FORENSIC ANALYSIS OF EXPLOSIONS

Jeff BarnhousePd.5

Explosions A product of combustion accompanied by the

creation of gasses and heat is an explosion. What creates an explosion is the rapid buildup of

gas pressure. Detonation occurs so rapidly that oxygen in the air cannot participate in the reaction. Leaving it that many explosions have their own source of oxygen.

Oxidizing agents- Chemicals that supply oxygen

Explosions and Chemistry

The most popular of all explosives is Black powder.

Black powder is classified as a low explosive.

1. 75% Potassium Nitrate (KNO3)2. 15% Charcoal (C7H4O)

3. 10% Sulfur (S)

Black powder in use

As heat is applied to black powder, oxygen is liberated from potassium nitrate and simultaneously combines with charcoal and sulfur to produce heat and gasses.

3C + S + 2KNO3 3CO2 + N2 + K2S

Here the arrows on the product side of the equation symbolizes the heat and gasses produced

Classifications of Explosives

2 classes of explosives, high and low.

Low Explosives have a speed of deflagration (burning). Rapid oxidation that produces heat, light , and a subsonic pressure wave.

High Explosives have a speed of detonation. Detonation refers to the creation of supersonic shock wave within the explosive charge.

Low Explosives

Low explosions decompose relatively slowly at rates up to 1,000 meters/second

Because of their slow burning rates, they produce a propelling or throwing action that makes them suitable as propellants for ammunition.

2 most widely used low explosives are Smokeless powder and Black powder

Smokeless & Black Powders

These are 2 of the most widely used explosives in the low explosive group.

Both can be easily purchased at a gunstore, allowing for easier access increasing the popularity.

Black Powder: Relatively stable mixture of potassium nitrate, charcoal, and sulfur.

Smokeless powder: Safest and most powerful low explosive. Contains nitrated cotton or nitrocellulose, or nitroglycerin mixed with nitrocellulose.

High explosives

High explosions include dynamite, TNT, PETN, and RDX.

They detonate almost instanteaously at rates of 1,000- 8,500 meters/second.

They produce a smashing or shattering effect on their target

Dynamite

Dynamite is used when a quick shattering action is desired.

Within dynamite is nitroglycerine, pulp, sodium nitrate, and calcium carbonate for a stabilizer.

Dynamite is rated by strength and the strength is determined by the weight percentage of nitroglycerine in the formula.

Ammonium Nitrate & TATP

This type of explosive uses a mixture of oxygen-rich ammonium nitrate with a fuel to form a low-cost and very stable explosive

Triacetone Triperoxide (TATP) is a homemade explosive that has been used as an improvised explosive by terrorist organizations in the Middle East

It us prepared by reacting the common ingredients of acetone and hydrogen peroxide in the presence of an acid catalyst such as hydrochloric acid.

Primary and Secondary explosions

Primary explosives are ultrasensitive to heat, shock, or friction, and under normal conditions detonate violently instead of burning.

Secondary explosives are relatively insensitive to heat, shock, or friction, and normally burn rather than detonate when ignited in small quantities in open air.

Detecting/Recovering evidence

On arrival of the crime scene where an explosion has been detonated, at the crater of impact all earth and other debris should be collected and taken in for investigation.

Wood, insulation, rubber, and other soft materials that are readily penetrated hold traces of the explosive.

The whole area needs to searched with great care to locate any trace of the detonating mechanism.

Collection and Packaging

All materials collected for examination by the laboratory must be placed in airtight sealed containers and labeled with all the pertinent information.

Soil and other soft loose materials are best stored in metal airtight containers such as clean paint cans.

Plastic bags should not be used to store substances suspect of containing explosive residues.

Iron Mobility Spectrometer

Preliminary identification of an explosive residue using the IMS can be made by noting the time it takes the explosive to move through a tube. A confirmatory test must follow.

All materials collected for the examination by the laboratory must be placed in sealed air-tight containers and labeled with all pertinent information.

Debris and articles collected from different areas are to be packaged in separate air-tight containers.

It has been demonstrated that some explosives can diffuse through plastic and contaminate nearby containers.

Lab Procedures

Typically, in the laboratory, debris collected at explosion scenes will be examined microscopically for unconsumed explosive particles.

Recovered debris may also be thoroughly rinsed with organic solvents and analyzed by testing procedures that include color spot tests, thin-layer chromatography, and gas chromatography–mass spectrometry.

Confirmatory identification tests may be performed on unexploded materials by either infrared spectrophotometer or X-ray diffraction.