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The Chemistry of Fire

The Chemistry of Fire. Sanford Herzon – Forensic Science Instructor Thomas Wootton High School. Objectives. 1. Define fire in terms of matter & energy 2. Define combustion 3. Define oxidation 4. Requirements for explosions

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The Chemistry of Fire

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  1. The Chemistry of Fire Sanford Herzon – Forensic Science Instructor Thomas Wootton High School

  2. Objectives 1. Define fire in terms of matter & energy 2. Define combustion 3. Define oxidation 4. Requirements for explosions 5. Identify famous fires that sparked legislation for fire safety

  3. Is fire matter?

  4. What is Matter? • Matter is anything that has mass and occupies space. • The flame itself is a mixture of gases • oxygen, carbon dioxide, carbon monoxide, water vapor, and vaporized fuel. • ……and so is matter.

  5. …and what is energy? • The light produced by the flame is energy, …not matter. • The heat produced is also energy, …not matter.

  6. Combustion Combustion is a type of oxidation reaction that generates light, heat, gases and soot (mostly carbon particles)

  7. Oxidation • Oxidation means to be chemically combined with oxygen. • .

  8. C + O2  --> CO2(This reaction occurs when there is enough oxygen for the formation of carbon dioxide.)

  9. 2C + O2--> 2CO(This reaction occurs when there is only enough oxygen for the formation of carbon  monoxide.)

  10. 2H2  + O2--> 2H2O

  11. Combustion or Oxidation? A combustion reaction occurs between alcohol and oxygen, producing heat and light (energy) and carbon dioxide and water. C2H5OH + 4 O2 -> 2 CO2 + 3 H2O + energy

  12. Calcium Carbide Very Dangerous!!!

  13. Calcium carbide (CaC2) reacts with water to form acetylene (C2H2), a gas used as a fuel in welding.CaC2 (s) + 2 H2O(l) ---> C2H2 (g) + Ca(OH) 2(s)

  14. Acetylene Torches

  15. Explosions Defined

  16. Acoustics assembly plant in Kentucky in 2003. 7 deaths.

  17. Dust explosion at an automotive parts plant in Indiana in 2003 set of by aluminum dust particles.

  18. How it happens Requirements for big booms. • Quick increase of volume of a gas or particles • Pressure • Oxygen Examples: Dust explosions, Nuclear explosions, Chemical explosions & Volcanic explosions

  19. Potassium Chlorate Demo

  20. Potassium Chlorate • KClO3, is a white, crystalline or powdery solid which is a very good oxidizing agent. • It is used in explosives, fireworks, matches, etc.  • When it decomposes under heating (or with catalyst like sulfuric acid), it releases molecular oxygen, O2: • 2KClO3(s)  —heat—>  2KCl(s)  +  3O2(g)

  21. In the presence of a catalyst such as sulfuric acid, potassium chlorate and table sugar react violently! • This releases large quantities of heat energy, a spectacular purplish flame, and a great deal of smoke.  • (The purple hue of the flame is due to the heating of the potassium.)

  22. 2 KClO3 + H2SO4 → 2 HClO3 + K2SO4 When sugar is added to this reaction, it burns: 8HClO3 + C12H22O11 → 11 H2O + 12 CO2 + 8 HCl

  23. These reactions release the energy you feel as heat and light.

  24. Famous Fires & Their Causes • MGM in Las Vegas - electrical • Triangle Fire - unknown • Great Chicago Fire – rumor/cow • San Francisco Fire - earthquake • Kobe City - earthquake • Texas City – explosions/smoking • King’s Cross – discarded match • Stardust - arson • Meridian Fire – spontaneous combustion • Hong Kong Office – welders spark

  25. 1871-The Great Chicago Fire • Rumored to be started by a cow kicking over a lantern in Mrs. O’leary’s barn. • The fire started on October 8 and burned until October 10th. • The fire destroyed four square miles and killed hundreds.

  26. Chicago Water Tower is one of the few buildings that survived the Great Fire. • Located on the Near North Side. • Today the building serves as an office of tourism.

  27. 1980-MGM Grand Casino - Las Vegas, Nevada • MGM killed 84 people • 679 injured • Still to date, largest # of hotel fire deaths. • Cause was determined to be an electrical problem. • Originated in the deli and quickly spread throughout the hotel. • The fire investigation report can be found at http://www.co.clark.nv.us/firedept/ccfd_mgm.htm.

  28. 2001 – Twin Towers, NYC • 2605 people died in the Towers and on the ground. • 147 died on the two airplanes that crashed into the buildings. • American #11 • United #175

  29. Fires That Sparked Prevention Iroquois Theater, Chicago, IL • Iroquois Theatre Fire -1903 • Oil painted canvas backdrops set fire by stage lights. 602 deaths. • New fire code required all public buildings to have doors open outwards. • Exits must be clearly marked. • Fire drills required in public venues.

  30. 1911- Triangle Fire in New York • 146 immigrant workers died in Greenwich Village, NYC • The record held up until September 11. • This incident lead to national legislation for labor reform and work safety.

  31. New London School (Texas) Explosion – 1937 • Natural gas explosion killing over 300 people mostly children. • Worldwide change – natural gas is mixed with a Thiol – organic sulfur compound

  32. Cocoanut Grove Nightclub Fire – 1942 • Boston nightclub had decorative wall & ceiling covered with paper palm trees. Lit by a match, fire killed 492 patrons. Dwelling capacity was under 500 but over 1000 attended. Only exit was single revolving door. • New Fire Code – Ban on flammable decorations in public places and single revolving doors.

  33. Winecoff Hotel Fire (Atlanta) – 1946 • Guests trapped on upper floors as hotel only had one exit stairway. No sprinkler system. 119 died. • Installation of Fire Alarms & Fire Escapes in tall public buildings

  34. Our Lady of the Angels School Fire -1958 • Fire in a Catholic Elementary School in Chicago. 92 children and 3 teachers died. • New Fire Codes – automated fire alarms, no petroleum based wax on floors, guidelines for placement of fire extinguishers.

  35. Fire Drills in Schools Montgomery County, Maryland requires that ten drills be held during the school year, with two during the first thirty days of school, and one per month thereafter

  36. There are two types of ignition Piloted Ignition This particular kind of ignition consists of a spark or a small flame providing the initial energy for a fire to ignite Spontaneous Ignition This is the result of a flame developing spontaneously in a flammable mixture of gases

  37. Elements of Fire Fuel – solids, liquids, gases Heat – high molecular activity Oxygen – O2 cause an uninhibited chain reaction

  38. FUELS

  39. Fuels can be solids, liquids or gases • SOLIDS LIQUIDS GASES • Wood DieselNatural Gas • Paper Petrolpetroleum gas • RubberAlcoholAcetylene

  40. HEAT

  41. Heat is a measure of the molecular activityoccurring within a substance. The higher the temperature, the faster the action of the molecules.

  42. OXYGENCombustion is a chemical reactionthat requires oxygen.  In most cases, oxygen for a fire is taken from the air

  43. Did you know?Normal atmosphere contains approximately 21 percentoxygen.  Burning will usually slow when the oxygen concentration is reduced to below 14 percent.

  44. THIS ALSO HAPPENS TO BE THE CONCENTRATION AT WHICH ANINDIVIDUAL WILL LOSE CONSCIOUSNESSbelow 14%

  45. The Chemistry of Fire Extinction • The principles of fire extinction consist of the elimination or removal of one or more of the four elements. • Fuel • Oxygen • Heat • Chain reaction

  46. Cooling • The most commonly used fire fighting medium is water. Water absorbs heat from the fire and cools the fuel to a temperature where it no longer produces flammable vapors

  47. Extinguishing • By excluding the oxygen in the surrounding atmosphere, the fire will be extinguished

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