Analysis of Explosives Ms. Scribner’s Forensic Science Class—Eisenhower High School

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