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forensics chem > Topic 2: arson > Flashcards

Topic 2: arson Flashcards

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1
Q

define arson

A
  • Arsonistheintentionalsettingofafiretoastructureorwildlandarea.
  • complexcrimeanddifficulttoprove.
  • extensivedestruction
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2
Q

what is a fire?

A
  • Rapidoxidationofamaterialinthechemicalprocessofcombustion.
  • Producesheatandlight
  • exothermicreaction
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3
Q

what are the requirements needed for combustion to be initiated and sustained?

A

oxygen, heat and fuel (fire triangle)

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4
Q

how to determine if the fire was an arson or an accident.

A

one or more of the components of the fire triangle was manipulated:
•increasethefuelloadbyaddingaccelerantorflammableitems. •Moreoxygenmaybeintroducedbyopening
windowsorpunchingholesinwallsortheceiling.

arson: intentional, multiple points of origin
accidental: e.g point of origin at electrical outlet

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5
Q

what are some other clues of origin?

A
  • Strangeodors
  • Accelerantsoakedragswillkeepthefireloworlocalized,nottravelingupasusual
  • Extensiveregionsoflowburn
  • Fasterandhotterfirethanwouldbeexpected.
  • Emptycontainersofaccelerants,timedelaydevices,andotheritemsleftbytheperpetrator.
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6
Q

how does an arson start? what does it involve?

A

•Fireinvolvesaccelerant(substanceusedtoaidthespreadoffire)
andincendiarydevice(adevicethatisdesignedtocausefire)
toigniteit.

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7
Q

what ais an accelerant? what are the 3 types of acclerants? give examples. what is the most common accelerant?

A

Accelerantisanythingthatisintentionallyplacedatascenetostartandsustainafire.
•Solid(wood,paper,roadflares),liquid(gasoline)orgas(naturalgas,propane)
•Gaseousaccelerantwillnotleavechemicalresiduesbutinstead there might bephysicalevidence(e.g containerusedtoholdordeliverit)

Themostcommonaccelerantsareliquidpetroleumdistillateproductssuchasgasoline,keroseneanddieselfuel.

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8
Q

what are some examples of an incendiary device used to start fires?

A

•Startfireswithacigarette,matches,firearms,

electricalsparkandaMolotovcocktail(petrolbomb).

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9
Q

what is the point of origin of a fire?

A

Placetolookfortracesofincendiarydeviceisthepointoforiginofafire.

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10
Q

what are some tell tale residues of an arson?

A

(i)soapusedasagellingagenttoconvertaflammableliquidintoanapalm‐like(highlyflammablestickjellyusedinbombs)mixture),
(ii)characteristicashresidues(e.g.decompositionproductsofaflare’sfuelandoxidiser)
(iii)residuesofcommercialmaterials(e.g.thermite(amixtureoffinelypowderedAl
andironoxidethatproducesaveryhightemperatureoncombustion,usedinwelding/bombs),gunpowder)
(iv)flammablemetalsfire(e.g.Li,Ketc)

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11
Q

what is reckless arson?

A

arson caused by reckless behaviour that leads to the destruction of property

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12
Q

describe the general 4 steps in arson investigation

A
  1. determinethecauseofafireandensuretheresponsibleparty
    isheldaccountable.
    Majorobjectivesofafireexaminationistherecognition,identification,and
    analysisoffirepatterns.

2.Anarsoninvestigationbeginswhenfirefightersarecalledtothesceneofafire.
3. specially trained arson investigatorsreviewthesceneandphysicalevidence,
andinterviewwitnessesaswellasfire‐fighters regarding their observations at the time of the fire.
4. a criminologist needs to detectandidentifyrelevantchemicalmaterialscollectedatthescene,
reconstructthecrimeandidentifydetonatingmechanisms.

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13
Q

what is a sniffer? (device)

A

•Highlysensitiveportablevapourdetector
•Valuableaidatthefirescenehowever
theoperatormustbeawareoftheprincipleofoperationoftheinstrumentsothatitmaybetuned
correctlybeforeuseanditsresultsareinterpretedcorrectly.
•Aidforthecollectionofsamplesforlaboratorysubmissionandtheirresultsarenotconclusiveregardingthepresenceorabsenceofanaccelerant.

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14
Q

what is a sniffer? (dog)

A
  • Accelerantdetectioncanines/dogs(ADC)
  • Conditionedtorecognizetheodourofhydrocarbonaccelerants.
  • Trainedarsondogs&itshandler
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15
Q

what are the 6 common fire patterns? what does a fire fire pattern indicate?

A

•ClassicV‐Shape •InvertedCone •ProtectedArea •CleanBurn •RunDownBurn •IgnitableLiquidPourPattern

Thefirepatternshouldindicatethepointoforiginorwherethefirebegan.

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16
Q

how is arson evidence collected?

A
  • Ashandsootdebrisshouldbecollectedfromthepointoforigin
  • Sealedinanairtightcontainer(Metalarsonevidencecans).
  • Debris is placed loosely in can, leaving plenty of headspace above.
  • Airtight seal that traps vapours, including residual volatile accelerants .•Theairtightcontainerwillensurethatthevaporsdonotescape.
  • Sampling of similar but uncontaminated sample as control
17
Q

what technique is used to analyse arson avidence? briefly describe the process.

A

GC
•Heat the airtight evidence container so that volatile residues will be driven off the collected material and trapped in the container’s headspace.

•Vapour is removed with syringe and injected into the GC.

18
Q

what are the 4 ASTM protocols for fire debris preparation?

A

1) E1385Steamdistillation
2) E1386Solventextraction
3) E1412Passiveheadspaceconcentration(absorption/elution)withactivatedcharcoal
4) E2154Solid‐phasemicroextraction

19
Q

briefly describe the process of steam distillation. what is effective and ineffective about this method?

A

•Firedebrisistransferredtoadistillationapparatus,andheatisapplied.
•Asit vaporises,theyarecooledandcondensed,droppingintoacollectionthimble.
•Anypetroleumproductsiscollectedasalayerontopofwater.

•Itiseffectiveinseparatingandconcentratingaccelerants,buttimeconsumingandmorevolatilecomponentscanbelost.

20
Q

briefly describe the process of solvent extraction. what is effective and ineffective about this method?

A
  • Solventextractionofdebriswithpentaneandcarbondisulphide(CS2).
  • Solventisaddedtotheevidence,collected&concentratedintoasmallvolume(about1‐5mL). •BothpentaneandCS2arenonpolarandwellsuitedtoextractpetroleumhydrocarbons,butbothalsohavelimitations.
  • Pentaneisvolatile,caretakenthatsolventextractdoesnotgotodryness.Ifitdoes,lighterweightfractionswillbelostalongwiththepentane. •CS2 isnotvolatile,butitistoxicandhasafoulodour.
  • Solventextraction,likesteamdistillation,canresultinalossofmorevolatilefractionsofresidualaccelerants.
21
Q

briefly describe the process of Passiveheadspaceconcentration(absorption/elution)with
activatedcharcoal. what is effective and ineffective about this method?

A
  • Allheadspacemethodsinvolveconcentratingvolatilesintoasolidphasebyabsorption.
  • Protocoliscalledtrapping,andinthecaseoffiredebris,trapismadeofcharcoal.
  • Apolymerstripcoatedwithcharcoalisdangledabovefiredebrisandevidencecanberesealed.
  • Gentleheatingdrivesvolatilesintovapourphase,fromwhichtheymovevia diffusiontothecharcoal,wheretheyareabsorbed.
  • Attheendofheatingtime,charcoalstripisremovedand subjected toGCanalysis.

•Itisporous,thusrelativelylargesurfacearea&moreeffectiveextraction. •Inert&relativelycheap.

22
Q

briefly describe the process of Solid‐phasemicroextraction. what is effective and ineffective about this method?

A
  • Theabsorbentsareusedtocoatthesilicaneedle.
  • SPMENeedleisdirectlyintroducedintoGCforthermaldesorption,orsolventextraction
  • Advantageisversatility,highsensitivity,solventless approach.
  • Fiber canbeimmersedinanaqueousmatrixifthefiredebrisiswaterlogged.

forensics chem (7 decks)

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