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EXPLOSIVES:

EXPLOSIVES:. Effects of an Explosion Classification of Explosives Low Explosives High Explosives Primary Secondary Conclusion. When an explosive is detonated, the material is instantly converted from a solid into a mass of rapidly expanding gases. Causes 3 primary effects: Blast pressure

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EXPLOSIVES:

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  1. EXPLOSIVES: • Effects of an Explosion • Classification of Explosives • Low Explosives • High Explosives • Primary • Secondary • Conclusion • When an explosive is detonated, the material is instantly converted from a solid into a mass of rapidly expanding gases. • Causes 3 primary effects: • Blast pressure • Fragmentation • Thermal effects Taken in part from a seminar by Jim Kahoe and Greg Brown

  2. Effects of an Explosion: Blast Pressure • At the time of detonation, the gases can rush out at velocities of up to 7,000 mph and can exert pressure of up to 700 tons per square inch. • This gas travels in a outward circular pattern like a giant wave, smashing and shattering everything in its path.

  3. Effects of an Explosion: Fragmentation • If a bomb is placed in an enclosed space, part of the energy released will shatter the casing and hurl them outward at 2,700 ft/sec. • Shrapnel – When objects are placed inside the bulk of the explosive material. These will travel faster then fragments because the energy that would have been spent shattering the casing is spent on propelling the shrapnel.

  4. Effects of an Explosion: Incendiary Thermal Effect • The least damaging of the three. • Varies from explosion to explosion. • Low explosives burn slower producing longer thermal effects then high explosives which create a high amount of energy but for only fractions of a second. • Plays a bigger role when combustible materials, such as gasoline, are used.

  5. Classification of Explosives • The speed at which explosives decompose enable explosives to be classified into 2 categories. • Low explosives – Velocity of detonation below 3,000 ft/s. • High explosives – Velocity of detonation above 3,000 ft/s.

  6. Order of Priorities Priority Composition of Products of Decomposition 1 A metal and chlorine Metallic chloride(solid) 2 Hydrogen and chlorine HCl (gaseous) 3 A metal and oxygen Metallic oxide (solid) 4 Carbon and oxygen CO (gaseous) 5 Hydrogen and oxygen H2O (gaseous) 6 CO and oxygen CO2 (gaseous) 7 Nitrogen N2 (elemental) 8 Excess oxygen O2 (elemental) 9 Excess hydrogen H2 (elemental)

  7. Balancing Chemical Explosion Equations * The progression is from top to bottom; you may skip steps that are not applicable, but you never back up. * At each separate step there are never more than two compositions and two products. * At the conclusion of the balancing, elemental forms, nitrogen, oxygen, and hydrogen, are always found in diatomic form. Example, TNT: C6H2(NO2)3CH3; constituents: 7C + 5H + 3N + 6O Using the order of priorities priority 4 gives the first reaction products: 7C + 6O -> 6CO with one mol of carbon remaining Next, since all the oxygen has been combined with the carbon to form CO, priority 7 results in: 3N -> 1.5N2 Finally, priority 9 results in: 5H > 2.5H2 The balanced equation, showing the products of reaction resulting from the detonation of TNT is: C6H2(NO2)3CH3 -> 6CO + 2.5H2 + 1.5N2 + C The number of moles of gas formed is 10. The product, carbon, is a solid.

  8. Volume of Products of Explosion The molecular volume of any gas at 0 °C and under normal atmospheric pressure is very nearly 22.4 liters or 22.4 cubic decimeters. Thus, considering the nitroglycerin reaction. C3H5(NO3)3 -> 3CO2 + 2.5H2O + 1.5N2 + .25O2 One mole of nitroglycerin produces 3 + 2.5 + 1.5 + .25 = 7.25 molecular volumes of gas; and these molecular volumes at 0 °C and atmospheric pressure form an actual volume of 7.25 X 22.4 = 162.4 liters of gas. (Note that the products H2O and CO2 are in their gaseous form.) Further, by employing Charles' Law for perfect gases, the volume of the products of explosion may also be calculated for any given temperature. This law states that at a constant pressure a perfect gas expands 1/273 of its volume at 0 °C, for each degree of rise in temperature. Therefore, at 15 °C the molecular volume of any gas is, V15 = 22.4 (1 + 15/273) = 23.63 liters per mol Thus, at 15 °C the volume of gas produced by the explosive decomposition of one gram molecule of nitroglycerin becomes V = 23.63 l (7.25 mol) = 171.3 liters/mo

  9. Low Explosives • Designed to burn or deflagrate • Used for military and civilian applications • Burning begins at one end of the charge and travels with blinding speed through the entire charge. • Primarily used as a propellant. • Black Powder • Smokeless Powder

  10. Smokeless Powder Black Powder • VOD – Similar to black powder • Composed of nitrocellulose, nitroglycerine, and various stabilizers. • Currently makes up all of the low explosives used for propellants. Can be found in the form of flakes, strips, sheets, balls, or cords. • History – Was perfected in 1884 and first put to military use by the French. • Velocity of Detonation (VOD) – 1,312 ft/s. • Composed of either potassium nitrate or sodium nitrate, charcoal, and sulfur. • History – Thought to originate in China in the 9th century for fireworks and signals. Also evidence of use in England around 1242 and by Arabs around 1300.

  11. High Explosives • Detonate instead of burn • Designed to shatter and destroy • Initiated by blasting cap or detonator • Made up of 2 components: • Primary high explosives • Secondary high explosives • VOD as high as 27,500 ft/s

  12. Primary High Explosives • Deliver an extremely sharp shock to the explosive and breaks the bonds of the molecules of the material and oxidizers. This initiates the explosion. • Extremely sensitive to shock, friction, flame, heat or any combination. • High explosive trains and boosters. • Used in blasting caps • Types of Primary High Explosives. • Lead Azide – VOD – 16,745 ft/s. • Lead Styphnate – VOD – 17,000 ft/s. • Mercury Fulminate – VOD – 14,780 ft/s. • Diazodinitrophenel (DDNP) – VOD – 21,700 ft/s.

  13. Secondary High Explosives TNT- Trinitrotoluene • Relatively insensitive • Manufactured for military and commercial use • TNT • Dynamite • RDX • ANFO • VOD-22,600 feet per second • Very stable among high explosives • Relatively insensitive to blows or friction • Used as booster charge for high explosives

  14. ANFO RDX Dynamite • VOD-26,800 feet/second • White crystalline solid • Usually mixed with other explosives, oils, waxes • Compositions A, B and C • VOD-12,000-15,000 feet/second • Mix of ammonium nitrate w/carbon carriers • Uses: construction, road building, and quarrying • VOD-3,600-23,600 feet/second • Uses: construction, road building, quarrying, mining

  15. Instrumental Methods of Analysis • IR can analyze for organics and nitrates • X-ray diffraction uses x-rays to analyze powders of organic salts. Can reveal the identity of salts • HPLC with ion selective detectors can also detect inorganic components of explosives • AA spectroscopy can reveal metal components of residues

  16. Summary

  17. Sources • DeHaan, John D. Kirk’s Fire Investigation. 4th Ed. Prentice Hall: New Jersey, 1997. • Johnson, Jesse L. Explosives, Propellant Powders, and Related Items. Office of Industries, U.S. International Trade Commission 1998. • National Institute of Justice. Guide for the Selection of Commercial Explosives Detection Systems for Law Enforcement Applications. NIJ Guide 100-99. U.S. Department of Justice 1999. • Nyden, Marc R. A Technical Assessment of Portable Explosives Vapor Detection Devices. NIJ Report 300-89. U.S. Department of Justice 1990. • Saferstein, Richard. Criminalistics: An Introduction to Forensic Science. 7th Ed. Prentice Hall: New Jersey, 2001. • http://www.sonic.net/~brucel/ • http://siri.uvm.edu/ftp/ppt/blast1/tsld001.htm • http://www.ordnance.org/explosives.htm • http://www.fireandsafety.eku.edu/VFRE-99/Recognition/High/high.htm • http://www.fireandsafety.eku.edu/VFRE-99/#Introduction

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