1. Explosives

2. 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

3. 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.

4. Explosives
Combustion (or decomposition) of explosives occurs so rapidly, that there isn’t 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

5. 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

6. 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.

7. 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

8. 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).

9. 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)

10. 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.

11. 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.

12. 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.

13. Alfred Nobel, Sweden

14. Diatoms

15. 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.

16. Electric Blasting Caps (Detonators)

17. Dynamite Today

18. 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-tetranitramine (related to RDX)

19. TNT (Non-initiating or secondary high explosive)
Trinitro Toluene
Most used by the military
Used in grenades, bombs, shells, or even alone.

20. 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.

21. PETN primacords attached to demolition explosives.

23. RDX is the most popular and powerful of the military explosives, often encountered in the form of pliable plastic known as C-4.

24. 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.

25. ANFOs in trucks
Dupont is a leading manufacturer of industrial and commercial ANFO

26. Homemade Explosives
Molotov Cocktails
ANFO

27. 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.

29. 1, 2, and 3 step Explosive Trains

30. Analysis of Explosives
Microscopy
Thin layer chromatography
Visualise with Greiss reagents
Infrared spectrophotometry
Detonator fragments

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

32. 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

33. The World Trade Center Bombing

34. 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

35. Goals of Investigation
Identify victims
Identify explosive
Recover bomb and timing device
Determine method of delivery

36. 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

37. Areas of Forensic Science
Explosives
Engineering
Questioned documents
Fingerprints
Pathology
DNA

38. The Murrah Building, Oklahoma City

39. 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

40. Goals of Investigation
Identify victims
Identify explosive
Find timer and bomb parts
Determine method of delivery

41. 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

42. Areas of Forensic Science
Anthropology
DNA and serology
Pathology
Entomology
Explosives
Trace evidence
Engineering
Questioned documents
Fingerprints

43. WTC Destruction

44. 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

45. 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.

46. 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

47. Areas of Forensic Science
Anthropology
DNA and serology
Odontology
Pathology
Entomology
Trace evidence
Questioned documents
Fingerprints
Tools and toolmarks

48. THE END