By the 1920's, automatic systems utilizing carbon dioxide were available. In 1928, work on the NFPA Standard for carbon dioxide extinguishing systems was begun. The mechanisms by which carbon dioxide extinguishes fire are rather well known. If we go back to the familiar fire triangle, we realize that an interaction between fuel, oxygen and heat is necessary to produce a fire condition. When these three elements are present in a proper relationship, fire will result.
Carbon dioxide extinguishes fire by physically attacking all three points of the fire triangle.
The primary attack is on the oxygen content of the atmosphere. The introduction of CO2 into the fire zone displaces sufficient oxygen in the atmosphere to extinguish the open burning. At the same time, the extinguishing process is aided by a reduction in the concentration of gasified fuel in the fire area. And finally, CO2 does provide some cooling in the fire zone to complete the extinguishing process. Such surface fires are usually the case when liquid fuels are involved.