Basics of Fire Behavior Chapter 1
Learning Objectives <ul><li>Describe the difference between fire and combustion </li></ul><ul><li>Describe the fire triang...
Learning Objectives (continued) <ul><li>List and describe the different stages of fire </li></ul><ul><li>List and describe...
Introduction <ul><li>Understanding of fire behavior is necessary to manage a  hazard </li></ul><ul><li>Fire protection sys...
Fire and Combustion <ul><li>Fire is beneficial when correctly managed and destructive when not managed </li></ul><ul><li>C...
The Fire Triangle <ul><li>Depicts relationship between fuel, air, and heat </li></ul><ul><li>All three elements must be pr...
The Fire Tetrahedron <ul><li>Depicts fire’s nature as uninhibited, chemical, self-sustaining chain reaction </li></ul><ul>...
Classes of Fire <ul><li>Early 1900s Underwriters Laboratories developed fire categorization </li></ul><ul><ul><li>Based on...
Class A Fires  and Extinguishing Agents <ul><li>Class A fires : ordinary combustibles such as cloth, grain, paper, rubber,...
Class B Fires  and Extinguishing Agents <ul><li>Class B fires: flammable and combustible liquids and gases </li></ul><ul><...
Class C Fires  and Extinguishing Agents <ul><li>Class C fires : energized electrical equipment </li></ul><ul><li>Shutting ...
Class D Fires  and Extinguishing Agents <ul><li>Class D fires : combustible metals </li></ul><ul><li>Manufacturing process...
Class K Fires  and Extinguishing Agents <ul><li>Class K fire: fires in cooking appliances using combustible oils and fats ...
Other Fire Classification Systems <ul><li>US and Canada use same classification system </li></ul><ul><li>Europe and Austra...
Fire and Flame Types <ul><li>Four types of fire: </li></ul><ul><ul><li>Diffusion flame </li></ul></ul><ul><ul><li>Smolderi...
Diffusion Flame <ul><li>Flame we see when we light a match </li></ul><ul><li>Most natural flame fires are diffusion flames...
Figure 1-8 Schematic of a diffusion flame
Smoldering <ul><li>Example: glow of charcoal in grill </li></ul><ul><li>No flame, but heat </li></ul><ul><li>Air flows ove...
Figure 1-9 Common examples of a smoldering fire
Spontaneous Combustion and Self-Heating <ul><li>Material undergoes oxidation where heat dissipation limited </li></ul><ul>...
Figure 1-10 Examples of fuel arrays  prone to spontaneous combustion
Premixed Flame <ul><li>Requires gas fuel and air mix to ignite </li></ul><ul><li>Gas fuel must be within flammable limits ...
Figure 1-11 Examples of premixed flames
The Stages of Fire <ul><li>Fires develop and evolve in stages: </li></ul><ul><ul><li>Pre-ignition </li></ul></ul><ul><ul><...
Pre-ignition Stage <ul><li>Requires some form of energy transfer </li></ul><ul><ul><li>Usually in the form of heat </li></...
Ignition Stage <ul><li>Three things are necessary to start a fire: </li></ul><ul><ul><li>Heat source </li></ul></ul><ul><u...
Growth Stage <ul><li>Adequate oxygen must be available </li></ul><ul><ul><li>May be gaseous or chemical oxidizer </li></ul...
Fully Developed Stage <ul><li>Combustible contents of compartment totally in flame </li></ul><ul><li>Flashover : transitio...
Decay Stage <ul><li>Fuel exhausted or oxygen level drops below 16% </li></ul><ul><li>Burning in the form of glowing combus...
Forms of Heat Transfer <ul><li>Three types of heat transfer: </li></ul><ul><ul><li>Conduction </li></ul></ul><ul><ul><li>C...
Conduction <ul><li>Transfer of heat from one body to another by direct contact </li></ul><ul><li>When exposing objects to ...
Convection <ul><li>Transfer of heat from one body to another through a medium such as liquid or gas </li></ul><ul><li>Exam...
Figure 1-18 Convection.  As air is heated, its molecules become excited and seek more space
Radiation <ul><li>Transfer of heat through electro-magnetic energy, such as light </li></ul><ul><li>Radiant heat travels i...
Methods of Extinguishing Fires <ul><li>Four methods to extinguish fires: </li></ul><ul><ul><li>Cooling </li></ul></ul><ul>...
Cooling <ul><li>One gallon of water can absorb 8,000 Btus </li></ul><ul><ul><li>Same amount of heat produced by one pound ...
Oxygen Reduction <ul><li>Control of air intake in area of fire helps reduce or remove oxygen supply </li></ul><ul><li>Foam...
Removing or Interrupting the Fuel Supply <ul><li>Backfires are set in wild land fires to remove fuel ahead of a hostile fi...
Interrupting the Chain Reaction <ul><li>Fire sustained by chemical reaction with combustion products </li></ul><ul><li>Dry...
Summary <ul><li>Fire triangle/tetrahedron </li></ul><ul><ul><li>Describe relationship between the components required for ...
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Chapter 01

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Chapter 01

  1. 1. Basics of Fire Behavior Chapter 1
  2. 2. Learning Objectives <ul><li>Describe the difference between fire and combustion </li></ul><ul><li>Describe the fire triangle and fire tetrahedron </li></ul><ul><li>List and describe the classes of fire and their relationship to extinguishing agents </li></ul><ul><li>List and describe the different types of fire </li></ul>
  3. 3. Learning Objectives (continued) <ul><li>List and describe the different stages of fire </li></ul><ul><li>List and describe methods of heat transfer </li></ul><ul><li>List and describe methods used to extinguish fires </li></ul>
  4. 4. Introduction <ul><li>Understanding of fire behavior is necessary to manage a hazard </li></ul><ul><li>Fire protection systems address a specific type and size of hazard </li></ul><ul><li>Understanding of fire chemistry is necessary to assess the fire hazard </li></ul><ul><li>Understanding of fire behavior is the basis for every manual fire attack </li></ul>
  5. 5. Fire and Combustion <ul><li>Fire is beneficial when correctly managed and destructive when not managed </li></ul><ul><li>Combustion : combustible material and an oxidizing agent produce heat or energy and other products </li></ul><ul><ul><li>Heat must be generated more rapidly than it is dissipated to continue the process </li></ul></ul><ul><li>Fire produces energy in form of heat, light, and flame </li></ul><ul><ul><li>Requires a combustible fuel, heat source, and oxygen </li></ul></ul>
  6. 6. The Fire Triangle <ul><li>Depicts relationship between fuel, air, and heat </li></ul><ul><li>All three elements must be present in sufficient quantities </li></ul><ul><li>Changing proportion determines whether fire will smolder, burn slowly, burn rapidly </li></ul><ul><li>Many methods are used to extinguish a fire </li></ul>
  7. 7. The Fire Tetrahedron <ul><li>Depicts fire’s nature as uninhibited, chemical, self-sustaining chain reaction </li></ul><ul><ul><li>After ignition occurs </li></ul></ul><ul><li>All four elements must be present </li></ul><ul><ul><li>Elimination of any results in extinguishment </li></ul></ul>Figure 1-2 The fire tetrahedron
  8. 8. Classes of Fire <ul><li>Early 1900s Underwriters Laboratories developed fire categorization </li></ul><ul><ul><li>Based on extinguishing agent </li></ul></ul><ul><li>Fires involve different materials </li></ul><ul><ul><li>Wrong agent could compound the hazard </li></ul></ul><ul><li>Matches extinguishing agent to fire hazard </li></ul><ul><li>Labels bearing the classification on packaging and literature </li></ul>
  9. 9. Class A Fires and Extinguishing Agents <ul><li>Class A fires : ordinary combustibles such as cloth, grain, paper, rubber, wood </li></ul><ul><li>Class A materials release approximately 8000 Btu per pound </li></ul><ul><li>Water is the most effective suppression agent </li></ul><ul><ul><li>Absorbs heat; reduces temperature below ignition temperature </li></ul></ul><ul><ul><li>Using water or Class A foam may be better than dry chemical agents and halon gas mixtures </li></ul></ul>
  10. 10. Class B Fires and Extinguishing Agents <ul><li>Class B fires: flammable and combustible liquids and gases </li></ul><ul><li>Class B agents smother or blanket </li></ul><ul><ul><li>Interrupt the chemical chain reaction </li></ul></ul><ul><ul><li>Keep oxygen away from flammable vapors </li></ul></ul><ul><li>Typical agents: foams, carbon dioxide, dry chemical agents, halons </li></ul>
  11. 11. Class C Fires and Extinguishing Agents <ul><li>Class C fires : energized electrical equipment </li></ul><ul><li>Shutting off electricity is critical </li></ul><ul><ul><li>May require additional suppression activities </li></ul></ul><ul><li>Only fires involving electrical equipment are class C fires </li></ul><ul><ul><li>When electricity is no longer involved, fire is reclassified </li></ul></ul>
  12. 12. Class D Fires and Extinguishing Agents <ul><li>Class D fires : combustible metals </li></ul><ul><li>Manufacturing process releases metal dust and particles </li></ul><ul><ul><li>Potentially explosive if airborne </li></ul></ul><ul><li>Class D extinguishing agents are “dry powder” and inert </li></ul><ul><ul><li>Reduce oxygen concentration </li></ul></ul><ul><ul><li>Extremely hazardous </li></ul></ul>
  13. 13. Class K Fires and Extinguishing Agents <ul><li>Class K fire: fires in cooking appliances using combustible oils and fats </li></ul><ul><li>Class K agents extinguish by saponification </li></ul><ul><ul><li>Fatty acids in cooking medium react with extinguishing agent and convert to foam </li></ul></ul><ul><ul><li>Soapy foam blankets surface of burning liquid </li></ul></ul><ul><ul><li>Cools liquid below autoignition temperature </li></ul></ul>
  14. 14. Other Fire Classification Systems <ul><li>US and Canada use same classification system </li></ul><ul><li>Europe and Australia use different classification systems </li></ul><ul><li>Different parts of the world have different classification systems </li></ul><ul><li>All classification systems are practical </li></ul>
  15. 15. Fire and Flame Types <ul><li>Four types of fire: </li></ul><ul><ul><li>Diffusion flame </li></ul></ul><ul><ul><li>Smoldering </li></ul></ul><ul><ul><li>Spontaneous combustion </li></ul></ul><ul><ul><ul><li>Self-heating </li></ul></ul></ul><ul><ul><li>Premixed flame </li></ul></ul><ul><li>Each requires fuel, source of heat, and oxygen </li></ul><ul><li>Each type of fire has unique characteristics </li></ul>
  16. 16. Diffusion Flame <ul><li>Flame we see when we light a match </li></ul><ul><li>Most natural flame fires are diffusion flames </li></ul><ul><li>Result of combustible gas emitted by burning material mixed with oxygen </li></ul><ul><li>Moves into reaction zone on either side of the flame </li></ul><ul><li>Combustion products diffuse from the flame </li></ul>
  17. 17. Figure 1-8 Schematic of a diffusion flame
  18. 18. Smoldering <ul><li>Example: glow of charcoal in grill </li></ul><ul><li>No flame, but heat </li></ul><ul><li>Air flows over the material surface, providing oxygen for combustion </li></ul><ul><li>Erupts into flame when sufficient oxygen and heat generated </li></ul><ul><li>May also be final phase of earlier fire event </li></ul>
  19. 19. Figure 1-9 Common examples of a smoldering fire
  20. 20. Spontaneous Combustion and Self-Heating <ul><li>Material undergoes oxidation where heat dissipation limited </li></ul><ul><li>Oxidation creates heat that cannot be dissipated </li></ul><ul><li>Temperature increases and promotes the reaction </li></ul><ul><li>Material smolders or flames if heat is sufficient </li></ul>
  21. 21. Figure 1-10 Examples of fuel arrays prone to spontaneous combustion
  22. 22. Premixed Flame <ul><li>Requires gas fuel and air mix to ignite </li></ul><ul><li>Gas fuel must be within flammable limits </li></ul><ul><ul><li>Lower and upper limit where mixture ignites </li></ul></ul><ul><ul><li>Example: acetylene flammable limit range 2.5% to 100% </li></ul></ul><ul><li>Changes in atmospheric pressure can alter flammable limit range </li></ul><ul><li>Knowing flammable limits is important to managing an incident </li></ul>
  23. 23. Figure 1-11 Examples of premixed flames
  24. 24. The Stages of Fire <ul><li>Fires develop and evolve in stages: </li></ul><ul><ul><li>Pre-ignition </li></ul></ul><ul><ul><li>Ignition </li></ul></ul><ul><ul><li>Growth </li></ul></ul><ul><ul><li>Fully developed </li></ul></ul><ul><ul><li>Decay or smoldering </li></ul></ul><ul><li>Fire suppression methods must be appropriate for the conditions </li></ul>
  25. 25. Pre-ignition Stage <ul><li>Requires some form of energy transfer </li></ul><ul><ul><li>Usually in the form of heat </li></ul></ul><ul><li>Generates gas from the fuel, which mixes with air </li></ul><ul><li>Fuel, in gas form, and oxygen must be in proper mixture to ignite </li></ul>
  26. 26. Ignition Stage <ul><li>Three things are necessary to start a fire: </li></ul><ul><ul><li>Heat source </li></ul></ul><ul><ul><li>Fuel </li></ul></ul><ul><ul><li>Oxygen </li></ul></ul><ul><li>Ignition occurs when more heat generated than dissipated </li></ul><ul><li>After ignition, no additional heat needed to continue the chain reaction </li></ul>
  27. 27. Growth Stage <ul><li>Adequate oxygen must be available </li></ul><ul><ul><li>May be gaseous or chemical oxidizer </li></ul></ul><ul><li>Amount of oxygen affects speed of growth </li></ul><ul><li>Amount, type, form of fuel are significant </li></ul><ul><li>Structure size, shape of walls, ceilings and roofs have significant impact </li></ul>
  28. 28. Fully Developed Stage <ul><li>Combustible contents of compartment totally in flame </li></ul><ul><li>Flashover : transition between growth stage and fully developed stage </li></ul><ul><ul><li>All combustible contents heat to ignition point and simultaneously ignite </li></ul></ul><ul><ul><li>Leads immediately to full development </li></ul></ul><ul><li>Stage regulated by amount of air and fuel </li></ul>
  29. 29. Decay Stage <ul><li>Fuel exhausted or oxygen level drops below 16% </li></ul><ul><li>Burning in the form of glowing combustion </li></ul><ul><li>Continues until: </li></ul><ul><ul><li>All fuel is completely exhausted </li></ul></ul><ul><ul><li>Temperature drops below ignition point </li></ul></ul><ul><li>Introduction of air may regenerate the fire </li></ul>
  30. 30. Forms of Heat Transfer <ul><li>Three types of heat transfer: </li></ul><ul><ul><li>Conduction </li></ul></ul><ul><ul><li>Convection </li></ul></ul><ul><ul><li>Radiation </li></ul></ul><ul><li>Hostile fires develop by heat transfer </li></ul><ul><li>Used every day to cook and heat homes </li></ul><ul><li>Key to reducing fire spread and extinguishing fires </li></ul>
  31. 31. Conduction <ul><li>Transfer of heat from one body to another by direct contact </li></ul><ul><li>When exposing objects to heat, movement of molecules increases </li></ul><ul><li>Heat energy attempts to move to lower temperature areas or objects </li></ul><ul><li>Rate of heat transfer dependent on efficiency of material as conductors </li></ul>
  32. 32. Convection <ul><li>Transfer of heat from one body to another through a medium such as liquid or gas </li></ul><ul><li>Example: automobile radiators </li></ul><ul><li>In building fires, heat transfers through the air in convection currents </li></ul><ul><li>Size and shape of fire compartment influences effect of convection </li></ul><ul><ul><li>Hurricane force winds can be generated due to updraft of convection currents </li></ul></ul>
  33. 33. Figure 1-18 Convection. As air is heated, its molecules become excited and seek more space
  34. 34. Radiation <ul><li>Transfer of heat through electro-magnetic energy, such as light </li></ul><ul><li>Radiant heat travels in a straight line </li></ul><ul><li>Has significant impact on the speed at which flashover occurs </li></ul><ul><li>Radiation is significant cause of fire spread from building to building </li></ul>
  35. 35. Methods of Extinguishing Fires <ul><li>Four methods to extinguish fires: </li></ul><ul><ul><li>Cooling </li></ul></ul><ul><ul><li>Oxygen reduction </li></ul></ul><ul><ul><li>Removing fuel supply </li></ul></ul><ul><ul><li>Interrupting the chain reaction </li></ul></ul><ul><li>Same basic methods used in design of extinguishment systems </li></ul>
  36. 36. Cooling <ul><li>One gallon of water can absorb 8,000 Btus </li></ul><ul><ul><li>Same amount of heat produced by one pound of common combustible material </li></ul></ul><ul><li>Water must be applied at sufficient rate and quantity to reach seat of the fire </li></ul><ul><li>Types of fuel, form, storage arrangement impact effectiveness of water systems </li></ul>
  37. 37. Oxygen Reduction <ul><li>Control of air intake in area of fire helps reduce or remove oxygen supply </li></ul><ul><li>Foam is a commonly used suppression agent </li></ul><ul><ul><li>Covers leaking fuel so oxygen cannot reach the fuel </li></ul></ul><ul><li>Carbon dioxide is heavier than air and displaces oxygen </li></ul><ul><ul><li>Effective in utility vaults </li></ul></ul>
  38. 38. Removing or Interrupting the Fuel Supply <ul><li>Backfires are set in wild land fires to remove fuel ahead of a hostile fire </li></ul><ul><li>Foams prevent liberation of vapors </li></ul><ul><ul><li>Provide cooling to spills and leaks </li></ul></ul><ul><li>Waterflow from sprinklers pre-wets adjacent fuels </li></ul><ul><ul><li>Makes it difficult for fuel to ignite </li></ul></ul>
  39. 39. Interrupting the Chain Reaction <ul><li>Fire sustained by chemical reaction with combustion products </li></ul><ul><li>Dry chemical, halon, and other clean agent suppression products disrupt the chain reaction </li></ul>
  40. 40. Summary <ul><li>Fire triangle/tetrahedron </li></ul><ul><ul><li>Describe relationship between the components required for combustion </li></ul></ul><ul><ul><li>Used by fire prevention codes to prevent hostile fires from occurring </li></ul></ul><ul><li>Fire classification determines type of extinguishment system to use </li></ul><ul><li>Five types of fire; five stages of fire </li></ul><ul><li>Understanding fire behavior is critical </li></ul>

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