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Fires & Explosions > Lecture 6 > Flashcards

Lecture 6 Flashcards

1
Q

What is the purpose of an explosive investigation?

A
  • An initial investigation is done to find out what happened
  • To determine what we can prove happened within specific parameters
  • To present evidence at trial
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2
Q

What are the different types of scientific evidence?

A
  • Classification
  • Identification
  • Quantification
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3
Q

Classification

A
  • Are these explosives linked?
  • If you found some explosive residues can that be linked to another source?
  • Can we work out where it came from or where it was made?
  • Can we be sure it’s linked to the IED that’s been detonated?
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4
Q

Identification

A

Is it TNT?

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5
Q

Quantification?

A
  • How much explosive material has been used?
  • This is important if someone uses larger amounts which has the potential to cause much more harm.
  • This can also be helpful if someone claims it was an accidental detonation because there are legal restrictions on how much material can be stored at once.
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6
Q

What are the 3 S’s in an explosive investigation?

A
  • Selectivity
  • Specificity
  • Sensitivity
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7
Q

Selectivity

A

Ability to determine an analyte from a mixture without other components (which vary!) interfering

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8
Q

Specificity

A

Nothing other than the desired analyte contributes to the result
Confident that nothing else can contribute to the result we are claiming

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9
Q

Sensitivity

A

Linear slope of the response (calibration curve)
Related to the amount and the limits of detection and quantification
Method, sample prep, volumes used all relate to this

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10
Q

What locations would we want to detect explosive residue from?

A
  • Suspects hands
  • Clandestine labs or explosive storage dumps
  • Explosion scenes
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11
Q

Explosion scenes

A

Can also be a failed or accidental explosion scene

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12
Q

Clandestine labs or explosive storage dumps

A
  • Need to take a lot of evidence
  • Look around the site for source of reagents used to make the explosives
  • The way the explosives are stored and planned to be detonated
    The materials and other aspects can be important evidence to build the case
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13
Q

Suspects hands

A

Take evidence from their hands, clothes, skin and other areas.

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14
Q

What should you check before starting an investigation at an explosion scene?

A
  • You have to make sure the scene is safe before starting an investigation
  • Any unexploded devices need to be rendered safe by an explosive ordinance technician
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15
Q

Once checking the scene is safe, what should you do?

A
  • The first thing you should do once it’s safe is to check to see if the explosive contains a viable device.
    Then look at the design, does it have the potential to actually be an effective explosive?
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16
Q

What should you consider when starting an explosive investigation?

A
  • Check if it contains a viable device.
  • From the design, does it have the potential to be an effective explosive?
  • Does it resemble anything encountered before?
  • Are they using materials to make illicit explosives?
  • Was a condensed phase (solid or liquid) explosive used?
  • What was the explosive?
  • How was it used?
  • How was it initiated?
  • Was it intended to cause harm or panic?
  • Was it used in the right way and used correctly for the type of explosive it is?
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17
Q

What needs to be considered when investigating an explosive that hasn’t been encountered before?

A

If it hasn’t been encountered before than additional precautions need to be taken - determine the chastity and volatility of the explosive, the housing and how it tended to be detonated

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18
Q

Why is it easier if an explosive has been encountered before?

A

If it has been encountered before it makes it easier as you will know its properties better.

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19
Q

What can the state of the explosive tell you?

A

Particulates and droplets tells you about the materials that might have been used

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20
Q

What should be true for an explosive from a military device?

A

If it was a military device it would have some form of tag that can identify it

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21
Q

What can be used to identify volatile components?

A

Mobile GC can be used to identify volatile components

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22
Q

How can you find the point of detonation?

A
  • The point of detonation is usually recognised by a crater
  • If the ground is ‘soft’ it is relatively easy to find
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23
Q

What is the problem with a detonation that isn’t in the floor?

A

If it’s been detonated on something other than the floor a lot of the material gets blown away so determining the specific detonation point can be challenging.

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24
Q

How can you protect the scene from contamination?

A

All personnel wear overalls, gloves, shoe covers, etc. to protect the scene

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25
Q

Why is an accurate cordon important?

A

Evidence may be scattered a considerable distance which is dependant on type of explosive, amount of gas generated, etc

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26
Q

What should be collected from an explosive scene?

A
  • All loose soil and debris to be collected from the scene and surroundings
  • These should be packaged securely in sealed and properly labelled containers
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27
Q

What may be found embedded in soft objects?

A

Residues may be found embedded in nearby soft objects (wood, rubber, bodies), this is often true for metal shards.

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28
Q

Where else may residues be found?

A
  • Residues are also found on surfaces of nearby metal objects, e.g. road signs
  • Don’t just look at the floor, look around.
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29
Q

What should the entire area be searched for?

A

Entire area searched for remains of detonating mechanisms and the explosive container

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30
Q

Detonator based evidence

A
  • Blasting cap,
  • Electronic timer,
  • Mobile phone, etc.
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31
Q

Explosive container pieces

A
  • Pipe section,
  • Pipe cap,
  • Pipe threads,
  • Melted/deformed plastic tubs, etc.
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32
Q

What residue would high and low explosives leave?

A
  • High explosives typically leave very small quantities of residue
  • Propellants and low explosives may leave larger quantities
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33
Q

What is a reoccurring problem with improvised explosive devices?

A

Improvised explosive devices often don’t fully explode or have a detonator malfunction (as in London 21st July 2005 copycat bombing)

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34
Q

How can rapid screening of bulk residues be accomplished?

A

Rapid screening for bulk residues can be accomplished using a portable instruments like a ‘suitcase GC’ or handheld Raman

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35
Q

What type of explosive leaves the most evidence behind?

A

propellants and low explosives

36
Q

What does SEM allow us to look at for explosives?

A

SEM allows us to look at detail at specific particulates, arrangement and size of fragments

37
Q

What can we obtain from EDX?

A

EDX allows us to get elemental identification however it is time consuming so you should make a decision on what to look at and prioritise)

38
Q

Why is GC used over HPLC?

A

GC is used more often as it can be used on volatile components

39
Q

What is ion chromatography used for?

A

It can detect nitrates and chlorates

40
Q

Mass Spectrometry

A

it is very sensitive so it’s good for trace amounts but it isn’t always the best detection method.

41
Q

Detectors used for explosive analysis

A
  • Mass Spectrometry
  • UV Vis
  • Flame Ionisation
  • Ion Mobility
42
Q

Spectroscopy used for explosive analysis

A
  • IR / Raman (Quick and Non-destructive)
  • X-ray (SEM & EDX)
43
Q

Separation Methods used for Explosive Analysis

A
  • HPLC
  • GC
  • Ion Chromatography
  • Electrophoresis
44
Q

What is required for trace explosive analysis?

A
  • Clean rooms
  • The background level of explosive material is extremely tightly controlled and well known.
45
Q

What do clean rooms ensure?

A

They ensure evidence is uncontaminated and admissible in court

46
Q

What are the control measures in a clean room?

A
  • Positive pressure
  • High-Efficiency Particulate Air (HEPA) Filters
  • Air particulate monitoring
  • Disposable equipment
47
Q

Positive pressure

A
  • Contaminants diffuse out of the controlled environment, and won’t allow any contaminants in.
  • The pressure is set higher than it is outside.
  • This means the contaminants migrate away naturally.
48
Q

High Efficiency Particulate Air Filters

A

This is done for the removal of contaminant particulates

49
Q

Air Particulate Monitoring

A

Air quality is monitored regularly to keep an eye on background levels and reviewed regularly. If anything goes up a particular level then it is investigated.

50
Q

Disposable Equipment

A

Gloves, shoe covers, lab coats, etc. that are double bagged on entry/exit

51
Q

What is the biggest source of contamination in a clean room?

A

The biggest source of contamination in a clean room is the analyst themselves as they’re bringing contaminants in from outside.

52
Q

Examination Area

A
  • Examination area when the evidence is processed and prepared.
  • This helps to prevent the spread of different contaminants
53
Q

How is the integrity maintained in a cleanroom?

A
  • Regular monitoring is used to maintain explosive cleanroom integrity
  • Environmental samples taken regularly
54
Q

What action should be taken if an explosive residue is <5 ng?

A

No action needs to be taken

55
Q

What action should be taken if an explosive residue is between 5-10ng?

A

Confirm the identify of the explosive and clean the area

56
Q

What action should be taken if an explosive residue is between 10-100 ng?

A

Clean area and re-test until sample tests negative, all analysis is paused to make sure the levels go back down.

57
Q

What action should be taken if an explosive residue is >100 ng?

A
  • This is Serious contamination.
  • Conduct enquiry to identify the contamination source and the type of contaminant it is.
  • Review potentially affected casework and decide how it might have affected it.
  • Clean and re-test until negative.
  • This doesn’t mean it would be admissible in court but it does need to be investigated
58
Q

What is the problem with explosive evidence?

A
  • This type of evidence can be difficult to bag
  • Packing the evidence correctly along with labelling is very important
59
Q

What does bulk analysis mean?

A
  • Bulk refers to mg or more
  • Quantitative analysis
  • Spectroscopy paired with non chemical evidence
60
Q

What does trace analysis refer to?

A
  • Trace refers to 10 to 100 ng
  • Often challenged in court
  • Needs to be ‘watertight’ 🡪 clean room techniques
  • The higher uncertainties are associated with this type of evidence
61
Q

What is headspace sampling used for?

A

Extraction of vapours for detection of volatile explosives and taggants

62
Q

How are trace explosives processed?

A

Extraction of vapours for detection of volatile explosives and taggants

63
Q

What are the two different types of headspace sampling used?

A
  • Static Headspace Sampling
  • Dynamic Headspace Sampling
64
Q

Static Headspace Sampling

A
  • Sample is placed in a sealed vial
  • Sample is heated up so the volatiles go into headspace
  • Headspace injection is done to extract the vapours and perform a GC analysis
65
Q

Dynamic Headspace sampling

A
  • Sample is placed in a secure vial
  • An interest gas is pushed through
  • Inert gas pulls out the volatiles
  • Headspace volatiles is drawn into a solid phase trap
  • The trap retains the explosive vapours
  • Concentrates sample before GC injection
  • Useful for trace quantities
66
Q

Solid Phase Microextraction (SPME)

A
  • Pre-concentration step before injection
  • Fused silica fibre coated with stationary phase
  • Stationary phase is usually PDMS
  • Desorb (by heating) from stationary phase into GC injector
67
Q

What does the dual function of SPME allow for?

A
  • Trace sample recovery
  • Preconcentration of sample
68
Q

Purpose of the SPME fibre

A
  • Use the SPME fibre so that the volatiles adhere strongly to
  • Coated with a similar material used in columns eg PDMS
  • This allows for a build up of the sample to increase the quantity we have
69
Q

How are particulate samples recovered?

A
  • Swabbing
  • Vacuuming
  • Solvent wash
70
Q

Swabbing

A
  • Smooth surfaces
  • Solvent is a polar mixture 🡪 e.g. water/acetone or water/MeOH
71
Q

Vacuuming

A
  • Good for fabric + particulates
  • Controlled tiny vacuums with filters that can bag evidence efficiently
72
Q

Solvent wash

A
  • Sonicate the whole sample in a suitable extraction solvent
  • Submerge the whole sample
73
Q

How are samples cleaned/pre-concentrated?

A
  • Solid Phase Extraction
  • Used to preconcentrate liquid samples
  • It is a small cartridge containing a sorbent material
74
Q

What are the different forms of Solid Phase Extraction (SPE)

A
  • Normal phase
  • Reverse phase
  • Ion exchange
  • Size exclusion
  • You can use a combination of these methods
75
Q

Normal phase SPE

A

Adsorbs polar components strongly (A)

76
Q

Reverse phase SPE

A

Adsorbs non-polar components strongly (B)

77
Q

Ion exchange SPE

A

Used for inorganic type components

78
Q

Size Exclusion SPE

A
  • Absorbs lower molecular weight strongly.
  • If you have a mixture of large and small this method might be preferable
79
Q

Conditioning of Reverse phase SPE

A
  • Clean the sorbent using ethyl acetate. This prepares the sample
  • Condition the sorbent using ethanol and water mixture (polar mix)
  • Apply sample (ethanol and water extract)
  • Analyse for inorganic species. The non-polar components stick to the non-polar sorbent in the cartidge
  • Wash sorbent with ethanol and water mix
  • Wash sorbent with MTBE and Pentane mix
  • This wash is done to wash out the non-polar components
  • Ethyl acetate is used to elute explosives
  • Analyse for organic high explosives
80
Q

In reverse phase SPE what does ethyl acetate do?

A

It prepares the sample

81
Q

What happens to the non polar sorbents in SPE?

A

Non polar components stick to the non polar sorbent in the cartridge

82
Q

How do we analyse explosives?

A

A separatory system combined with an explosive specific detection system

83
Q

Whats the problem with using standard analytical techniques to analyse explosives?

A
  • Standard analytical techniques (GC/MS, LC/MS) don’t always provide sufficient evidence
  • Non-explosive compounds may have very similar molecular weights and retention times
84
Q

What are the detectors used for the analysis of explosives?

A
  • Chemiluminscence
  • Thermal Energy Analyser
85
Q

Chemiluminscence Detector

A

C-NO2, N-NO2, O-NO2 groups

86
Q

Thermal Energy Analyser

A
  • Controlled pyrolysis to form NO
  • Pyrolysis is the thermal decomposition in the absence of air
87
Q
A

Fires & Explosions (18 decks)

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