Introduction to Fire Protection 3rd Edition
Chapter 4 Chemistry and Physics of Fire
Objectives <ul><li>Define the difference between the fire triangle and the fire tetrahedron </li></ul><ul><li>Describe wha...
Objectives (con’t.) <ul><li>Explain the process of pyrolysis </li></ul><ul><li>Describe the properties affecting solid fue...
Objectives (con’t.) <ul><li>Differentiate heat and temperature </li></ul><ul><li>Illustrate the four methods of heat trans...
Introduction <ul><li>Fire can be better controlled by understanding  its chemical and physical properties </li></ul><ul><u...
Fire Defined <ul><li>Fire : Rapid self-sustaining oxidation process accompanied by the evolution of heat and light in vary...
Fire Triangle <ul><li>Three sides represent elements  (see Figure 4-1) </li></ul><ul><ul><li>Originally: fuel, heat, and a...
Fire Tetrahedron <ul><li>Four sides represent elements  (see Figure 4-2) </li></ul><ul><ul><li>Fuel </li></ul></ul><ul><ul...
Oxidizer <ul><li>Oxygen is the most common </li></ul><ul><ul><li>Air contains 21% oxygen </li></ul></ul><ul><li>Increasing...
Fuel <ul><li>Described as anything that will burn </li></ul><ul><li>Most common fuels contain carbon and hydrogen </li></u...
Fuel (con’t.) <ul><li>Occurs in three states of matter </li></ul><ul><li>State is often temperature dependent </li></ul><u...
Solid Fuels <ul><li>Factors affecting rate of pyrolysis </li></ul><ul><ul><li>Size </li></ul></ul><ul><ul><li>Arrangement ...
Flame Spread <ul><li>Steiner Tunnel tests how rapidly a fire spreads on interior finishes  </li></ul><ul><ul><li>Measures ...
Liquid Fuels <ul><li>Liquids flow like water but do not readily separate </li></ul><ul><li>Specific gravity : weight of a ...
Liquid Fuels (con’t.) <ul><li>Vapor pressure : pressure exerted by vapor molecules on the sides of a container </li></ul><...
Liquid Fuels (con’t.) <ul><li>Flash point : minimum temperature of a liquid at which it gives off vapors sufficient to for...
Gas/Vapor Fuels <ul><li>Gas/vapor fuels : fluid that has neither independent shape nor volume but tends to expand indefini...
Gas/Vapor Fuels (con’t.) <ul><li>Lower flammable limit : lower concentration of gas or vapor in air below which it is not ...
Gas/Vapor Fuels (con’t.) <ul><li>Classification of gases </li></ul><ul><ul><li>Flammable and nonflammable </li></ul></ul><...
Heat and Temperature <ul><li>Heat is a form of energy </li></ul><ul><li>Sources of heat </li></ul><ul><ul><li>Chemical: br...
Heat and Temperature (con’t.) <ul><li>British thermal unit  (BTU): amount of heat required to raise the temperature of one...
Temperature <ul><li>Measure of the hotness or coldness of something expressed in degrees </li></ul><ul><li>Fahrenheit </li...
Heat Transfer <ul><li>Conduction : transfer of heat through a medium without visible motion </li></ul><ul><li>Convection :...
Heat Transfer (con’t.) <ul><li>Radiation : transfer of heat through wavelengths of energy </li></ul><ul><li>Direct flame i...
Classification of Fires <ul><li>Class A: ordinary combustibles  </li></ul><ul><li>Class B: flammable liquids </li></ul><ul...
Stages of Fire <ul><li>Incipient </li></ul><ul><ul><li>Smoke and heat produced </li></ul></ul><ul><li>Free burning </li></...
Stages of Fire (con’t.) <ul><li>Ignition </li></ul><ul><li>Growth </li></ul><ul><li>Fully developed </li></ul><ul><li>Deca...
Ignition Stage <ul><li>Oxygen in surrounding air approximately 21% </li></ul><ul><li>Fire ignited and burns on its own </l...
Growth Stage <ul><li>More fuel reaches ignition temperature </li></ul><ul><li>Heat transferred to other combustibles </li>...
Growth Stage (con’t.) <ul><li>Water applied to ceiling to reduce temperatures </li></ul><ul><li>Flashover may occur if not...
Fully Developed Stage <ul><li>All fuels burning </li></ul><ul><li>Structure </li></ul><ul><ul><li>Room and contents or ent...
Decay Stage <ul><li>Fire has run out of fuel  or  oxygen </li></ul><ul><li>In a sealed environment </li></ul><ul><ul><li>W...
Backdraft <ul><li>Combustible fire gases are prevalent in atmosphere </li></ul><ul><li>Gases are at or above their ignitio...
<ul><li>In order to choose and apply the proper extinguishing agents to fires, you must: </li></ul><ul><ul><li>Study the p...
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Chapter 04

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

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