Fire and ignitable liquid residues

Question 1

What is in the fire tetrad?

Answer 1

Oxygen(if falls below 15% then combustion stops because flames can no longer be supported and will go out. Also include chemical oxidisers such as ammonium nitrate and H2O2 with readily released o2) , fuel (organic material containing H+C), ignition(gases released from heated objects mixed with oxidising agent that gives heat opportunity to ignite gas) and heat (more energy released and temp increases)

Question 2

What are the 3 types of combustion?

Answer 2

Flaming combustion, Glowing combustion and explosive combustion

Question 3

What is flaming combustion?

Answer 3

Ignition temp of fuel is reached and combustion begins

Question 4

What is glowing combustion?

Answer 4

Burning without flame, oxygen limited, aka smouldering, occurs on surface of solid fuel in absence of high heat enough to pyrolyse

Question 5

When solid object burns it will either do what?

Answer 5

Pyrolysis or Pulverisation

Question 6

What is pyrolysis?

Answer 6

Under heat flow, decomposition solid producing gas products

Question 7

What is pulverisation?

Answer 7

Transformation of a solid into small particles with form a cloud mixed with air

Question 8

What is flash point?

Answer 8

Lowest temperature at which fuel can form an ignitable mixture with air

Question 9

What is fire point?

Answer 9

Temperature at which the vapour continues to burn after being ignited

Question 10

What is the Auto-ignition temperature (AIT)?

Answer 10

Temperature at which fuel will ignite on its own without additional ignition source

Question 11

What is the aim of fire investigation?

Answer 11

To find origin, cause and spread

Question 12

What are the 3 modes of heat transfer?

Answer 12

Conduction, radiation and convection

Question 13

What is conduction?

Answer 13

Movement of heat through solid object via electrons and atoms within heated object which collide with each other. Objects such as metals with loosely held electrons are good conductors of heat. Objects at scene could conduct heat

Question 14

What is radiation?

Answer 14

Transfer of heat energy from heated surface via electromagnetic radiation. All surfaces facing heated surfaces impacted by radiant heats

Question 15

What is convection?

Answer 15

Transfer of heat as result of movement of molecules within a liquid or gas. As heat up, it moves upwards and by convection radiates heat to surface below. Convection air can cause pyrolysis

Question 16

Define arson

Answer 16

Reckless or malicious and intentional act of starting a fire or causing an explosion

Question 17

Define accelerant

Answer 17

Introduced to scene to help initiate fire, spread fire, increase intensity of fire. Could be ignitable liquid or combustible material (paper) or improves mixtures (sugar and chlorate). May not burn completely and instead may soak into carpet and materials leaving residues after fire

Question 18

What are detection techniques for accelerants?

Answer 18

Point of origin, multiple seats, burn patterns, instruments, canines

Question 19

What are collection methods for fire scenes?

Answer 19

For sample use air tight containers and always get control. Or package in fresh nylon bag or arson tin

Question 20

What are the 6 laboratory preparation techniques for fire scenes?

Answer 20

Steam distillation, Solvent extraction, direct headspace, SPME, Dynamic headspace and Passive headspace

Question 21

What is steam distillation?

Answer 21

Accelerant separated from liquid or solid by vaporisation and subsequently condensed to liquid. Old technique, high risk of contamination, lots of time required, lack of sensitivity and limited range of products successful

Question 22

What is solvent extraction?

Answer 22

Solvent placed within debris that extracts accelerant residues. Liquid is then decanted, filtered and concentrated through evaporation. Matrix products also extracted. Bad is labour intensive, destructive and lots of solvent

Question 23

What is direct headspace?

Answer 23

Sample headspace drawn through gas syringe which is directly injected in GC. Used as first screening. Advantages are interferences reduced. Disadvantage is less concentrated samples will give poor resulting chromatograms and heavy products

Question 24

What is Dynamic headspace?

Answer 24

Adsorbent tube or purge. Vapour of sample forced over or through adsorbent material at given temp. Accelerant vapours trapped in adsorbing material which later extracted usually by solvent extraction. Temp 60-90 degrees

Question 25

What is passive headspace?

Answer 25

Adsorbent (activated charcoal strip) placed within debris in container. Container then heated for period of time. Reversible equilibrium of same volatiles occurs between adsorbent and matrix where volatiles have higher affinity for adsorbent. Adsorbent removed and accelerant residues extracted

Question 26

What are the 2 desorption techniques?

Answer 26

Solvent extraction (adsorbent placed into solvent and washed. Solvent now contains accelerant residues, collected and injected into GC) and thermal desorption (high speed heating of adsorbent to release residues)

Question 27

What is the GCMS used for in fire scene?

Answer 27

Visual comparison to library, retention time, compound ratio. Kerosene is more in middle with curve at bottom and petrol is straight up and flat

Question 28

What is MS used for in fire scene?

Answer 28

Extracted ion profiling, target compound analysis