EXPLOSIONS

Arson or Explosions

• Often an explosion starts a fire. However, the bomb specialist will investigate the scene to determine if the explosion was intentionally set. The fire is considered a by-product of the explosion.

What is an Explosion?

• An explosion is the product of combustion accompanied by the creation of gases and heat at a very rapid rate.

• As these gases are released from confinement, they produce a blast effect, or an outward rush of gas—at a rate of up to 7,000 mph.

Explosive Components

An explosive device is comprised of three components:

1. A type of fuel2. An oxidizer 3. An igniter

Categories of Explosives

• Explosives are categorized by the speed at which they decompose.

• The two categories of explosives are low and high.

Low Explosives

•A low explosive decomposes at the speed of deflagration. •Deflagration (burning) is a rapid oxidation reaction accompanied by a sub-sonic pressure wave.•Low explosives decompose at a velocity of less than 1000 meters per second.•These explosives burn only at the surface.

Low Explosives (cont)

Low explosives produce a propelling or throwing action. This makes them suitable as propellants for ammunition or sky rockets.

The danger of low explosives should not be underestimated. If confined in a small container, the force of deflagration is very lethal.

Examples of Low Explosives• This category includes:

black powderchlorate powderfireworksflash powdernatural gas-air

smokeless powder

Examples of Low Explosives (cont)

Low Explosives (cont)

• The most widely used low explosive is black powder. This powder is readily available in gun stores or may be homemade.

• The most powerful low explosive is smokeless powder.

Low Explosives (cont)

• Chlorate powder is more sensitive and may ignite from the heat generated in a chemical reaction with sugar.

• A mixture of air and gaseous fuel will explode only when combined in certain ratios.

Low Explosives (cont)

• Fireworks or pyrotechnics are low explosives that are used as a form of entertainment.

• Due to the potential for danger, fireworks are legally restricted.

High Explosives

• A high explosive decomposes at the speed of detonation.

• Detonation is an extremely rapid oxidation reaction accompanied by an intense, high-speed shock wave.

• High explosives decompose instantaneously at a velocity of 1000-8500 meters per second.

• These explosives produce a smashing or shattering effect on the target.

• High explosives generally require a primer or blasting cap.

Two Groups of High Explosives

• High explosives are divided into two groups: primary and secondary.

• These groups are based on the sensitivity to heat, shock or friction.

Primary Explosives

• Primary explosives are the group of high explosives that are ultrasensitive to heat, shock or friction.

• Primary explosives detonate violently. Therefore, they are used as primers to detonate other explosives in a chain reaction.

Examples of Primary Explosives

• Primary Explosives, the main ingredient in blasting caps, include:

Lead AzideLead Styphnate

Diazodinitrophenol (DDNP)

Examples of Blasting Caps

Secondary Explosives

• Secondary explosives are relatively insensitive to heat, shock and friction.

• These explosives are used for commercial and military blasting.

• Secondary explosives generally require a detonator.

Example of Secondary Explosives

• Secondary explosives include:

Dynamite

TNT (trinitrotoluene)PETN (pentaerythritoltetranitrate)RDX (cyclotrimethylenetrinitramine)ANFO (ammonium nitrate/fuel oil)

Examples of Secondary Explosives (cont)

Dynamite

• In 1866, Alfred Nobel experimented with methods that would desensitize nitroglycerin. His experiments led to the invention of dynamite.

• In 1867, Nobel patented his invention.• When he died, in 1896, Nobel left a 9

million dollar endowment for the establishment of the Nobel Prize.

Dynamite (cont)

• Dynamite is sold in the form of a stick that is approximately 20 cm in length and 2.5 cm in diameter.

• Dynamite has 60% greater energy density than TNT.

• The main uses of dynamite are mining and construction.

TNT

• TNT is the most commonly used explosive by the military.

• TNT is poisonous and any contact with skin turns the skin a bright yellow.

PETN• PETN is an ultrasensitive high explosive.• It is used in detonating cords or primacords.

These cords are used to connect a series of explosive charges so all will detonate simultaneously.

RDX• RDX was one of the

first plastic explosives.

• It was widely used in WWII.

• This explosive is used in controlled demolition. The demolition of the Jamestown Bridge used RDX.

ANFO

• ANFO accounts for 80% of all explosive use in North America.

• Ammonium nitrate is widely used as a fertilizer, but when mixed with the correct concentration of fuel oil it becomes an explosive.

• ANFO is relatively inexpensive to manufacture.

Homemade Explosives

• TATP (triacetone triperoxide) is one type of homemade explosive. It is a mixture of acetone, hydrogen peroxide and hydrochloric acid.

• It is an impact-sensitive explosive that is very powerful when packed into small containers.

A Flow Chart of Explosives

The Damage

• The main damage from explosives occur due to:• flying shrapnel

• rapidly expanding gases create extreme pressure on the walls of the container. The container burst and sends shrapnel in all directions.

• self-propagating wave• caused by rapidly expanding gases

compressing the surrounding air.• can reach speeds of 7000 mph.

Detection and Collection of Evidence• First, investigators will locate the

crater that is at the origin of the blast.

• All loose dirt and debris is removed from the crater and sent to the lab.

• Any object penetrated by the shrapnel is collected.

Detection and Collection of Evidence (cont)• Residues from the

surfaces of nearby objects is also collected.

• All pieces of shrapnel are packaged and sent to the lab.

Detection and Collection of Evidence (cont)• The Ion Mobility Spectrometer (IMS) is a

portable detection machine that uses a vacuum to collect explosive residues from surfaces.

• The vaporized residue is converted to electrically charged ions that move through an electric field.

• Different ions move at different rates depending on their size and structure, which allows for identification.

Ion Mobility Spectrometer

Bomb ThreatTrained dogs are able to detect the scent of

explosives, even a few yards away. They are useful anywhere--airplanes, schools, hotels, parking lots, etc.

Bomb Threats

Once a bomb threat or a suspicious package has been detected, the bomb squad or a robot can be dispatched to disarm it.

Analysis of the Evidence

• Any recovered debris is rinsed with organic solvent and analyzed using color tests, thin-layer chromatography and gas chromatography/mass spectrometry.

• Unexploded devices are identified through X-ray diffraction or infrared spectrophotometry.