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Analysis of Explosives

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joer
24 diapositives · 520 Views · Jan 01, 2020

Learn about the chemistry of explosions, analysis methods of explosives, and the role of forensic science in investigating major terrorist acts. Explore different types of explosives, investigative goals, evidence sought, and areas of forensic science applied.

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Analysis of Explosives
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  1. Analysis of Explosives

  2. Introduction • Most bombing incidents involve homemade explosive devices • There are a great many types of explosives and explosive devices • Lab must determine type of explosives and, if possible, reconstruct the explosive device

  3. Chemistry of Explosion • Essentially a combustion reaction - like a fire • Major difference is speed of reaction • Damage caused by rapidly escaping gases and confinement

  4. Types of Explosives • Low explosives • Escaping gases up to about 3000fps • Crucial element is physical mixture of oxygen and fuel • Examples are black and smokeless powders • Black powder is mixture of potassium nitrate, charcoal and sulfur • Smokeless powder is nitrocellulose and perhaps nitroglycerine

  5. Types of Explosives • High explosives • Velocity of escaping gases up to 10,000fps • Oxygen usually contained infuel molecule • Two types • Initiating - Senistive, will detonate readily when subjected to heat or shock. Used to detonate other explosives in explosive train • Noninitiating - relatively insensitive, requires heat or shock. Includes TNT or PETN

  6. Types of Explosives • Ammonium nitrate based • Water gels • Emulsions • ANFO’s

  7. Analysis of Explosives • Microscopy • Thin layer chromatography • Visualise with Greiss reagents • Infrared spectrophotometry • Detonator fragments

  8. The Role of Forensic Science in the Investigation of Major Acts of Terrorism

  9. Introduction • A major terrorist act can generate huge amounts of evidence that can help in the investigation • Different acts call for different strategies • This talk will examine three major terrorist acts in the US during the past 10 years with emphasis on the forensic science aspects: • World Trade Center Bombing • Murrah building in Oklahoma City bombing • World Trade Center destruction

  10. The World Trade Center Bombing

  11. The Scenario • Urea nitrate bomb put into truck and driven into underground WTC garage and parked at 4th level down • Subsequent explosion did extensive damage to several levels of the garage and less damage to other levels • Although goal was to topple WTC, little structural damage was done • Some loss of life

  12. Goals of Investigation • Identify victims • Identify explosive • Recover bomb and timing device • Determine method of delivery

  13. Evidence Sought • Investigators had to remove large quantities of concrete, steel and cars to get to bomb seat • Bomb seat contained most of the important evidence • Bomb parts; timer, casing, etc. • Explosive residue • Parts of truck that contained explosive

  14. Areas of Forensic Science • Explosives • Engineering • Questioned documents • Fingerprints • Pathology • DNA

  15. The Murrah Building, Oklahoma City

  16. The Scenario • ANFO explosive and timer packed into a rented truck, which was then parked outside Murrah building • Explosive confined to closed space such as truck is much more powerful • Resulting explosion resulted in severe damage to building and loss of more than 100 lives

  17. Goals of Investigation • Identify victims • Identify explosive • Find timer and bomb parts • Determine method of delivery

  18. Evidence Sought • Easier to find than in WTC because bomb seat outside building • Explosive residues • Bomb parts • Bodies and body parts; cadaver dogs, flies • Personal effects; helps in identification of human remains

  19. Areas of Forensic Science • Anthropology • DNA and serology • Pathology • Entomology • Explosives • Trace evidence • Engineering • Questioned documents • Fingerprints

  20. WTC Destruction

  21. The Scenario • Large airplanes, loaded with fuel, crash into WTC buildings • Raging fires ignite everything in building above crash sites. • Metal supports melt from heat • Building collapses due to inability to support its own weight after structural damage • Thousands of people killed

  22. Goals of Investigation • Cause known, no need to determine how destruction occurred • Recover and identify bodies, parts of bodies and charred remains • Recover personal effects that might help identify victims or perpetrators • Evidence that might determine how hijackings occurred.

  23. Evidence Sought • Bodies and body parts; cadaver dogs, flies • Charred remains • Personal effects • Trace evidence such as charred papers • Weapons such as knives • Constraining devices such as wire

  24. Areas of Forensic Science • Anthropology • DNA and serology • Odontology • Pathology • Entomology • Trace evidence • Questioned documents • Fingerprints • Tools and toolmarks