Fires 8 - Ignition and Investigation

Question 1

What is needed to achieve ignition of a fuel?

Answer 1

the fuel (even if it is just a small part of it) needs to have its temperature raised to its ignition temperature

using a source of heat

Question 2

In what 6 ways can we heat things up?

Answer 2

1 - light
2 - electricity
3 - friction
4 - contact with something hot
5 - chemical reaction
6 - nuclear fission

Question 3

What is required for radiation to effectively heat a fuel?

Answer 3

the fuel must be able to absorb more heat than it can dissipate

(if it absorbs the same amount of heat it dissipates, radiation won’t heat the fuel)

Question 4

What can radiant heat from another fire cause?

What is the term for this?

In what settings do we see this?

Answer 4

radiant heat from another fire can induce another fire

flashover (essentially the radiation component applied to a whole room)

• household settings (fireplaces and heaters, stoves, floodlights and lamps etc. - anything in close proximity can be charred/ignited)

Question 5

how can sunlight be focussed by lenses or mirrors?

give two examples where this may happen

Answer 5

it involves focussing the lens just right therefore light-initiated fire is almost impossible

broken glass and bottles e.g. wildfires

shaving mirrors at home are convex so can focus light

Question 6

define electrical arcs/sparks

what are electrical arcs/sparks essentially?

when do electrical arcs/sparks occur?

what state of fuel do electrical arcs/sparks ignite?

give examples of electrical arcs/sparks?

Answer 6

involves the movement of current through a gas producing plasma (5000 degrees)

little zaps of electricity

occurs when there is a build up of charge either side of two things

ignites gases or vapours as it is very localised - doesn’t ignite solid fuels

static sparks, spark plugs, hob sparks, lightning
e.g. door handle and your hand - build up of charge is big enough to ionise the gas between into a plasma so get a zap

Question 7

what is the difference between an electrical spark and an electrical arc?

Answer 7

spark is short
arc occurs over a prolonged period of time and is maintained

Question 8

In what two ways can electricity cause a fire?

Answer 8

by direct contact with electricity particularly in gases and vapours

can also happen with overheating

Question 9

How does electricity and overheating cause a fire?

Answer 9

• electrical currents generate heat when they meet resistance
• amount of current that a wire can carry is proportional to its diameter, material and covering
• this is normally enough to handle heat produced but when it isn’t, this is what causes a fire

Question 10

In what four ways can heat build up in a wire?

Answer 10

1 - excessive current (wrong fuse, short circuit)

2 - tightly coiled wires which can’t dissipate heat

3 - poor or loose connection e.g. wire on a screw terminal

4 - insulation breakdown - charred wood/plastic (insulator) becomes a semi-conductor then the current can flow through material, heats up, catches alight

5 - aluminium fittings (rare but can be found in old wiring systems) - not as good a conductor as copper, makes oxide films which creates a heat barrier. after formed oxide layer on aluminium surface, it will overheat when you put too much current through it. anything near aluminium fitting could reach ignition temperature

Question 11

How do lighters work?

Answer 11

friction initiated fire

• lighters contain ferrocerium (Fe/Ce alloy) flint
• the friction from striking this generates hot shavings (mechanical sparks)
• Ce has an ignition temperature of 150 - 180 degrees
• these sparks are formed near the fuel that comes out when your thumb depresses the switch which then ignites the fuel (light petroleum distillate vapour or butane gas) - fuel is pushed out with right fuel/air ratio

Question 12

What settings can friction initiated fires occur in?

Answer 12

• can occur in poorly lubricated train bearings (i.e. trains and industrial machinery)
• if the heat generated is great enough one of the two surfaces rubbing together can disintegrate and produce shower of incandescent particles
• spread to things around it and cause them to reach ignition temps

not likely to occur in the home

Question 13

explain process of spontaneous combustion

Answer 13

• some substances have naturally occurring exothermic reactions (chemical oxidation, biological fermentation etc.)
• heat is lost from surface of the material and this is fast enough that the heat doesn’t build up
• if the dissipation isn’t quick enough, the temp starts to rise in the interior
• this accelerates the reaction so the heat generated gets lost more rapidly - results in an equilibrium temperature
• in a large quantity of material, the surface area is relatively small. as material gets bigger, relative surface area gets smaller but there is more material to heat up so it takes a long time
• therefore equilibrium temp is higher for larger quantities of material
• if temp exceeds auto-ignition temp, a fire can start within the bulk of the material
• this process can take a considerable time (many hours)

Question 14

Give examples of chemical reactions that can mimic arson attacks

Answer 14

• fire in rubbish bin can look intentional
• microbe breaking down sawdust, coal dust, hay, straw and landfill waste
• unsaturated (‘drying’) oils that are soaked into rags, paper etc.
• unsaturated C=C bonds oxidise in air exothermically
• more C=C bonds = increase in likelihood of hazard
• some reactive species like K, Na metal that oxidise in air

Question 15

Explain how gas fires occur

Why are they not likely?

Answer 15

• excessive gas isn’t commonly the cause of a fire
• when a gas fire does occur, the fires are usually caused by an initial explosion
• gas awareness is good so mistakes aren’t frequent
• any hot surfaces in boilers are tucked away and well insulated

Question 16

How can arsonists disguise an intentional fire?

But what is problem with this?

Answer 16

• by setting it under an oven, BBQ etc.
• but need to prove a fault in gas appliance to rule out arson
• accidental fire needs evidence of not only origin but faults too

Question 17

What can initiate accidental gas fires?

Answer 17

broken furnaces or driers can initiate fires by thermostat failure

Question 18

What are common sources of gas flames?

Answer 18

• open/naked flames
• cooking oils, grease, towels, clothing, paper near them
• Bunsen burners
• portable gas stoves

Question 19

Define hot and burning fragments

What does their distance depend on and give a common range

Provide three sources

Answer 19

• bits of wood, cardboard, paper which can travel whilst flaming
• also called sparks - confusing
• distance travelled depends on material, size and wind
• common range: 6 - 12 m as most extinguish before getting further
• sources: rubbish, bonfires, lanterns

Question 20

What can be said about cigarettes in fire investigations?

Answer 20

• cigarettes are probably blamed more often than they should be - it is usually because of a discarded match
• this is because cigarette has a low heat release rate (around 5kW) - needs direct contact with fuel for some time
• cigarette in toilet roll will ignite in 20 minutes
• ignition of gasoline vapours with cigarette is harder than would expect - films are misleading
• synthetic fibres are much less vulnerable than natural fibres to smouldering after cigarette contact
• smoking in bed: cotton sheets smoulder and eventually find fuel for flaming combustion

Question 21

What happens in court when an expert witness is challenged?

Answer 21

when an expert witness is challenged, the judge must determine whether the expert’s testimony has a reliable basis in the knowledge and experience of the relevant discipline

Question 22

in 1993, what was said about expert witness opinions?

What changed in 1998?

Answer 22

a fire investigator could offer an opinion that a fire was arson by looking at evidence (no tests, proof of excluding other possible causes)

court held that fire investigation is a scientific discipline and not experience-based opinion
- a fire is something that is grounded in physical phenomenon and is demonstrable - need to be able to show with scientific answers, not just opinion

Question 23

What happened in Michigan Millers’ Mutual vs Benfield in 1998?

What is gist of case?

Answer 23

expert witness interjected a lot of personal opinion in testimony based ONLY on previous experience

• case involved a house fire in which the insurance company, Michigan Miller’s Mutual refused to pay on the policy based in part on the fire being incendiary and the involvement of an insured party in setting the fire
• fire investigator with over 30 years experience testified the fire was started on top of dining room table where some clothing, papers and ordinary combustibles had been piled together
• he examined the fire scene primarily by visual observation and concluded that the fire was incendiary based upon absence of any evidence of an accidental cause
• he observed empty undamaged bottle of lamp oil with cap removed - fire had been accelerated with lamp oil
• expert opinion that fire had been accelerated by lamp oil bottle was rejected as no scientific proof oil was in bottle before fire and no fire debris sample was taken to prove presence or absence
• rejected because:
• no scientific proof and applies no scientific method
• relies on his experience
• no scientific tests or analyses
• says no source or origin found so must be arson

GIST:
- expert witness cannot form their conclusions solely on intuition and experience
- opinion of expert witness must have scientific basis (something testable) that informs the opinion presented

Question 24

What three things sets fire scenes aside from other forensic investigations and makes them more complicated?

Answer 24

• this scene is dominated by destruction
• it devolves over the course of the crime
• a lot of typical evidence (e.g. DNA) us going to be degraded
• fires/explosions may be intentional or unintentional
• deliberate fires are committed by offender who has usually left a long time before the fire scene is formed

Question 25

What are roles of forensic investigators in fire investigation?

Answer 25

• detection and identification of material
• evidence gathering
• using evidence to describe fires ignition and spread and that might give some indicators about suspect or motive for fire

Question 26

What will be damaged and destroyed at the scene?

What will be affected far from scene?

What effect does this have on evidence collection and cordon planning?

Answer 26

anything flammable at the scene e.g. paper documents that help identify a person or cause of crime if it is arson

materials and surfaces that are far from initial scene will covered in soot and debris or affected by heat

• affects ability to recover evidence e.g. harder to take prints/DNA samples from because covered in soot
• set cordons wider than initial scene

Question 27

What effect do first responders have on the scene?

Answer 27

• evidence is destroyed as fire is combatted by first responders (surfactants, fire suppressants - may make evidence gathering trickier as residues can look like accelerants)
• evidential integrity is the investigators priority but they are not at the scene first
• first responder is on scene first and their priority is safety and prevention of further spread and this involves ruining the scene
• firefighting techniques can cause physical damage:
• doors and windows broken
• ceilings collapse under weight of water
• objects disturbed or removed

Question 28

What effect does post fire clean up have on the scene?

Answer 28

• it can damage evidence
• need to reconstruct scene as best as possible after postfire e.g. was window broken by fire or was it already broken?

Question 29

What is the first question a fire investigator should ask? What are two subsequent questions

how do we answer these questions?

Answer 29

• where did the fire start?
• how did it start and how did it spread
• physical evidence:
• burn patterns - the fire will burn a certain way because it follows rules of chem/phys so can tell where fire started and how it spread
• smoke records - the way smoke spreads throughout area will also follow laws of physics so will get deposited deposited in some places and not others - tells you what areas were exposed to smoke, and which weren’t
• temperature indications – some physical indicators that will occur at a high enough temperature like “spalling” (surface flaking) of plaster.
• debris layer sequences - can tell what fell first in a fire by looking at the order they’re lying on top of each other
• remains of ignition devices or suspicious containers?
• chemical evidence
• analysis of trace residues
• presence of accelerants?
• related (circumstantial) evidence:
• evidence of forced entry? removal of goods before fire?
• soot from the fire will show drag marks from items moved by first responders
• witness statements (“rapid spread of fire” isn’t proof of arson)

Question 30

what are the other subsequent questions to be asked by fire investigator?

what is a concern?

Answer 30

• what is impetus for fire?
• is it arson? accident? or negligence?
• insurance investigators and loss adjustors may also be involved: (financial fraud to profit from buildings/contents insurance? intentional fires to destroy business records of tax fraud?) - particularly true during economic recession
• clearance and site demolition e.g. site owners

Question 31

despite the first question asked, what is the first thing to be addressed at scene?

Answer 31

• first priority is always safety for first responders, fire investigators, bystanders, witnesses and property owners
• there may be casualties or bodies that need to be extracted but these alone have important evidential considerations

Question 32

What can be told if there is a body at the scene?

Answer 32

• smoke in lungs and CO is blood is indicative of smoke inhalation (most common cause of fire deaths)
• absence of smoke in lungs or CO in blood suggests victim died prior to fire
• this is contributory evidence but not infallible proof of arson

Question 33

What are the hazards that must be addressed before fire investigation can begin?

what must this risk assessment be?

Answer 33

• structural collapse of building
• live electrical cables
• damaged sewers/drainage (biohazard)
• dust inhalation hazards (asbestos)
• unknown building contents (toxic chemicals and biohazards) - industrial warehouses, clandestine laboratories used to make drugs or explosives
• risk assessment must be dynamic and must be constantly assessed

Question 34

What do we know about the seat of the fire (point of ignition)?

Answer 34

• the point of origin has burnt the longest
• something caused the initial ignition of a fuel package
• fires burn upwards - the lowest point of burning is generally the seat of the fire

Question 35

How can we determine seat of fire?

What must be noted?

What other indicators can we use to determine seat of fire?

What is this useful for?

Answer 35

• characteristic ‘v’ shaped smoke pattern on adjacent walls
• caused by rapid circulation of fire
• they will look like they point down towards the seat of the fire - examine floor, undersides of furniture and shelves
• but remember to look out for prevailing draughts and winds
• check stairways, lift shafts, holes in floors and roofs, open windows
• face of material exposed to fire will typically show greatest extent of damage
• useful for reconstruction of fire

Question 36

How do glasses and plastics melt?

Answer 36

towards the heat of the fire

Question 37

If lift item up at fire scene and there was no ash residue under what would this suggest?

Answer 37

it is undisturbed

Question 38

How can the V vary?

Explain a ***** version of this

Answer 38

can be very small

electrical fire originating from plug socket

but plug socket is clean which could mean two things:
- there is something chunky plugged in that shielded the outlet
- fire is caused by a loose terminal on the inside of the wall rather than something plugged

Question 39

How can walls be damaged after fire?

Answer 39

spalling - plaster or concrete breaking off from walls
- they both contain water so when get hot they boil
- this makes the surface of the wall break off
- this shows that certain part of the wall reached a specific high temperature

smoke record - spalling happened after smoke exposure
- bits fallen off have no soot on them
- soot has flaked off

Question 40

When investigating a fire, where is the first place to start?

What to look for?

Answer 40

start at outermost region of cordon then work way in

look for:
- irregular burn patterns that don’t fit the profile of an apparent fuel
- trail evidence – ‘streamers’ from liquid accelerants, trails of paper etc. (streamers – if you slosh a fuel around, you will have splashes that will burn faster)
- containers that could house accelerants (preliminary)
- ignition devices – discarded matches, lighters, timers etc.
- evidence of forced entry (circumstantial) - must check isn’t forced entry by emergency services

Question 41

Why may a digger be required?

Answer 41

for excavation of debris layers using a digger to reconstruct scene may be required

• it will tell you about layers of debris

Question 42

What is imperative to aid with reconstruction and to keep everyone on track?

Answer 42

• take contemporaneous notes, sketches and photographs

Question 43

What can be said if a fire has multiple seats (more than one place the fire started)?

Answer 43

evidence for arson but not proof

Question 44

What can cause multiple seats of fire?

Answer 44

radiation induced flashover but debris ordering can tell you if it was a secondary fire