Lecture 20 Flashcards
what type of burn pattern suggests an accelerant was used (4)
severe and localised damage
not uniform across a floor
coming out from the source and expanding due to how liquids absorb through materials
a ‘sloshing’ pattern or spots just outside of the main part are likely to suggest a liquid was used
what is meant by a streamer or a trailer spot of accelerant
the little spot seen just away from the main area
suggesting liquid has splashed on a hard floor
what is meant by a smoke record and what is it used for
the smoke deposits left on all open surfaces
a good indicator of what may have happened at a scene
regions without smoke deposits are likely to have been covered
glass can show if broken before or after fire
objects on desks leave ‘shadows’
door frames show door position
what three things can be used to help reconstruct a fire scene
witness statements
pre-fire photos - use of social media and digital records make this easier
matching objects up to burn patterns
what three things are done/used by firefighters that can destroy a fire scene
high pressure hoses
windows smashed for ventilation
items cleared out to take away fuel that could increase fire
what do arcing wires develop
what does this suggest
beads at the ends
this suggests the electrical fault was prior to the fire
why is the excavation of the debris at a fire scene needed
debris may have fallen and could cover the seat of the fire or remnants of ignition sources
what type of electrical good may be the cause of a fire
counterfeit ones e.g chargers
due to design faults or incorrect use
what can excess current in a cable do
melt the insulation and this means wires can come into contact
fires cause ……. but ……. also cause fires
electrical faults
what are two examples of timing devices that may be used in an arson
a candle burning until it reaches a fuel source
soldering connections into an automated socket timer
what information is lab testing of samples used for
information regarding the ignition of a fire
in the search of liquid residues
what is the presence of accelerants at a scene evidence but not proof of
how are these identified
arson
using chemical analysis
where is unburnt accelerant likely to be at a scene
within porous materials
carpets, floorboards, upholstery, plaster, rags, floor cracks, concrete
these places are where we want to swab
where is unburnt accelerant less likely to be present
when flashover has occurred
what can be sprinkled over concrete surfaces to absorb traces of accelerant
absorbent mineral powders e.g diatomaceous earth or celite
disposable nappies have also seen to be used in an emergency
what three methods can be used for the detection of accelerants for on site analysis
but what does this do and what else is needed for evidence to go to court
portable GC-MS or in lab
sniffer dogs = less reliable but high sensitivity
portable hydrogen sniffer - organic vapours affect the electrical conductivity of a semiconductor detector
only indicates possible accelerants, lab samples and analysis is still needed
what three samples are needed from a fire scene
fire sample = near as possible to the seat of the fire
comparative control sample = same material as fire sample but from elsewhere in the room and uncontaminated with accelerant
negative control sample = tools and containers of the same type used in the sampling process (ensures no contamination)
why is time of the essence to collect unburnt accelerants
they are volatile liquids so need to collect before they evaporate
is it illegal to possess accelerants such as petrol, diesel or butane
no
what samples should be taken from a suspect of a fire scene if there is one
clothing, materials from thei premises, hand swabs
how could samples from a fire scene be packaged (5)
in airtight containers so they can retain long chain hydrocarbons and aromatic molecules e.g toluene and xylene
ordinary evidence bags are too porous
bags must be free of plasticisers - seal by knotting the neck and sealing with a cable tie, often see double bagging of an inner nylon and then outer polyethylene or polypropylene
glass jars and metal lids - lid needs to withstand vapour pressure of liquids
metals cans - not lined with plastic as this is a hydrocarbon, resistant to puncture but not good for corrosive samples
give 4 types of samples that may be taken from a fire scene
flooring where accelerant was
(include burnt and unburnt and underlay, at least 1m^2)
swab-able surfaces
(tiles and lightbulbs)
floorboards
soil
(under completely burnt floorboards)
ALWAYS REMEMBER CONTROLS
what is essential for the tracking of fire scene evidence (3)
accurate labelling of samples - record original location in contemporaneous notes
good record keeping ensures the chain of custody - ideally electronic records
tamper evident seals on sample bags
