CHAPTER 4 FUNDAMENTALS OF FIRE FIGHTING

Fire is a constant potential hazard aboard ship. You must take all possible measures to prevent fires from starting. If a fire does start, you must immediately report the fire to the officer of the deck and then extinguish it rapidly. Often a fire will start in conjunction with other damage caused by enemy action, storms, or an accident, Some fires are caused by Hull Maintenance Technicians doing welding, brazing, or cutting. Fires must be extinguished rapidly. Otherwise, they could easily cause more damage than the initial casualty. In fact, a fire could cause the loss of a ship even after the original damage has been repaired or minimized.

As a Damage Controlman, you will need to know a great deal about fires, You need to know how to identify the different classes of fires, how to extinguish them, and how to use and maintain the fire fighting equipment systems and equipment. The more you learn, the more you will be able to contribute effectively to the safety of your ship.

In this chapter, we deal with the fundamentals of fire fighting. These include the nature of fire, the classification of fires, the fundamentals of extinguishment, and the extinguishing agents used.

FIRE COMPONENTS

Three components are required for a fire. These are a combustible material, a sufficiently high temperature, and a supply of oxygen. You will hear these components referred to as the fire triangle consisting of fuel, heat, and oxygen (fig. 4-l). Fires are generally controlled and extinguished by eliminating one side of the fire triangle. That is, if you remove either the fuel, heat, or oxygen, you can prevent or extinguish a fire. We will discuss the extinguishment of fires later in this chapter.

HEAT

Fire is also called burning or combustion. This is a rapid chemical reaction that releases energy in the form of light and noticeable heat. Most combustion involves rapid OXIDATION. Oxidation is the chemical reaction by which oxygen combines chemically with the elements of the burning substance.

Even when oxidation proceeds slowly, such as a piece of iron rusting, a small amount of heat is generated. However, this heat usually dissipates before there is any noticeable rise in the temperature of the material being oxidized. With certain types of materials, slow oxidation can turn into fast oxidation (fire) if the heat is not dissipated, These materials are normally stowed in a confined space where the heat of oxidation cannot be dissipated rapidly enough. This is known as spontaneous combustion. Materials such as rags or papers that are soaked with either animal fats, vegetable fats, paints, or solvents are particularly subject to spontaneous combustion.

For a combustible fuel or substance to catch on fire, it must have an ignition source and be hot enough to burn. The lowest temperature at

Figure 4-1.-The fire triangle.

which a flammable substance gives off vapors that will burn when a flame or spark is applied is known as the FLASH POINT. THE FIRE POINT is the temperature at which the fuel will continue to burn after it has been ignited. The fire point is usually a few degrees higher than the flash point. The auto-ignition or self-ignition point is the lowest temperature to which a substance must be heated to give off vapors that will burn without the application of a spark or flame. In other words, the auto-ignition point is the temperature at which spontaneous combustion occurs. The auto-ignition point is usually at a much higher temperature than the fire point.

The range between the smallest and the largest amounts of vapor in a given quantity of air that will burn or explode when ignited is called the

flammable range or the explosive range. For example, let us say that a substance has a flammable or explosive range of 1 to 12 percent. This means that either a fire or an explosion can occur if the atmosphere contains more than 1 percent but less than 12 percent of the vapor of this substance. In general, the percentages referred to in connection with flammable or explosive ranges are percentages by volume.

FUEL

One of the components of the fire triangle is fuel. Fuels take on a wide variety of characteristics. A fuel may be a solid, liquid, or even a vapor. Some of the fuels you will come into contact with are rags, paper, wood, oil, paint, solvents, and magnesium metals. This is by no means a complete list, but only examples.

OXYGEN

The air that you breath contains 20.8 percent oxygen. All fires need oxygen to continue to burn. Some fires will burn with only 6 percent oxygen. However, there are some fires that will produce their own oxygen. Further discussion on oxygen and its association with the control and extinguishment of fires will be covered in the appropriate sections of this chapter.

FIRE CLASSIFICATIONS

Fires are classified according to the nature of the combustibles (or fuels) involved. The classification of any particular fire is of great importance since it determines the manner in which

the fire must be extinguished. Fires are classified as being either class ALFA, class BRAVO, class CHARLIE, or class DELTA fires.

Class ALFA (A) fires are those that occur in such ordinary combustible materials as wood, cloth, paper, upholstery, and similar materials. Class A fires are usually extinguished with water, using high or low velocity fog or solid streams. Class A fires leave embers or ashes and must always be overhauled.

Class BRAVO (B) fires are those that occur in the vapor-air mixture over the surface of flammable liquids, such as gasoline, jet-fuels, diesel oil, fuel oil, paints, thinners, solvents, lubricating oils, and greases. Dry chemical (PKP), aqueous film forming foam (AFFF), HaIon 1301, carbon dioxide (CO2), or water fog can be used to extinguish class B fires. The agent you use will depend upon the circumstances of the fire.

Class CHARLIE (C) fires are those which occur in electrical equipment. Nonconducting extinguishing agents, such as PKP, CO2, and Halon 1301 are used to extinguish class C fires. Carbon dioxide and Halon 1301 are preferred because they leave no residue.

Class DELTA (D) fires occur in combustible metals, such as magnesium, titanium, and sodium. Special techniques have been developed to control this type of fire. If possible, the burning material should be jettisoned overboard. Most class D fires are fought by applying large amounts of water on the burning material to cool it down below its ignition temperature. However, magnesium fires can be smothered by covering the magnesium with lots of dry sand.