Chemistry - Fire And Explosions Flashcards
If a body was found burnt in a bed, you suspect the fire was intentionally lit, which of these clues would support arson?
High concentration of flammable liquid trace in one location
What is an accelerant?
A highly flammable chemical mixture, usually a liquid that hastens the spread of fire
What is an explosion from a chemical point of view?
The result of a rapid and violent chemical reaction of transformation
What are the 2 explosive chemical categories?
- nitrogen containing organic species
- peroxide containing species
What are nitrogen containing organic species?
By fat the largest group and its members be,omg to both decomposition or reactants in mixture explosion categories
What are peroxide containing species?
An emergency category of ‘improvised’ explosives.
What is the trend in explosives?
Increase in use of improvised explosives
Chemical reaction tests
- colour change
- eg Greiss test: used to detect the presence of nitrite
- lower confidence tests
When is HPLC, GC or MS used to analyse explosives?
Many explosives counpounds are organic molecules and thus their starting materials and derivatives can be analysed using these techniques
Commercially produced explosives…….
- have impurities added deliberately to chemically ‘stamp’ a batch
- this allows for trace analysis to track the source of an explosive if it has been used improperly
What is ICP-MS used for in explosive investigations?
Used to examine, identify and characterise metal fragments from explosion sites used in bombs as components or casings
What safety considerations must be made when working with explosive materials?
- maximum allowable working quantities
- correct storage and disposal
- use of derivative agents
- safety shields and protections
UV vis and IR spectroscopy techniques
- emit or absorb a unique spectra based on each molecule
What type of samples are suitable for UV vis and IR spectroscopy?
Liquid samples, no sample preparation required
What does TATP stand for?
Triacetone triperoxide
Why can TATP and its derivatives not be analysed by GC?
Because of its sensitivity to heat and instability when dry
Can HPLC be used to analyse TATP?
Can be used
Why is UV Vis spectroscopy not possible for the analysis of TATP?
It’s not optically active in those wavelengths
UV radiation and TATP
UV radiation can be used to decompose TATP to peroxide and a derivation agent that will react with the peroxide and fluoresce
What does ion mobility spectrometry allow for?
Rapid targeting of specific molecules
What does ion mobility spectrometry test for?
Nitrogen containing explosives
Where are swans taken from for ion mobility spectrometry?
Clothing, shoes and person belongings
Can be inserted directly into the instruments
Time & forensic chemistry
- time between an explosion and collection of samples
- time needed to run a test for the presence of explosives
