1. FORENSIC ASPECTS of Arson and Explosives
SFS4. Students will evaluate the role of ballistics, tool marks and evidence of arson in forensic investigation.
D. Evaluate possible indicators of arson and criminal bombing.

2. Introduction
Arson and explosions often present complex and difficult circumstances to investigate because
the perpetrator has, typically, thoroughly planned the act
the perpetrator is not present during the act
the destruction is so extensive

3. INTRODUCTION The criminalist’s function is rather limited to…
detecting and identifying relevant chemical materials collected at the scene
reconstructing and identifying igniters or detonating mechanisms

4. ARSON

5. DEFINITIONS
Arson is the conflagration, or uncontrolled burning, of any real property without consent or with unlawful intent
Arson is prosecuted with attention to degree of severity in the alleged offense
The analysis of fire-related incidents is called fire investigation

6. The Chemistry of Fire
Chemically, fire is a type of oxidation, which is the combination of oxygen with other substances to produce new substances.
CH4 + 2O2  CO2 + 2H2O
Oxidation reactions typically result in large energy release, mainly as heat and/or light.

7. The FIRE TRIANGLE (or TETRAHEDRON)
Fuel
Oxygen in sufficient quantity to combine with the fuel.
Sufficient heat to initiate the combustion and sustain the reaction.

8. The Chemistry of Fire
The autoignition temperature of a fuel is the minimum temperature needed to spontaneously ignite it without a spark or flame.
White Phosphorus – 34°C
Gasoline – 280°C
Hydrogen – 530°C

9. The Chemistry of Fire
The heat evolved when a substance burns is known as heat of combustion.
Wood – 21.7 kJ/kg
Gasoline – 47.3 kJ/kg
Hydrogen – kJ/kg

10. The Chemistry of Fire
An additional factor, besides the liberation of energy, needed to explain fire is
the rate or speed at which the oxidation reaction takes place.
A fuel will achieve a reaction rate with oxygen sufficient to produce a flame only when it is in the gaseous state.

11. The Chemistry of Fire
A liquid burns when the temperature is high enough to vaporize it – at the flash point.
A solid must be hot enough to decompose into gaseous products – pyrolysis.

12. The Chemistry of Fire
Glowing combustion or smoldering is burning at the fuel-air interface
Cigarette embers, charcoal
Spontaneous combustion, which is rare, is the result of a natural heat-producing process in poorly ventilated containers or areas.

13. The Fire Scene
The arson investigator needs to begin examining a fire scene for signs of arson as soon as the fire has been extinguished.
The necessity to begin an immediate investigation even takes precedence over the requirement to obtain a search warrant.

14. The Fire Scene
Experience shows that most arsons are started with petroleum-based accelerants.
The search of the fire scene must focus on finding the fire’s origin, which may be most productive in any search for an accelerant or ignition device.

15. The Fire Scene Some telltale signs of arson include…
evidence of separate and unconnected fires
use of “streamers” to spread the fire from one area to another
evidence of severe burning found on the floor as opposed to the ceiling of a structure, due to a flammable liquid.

16. The Fire Scene
Normally, a fire has a tendency to move in an upward direction, so the probable origin will most likely be the lowest point showing the most intense characteristics of burning.
Fortunately, combustible liquids are rarely entirely consumed during a fire.

17. EVIDENCE Collection
At the suspected point of origin of a fire, ash and soot, along with porous materials which may contain excess accelerant, should be collected and stored in airtight containers, leaving an airspace to remove samples.
It is important that a sampling of similar but uncontaminated control specimens be collected.

18. EVIDENCE Collection
Traces of flammable liquid residues may be located with a vapor detector (sniffer).
Trained dogs can detect 1: (1 part per billion)

19. EVIDENCE Collection A search for igniters must also be conducted.
Matches
An electrical sparking device
Parts of a “Molotov cocktail”

20. EVIDENCE ANALYSIS
In the laboratory, the gas chromatograph is the most sensitive and reliable instrument for detecting and characterizing flammable residues.
The GC separates the chemical components and produces a chromatographic pattern characteristic of a particular fuel.

21. EVIDENCE ANALYSIS
By comparing select gas chromatographic peaks recovered from fire-scene debris to known flammable liquids, a forensic analyst may be able to identify the accelerant used to initiate the fire.

22. GC/ms ANALYSIS

23. GC Analysis Gas chromatograph of vapor from a genuine gasoline sample.
Gas chromatograph of vapor from debris recovered at a fire site.

24. EXPLOSIVES

25. DEFINITIONS
An explosive is a reactive substance that can produce an explosion.
An explosion is a rapid increase in volume and release of energy in an extreme manner, usually with the generation of high temperatures and the release of gases.

26. Explosions
A sudden buildup of gas pressure produces a shock wave.

27. Types of Explosives
If the shock wave is subsonic, the oxidation reaction is called a deflagration
The source explosive material is said to be a “low explosive”
If the shock wave is supersonic, the oxidation reaction is called a detonation
The source explosive material is said to be a “high explosive”

28. “low explosives”
The most widely used are black powder and smokeless powder.
Black powder is a mixture of potassium or sodium nitrate, charcoal, and sulfur.
Because it burns slowly, it is often used as a fuse to a high explosive
Smokeless powder consists of nitrocellulose (plant fiber + H2SO4/HNO3)
More stable, yet powerful, than BP

29. “high explosives” They can be characterized by their sensitivity to
Impact
Heat
Friction
Primary explosives are highly sensitive
Secondary explosives are fairly insensitive
Tertiary explosives are least sensitive

30. “high explosives”
Primary explosives provide the major ingredients found in blasting caps or primers used to detonate other explosives.
Nitroglycerin (in its pure form)

31. “high explosives”
Secondary explosives will normally burn rather than detonate if ignited in small quantities in the open air.
Dynamite – composed of nitroglycerin mixed with diatomaceous earth
Trinitrotoluene (TNT)

32. “high explosives” Research Department Explosive (RDX)
Composition C-4 – plasticized RDX

33. “high explosives”
Tertiary explosives, also called blasting agents, are so insensitive to shock that ignition by both primary and secondary explosives is required.
Primarily used in large-scale mining and construction and terrorism
Ammonium Nitrate/Fuel Oil (AMFO)

34. EVIDENCE Collection
The entire explosion 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.

35. EVIDENCE Collection
Often a crater is located at the origin and loose soil and other debris must be preserved from its interior for laboratory analysis.

36. EVIDENCE Collection
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.

37. Evidence analysis
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.

38. EVIDENCE Analysis
Ion Mobility Spectrometry can be used to preliminarily identify an explosive residue
Used in airports and by the US Army in Improvised Explosive Device (IED) examination.

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