analysis of explosives ms. scribner’s forensic science class—eisenhower high school
TRANSCRIPT
Analysis of Explosives
Ms. Scribner’s Forensic Science Class—Eisenhower High School
Introduction
Most bombing incidents involve homemade explosive devices
There are a great many types of explosives and explosive devices
Lab must determine type of explosives and, if possible, reconstruct the explosive device
Explosives
Combustion (or decomposition) of explosives occurs so rapidly, that there isn’t enough time for the oxygen in the surrounding atmosphere to combine with the fuel.
Therefore, many explosives must have their own source of oxygen – or oxidizing agents
Definitions
Explosion—sudden release of chemical or mechanical energy caused by an oxidation or decomposition reaction that produces heat and a rapid expansion of gases.
Definitions
Reagent—a substance used to produce a chemical reaction to detect, measure, or produce other substances.
Spot tests can be
administered to
identify
IED--An improvised explosive device is a bomb constructed and deployed in ways other than in conventional military action. It may be constructed of conventional military explosives, such as an artillery round, attached to a detonating mechanism. IEDs are commonly used as roadside bombs.
Chemistry of Explosion
Essentially a combustion reaction - like a fire
Major difference is speed of reaction
Damage caused by rapidly escaping gases and confinement
Definitions
High explosives—chemicals that oxidize extremely rapidly, producing heat, light and a shock wave; will explode even if not confined
Low explosives—chemicals that oxidize rapidly, producing heat, light, and a pressure wave; will explode only when confined.
Types of Explosives Low explosives
• Escaping gases up to about 3000fps (foot per second)
• Crucial element is physical mixture of oxygen and fuel
• Examples are black and smokeless powders Black powder is mixture of potassium nitrate, charcoal
and sulfur Smokeless powder is nitrocellulose and perhaps
nitroglycerine
Types of Explosives
High explosives• Velocity of escaping gases up to 10,000fps• Oxygen usually contained infuel molecule
Two types• Initiating - Senistive, will detonate readily when
subjected to heat or shock. Used to detonate other explosives in explosive train
• Noninitiating - relatively insensitive, requires heat or shock. Includes TNT or PETN
Classification by Use
Commerical Explosions: Ammonium Nitrate fuel oil (ANFO), black powder, dynamite
Military Explosions: RDX (commonly known as C-4), PETN, PETN mixed with TNT to make grenades
IED—low explosives placed into confinded containers
Ammonium nitrate based
• Water gels• Emulsions--are intimate mixtures of oxidizers
and carbonaceous fuels made as water in oil type of Emulsions used for blasting in quarries, stripping in underground metal mines, tunneling, well sinking, and road construction .
• ANFO’s--ammonium
nitrate/fuel oil) is a widely used
bulk industrial explosive mixture
Analysis of Explosives
Microscopy
Thin layer chromatography
• Visualise with Greiss reagents
Infrared spectrophotometry
Detonator fragments
Microscopic Examination
Perforated disc Tube Ball Disc Rod Lamel
1, 2, and 3 step Explosive Trains
Explosive Trains
The Role of Forensic Science in the Investigation of Major
Acts of Terrorism
A forensic science technician, also referred to as a criminalist, gathers, interprets and analyzes evidence using forensic science techniques and tests.
Analyze and test tissue samples Test chemical substances and physical materials Interpret lab findings Collect criminal evidence Reconstruct crime scenes Testify as expert witness during trials
First World Trade Center Bombing
1993 The Scenario—first bombing attempt
Urea nitrate bomb put into truck and driven into underground WTC garage and parked at 4th level down
Subsequent explosion did extensive damage to several levels of the garage and less damage to other levels
Although goal was to topple WTC, little structural damage was done
Some loss of life
Goals of Investigation
Identify victimsIdentify explosiveRecover bomb and timing
deviceDetermine method of delivery
Evidence Sought
Investigators had to remove large quantities of concrete, steel and cars to get to bomb seat
Bomb seat contained most of the important evidence
Bomb parts; timer, casing, etc. Explosive residue Parts of truck that contained explosive
Areas of Forensic Science
Explosives Engineering Questioned documents Fingerprints Pathology DNA
The Murrah Building, Oklahoma City
Domestic Terrorism
The Scenario--1995 ANFO explosive and timer
packed into a rented truck, which was then parked outside Murrah building
Explosive confined to closed space such as truck is much more powerful
Resulting explosion resulted in severe damage to building and loss of more than 100 lives
Goals of Investigation
Identify victimsIdentify explosiveFind timer and
bomb partsDetermine method
of delivery
Evidence Sought
Easier to find than in WTC because bomb seat outside building
Explosive residues Bomb parts Bodies and body parts; cadaver dogs,
flies Personal effects; helps in identification
of human remains
Areas of Forensic Science
Anthropology DNA and serology Pathology Entomology Explosives Trace evidence Engineering Questioned documents Fingerprints
WTC Destruction-2001
The Scenario Large airplanes, loaded with fuel, crash into WTC
buildings Raging fires ignite everything in building above crash
sites. Metal supports melt from heat Building collapses due to inability to support its own
weight after structural damage Thousands of people killed
http://www.history.com/topics/9-11-attacks 4min video
Goals of Investigation
Cause known, no need to determine how destruction occurred
Recover and identify bodies, parts of bodies and charred remains
Recover personal effects that might help identify victims or perpetrators
Evidence that might determine how hijackings occurred.
Evidence Sought
Bodies and body parts; cadaver dogs, flies
Charred remains Personal effects Trace evidence such as charred papers Weapons such as knives Constraining devices such as wire
Areas of Forensic Science
Anthropology DNA and serology Odontology Pathology Entomology Trace evidence Questioned documents Fingerprints Tools and toolmarks
Boston Bombing—April 15, 2013
Two pressure cooker bombs exploded during the Boston Marathon at 2:49 pm
killing 3 people and injuring an estimated 264 others. The bombs exploded about 12 seconds and 210 yards (190 m) apart, near the finish line on Boylston Street
A pressure cooker bomb is an The IED was created by inserting explosive material into a pressure cooker and attaching a blasting cap into the cover of the cooker.
Pressure cooker bombs have been used in a number of attacks---
2006 Mumbai train bombings, 2010 Stockholm bombing (failed to explode), 2010 Times Spare car bombing attempt (failed to explode)
Goals of Investigation
Cause known, no need to determine how destruction occurred
Recover and identify bodies, parts of bodies and charred remains
Recover personal effects that might help identify victims or perpetrators
Evidence that might determine how the object was left at the scene.
Evidence Sought
Photos of person of interest Personal effects Bomb parts; timer, casing, etc. Explosive residue Constraining devices such as pieces of
the pressure cooker, wire or duct tape
Areas of Forensic Science
Anthropology DNA and serology Odontology Pathology Entomology Trace evidence Questioned documents Fingerprints Tools and toolmarks