Essentials of Fire Fighting , 5 th Edition - PowerPoint PPT Presentation

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Essentials of Fire Fighting , 5 th Edition

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  1. Essentials of Fire Fighting, 5th Edition Chapter 3 — Fire Behavior Firefighter I

  2. Chapter 3 Lesson Goal • After completing this lesson, the student shall be able to summarize physical and chemical changes and reactions that occur with fire and the factors involved in fire development. Firefighter I

  3. Specific Objectives 1. Describe physical and chemical changes of matter related to fire. 2. Discuss modes of combustion, the fire triangle, and the fire tetrahedron. 3. Explain the difference between heat and temperature. (Continued) Firefighter I

  4. Specific Objectives 4. Describe sources of heat energy. 5. Discuss the transmission of heat. 6. Explain how the physical states of fuel affect the combustion process. 7. Explain how oxygen concentration affects the combustion process. (Continued) Firefighter I

  5. Specific Objectives 8. Discuss the self-sustained chemical reaction involved in the combustion process. 9. Describe common products of combustion. 10. Distinguish among common classifications of fires. (Continued) Firefighter I

  6. Specific Objectives 11. Describe the stages of fire development within a compartment. 12. Summarize factors that affect fire development within a compartment. 13. Describe methods used to control and extinguish fire. Firefighter I

  7. Matter is… anything that occupies space and has mass (weight). Firefighter I

  8. Physical and Chemical Changes of Matter Related to Fire • Physical change • Water freezing • Water boiling • Chemical reaction • Reaction of two or more substances to form other compounds • Oxidation (Continued) Firefighter I

  9. Physical and Chemical Changes of Matter Related to Fire • Chemical and physical changes • Usually involve exchange of energy • Potential energy released and changed to kinetic energy • Exothermic reaction • Endothermic reaction Firefighter I

  10. Combustion — Modes Firefighter I

  11. Fire Triangle Firefighter I

  12. Fire Tetrahedron Firefighter I

  13. Heat as Energy • Heat is a form of energy. • Potential energy — Energy possessed by an object that may be released in the future • Kinetic energy — Energy possessed by a moving object Firefighter I

  14. Temperature • Temperature is a measurement of kinetic energy • Heat energy moves from objects of higher temperature to those of lower temperature. • Understanding this movement is important Firefighter I

  15. Measuring energy • Not possible to measure directly • Work means increasing temperature • Measured in joules in International System of Units or metric system • Measured in British thermal units in customary system Firefighter I

  16. Scales Used to Measure Temperature • Celsius — Metric • Fahrenheit — Customary Firefighter I

  17. Conversion of Energy Into Heat • Heat is the energy component of tetrahedron • Fuel is heated = temperature increases • Starting ignition • Forms of ignition Firefighter I

  18. Chemical Heat Energy • Most common heat source in combustion reactions • Oxidation almost always results in production of heat • Self-heating Firefighter I

  19. Electrical Heat Energy • Can generate temperatures high enough to ignite any combustible materials near heated area • Can occur as • Resistance • Overcurrent/overload • Arcing • Sparking Firefighter I

  20. Mechanical Heat Energy • Generated by friction or compression • Movement of two surfaces against each other creates heat of friction • Movement results in heat and/or sparks being generated • Heat of compression generated when gas compressed Firefighter I

  21. Transfer of Heat • Basic to study of fire behavior • Affects growth of any fire • Knowledge helps firefighters estimate size of fire before attacking • Heat moves from warmer objects to cooler objects (Continued) Firefighter I

  22. Transfer of Heat • Rate related to temperature differential of bodies and thermal conductivity of material • Greater the temperature differences between bodies, greater the transfer rate • Measured as energy flow over time Firefighter I

  23. Conduction • Transfer of heat within a body or to another body by direct contact • Occurs when a material is heated as a result of direct contact with heat source • Heat flow depends on several factors Firefighter I

  24. Convection • Transfer of heat energy from fluid to solid surface • Transfer of heat through movement of hot smoke and fire gases • Flow is from hot fire gases to cooler components Firefighter I

  25. Radiation • Transmission of energy as electromagnetic wave without intervening medium (Continued) Firefighter I

  26. Radiation • Thermal radiation results from temperature • Affected by several factors • Energy travels in straight line at speed of light Firefighter I

  27. Passive Agents • Materials that absorb heat but do not participate in combustion • Fuel moisture = passive agent • Relative humidity and fuel moisture Firefighter I

  28. Fuel • Material being oxidized in combustion process • Reducing agent • Inorganic or organic; organic most common (Continued) Firefighter I

  29. Fuel • Organic can be broken into: • Hydrocarbon-based • Cellulose-based • Key factors influencing combustion process • Physical state of fuel • Distribution or orientation of fuel Firefighter I

  30. Gaseous Fuel • Must be gaseous for flaming combustion • Methane, hydrogen, etc. most dangerous because exists naturally in state required for ignition • Has mass but no definite shape or volume Firefighter I

  31. Liquid Fuel • Has mass and volume but no definite shape except for flat surface • Assumes shape of container • Will flow downhill and pool in low areas • Density is compared to that of water • Must be vaporized in order to burn Firefighter I

  32. Liquid Fuel Characteristics Flash point (Continued) Firefighter I

  33. Liquid Fuel Characteristics • Fire point • Surface area • Solubility • Fire fighting considerations Firefighter I

  34. Solid Fuel • Definite size and shape • May react differently when exposed to heat • Pyrolysis evolves solid fuel into fuel gases/vapors. • As it is heated, begins to decompose, giving off combustible vapors (Continued) Firefighter I

  35. Solid Fuel • Commonly the primary fuel • Surface-to-mass ratio — Primary consideration in ease or difficulty of lighting • Proximity/orientation of solid fuel relative to source of heat affects the way it burns Firefighter I

  36. Heat of Combustion/Heat Release Rate • Heat of combustion — Total amount of energy released when a specific amount of fuel is oxidized • Usually expressed in kilojoules/gram (kJ/g) • Heat release rate (HRR) — Energy released per unit of time as fuel burns • Usually expressed in kilowatts (kW) Firefighter I

  37. Oxygen • In air, is the primary oxidizing agent in most fires • Air consists of about 21 percent oxygen • Other materials can react with fuels in same way Firefighter I

  38. Oxygen Concentrations • At normal ambient temperatures, materials can ignite/burn at concentrations as low as 14 percent. • When limited, flaming combustion may diminish; combustion will continue in surface or smoldering mode. (Continued) Firefighter I

  39. Oxygen Concentrations • At high ambient temperatures, flaming combustion may continue at much lower oxygen concentrations. • Surface combustion can continue at extremely low oxygen concentrations. (Continued) Firefighter I

  40. Oxygen Concentrations • When higher than normal, materials have different burning characteristics. • Fires in oxygen-enriched atmospheres are difficult to extinguish and present a potential safety hazard. • Flammable explosive range — Range of concentrations of fuel vapor and air Firefighter I

  41. Self-Sustained Chemical Reaction • Very complex • Example: Combustion of methane and oxygen (Continued) Firefighter I

  42. Self-Sustained Chemical Reaction Firefighter I

  43. Flaming Combustion • Sufficient heat causes fuel/oxygen to form free radicals, initiates self-sustained chemical reaction • Fire burns until fuel/oxygen exhausted or extinguishing agent applied • Agents may deprive process of fuel, oxygen, sufficient heat for reaction Firefighter I

  44. Surface Combustion • Distinctly different from flaming combustion • Cannot be extinguished by chemical flame inhibition • Must be extinguished by working on one side of the fire triangle Firefighter I

  45. General Products of Combustion Include Heat, Smoke, Light • Heat, smoke impact firefighters most • Heat generated during fire helps spread fire • Lack of protection from heat may cause burns and other health issues • Toxic smoke causes most fire deaths Firefighter I

  46. Common Products of Combustion • Carbon monoxide • Hydrogen cyanide • Carbon dioxide Firefighter I

  47. Hazards to Firefighters • Toxic effects of smoke inhalation not results of any one gas • Smoke contains a wide range of irritating substances that can be deadly • Firefighters must use SBCA when operating in smoke Firefighter I

  48. Flame • Visible, luminous body of a burning gas • Becomes hotter, less luminous when burning gas mixes with proper amounts of oxygen • Loss of luminosity caused by more complete combustion of carbon • Product of combustion Firefighter I

  49. Class A Fires • Involve ordinary combustible materials • Primary mechanism of extinguishment is cooling to reduce temperature of fuel to slow or stop release of pyrolysis products Firefighter I

  50. Class B Fires • Involve flammable and combustible liquids and gases • Those involving gases can be extinguished by cutting off gas supply • Can be extinguished with appropriately applied foam and/or dry chemical agents Firefighter I