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Transcript of Explosives
Collection and Analysis of Evidence of Explosives
The entire bomb site must be systematically searched to find any trace of a detonating device or other foreign object to the sight.
The scientist must identify the location of the blast crater and collect/preserve loose soil and other debris from the sight.
Ion Mobility Spectrometer
-The residues placed in the device are vaporized with heat. The substances are then exposed to a beam of electrons or beta rays and become charged molecules/ions. The charged particles are then allowed to move through a tube under the influence of an electric field. The explosive can be identified by the time its takes the particles to move through the tube.
Collection and Packaging
-Must be placed into airtight sealed containers and labeled with all information. Loose materials and sharp-edged objects should be placed into metal containers
-Debris collected from different areas should be packaged separately
Case Files: Liquid Explosives
Security agencies in the U.S. and Great Britain discovered a terrorist plot to destroy commercial planes using liquid explosives. Liquid explosives can be easily purchased and can be made by combining easy to obtain chemicals. After 9/11 security shifted its focus to solid explosives. In 2001, Richard Rein was arrested for attempting to blow up a flight out of Paris. TATP (triacetone triperoxide) and a detonator was discovered. Current scanning devices in airports can detect nitrogen-based chemicals but not peroxide-based.
Analysis of Evidence Explosives
Once the debris from the bomb scene are recovered and returned to the lab they are examined for any unconsumed explosive and identified by using a water color test to determine the different particles. Once analyzed the debris is then finally screened by either TLC, HPLC, X ray diffraction or mass spectrometry.
Is a proposal that in all commercial explosives that sets of small colored chips are added in manufacturing so that after an explosion they can survive to be identified and with the interchangeable patterns the type and manufacturer can be identified.
Types of Explosives
Classified as either high or low
Deflagration (the speed of decomposition for a low reaction)- rapid oxidation reaction accompanied by a small pressure wave
Detonation (the speed of decomposition for a high reaction)- extremely rapid, accompanied by an intense shock wave
Fire needs oxygen so most fire oxidation reactions take the oxygen from the air --> however explosions occur so rapidly that oxygen in the air cannot participate
Oxidizing Agents- substance that supplies oxygen to a reaction
In Black powder this agent is KNO3
Low Explosive- Velocity is less than 1,000 m/s
Black Powder- Mixture of KNO3, C, and S
Safety Fuse- A cord containing a core of black powder that is meant to carry a flame at a uniform rate
Smokeless Powder (single-base)- Contains nitrocellulose
Smokeless Powder (double-base)- Consists of nitrocellulose and nitroglycerin
Common oxidizing agents- chlorate mixture & gas-air mixture
Detonation with velocity greater than 1,000 m/s
Primary Explosives- High explosive that is easily detonated
Secondary Explosives- High explosive, relatively insensitive
Ammonium Nitrate Explosives & TATP
Dynamite used to be exclusively nitroglycerin-based
Now ammonium nitrate explosives are widely used
ANFO's (ammonium nitrate/ fuel oil)
TATP- Triacetone Triperoxide, primary explosive recently used by terrorists
Military High Explosives
Most popular form is C-4. Often in the form of a pliable plastic of doughlike consistency, known as a composition. TNT was used on a large scale in WWII
Commercially the chemical is used as the core in a detonating cord. Cord allows for simultaneous detonation
High explosives must be detonated by an initiating explosion.
Usually blasting caps filled with lead azide