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Chapter 04


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  • 1. Introduction to Fire Protection 3rd Edition
  • 2. Chapter 4 Chemistry and Physics of Fire
  • 3. Objectives
    • Define the difference between the fire triangle and the fire tetrahedron
    • Describe what constitutes an oxidizer
    • Describe what constitutes a fuel
    • Illustrate the states of matter
  • 4. Objectives (con’t.)
    • Explain the process of pyrolysis
    • Describe the properties affecting solid fuels
    • Describe the properties affecting liquid fuels
    • Describe the properties affecting gas fuels
  • 5. Objectives (con’t.)
    • Differentiate heat and temperature
    • Illustrate the four methods of heat transfer
    • Illustrate the five classifications of fire
    • Describe the four stages of fire
  • 6. Introduction
    • Fire can be better controlled by understanding its chemical and physical properties
      • Ability to predict what fire will do with available fuel and where it is headed
      • Ability to choose appropriate extinguishing agent and method of application
  • 7. Fire Defined
    • Fire : Rapid self-sustaining oxidation process accompanied by the evolution of heat and light in varying intensities
    • Combustion : A chemical reaction that releases energy as heat and, usually, light
  • 8. Fire Triangle
    • Three sides represent elements (see Figure 4-1)
      • Originally: fuel, heat, and air
      • More accurate: fuel, energy, and oxidizer
  • 9. Fire Tetrahedron
    • Four sides represent elements (see Figure 4-2)
      • Fuel
      • Energy
      • Oxidizer
      • Chemical chain reaction
  • 10. Oxidizer
    • Oxygen is the most common
      • Air contains 21% oxygen
    • Increasing amount of oxidizer will increase intensity of fire
    • Other oxidizers include fluorine and chlorine
  • 11. Fuel
    • Described as anything that will burn
    • Most common fuels contain carbon and hydrogen
    • Complete combustion yields carbon dioxide and water vapor
    • Most combustion is incomplete due to several factors
      • Size, arrangement, contaminants, lack of sufficient oxidizer
      • Yields smoke and other fire gases
  • 12. Fuel (con’t.)
    • Occurs in three states of matter
    • State is often temperature dependent
    • Both fuel and oxidizer must be in gaseous state to combine
    • Pyrolysis : fuel is vaporized by input heat
    • Ignition temperature : when fuel is hot enough to self-sustain combustion
  • 13. Solid Fuels
    • Factors affecting rate of pyrolysis
      • Size
      • Arrangement
      • Continuity
      • Moisture content
  • 14. Flame Spread
    • Steiner Tunnel tests how rapidly a fire spreads on interior finishes
      • Measures flame spread, temperature, and smoke density
      • May measure and analyze combustion gases
  • 15. Liquid Fuels
    • Liquids flow like water but do not readily separate
    • Specific gravity : weight of a liquid compared to the weight of an equal volume of water
    • Volatility : ease with which a fuel gives off vapors
  • 16. Liquid Fuels (con’t.)
    • Vapor pressure : pressure exerted by vapor molecules on the sides of a container
    • Boiling point : when the vapor pressure equals atmospheric pressure
    • Vapor density : relative density of a vapor or gas as compared to air
  • 17. Liquid Fuels (con’t.)
    • Flash point : minimum temperature of a liquid at which it gives off vapors sufficient to form an ignitable mixture with air
    • Miscibility : ability of a substance to mix with water
  • 18. Gas/Vapor Fuels
    • Gas/vapor fuels : fluid that has neither independent shape nor volume but tends to expand indefinitely
    • Upper flammable limit : maximum concentration of gas or vapor in air above which it is not possible to ignite the vapors (too rich to burn)
  • 19. Gas/Vapor Fuels (con’t.)
    • Lower flammable limit : lower concentration of gas or vapor in air below which it is not possible to ignite vapors (too lean)
    • Flammable range : proportion of gas or vapor in air between the upper and lower flammable limits
  • 20. Gas/Vapor Fuels (con’t.)
    • Classification of gases
      • Flammable and nonflammable
    • Some nonflammable support combustion (oxygen)
    • Caution : flammable vapors are not always visible
  • 21. Heat and Temperature
    • Heat is a form of energy
    • Sources of heat
      • Chemical: breaking down and recombination of molecules
      • Mechanical: friction, friction sparks
      • Electrical: arcs and sparks
      • Nuclear: fission and fusion
  • 22. Heat and Temperature (con’t.)
    • British thermal unit (BTU): amount of heat required to raise the temperature of one pound of water one degree Fahrenheit
    • Calorie : amount of heat required to raise the temperature of one gram of water one degree Celsius
  • 23. Temperature
    • Measure of the hotness or coldness of something expressed in degrees
    • Fahrenheit
      • Freezing temperature: 32 o
      • Boiling temperature: 212 o
    • Celsius
      • Freezing temperature: 0 o
      • Boiling temperature: 100 o
  • 24. Heat Transfer
    • Conduction : transfer of heat through a medium without visible motion
    • Convection : transfer of heat through a circulating medium (see Figure 4-16)
  • 25. Heat Transfer (con’t.)
    • Radiation : transfer of heat through wavelengths of energy
    • Direct flame impingement (auto exposure) combines all three (see Figure 4-18)
  • 26. Classification of Fires
    • Class A: ordinary combustibles
    • Class B: flammable liquids
    • Class C: energized electrical
    • Class D: combustible metals
    • Class K: cooking materials
      • Note : Many fires involve more than one
      • classification
  • 27. Stages of Fire
    • Incipient
      • Smoke and heat produced
    • Free burning
      • Heat production increases
      • Fire spreads to other fuels
    • Smoldering
      • Flames die out, glowing combustion
    • Phases of fire have evolved into four stages
  • 28. Stages of Fire (con’t.)
    • Ignition
    • Growth
    • Fully developed
    • Decay
  • 29. Ignition Stage
    • Oxygen in surrounding air approximately 21%
    • Fire ignited and burns on its own
    • Combustion reaction begins to accelerate
  • 30. Growth Stage
    • More fuel reaches ignition temperature
    • Heat transferred to other combustibles
    • Fire builds in intensity
    • In a confined area, room temperature increases
      • Ceiling temperature may easily reach 1000 0 F
    • Rollover starts to occur
  • 31. Growth Stage (con’t.)
    • Water applied to ceiling to reduce temperatures
    • Flashover may occur if not cooled
      • Tongues of flame roll across ceiling
      • Radiant heat affects materials in room, raising them to ignition temperature
      • Materials in room ignite all at once
    • Firefighters can not survive flashover
    • PPE and breathing apparatus may fail
  • 32. Fully Developed Stage
    • All fuels burning
    • Structure
      • Room and contents or entire structure
    • Wildland
      • Fire is moving across the countryside
  • 33. Decay Stage
    • Fire has run out of fuel or oxygen
    • In a sealed environment
      • When oxygen is below 15%, combustion is slowed
      • Pyrolysis continues to occur
      • Room is superheated and charged with smoke and combustible gases
      • If oxygen is introduced, backdraft can occur
  • 34. Backdraft
    • Combustible fire gases are prevalent in atmosphere
    • Gases are at or above their ignition temperature
    • Oxygen content is too low for ignition (too rich to burn)
    • Oxygen is introduced
    • Gases ignite with explosive force
  • 35.
    • In order to choose and apply the proper extinguishing agents to fires, you must:
      • Study the physical and chemical properties of fire
      • Understand the combustion process
      • Learn about heat transfer
      • Know the classifications and stages of fire