That means it doesn't produce any kind of toxic or other by products when it is used to put out a fire. It's also non-conductive, so a person could spray it on an electrical fire and not worry about it. CO2 is also a good fire suppressant because it works against 2 parts of the "fire triangle." The fire triangle is composed of fuel, oxygen, and heat. Those three things together provide an environment that is conducive to fire. CO2 works against the oxygen and heat components. A CO2 extinguisher first displaces a lot of oxygen near the fire. Without oxygen, the fire is robbed of its ability to "breathe." Second, when the CO2 gas comes out, it expands and rapidly cools. That reduces a lot of the potential heat that might cause another flare up.
Carbon dioxide is heavier than air, so it creates a blanket around the burning fuel and displaces the oxygen necessary to maintain combustion. CO2 is a colorless and, in normal concentrations, odorless gas. It is non-combustible and doesn't react with burning materials, so it doesn't create any toxic or other by-products when used to suppress a fire and doesn't leave a residue behind like powder or foam extinguisher would, so it’s a clean gas.
Carbon dioxide is non-conductive, making it an ideal fire suppressant for use on electrical and electronic equipment.
However, it should not be used in confined spaces and where there is a likelihood of presence of magnesium since Carbon dioxide will burn on reaction with magnesium and the result is the formation of magnesium oxide and carbon as soot.