Explosives & Improvised Explosive Devices

Stages of Explosives Investigations

Prevention > Reaction > Reconstruction

Explosives

Substances that undergo a rapid oxidation reaction with the production of a large quantity of gases

Whether an explosive is high or low is determined by:

The speed at which they decompose

Low Explosives

Confined to a container, i.e. a pipe. Speed of decomposition is called deflagration causing container to explode into shrapnel.

Common Low Explosives

Black Power (potassium/sodium nitrate, charcoal, & sulfur) and Smokeless Powder (nitrated cotton(nitrocellulose)/nitroglycerin & nitrocellulose)

High Explosives

Primary and Secondary; commercial and military (TNT, PETN, & RDX); Speed of decomposition called detonation

Primary Explosives

Ultra sensitive and provide the major ingredients in blasting caps or primers used to detonate other explosives

Secondary Explosives

Relatively insensitive and have to be detonated by primary explosives

RDX

Most popular and powerful military explosive, commonly used in C-4 form.

Triacetone Triperoxide (TATP)

A homemade explosive used by terrorist organizations. Made by combining acetone and peroxide in the presence of an acid.

Propagation Reaction

A reaction or process that moves in a direction like a flame front

Linear Burn Rate

Measuring the distance of a flame over a given time

Deflagration

An oxidative decomposition/burning in which propagation speed is slower than the speed of sound. Direction of flow of reaction is opposite of reaction front

Explosions

A sudden, rapid, often violent release of hot expanding gases; pressure/blast waves

Schlieren Imaging

Photographs pressure waves

Detonation

Occurs when speed of the reaction front exceeds the speed of sound; shockwave

Shockwave

When a pressure wave exceeds the speed of sound

Improvised Explosive Devices (IEDs)

I.e. pipe bombs; made with materials that can be easily purchased

Molecular Explosives

Singular molecules such as Nitroglycerin, Ammonium Nitrate, and Fuel Oil

The Ion Mobility Spectrometer is used to:

Screen objects for the presence of explosive residues

Fragments can be used to

Reconstruct a bomb; can link serial bombings

Debris is collected in

Airtight paint cans