Firefighter I. Copyright © Texas Education Agency 2011. All rights reserved. Images and other...

Extinguishing Properties of Water

Firefighter I

Copyright © Texas Education Agency 2011. All rights reserved.Images and other multimedia content used with permission. 2

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Physical Characteristics Of Water• Solid – ice at 32° F (0° C) • Liquid – between 32° and

212° F (0° – 100° C)

• Gas – invisible water vapor at 212° F or 100° C

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Physical Characteristics Of Water (continued)Weighs 8.33 pounds per gallonExpands to 1700 times its original volume

when converted to steam at 212° F

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Law of Specific HeatThe measurement of the heat absorbing capacity of a

substanceWater is noncombustible and can absorb large amounts of

heatHeat absorbed by water spray (fog) causes the hot gas layer

to contract in an indirect attack in a compartment fire

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Law of Latent HeatLatent heat – the amount

of heat energy absorbed or released during a change of state (solid<->liquid<->gas)

Latent Heat of Vaporization – the energy that is required to change a substance from a liquid state to a gaseous state

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Law of Heat Flow• The 2nd law of thermodynamics – heat flows

spontaneously from a hot to a cold body• For heat to be transferred, the two bodies must

be at different temperatures• Heat moves from warm or hot objects to cooler

objects• The rate at which the heat transfer occurs is

dependent on the• temperature difference between the two objects• conductivity of the materials involved• the greater the difference, the greater the

transfer rate7


Advantages of Water as an Extinguishing AgentReadily available and considered inexpensiveHas greater heat absorbing capability (higher

specific heat) than most common extinguishing agents

Takes a relatively large amount of heat to completely convert to steam (high latent heat of vaporization)

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Advantages of Water as an Extinguishing Agent (continued)Used in many different forms

or ways:– As a solid stream– As a broken stream– From a fog nozzle– Straight stream– Narrow pattern fog stream– Wide pattern fog stream

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Disadvantages of Water as an Extinguishing AgentHigh surface tensionCan react readily with some materials like

combustible metalsAllows radiant heat to pass through itFreezes at 32° F or 0° CConducts electricity readily

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Disadvantages of Water as an Extinguishing Agent (continued)Class D fires involve combustible metals that

water readily reacts with if it’s used as an extinguishing agent

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Summary Water can extinguish fire in various ways.

Primarily water is used to cool by absorbing heat.

Water can also smother a fire by diluting or eliminating oxygen and thwarting the combustion process

Through the vaporization process, water absorbs heat as it is converted to steam.

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Resources0135151112, Essentials of Firefighting (5th

Edition), International Fire Service Training Association (IFSTA)

Images used with permission by IFSTA.

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