Explosions 6 Flashcards
What is the purpose of an explosive investigation?
initial investigation - what happened
evidence at trial - what can we prove happened within specific parameters
What are the 3 types of scientific evidence?
Determine these
classification - are explosives linked
identification - what is it
quantification - how much
What are the three S’s in explosive investigation?
Determine these.
selectivity - ability to determine an analyte from a mixture without other components interfering
specificity - confident that nothing other than desired analyte contributes to the result we are claiming
sensitivity - related to LOD and LOQ. method, sample prep and volume contribute to sensitivity.
What happens if a value is close to limit of detection?
will be heavily scrutinised
What locations would we want to detect explosive residue from?
suspects hands, clothes and skins
clandestine labs or explosive storage dumps to find any materials/explosives, ways they’ve been stored, planned to be detonated
explosion scenes (or failed attempt at an explosion)
What happens at a post explosive scene?
any unexploded devices would be rendered safe by explosive ordinance technicians
does it contain a viable device (does it have potential to be an effective explosive device) ?
does it resemble anything encountered before?
was a condensed phase (solid or liquid) explosive used?
what was the explosive?
how was it used (harm, scaremongering, correct way)?
how was it initiated?
What do we do at post explosive scene if it does/doesn’t resemble something we have encountered before?
does - much easier to determine what evidence to collect
doesn’t - additional precautions need to be put in place
How can we tell about type of materials found at post explosive scene?
look at particulates or droplets
What must all personnel at scene adhere to?
Wear PPE (overalls, gloves, shoe covers etc.
How do we usually recognise point of detonation?
As a crater/cracks in ground
if not detonated on ground, harder to find point of detonation
What 2 factors effect the distance that evidence can be scattered at a post explosive scene?
What effect does this have?
type of explosive
amount of gas generated in detonation
Need to set up approximate cordons
What must be collected from scene and surroundings? and how?
all loose soil and debris
package securely in sealed and properly labelled containers
What type of residues may be found embedded at post explosive scene?
Where?
What is important to note when recovering residues?
metal shards
nearby soft objects (wood, rubber, bodies) and nearby metal objects (road signs)
Can’t just look at floor, have to look around (3D scene)
What surface at post explosive scenes is typically good to collect evidence from?
smooth metal surfaces
What are the 2 types of remains found at post explosive scene? Give examples.
detonating mechanism based evidence - blasting cap, electronic timer, mobile phone etc.
explosive container pieces - pipe section, pipe cap, pipe threads, melted/deformed plastic tubs
Comment on amounts of residue left behind by low/high explosives?
low explosives (and propellants) - larger quantities
high explosives - smaller quantities
What happens to IED’s often?
don’t often fully explode, or have a detonator malfunction (they fizzle out)
How can we carry out rapid screening for bulk residues found at post explosive scene?
portable instruments like suitcase GC or handheld Raman
Explain the 2 types of spectroscopy equipment used in explosive analysis labs?
IR/Raman - very quick and non-destructive
X-ray (SEM-EDX) - more time consuming than raman
SEM - looks at morphological properties of particulates
EDX - looks at elemental composition (can scan across and see if have over threshold levels)
State the 3 types of separation equipment used in explosive analysis labs?
HPLC/GC (GC used more as often got volatile components)
Ion chromatography
Electrophoresis
State the 4 types of detector equipment used in explosive analysis labs?
Mass spectrometry - most sensitive but not always most robust
UV-Vis
Flame ionisation
Ion mobility
What are clean room techniques?
What do clean rooms ensure?
What are four control measures within these?
required for trace explosive analysis to control background levels of explosive materials
ensure evidence is uncontaminated and admissible in court
- positive pressure - contaminants diffuse out of the controlled environment (atmospheric pressure set higher than outside so contaminants migrate outside)
- high efficient particulate air (HEPA) filters - removal of contaminant particulates
- air particulates monitoring (readings taken of background levels and reviewed regularly, if over certain level it will be investigated)
- disposable equipment (gloves, show covers, lab coats etc. that are double bagged on entry/exit
What is biggest contamination of clean room?
analyst as they bring in contaminants from outside
What are the allowed levels of explosive residues in a clean room?
<5 ng - none
5 - 10 ng - confirm identity of explosive and clean area (not too serious)
10-100 ng - clean area, pause all analyses and retest until sample tests negative
> 100 ng (more serious contamination) - conduct formal enquiry to identify contamination source and type of contaminant. review potentially affected casework and analyses. decide how contamination might have affected casework. Doesn’t necessarily mean won’t be admissible in court, just need to investigate it. Clean and re-test until negative.
