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Chapter 4 Fire-Related Chemistry and Physics
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Introduction To appreciate how fire is controlled, we must first understand the chemical and physical properties of fire itself Information can be used to predict what the fire will do with the available fuel and where it is headed With this knowledge, we are able to choose the proper extinguishing agent and its method of application 1-
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Fire Triangle and Fire Tetrahedron
Learning Objective 1 Fire Triangle and Fire Tetrahedron FIRE DEFINED Rapid, self-sustaining oxidation process accompanied by the evolution of heat and light in varying intensity Combustion described as a chemical reaction that releases energy as heat and usually as light RUSTING OF IRON Not considered combustion Proceeds at a slow rate
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Fire Triangle and Fire Tetrahedron
Learning Objective 1 Fire Triangle and Fire Tetrahedron FIRE TRIANGLE Originally based on three elements Fuel Air Heat FIRE TETRAHEDRON Fourth component called chemical chain reaction Produces free radicals
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Describe What Constitutes an Oxidizer
Learning Objective 2 Describe What Constitutes an Oxidizer CHEMISTRY OF FIRE Two basic necessary components Oxidizer Fuel OXIDIZER Evolves or generates oxygen Oxygen is most common oxidizer Most fires are burning at 21% oxygen
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Describe What Constitutes an Oxidizer
Learning Objective 2 Describe What Constitutes an Oxidizer FLOURINE AND CHLORINE Listed under halogen family on periodic table Both naturally occur as gases Flourine is a much stronger oxidizer than oxygen Fire in a flourine atmosphere will burn more rapidly than one occurring in air
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Describe What Constitutes a Fuel
Learning Objective 3 Describe What Constitutes a Fuel FUEL Described as anything that will burn Carbon and hydrogen are two most common Hydrocarbons Main element in organic fuels, fuels that were at one time living things Other elements as fuels, including metals Sodium, aluminum, magnesium
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Describe What Constitutes a Fuel
Learning Objective 3 Describe What Constitutes a Fuel FIRES INVOLVING CARBON, HYDROGEN, AND OXYGEN Two byproducts of complete combustion Water vapor Carbon dioxide Byproducts of incomplete combustion Smoke Carbon monoxide (CO) Carbon dioxide (CO²) Other fire gases
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Illustrate the States of Matter
Learning Objective 4 Illustrate the States of Matter FUEL MAY OCCUR IN THREE STATES OF MATTER Solid Liquid Gas MOLECULES AND TEMPERATURE Molecules in liquids vibrate faster than those in solids, and gas molecules vibrate the fastest of the three As this vibration increases, solids become liquids and liquids become gases
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Explain the Process of Pyrolysis
Learning Objective 5 Explain the Process of Pyrolysis PYROLYSIS Chemical decomposition of matter through heat Combustion occurs when fuel has been converted to vapor or gas Oxidizer and fuel must be gaseous for recombination Solid and liquid fuels are converted to gaseous state by the application of energy
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Explain the Process of Pyrolysis
Learning Objective 5 Explain the Process of Pyrolysis IGNITION TEMPERATURE Combustion continues without external input of heat FREE RADICALS Longer molecules break into shorter molecules Byproduct of the fuel that directly combines with the oxidizer
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Properties Affecting Solid Fuels
Learning Objective 6 Properties Affecting Solid Fuels FACTORS AFFECTING SOLID FUEL PYROLIZATION Mass Arrangement Continuity Moisture content
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Properties Affecting Solid Fuels
Learning Objective 6 Properties Affecting Solid Fuels MEASURING FLAME SPREAD Steiner tunnel Test consists of a 25’ vented tunnel A fan draws the flame across the surface of the material being tested Flame spread is determined visually through windows built into the tunnel
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Properties Affecting Liquid Fuels
Learning Objective 7 Properties Affecting Liquid Fuels LIQUID FUELS Molecules flow freely but do not readily separate Will assume the shape of their container Physical properties make them difficult to extinguish They increase the hazards to persons and property If spilled, will flow and increase in size
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Properties Affecting Liquid Fuels
Learning Objective 7 Properties Affecting Liquid Fuels OTHER IMPORTANT PROPERTIES OF LIQUIDS Specific gravity Volatility Vapor pressure Boiling point Vapor density Flash point Miscibility
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Properties Affecting Gas Fuels
Learning Objective 8 Properties Affecting Gas Fuels GAS AND VAPOR FUEL CHARACTERISTICS Defined as a fluid that has no shape or volume and tends to expand indefinitely Always fill the container in which they are stored FLAMMABLE RANGES Upper flammable limit Lower flammable limit Flammable range
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Differentiate Heat and Temperature
Learning Objective 9 Differentiate Heat and Temperature SOURCES OF HEAT (FORM OF ENERGY) Chemical Mechanical Electrical Nuclear MEASUREMENTS OF HEAT British thermal unit (BTU) Calorie (metric term) Joule (international system of units)
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Differentiate Heat and Temperature
Learning Objective 9 Differentiate Heat and Temperature MEASUREMENTS OF TEMPERATURE The measure of the hotness or coldness of an object Fahrenheit Celsius Kelvin Rankine
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Illustrate the Four Methods of Heat Transfer
Learning Objective 10 Illustrate the Four Methods of Heat Transfer ENERGY TRANSFERS FROM HEAT SOURCE TO FUEL Conduction Convection Radiation Direct flame impingement or autoexposure
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Illustrate the Four Methods of Heat Transfer
Learning Objective 10 Illustrate the Four Methods of Heat Transfer STRUCTURE FIRE AND HEAT TRANSFER METHODS Fire starts in a stack of boxes in a warehouse, convection catches the ceiling on fire Fire spreads up the stack due to direct flame impingement Radiated heat spreads the fire to piled stock several feet away A pipe running through the wall heats to the point that stock on the other side of the wall ignites
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Illustrate the Five Classifications of Fire
Learning Objective 11 Illustrate the Five Classifications of Fire FIRE HAS BEEN DIVIDED INTO BASIC CLASSIFICATIONS Class A: Ordinary combustibles Class B: Flammable liquids Class C: Energized electrical Class D: Combustible metals Class K: Cooking materials
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Describe the Four Stages of Fire
Learning Objective 12 Describe the Four Stages of Fire FOUR STAGES OF FIRE DEVELOPMENT Ignition Fire ignites and reaches a point where it no longer needs input heat from outside sources to keep burning Growth Fire releases heat, bringing more fuel to its ignition temperature Heat is transferred to nearby surfaces though radiation Cont.
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Describe the Four Stages of Fire
Learning Objective 12 Describe the Four Stages of Fire FOUR STAGES OF FIRE DEVELOPMENT Fully developed All available fuels in the fire’s perimeter are burning Decay Occurs when the fire has run out of available fuel Suppression action has reduced the fire to smoldering embers
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Describe the Four Stages of Fire
Learning Objective 12 Describe the Four Stages of Fire FLASHOVER The contents in the room are brought to their ignition temperature and if sufficient oxygen is present, flashover can occur If a flashover were to take place, temperatures, even at floor level, would rise dramatically Firefighters cannot survive in a room with a flashover, even wearing full PPE and SCBA
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Describe the Four Stages of Fire
Learning Objective 12 Describe the Four Stages of Fire BACK DRAFT Flame may die out and glowing combustion takes place Pyrolysis continues to occur, with amounts of combustible gases produced Room is now superheated and charged with smoke and combustible fire gases Fire gases and smoke are alternately forced out and sucked back into the structure
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Summary This chapter introduces the chemical and physical properties of the elements found in fires and what actually occurs during the combustion reaction A solid understanding of the combustion process and the stages of fire must be in place before we discuss the selection, application, and tactics of extinguishing agents 1-
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