The principle which most closely describes how water extinguishes fire is:

• A. Removal of fuel
• B. Reduction of temperature
• C. Exclusion of oxygen
• D. Interruption of the chemical chain reaction

Answer: (B)

Water extinguishes most fires primarily by cooling. When applied, it absorbs a lot of heat from the fuel and surrounding environment. As it heats up, water changes to steam, which requires a large amount of energy. This heat absorption lowers the fuel’s temperature and slows the heat transfer that keeps the flame going, eventually dropping below the fuel’s ignition temperature and stopping combustion. Water isn’t mainly removing fuel, excluding oxygen, or interrupting the chemical reactions happening in the flame; its dominant effect is the rapid cooling that suppresses the fire.