Chapter 04


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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>Fuel </li></ul><ul><li>Heat </li></ul><ul><li>Oxygen </li></ul>
  9. 9. FIRE TETRAHEDRON <ul><li>Fuel </li></ul><ul><li>Heat </li></ul><ul><li>Oxidizer </li></ul><ul><li>Chain Reaction </li></ul>Fuel Oxygen
  10. 11. ELEMENTS OF FIRE <ul><li>FUEL - Something that will Burn. </li></ul><ul><li>HEAT - Ignition Source, Starts the FIRE </li></ul><ul><li>OXYGEN - Supports Combustion </li></ul><ul><li>Chemical Chain Reaction - Must have all three elements. </li></ul>
  11. 12. 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>
  12. 13. 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>
  13. 14. 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>
  14. 15. PYROLYSIS <ul><li>The chemical decomposition of matter through the action of heat </li></ul><ul><li>Solid and liquid fuels are converted to the gaseous state by the application of energy thru this process i.e. the flame of a candle floating a small distance above the wick </li></ul>
  15. 17. FIRE TERMS <ul><li>FIRE POINT </li></ul><ul><li>• The minimum temperature to which a material must be heated in order to sustain combustion after ignition by an external source. </li></ul><ul><li>• Also called Ignition Temperature. </li></ul>
  16. 18. 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>
  17. 19. 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>
  18. 20. 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>
  19. 21. 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>
  20. 22. 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, the lower the Flash point in degrees the more DANGEROUS the fuel. </li></ul><ul><li>Miscibility : ability of a substance to mix with water </li></ul>
  21. 23. 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>
  22. 24. 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>
  23. 25. 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>
  24. 27. 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>
  25. 28. 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>
  26. 29. 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>
  27. 30. 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>
  28. 33. 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>
  29. 35. 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>
  30. 36. CLASS A FIRES <ul><li>• Ordinary Combustible Materials </li></ul><ul><li>• Wood, Paper, Cloth, Plastic, etc. </li></ul>
  31. 37. CLASS B FIRES <ul><li>• Flammable & Combustible Liquids </li></ul><ul><li>• Flammable & Combustible Gases </li></ul><ul><li>• Gasoline, Kerosene, Grease, Oil </li></ul>
  32. 38. CLASS C FIRES <ul><li>• Energized Electrical Equipment </li></ul><ul><li>• Wires, Motors, Switches, Lights, Cables, Receptacles, Computers </li></ul>
  33. 39. CLASS D FIRES <ul><li>• Combustible Metals </li></ul><ul><li>• Magnesium, Titanium, Sodium. </li></ul><ul><li>• Identified by the Suffix “ IUM “ </li></ul><ul><li>• React Violently with WATER </li></ul>
  34. 40. 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>
  35. 41. 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>
  36. 42. STAGES OF FIRE <ul><li>INCIPIENT PHASE </li></ul><ul><li>• Just Started. </li></ul><ul><li>• Free Burning Fire. </li></ul><ul><li>• Normal Oxygen 21%. </li></ul><ul><li>• Don’t Have High Temperatures. </li></ul><ul><li>• Thermal Balance is not Yet Disturbed. </li></ul><ul><li>• Breathing is barely affected. </li></ul>
  37. 43. FIRE BEHAVIOR <ul><li>FREE BURNING PHASE OR </li></ul><ul><li>GROWTH STAGE </li></ul><ul><li>• Fire is expanding. </li></ul><ul><li>• Oxygen Supply less than 21%. </li></ul><ul><li>• Breathing Difficult, SCBA must be used </li></ul><ul><li>• Carbon monoxide levels are high. </li></ul><ul><li>• Temperatures between 1200° - 1600° F. </li></ul>
  38. 45. 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>
  39. 48. 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>
  40. 50. FIRE BEHAVIOR <ul><li>SMOLDERING PHASE </li></ul><ul><li>• Free burning has ended. </li></ul><ul><li>• Insufficient oxygen. Less than 16%. </li></ul><ul><li>• Carbon monoxide, fatal range. </li></ul><ul><li>• Backdraft explosion possible. </li></ul><ul><li>• Most Dangerous stage to the Firefighter. </li></ul>
  41. 51. 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>
  42. 52. 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>
  43. 55. EXTINGUISHMENT of FIRE <ul><li>• Removal of one of the three elements, or by breaking the chemical chain reaction. </li></ul><ul><li>• Removal of Heat -Water is used to cool the fuel below its ignition temperature. </li></ul><ul><li>• Removal of Oxygen- Co2 is used to sweep away the oxygen. </li></ul>
  44. 56. EXTINGUISHMENT of FIRE <ul><li>• Removal of Fuel- Shut off valve, deenergize electrical equipment. </li></ul>
  45. 57. <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