FORENSIC INVESTIGATION OF EXPLOSIONS

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FORENSIC INVESTIGATION OF EXPLOSIONS

• Chapter 14

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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.

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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.

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Explosions
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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

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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

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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
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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.

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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.

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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.

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Explosions

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

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High Explosives

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  market and has been replaced by ammonium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

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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.

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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.

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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.

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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).

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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.

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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 chromatographymass spectrometry.

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Back at the Lab

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

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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 crystals
  planes, they combine with one another to form a
  series of light and dark bands known as a
  diffraction pattern.

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X-ray Diffraction

• Every compound is known to produce its own unique
  diffraction pattern, thus giving analysts a means
  for fingerprinting crystalline compounds.

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X-Ray Diffraction Results

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Modern Bombs
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Famous Bomb Sites
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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

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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

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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

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Fission Nuclear Bombs
Video
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Fusion Nuclear Bomb
Video
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Fusion Nuclear Bombs
Video
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