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CVFD Training – Fire Behavior

CVFD Training – Fire Behavior. SFFMA Training Objectives: 15-01.01 – 15-01.11. Matter is…. anything that occupies space and has mass (weight). Physical and Chemical Changes of Matter Related to Fire. Physical change Water freezing Water boiling Chemical reaction

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CVFD Training – Fire Behavior

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  1. CVFD Training – Fire Behavior SFFMA Training Objectives: 15-01.01 – 15-01.11

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

  3. 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

  4. 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

  5. DISCUSSION QUESTION What are some examples of physical and chemical changes of matter? Firefighter I

  6. Combustion — Modes Firefighter I

  7. Fire Triangle Firefighter I

  8. Fire Tetrahedron Firefighter I

  9. 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

  10. 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

  11. 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

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

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

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

  15. 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

  16. 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 (Continued) Firefighter I

  17. Mechanical Heat Energy Firefighter I

  18. DISCUSSION QUESTION What are some examples of chemical, electrical, and mechanical sources of heat energy? Firefighter I

  19. 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

  20. 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

  21. 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

  22. 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

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

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

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

  26. DISCUSSION QUESTION What is the impact of high fuel moisture on fire spread? Firefighter I

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

  28. 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

  29. 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

  30. 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

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

  32. DISCUSSION QUESTION From a practical standpoint, why should the flash point generally be considered the temperature at which a liquid or gas will sustain combustion? 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 (Continued) Firefighter I

  35. Solid Fuel • Pyrolysis evolves solid fuel into fuel gases/vapors. • As it is heated, begins to decompose, giving off combustible vapors (Continued) Firefighter I

  36. Solid Fuel • Commonly the primary fuel • Surface-to-mass ratio — Primary consideration in ease or difficulty of lighting (Continued) Firefighter I

  37. Solid Fuel • Proximity/orientation of solid fuel relative to source of heat affects the way it burns Firefighter I

  38. 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

  39. 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

  40. 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

  41. 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

  42. 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

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

  44. Self-Sustained Chemical Reaction Firefighter I

  45. 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

  46. 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

  47. 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

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

  49. 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

  50. 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

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