Explosives

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Explosives
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Introduction to Explosives

• 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

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Explosives

• An explosive is a material that undergoes rapid
  exothermic oxidation reaction (combustion),
  producing immense quantities of gas.
• The build-up of gas pressure in a confined space
  is the actual Explosion. The damage is caused
  by rapidly escaping gases and confinement.

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Explosives

• Combustion (or decomposition) of explosives
  occurs so rapidly, that there isnt enough time
  for the oxygen in the surrounding atmosphere to
  combine with the fuel.
• Therefore, many explosives must have their own
  source of oxygen or oxidizing agents

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Types of Explosives

• Low explosives
• Combustion is relatively slow less than 1000
  meters per second
• This low-speed combustion is called deflagration
• 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
  nitro-glycerine

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Black Powder (Low Explosive)

• Black powder contains
• 75 Potassium Nitrate (KNO3)
• 15 Charcoal (C)
• 10 Sulfur (S)
• The KNO3 is the oxidizing agent.
• When heat is applied to the powder, the oxygen
  from KNO3 is liberated.
• It combines with the carbon (fuel) and sulfur
  (for stable combustion).
• The combustion of charcoal and sulfur produces 2
  gases CO2 and N2.
• The buildup of gases in the cartridge, propels
  the bullet forward in bullet cartridges.

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Black Powder Reaction

• 3C S 2KNO3 ? 3CO2 N2 K2S heat

Carbon in charcoal is fuel
Sulfur stabilizes combustion
Saltpeter is the oxidizing agent
Carbon dioxide gas
Nitrogen gas
Potassium Sulfide solid
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Smokeless Powder

• Used as propellant in firearms and other weapons.
• There are 3 types
• Single-base contains nitrocellulose
• Double-base contains nitrocellulose and
  nitroglycerine
• Triple-base contains nitrocellulose,
  nitroglycerine and nitroguanidine
• Produce very little smoke when burned, unlike
  black powder.
• The reason that they are smokeless is that the
  combustion products are mainly gaseous, compared
  to around 55 solid products for black powder
  (potassium carbonate, potassium sulfate residues).

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Types of Explosives part deux

• High explosives they detonate (explode) rather
  than deflagrate (burn)
• Combustion can range from 1000 mps to 10,000 mps
• Oxygen usually contained in fuel molecule
• Two types
• Initiating (or primary explosives)
• Sensitive, will detonate readily when subjected
  to heat or shock.
• Used to detonate other explosives in explosive
  train (a triggering sequence that ends up in a
  detonation of explosives)
• Includes Nitroglycerine
• Noninitiating (or secondary explosives)
• relatively insensitive, to heat, friction or
  shock, need special detonators such as low
  explosives.
• Includes Dynamite, TNT, PETN, and RDX
• ANFOs or (Ammonium Nitrate Fuel Oil) (These are
  actually tertiary)

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Nitroglycerin (Initiating or primary high
explosive)

• In its pure form, it is a contact explosive
  (physical shock can cause it to explode) and
  degrades over time to even more unstable forms.
• This makes it highly dangerous to transport or
  use.
• In this undiluted form, it is one of the most
  powerful high explosives, comparable to the newer
  military explosives
• Believe it or not, it is also used as heart
  medication it is a vasodilator.

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How does it work?

• The explosive power of nitroglycerin is derived
  from detonation energy from the initial
  decomposition causes a pressure gradient that
  detonates the surrounding fuel.

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Dynamite

• A creation of Alfred Nobel (he also dabbled in
  pure nitroglycerine and its explosive qualities)
• He liked the oomph of nitroglycerine, but not
  its sensitivity.
• He discovered that kieselguhr or diatomaceous
  earth would absorb the nitroglycerine, but not
  reduce its explosive force.

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Alfred Nobel, Sweden
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Diatoms
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Ingredients of Dynamite

• Original dynamite consisted of three parts
  nitroglycerin, one part diatomaceous earth and a
  small admixture of sodium carbonate.
• This mixture was formed into short sticks and
  wrapped in paper, with a fuse or a cord with a
  core of powder, that will transport the fire to
  the cylinder.
• Today, ammonium nitrate based dynamite is made
  and the fuse has been replaced with electronic
  detonators called blasting caps.

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Electric Blasting Caps (Detonators)
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Dynamite Today
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High Explosives Acronyms

• TNT Trinitro Toluene
• PETN PentaErythritol TetraNitrate, also known
  as pentrite. PETN is also used as a vasodilator,
  similar to nitroglycerin. Used as medicine for
  heart diseases.
• RDX Cyclotrimethylenetrinitramine
• HMX or Octagon Cyclotetramethylene-tetranitramin
  e (related to RDX)

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TNT (Non-initiating or secondary high explosive)

• Trinitro Toluene
• Most used by the military
• Used in grenades, bombs, shells, or even alone.

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PETN

• PETN and TNT used together to make small-caliber
  projectiles
• Commercially used (mining, demolition, etc.)
• PETN is used in detonation cords or Primacords.
  These cords are used to create a series of
  explosions.

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PETN primacords attached to demolition explosives.
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• 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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ANFO

• Ammonium nitrate (oxidizer) or urea nitrate,
  soaked in a highly combustible hydrocarbon (fuel)
  usually a fuel oil.
• Easy to make, safe to handle
• Ammonium nitrate is found in fertilizers, so
  ANFOs are a favorite type of homemade bombs.

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ANFOs in trucks
Dupont is a leading manufacturer of industrial
and commercial ANFO
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Homemade Explosives

• Molotov Cocktails
• ANFO

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Molotov cocktail

• In its simplest form, a Molotov cocktail is a
  glass bottle containing gasoline usually with a
  source of ignition such as a burning, fuel
  soaked, rag wick held in place by the bottle's
  stopper.
• In action the fuse is lit and the bottle hurled
  at a target such as a vehicle or fortification.
  When the bottle smashes on impact, the ensuing
  cloud of gasoline droplets and vapor is ignited,
  causing an immediate fireball followed by a
  raging fire as the remainder of the fuel is
  consumed.
• Other flammable liquids such as wood alcohol and
  turpentine have been used in place of gasoline.
• Thickening agents such as motor oil have been
  added to the fuel, analogously to the use of
  napalm, to help the burning liquid adhere to the
  target and create clouds of thick choking smoke.

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1, 2, and 3 step Explosive Trains
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Analysis of Explosives

• Microscopy
• Thin layer chromatography
• Visualise with Greiss reagents
• Infrared spectrophotometry
• Detonator fragments

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

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The World Trade Center Bombing
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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

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Goals of Investigation

• Identify victims
• Identify explosive
• Recover bomb and timing device
• Determine method of delivery

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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

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Areas of Forensic Science

• Explosives
• Engineering
• Questioned documents
• Fingerprints
• Pathology
• DNA

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The Murrah Building, Oklahoma City
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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 caused severe damage to
  building and loss of more than 100 lives

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Goals of Investigation

• Identify victims
• Identify explosive
• Find timer and bomb parts
• Determine method of delivery

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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

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Areas of Forensic Science

• Anthropology
• DNA and serology
• Pathology
• Entomology
• Explosives
• Trace evidence
• Engineering
• Questioned documents
• Fingerprints

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WTC Destruction
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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

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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.

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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

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Areas of Forensic Science

• Anthropology
• DNA and serology
• Odontology
• Pathology
• Entomology
• Trace evidence
• Questioned documents
• Fingerprints
• Tools and toolmarks

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THE END