FORENSIC INVESTIGATION OF EXPLOSIONS

FORENSIC INVESTIGATION OF EXPLOSIONS Chapter 14

Unit Objectives • Understand how explosives are classified • List some common commercial, homemade and military explosives. • Describe how to collect physical evidence at the scene of an explosion. • Describe laboratory procedures used to detect and identify explosive residues.

Explosions A chemical explosive is a compound or a mixture of compounds which, when subjected to heat, impact, friction, or shock, undergoes very rapid, self-propagating, heat- producing decomposition.

Explosions

Shock Wave • It is this sudden buildup of gas pressure that constitutes the nature of an explosion. • The speed at which explosives decompose permits their classification as high or low explosives. • Video: Rocket fuel production plant shock wave. http://www.youtube.com/watch?v=_KuGizBjDXo

Gunpowder • The most widely used explosives in the low-explosive group are black powder and smokeless powder. Burn rate is less than 3000 ft/second • Black powder is a mixture of potassium or sodium nitrate, charcoal, and sulfur. Video • Smokeless powder consists of nitrated cotton (nitrocellulose) or nitroglycerin and nitrocellulose. Video

Explosions • Among the high explosives, primary explosives are ultra-sensitive to heat, shock, or friction and provide the major ingredients found in blasting caps or primers used to detonate other explosives. Examples are DDNP and lead azide. Web site • Burn rates are 3000 –9000 ft/second. Blasting Caps

DDNP • DDNP, an acronym for diazodinitrophenol, is a picric acid derivative with somewhat good stability and explosive velocity. It is still susceptible to heat, friction, and shock making it a primary explosive. Its preparation is very simple, needing only picramic acid, sodium or potassium nitrite, and some dilute hydrochloric or sulfuric acid. This compound was first prepared by Dr. Griess in 1858, and this led him to conduct ground breaking research on the diazotization reaction.

Secondary Explosives • Secondary explosives are relatively insensitive to heat, shock, or friction and will normally burn rather than detonate if ignited in small quantities in the open air. Dynamite & TNT, PETN, RDX • Diagram of dynamite. • Sawdust soaked in nitroglycerin. • Protective coating surrounding the explosive material. • Blasting cap. • Electrical cable (or fuse) connected to the blasting cap.

Dynamite • Dynamite is an explosive material based on nitroglycern, initially using diatomaceous earth or another absorbent substance such as powdered shells, clay, sawdust, or wood pulp. Dynamite was invented by the Swedish chemist Alfred Nobel 1867. Remember Nobel Prizes? • Dynamite is usually sold in the form of sticks about 8 in (20 cm) long and about 1.25 in (3.2 cm) in diameter, with a weight of about 0.5 lb (0.23 kg). Other sizes also exist. • Dynamite is a high explosive, which means it detonates rather than deflagrates. While trinitrotoluene (TNT) is used as the standard for gauging explosive power, dynamite has more than a 60% greater energy density than TNT.

Explosions • This group comprises the majority of commercial and military blasting, such as dynamite, TNT, PETN, and RDX.

High Explosives • In recent years, nitroglycerin-based dynamite has all but disappeared from the industrial explosive market and has been replaced by ammonium nitrate–based explosives (i.e., water gels, emulsions, and ANFO explosives). • Secondary explosives must be detonated by a primary explosive.

High Explosives • In many countries outside the United States, the accessibility of military high explosives to terrorist organizations makes them very common constituents of homemade bombs. • RDX is the most popular and powerful of the military explosives, often encountered in the form of pliable plastic known as C-4.

High Explosives • Triacetone triperoxide (TATP) is a homemade explosive that has been used by terrorist organizations. • TATP can be made by combining acetone and peroxide in the presence of an acid. • Its existence has led to the banning of most liquids on commercial aircraft.

Collection and Analysis • The entire bomb site must be systematically searched with great care given to recovering any trace of a detonating mechanism or any other item foreign to the explosion site. • Objects located at or near the origin of the explosion must be collected for laboratory examination.

Collection and Analysis • Often a crater is located at the origin and loose soil and other debris must be preserved from its interior for laboratory analysis. • One approach for screening objects for the presence of explosive residues in the field or laboratory is the ion mobility spectrometer (IMS).

Collection and Analysis • 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.

Back at the Lab • 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, infrared spectrometry and gas chromatography–mass spectrometry.

Back at the Lab • Confirmatory identification tests may be performed on unexploded materials by either infrared spectrophotometry or X-ray diffraction. 1 2 3

X-ray Diffraction • X-ray diffraction is applied to the study of solid, crystalline materials. • As the X-rays penetrate the crystal, a portion of the beam is reflected by each of the atomic planes. • As the reflected beams leave the crystal’s planes, they combine with one another to form a series of light and dark bands known as a diffraction pattern.

X-ray Diffraction • Every compound is known to produce its own unique diffraction pattern, thus giving analysts a means for “fingerprinting” crystalline compounds.

X-Ray Diffraction Results

Modern Bombs

Famous Bomb Sites

Famous Bombings • Oklahoma City Bombing 1995 , 168 dead • Twin World Trade Center 1993 & 2001 , 3000 dead after 9-11. • US Embassy barracks 1983 • USS Cole while in port October 2000 • Pan Am Flight Lockerbie, Scotland:N.Y.-bound Pan-Am Boeing 747 exploded in flight from a terrorist bomb and crashed into Scottish village, killing all 259 aboard and 11 on the groundListing of bombings web site

Nuclear Bombs • Normal chemical explosions are different from nuclear bombs in that they only use the electron bonds for energy. • Nuclear bombs use the atomic binding force from the center of the atom. There are two types of nuclear bombs: Fission and Fusion. Reference web site Fission bombs split the nucleus. • Fusion bombs combine nuclei into larger atoms. • Nuclear bombs are thousands of times more powerful than chemical bombs. The biggest nuclear bomb ever made was equal to 50 million tons of TNT. Web site video

History of Nuclear Bombs Video • The atomic bomb was first developed by German and American scientists including Einstein. The first two fission bombs were used by the USA on Japan to end WWII. These are the only 2 ever used during war on an enemy. • Over 2000 have been exploded in testing • The damage from nuclear bombs would be much greater than chemical bombs. Video

Fission Nuclear Bombs Video

Fusion Nuclear Bomb Video

Fusion Nuclear Bombs Video How to survive

FORENSIC INVESTIGATION OF EXPLOSIONS