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Fire Behavior

5. Fire Behavior. Objectives (1 of 4). Describe the chemistry of fire. Define the three states of matter. Describe how energy and work are interrelated. Describe the conditions needed for a fire. Explain the chemistry of combustion. Describe the products of combustion.

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Fire Behavior

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  1. 5 Fire Behavior

  2. Objectives (1 of 4) • Describe the chemistry of fire. • Define the three states of matter. • Describe how energy and work are interrelated. • Describe the conditions needed for a fire. • Explain the chemistry of combustion. • Describe the products of combustion.

  3. Objectives (2 of 4) • Explain how fires can spread by conduction, convection, and radiation. • Describe the four methods of extinguishing fires. • Define Class A, B, C, D, and K fires. • Describe the characteristics of solid-fuel fires.

  4. Objectives (3 of 4) • Describe the ignition phase, growth phase, fully developed phase, and decay phase of a fire. • Describe the characteristics of a room-and-contents fire. • Explain the causes and characteristics of flameover, flashover, thermal layering, and backdraft.

  5. Objectives (4 of 4) • Describe the characteristics of liquid-fuel fires. • Define the characteristics of gas-fuel fires. • Describe the causes and effects of a boiling liquid expanding vapor explosion (BLEVE). • Describe the process of reading smoke.

  6. Introduction • Fire has been around since the beginning of time. • Destruction of lives and property by uncontrolled fires has occurred since just as long.

  7. The Chemistry of Fire • Understanding the conditions needed for a fire to ignite and grow will increase your effectiveness. • Being well trained in fire behavior will allow the fire fighter to control a fire utilizing less water.

  8. What Is Fire? • Rapid chemical process that produces heat and usually light • Fire is neither solid nor liquid. • Wood is a solid, gasoline is a liquid, and propane is a gas—but they all burn.

  9. Matter • Atoms and molecules • Three states • Solid • Liquid • Gas

  10. Solids • Definite shape • Stokes most uncontrolled fires • Expands when heated and contracts when cooled

  11. Liquids • Assume the shape of their containers • Most will turn into gases when sufficiently heated • Has a definite volume

  12. Gases • Have neither independent shape nor volume • Expand indefinitely • Mixture of gases in air maintain a constant composition • 21% Oxygen • 78% Nitrogen • 1% Other gases

  13. Fuel • Form of energy • Energy released in the form of heat and light has been stored before it is burned

  14. Types of Energy • Chemical • Mechanical • Electrical • Light • Nuclear

  15. Chemical Energy • Energy created by a chemical reaction. • Some of these reactions produce heat and are referred to as exothermic reactions. • Some of these reactions absorb heat and are referred to as endothermic reactions.

  16. Mechanical Energy • Converted to heat when two materials rub against each other and create friction • Heat is also produced when mechanical energy is used to compress air in a compressor.

  17. Electrical Energy • Produces heat while flowing through a wire or another conductive material • Other examples of electrical energy • Heating elements • Overloaded wires • Electrical arcs • Lightning

  18. Light Energy • Caused by electromagnetic waves packaged in discrete bundles called photons • Examples of light energy • Candles • Light bulbs • Lasers

  19. Nuclear Energy • Created by nuclear fission or fusion • Controlled (nuclear power plant) • Uncontrolled (atomic bomb explosion) • Release radioactive material

  20. Conservation of Energy • Energy cannot be created or destroyed by ordinary means. • Energy can be converted from one form to another. • Chemical energy in gasoline is converted to mechanical energy when a car moves along a road.

  21. Conditions Needed for Fire • Three basic factors required for combustion: • Fuel • Oxygen • Heat • Chemical chain reactions keep the fire burning.

  22. Chemistry of Combustion (1 of 2) • Compounds of atoms and molecules • Almost all fuels are hydrocarbons • Consist of both hydrogen and carbon atoms • Wide variety of other molecules that release toxic by-products • Incomplete combustion produces large quantities of deadly gases

  23. Chemistry of Combustion (2 of 2) • Oxidation • Combustion • Pyrolysis

  24. Products of Combustion • Combustion produces smoke and heat. • Specific products depend on: • Fuel • Temperature • Amount of oxygen available • Few fires consume all available fuel.

  25. Smoke • Airborne products of combustion • Consists of: • Ashes • Gases • Aerosols • Inhalation of smoke can cause severe injuries.

  26. Smoke Contents (1 of 2) • Particles • Solid matter consisting of unburned, partially, or completely burned substances • Vapors • Small droplets of liquids suspended in air • Oils from the fuel or water from suppression efforts

  27. Smoke Contents (2 of 2) • Gases • Most gases produced by fire are toxic. • Common gases include: • Carbon monoxide • Hydrogen cyanide • Phosgene

  28. Fire Spread • Three methods of fire spread: • Conduction • Convection • Radiation

  29. Conduction • Heat transferred from one molecule to another (direct contact) • Good conductors absorb heat and transfer it throughout the object.

  30. Convection • Circulatory movement in areas of differing temperatures • Creates convection currents

  31. Convection Within a Room • Hot gases rise, then travel along the ceiling. • Convection may carry the fire outside the room of origin

  32. Radiation • Transfer of heat in the form of an invisible wave • Travels in all directions • Is not seen or felt until it strikes an object and heats its surface

  33. Methods of Extinguishment • Cool the burning material. • Exclude oxygen. • Remove fuel. • Break the chemical reaction.

  34. Classes of Fire • Five classes of fires: • Class A • Class B • Class C • Class D • Class K

  35. Class A • Involve ordinary solid combustibles • Wood • Paper • Cloth • Cool the fuel with water

  36. Class B • Involve flammable or combustible liquids • Gasoline • Kerosene • Oils • Shut off the fuel supply or use foam to exclude oxygen from the fuel

  37. Class C • Involve energized electrical equipment • Attacking a Class C fire with an extinguishing agent that conducts electricity can result in injury or death.

  38. Class D • Involve combustible metals • Sodium • Magnesium • Titanium • The application of water will result in violent explosions • Must be attacked with special agents

  39. Class K • Involve combustible cooking oils and fats • Special extinguishers are available to handle this type of fire.

  40. Solid Fuels • Most fires encountered involve solid fuels. • Do not actually burn in the solid state • Must be heated or pyrolyzed to decompose into vapor • May change directly from a solid to a gas • Wood does not have a fixed ignition temperature

  41. Solid-Fuel Fire Development • Four distinct phases: • Ignition • Growth • Fully developed • Decay

  42. Ignition Phase • Fuel, heat, and oxygen are present. • Flame produces a small amount of radiated energy. • Convection and radiation heat the fuel.

  43. Growth Phase • Kindling starts to burn, increasing convection of hot gases upward. • Energy radiates in all directions. • Major growth in an upward direction

  44. Fully Developed Phase • Produces the maximum rate of burning • Fire will burn as long as fuel and oxygen remain.

  45. Decay Phase • Fuel is nearly exhausted • Rate of burning slows • Flames become smoldering embers

  46. Key Principles of Solid-Fuel Fire Development (1 of 2) • Hot gases and flame tend to rise. • Convection is the primary factor in spreading the fire upward. • Downward spread occurs primarily from radiation and falling chunks of flaming material. • If there is no remaining fuel, the fire will go out.

  47. Key Principles of Solid-Fuel Fire Development (2 of 2) • Variations in the direction of fire spread occur if air currents deflect the flame. • The total material burned reflects the intensity of the heat and the duration of the exposure to the heat. • An adequate supply of oxygen must be available to fuel a free-burning fire.

  48. Room Contents • Synthetic products prevalent today made from petroleum products. • These produce dense smoke that can be highly toxic. • Newer paints • Carpets • Furniture

  49. Ignition Phase • Flame begins small and localized • Convection of hot gases is the primary means of fire growth • Fire could probably be extinguished with a portable fire extinguisher

  50. Growth Phase • Additional fuel is drawn into the fire. • Convection current carries hot gases to the ceiling • Flames spread upward and outward • Radiation starts to play a greater role • Growth is limited by the fuel and oxygen available

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