forensic sciences ii

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Arson and Explosion Investigations. . Difficulties of Investigations. Incidents are usually committed at convenience of perpetratorThoroughly plannedPerpetrator is usually far from sceneProof of commission of offense rendered more difficult because of destruction of crime sceneInvestigative process must establish modus operandi.

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forensic sciences ii

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1. FORENSIC SCIENCES II Instructor: Ms. R. M. Brown Email: [email protected] Or [email protected]

3. Difficulties of Investigations Incidents are usually committed at convenience of perpetrator Thoroughly planned Perpetrator is usually far from scene Proof of commission of offense rendered more difficult because of destruction of crime scene Investigative process must establish modus operandi

4. Function of Criminalist Limited to: detection and identification of chemical materials collected at the scene reconstruction and identifica- tion of ignitors or detonating mechanisms

5. Firestarters Trace amounts of gasoline, kerosene, etc. can be detected in debris No test to determine if arsonist used paper or pile of rubbish to start fire Accidental causes: Faulty wiring Overheated motors/improperly cleaned and regulated heating systems Cigarettes

6. Historical Perspectives of Fire Ancient Greek philosophers believed fire was one of the four basic elements Alchemists thought fire was an instrument of transformation changing one element into another Today, we know fire is a transformation process during which O2 is combined with another sub-stance to produce heat and light

7. Chemistry of Fire Oxidation – combination of oxygen with other substances to produce new substances CH4 + 2 O2 CO2 + H2O Not all oxidation reactions produce fire – some produce metal oxides 4 Fe + 3 O2 2 Fe2O3

8. Oxidation Oxidation equations don’t show entire picture: Gasoline will not burn when exposed to air – needs a spark Energy is often needed to initiate some oxidation reactions

9. Energy Energy is the combined ability or potential of a system or materials to do work Types of energy: Heat energy Chemical energy Electrical energy Mechanical Nuclear Light

10. Combustion An oxidation reaction in which more energy is released than is needed for the reaction Excess energy is called heat of combustion An exothermic reaction liberates heat when chemical bonds are broken

12. Ignition Temperature Iron will oxidize at normal outdoor temperatures Fuels require much higher temperature to oxidize Ignition temperature is quite high for most common fuels Fire will continue to burn until O2 supply or fuel is exhausted

13. Flash Point Liquid fuels will not oxidize (burn); they must first become vaporized Flash point and ignition temper-ature are not the same Pyrolysis is necessary before solid fuels will burn

14. Spontaneous Combustion Conditions for this phenomenon are limited and rarely accounts for cause of a fire Result of natural heat-producing process in poorly ventilated containers or areas Hay in a barn Poor storage of oil-soaked rags

15. Oxidizing Agents Some chemicals supply oxygen to chemical reactions Important to explosions

16. Requirements of Combustion Fuel must be present O2 must be available in sufficient quantity to combine with the fuel Heat must be applied to initiate combustion Sufficient heat must be generated to sustain the reaction

17. Heat Transfer Three mechanisms of heat transfer Conduction Convection Radiation

18. Searching a Fire Scene Must be done ASAP Most accelerants are petroleum based and will evaporate Necessity to begin immediate investigation supersedes obtaining a search warrant Focus is on finding point of origin

19. Determination of Accelerant Use More severe burning on the floor indicates use of accelerant Use of streamers Charring on bottom of furniture, shelves, and other items as contrasted with the top sides Very rarely is all of an accelerant consumed Some soaks into porous surfaces and cracks Allows for identification in lab

20. Movement of Fire Fire has a tendency to move upward Probably origin is lowest point showing most intense characteristics of burning

21. Help for the Fire Investigator Portable vapor detectors – not definitive, but useful for screening Dogs trained to recognize odor of hydrocarbon accelerants Fire Research Laboratory

22. Hydrocarbons Vast majority of arsons are initiated by petroleum distillates Usually hydro- carbons

23. Collection and Preservation of Arson Evidence 2 – 3 quarts of ash and soot debris from point of origin is routinely collected All porous materials or substances suspected of containing flammable residue Packaged in airtight containers, leaving some airspace Polyethylene bags not suitable

24. Substrate Control Collection of all materials suspected of containing volatile liquids be accompanied by a sampling of similar, but uncon-taminated control specimens from another area of the fire scene

25. Ignitors The most common is matches Cigarettes, firearms, Molotov cocktails, ammunition, mechanical match striker, and electrical sparking device Complex devices are more likely to survive the fire

26. Analysis of Flammable Residues Gas chromatograph is the most sensitive and reliable GC separates the hydrocarbon components and produces chromatographic pattern characteristic of a particular petroleum product Vapor concentration with GC is extremely sensitive

27. Explosives An explosion is the product of combustion at a rapid rate Upon detonation, large volumes of gases exert pressure on container walls – produces shrapnel Upon release from confine- ment, gaseous products suddenly expand and compress surrounding air producing blast effect

28. Low Explosives Decompose slowly Suitable as propellants for ammunition or skyrockets Most widely used – black powder and smokeless powder Only requirements: fuel and oxidizing agent Natural gas

29. Deflagration

30. High Explosives Primary explosives – ultrasensitive to shock, heat, or friction Secondary explosives – relatively insensitive to shock, heat, or friction

31. Detonation Refers to the creation of a supersonic shock wave within the explosive charge

32. Primary Explosives Detonate violently instead of burning Usually used to detonate other explosives through a chain reaction Often referred to as primers Lead azide, lead styphnate, diazodinitrophenol

33. Secondary Explosives Will burn rather than detonate Majority of high explosives used for commercial and military blasting TNT, RDX, PETN, dynamite, ANFO, tetryl

34. Explosions Nitroglycerin based dynamite has been replaced by ammonium nitrate based explosives (water gels, emulsions, ANFO explosives) Secondary explosives must be detonated by a primary explosive RDX – most popular and powerful military explosives (C-4)

35. Terrorism Terrorist organizations – homemade bombs using high explosives TATP – triacetone triperoxide – combination of acetone and peroxide in presence of an acid Led to the banning of most liquids on commercial airplanes

36. Evidence of Explosion Presence of crater at origin of blast Loose soil and debris Objects near the origin of detonation

37. Collection and Analysis of Explosives Single most important step in the detection and analysis of explosive residues collection of appropriate samples from the scene of the explosion Undetonated residues Items foreign to explosion site Ultimately rests on skill of investigator All materials must be in sealed containers – metal containers or plastic bags

38. Preliminary Identification IMS – measurement of time it takes for explosive to move through a tube Confirmatory tests must follow

39. Analysis Following microscopic exam, debris is rinsed with acetone Acetone then concentrated and analyzed TLC, HPLC, GC-MS IS – for organic explosives (RDX) X-ray diffraction for inorganics (KNO3)

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