Explosives

Explosives

You need an oxidizer and a fuel for something to burn

an explosion is really just a rapid expansion of gas

some explosives have an oxidizer and fuel portion in the same molecule

Types of Explosives

Low Explosives - velocity of deflagration (detonation) is less than 1000 m/s

examples: black powder, smokeless powder, methane

High Explosives - velocity of detonation is greater than 1000 m/s

Low Explosives

Burn rather than explode unless contained (as in a pipe bomb)

Natural gas from 5-14% in air is explosive, less or more will not ignite. Lean mixture (close to 5%) will explode and burn out while rich mixtures will explode and then generate a fire when the air rushes back in.

High Explosives

Primary Explosives - unstable to heat, shock, friction

they explode violently rather than burn

are used as primers to set off a secondary explosive

examples: lead azide, lead styphnate, diazodinitrophenol,

High Explosives

Secondary Explosives - fairly stable to heat, shock, friction

tend to burn instead of explode if ignited in small quantities

examples: nitroglycerin, trinitrotoluene (TNT), cyclotrimethylenetrinitramine (RDX), pentaerythritol tetranitrate (PETN), and 2,4,6- trinitrophenylmethylnitramine (tetryl)

High Explosives

H2C

NCH2

N

CH2

N

NO2

O2N NO2

RDX

C

HC

C

CH

C

CO2N NO2

NO2

NNO2H3C

tetryl

C

HC

C

CH

C

CO2N NO2

NO2

CH3

CH2

CH2

CCH2H2C

O

NO2

O

NO2

OO2N

OO2N

PETN

TNT

Dynamite

Alfred Nobel

Initially nitroglycerin and celite (diatomaceous earth) then nitroglycerin and wood pulp

40% dynamite means 40% nitroglycerin by mass

military dynamite is TNT and RDX based

Ammonium NitrateToday, dynamite is an ammonium nitrate based explosive usually

Ammonium nitrate (NH4NO4) water gel (thick, like toothpaste) is mixed with a sugar gel and aluminum

supersaturated NH4NO4 is mixed with droplets of oil (diesel), small glass spheres are added that control explosion properties

NH4NO4 solid is mixed with diesel (ANFO)

Military Explosives

C4 - 91% RDX and 9% plasticizer, used in hand grenades, mines, and for general demolition

B4 - 60% RDX, 40% TNT (small amount of calcium silicate), used for artillery shells

A3 - 91% RDX, 9% wax, used in artillery shells

TNT - used in artillery shells, bombs, grenades and military dynamite

Military Explosives

PETN - used for small caliber artillery and grenades, used as primacord to connect explosives to allow them to detonate almost simultaneously

Bombs

Low Explosive Bomb

needs to be contained to cause maximum damage

if not contained, will not produce a crater (“gentle push” instead of shattering blow), typical for natural gas explosions

Bombs

High Explosive

may or may not be contained

will have a crater

materials nearby will be shattered instead of bent

Collecting Evidence

wear coveralls, shoe covers, etc to prevent contamination

should collect soil from crater or origin of explosion

collect wood, rubber, fabric - could be penetrated by explosive particles

nonporous materials - may have explosive residue on surface

Collecting Evidence

look for traces of a detonating mechanism

collect evidence in metal containers or plastic bags

keep plastic bags separated because explosives can seep through and cross-contaminate

Identifying Explosives

Color Tests (presumptive)

explosive diphenylamine alcoholic KOHsodium sulfite

and KOHchlorate blue no change no change

nitrate blue no change no change

nitroglycerin blue no change no change

PETN blue no change no change

RDX blue no change no change

TNT no color red red or pink

Identifying Explosives

Microscopic Examination

smokeless powder is pressed into grains with characteristic shape and size

Identifying Explosives

TLC (to get an idea what is in it)

IR spectroscopy

HPLC (why not GC)?

The methods above are only good for molecular explosives, not ammonium nitrate ones (salts)

Taggant Programs

Taggants are small color-coded pieces of material added to an explosive to identify it

Currently only used in Switzerland

Causes changes to explosive properties and can react with explosives

Testing of taggants in the US resulted in the destruction of the Goex plant in East Camden, Arkansas in 1979 within 8 hours.