Forensics exam on Chapters 14, 15, 16, and 17 (Chapter 16)

Low Explosives

-The most widely used explosives in the low-explosive group are black powder and smokeless powder. -Black powder is a mixture of potassium or sodium nitrate, charcoal, and sulfur. -Smokeless powder consists of nitrated cotton (nitrocellulose) or nitroglycerin and nitrocellulose. -Several hundred tons/inch 2

Physical State of the Fuel

-A fuel achieves a reaction rate with oxygen sufficient to produce a flame only when it is in the gaseous state. -A liquid burns when the temperature is high enough to vaporize the fuel. The flash point is the lowest temperature at which a liquid produces enough vapor to burn. -A solid such as wood burns only when exposed to heat hot enough to decompose into gaseous products (pyrolysis). -Glowing combustion or smoldering is burning at the fuel-air interface, such as a cigarette, the embers of a wood fire, or a charcoal fire.

Ion Mobility Spectrometer (IMS)

-A portable Handheld detector uses a vacuum or has a sample collection site which accepts a wipe. -Any explosive material is vaporized and subject to a beam of electrons or beta rays emitted by radioactive nickel.

Collection and Analysis Part 2

-All materials collected for the examination by the laboratory must be placed in sealed air-tight containers and labeled with all pertinent information. -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.

High Explosives Ammonium Nitrate Explosives Part 1

-Ammonium nitrate based explosives combine oxygen rich ammonium nitrate with a fuel. -They can consist of water gels, emulsions and ANFO(ammonium nitrate fuel oil)explosives -Gels: characterized by water resistant nature and are employed for underwater blasting.

Introduction

-Arson investigations often present complex and difficult circumstances to investigate due to the fact that the perpetrator has thoroughly planned the act, is not present during the act, and the destruction is so extensive. -The criminalist's function is rather limited to detecting and identifying relevant chemical materials collected at the scene and reconstructing and identifying igniter mechanisms.

Heat of Combustion of Various Fuels

-Asimina triloba- Pawpaw- largest edible fruit Indigenous to the US

Collection of Fire Scene Evidence

-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. -Substrate Control must also be taken Traces of flammable liquid residues may be located with a vapor detector (sniffer) or a trained canine.

Analysis

-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 by testing procedures that include "color spot tests, thin-layer chromatography"(dated), and gas chromatography/mass spectrometry. -Confirmatory identification tests may be performed on unexploded materials by infrared(IR) spectrophotometry.

High Explosives Ammonium Nitrate Explosives Part 2

-Emulsion explosives: consist of two distinct phases, oil and a water phase. Super saturated solution of ammonium nitrate within a hydrocarbon fuel source such as oil and an emulsifying agents. -Emulsifying agent can be micron-sized glass, resin, or ceramic spheres (microspheres or microballons). Size of the emulsifying agent controls the explosion's sensitivity and detonationvelocity -ANFO (ammonium nitrate fuel oil)- safe to handle, cheep and widely used in the mining industry. Ammonium nitrate in the form of fertilizer. 1993 bombing attempt of the world trade center

Indicators of Arson Part 2

-Evidence of severe burning found on the floor of a structure is indicative of a flammable liquid. -Discovery of an ignition device: The most common igniter is a match, but arsonists can construct many other types of devices to start a fire, including burning cigarettes, firearms, ammunition, a mechanical match-striker, electrical sparking devices, and a "Molotov cocktail." -combustible liquids are rarely entirely consumed during a fire.

Explosions

-Explosives are substances that undergo a rapid oxidation reaction with the production of large quantities of gases. -It is this sudden buildup of gas pressure that constitutes the nature of an explosion. -The speed at which explosives decompose permits their classification as high or low explosives.

Oxidation

-Fire is a type of oxidation reaction, which is the combination of oxygen with other substances to produce new substances. -Not all oxidation reactions proceed in a manner that one associates with a fire; e.g., rusting. -An oxidation reaction is associated with the concept of energy. Energy is classified as the ability of a system to do work. Energy takes many forms; e.g., heat, light and ATP converting to ADP (Adenosine triphosphate). -All oxidation reactions are examples in which more energy is liberated than what is required to initiatethe reaction. These are known as exothermic reactions.

Military and Peroxide Explosives

-In many countries outside the United States, the accessibility of military high explosives to terrorist organizations makes them very common constituents of homemade bombs. -RDX is the most popular and powerful of the military explosives, often encountered in the form of pliable plastic known as C-4. -PETN (pentaerythritol tetranitrate) is used in TNT(trinitrotoluene) mixtures for small-caliber projectiles and grenades. -Detonating cords are made of PETN -Detonators. Bombs made of high explosives must be detonated by an initiating explosion -blasting cap: composed of lead azide and PETN or RDX Initiation by a burning fuse or electrical current

Classification of explosives

-Low explosives. The speed of decomposition is called detonation Produces- heat, light and a subsonic pressure wave decompose at a rate of less 1,000 m/s due to slow rate they produce a propelling force -Black powder -Chlorate Mixtures High explosives are characterized by the speed of Deflagration. Deflagration refers to the creation of a supersonic shock wave -Detonation rates of 1,000-8,500 m/s

High Explosives Part 2

-Secondary explosives must be detonated by a primary explosive. -The speed of decomposition is known as deflagration. Its extremely rapid producing a supersonic shock wave creating a blast effect with an outward rush of gases at speeds as high as 7,000 miles per hour.

Indicators of Arson Part 1

-Some telltale signs of arson include evidence of separate and unconnected fires, the use of "streamers" to spread the fire from one area to another. An irregularly shaped pattern on the floor resulting from the pouring of accelerant onto the surface. -Normally, a fire has a tendency to move in an upward direction, and thus the probable origin will most likely be the lowest point showing the most intense characteristics of burning. -Many factors like drafts and building configuration can alter burn patterns and the Depth of char. -Transition from flashover to full-room involvement will dominate burn patterns.

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 search of the fire scene must focus on finding the fire's origin, which may be revile an accelerant or ignition device.

Laboratory Recovery of Flammable Residues

-The easiest way to recover accelerant residues from fire-scene debris is to heat the airtight container -The vapor or headspace is then removed with a syringe. -When the vapor is injected into the gas chromatograph, the sample is separated into its components, and each peak is recorded on the chromatogram. -In the vapor concentration technique, a charcoal strip is placed in the airtight debris container when it is heated.

Collection and Analysis Part 1

-The entire bomb site must be systematically searched to recover any trace of a detonating mechanism or any other item foreign to the explosion site.

Combustion

-To start fire, the minimum temperature needed to spontaneously ignite fuel, known as ignition temperature, must be reached. -Once combustion starts enough energy in the form of heat and light (flame) is liberated, a portion of which is used to sustain the fire. Fire is a chain reaction. -The heat given off when a substance burns is known as heat of combustion.

TATP (Triacetone triperoxide)

-Triacetone triperoxide (TATP) is a homemade explosive that has been used by terrorist organizations in the middle east. -TATP can be made by combining acetone and peroxide in the presence of an acid. -Friction and impact sensitive -Its existence has led to the banning of most liquids on commercial aircraft. -2005 London transit bombing "shoe bomber" 2001 November 2015 Paris attacks, 2016 Brussels bombings, Manchester Arena bombing, June 2017 Brussels attack and Parsons Green bombing

High Explosives Part 1

Among the high explosives: -Primary explosives are ultra-sensitive to heat, shock, or friction and provide the major ingredients found in blasting caps or primers used to detonate other explosives. -Secondary explosives are relatively insensitive to heat, shock, or friction and will normally burn rather than detonate if ignited in small quantities in the open air. -This group comprises the majority of commercial and military blasting, such as dynamite, TNT(trinitirtoluene), PETN, and RDX.