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Explosives and Explosions

Explosives and Explosions. I. Characteristics of Explosives and Explosions. An explosion is a very rapid chemical reaction that produces heat and gaseous products Explosions produce a large amount of heat (an exothermic reaction) in a very short time period

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Explosives and Explosions

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  1. Explosives and Explosions

  2. I. Characteristics of Explosives and Explosions • An explosion is a very rapid chemical reaction that produces heat and gaseous products • Explosions produce a large amount of heat (an exothermic reaction) in a very short time period • Molecular fragmentation converts the solid explosive material into an enormous number of gas molecules which will occupy a much greater volume, further enhanced by the very high temperature of the explosion

  3. I. Characteristics of Explosives and Explosions • The rapidly expanding gases compress the air creating a physical force known as a shock wave • It is the shock wave that is responsible for much of the damage associated with an explosion

  4. II. The Three Major Classes of Explosives 1. Low Explosives: • Low explosives are materials that burn rapidly and will only explode if contained • Examples include smokeless powder and fireworks (pyrothechnics) • Smokeless powders consist of nitrocellulose and black powder

  5. II. The Three Major Classes of Explosives 2. Primary High Explosives: • Are used as primers or detonators • Are sensitive to shock, heat, and electrical spark • Examples include nitroglycerine, and mercury fulminate & lead styphnate which are used as primers in cartridges and blasting caps

  6. II. The Three Major Classes of Explosives 3. Secondary High Explosives: • High explosives do not have to be contained to explode • Are relatively stable and safe to handle • Initiation requires an electrical spark, fuse, intense heat, or sharp blow • Examples include dynamite, TNT, PETN, RDX, & ammonium nitrate

  7. III. The Explosive Train or Device • The explosive train is the combination of components needed for a successful explosion (i.e. a bomb) • An explosive device or train has three primary components: • The igniter starts the event (e.g. a spark) • The primer or detonator contains a primary high explosive (e.g. blasting cap) • The main charge is a low explosive or secondary high explosive (e.g. dynamite)

  8. IV. The Role of the Scene Investigator • The investigator must sort through all of the debris to find any portion of the explosive device and residue • The debris is examined and any large pieces that do not appear to have been near the center of the explosion are removed • The remaining debris is sifted through screens and examined for portions of the explosive device or items that show evidence of being close to the seat of the explosion • Promising pieces are forwarded to the lab

  9. V. Laboratory Analysis of Explosives and Explosive Residues 1. Examination of an Unexploded Device: • The device must first be rendered safe • A detailed description is then made of each component and how they are connected to form the explosive train • The chemical nature of the explosive ingredients is then determined, as an investigative lead and possible identification of the manufacturer

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