Types of fire extinguishers and their contents

http://www.fire-extinguisher101.com/ for images and more information

A Wet foam: Water and surfactants.

Used for fires of paper, wood, cardboard, and most plastics. Removes heat and foam helps exclude oxygen. Red extinguishers.

B Carbon dioxide: Compressed CO2
Used for fires of liquids such as gasoline, solvents, kerosene, grease and oil. CO₂ gas dilutes the available oxygen. Large wide nozzle.

C Carbon dioxide: Compressed CO₂
Used for fires of electrical equipment, such as appliances, wiring, circuit breakers and outlets. CO₂ dilutes the available oxygen. Large wide nozzle. CO₂ extinguishers are rated for type B and C fires

D Dry powder: Fine spray of NaCl
Used for fires of Mg, Ti, Li, K and Na metals. Found mainly in chemistry laboratories. Separates fuel from oxygen and heat as the sodium chloride melts onto the metal surface creating a protective layer.
Large yellow extinguishers.

K Wet chemical: KOAc, potassium citrate, or K2CO₃
Used for fires of cooking oils, trans-fats, or fats in cooking appliances. Found in restaurants and cafeteria kitchens. Alkaline conditions cause saponification of fatty acids which generates a layer of foam that excludes oxygen. Large silver extinguishers.

A/B/C Dry chemical: Siliconized monoammonium phosphate and ammonium sulfate
Most commonly used fire extinguishers.. Creates a barrier between oxygen and the fuel.
Red extinguishers.

B/C Halogenated: Halon 1211 CF₂ClBr
H3R Clean Agents Halon fire extinguishers. Contain recycled Halon 1211 with N₂ propellant. Ideal for sensitive electronic equipment. Stops the chemical chain reaction.