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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.