Explosions 6

Question 1

What is the purpose of an explosive investigation?

Answer 1

initial investigation - what happened
evidence at trial - what can we prove happened within specific parameters

Question 1

What are the 3 types of scientific evidence?

Determine these

Answer 1

classification - are explosives linked
identification - what is it
quantification - how much

Question 2

What are the three S’s in explosive investigation?

Determine these.

Answer 2

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.

Question 3

What happens if a value is close to limit of detection?

Answer 3

will be heavily scrutinised

Question 4

What locations would we want to detect explosive residue from?

Answer 4

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)

Question 5

What happens at a post explosive scene?

Answer 5

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?

Question 6

What do we do at post explosive scene if it does/doesn’t resemble something we have encountered before?

Answer 6

does - much easier to determine what evidence to collect
doesn’t - additional precautions need to be put in place

Question 7

How can we tell about type of materials found at post explosive scene?

Answer 7

look at particulates or droplets

Question 8

What must all personnel at scene adhere to?

Answer 8

Wear PPE (overalls, gloves, shoe covers etc.

Question 9

How do we usually recognise point of detonation?

Answer 9

As a crater/cracks in ground

if not detonated on ground, harder to find point of detonation

Question 10

What 2 factors effect the distance that evidence can be scattered at a post explosive scene?

What effect does this have?

Answer 10

type of explosive
amount of gas generated in detonation

Need to set up approximate cordons

Question 11

What must be collected from scene and surroundings? and how?

Answer 11

all loose soil and debris

package securely in sealed and properly labelled containers

Question 12

What type of residues may be found embedded at post explosive scene?

Where?

What is important to note when recovering residues?

Answer 12

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)

Question 13

What surface at post explosive scenes is typically good to collect evidence from?

Answer 13

smooth metal surfaces

Question 14

What are the 2 types of remains found at post explosive scene? Give examples.

Answer 14

detonating mechanism based evidence - blasting cap, electronic timer, mobile phone etc.

explosive container pieces - pipe section, pipe cap, pipe threads, melted/deformed plastic tubs

Question 15

Comment on amounts of residue left behind by low/high explosives?

Answer 15

low explosives (and propellants) - larger quantities

high explosives - smaller quantities

Question 16

What happens to IED’s often?

Answer 16

don’t often fully explode, or have a detonator malfunction (they fizzle out)

Question 17

How can we carry out rapid screening for bulk residues found at post explosive scene?

Answer 17

portable instruments like suitcase GC or handheld Raman

Question 18

Explain the 2 types of spectroscopy equipment used in explosive analysis labs?

Answer 18

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)

Question 19

State the 3 types of separation equipment used in explosive analysis labs?

Answer 19

HPLC/GC (GC used more as often got volatile components)
Ion chromatography
Electrophoresis

Question 20

State the 4 types of detector equipment used in explosive analysis labs?

Answer 20

Mass spectrometry - most sensitive but not always most robust
UV-Vis
Flame ionisation
Ion mobility

Question 21

What are clean room techniques?

What do clean rooms ensure?

What are four control measures within these?

Answer 21

required for trace explosive analysis to control background levels of explosive materials

ensure evidence is uncontaminated and admissible in court

1. positive pressure - contaminants diffuse out of the controlled environment (atmospheric pressure set higher than outside so contaminants migrate outside)
2. high efficient particulate air (HEPA) filters - removal of contaminant particulates
3. air particulates monitoring (readings taken of background levels and reviewed regularly, if over certain level it will be investigated)
4. disposable equipment (gloves, show covers, lab coats etc. that are double bagged on entry/exit

Question 22

What is biggest contamination of clean room?

Answer 22

analyst as they bring in contaminants from outside

Question 23

What are the allowed levels of explosive residues in a clean room?

Answer 23

<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.

Question 24

Define ‘trace’ and ‘bulk’ analysis for explosive evidence?

Answer 24

bulk - mg or more
- quantitative analysis
- spectroscopy paired with non-chemical evidence

trace - 10 to 100 ng
- often scrutinised/challenged in court due to higher uncertainties
- must be watertight (clean room techniques)

Question 25

What is important with evidence?

Answer 25

bagging and labelling of evidece

Question 26

How are trace explosives processed?

In what 3 ways?

Answer 26

Extraction of vapours for detection of volatile explosives and taggants (volatile)

Static Headspace Sampling
Dynamic Headspace Sampling
Solid Phase Microextraction (SPME)

Question 27

In what 3 ways are particulate samples recovered?

Answer 27

swabbing (good for smooth surfaces) - use a polar mixture for solvent (water/acetone or water/MeOH)

vacuuming - controlled vacuum that can bag evidence efficiently)

solvent wash - sonicate whole sample in suitable extraction solvent

Question 28

How are samples ‘cleaned’/pre-concentrated?

In what 4 ways can this be done?

Answer 28

Solid phase extraction (SPE) - small cartridge containing a sorbent material

4 types of SPE:
normal phase - adsorbs polar components strongly
reverse phase - adsorbs non-polar components strongly
ion exchange - useful for inorganic type compounds
size exclusion - adsorbs lower molecular weight strongly

can do combination of options

Question 29

How does SPE conditioning work?

Give examples for a reverse phase examples

Answer 29

Clean sorbent material (ethyl acetate)
Condition solvent using polar solvent mix (ethanol/water)
Apply sample (ethanol/water extract)
Non-polar compounds will stick to non-polar sorbent material in cartridge
Wash through and lot of inorganic compounds will fall through
Wash sorbent with polar mix then non-polar mix to wash out non-polar components
Elution of explosive residues using starting solvent (mid-polarity - ethyl acetate)

Question 30

How is static headspace sampling used to process trace explosives?

Answer 30

Sample placed in a sealed container
Heated
Volatile go into headspace, extracted and injected into GC

Question 31

How is dynamic headspace sampling used for processing of trace explosives?

What is it useful for?

Answer 31

Pushing through an inert gas into our vial containing our evidence
Headspace drawn into a solid phase trap
Retains explosive vapours
Concentrates sample before GC injection

Useful for trace quantities

Question 32

How is solid phase microextraction (SPME) used for processing trace explosives?

Why is it useful?

Answer 32

Pre-concentration step before injection
Fused silica fibre coated with stationary phase (usually PDMS)
Desorb (by heating) from stationary phase into GC injector

Dual function: helps with trace sample recovery and pre-concentration