FIRE-FIGHTING AGENTS. —Many materialsmay be used as fire-fighting agents. The followingare the fire-fighting agents used most often aboardnaval ships:• Water. Water is a cooling agent, andaboard ship the sea provides an inexhaustiblesupply. If the surface temperature of a fire canbe lowered below the fuels’ ignition temperature,the fire will be extinguished. Water is mostefficient when it absorbs enough heat to raise itstemperature to 212°F (l00°C). At thistemperature, the water will absorb still more heatuntil it changes to steam. The steam carries awaythe heat, which cools the surface temperature.A secondary method of water extinguishmentis caused by steam smothering. When waterchanges into steam by absorbing heat, it expandsabout 1,700 times in volume. The large quantityof steam displaces the air from the fuel, whichsmothers the fire. Steam-smothering systems areinstalled in boiler casings and catapult troughs.• Aqueous Film-Forming Foam. Aqueousfilm-forming foam (AFFF) is composed ofsynthetically produced materials similar to liquiddetergents. These film-forming agents are capableof forming water solution films on the surface offlammable liquids. The Navy mixes AFFF byvolume in the following proportion: 6 parts ofAFFF concentrate to 94 parts water.AFFF concentrate is a clear to slightly amber-colored liquid concentrate. The AFFF solution ofwater and concentrate possesses a low viscosityand spreads quickly over a surface. AFFFconcentrate is nontoxic and biodegradable indiluted form. AFFF concentrate may be storedfor long periods without losing its effectiveness.The concentrate will freeze when exposed totemperatures below 32°F (0°C) but can bereused when thawed.AFFF, when mixed with water, provides threefire-extinguishing advantages. First, it forms anaqueous film on the surface of the fuel, whichprevents the escape of the hydrocarbon fuelvapors. Second, the layer of foam effectivelyexcludes oxygen from the fuel surface. Third, thewater content of the foam provides a coolingeffect.Foam is used mainly to extinguish burningflammable or combustible liquid spill fires(class B). AFFF has excellent penetratingcharacteristics and is superior to water inextinguishing class A fires.• Carbon Dioxide (CO2). CO2 extinguishesfires by smothering. Co2 is about 1.5 timesheavier than air. That makes CO2 a suitableextinguishing agent because it tends to settle andblanket the fire.CO2 is a dry, noncorrosive gas that is inertwhen in contact with most substances and willnot leave a residue that damages machinery orelectrical equipment. In both the gaseous state andthe finely divided solid (snow) state, it is a non-conductor of electricity y regardless of voltage. CO2can be safely used in fighting electrical fires.C O2 extinguishes the fire by diluting anddisplacing its oxygen supply. If gaseous CO2 isdirected into a fire so that sufficient oxygen-supporting combustion is no longer available, theflames will die out. Depending on what is fuelingthe fire, that action will take place when the21-percent oxygen content, normally present inair, is diluted with CO2 below 15 percent oxygen.Some ordinary combustible class A fires requirethat the oxygen content be reduced to less than6 percent to extinguish glowing combustion(smoldering fire). CO2 has limited coolingcapabilities, may not cool the fuel below itsignition temperature, and is more likely than otherextinguishing agents to allow reflash. Therefore,the fire fighter must remember to stand by withadditional backup extinguishers. The temperatureof the burning substance and its surroundingsmust be below its ignition temperature if the fireis to remain extinguished.CO2 is not an effective extinguishing agentfor fires in materials that produce their ownoxygen supply (as an example, aircraft parachuteflares). Fires involving reactive metals, such asmagnesium, sodium, potassium, or titanium,cannot be extinguished with CO2. Because of therelatively high temperatures involved, these metalfuels decompose CO2 and continue to burn.WARNINGC O2 can produce unconsciousness anddeath when present in fire-extinguishingconcentrations. The reaction in such casesis more closely related to suffocation. Aconcentration of 9 percent will cause mostpeople to lose consciousness within a fewminutes. Caution must be exercised whendischarging CO2 in confined spaces.7-11
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