Chapter 14: Arson and Explosives

1. Chapter 14: Arson and Explosives Dr. J. T. Spencer Adjunct T. L. Meeks CHE 113

2. Learning Objectives Forensic Investigations may deal with the causes of fires and explosions…

3. Learning Objectives • What is fire and what are the roles of the components in the fire tetrahedron • What type of information is part of a fire investigation • What is meant by arson and what are some of the telltale clues to intentional fires

4. Learning Objectives • What are the common explosives used today and how are they classified • How are the identities of explosives determined in the laboratory

5. Fire • Rapid Oxidation of chemicals to release energy (usually as heat, light, noise) • Difference between combustion and explosion is mostly the rate of the reaction: • Combustion slower – explosion fast

6. Oxidation Reactions • Is the combination of oxygen with other substances to produce new substances • Are reactions that exothermic (give off heat) • Involve both oxidation and reduction • Not all oxidation reactions result in flames!– rusting– metabolism • Transfer of electrons • Gain electrons – reduction • Lose electrons - oxidation • Rate of reaction determines the nature of the reaction • Chemicals that supply oxygen (lose electrons) are known as oxidizing agents

7. Requirements for Combustion • A fuel must be present • Oxygen must be available in sufficient quantity to combine with the fuel • Heat must be applied to initiate the combustion and sufficient heat must be generated to sustain a reaction. • Ignition temp is the minimum temperature at which fuel vapor will ignite Accelerant: any material used to start or sustain a fire.

8. Components for Combustion • Components needed for starting, growing and sustaining a fire: • Heat • auto-ignition temperature (or kindling point) minimum temperature where a substance will spontaneously ignite without an external ignition. • flash point: lowest temperature where a fuel will vaporize sufficiently to form an ignitable mixture with air. • Fuel • flammability limits: air/fuel mixtures beyond these limits, combustion cannot be sustained • Oxygen (oxidizer) • Chain-reaction

9. Components for Combustion • Components needed for starting, growing and sustaining a fire: • Heat • Fuel • Oxygen (oxidizer) • Chain-reaction

10. Components for Combustion • Fire Suppression: • Heat Suppression • Fuel Suppression • Oxidant Suppression • Chain-reaction Suppression

11. Stages of Fire Temperature

12. Types of Fire In the US, fires are classified into groupings depending upon the source of fuel. The classification of the fire is used to determine the best way to suppress the fire. The categories of fires are: • Class A fire: Ordinary combustibles such as wood, paper, cloth, trash, cardboard, and PVC; • Class B fire: Flammable liquid or gaseous fuels such benzene, gasoline, oil, butane, propane, and natural gas;

13. Types of Fire In the US, fires are classified into groupings depending upon the source of fuel. The classification of the fire is used to determine the best way to suppress the fire. The categories of fires are: • Class C fire: Involving live electrical equipment, often caused by short circuits or overheated electrical cables; • Class D fire: Combustible metals and alloys, such as iron, aluminum, sodium, and magnesium

14. Types of Fire In the US, fires are classified into groupings depending upon the source of fuel. The classification of the fire is used to determine the best way to suppress the fire. The categories of fires are: • Class K fire: Cooking media that contain vegetable or animal fat and oils.

15. Fire Dynamics Heat Suppression: The most common firefighting agent is water. Water largely acts to cool the fire by absorbing large amounts of energy. Compounds that cool the fire can help to bring it under control.

16. Fire Dynamics Oxidation Suppression: Carbon dioxide and sodium bicarbonate (solid extinguisher) act to smother the fire by removing oxygen from the equation. • Requires large amounts of CO2 • 75% of surface must be covered • Inert gases can be used instead due to the toxicity of CO2

17. Fire Dynamics Fuel Suppression: Removal of the fuel occurs by either physically isolating the fuel source or interrupting the flow of fuel into the fire, such as turning off a gas valve.

18. Fire Dynamics Chain Reaction Suppression: Halon acts at high temperatures to produce halogen atom radicals that rapidly react with radicals produced in the combustion chemical chain reaction • Removing the chain-continuing radicals interrupts the combustion process, terminating the fire even when sufficient heat, fuel and oxygen are present.

19. Fire Behavior Smoldering/Growth Stage: Small amounts of visible smoke may be visible at the beginning of this stage as the heat and mixture of fuel and oxidizer reaches a point to support active combustion, initially a relatively slow rate. As this oxidation reaction continues, the temperature rises, increasing the rate of the oxidation reaction.

20. Fire Behavior Smoldering/Growth Stage: The heat can be transferred by a number of means including radiation, convection, diffusion and conduction Initially, the fire’s growth is controlled by the properties of the fuel but, as the fire grows, it becomes controlled by the amount of oxygen present, often called ventilation- controlled fire growth.

21. Fire Behavior Full Development/Active Fire Stage: The critical combination of all the necessary elements must be in place to lead to a raging fire. • A flashover may take place leading into this stage. • the rapid transition to a fully developed fire by the nearly simultaneous ignition of all the flammable materials within an enclosed space. • occurs when the surfaces in an enclosed space are rapidly heated

22. Fire Behavior Full Development/Active Fire Stage: The critical combination of all the necessary elements must be in place to lead to a raging fire. • A flashover may take place leading into this stage. • the large amounts of unburned flammable gases that have accumulated from the pyrolysis of the surfaces • http://www.youtube.com/watch?v=QqMVm72FMRk

23. Fire Behavior Full Development/Active Fire Stage: The critical combination of all the necessary elements must be in place to lead to a raging fire. • A backdraft may take place later in this stage. • possible when a fire burns in an enclosed space and uses up much of its oxygen supply, starving the fire • the fire itself decreases even though there is still plenty of gaseous fuel.

24. Fire Behavior Full Development/Active Fire Stage: The critical combination of all the necessary elements must be in place to lead to a raging fire. • A backdraft may take place later in this stage. • occurs, often explosively, when oxygen is rapidly reintroduced to the accumulated unburned fuel such as by opening a window or from a roof collapse, leading to a sudden increase of oxygen leading to a flash of combustion • http://abcnews.go.com/GMA/video/giant-backdraft-explosion-caught-on-tape-18703524

25. Fire Behavior Decay Stage: the final stage of the fire when either the fuel is consumed or, due to firefighting efforts, one or more of the elements in the fire tetrahedron have been removed. • After the active flames have been extinguished, the fire may continue to smolder for days.

26. Arson Investigation • Presence of gasoline, kerosene or turpentine in debris • Liquid gasoline may be compared for origin • Criminalist may be able to reconstruct the ignition mechanism used

27. Arson Investigation Arsonis the criminal act of intentionally setting fire without lawful consent • Fire Pattern • Debris • Fire Growth and features • Accelerants • Other

28. Arson Investigation Arson is the criminal act of intentionally setting fire without lawful consent • Fire Pattern • Debris • Fire Growth and features • Accelerants • Other

29. Arson Evidence Physical evidence • incendiary devices (including matches, torches, lighter, firearms, and others • impression evidence (e.g., footprints, fingerprints, tool marks, etc.) • the location and pattern of debris

30. Arson Evidence Physical evidence • the presence of any trace evidence (e.g., hair, fibers, clothing, chemical residues, odors, etc.) • any unusual structural arrangements and burn patterns

31. Arson Evidence Care must be taken to prevent any contamination of the samples and keep them in as close to the original condition as possible until they reach the laboratory. • Accelerants are most often trapped in porous materials, such as wood, cloth, carpeting, and similar. • Collecting these types of samples in suspected points of origin are important as often the best source of accelerants.

32. GC Analysis • Hydrocarbon:any compound consisting only of carbon and hydrogen • Thin-layer chromatography is also useful for screening debris • Unevaporated gasoline • 90% evaporated gasoline • Unevaporated kerosene • 90% evaporated gasoline

33. GC Analysis

34. Explosives: Energetic Materials • Definitions • Compounds that react very quickly to produce heat, light, and the rapid outward expansion of gasses • Time is key! • Types • Chemical and Physical • High explosives - explosive charge that reacts at a speed greater than 1,000 m (1094 yards) per second • Detonation - high explosives yielding supersonic pressure waves (shock waves faster than the speed of sound, 343 m/s).

35. Explosives: Energetic Materials • Definitions • Compounds that react very quickly to produce heat, light, and the rapid outward expansion of gasses • Time is key! • Types • Chemical and Physical • Low explosives- reactions that occur at rates of less than 1,000 m/sec. • Deflagrations - propagated mainly by a flame front rather than a supersonic shock wave .

36. Explosives: Energetic Materials • Requirements • Must contain fuel AND oxidant • Separately: ANFO (ammonium nitrate/fuel oil explosive) • Together: TNT • Types • Primary: sensitive to heat, flame, shock or friction and typically detonate quickly • Secondary: relatively stable to heat, shock, electrical discharge, and friction and usually require much more energy to detonate

37. Explosives: Energetic Materials

38. Primary (Initiating) High Explosivesused in detonators • Lead azide, lead styphnate and diazodinitrophenol • Major ingredient of blasting cap • Not used as main charge b/c so sensitive; however, are used to detonate noninitiating explosives • PETN (pentaerythritol tetranitrate) • TNT (trinitrotoluene) • Dynamite • Smokeless powder (nitrocellulose)

39. Damage from High Explosives • Shock Wave • Heat • Flying Debris

40. Damage from High Explosives • Shock Wave • Heat • Flying Debris

41. Low Explosives & Black Powder • Explosive with a velocity of detonation less than 1,000 meters per second. • Ex.) • PETN (pentaerythritol tetranitrate) • TNT (trinitrotoluene) • Dynamite • Smokeless powder (nitrocellulose)- nonmilitary issued • Black powder • Black Powder ingredients: potassium nitrate, carbon & sulfur • Potassium chromate + Sulfuric acid + sugar can create a low explosive

42. Military Explosives: High Explosives • RDX (cyclotrimethlylenetrinitramine) the most powerful & popular • In the form of pliable plastic of dough-like consistency composition C-4 • PETN is used in TNT mixtures for small-caliber projectiles and granades

43. Spontaneous Combustion • A natural heat-producing process that may give rise to a fire in the presence of sufficient air & fuel • Ex.) hay stored in barns growing medium for bacteria which generate heat • Ex.) rags soaked w/ highly unsaturated oils, such as linseed oil • Ex.) Not people Dr. John Bentley Mrs. M H Reeser