Military

 

Chapter 11

Shipboard Fire Fighting

Fire aboard ship is a terrifying experience. It is a situation where the crew must work together as a team to survive. To do this you must know the type of fire you are fighting, select the right extinguishing agent, and know how to use the fire fighting equipment aboard ship to put out the fire. Once you understand what fire is, then you can take the proper actions for putting the fire out. This chapter covers the following:
  • Definition of fire.
  • Classes of fire.
  • Effective agents to control and extinguish each class of fire.
  • Types of fire fighting equipment.
  • Different types of self-contained breathing apparatus.

CHEMISTRY OF FIRE

11-1. Oxidation is a chemical process in which a substance combines with oxygen. During this process, energy is given off, usually in the form of heat. Rusting iron and rotting wood are common examples of slow oxidation. Fire, or combustion, is rapid oxidation; the burning substance combines with oxygen at a very high rate. Energy is given off in the form of heat and light. Because this energy production is so rapid, we can feel the heat and see the light as flames.
THE START OF A FIRE
11-2. All matter exists in one of three states: solid, liquid, or gas (vapor). The atoms or molecules of a solid are packed closely together, and those of a liquid are packed loosely. The molecules of a vapor are not packed together at all; they are free to move about. In order for a substance to oxidize, its molecules must be pretty well surrounded by oxygen molecules. The molecules of solids and liquids are packed too tight to be surrounded by oxygen molecules. Therefore, only vapors can burn.

11-3. When a solid or liquid is heated, its molecules move about rapidly. If enough heat is applied, some molecules break away from the surface to form a vapor just above the surface. This vapor can now mix with oxygen. If there is enough heat to raise the vapor to its ignition temperature, and if there is enough oxygen present, the vapor will oxidize rapidly--it will start to burn.
BURNING
11-4. What we call burning is the rapid oxidation of millions of vapor molecules. The molecules oxidize by breaking apart into individual atoms and recombining with oxygen into new molecules. It is during the breaking-recombining process that energy is released as heat and light. 11-5. The heat that is released is radiant heat, which is pure energy. It is the same sort of energy that the sun radiates and that we feel as heat. It radiates, or travels, in all directions. Therefore, part of it moves back to the seat of the fire, to the "burning" solid or liquid (the fuel). 11-6. The heat that radiates back to the fuel is called radiation feedback (Figure 11-1). Part of this heat releases more vapor and part of it raises the vapor to the ignition temperature. At the same time, air is drawn into the area where the flames and vapor meet. The result is that there is an increase in flames as the newly formed vapor begins to burn.

 


Figure 11-1. Radiation Feedback

 

THE FIRE TRIANGLE

11-7. The following are the three things that are required for combustion. Fuel (to vaporize and burn), oxygen (to combine with fuel vapor), and heat (to raise the temperature of the fuel vapor to its ignition temperature). The fire triangle illustrates these requirements (Figure 11-2). It also illustrates two important facts in preventing and extinguishing fires.
  • If any side of the fire triangle is missing, a fire cannot start.
  • If any side of the fire triangle is removed, the fire will go out.
A fire can be extinguished by destroying the fire triangle. If fuel, oxygen, or heat is removed, the fire will die out. If the chain reaction is broken, the resulting reduction in vapor and heat production will put out the fire. Additional cooling with water may be necessary where smoldering or reflash is possible.

 


Figure 11-2. Fire Triangle With One Side Missing

 

FUELS AND FUEL CHARACTERISTICS
11-8. Fuels and fuel characteristics are important for the mariner to know so that they can identify what fire fighting agent should be used in fighting a fuel fire.

Solid Fuels

11-9. The most obvious solid fuels are wood, paper, and cloth. These can be found aboard ship as cordage, canvas, dunnage, furniture, plywood, wiping rags, and mattresses. The paint on bulkheads is also a solid fuel. Vessels may carry a wide variety of solid fuels as cargo (from baled materials and goods in cartons to loose materials, such as grain). Metals such as magnesium, sodium, and titanium are also solid fuels that may be carried as cargo.

Ignition Temperature

11-10. The ignition temperature of a substance (solid, liquid, or gas) is the lowest temperature at which sustained combustion will occur without the application of a spark or flame. Ignition temperatures vary among substances. For a given substance, the ignition temperature also varies with bulk, surface area, and other factors. The ignition temperatures of common combustible materials is between 149C (300F) and 538C (1,000F).

Liquid Fuels

11-11. The flammable liquids most commonly found aboard ship are bunker fuel, lubricating oil, diesel oil, kerosene, and oil-base paints and their solvents. Cargo may also include flammable liquids and liquified flammable gases.

Vaporization

11-12. Flammable liquids release vapor in much the same way as solid fuels. The rate of vapor release is greater for liquids than for solids, since liquids have less closely packed molecules. Liquids can also release vapor over a wide temperature range. Gasoline starts to give off vapor at -43C (-45F). This makes gasoline a continuous fire hazard; it produces flammable vapor at normal temperatures. Heating increases the rate of vapor release.

11-13. Heavier flammable liquids such as bunker oil and lubricating oil must be heated to release sufficient vapor for combustion. Lubricating oils can ignite at 204C (400F). A fire reaches this temperature rapidly, so that oils directly exposed to a fire will soon become involved. Once a light or heavy flammable liquid is burning, radiation feedback and the chain reaction quickly increases flame production.

11-14. The vapor produced by a flammable liquid is heavier than air. This makes the vapor very dangerous because it will seek low places, dissipate slowly, and travel to a distant source of ignition. For example, vapor escaping from a container can travel along a deck and down deck openings until it contacts a source of ignition (such as a spark from an electric motor). If the vapor is properly mixed with air, it will ignite and carry fire back to the leaky container. The result can be a severe explosion and fire.

Flash Point

11-15. The flash point of a liquid fuel is the temperature at which it gives off sufficient vapor to form an ignitable mixture near its surface. Sustained combustion takes place at a slightly higher temperature, referred to as the fire point of the liquid. The flash points and fire points (temperatures) of liquids are determined in controlled tests.

Gaseous Fuels

11-16. There are both natural and manufactured flammable gases. Those that may be found on board a vessel include acetylene, propane, and butanes.

Burning

11-17. Gaseous fuels are already in the required vapor state. Only the correct intermix with oxygen and sufficient heat are needed for ignition. Gases, like flammable liquids, always produce a visible flame; they do not smolder.

Explosive Range (Flammable Range)

11-18. A flammable gas or the flammable vapor of a liquid must mix with air in the proper proportion to make an ignitable mixture. The smallest percentage of a gas (or vapor) that will make an ignitable air-vapor mixture is called the lower explosive limit of the gas (or vapor). If there is less gas in the mixture, it is too lean to burn. The greatest percentage of a gas (or vapor) in an ignitable air-vapor mixture is called its upper explosive limit. If a mixture contains more gas than the UEL, it is too rich to burn. The range of percentages between the lower and upper explosive limits is called the explosive range of the gas or vapor.

OXYGEN

11-19. The oxygen side of the fire triangle refers to the oxygen content of the surrounding air. Ordinarily, a minimum concentration of 16 percent oxygen in the air is needed to support flaming combustion. However, smoldering combustion can take place in about 3 percent oxygen. Air normally contains about 21 percent oxygen, 78 percent nitrogen, and 1 percent other gases, principally argon.

HEAT

11-20. Heat is the third side of the fire triangle. When sufficient heat, fuel, and oxygen are available, the triangle is complete and fire can exist. Heat of ignition initiates the chemical reaction that is called combustion. It can come from the flame of a match, sparks caused by ferrous metals striking together, heat generated by friction, lightning, an oxyacetylene torch cutting or welding metal, an electric short circuit, an electric arc between conductors, or the overheating of an electric conductor or motor.

CLASSES OF FIRE

11-21. There are four types or classes of fires (labeled A through D) according to their fuels. However, some fuels are found in combinations, and electrical fires always involve some solid fuel. Therefore, for fire fighting purposes, there are actually six classes:
  • Class A Fires (common flammable solid fuel).
  • Class B Fires (flammable liquid or gaseous fuel).
  • Combined Class A and Class B fires (solid fuel combined with liquid or gaseous fuel).
  • Combined Class A and Class C fires (solid fuel combined with electrical equipment).
  • Combined Class B and Class C fires (liquid or gaseous fuel combined with electrical equipment).
  • Class D fires (combustible-metal fuel).
This list includes every known type of fire. Note that the environment of a fire, that is, where it occurs, does not affect its classification. For example, Class B fires are Class B fires whether they occur in an engine room or on a pier.

11-22. The main purpose of this classification scheme is to help crew members pick the best extinguishing agent. The choice of an extinguishing agent depends on the class of fire, the hazards involved, and the agents available. It is not enough to know that water is best for putting out a class. A fire because it cools, or that a dry chemical works well in knocking down the flames of a burning liquid. The extinguishing agent must be applied properly and sound fire fighting techniques must be used.

EXTINGUISHING AGENTS

11-23. An extinguishing agent is a substance that will put out a fire. Every extinguishing agent operates by attacking one or more sides of the fire triangle.
  • Cooling. Reduces the temperature of the fuel below its ignition temperature. This is a direct attack on the heat side of the fire triangle (see Figure 11-3).
  • Smothering. Separates the fuel from the oxygen. This can be considered as an attack on the edge of the fire triangle where the fuel and oxygen sides meet (see Figure 11-4).
  • Oxygen dilution. Reduces the amount of available oxygen below that needed to sustain combustion. This is an attack on the oxygen side of the triangle (see Figure 11-5).

 


Figure 11-3. Effects of Cooling


Figure 11-4. Effects of Smothering

 


Figure 11-5. Effects of Oxygen Dilution

 

TYPES OF EXTINGUISHING AGENTS

11-24. Eight extinguishing agents are in common use. Each is applied to the fire as a liquid, gas, or solid, depending on its extinguishing action and physical properties. Some may be used on several types of fires, where others are more limited in use (see Table 11-1).

 

Table 11-1. The Eight Common Extinguishing Agents

LIQUIDS

WATER SPRAY
FOAM

GASES

CARBON DIOXIDE (CO2)
HALON 1301

SOLIDS (DRY CHEMICAL)

MONOAMMONIUM PHOSPHATE
BICARBONATE
POTASSIUM BICARBONATE
POTASSIUM CHLORIDE

 

EXTINGUISHING AGENTS FOR THE DIFFERENT CLASSES OF FIRE

11-25. It is necessary to use the most suitable type of extinguishing agent to put out a fire. Select an extinguishing agent that will do the task in the least amount of time, cause the least damage, and result in the least danger to crew members (Figure 11-6).

11-26. Class A fires involve common combustible solids such as wood, paper, cloth, and plastics and are most effectively extinguished by water, a cooling agent. Foam and dry chemical may also be used; they act mainly as smothering agents.

11-27. Class B fires involve oils, greases, gases, and other substances that give off large amounts of flammable vapors. A smothering agent is most effective. Water fog, dry chemical, foam, and carbon dioxide (CO2) may be used. However, if the fire is being supplied with fuel by an open valve or a broken pipe, a valve on the supply side should be shut down. This may extinguish the fire or, at least, make extinguishing less difficult and allow the use of much less extinguishing agent.

 


Figure 11-6. Actions of Extinguishing Agents on the Different Classes of Fire

 

11-28. In a gas fire, it is imperative to shut down the control valve before you extinguish the fire. If the fire were extinguished without shutting down the valve, flammable gas would continue to escape. The potential for an explosion, more dangerous than the fire, would then exist. It might be necessary to extinguish a gas fire before shutting down the fuel supply in order to save a life or to reach the control valve; however, these are the only exceptions.

11-29. Combined Class A and Class B fires involve both solid fuels and flammable liquids or gases. Water spray and foam may be used to smother these fires. These agents also have some cooling effect on the fire. Carbon dioxide has also been used to extinguish such fires in closed spaces.

11-30. Combined Class A and Class C fires involve energized electrical equipment and a non-conducting extinguishing agent must be used. Carbon dioxide, Halon, and dry chemical are the most efficient agents. Carbon dioxide dilutes the oxygen supply, while the others are chain-breaking agents.

11-31. Combined Class B and Class C fires involve flammable liquids or gases and electrical equipment. A nonconducting extinguishing agent is required, such as Halon or dry chemical acting as a chain breaker. They may also, in closed spaces, be extinguished with CO2.

11-32. Class D fires involve combustible metals such as potassium, sodium and their alloys, magnesium, zinc, and powdered aluminum. They burn on the metal surface at a very high temperature and often with a brilliant flame. Water should not be used on Class D fires, as it may add to the intensity or cause the molten metal to splatter. This, in turn, can extend the fire and inflict painful and serious burns on those in the vicinity.

11-33. Fires in combustible metals are generally smothered and controlled with specialized agents known as dry powders. Dry powders are not the same as dry chemicals, although many people use the terms interchangeably. The agents are used on entirely different types of fires: dry powders are used only to extinguish combustible-metal fires. Dry chemicals may be used on other fires, but not on Class D fires.

WATER

11-34. Water is primarily a cooling agent. It absorbs heat and cools burning materials more effectively than any other of the commonly used extinguishing agents. Water has an important secondary effect. When it turns to steam, it converts from the liquid state to the gaseous (vapor) state. Seawater is just as effective in fighting first as fresh water.

Straight Streams

11-35. The straight stream, sometimes called the solid stream, is the oldest and most commonly used form of water for fire fighting.

Efficiency of Straight Streams

11-36. The distance that a straight stream travels before breaking up or dropping is called its reach. Reach is important when it is difficult to approach close to a fire. Actually, despite its name, a straight stream is not really straight. Like any projectile, it has two forces acting upon it. The velocity imparted by the nozzle gives it reach, either horizontally or at an upward angle, depending on how the nozzleman aims the nozzle. The other force, gravity, tends to pull the stream down, so the reach ends where the stream encounters the deck.

11-37. Probably less than 10 percent of the water from a straight stream actually absorbs heat from the fire. This is because only a small portion of the water surface actually comes in contact with the fire, and only water that contacts the fire absorbs heat.

Using Straight Streams

11-38. A straight stream should be directed into the seat of the fire. This is important; for the most cooling, the water must touch the material that is actually burning. A solid stream that is aimed at the flames is ineffective. The main use of solid streams is to break up the burning material and penetrate to the seat of a Class A fire.

Low-Velocity Fog Streams

11-39. Low-velocity fog streams are obtained by using an applicator along with a combination nozzle. Applicators are tubes or pipes that are angled at 60 or 90 at the water outlet end. They are stowed for use with the low-velocity head already in place on the pipe. Some heads are shaped somewhat like a pineapple, with tiny holes angled to cause minute streams to bounce off one another and create a mist. Some heads resemble a cage with a fluted arrow inside. The point of the arrow faces the opening in the applicator tubing. Water strikes the fluted arrow and then bounces in all directions, creating a fine mist.

11-40. For 1 1/2-inch nozzles, 4-foot, 60 angle and 10-foot, 90 angle applicators are approved for shipboard use. For 2 1/2-inch nozzles, 12-foot, 90 angle applicators are approved. Other lengths with different angles are sometimes found. The 4-foot applicator is intended for the 1 1/2-inch combination nozzles fitted in propulsion machinery spaces containing oil-fired boilers, internal combustion machinery, or fuel units.

11-41. Low-velocity fog streams are effective in combating Class B fires in spaces where entry is difficult or impossible. Applicators can be poked into areas that cannot be reached with other types of nozzles (Figure 11-7). They are also used to provide a heat shield for fire fighters advancing with foam or high-velocity fog. Low-velocity fog can be used to extinguish small tank fires, especially where the mist from the applicator can cover the entire surface of the tank. However, other extinguishing agents, such as foam and carbon dioxide, are usually more effective.

 


Figure 11-7. Low-Velocity Fog Applicators

 

Limitations of Fog Streams

11-42. Fog streams do not have the accuracy or reach of straight streams. Improperly used, they can cause injury to personnel, as in a blowback situation. While they can be effectively used on the surface of a deepseated fire, they are not as effective as solid streams in soaking through and reaching the heart of the fire.

11-43. In some instances, there may be an obstruction between the fire and the nozzleman. Then the stream can be bounced off a bulkhead or the overhead to get around the obstacle (Figure 11-8). This method can also be used to break a solid stream into a spray-type stream, which will absorb more heat. It is useful in cooling an extremely hot passageway that is keeping fire fighters from advancing toward the fire. A combination fog-solid nozzle could be opened to the fog position to achieve the same results.

 


Figure 11-8. Bouncing a Straight Stream Off the Overhead

 

Fog Streams

11-44. The fog (or spray) nozzle breaks the water stream into small droplets. These droplets have a much larger total surface area than a solid stream. Therefore, a given volume of water in fog form will absorb much more heat than the same volume of water in a straight stream (Figure 11-9).

11-45. The greater heat absorption of fog streams is important where the use of water is limited. Less water need be applied to remove the same amount of heat from a fire. Also, more of the fog stream turns to steam when it hits the fire.

 


Figure 11-9. Advantages and Disadvantages of Straight and Fog Streams

 

Combination Nozzle Operation

11-46. Depending on the position of its handle, the combination nozzle will produce a straight stream or high-velocity fog stream. Combination nozzles are available for use with 1 1/2- and 2 1/2-inch hoses. Reducers can be used to attach a 1 1/2-inch nozzle to a 2 1/2-inch hose.

11-47. Create a straight stream by pulling the nozzle handle all the way back toward the operator (Figure 11-10). Create a fog stream by pulling the handle back halfway. In other words, the handle is perpendicular to the plane of the nozzle (Figure 11-11). Shut down the nozzle, from any opened position, by pushing the handle forward as far as it will go (Figure 11-12).

 


Figure 11-10. Creating a Straight Stream


Figure 11-11. Creating a Fog Stream

 


Figure 11-12. Shutting Down the Nozzle

 

11-48. The low-velocity fog applicator must be attached with the nozzle shut down. First, the high-velocity tip is removed. Then the straight end of the applicator is snapped into the fog outlet and locked with a quarter-turn. A low-velocity fog stream is obtained with the nozzle handle in the fog position (halfway back).

11-49. When any nozzle is to be used, the handle should be in the closed position until the water reaches the nozzle. The hose will bulge out, and the nozzleman will feel the weight of the water. Before pushing the handle to an open position, he should let the entrained air out of the nozzle. To do this, turn a bit sideways with the nozzle and slowly open it until a spatter of water comes out. Now the nozzle is directed at the target. The backup man closes up to the nozzleman and takes some of the weight of the hose and the back pressure from the nozzle. The nozzle is opened to the desired position, and the fire is attacked.

11-50. Straight and fog streams can be very effective against Class A fires in the hands of skilled operators. Fog streams can also be used effectively against Class B fires. However, it is important that crewmen have actual experience in directing these streams during drills. Applicators should also be broken out at drills so crewmen can get the feel of these devices.

FOAM

11-51. Foam is a blanket of bubbles that extinguishes fire, mainly by smothering. Mixing water and a foam-making agent (foam concentrate) produces bubbles. The result is called a foam solution. The various foam solutions are lighter than the lightest of flammable oils. Consequently, when applied to burning oils, they float on the surface of the oil (Figure 11-13).

 

Figure 11-13. Foam

Extinguishing Effects of Foam

11-52. Fire-fighting foam is used to form a blanket on the surface of flaming liquids, including oils. The blanket of foam keeps flammable vapors from leaving the surface and keeps oxygen from reaching the fuel. Fire cannot exist when the fuel and oxygen are separated. The water in the foam also has a cooling effect, which gives foam its Class A extinguishing capability. 11-53. The ideal foam solution should flow freely enough to cover a surface rapidly, yet stick together enough to provide and maintain a vapor-tight blanket. The solution must retain enough water to provide a long-lasting seal. Rapid loss of water would cause the foam to dry out and break down (wither) from the high temperatures associated with fire. The foam should be light enough to float on flammable liquids, yet heavy enough to resist winds. 11-54. The quality of foam is generally defined in terms of its 25 percent drainage time, its expansion ratio, and its ability to withstand heat (burnback resistance). These qualities are influenced by:
  • The chemical nature of the foam concentrates.
  • The temperature and pressure of the water.
  • The efficiency of the foam-making device.
11-55. Foams that lose their water rapidly are the most fluid. They flow around obstructions freely and spread quickly. Such foams would be useful in engine room or machinery space fires. They would be able to flow under and around machinery, floor plates, and other obstructions. The two basic types of foam are chemical and mechanical.
  • Chemical foam. You can form chemical foam by mixing an alkali (usually sodium bicarbonate) with an acid (usually aluminum sulfate) in water (Figure 11-14). When chemical foam was first introduced, these substances were stored in separate containers. They are now combined in a sealed, airtight container. A stabilizer is added to make the foam tenacious and long-lived. When these chemicals react, they form a foam or froth of bubbles filled with carbon dioxide gas. The carbon dioxide in the bubbles has little or no extinguishing value. Its only purpose is to inflate the bubbles. From 7 to 16 volumes of foam are produced for each volume of water.

 


Figure 11-14. Production of Chemical Foam

 

  • Aqueous film-forming foam. This foam was developed by the US Naval Research Laboratory to be used in a twinned system: a flammable liquid fire would be quickly knocked down with a dry chemical; then AFFF would be applied to prevent reignition. However, the AFFF proved more effective than expected, and it is now used without the dry chemical. AFFF controls the vaporization of flammable liquids by means of a water film that forms as the foam is applied. Like other foams, it cools and blankets. This double action gives a highly efficient, quick-acting foam cover for combustible-liquid spills. It has a low viscosity and spreads quickly over the burning material. Water draining from this type of foam has a low surface tension, so AFFF can be used on mixed Class A and Class B fires. The draining water penetrates and cools the Class A material, while the film blankets the Class B material. AFFF can be produced from freshwater or seawater. AFFF can be used with, before, or after dry chemicals. AFFF concentrates should not be mixed with the concentrates of other foams, although in foam form they may be applied to the same fire successfully.

Advantages of Foam

11-56. In spite of its limitations, foam is quite effective in combating Class A and Class B fires. Many advantages of foam include the following:
  • Very effective smothering agent. Also provides cooling as a secondary effect.
  • Sets up a vapor barrier that prevents flammable vapors from rising. The surface of an exposed tank can be covered with foam to protect it from a fire in a neighboring tank.
  • Some use on Class A fires because of its water content. AFFF is especially effective, as are certain types of wet-water foam. Wet-water foam is made from detergents; its water content quickly runs out and seeps into the burning material.
  • Effective in blanketing oil spills. However, if the oil is running, an attempt should be made to shut down a valve if such action would stop the flow. If that is impossible, the flow should be dammed. Foam should be applied on the upstream side of the dam (to extinguish the fire) and on the downstream side (to place a protective cover over any oil that has seeped through).
  • Most effective extinguishing agent for fires involving large tanks of flammable liquids.
  • Made with freshwater or seawater and hard or soft water.
  • Does not break down readily; it extinguishes fire progressively when applied at an adequate rate.
  • Stays in place, covers, and absorbs heat from materials that could cause reignition.
  • Uses water economically. Does not tax the ship's fire pumps.
  • Concentrates are not heavy, and foam systems do not take up much space.

Limitations on the Use of Foam

11-57. Foams are effective extinguishing agents when used properly. However, some limitations on foam include the following:
  • Because they are aqueous (water) solutions, they are electrically conductive and should not be used on live electrical equipment.
  • Like water, foams should not be used on combustible-metal fires.
  • Many must not be used with dry chemical extinguishing agents. AFFF is an exception to this rule and may be used in a joint attack with dry chemical.
  • Sufficient foam must be on hand to make sure that the entire surface of the burning material can be covered. In addition, there must be enough foam to replace foam that is burned off and to seal breaks in the foam surface.
11-58. The premixed foam powder may be stored in cans and introduced into the water during firefighting operations. For this, a device called a foam hopper is used. The two chemicals may be premixed with water to form an aluminum sulfate solution and a sodium bicarbonate solution. The solutions are then stored in separate tanks until the foam is needed. At that time, the solutions are mixed to form the foam.

11-59. Many chemical foam systems, both aboard ship and in shore installations, are still in use. However, these systems are being phased out in favor of the newer mechanical foam or, as it is sometimes called, air foam.

Mechanical (Air) Foam

11-60. Mechanical foam is produced by mixing a foam concentrate with water to produce a foam solution (Figure 11-15). The turbulent mixing of air and the foam solution produces bubbles. As the name air foam implies, the bubbles are filled with air. Aside from the workmanship and efficiency of the equipment, the degree of mixing determines the quality of the foam. The design of the equipment determines the quantity of foam produced.

11-61. There are several types of mechanical foams. They are similar in nature, but each has its own special fire-fighting capabilities. Mechanical foams are produced from proteins, detergents (which are synthetics), and surfactants. The surfactants are a large group of compounds that include detergents, wetting agents, and liquid soaps. Surfactants are used to produce aqueous film-forming foam, commonly referred to as AFFF.

 


Figure 11-15. Production of Mechanical (Air) Foam

 

CARBON DIOXIDE

11-62. CO2 extinguishing systems have, for a long time, been approved for ship installation as well as for industrial occupancies ashore. Aboard ship, carbon dioxide has been approved for cargo and tank compartments, spaces containing internal combustion or gas-turbine main propulsion machinery, and other spaces.

Extinguishing Properties of Carbon Dioxide

11-63. Carbon dioxide extinguishes fire mainly by smothering. It dilutes the air surrounding the fire until the oxygen content is too low to support combustion. For this reason, it is effective on Class B fires, where the main consideration is to keep the flammable vapors separated from oxygen in the air. CO2 has a very limited cooling effect. It can be used on Class A fires in confined spaces, where the atmosphere may be diluted sufficiently to stop combustion. However, CO2 extinguishing takes time. The concentration of carbon dioxide must be maintained until all the fire is out. Constraint and patience are needed.

11-64. Carbon dioxide is sometimes used to protect areas containing valuable articles. Unlike water and some other agents, carbon dioxide dissipates without leaving a residue. Since it does not conduct electricity, it can be used on live electrical equipment. However, fire fighters must maintain a reasonable distance when using a portable CO2 extinguisher or a hose line from a semiportable system on high voltage gear.

Uses of Carbon Dioxide

11-65. Carbon dioxide is used primarily for Class B and Class C fires. It may also be used to knock down a Class A fire. It is particularly effective on fires involving:
  • Flammable oils and greases.
  • Electrical and electronic equipment, such as motors, generators, and navigational devices.
  • Hazardous and semihazardous solid materials (such as some plastics, except those that contain their own oxygen [like nitrocellulose)].
  • Machinery spaces, engine rooms, paint, and tool lockers.
  • Cargo spaces which can be flooded with carbon dioxide.
  • Galleys and other cooking areas, such as diet kitchens.
  • Compartments containing high value cargo, delicate machinery, and other material that would be ruined or damaged by water or water-based extinguishing agents.
  • Spaces where after-fire cleanup would be a problem.

Limitations on the Use of Carbon Dioxide

11-66. CO2 portable extinguishers are used primarily for small electrical fires (Class C) and have limited effectiveness on Class B fires. Their use will be confined to Class B pool fires no greater than four square feet. Successful operation requires close approach due to the extinguisher's characteristics short range (4 to 6 feet).
  • Effectiveness. CO2 is not effective on substances that contain their own oxygen (oxidizing agents).
  • Outside use. To be fully effective, the gas must be confined. For this reason, CO2 is not as effective outside as it is in a confined space. This does not mean that it cannot be used outside.
  • Possibility of reignition. Compared with water, carbon dioxide has a very limited cooling capacity. It may not cool the fuel below its ignition temperature and it is more likely than other extinguishing agents to allow reflash.
  • Hazards. Although carbon dioxide is not poisonous to the human system, it is suffocating in the concentration necessary for extinguishment. A person exposed to this concentration would suffer dizziness and unconsciousness. Unless removed quickly to fresh air, the victim could die.

DRY CHEMICALS

11-67. Dry chemical extinguishing agents are chemicals in powder form. They should not be confused with dry powders, which are intended only for combustible metal fires.

Types of Chemical Extinguishing Agents

11-68. Five different types of dry chemical extinguishing agents are in use. Like other extinguishing agents, dry chemicals may be installed in a fixed system or in portable and semiportable extinguishers.
  • Sodium bicarbonate. This is the original dry chemical extinguishing agent. It is generally referred to as regular dry chemical and is widely used because it is the most economical dry chemical agent. It is particularly effective on animal fats and vegetable oils because it chemically changes these substances into nonflammable soaps. Therefore, sodium bicarbonate is used extensively for galley range, hood, and duct fires. There is one possible problem with sodium bicarbonate: fire has been known to flash back over the surface of an oil fire when this agent is used.
  • Potassium bicarbonate (Purple-K). Although usually used alone, this dry chemical was originally developed to be used with AFFF in a twinned system. It is most effective on liquid fuel fires in driving flames back and has a good reputation for eliminating flashback. It is more expensive than sodium bicarbonate.
  • Potassium chloride. Potassium chloride was developed as a dry chemical that would be compatible with protein-type foams. Its extinguishing properties are about equal to those of potassium bicarbonate. One drawback is its tendency to cause corrosion after it has extinguished a fire.
  • Urea potassium bicarbonate. This is a British development. It is not widely used because it is expensive.
  • Monoammonium phosphate (ABC, multipurpose). Monoammonium phosphate is called a multipurpose dry chemical because it can be effective on Class A, Class B, and Class C fires. Ammonium salts interrupt the chain reaction of flaming combustion. The phosphate changes into metaphosphoric acid, a glassy fusible material, at fire temperatures. The acid covers solid surfaces with a fire retardant coating. Therefore, this agent can be used on fires involving ordinary combustible materials such as wood and paper, as well as on fires involving flammable oils, gases, and electrical equipment. However, it may only control, but not fully extinguish, a deep-seated fire.

Extinguishing Effects of Dry Chemicals

11-69. Dry chemical agents extinguish fire by cooling, smothering, shielding of radiant heat, and by breaking the combustion chain.
  • Cooling. No dry chemical exhibits any great capacity for cooling. However, a small amount of cooling takes place simply because the dry chemical is at a lower temperature than the burning material.
  • Smothering. When dry chemicals react with the heat and burning material, some carbon dioxide and water vapor are produced. These dilute the fuel vapors and the air surrounding the fire. The result is a limited smothering effect.
  • Shielding of radiant heat. Dry chemicals produce an opaque cloud in the combustion area. This cloud reduces the amount of heat that is radiated back to the heart of the fire, that is, the opaque cloud absorbs some of the radiation feedback that is needed to sustain the fire.

Uses of Dry Chemicals

11-70. Monoammonium phosphate (ABC, multipurpose) dry chemical may, as its name implies, is used on Class A, Class B, and Class C fires and combinations of these. However, as noted above, ABC dry chemical may only control, but not extinguish, some deep-seated Class A fires and an auxiliary extinguishment method, such as a water hose line, is required. All dry chemical agents may be used to extinguish fires involving the following:
  • Flammable oils and greases.
  • Electrical equipment.
  • Hoods, ducts, and cooking ranges in galleys and diet kitchens.
  • The surfaces of baled textiles.
  • Certain combustible solids such as pitch, naphthalene, and plastics (except those that contain their own oxygen).
  • Machinery spaces, engine rooms, paint lockers, and tool lockers.
Dry chemical extinguishing agents are very effective on gas fires. However, gas flames should not be extinguished until the supply of fuel has been shut down upstream of the fire.

Limitations on the Use of Dry Chemicals

11-71. The limitations on the use of dry chemicals are as follows:
  • The discharge of large amounts of dry chemicals could affect people in the vicinity.
  • Like other extinguishing agents that contain no water, dry chemicals are not effective on materials that contain their own oxygen.
  • Dry chemicals may deposit an insulating coating on electronic or telephonic equipment, affecting the operation of the equipment.
  • Dry chemicals are not effective on combustible metals such as magnesium, potassium, sodium, and their alloys, and in some cases may cause a violent reaction.
  • Where moisture is present, a dry chemical agent may corrode or stain surfaces on which it settles.

 

WARNING
DRY CHEMICAL EXTINGUISHING AGENTS ARE CONSIDERED NONTOXIC, BUT THEY MAY HAVE IRRITATING EFFECTS WHEN BREATHED. FOR THIS REASON, A WARNING SIGNAL, SIMILAR TO THE ONE USED IN CARBON DIOXIDE SYSTEMS, SHOULD BE INSTALLED IN ANY SPACE THAT MIGHT BE TOTALLY FLOODED WITH DRY CHEMICALS. BREATHING APPARATUSES AND LIFELINES MUST ALSO BE AVAILABLE IN CASE CREWMEN MUST ENTER THE SPACE BEFORE IT IS ENTIRELY VENTILATED. TABLE 11-2 DESCRIBES THE SIGNALS THAT ARE USED BETWEEN THE OBA WEARER AND TENDER.

 

Table 11-2. Lifeline Signals Between OBA Wearer and Tender

 

MEANING

 
PULLS ON
LINE

TENDER TO WEARER

 

WEARER TO TENDER

1

Are you all right?

 

I am all right.

2

Advance.

 

I am going ahead.

3

Back out.

 

Take up my slack.

4

Come out immediately.

 

Send help.

DRY POWDERS

11-72. Dry powders were developed to control and extinguish fires in combustible metals. These are Class D fires which involve the following metals:
  • Magnesium.
  • Potassium.
  • Sodium and their alloys.
  • Titanium.
  • Zirconium.
  • Powdered or fine aluminum.
  • Some lesser known metals.
As mentioned earlier, dry chemicals and dry powders are not the same. Dry powders are the only extinguishing agents that can control and extinguish metal fires without causing violent reactions. Other extinguishing agents may accelerate or spread the fire, injure personnel, cause explosions, or create conditions more hazardous than the original fire. Dry powders act mainly by smothering, although some agents also provide cooling.

11-73. Two commercially available dry powders are composed mostly of graphite. The graphite cools the fire and creates a very heavy smoke that helps smother the fire. These agents are also effective on all the metals listed above. They are applied with a scoop or shovel.

11-74. Dry powder with a sodium chloride (salt) base is propelled from portable extinguishers by carbon dioxide and from large containers or fixed systems by nitrogen. The powder is directed over the burning metal. When it drops, it forms a crust on the metal and smothers the fire. Like the graphite types, it is effective on the combustible metals mentioned above.

HALOGENATED EXTINGUISHING AGENTS (HALON)

11-75. Halogenated extinguishing agents are made up of carbon and one or more of the halogen elements: fluorine, chlorine, bromine, and iodine. Halon 1301 enters the fire area as a gas. Most authorities agree that the Halon acts as a chain breaker. However, it is not known whether it will slow the chain reaction, break it up, or cause some other reaction. Halon 1301 is stored and shipped as a liquid under pressure. When released in the protected area, it vaporizes to an odorless, colorless gas and is propelled to the fire by its storage pressure. Halon 1301 does not conduct electricity. The extinguishing properties of Halon 1301 allow its use on a number of different types of fire. These include:
  • Fires in electrical equipment.
  • Fires in engine rooms, machinery spaces, and other spaces involving flammable oils and greases.
  • Class A fires in ordinary combustibles. However, if the fire is deep-seated, a longer soaking time may be needed or a standby hose line may be used to complete the extinguishment.
  • Fires in areas where articles of high value may be stored and are damaged by the residue of other agents.
  • Fires involving electronic computers and control rooms.
There are few limitations on the use of Halon agents. However, they are not suited for fighting fires in materials containing their own oxygen or combustible metals and hydrides.

 

WARNING


HALON 1301 MAY CAUSE DIZZINESS AND IMPAIRED COORDINATION IF INHALED. IF HALON 1301 IS TO BE USED FOR THE TOTAL FLOODING OF NORMALLY OCCUPIED SPACES, AN EVACUATION ALARM MUST BE PROVIDED. PERSONNEL SHOULD LEAVE THE AREA PROMPTLY ON HEARING THE ALARM. WHEN A HALON 1301 EXTINGUISHER IS USED, THOSE NOT DIRECTLY INVOLVED IN THE OPERATION SHOULD LEAVE THE AREA IMMEDIATELY. THE EXTINGUISHER OPERATOR SHOULD STEP AWAY AS SOON AS THE APPLIANCE IS DISCHARGED. THE AREA SHOULD BE VENTED WITH FRESH AIR BEFORE IT IS REENTERED. IF IT IS NECESSARY TO REMAIN IN OR ENTER AN AREA WHERE HALON 1301 HAS BEEN DISCHARGED, A BREATHING APPARATUS AND LIFELINES SHOULD BE USED. THE ONLY VALID REASON FOR SUCH ENTRY WOULD BE TO SAVE A LIFE OR TO MAINTAIN CONTROL OF THE SHIP.

 

HEPTAFLUOROPROPANE (HFC227EA) OR FM-200

11-76. HFC227ea or FM-200 is a clear, odorless gas. It has been developed as a total compartment flooding system to replace Halon 1301. As good environmental stewards, the Army has decided on a program of removal of all Halon 1301 fixed firefighting systems aboard vessels. FM-200 will provide the same firefighting capabilities as Halon with a much less harmful effect on the environment. FM-200 is not an ozone-depleting chemical. It works in much the same manner as Halon. The same precautions for the use of Halon should be adhered to when using FM-200. FM-200 can potentiate the effects of adrenalin at concentrations greater than 9 percent. This chemical also produces hydrogen fluoride, a corrosive, when super heated.

PORTABLE FIRE EXTINGUISHERS

11-77. Portable extinguishers can be carried to the fire area for a fast attack. However, they contain a limited supply of extinguishing agent. The agent is quickly expelled from the extinguisher; in most cases, continuous application can be sustained for only a minute or less. For this reason, it is extremely important to back up the extinguisher with a hose line. If the extinguisher does not have the capacity to put the fire out completely, the hose line can be used to finish the job. A crewman who is using an extinguisher cannot advance a hose line at the same time, so the alarm must be sounded as soon as a fire is discovered to alert the ship's personnel to the situation.

11-78. There is a right way and many wrong ways to use a portable fire extinguisher. Crew members who have had little training with these appliances waste extinguishing agent through improper application. At the same time, untrained personnel tend to overestimate their extinguishing ability. Periodic training sessions, including practice with the types of extinguishers carried onboard, are the best insurance against inefficient use of this equipment. Extinguishers that are due to be discharged and inspected may be used in these training sessions.

CLASSES OF FIRE EXTINGUISHERS

11-79. Every portable extinguisher is classified in two ways, with one or more letters and with a numeral. The letter or letters indicate the classes of fires on which the extinguisher may be used. These letters correspond exactly to the four classes of fires. For example, Class A extinguishers may be used only on Class A fires--those involving common combustible materials. Class AB extinguishers may be used on fires involving wood or diesel oil or both.

11-80. The numeral indicates either the relative efficiency of the extinguisher or its size. This does not mean the size of fire on which to use the extinguisher; rather, the numeral indicates how well the extinguisher will fight a fire of its class.

11-81. The NFPA rates extinguisher efficiency with Arabic numerals. The UL tests extinguishers on controlled fires to determine their NFPA ratings. A rating such as 2A or 4A on an extinguisher would be an NFPA rating. (A 4A rating will extinguish twice as much Class A fire as a 2A rating; a 20B rating will extinguish four times as much Class B fire as a 5B rating.)

11-82. The Coast Guard uses Roman numerals to indicate the sizes of portable extinguishers. The numeral I indicates the smallest size and V the largest. A BIII Coast Guard rating indicates a medium-sized extinguisher suitable for fires involving flammable liquids and gases. The Coast Guard ratings of the different types of extinguishers are shown in Table 11-3.

Table 11-3. United States Coast Guard Extinguisher Classification Table

TYPE

SIZE

WATER

(GALLONS)

FOAM

(GALLONS)

DIOXIDE

(POUNDS)

CHEMICAL

(POUNDS)

A

B

B

B

B

B

C

C

II

I

II

III

IV

V

I

II

2 1/2

2 1/2

1 1/4

2 1/2

12

20

40

 

4

15

35

50

100

4

15

 

2

10

20

30

50

2

10

TEST AND INSPECTION

11-83. Army fire regulations require masters or persons in charge to have portable and semiportable fire extinguishers and fixed fire-extinguishing systems tested and inspected "at least once in every 12 months." When tests are completed, a tag will be placed on each extinguisher, showing the date and the person who completed the tests.

GENERAL SAFETY RULES FOR PORTABLE EXTINGUISHERS

11-84. There are some general safety rules you should follow when using portable extinguishers. These are as follows:
  • When you discover a fire, call out your discovery, sound the fire alarm, and summon help.
  • Never pass the fire to get to an extinguisher. You can get trapped in a dead-end passageway.
  • If you must enter a room or compartment to combat the fire, keep an escape path open. Never let the fire get between you and the door.
  • If you enter a room or compartment and your attack with a portable extinguisher fails, get out immediately. Close the door to confine the fire and prepare to fight the fire while waiting for previously summoned help. Your knowledge of the situation will aid those responding.

WATER EXTINGUISHERS

11-85. Extinguishers that use water or a water solution, as the extinguishing agents, are suitable only for Class A fires. There are five types of water extinguishers, but only two are currently produced. In 1969, the manufacture of the inverting types of extinguishers (the soda-acid, foam, and cartridge-operated) was discontinued. However, since a large number of inverting extinguishers are still in use, they will be discussed along with the stored-pressure water extinguisher.

Soda-Acid Extinguisher

11-86. The soda-acid extinguisher (Figure 11-16) comes only in a 2 1/2-gallon size that carries an NFPA rating of 2A. It weighs about 30 pounds when charged, has a reach of 30 to 40 feet, and expends itself in about 55 seconds. The shell of the extinguisher is filled with a solution of 1 1/2 pounds of sodium bicarbonate in 2 1/2 gallons of water. The screw-on cap contains a cage that holds an 8-ounce bottle, half filled with sulphuric acid, in an upright position. A loose stopper in the top of the acid bottle prevents acid from splashing out before the extinguisher is to be used.

11-87. The extinguisher is carried to the fire by means of the top handle. At the fire, the extinguisher is inverted, the acid mixes with the sodium bicarbonate solution forming carbon dioxide gas, and the pressure of the CO2 propels the water out through the nozzle. The stream must be directed at the seat of the fire and moved back and forth to hit as much of the fire as possible. The nozzle should be aimed at the fire until the entire content of the extinguisher is discharged. Remember that water is available for less than a minute!

 


Figure 11-16. Water (Soda-Acid) Extinguisher

 

11-88. The extinguishing agent, sodium bicarbonate solution mixed with acid, is more corrosive than plain water. The operator should avoid getting the agent on his skin or in his eyes, as the acid could cause burning. Soda-acid extinguishers must also be carefully maintained. When the extinguisher is inverted, a pressure of 130 psi or more is generated. If the container is corroded or otherwise damaged, this pressure could be sufficient to burst the container.

Cartridge-Operated Water Extinguisher

11-89. The cartridge-operated water extinguisher (Figure 11-17) is similar in size and operation to the soda-acid extinguisher. The most common size is 2 1/2 gallons, with an NFPA rating of 2A. It has a range of 30 to 40 feet. The container is filled with water or an antifreeze solution. The screw-on cap contains a small cylinder of CO2; when the cylinder is punctured, the gas provides the pressure to propel the extinguishing agent.

 


Figure 11-17. Cartridge-Operated Water Extinguisher

 

11-90. When using the extinguisher, it is first carried to the fire, then inverted and bumped against the deck (Figure 11-18, step 1). This ruptures the CO2 cylinder and expels the water. The stream should be directed at the seat of the fire (Figure 11-18, step 2). The nozzle should be moved back and forth to quench as much of the burning material as possible in the short time available (Figure 11-18, step 3). The discharge time is less than 1 minute. The entire contents of the extinguisher must be discharged, since the flow cannot be shut off.

 


Figure 11-18. Using the Cartridge-Operated Extinguisher

11-91. As with the soda-acid extinguisher, the container is not subject to pressure until it is put to use. Any weakness in the container may not become apparent until the container fails.

Pin-Type Cartridge-Operated Extinguisher

11-92. A newer version of the cartridge-operated water extinguisher need not be inverted for use. Instead, you can pull the pin out of the cartridge with the extinguisher in an upright position. A lever is squeezed to discharge the extinguishing agent (water or antifreeze solution).

11-93. The cartridge is fitted with a pressure gauge. The gauge should be checked periodically to ensure that the cartridge pressure is within its operating range. Otherwise, maintenance is similar to that for the inverting-type cartridge extinguisher.

Stored-Pressure Water Extinguisher

11-94. The stored-pressure water extinguisher (Figure 11-19) is the most commonly used portable fire-fighting appliance. The 2 1/2-gallon size has an NFPA rating of 2A. It weighs about 30 pounds and has a horizontal range of 35 to 40 feet. In continuous operation, it will expend its water in about 55 seconds. However, it may be used intermittently to extend its operational time.

 


Figure 11-19. Stored-Pressure Water Extinguisher

11-95. The container is filled with water, or an antifreeze solution, to within about 6 inches of the top (most extinguishers have a fill mark stamped on the container). The screw-on cap holds a lever-operated discharge valve, a pressure gauge, and an automobile tire-type valve. The extinguisher is pressurized through the air valve, with either air or an inert gas, such as nitrogen. The normal charging pressure is about 100 psi. The gauge allows the pressure within the extinguisher to be checked at any time. Most gauges are color-coded to indicate normal and abnormal pressures.

11-96. The extinguisher is carried to the fire, and the ring pin or other safety device is removed. The operator aims the nozzle with one hand and squeezes the discharge lever with the other hand. The stream should be directed at the seat of the fire. It should be moved back and forth to make sure the burning material is completely covered. Short bursts can be used to conserve the limited supply of water.

11-97. As the flames are knocked down, the operator may move closer to the fire. By placing the tip of one finger over the nozzle, the operator can get a spray pattern that will cover a wider area.

FOAM EXTINGUISHERS

11-98. Foam extinguishers are similar in appearance to those discussed previously, but have a greater extinguishing capability. The most common size is 2 1/2 gallons, with an NFPA rating of 2A:4B. This indicates that the extinguisher may be used on both Class A and Class B fires. It has a range of about 30 to 40 feet and a discharge duration of slightly less than a minute.

11-99. The extinguisher is charged by filling it with two solutions that are kept separated (in the extinguisher) until ready to use. These solutions are commonly called the A and B solutions. Their designations have nothing to do with fire classifications.

11-100. The foam extinguisher is carried to the fire right side up and then inverted. This mixes the two solutions, producing a liquid foam and CO2 gas. The CO2 acts as the propellant and fills the foam bubbles. The liquid foam expands to about eight times its original volume. This means the 2 1/2-gallon extinguisher will produce 18 to 20 gallons of foam.

11-101. The foam should be applied gently on burning liquids. Do this by directing the stream in front of the fire and causing the foam to bounce back onto the fire. The stream may also be directed against the back wall of a tank or a structural member to allow the foam to run down and flow over the fire. Chemical foam is stiff and flows slowly. For this reason, the stream must be directed to the fire from several angles for complete coverage of the burning materials (see also Figure 11-20). For fires involving ordinary combustible materials, the foam may be applied in the same way, as a blanket, or the force of the stream may be used to get the foam into the seat of the fire.

11-102. Foam extinguishers are subject to freezing and cannot be stored in temperatures below 4.4 C (40 F). Once activated, these extinguishers will expel their entire foam content; it should all be directed onto the fire. As with other pressurized extinguishers, the containers are subject to rupture when their contents are mixed. Maintenance consists mainly of annual discharging, inspection, cleaning, and recharging.

 


Figure 11-20. Operating a Foam Extinguisher on a Flammable Liquid Fire

 

CARBON DIOXIDE (CO2) EXTINGUISHER

11-103. These are used primarily on Class B and Class C fires. The most common sizes of portable extinguishers contain from 5 to 20 pounds of CO2, not including the weight of the relatively heavy shell. The CO2 is mostly in the liquid state, at a pressure of 850 psi at 21 C (70 F). The 5-pound size is rated 5B:C and the 15-pound size has a rating of 10B:C. Depending on the size of the extinguisher, the range varies between 3 to 8 feet and the duration between 8 to 30 seconds.

11-104. Carry the extinguisher to the fire in an upright position. The short range of the CO2 extinguisher means the operator must get fairly close to the fire. Place the extinguisher on the deck and remove the locking pin. The discharge is controlled either by opening a valve or by squeezing two handles together. The operator must grasp the hose handle and not the discharge horn (see Figure 11-21). The CO2 expands and cools very quickly as it leaves the extinguisher. The horn gets cold enough to frost over and cause severe frostbite. When a CO2 extinguisher is used in a confined space, the operator should guard against suffocation by wearing a breathing apparatus.


Figure 11-21. Procedure for Using the CO2 Extinguisher

 

Class B Fires

11-105. The horn should be aimed first at the base of the fire nearest the operator. The discharge should be moved slowly back and forth across the fire. At the same time, the operator should move forward slowly. The result should be a "sweeping" of the flames off the burning surface, with some carbon dioxide "snow" left on the surface.

11-106. Whenever possible, a fire on a weather deck should be attacked from the windward side. This will allow the wind to blow the heat away from the operator and to carry the CO2 to the fire. CO2 extinguishers generally do not perform well in windy conditions. The blanket of CO2 gas does not remain on the fire long enough to permit the fuel to cool down.

Class C Fires

11-107. The discharge should be aimed at the source of a fire that involves electrical equipment. The equipment should be de-energized as soon as possible to eliminate the chance of shock and the source of ignition.

Maintenance of CO2 Extinguishers

11-108. Several times each year, CO2 extinguishers should be examined for damage and to make sure that they are not empty. At annual inspection, these extinguishers should be weighed. The manufacturer should recharge any extinguisher that has lost more than 10 percent of its CO2 weight. Recharge a CO2 extinguisher after each use, even if it was only partly discharged.

DRY POWDER EXTINGUISHER

11-109. Dry powder (not dry chemical) is the only extinguishing agent that may be used on combustible metal (Class D) fires. The only dry power extinguisher (Figure 11-22) for Class D fires is a 30-pound cartridge-operated model that looks much like the cartridge-operated dry chemical extinguisher. One difference is that the Class D extinguisher has a range of only 6 to 8 feet. The extinguishing agent is sodium chloride, which forms a crust on the burning metal.

11-110. To operate, remove the nozzle from its retainer and press the puncture lever. This allows the propellant gas (CO2 or nitrogen) to activate the extinguisher. The operator then aims the nozzle and squeezes the grips to apply the powder to the surface of the burning metal.

 


Figure 11-22. Dry Power Extinguisher

11-111. The operator should begin the application of dry powder about 6 to 8 feet from the fire. The squeeze grips may be adjusted for the desired rate of flow to build a thick layer of powder over the entire involved area. The operator must be careful not to break the crust that forms when the powder hits the fire (see also Figure 11-23).

 


Figure 11-23. Procedure for Operating the Dry Powder Extinguisher

11-112. A large amount of dry powder is sometimes needed to extinguish a very small amount of burning metal. A brown discoloration indicates a hot spot, where the layer of dry powder is too thin. An additional agent should be applied to the discolored areas. When the fire involves small metal chips, the agent should be applied as gently as possible so the force of the discharge does not scatter burning chips.

11-113. Class D dry powder also comes in a container, for application with a scoop or shovel. This agent should also be applied very gently. A thick layer of powder should be built up, and the operator should be careful not to break the crust that forms.

HALON EXTINGUISHERS

11-114. Halon 1301 (with an NFPA rating of 5 B:C) is available only in a 2 1/2-pound portable extinguisher. Its horizontal range is from 4 to 6 feet and its discharge time is 8 to 10 seconds. The extinguishing agent is pressurized in a lightweight steel or aluminum alloy shell. The cap contains the discharge control valve and discharge nozzle.

11-115. Carry the extinguisher to the fire and then remove the locking pin. Control the discharge by squeezing the control valve-carrying handle. Direct the Halon at the seat of a Class B fire and apply with a slow, side-to-side sweeping motion. It should be directed at the source of an electrical fire (see Figure 11-24).

 


Figure 11-24. Operation of Halon Extinguishers

PURPLE-K EXTINGUISHER

11-116. PKP extinguishers are dry chemical extinguishers, provided primarily for use on Class B fires. PKP is nontoxic and is four times as effective as CO2 for extinguishing fuel fires. PKP is effective on Class C fires, but do not use if CO2 is available. Also, do not use on internal fires in gas turbines or jet engines because it leaves a residue that cannot be completely removed without disassembly of the engine.

11-117. The PKP extinguisher weighs about 18 pounds and uses CO2 as the expellant gas. The extinguisher shell is not pressurized until it is to be used. Maximum range of the extinguisher is 20 feet from the nozzle and expellant will last for 18 to 20 seconds. Operating procedures (see also Figure 11-25) are as follows:
  • Pull the locking pin from the seal cutter assembly.
  • Sharply strike the puncture lever to cut the gas cartridge seal. The extinguisher is now charged and ready for use.