Lecture 4 - Explosions 4

Question 1

what are Clandestine explosives

Answer 1

improvised/ self made explosives

VERY DANGEROUS

Question 2

where are Clandestine explosives used

Answer 2

terrorist attacks

their manufacture is normally uncontrolled and done by less experienced personnel

Question 3

what are the less experience personnel unaware of when manufacturing Clandestine explosives (3)

Answer 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

Question 4

name one common Clandestine explosive

what are the two forms this can be produced in

Answer 4

acetone peroxide

can be produced in the dimer (DATP) and trimer (TATP) form

Question 5

what is the oxygen balance of TATP

what are the products of this detonating

Answer 5

-151%

it is so oxygen deficient it doesn’t even produce CO

we get reformation of acetone and ozone

Question 6

why is TATP often used as a Clandestine explosive

Answer 6

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)

Question 7

why is TATP considered not an effective explosive

Answer 7

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

Question 8

what makes other explosives fluoresce under UV

Answer 8

if they contain aromatic rings or chromophores

Question 9

what analytical techniques would be suitable and not suitable for analysis of TATP

Answer 9

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

Question 10

how can peroxidase enzymes be used for detection of TATP

Answer 10

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

Question 11

what is wrong with testing of explosive substances on site making it not good for trace analysis

Answer 11

the techniques are not sensitive

GC-MS can be used at the lab but not on site

Question 12

Is hydrogen peroxide a good oxidiser or fuel in explosives

Answer 12

good oxidiser

H2O2 can break down into OH radicals easily which are very good oxidisers

Question 13

what do fine powders provide making them a potentially powerful explosive

Answer 13

a high surface area for the reaction to occur

Question 14

what happens to an explosive if it gets damp prior to detonation

Answer 14

it is unlikely to detonate properly, it is likely to fizzle out

Question 15

give another two examples of Clandestine bombs we looked at

Answer 15

the fertiliser bomb = ANFO

the Annie bomb = ANFO + nitrobenzene

Question 16

why are the use of explosives generally easily detectable

Answer 16

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

Question 17

what are taggants

Answer 17

additives giving explosives a traceable signature

are not effective explosives themselves and are added in trace amounts

Question 18

what are some examples of explosive taggants

Answer 18

DMNB
ethylene glycol dinitrate
nitrotoluene

Question 19

what are pre-detonation taggants used for and where are they used

Answer 19

to prevent attacks

used in high security systems e.g airportsh

Question 20

how are pre-detonation taggants normally detected

Answer 20

using sniffer dogs or mass spectrometry based systems

Question 21

why is the use of sniffer dogs beneficial but also not

Answer 21

beneficial = mobile and can detect low concentrations = ppm levels

not = sometimes ppm levels may not be enough to detect trace amounts

Question 22

due to sniffer dogs not being able to detect low enough concentration of taggant what analytical technique is used instead

Answer 22

ion mobility spectrometry

Question 23

explain how ion mobility spectrometry works

Answer 23

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

Question 24

how does the drift gas in ion mobility spectrometry achieve good separation of molecules

Answer 24

it is inert so wont react e.g argon or nitrogen

if restricts the movement larger molecules more than smaller ones separating them

Question 25

why is ion mobility spectrometry better than GC or LC here

Answer 25

faster so suitable for high security settings

Question 26

what are ion mobility spectrometers often combined with to identify the ions

Answer 26

a mass spectrometer e.g TOF or quadrupole analysers

Question 27

how does an electric field affect the movements of molecules in ion mobility spectrometry

Answer 27

stronger electric field = faster movement of molecules

Question 28

what is an example of a homemade nitrocellulose-like material

Answer 28

adding nitric acid to a sock

sock = cellulose
when treated with nitric acid it can form nitrocellulose

when lit:
normal sock burns
nitro sock explodes (we get rapid deflagration)

Question 29

why are homemade nitrocellulose materials dangerous

Answer 29

they have the potential to generate huge amounts of energy

this can be uncontrollable as it is difficult to remove the oxygen once the deflagration has begun

Question 30

what is an example of an improvised explosive propelled weapon

Answer 30

plastic explosive e.g Semtex = RDX and PETN

explosive mixtures based on what is availabl to peopl