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Forensic Science: The Basics Chapter 20 Fires and Explosions

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1 Forensic Science: The Basics Chapter 20 Fires and Explosions
Jay A. Siegel,Ph.D. Power point presentation by Greg Galardi, Peru State College, Peru Nebraska Presentation by Greg Galardi, Peru State College CRC Press, Jay A. Siegel Ph.D.

2 CRC Press, Jay A. Siegel Ph.D.
What is a Fire? A fire is the evolution of energy in the form of light and heat and smoke as a result of combustion Combustion is a type of chemical reaction whereby a fuel reacts with oxygen to release energy Reactions that give off energy are exothermic Presentation by Greg Galardi, Peru State College CRC Press, Jay A. Siegel Ph.D.

3 CRC Press, Jay A. Siegel Ph.D.
Fire Δ greek letter Delta in chemistry and physics means heat energy Heat put into a reaction is considered activation energy Amount of activation energy needed to get reaction started is little in comparison to energy emitted by reaction Presentation by Greg Galardi, Peru State College CRC Press, Jay A. Siegel Ph.D.

4 CRC Press, Jay A. Siegel Ph.D.
Gasoline Is a petroleum distillate that contains more than 300 substances Most are hydrocarbons, which are substances made up of carbon and hydrogen Octane is a compound in gasoline that combusts with oxygen Presentation by Greg Galardi, Peru State College CRC Press, Jay A. Siegel Ph.D.

5 Substances that Fuel Combustion Reactions
Wood Plastic Natural and synthetic fibers Carpeting Tile Drywall Most building materials Presentation by Greg Galardi, Peru State College CRC Press, Jay A. Siegel Ph.D.

6 How are Fires Extinguished?
Fire tetrahedron explains how fires start and end: Fuel + Oxygen+ Activation Energy + Chemical Reaction All four elements must be present to have a fire Combustion reactions are relatively slow and produce little energy compared to reactions that cause explosions Presentation by Greg Galardi, Peru State College CRC Press, Jay A. Siegel Ph.D.

7 Deliberately Set Fires: Arson and Incendiary
Incendiary fire means a fire is willfully and intentionally set Arson refers to crime of setting incendiary fires 37,000 arson fires set in 2003 cost almost 700 million Presentation by Greg Galardi, Peru State College CRC Press, Jay A. Siegel Ph.D.

8 Arson Fire Facts as Reported by FEMA (2001)
Arson is leading cause of fire and 2nd leading cause of death 50% of arson fires occur outdoors 30% occur in buildings, and 20% in vehicles Half of all arson arrests are for juveniles Poorer neighborhoods experience 14 times the number of fires as well off areas Church arson have increased since 1996 Presentation by Greg Galardi, Peru State College CRC Press, Jay A. Siegel Ph.D.

9 CRC Press, Jay A. Siegel Ph.D.
Accelerants Are a fuel used to start a fire that otherwise couldn’t be easily started or make a fire burn faster Are generally liquids that require low activation energy so they can be readily combusted Undergo highly exothermic reactions so plenty of energy around to keep fire going Gasoline, charcoal lighters, paint thinners Leave residues behind that can be detected Presentation by Greg Galardi, Peru State College CRC Press, Jay A. Siegel Ph.D.

10 Investigation of Fire Scenes
Very difficult as there is generally no light, heat or air conditioning Structure is weakened by water Fire scene investigator must determine point of origin Determine if fire is accidental or purposeful Presentation by Greg Galardi, Peru State College CRC Press, Jay A. Siegel Ph.D.

11 CRC Press, Jay A. Siegel Ph.D.
Fire Types Natural cause- lightning strike Accidental – drops match in bed Deliberate - arson Presentation by Greg Galardi, Peru State College CRC Press, Jay A. Siegel Ph.D.

12 Determination of Arson
Two ways: Presence of fire setting device such as a Molotov cocktail Elimination of all possible or natural causes of fire Presentation by Greg Galardi, Peru State College CRC Press, Jay A. Siegel Ph.D.

13 CRC Press, Jay A. Siegel Ph.D.
Point of Origin Is location where the fire started Residue of accelerant may be there if arson is suspected Is point where most extensive burning takes place and often gets the hottest Investigators look for V-patterns, spalling-blistering of concrete, beginning of fire trail and obvious presence of accelerants Presentation by Greg Galardi, Peru State College CRC Press, Jay A. Siegel Ph.D.

14 Evidence at Fire Scenes
Fire trails may be present Fingerprints, hairs, fibers, shoe prints, blood and documents can survive a fire under the right circumstances Presentation by Greg Galardi, Peru State College CRC Press, Jay A. Siegel Ph.D.

15 CRC Press, Jay A. Siegel Ph.D.
Role of Accelerants Presence of residues from a fuel can be highly indicative of arson fire Accelerants can greatly increase damage by fire sue to heat they give off Accelerants may affect other systems, such as gas, etc, which may increase fire Presentation by Greg Galardi, Peru State College CRC Press, Jay A. Siegel Ph.D.

16 Detection and Collection of Accelerants
Evidence investigators look for includes extreme heat, damage, sooty v-pattern burning and fire trails Hydrocarbon sniffer instruments and arson dogs may be used by arson investigators Materials that easily absorb liquids include bedding, furniture with cushions, carpeting, clothing and soil Presentation by Greg Galardi, Peru State College CRC Press, Jay A. Siegel Ph.D.

17 Detection and Collection of Accelerants
Accelerants are volatile and must be packed in airtight containers Unused paint cans are recommended for packaging evidence Empty glass jars with screw tops also serve as collectors of evidence Airtight bags also work for this purpose Presentation by Greg Galardi, Peru State College CRC Press, Jay A. Siegel Ph.D.

18 Concentration Methods for Accelerants
Forensic scientists separate and concentrate accelerant residues after receiving evidence Concentration methods are: Passive headspace – airtight container is slightly heated to allow for sampling of headspace vapor with gas syringe and GC is used to test Adsorption/elution- pump is used to force air into container, and expelled vapors are trapped in charcoal. Charcoal is removed, solvent poured over, and dissolved accelerant is tested via GC Presentation by Greg Galardi, Peru State College CRC Press, Jay A. Siegel Ph.D.

19 Concentration Methods for Accelerants
Solid Phase Microextraction (SPME)-syringe coated with charcoal is inserted into headspace and reside is heated. After 30 minutes needle, which is now coated with accelerant residue, is tested in GC Solvent Extraction- suitable solvent is mixed with fire residue. Mixture filtered and solvent evaporated to small volume and injected into GC Presentation by Greg Galardi, Peru State College CRC Press, Jay A. Siegel Ph.D.

20 Analysis of Fire Scene Residues
Gas Chromatography (GC) coupled to a mass spectrometer is typical method of analysis of accelerants Presentation by Greg Galardi, Peru State College CRC Press, Jay A. Siegel Ph.D.

21 CRC Press, Jay A. Siegel Ph.D.
Explosions Chemical explosions are combustions like fires Difference is amount of energy emitted by given amount of fuel and how intimate oxygen is mixed with fuel Two types of explosions: Deflagrations Detonations Presentation by Greg Galardi, Peru State College CRC Press, Jay A. Siegel Ph.D.

22 CRC Press, Jay A. Siegel Ph.D.
Deflagration Oxygen is physically mixed with fuel and is in a form where the O is bonded to other atoms that form weaker bonds than O2 which requires less activation energy to break Black powder is an explosive that deflagrates Activation for black powder is a match or spark Reaction will produce gases that escape at velocities up to sped of sound (740 miles per hour or 1100 feet per second) Presentation by Greg Galardi, Peru State College CRC Press, Jay A. Siegel Ph.D.

23 CRC Press, Jay A. Siegel Ph.D.
Detonation Is essentially an instantaneous explosion So powerful escaping gases travel at speeds greater than mach 1 Explosives in this category are high explosives Two types of high explosives are initiating and non-initiating Initiating explosives are sensitive to detonation- nitroglycerine Non-initiating explosives, such as dynamite, require a booster charge Presentation by Greg Galardi, Peru State College CRC Press, Jay A. Siegel Ph.D.

24 CRC Press, Jay A. Siegel Ph.D.
Explosives Plastique (plastic) is latest generation of explosives Contain PETN or RDX mixed with a polymer plastic with consistency of clay Can be shaped or molded so blast may be directed specific ways Highly popular in demolitions, especially of buildings Presentation by Greg Galardi, Peru State College CRC Press, Jay A. Siegel Ph.D.

25 CRC Press, Jay A. Siegel Ph.D.
Dynamite One of most potent and popular of all chemical high explosives Fuel in dynamite is nitroglycerine, which is mixed with diatomaceous earth and calcium carbonate. Needs blasting cap or primer cord to detonate it Alfred Nobel invented dynamite, Nobel funded Nobel Peace Prize starting in 1901 Presentation by Greg Galardi, Peru State College CRC Press, Jay A. Siegel Ph.D.

26 Analysis of Explosive Residues
Can be particularly difficult because they are scattered over great distances Hot gases formed at explosion race away from point of explosion (bomb seat) at high velocities, creating a blast pressure Analysis relies upon two types of evidence: Unburned or partially burned residues of explosive Pieces of explosive device Presentation by Greg Galardi, Peru State College CRC Press, Jay A. Siegel Ph.D.

27 Analysis of Explosive Residues
Finding parts of explosive devices is critical, especially in terrorist bombings May differentiate devices of specific terrorist organizations Griess test is one of most important tests for explosive residues Two step test that detects presence of nitrites and nitrates Residue can be spotted on TLC, and sprayed with two reagents that make up Griess test, which will be an orange or red spot on plate Presentation by Greg Galardi, Peru State College CRC Press, Jay A. Siegel Ph.D.

28 Analysis of Explosive Residues
Locating unburned explosive materials assists, as it can be analyzed directly by instrumental or other methods and exact explosive identified easily Exploded material leaves behind ions such as nitrite or nitrate, however, these are found in soil anyway Presentation by Greg Galardi, Peru State College CRC Press, Jay A. Siegel Ph.D.

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