Chapter 04
- 1. Introduction to Fire Protection 3rd Edition
- 2. Chapter 4 Chemistry and Physics of Fire
- 3. Objectives Define the difference between the fire triangle and the fire tetrahedron Describe what constitutes an oxidizer Describe what constitutes a fuel Illustrate the states of matter
- 4. Objectives (con’t.) Explain the process of pyrolysis Describe the properties affecting solid fuels Describe the properties affecting liquid fuels Describe the properties affecting gas fuels
- 5. Objectives (con’t.) Differentiate heat and temperature Illustrate the four methods of heat transfer Illustrate the five classifications of fire Describe the four stages of fire
- 6. Introduction Fire can be better controlled by understanding its chemical and physical properties Ability to predict what fire will do with available fuel and where it is headed Ability to choose appropriate extinguishing agent and method of application
- 7. Fire Defined Fire : Rapid self-sustaining oxidation process accompanied by the evolution of heat and light in varying intensities Combustion : A chemical reaction that releases energy as heat and, usually, light
- 8. FIRE TRIANGLE Fuel Heat Oxygen
- 9. FIRE TETRAHEDRON Fuel Heat Oxidizer Chain Reaction Fuel Oxygen
- 11. ELEMENTS OF FIRE FUEL - Something that will Burn. HEAT - Ignition Source, Starts the FIRE OXYGEN - Supports Combustion Chemical Chain Reaction - Must have all three elements.
- 12. Oxidizer Oxygen is the most common Air contains 21% oxygen Increasing amount of oxidizer will increase intensity of fire Other oxidizers include fluorine and chlorine
- 13. Fuel Described as anything that will burn Most common fuels contain carbon and hydrogen Complete combustion yields carbon dioxide and water vapor Most combustion is incomplete due to several factors Size, arrangement, contaminants, lack of sufficient oxidizer Yields smoke and other fire gases
- 14. Fuel (con’t.) Occurs in three states of matter State is often temperature dependent Both fuel and oxidizer must be in gaseous state to combine Pyrolysis : fuel is vaporized by input heat Ignition temperature : when fuel is hot enough to self-sustain combustion
- 15. PYROLYSIS The chemical decomposition of matter through the action of heat Solid and liquid fuels are converted to the gaseous state by the application of energy thru this process i.e. the flame of a candle floating a small distance above the wick
- 17. FIRE TERMS FIRE POINT • The minimum temperature to which a material must be heated in order to sustain combustion after ignition by an external source. • Also called Ignition Temperature.
- 18. Solid Fuels Factors affecting rate of pyrolysis Size Arrangement Continuity Moisture content
- 19. Flame Spread Steiner Tunnel tests how rapidly a fire spreads on interior finishes Measures flame spread, temperature, and smoke density May measure and analyze combustion gases
- 20. Liquid Fuels Liquids flow like water but do not readily separate Specific gravity : weight of a liquid compared to the weight of an equal volume of water Volatility : ease with which a fuel gives off vapors
- 21. Liquid Fuels (con’t.) Vapor pressure : pressure exerted by vapor molecules on the sides of a container Boiling point : when the vapor pressure equals atmospheric pressure Vapor density : relative density of a vapor or gas as compared to air
- 22. Liquid Fuels (con’t.) Flash point : minimum temperature of a liquid at which it gives off vapors sufficient to form an ignitable mixture with air, the lower the Flash point in degrees the more DANGEROUS the fuel. Miscibility : ability of a substance to mix with water
- 23. Gas/Vapor Fuels Gas/vapor fuels : fluid that has neither independent shape nor volume but tends to expand indefinitely Upper flammable limit : maximum concentration of gas or vapor in air above which it is not possible to ignite the vapors (too rich to burn)
- 24. Gas/Vapor Fuels (con’t.) Lower flammable limit : lower concentration of gas or vapor in air below which it is not possible to ignite vapors (too lean) Flammable range : proportion of gas or vapor in air between the upper and lower flammable limits
- 25. Gas/Vapor Fuels (con’t.) Classification of gases Flammable and nonflammable Some nonflammable support combustion (oxygen) Caution : flammable vapors are not always visible
- 27. Heat and Temperature Heat is a form of energy Sources of heat Chemical: breaking down and recombination of molecules Mechanical: friction, friction sparks Electrical: arcs and sparks Nuclear: fission and fusion
- 28. Heat and Temperature (con’t.) British thermal unit (BTU): amount of heat required to raise the temperature of one pound of water one degree Fahrenheit Calorie : amount of heat required to raise the temperature of one gram of water one degree Celsius
- 29. Temperature Measure of the hotness or coldness of something expressed in degrees Fahrenheit Freezing temperature: 32 o Boiling temperature: 212 o Celsius Freezing temperature: 0 o Boiling temperature: 100 o
- 30. Heat Transfer Conduction : transfer of heat through a medium without visible motion Convection : transfer of heat through a circulating medium (see Figure 4-16)
- 33. Heat Transfer (con’t.) Radiation : transfer of heat through wavelengths of energy Direct flame impingement (auto exposure) combines all three (see Figure 4-18)
- 35. Classification of Fires Class A: ordinary combustibles Class B: flammable liquids Class C: energized electrical Class D: combustible metals Class K: cooking materials Note : Many fires involve more than one classification
- 36. CLASS A FIRES • Ordinary Combustible Materials • Wood, Paper, Cloth, Plastic, etc.
- 37. CLASS B FIRES • Flammable & Combustible Liquids • Flammable & Combustible Gases • Gasoline, Kerosene, Grease, Oil
- 38. CLASS C FIRES • Energized Electrical Equipment • Wires, Motors, Switches, Lights, Cables, Receptacles, Computers
- 39. CLASS D FIRES • Combustible Metals • Magnesium, Titanium, Sodium. • Identified by the Suffix “ IUM “ • React Violently with WATER
- 40. Stages of Fire Incipient Smoke and heat produced Free burning Heat production increases Fire spreads to other fuels Smoldering Flames die out, glowing combustion Phases of fire have evolved into four stages
- 41. Stages of Fire (con’t.) Ignition Growth Fully developed Decay
- 42. STAGES OF FIRE INCIPIENT PHASE • Just Started. • Free Burning Fire. • Normal Oxygen 21%. • Don’t Have High Temperatures. • Thermal Balance is not Yet Disturbed. • Breathing is barely affected.
- 43. FIRE BEHAVIOR FREE BURNING PHASE OR GROWTH STAGE • Fire is expanding. • Oxygen Supply less than 21%. • Breathing Difficult, SCBA must be used • Carbon monoxide levels are high. • Temperatures between 1200° - 1600° F.
- 45. Growth Stage (con’t.) Water applied to ceiling to reduce temperatures Flashover may occur if not cooled Tongues of flame roll across ceiling Radiant heat affects materials in room, raising them to ignition temperature Materials in room ignite all at once Firefighters can not survive flashover PPE and breathing apparatus may fail
- 48. Fully Developed Stage All fuels burning Structure Room and contents or entire structure Wildland Fire is moving across the countryside
- 50. FIRE BEHAVIOR SMOLDERING PHASE • Free burning has ended. • Insufficient oxygen. Less than 16%. • Carbon monoxide, fatal range. • Backdraft explosion possible. • Most Dangerous stage to the Firefighter.
- 51. Decay Stage Fire has run out of fuel or oxygen In a sealed environment When oxygen is below 15%, combustion is slowed Pyrolysis continues to occur Room is superheated and charged with smoke and combustible gases If oxygen is introduced, backdraft can occur
- 52. Backdraft Combustible fire gases are prevalent in atmosphere Gases are at or above their ignition temperature Oxygen content is too low for ignition (too rich to burn) Oxygen is introduced Gases ignite with explosive force
- 55. EXTINGUISHMENT of FIRE • Removal of one of the three elements, or by breaking the chemical chain reaction. • Removal of Heat -Water is used to cool the fuel below its ignition temperature. • Removal of Oxygen- Co2 is used to sweep away the oxygen.
- 56. EXTINGUISHMENT of FIRE • Removal of Fuel- Shut off valve, deenergize electrical equipment.
- 57. In order to choose and apply the proper extinguishing agents to fires, you must: Study the physical and chemical properties of fire Understand the combustion process Learn about heat transfer Know the classifications and stages of fire Summary