The letter "B" in a B I extinguisher indicates the type of fire the extinguisher is designed to handle. Fire extinguishers are classified according to the type and size of fire they can handle.
FIRE TYPES ARE:
CLASS A: Combustible solids such as wood
CLASS B: Flammable liquids such as gasoline
CLASS C: Electrical fires
Wood or paper fires (Class A) can be handled with water. However, water should never be applied to electrical (Class C) or flammable liquid (Class B) fires, as the water will only spread flammable liquid fires and will conduct electricity. Most fire extinguishers can put out Class B and C fires.
FOR MARINE USE, IT IS RECOMMENDED THAT YOU FIND AN EXTINGUISHER THAT CAN PUT OUT CLASS A, B, AND C FIRES.