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The Wily Coyote Lecture Fires and Explosions

The Wily Coyote Lecture Fires and Explosions. CME 470. Caution!. Fire vs. Explosion. Fires: release energy slowly Explosions: rapid release of energy. Fire or Explosion?. Fire Triangle. Fuels Solids: plastic, wood dust fiber, metal particles Liquids: gasoline, acetone, ether, pentane

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The Wily Coyote Lecture Fires and Explosions

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  1. The Wily Coyote LectureFires and Explosions CME 470 Eric Grulke. fires & explosions. CME 470

  2. Caution! Eric Grulke. fires & explosions. CME 470

  3. Fire vs. Explosion • Fires: release energy slowly • Explosions: rapid release of energy Eric Grulke. fires & explosions. CME 470

  4. Fire or Explosion? Eric Grulke. fires & explosions. CME 470

  5. Fire Triangle • Fuels • Solids: plastic, wood dust fiber, metal particles • Liquids: gasoline, acetone, ether, pentane • Vapors: acetylene, propane, CO, H2 • Oxidizers • Solids: metal peroxides, ammonium nitrate • Liquids: H2O2, nitric acid, perchloric acid • Vapors: O2, F2, Cl2 • Ignition sources • Sparks • Flames • Static electricity • heat Eric Grulke. fires & explosions. CME 470

  6. The Fire Triangle Eric Grulke. fires & explosions. CME 470

  7. Definitions • Combustion: chemical reaction in which fuel combines with oxidant and releases energy • Ignition: start of the burning process • Autoignition temperature: T such that mixture can self-ignite • Flash Point: lowest temperature at which the liquid will volatilize enough vapor to form an ignitable mixture Eric Grulke. fires & explosions. CME 470

  8. Definitions • Fire point: lowest T at which vapor above a liquid will burn • Flammability limits: burning occurs between LFL and UFL (LEL and UEL) • Explosion: rapid expansion of gases with fast pressure or shock wave • Mechanical Explosion: explosion due to vessel failure, high pressure non-reactive gas Eric Grulke. fires & explosions. CME 470

  9. Definitions • Deflagration: explosion with shock wave moving at a speed lower than speed of sound • Detonation: explosion with shock wave moving faster than speed of sound • Confined explosion: explosion inside vessel or building • Unconfined explosion: flammable gas spill Eric Grulke. fires & explosions. CME 470

  10. Definitions • Boiling liquid expanding vapor explosion (BLEVE): vessel containing liquid at T>Tb ; explosive vaporization of vessel contents • Dust explosion: rapid combustion of fine particles • Shock wave: pressure wave moving through a gas • Overpressure: P as f(shock wave) Eric Grulke. fires & explosions. CME 470

  11. Flammability Characteristics of Liquids and Gases • Liquids – use flash point temperature to characterize the fire and explosion hazards • FPT – determined in open-cup apparatus; open flame over liquid which is heated; closed-cup apparatus gives lower T Eric Grulke. fires & explosions. CME 470

  12. Flammability Characteristics of Liquids and Gases Eric Grulke. fires & explosions. CME 470

  13. Flammability Characteristics of Liquids and Gases Eric Grulke. fires & explosions. CME 470

  14. Flash Point • FP’s are tabulated • Multicomponent mixtures: one component is flammability and its characteristics are known • Estimate is based on the partial pressure of the flammable component K. Satyanarayana, P. G. Rao, Improved equation to estimate flash points of organic compounds, J. Hazardous Materials, 32, 81-85 (1992). Coefficients tabulated for chemical groups. Eric Grulke. fires & explosions. CME 470

  15. Example 6-1. Flash point of MeOH solution Eric Grulke. fires & explosions. CME 470

  16. Saturation Vapor Pressure for Methanol Eric Grulke. fires & explosions. CME 470

  17. Concentration of Flammable Gas (vol%) Eric Grulke. fires & explosions. CME 470

  18. Vapor Flammability • LFLs and UFLs can be computed for mixtures using an equation by Le Chatelier Eric Grulke. fires & explosions. CME 470

  19. LFL = f(T, P) Eric Grulke. fires & explosions. CME 470

  20. Estimating LFL, UFL Cst is the volume % fuel in fuel plus air Eric Grulke. fires & explosions. CME 470

  21. Minimum Oxygen Concentration • LFL is based on fuel in air • A minimum oxygen level is needed to propagate a flame • Below the MOC, the flame cannot generate enough energy to heat the mixture for self-propagation • MOC is estimated using the stoichoimetry of the combustion and the LFL Eric Grulke. fires & explosions. CME 470

  22. Minimum Ignition Energies Eric Grulke. fires & explosions. CME 470

  23. Ignition Sources of Major Fires Eric Grulke. fires & explosions. CME 470

  24. Reaction and Pressure Fronts Propagating Through a Pipe Eric Grulke. fires & explosions. CME 470

  25. Test Apparatus for Acquiring Vapor Explosion Data Eric Grulke. fires & explosions. CME 470

  26. Typical Pressure Versus Time Data Obtained from Explosivity Apparatus Eric Grulke. fires & explosions. CME 470

  27. Pressure Rate and Maximum Explosion Pressure as a Function of Vapor Concentration Eric Grulke. fires & explosions. CME 470

  28. Typical Explosion Data Exhibiting the Cubic Law Eric Grulke. fires & explosions. CME 470

  29. Average Kg Values for Selected Gases Eric Grulke. fires & explosions. CME 470

  30. Average KSt Values for Selected Dusts Eric Grulke. fires & explosions. CME 470

  31. Effect of Initial Pressure on Maximum Explosion Pressure and Rate Eric Grulke. fires & explosions. CME 470

  32. Explosion Data for Propane Showing Peaks Indicative of the Onset of Detonation Eric Grulke. fires & explosions. CME 470

  33. Damage Produced by Overpressure Eric Grulke. fires & explosions. CME 470

  34. Correlation Between Overpressure and Scaled Distance, English Engineering Units Eric Grulke. fires & explosions. CME 470

  35. Correlation Between Overpressure and Scaled Distance, SI Units Eric Grulke. fires & explosions. CME 470

  36. Maximum Horizontal Range of Blast Fragments Eric Grulke. fires & explosions. CME 470

  37. Images from Wikipedia.org Case study: TNT Eric Grulke. fires & explosions. CME 470

  38. 2,4,6-trinitrotoluene CAS Reg # 118-96-7 Formula: C7H5N3O6 Fw = 227.13 kg/kmol Names: TNT, Trotyl, Triton, … Density: 1654 kg/m3 Melting point: 80.35 C; boiling point: 295 C (decomposition) Solubility: 0.13g/L in water; soluble in ether, acetone, benzene, pyridine EU classification: explosive (E), toxic (T), environmental hazard (N) NFPA 704 Trinitrotoluene Eric Grulke. fires & explosions. CME 470

  39. background • Common explosive with convenient handling properties • C6H2(NO2)3CH3 • Standard measure of explosive strength • Synthesis:multi-step process. Nitration of toluene (nitric + sulfuric acid) to MNT/separation/nitration to DNT then nitration to TNT in anhydrous mixtures of nitric acid + oleum. NOX in feed nitric acid must be controlled to prevent oxidation of methyl group. • Stabilization: aqeous sodium sulfite to remove less stable isomers and other byproducts. Rinse water is a significant pollutant. Eric Grulke. fires & explosions. CME 470

  40. applications • Common explosive for military and industrial applications • Low sensitivity to shock & friction; ignition temperature is well above the melting point • Does not sorb water, relatively stable. • Block sizes: 0.25, 0.5 and 1 kg. • Synergistic blends with other exposives Eric Grulke. fires & explosions. CME 470

  41. Explosive characteristics • Explosives decompose to elements, stable molecules (mostly) without the aid of external oxidizing agents. • Exothermic, high activation energy • Carbon is a product, leading to sooty appearance of explosions • Ignition with a high velociy initiator or by concussion • Reference point – Figure of Insensitivity • The Figure of Insensitiveness is determined from impact testing, typically using a drop-weight tower. In this test, a small sample of the explosive is placed on a small steel anvil which is slotted into a recess in the base of the drop tower. A cylindrical, 1 kilogram steel weight (mounted inside a tube to accurately guide its descent to the impact point in the centre of the anvil) is then dropped onto the test specimen from a measured height. The specimen is monitored both during and after this process to determine whether initiation occurs. This test is repeated many times, varying the drop height according to a prescribed method. Various heights are used, starting with a small distance (e.g. 10 cm) and then progressively increasing it to as high as 3 metres. The series of drop heights and whether initiation occurred are analysed statistically to determine the drop height which has a 50% likelihood of initiating the explosives. The intention of these tests is to develop safety policies/rules which will govern the design, manufacturing, handling and storage of the explosive and any munitions containing it. Eric Grulke. fires & explosions. CME 470

  42. Energy content • 4.6 megajoules/kg (energy density) • Nuclear weapons are measured in megatons of TNT • Gunpowder: 3 MJ/kg • Dynamite: 7.5 MJ/kg • Gasoline: 47.2 MJ/kg (gas+O2=10.4 MJ/kg) Eric Grulke. fires & explosions. CME 470

  43. 500 ton TNT explosion, 1965, wikipedia.org Note white blast wave at water surface and condensate cloud caused by shock wave. Eric Grulke. fires & explosions. CME 470

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