THE REMOVAL OF HEAT

The fire will go out if you can remove enough heat by cooling the fuel to a temperature below that at which it will support combustion.

Heat may be transferred in three ways: by radiation, by conduction, and by convection. In the process known as radiation, heat is radiated in all directions. Radiated heat is what causes you to feel hot when you stand near an open fire. In conduction, heat is transferred through a substance or from one substance to another by direct contact from molecule to molecule. Therefore, a thick steel bulkhead with a fire on one side can conduct heat from the fire and transfer the heat to the adjoining compartments. In convection, the air and gases rising from a fire are heated. These gases can then transfer the heat to other combustible materials that are within reach. Heat transferred by convection is a particular danger in ventilation systems. These systems may carry the heated gases from the fire to another location several compartments away. If there are combustibles with a low flash point within a compartment served by the same ventilation system, a new fire may start.

To eliminate the heat side of the fire triangle, cool the fire by applying something that will absorb the heat. Although several agents serve this purpose, water is the most commonly used cooling agent. Water may be applied in the form of a solid stream, as a fog, or used together with AFFF.

THE CONTROL OF OXYGEN

Oxygen is the third component of the fire triangle. Oxygen is difficult to control because you obviously cannot remove the oxygen from the atmosphere that normally surrounds a fire. However, oxygen can be diluted or displaced by other substances that are noncombustible.

If a fire occurs in a closed space, it can be extinguished by diluting the air with carbon dioxide (C02) gas. This dilution must proceed to a certain point before the flames are extinguished. To reach this point, all ventilation systems to the space must be secured. Once this point has been reached, no fire can exist. In general, a large enough volume of C02 must be used to reduce the oxygen content to 15 percent or less.

AFFF foam will also keep oxygen from reaching the burning materials thus smothering the fire.

THE REDUCTION OF THE RATE OF COMBUSTION

Dry chemical fire extinguishing agents and Halon 1301 do not extinguish fires by cooling or smothering. Instead, they are believed to interrupt the chemical reaction of the fuel and oxygen. This reduces the rate of combustion, and the fire is extinguished quickly.

THE IMPORTANCE OF SPEED IN FIRE FIGHTING

Speed is very important in fire fighting. If you allow a fire to burn without confining or extinguishing it, the fire can spread rapidly. A small fire in a trash can may spread to other combustibles and become a large fire that could affect several compartments or even the whole ship. The cost of damage that may have originally been a few dollars could end up costing millions of dollars. Therefore, the ship's fire party must get to the scene with their equipment and start fighting the fire as soon as possible. Any delay that allows the fire to spread will make it more difficult to extinguish the fire with the personnel and equipment available.

EXTINGUISHING AGENTS

The agents commonly used by Navy fire fighters include water, AFFF, dry chemicals, carbon dioxide (CO2), and Halon 1301. The agent or agents that you will use in any particular case will depend upon the classification of the fire and the general circumstances.

WATER

Cooling is the most common method of fire

extinguishment, and water is the most effective cooling agent. Fortunately, water is available in large quantities. Of all the extinguishing agents being used by the Navy, water has the greatest capacity for heat absorption. Therefore, you can cool most burning substances below their ignition points by the application of water.

Aboard ship you will normally apply water to the fire by the use of an all-purpose nozzle. We will discuss the all-purpose nozzle in more detail in chapter 5 of this training manual. The allpurpose nozzle allows you to apply water to the fire as a solid stream, as high velocity water fog, or as low velocity water fog. When you need to reach a fire that is some distance away, or when you need penetrating power, you should use the solid stream. However, water fog is preferred over a solid stream in most cases. A given amount of water in the fog will absorb more heat than the same amount of water in a solid stream. The total amount of water that must be pumped into the ship to fight a given fire will also be reduced when using the fog. All water used for fire fighting must be pumped overboard or otherwise disposed of; this is a definite advantage of using the fog form. In addition to cooling the fire, fog tends to smother the fire by displacing the oxygen.

Because of the cooling capacity of the finely divided water particles, fog can be used successfully on class B fires as well as on class A fires. If you use fog on a class B fire, you need to remember that a danger of a reflash exists until you cool the entire surface of the fuel down below the flash point.

Water is not recommended as an extinguishing agent for electrical fires except as a last resort. When water is properly broken up into a fine spray or fog by the nozzles operating at the designed pressure, the fog does not conduct electric current. But if you shift to a solid stream, or if you accidentally touch the nozzle or the applicator to the electrical equipment, the danger of electrical shock is great. Sometimes it may be necessary to use water fog to fight an electrical fire. In these cases, do not advance the nozzle any nearer to the power source than is absolutely necessary for proper use of the fog pattern.

Water fog gives you considerable protection by forming a screen of water droplets between you and the fire. This fog screen protects you against the intense heat of the fire. This gives you a certain amount of maneuverability in attacking the fire. Water fog also tends to dilute or absorb various vapors and to wash fumes and smoke from the atmosphere. You can help clear smoke from the area by occasionally directing the fog pattern upward for a few seconds.

Before you enter a burning compartment, reduce the heat and flame by a liberal application of water fog. Place the fog into the compartment through doors and other accesses. In the early stages of a large fire, a good deal of the fog applied will turn into steam. The steam will help to smother the fire. You must remember to stand clear of openings, since there is likely to be a violent outward rush of hot gases that are displaced by the steam.

FOAM

Foam is a highly effective extinguishing agent for smothering large fires, particularly those in oil, gasoline, and jet fuels.

AFFF, also known as "light water," is a synthetic, film-forming foam designed for use in shipboard fire fighting systems. The foam proportioning/injection equipment generates a white foam blanket. AFFF proportioning equipment will be discussed in chapter 5 of this

training manual. AFFF is equivalent to seawater when it is used to extinguish class A fires.

The unique action of AFFF stems from its ability to make a light-water film float on flammable fuels. As foam is applied over the flammable liquid surface, an aqueous solution drains from the foam bubbles and floats out over the surface to provide a vapor seal. This aqueous film-forming action enhances extinguishment and prevents reflash, even when the foam blanket is disturbed. Fuels which have not been ignited may also be protected with this same action.

AFFF can be used alone or in combination with Purple-K-Powder (PKP), which will be discussed in the next section.