The document discusses the basics of fire behavior including: 1) The fire triangle/tetrahedron which depicts the relationship between fuel, heat, and oxygen/chemical chain reaction required for combustion. 2) The different classes of fire (A-K) and their corresponding extinguishing agents. 3) The five types of fires - diffusion, smoldering, spontaneous combustion, self-heating, and premixed flame. 4) The five stages of fire - pre-ignition, ignition, growth, fully developed, and decay.

1. Basics of Fire Behavior Chapter 1

2. Learning Objectives Describe the difference between fire and combustion Describe the fire triangle and fire tetrahedron List and describe the classes of fire and their relationship to extinguishing agents List and describe the different types of fire

3. Learning Objectives (continued) List and describe the different stages of fire List and describe methods of heat transfer List and describe methods used to extinguish fires

4. Introduction Understanding of fire behavior is necessary to manage a hazard Fire protection systems address a specific type and size of hazard Understanding of fire chemistry is necessary to assess the fire hazard Understanding of fire behavior is the basis for every manual fire attack

5. Fire and Combustion Fire is beneficial when correctly managed and destructive when not managed Combustion : combustible material and an oxidizing agent produce heat or energy and other products Heat must be generated more rapidly than it is dissipated to continue the process Fire produces energy in form of heat, light, and flame Requires a combustible fuel, heat source, and oxygen

6. The Fire Triangle Depicts relationship between fuel, air, and heat All three elements must be present in sufficient quantities Changing proportion determines whether fire will smolder, burn slowly, burn rapidly Many methods are used to extinguish a fire

7. The Fire Tetrahedron Depicts fire’s nature as uninhibited, chemical, self-sustaining chain reaction After ignition occurs All four elements must be present Elimination of any results in extinguishment Figure 1-2 The fire tetrahedron

8. Classes of Fire Early 1900s Underwriters Laboratories developed fire categorization Based on extinguishing agent Fires involve different materials Wrong agent could compound the hazard Matches extinguishing agent to fire hazard Labels bearing the classification on packaging and literature

9. Class A Fires and Extinguishing Agents Class A fires : ordinary combustibles such as cloth, grain, paper, rubber, wood Class A materials release approximately 8000 Btu per pound Water is the most effective suppression agent Absorbs heat; reduces temperature below ignition temperature Using water or Class A foam may be better than dry chemical agents and halon gas mixtures

10. Class B Fires and Extinguishing Agents Class B fires: flammable and combustible liquids and gases Class B agents smother or blanket Interrupt the chemical chain reaction Keep oxygen away from flammable vapors Typical agents: foams, carbon dioxide, dry chemical agents, halons

11. Class C Fires and Extinguishing Agents Class C fires : energized electrical equipment Shutting off electricity is critical May require additional suppression activities Only fires involving electrical equipment are class C fires When electricity is no longer involved, fire is reclassified

12. Class D Fires and Extinguishing Agents Class D fires : combustible metals Manufacturing process releases metal dust and particles Potentially explosive if airborne Class D extinguishing agents are “dry powder” and inert Reduce oxygen concentration Extremely hazardous

13. Class K Fires and Extinguishing Agents Class K fire: fires in cooking appliances using combustible oils and fats Class K agents extinguish by saponification Fatty acids in cooking medium react with extinguishing agent and convert to foam Soapy foam blankets surface of burning liquid Cools liquid below autoignition temperature

14. Other Fire Classification Systems US and Canada use same classification system Europe and Australia use different classification systems Different parts of the world have different classification systems All classification systems are practical

15. Fire and Flame Types Four types of fire: Diffusion flame Smoldering Spontaneous combustion Self-heating Premixed flame Each requires fuel, source of heat, and oxygen Each type of fire has unique characteristics

16. Diffusion Flame Flame we see when we light a match Most natural flame fires are diffusion flames Result of combustible gas emitted by burning material mixed with oxygen Moves into reaction zone on either side of the flame Combustion products diffuse from the flame

17. Figure 1-8 Schematic of a diffusion flame

18. Smoldering Example: glow of charcoal in grill No flame, but heat Air flows over the material surface, providing oxygen for combustion Erupts into flame when sufficient oxygen and heat generated May also be final phase of earlier fire event

19. Figure 1-9 Common examples of a smoldering fire

20. Spontaneous Combustion and Self-Heating Material undergoes oxidation where heat dissipation limited Oxidation creates heat that cannot be dissipated Temperature increases and promotes the reaction Material smolders or flames if heat is sufficient

21. Figure 1-10 Examples of fuel arrays prone to spontaneous combustion

22. Premixed Flame Requires gas fuel and air mix to ignite Gas fuel must be within flammable limits Lower and upper limit where mixture ignites Example: acetylene flammable limit range 2.5% to 100% Changes in atmospheric pressure can alter flammable limit range Knowing flammable limits is important to managing an incident

23. Figure 1-11 Examples of premixed flames

24. The Stages of Fire Fires develop and evolve in stages: Pre-ignition Ignition Growth Fully developed Decay or smoldering Fire suppression methods must be appropriate for the conditions

25. Pre-ignition Stage Requires some form of energy transfer Usually in the form of heat Generates gas from the fuel, which mixes with air Fuel, in gas form, and oxygen must be in proper mixture to ignite

26. Ignition Stage Three things are necessary to start a fire: Heat source Fuel Oxygen Ignition occurs when more heat generated than dissipated After ignition, no additional heat needed to continue the chain reaction

27. Growth Stage Adequate oxygen must be available May be gaseous or chemical oxidizer Amount of oxygen affects speed of growth Amount, type, form of fuel are significant Structure size, shape of walls, ceilings and roofs have significant impact

28. Fully Developed Stage Combustible contents of compartment totally in flame Flashover : transition between growth stage and fully developed stage All combustible contents heat to ignition point and simultaneously ignite Leads immediately to full development Stage regulated by amount of air and fuel

29. Decay Stage Fuel exhausted or oxygen level drops below 16% Burning in the form of glowing combustion Continues until: All fuel is completely exhausted Temperature drops below ignition point Introduction of air may regenerate the fire

30. Forms of Heat Transfer Three types of heat transfer: Conduction Convection Radiation Hostile fires develop by heat transfer Used every day to cook and heat homes Key to reducing fire spread and extinguishing fires

31. Conduction Transfer of heat from one body to another by direct contact When exposing objects to heat, movement of molecules increases Heat energy attempts to move to lower temperature areas or objects Rate of heat transfer dependent on efficiency of material as conductors

32. Convection Transfer of heat from one body to another through a medium such as liquid or gas Example: automobile radiators In building fires, heat transfers through the air in convection currents Size and shape of fire compartment influences effect of convection Hurricane force winds can be generated due to updraft of convection currents

33. Figure 1-18 Convection. As air is heated, its molecules become excited and seek more space

34. Radiation Transfer of heat through electro-magnetic energy, such as light Radiant heat travels in a straight line Has significant impact on the speed at which flashover occurs Radiation is significant cause of fire spread from building to building

35. Methods of Extinguishing Fires Four methods to extinguish fires: Cooling Oxygen reduction Removing fuel supply Interrupting the chain reaction Same basic methods used in design of extinguishment systems

36. Cooling One gallon of water can absorb 8,000 Btus Same amount of heat produced by one pound of common combustible material Water must be applied at sufficient rate and quantity to reach seat of the fire Types of fuel, form, storage arrangement impact effectiveness of water systems

37. Oxygen Reduction Control of air intake in area of fire helps reduce or remove oxygen supply Foam is a commonly used suppression agent Covers leaking fuel so oxygen cannot reach the fuel Carbon dioxide is heavier than air and displaces oxygen Effective in utility vaults

38. Removing or Interrupting the Fuel Supply Backfires are set in wild land fires to remove fuel ahead of a hostile fire Foams prevent liberation of vapors Provide cooling to spills and leaks Waterflow from sprinklers pre-wets adjacent fuels Makes it difficult for fuel to ignite

39. Interrupting the Chain Reaction Fire sustained by chemical reaction with combustion products Dry chemical, halon, and other clean agent suppression products disrupt the chain reaction

40. Summary Fire triangle/tetrahedron Describe relationship between the components required for combustion Used by fire prevention codes to prevent hostile fires from occurring Fire classification determines type of extinguishment system to use Five types of fire; five stages of fire Understanding fire behavior is critical