DRY CHEMICALS

Dry chemical powders extinguish a fire by a rather complicated chemical mechanism. They do not smother the fire and they do not cool it. Instead, they interrupt the chemical reaction, known as fire, by suspending fine particles in the fire. In effect, the dry chemicals put a temporary screen between the heat, oxygen, and fuel and maintain this screen just long enough for the fire to be extinguished.

Several types of dry chemicals have been used as fire extinguishing agents. For Navy use, the most important agent of this kind at present is potassium bicarbonate, also known as Purple-K-Powder or PKP. PKP is used to extinguish class B and class C fires because it is very effective against these fires. However, it is both corrosive and abrasive and should be used on class C fires only in emergencies. PKP is primarily used in portable 18-pound extinguishers. However, 9- and 27-pound portable extinguishers are also available for portable use. PKP can be used in conjunction with AFFF. Portable PKP extinguishers and the special equipment for using PKP and AFFF together are described in chapter 5 of this training manual.

CARBON DIOXIDE

Carbon dioxide (CO2) is an effective agent for extinguishing fires by smothering them. That is, CO2 reduces the amount of oxygen available for combustion. This smothering action is temporary. You must remember that the fire can quickly rekindle if oxygen is again admitted to hot embers.

CO2 is a dry, noncorrosive gas that is inert when in contact with most substances. It is heavier than air and remains close to the surface. CO2 does not damage machinery or other equipment. Since it is a nonconductor of electricity, CO2 can safely be used to fight fires that might present electric shock hazards. However, the frost that collects on the horn of a CO2 extinguisher does conduct electricity. Therefore, you should be careful and never allow the horn to come into contact with electrical components.

Aboard ship, CO2 fire extinguishing equipment includes 15-pound CO2 extinguishers, 50-pound CO2 hose and reel installations, and 50-pound CO2 installed flooding systems.

Although CO2 is nonpoisonous, it is dangerous because it does not provide a suitable atmosphere for breathing. Asphyxiation can result from breathing CO2. OBA's must be worn when CO2 is used below decks or in confined spaces.

HALON 1301

Halon 1301 (bromtrifluoromethane) is a relatively new fire extinguishing agent used in the Navy. Halon 1301 is a colorless, odorless gas with a density approximately five times that of air. It does not conduct electricity or leave a residue. Halon 1301 is stored in compressed gas cylinders for shipboard use.

This extinguishing agent is effective against class A, class B, and class C fires. The fires are not extinguished by smothering or cooling. The chemical reaction of fire is interrupted, as is the case of using PKP. HaIon 1301 decomposes upon contact with flames that are approximately 900F (482C). For Halon 1301 to function effectively as an extinguishing agent, it must decompose. However, as it decomposes, several other products such as hydrogen fluoride (HF) and hydrogen bromide (HBr) are formed. Both gases are irritating to the eyes, skin, and upper respiratory tract. Chemical burns are also possible.

You should not stay in a space where HaIon 1301 has been released unless you are wearing an OBA. However, you can safely be exposed to concentrations of 5 to 7 percent for a period up to 10 minutes. In fact, carbon monoxide along with oxygen depletion, heat, and smoke present a greater danger to you than Halon 1301. Chapter 5 of this training manual will discuss Halon 1301 fire extinguishing systems.

SUMMARY

In this chapter, you were introduced to the fundamentals of fire fighting. We identified the three elements required to have a fire along with the classifications of fires. You should now be aware of the effects of fire and the different types of gases you may encounter while fighting a fire. Remember, no two fires are identical; you will have to determine the best method or extinguishing agent to use when fighting a fire. Safety is to be observed always. Never assume a compartment's atmosphere is safe for humans. A deadly gas may be present just waiting for a victim. Do not let the victim be you. The equipment used to test a compartment's atmosphere will be discussed in chapter 6 of this training manual.

CHAPTER 5

FIRE-FIGHTING EQUIPMENT AND SYSTEMS

To fight fires effectively, you must have a thorough knowledge of the fire-fighting equipment and systems. The extinguishing agents used in the Navy are discussed in chapter 4 of this manual. This chapter deals with the equipment and systems that are commonly used aboard naval ships to apply the extinguishing agents to fires. This information is general in nature. It should be supplemented by a careful study of the fire-fighting equipment and systems available on your own ship. You will find the manufacturers' technical manuals for the systems and equipment on your ship a source of valuable information.

FIREMAIN SYSTEMS

The firemain system receives water pumped from the sea. It distributes this water to fireplugs, sprinkling systems, flushing systems, machinerycooling-water systems, washdown systems, and other systems as required. The firemain system is used primarily to supply the fireplug and the sprinkling systems; the other uses of the system are secondary.

Naval ships have three basic types of firemain systems: the single-main system, the horizontalloop system, and the vertical-loop system. The type of firemain system in any particular ship depends upon the characteristics and functions of the ship. Small ships generally have straight-line, single-main systems. Large ships usually have one of the loop systems or a composite system, which is some combination or variation of the following three basic types. l The single-main firemain system consists

of one main that extends fore and aft. The main is generally installed near the centerline of the ship, extending forward and aft as far as necessary. l The horizontal-loop firemain system

consists of two single fore-and-aft, crossconnected mains. The two mains are installed in the same horizontal plane but are separated athwartships as far as practical.

. The vertical-loop firemain system consists of two single fore-and-aft, cross-connected mains. The two mains are separated both horizontally and vertically. As a rule, the lower main is located below the lowest complete watertight deck, and the upper main is located below the highest complete watertight deck. l A composite firemain system consists of

two mains installed on the damage control deck and separated athwartships. A bypass main is installed at the lower level near the centerline. Cross connections are installed alternately between one service main and the bypass main.