Chapter 5 Explosions © 2012 Cengage Learning. All Rights Reserved

Introduction—Objectives Identify the characteristics of gases. Compare and contrast the categories of explosives. Differentiate between components of the various types of explosives. Describe the methods of detecting, collecting, and processing explosion evidence. List some common analytical techniques used for explosives and explosive residue. Define terrorism. Forensic Science II: Explosions, Chapter 5 © 2012 Cengage Learning. All Rights Reserved

Introduction—Vocabulary explosion - the sudden release of chemical or mechanical energy caused by an oxidation or decomposition reaction that produces heat and a rapid expansion of gases high explosives - chemicals that oxidize extremely rapidly,producing heat, light, and a shock wave; will explode even when not confined kinetic molecular theory - a theory that states that the behavior of gases is predictable and explainable based on certain assumptions Forensic Science II: Explosions, Chapter 5 © 2012 Cengage Learning. All Rights Reserved

Introduction—Vocabulary low explosives - chemicals that oxidize rapidly, producing heat,light, and a pressure wave; will explode only when confined reagent - a substance used to produce a chemical reaction to detect, measure, or produce other substances terrorism - the intentional use of force or violence to coerce or intimidate governments or other large organized groups Forensic Science II: Explosions, Chapter 5 © 2012 Cengage Learning. All Rights Reserved

Timothy McVeigh April 19, 1995—Timothy McVeigh loaded a rental truck with ammonioum-nitrate fertilizer and other chemicals. When detonated, the explosion demolished one-third of the 7-story Murrah Federal Bldg. 70 people died, including 19 children. The FBI created a criminal profile. How was Timothy found and convicted? 5 Forensic Science II: Explosions, Chapter 5 © 2012 Cengage Learning. All Rights Reserved

Introduction to Explosions Like fire Caused by a chemical reaction—either by Oxidation—two substances combine to form a new substance Decomposition—a single compound breaks down A large amount of gas and energy is released very quickly Forensic Science II: Explosions, Chapter 5 © 2012 Cengage Learning. All Rights Reserved

Properties of Gas (Obj 5.1) Kinetic Molecular Theory —the behavior of gases is predictable Gases are made up of rapidly and randomly moving particles Most of the volume of a gas is empty space. Why? When a gas particle collides with the container or with other particles, there is no net loss of energy. The average kinetic energy is directly proportional to the temperature of the gas. There is no force of attraction between gas particles or between the particles and the walls of the container. Forensic Science II: Explosions, Chapter 5 © 2012 Cengage Learning. All Rights Reserved

Properties of Gas Forensic Science II: Explosions, Chapter 5 © 2012 Cengage Learning. All Rights Reserved

Properties of Gas Combined Gas Law—an equation that describes the relationship among volume, temperature, and pressure in confined gases. Forensic Science II: Explosions, Chapter 5 © 2012 Cengage Learning. All Rights Reserved

Properties of Gas Figure 5-5 A If the temperature of the enclosed gas increases and volume is held constant, the pressure increases. Forensic Science II: Explosions, Chapter 5 © 2012 Cengage Learning. All Rights Reserved

Properties of Gas Figure 5-5 B If the volume of the enclosed gas increases and temperature remains constant, the pressure decreases. Forensic Science II: Explosions, Chapter 5 © 2012 Cengage Learning. All Rights Reserved

Characteristics of an Explosion (Obj 5.2) Wave—a disturbance in matter that carries energy Longitudinal wave—a pressure wave Compressions Rarefactions Shrapnel Forensic Science II: Explosions, Chapter 5 © 2012 Cengage Learning. All Rights Reserved

Low Explosives (Obj 5.2, 5.3) Materials that burn rapidly but explode only when confined in a container Deflagration—the resulting combustion reaction Rapid, intense burning Pressure waves at less than 340 meters / sec. Often used as propellants, such as a bullet Forensic Science II: Explosions, Chapter 5 © 2012 Cengage Learning. All Rights Reserved

High Explosives (Obj 5.2, 5.3) Materials that Detonates easily Produces pressure waves to 8500 meters / sec. Shock wave moves faster than speed of sound Detonation—an explosion that causes violent disruption to the surrounding area Forensic Science II: Explosions, Chapter 5 © 2012 Cengage Learning. All Rights Reserved

High Explosives Primary High Explosives Secondary High Explosives Extremely sensitive to heat, pressure, and movement Usually too volatile for most uses Nitroglycerin Secondary High Explosives Less sensitive Often used for military and commercial purposes TNT and dynamite Forensic Science II: Explosions, Chapter 5 © 2012 Cengage Learning. All Rights Reserved

Fireworks Forensic Science II: Explosions, Chapter 5 © 2012 Cengage Learning. All Rights Reserved

Collecting Evidence (Obj 5.4) Soil samples Debris from inside the crater Traces of explosive residue Detonating devices Other pieces of the explosive device Forensic Science II: Explosions, Chapter 5 © 2012 Cengage Learning. All Rights Reserved

Microscopic Examination (Obj 5.5) Low-power stereomicroscopy Examine the debris for unexploded material Forensic Science II: Explosions, Chapter 5 © 2012 Cengage Learning. All Rights Reserved

Color Spot Tests (Obj 5.5) Reagent—a substance used to produce a chemical reaction to detect, measure, or produce other substances Modified Griess Test—detects presence of nitrate compounds Diphenylamine Test—detects most explosive residues, but not TNT Alcoholic potassium hydroxide (KOH)— detects TNT Forensic Science II: Explosions, Chapter 5 © 2012 Cengage Learning. All Rights Reserved

Color Spot Tests Forensic Science II: Explosions, Chapter 5 © 2012 Cengage Learning. All Rights Reserved

Chromatography (Obj 5.5) Thin Layer Chromatography (TLC) Presumptive test for explosives Rf values from TLC provide tentative identification of the components of the mixture A cellulose or silica gel plate as the stationary phase Forensic Science II: Explosions, Chapter 5 © 2012 Cengage Learning. All Rights Reserved

Chromatography Forensic Science II: Explosions, Chapter 5 © 2012 Cengage Learning. All Rights Reserved

Confirmatory Tests (Obj 5.5) Infrared spectroscopy A beam of infrared light passes through a sample Measure how much energy is absorbed Gas chromatography-mass spectroscopy Gas chromatography separates a substance into its compounds Mass spectroscopy breaks down the compounds into smaller charged particles and separates them based on their mass and charge Forensic Science II: Explosions, Chapter 5 © 2012 Cengage Learning. All Rights Reserved

Examining Physical Evidence (Obj 5.5) Examples: Pieces of wire Pieces of pipe Detonation devices Fingerprints Residue on clothes Timing devices Forensic Science II: Explosions, Chapter 5 © 2012 Cengage Learning. All Rights Reserved

Terrorism The intentional us of force or violence to coerce or intimidate governments or other organized groups. Groups or individuals Common reasons Political Environmental Religious Forensic Science II: Explosions, Chapter 5 © 2012 Cengage Learning. All Rights Reserved

Chapter Summary An explosion is an oxidation or decomposition reaction that releases a lot of gas and energy very quickly. Knowledge of the kinetic molecular theory is important in the investigation of explosions. Low explosives burn rapidly but explode only when confined. The burning of a low explosive is called deflagration. Forensic Science II: Explosions, Chapter 5 © 2012 Cengage Learning. All Rights Reserved

Chapter Summary High explosives can explode even when they are not confined, causing a violent disruption. Primary high explosives, such as nitroglycerin, are extremely sensitive to heat, pressure, and movement. Secondary high explosives are not as sensitive to heat or shock, but are capable of violent explosions. These are typically used by the military or for mining or construction. Forensic Science II: Explosions, Chapter 5 © 2012 Cengage Learning. All Rights Reserved

Chapter Summary Investigators collect soil samples and debris from an explosion’s point of origin. They search for explosive residue, pieces of the explosive device, or detonating devices. The crime lab examines evidence under a stereomicroscope. The crime lab can also wash the debris with acetone to dissolve the explosives and then analyze it to identify the type of explosive. Forensic Science II: Explosions, Chapter 5 © 2012 Cengage Learning. All Rights Reserved

Chapter Summary Thin layer chromatography is a presumptive test to provide a preliminary identification. Forensic scientists then perform confirmatory tests, such as infrared spectroscopy and gas chromatography–mass spectroscopy. Explosions are often caused by acts of terrorism. Terrorism may be politically, environmentally, or religiously motivated. Forensic Science II: Explosions, Chapter 5 © 2012 Cengage Learning. All Rights Reserved