Fire extinguishers with a CLASS B rating is appreciated for a fire involving a flammable liquid. Class B fire extinguishers are good when liquids, oil, gasoline, kerosene, or paint has ignited into flames. The Class B fire extinguishers have two commonly used chemicals that destroy the fire, Monoammonium phosphate and sodium bicarbonate. What the Monoammonium phosphate does is smothers the fire, while the sodium bicarbonate makes a chemical reaction that extinguishes the fire.