Class B Class  B  fires  occur  with  flammable  liquid substances. Examples of class B fires are gasoline, jet fuels, paints, grease, and any petroleum-based product. These and other combustible substances do not leave embers or ashes.  Class B fires are extinguished by providing a barrier between the burning substance and oxygen necessary for combustion. Chemical and mechanical foams produce such a barrier and are known as permanent smothering agents, but their effect is only temporary. The application must be renewed if there is any danger of reignition. The extinguishing agents recommended for combating class B fires are CO₂, PKP, Halon, and Aqueous Film-Forming Foam (AFFF). NOTE: Water by itself is  NOT  recommended for use on class B fires. Class C Class C fires are energized electrical fires that are attacked at prescribed distances by using nonconductive agents such as CO₂   and Halon 1211. The most effective tactic is to de-energize the system and handle the fire as a class A fire. When fires are not deep seated, clean agents that pose no cleanup problem, such as Halon 1211 or CO₂, are the preferred extinguishing agents. WARNING Water in any form, particularly salt water, is dangerous when used on electrical equipment. Class D Class D fires are combustible metals, such as magnesium and titanium. Water in large quantities, as high velocity fog, is the recommended extinguishing agent. When water is applied to burning class D materials, there may be small explosions. The fire fighter should apply water from a safe distance or from behind shelter. Metal fires on board ships are commonly associated with aircraft wheel structures. EXTINGUISHING AGENTS There are many materials that may be used as fire-fighting agents. The primary agents discussed in the following paragraphs are the most extensively used aboard naval ships. Water Water is a cooling agent, and on board ship, the sea provides an inexhaustible supply. If the surface temperature of a fire can be lowered below the fuel's ignition temperature, the fire will be extinguished. Water is most efficient when it absorbs enough heat to raise its temperature to 212°F (100°C) or boiling point. At this temperature, the seawater will absorb still more heat until it changes to steam. The steam carries away the heat, which cools the surface temperature. Water in the form of fog is very effective for fire-fighting purposes. Additionally, water fog can provide protection to fire fighters from heat. However, the fog must be applied directly to the area to be cooled if its benefits are to be realized. Water in the form of a straight stream (also called solid stream) is used to reach into smoke-filled spaces or areas at a distance from the fire fighter.  When a straight stream is needed as an extinguishing agent, it should be directed into the seat of the fire. For maximum cooling, the water must come in direct contact with the burning material. A straight stream is best used to break up and penetrate materials. Aqueous Film-Forming Foam (AFFF) AFFF is composed of synthetically produced materials similar to liquid detergents. These film-forming agents are capable of forming water solution films on the surface of flammable liquids. AFFF concentrate is nontoxic and biodegradable in diluted form. When proportioned with water, AFFF provides three fire-extinguishing advantages. 1. An aqueous film is formed on the surface of the fuel that prevents the escape of the fuel vapors. 2. The layer effectively excludes oxygen from the fuel surface. 3. The water content of the foam provides a cooling effect. The primary use of AFFF is to extinguish burning flammable or combustible liquid spill fires (class B). AFFF has excellent penetrating characteristics and is superior to water in extinguishing class A fires. Carbon Dioxide (CO₂) CO₂    is an inert gas and extinguishes fires by smothering them. CO₂  is about 1.5 times heavier than air, which makes it a suitable extinguishing agent 12-3