Lecture 4 - Explosions 4 Flashcards
what are Clandestine explosives
improvised/ self made explosives
VERY DANGEROUS
where are Clandestine explosives used
terrorist attacks
their manufacture is normally uncontrolled and done by less experienced personnel
what are the less experience personnel unaware of when manufacturing Clandestine explosives (3)
quality control and impurities within starting material or products - can increase shock sensitivity due to impurities
the correct temp control needed resulting in runaway synthesis = chain reaction that can cause harm or accidental detonation
the exact products they have made - due to no analytical equipment
name one common Clandestine explosive
what are the two forms this can be produced in
acetone peroxide
can be produced in the dimer (DATP) and trimer (TATP) form
what is the oxygen balance of TATP
what are the products of this detonating
-151%
it is so oxygen deficient it doesn’t even produce CO
we get reformation of acetone and ozone
why is TATP often used as a Clandestine explosive
TATP can be made from hydrogen peroxide and acetone = readily available
detection of TATP is difficult as it does not contain nitro groups or metallic elements such as aluminium or iron oxide
it also have no significant UV exposure (fluorescence)
why is TATP considered not an effective explosive
the process upon detonation is endothermic and doesn’t produce a large volume of gas = not an effective explosive - called an entropic explosion
the explosive tends to fizzle out or fail rather than blow up
what makes other explosives fluoresce under UV
if they contain aromatic rings or chromophores
what analytical techniques would be suitable and not suitable for analysis of TATP
HPLC and UV-Vis = not good as there is no strong UV or visible light absorption
GC-MS could be done as TATP is volatile but this is hard to do as TATP decomposes and is impractical for field work
the use of peroxidase enzymes is good for on site analysis
how can peroxidase enzymes be used for detection of TATP
these enzymes cause TATP to go back into hydrogen peroxide and acetone
then a test for hydrogen peroxide can be done
under UV light there will be a colour change from colourless to green
what is wrong with testing of explosive substances on site making it not good for trace analysis
the techniques are not sensitive
GC-MS can be used at the lab but not on site
Is hydrogen peroxide a good oxidiser or fuel in explosives
good oxidiser
H2O2 can break down into OH radicals easily which are very good oxidisers
what do fine powders provide making them a potentially powerful explosive
a high surface area for the reaction to occur
what happens to an explosive if it gets damp prior to detonation
it is unlikely to detonate properly, it is likely to fizzle out
give another two examples of Clandestine bombs we looked at
the fertiliser bomb = ANFO
the Annie bomb = ANFO + nitrobenzene
why are the use of explosives generally easily detectable
due to the presence of taggants
in the making of an explosive properties are included that can be easily detected (volatile) and are not commonly used in the normal environment
what are taggants
additives giving explosives a traceable signature
are not effective explosives themselves and are added in trace amounts
what are some examples of explosive taggants
DMNB
ethylene glycol dinitrate
nitrotoluene
what are pre-detonation taggants used for and where are they used
to prevent attacks
used in high security systems e.g airportsh
how are pre-detonation taggants normally detected
using sniffer dogs or mass spectrometry based systems
why is the use of sniffer dogs beneficial but also not
beneficial = mobile and can detect low concentrations = ppm levels
not = sometimes ppm levels may not be enough to detect trace amounts
due to sniffer dogs not being able to detect low enough concentration of taggant what analytical technique is used instead
ion mobility spectrometry
explain how ion mobility spectrometry works
molecule are ionised by an electric field generating anions and cations
these ions are fired through a drift tube against a drift gas - the direction of this gas is against the ions to stop molecules moving through too quickly
there is a detector at the end of the drift tube
how does the drift gas in ion mobility spectrometry achieve good separation of molecules
it is inert so wont react e.g argon or nitrogen
if restricts the movement larger molecules more than smaller ones separating them
