There are three elements required for a fire: fuel, oxygen, and heat. There are four classes of fire based on the type of fuel: Class A involves ordinary combustibles like wood and paper; Class B involves flammable liquids; Class C involves energized electrical equipment; and Class D involves combustible metals. Class K involves cooking oils, trans-fats, or fats. Proper precautions and safety measures must be taken for each class to prevent fires from starting.