2. Fire
Fire is a chemical reaction that takes place when fuel, heat, and oxygen combine in an
uninhabited chain reaction.
To stop burning of fire, any one out of the three elements present in fire triangle should
be removed.
Remove any one of the elements and the fire goes out because you have stopped the
continuing chemical reaction.
Because only gases burn, solid and liquid fuels must be heated until they become
vapour before they can burn.
Heat chemically decomposes a fuel into its gaseous elements. This decomposition is
chemically known as pyrolysis.
For example: When wood is heated, it pyrolyzes to form hydrogen, oxygen, ethane and
methane gases, and methyl alcohol. It is these highly flammable vapours which burn.
3. Fire
Fuel in vapour form in its normal state, like natural gas, does not need to be
pyrolyzed.
Most fuels are compounds of carbon, hydrogen, and oxygen along with traces of
mineral matter.
When the fuels burn completely and freely in air, the carbon reacts with the
oxygen, forming carbon dioxide, and the hydrogen combines with the oxygen,
forming water vapour. The mineral matter remains behind as ash. As the oxygen in
the fuel is used up, oxygen is drawn from the air to continue the reaction. Mainly
the fire spreads by transferring heat energy in three ways i.e. Radiation,
Convection and Conduction.
4. Elements of Fire
Fire was earlier understood chemically as a three-pronged chemical reaction. The
requirements of fire itself was explained as a fire triangle.
5. Elements of Fire
But in the present day, fire is chemically understood as a tetrahedron, meaning
there is one requisite of fire – the uninhibited chain reaction.
6. Elements of Fire - Fuel
This is anything that will burn. Fuel must be available for ignition. It may be in the
form of a solid, a flammable liquid or gaseous state.
Solids may be wood, cloth or paper. Examples of flammable liquids are kerosene,
oil and gasoline.
Vapours from paint, gasoline and other flammable materials are considered
gaseous.
Understanding that there are invisible, potentially dangerous vapours surrounding
flammable chemicals is very important. Natural gas and propane are other
examples of flammable materials in a gaseous state.
7. Elements of Fire - Oxygen
This is needed for combustion. Fires use oxygen to maintain a state of combustion
(burning).
Fires also produce smoke and poisonous gases.
8. Elements of Fire - Heat
Combustible materials may catch fire at ignition temperatures.
Heat is needed to start a fire.
For many items found in the home, the combustion temperature is 400 - 600
degrees Fahrenheit.
Some items may ignite more easily than others.
9. Elements of Fire – Uninhibited Chain
Reaction
The final face of the tetrahedron is the uninhibited chain reaction that is enabled by
the reaction between fuel, heat and oxygen.
An ininhibited chain reactions refers to the self-perpetuating capacity of
combustion.
Because of the continual reactions taking place between fuel and oxygen, which
generates surplus mounts of heat energy, the flame will always be hot enough to
keep the fuel at ignition temperature.
Therefore, the fire will continue to burn as long as there is enough fuel and oxygen
available. This process finishes when these sources have been expended.
10. Conditions & Classification of fire
Even though fire is a chemical reaction, fire reacts in different stages during the
entire fire ‘process’.
Every fire stage is different from another.
Similarly fire which burns over different fuels also behave differently.
For fire safety, knowledge of the stage and fuel of fire is important to choose the
type of fire extinguishing method.
For forensic science too it is important to study the different types of fire in order to
be able to ascertain the cause and origin of fire.
11. Stages / Phases of fire
The burning process occurs in clearly defined stages.
For a fire fighter it is important to recognize different phases of fire so that he can
understand the different levels of burning fires and to fight against it using different
tools.
These phases are classified on the basis of atmospheric conditions around the fire.
12. Stages / Phases of fire
0
1
2
3
4
5
6
Incipient Free burning Smouldering Extinguished
Series 1
13. Stages / Phases of fire
The phases of fire are understood as
Incipient / Growth stage
Free-burning / Fully grown stage
Smouldering / Decaying stage
Extinguished / Decayed stage
14. Stages / Phases of fire
Incipient/Initial Phase (Growth Stage)
This is the first phase; here fire produces water vapor, carbon dioxide, perhaps a
small quantity of sulfur dioxide, carbon monoxide and other gases.
Also in this phase the air oxygen content is reduced and produces fire.
The fire may be producing a flame temperature well above 1,0000 F (537 C), yet
the temperature in the room at this stage may be only slightly increased.
15. Stages / Phases of fire
Free-Burning Phase (Fully Developed Stage)
The second phase involves all the burning activities of the fire.
In this phase, air rich in oxygen is strained into the flame and convection carries
heat to the upper most regions.
It must be kept in mind that fire burns outwards and upwards always. That is why
the tongue-shape of fire.
The gases heated up spreads out from the top downward, resulting in increased
concentration of cooler air at low levels and results in the ignition of combustible
material.
16. Stages / Phases of fire
Free-Burning Phase (Fully Developed Stage)
Due to this heated air, firefighters are taught to keep low and use protective
breathing equipment. One breath of this super-heated air can sear the lungs.
At this point, the temperature in the upper regions can exceed 1,3000F (700 C).
In the later stages of fire, it starts to progress and oxygen is continuously
consumed by it and to the point where there is insufficient oxygen to react with the
fuel.
The fire is then reduced to the smoldering phase and needs only a supply of
oxygen to burn rapidly or explode.
17. Stages / Phases of fire
Smoldering Phase (Decay Stage)
In the third phase, flame may cease to exist if the area of confinement is sufficiently air-
tight.
In this instance, burning is reduced to glowing embers. the room becomes completely
filled with dense smoke and gasses to the extent that it is forced from all cracks under
pressure.
The fire will continue to smolder, and the room will completely fill with dense smoke and
gasses of combustion at a temperature well over 1000F (537 C).
The intense heat will have vaporized the lighter fuel fractions such as hydrogen and
methane from the combustible material in the room.
These fuel gases will be added to those produced by the fire and will further increase
the hazard to the firefighter and create the possibility of a backdraft / flashover.
18. Stages / Phases of fire
Extinguished Phase (Decayed Stage)
In this phase, the fire slowly gets burnt out and the temperature also falls down
rapidly.
The important point to keep in mind is that if the requirements for fire is provided to
the extinguished fire at this stage also, fire can restart.
This is the reason why even after extinguishing fires, fire safety personnel are
taught to stay in the fire scene until they are extremely sure that there is no more
risk of fire.
19. Stages / Phases of fire
In Forensic Science, understanding the stage at which a fire was when first
attendants / complainants witnessed it can prove important.
The color of flame, the temperature, the wind current, the odor etc. are important
findings in the investigation point of view.
20. Types of fire
Fire can also be classified on the basis of what is burning.
A wildfire and a building on fire – are totally different in the way they burn, in the
way in which they need to be extinguished etc.
21. Types of fire
Class A fire
A class “A” fire can involve any material that has a burning ember or leaves an
ash. Some examples of class “A” fires are wood, paper, or pulp. The adopted
method for quenching fire of class “A” is to remove the heat.
Water is considered to be most common agent, but other agents such as foam and
dry chemical can be effectively used.
It is the most common of fires.
22. Types of fire
Class B fire
A class "B" fire involves flammable liquid or gas. Familiar examples would be
gasoline, oil, propane and natural gas.
A variety of fire extinguishing agents is used on flammable liquid fires employing all
theories of fire extinguishment. Which agent is best to use is dependent upon the
circumstances involved.
Flammable liquids do not ignite in their liquid state, rather it is the vapors being
generated by these liquids that ignite. The mixture of oxygen and flammable
vapors in proper proportion needs only an ignition source to start the combustion
process.
23. Types of fire
Class C fire
Class "C" fires involve live electrical equipment and require the use of an
extinguishing agent and / or extinguisher that will not conduct electricity back to the
fire fighters.
Electricity is an energy source and an ignition source, but by itself it will not burn.
Instead, the live electrical equipment may serve as a source of ignition for a class
A fire such as insulation and packing or a class B fire.
24. Types of fire
Class D fire
Class "D" fires involve exotic metals such as titanium, zirconium, magnesium and
sodium. These fires require special agents such as dry powder and special
application techniques.
The extinguishing agents and techniques used on "A", "B" or "C" fires will not work
on class "D" fires, nor will the agents and techniques used for class "D" fires work
on any other classification of fire.
Many common agents like water will actually react to burning metals and increase
the intensity of the fire in a violent manner.
25. Types of fire
Class K fire
Class K fires are fires with substances such as animal and vegetable fats present
in commercial cooking oils and greases.
These types of fires can only be effectively quenched with a Class K fire
extinguisher.
26. Types of fire
Type of Fire American Classification European Classification Australian
Classification
Solids A A A
Liquids B B B
Gasses B C C
Electricity C Not classified E
Metals D D D
Oils K F F
27. Types of fire
Type of Fire Extinguishing method
Solids Water
Liquids Co2; Dry powder
Gasses Co2; Dry powder
Metals Dry powder
Electricals Co2; Dry powder
Oils Fire blanket
33. Fire patterns
Fire patterns are forensically very significant.
A fire pattern is any visible or measurable change or identifiable shape formed due
to a fire.
It must not be confused with fire effects. Fire effects is the artifacts which are left
behind after the fire has acted on material objects - it could be melting, charring,
ashing etc.
Fire effects would be the same for a accidental and incidental fire. But fire patterns
would change dramatically.
34. Fire patterns
Accurate interpretation of a fire pattern can help fire investigators to identify the
correct origin of fire and therefore even the cause of fire.
The initial understanding was that fire always burns upwards and outwards. But
now the scientific understanding is that fire's natural tendency is to burn upwards
and outwards but it need not be the case always and its behavior is determined by
many factors.
Fire patterns can result from several different kinds of interactions between the fire
and its surroundings. The best understood interactions are those that occur
between the fire plume and a nearby vertical surface. Such patterns are often
called truncated cone patterns, inverted cone patterns or 'V' shape patterns.
35. Fire patterns
But a V shaped pattern is not the only pattern we encounter.
Plume generated patterns
Confinement patterns
Movement patterns
Irregular patterns
Spalling
Electrical damage
Clean burn
Intensity patterns
Ventilation generated fire patterns
36. Plume generated patterns
A plume is a spreading shape of smoke. Plume generated patterns are usually
seen in indoor fire scenes.
Fire patterns evolve during the course of fire. When the fire has just started and is
new, the pattern in an adjacent wall will assume the shape of the flame - it is
usually an inverted cone pattern. This is a sign of a new and young fire.
40. Plume generated patterns
Columnar patterns have a short lifespan and quickly reaches the top of the room
(ceiling) and forms a semicircular pattern on the ceiling.
42. Plume generated patterns
Note that the semicircular pattern is actually the top of a 3-dimensional V shape /
cone shape. Also note that fixing the pattern on a ceiling is more difficult than fixing
it on the wall.
A typical plume pattern can help in locating the origin of fire.
43. Confinement pattern
As the name suggests, confine patterns are seen when fire has little way to escape
from an indoor scenario. A hot gas layer traps beneath the ceiling when this
happens. So there is smoking on the top sides of the room than the lower sides of
the room.
45. Confinement pattern
This does not stay the same. Fire is a chemical process and continues to quench
the ceiling or the walls. Therefore, the celling will fail (or fall) when fire continues its
course. This becomes useful in fire cases in multi-level structures. Fire
investigators in confinement fire cases can easily fix which floor the fire broke out
by the confinement patterns, roof collapse sequence etc.
47. Confinement pattern
A different scenario of confinement fire is when the fire breaks the ceiling as well
as the top portion of the walls. Again this happens because fire is a chemical
process and when fire is sustained, it quenches the ceiling and then starts
quenching the walls. In this case, the pattern to watch out for is the greying /
smoking pattern in the other side of the wall after the wall is penetrated through.
This is called a 'horizontal confinement pattern' because the damage happens in
the horizontal dimension.
49. Movement pattern
When fire moves from one room to another, the movement is patterned / recorded
en-route. The patterns to look out for are most commonly seen in at or near
doorways. Movement patterns are useful in tracing fire back to its origin. The
patterns are typically diagonal patterns upward from the doorway.
51. Movement pattern
In such cases, the movement pattern is diagonal, but the side where the damage
is more points toward the origin of fire. In figure 7, the fire had originated from the
room on the left side and has propagated on to the room on the right side of the
door.
52. Irregular pattern
These are typically seen on floors. They are irregular shaped smoking patterns
and interestingly resemble a liquid that has flown across the floor. Previously the
understanding was that whenever irregular patterns are seen in fire cases, it meant
arson as the pattern is that of fuel that has been used to intentionally set fire (also
known as pour pattern).
54. Irregular pattern
But today the understanding has changed. While the above understanding is true,
there can be instances where the irregular patterns would be seen in cases without
use of fuel. In confinement fire cases, the heat which builds up in the top of the
room, radiates back to the floor. This radiation is high temperature heat (This
radiation is known as a phenomenon called ‘flashover’ which we will learn in a
future lesson). This burns up the floor. Carpets, clothes etc. which can be on the
floor get burnt up and the patterns of them burning stays on as irregular patterns.
56. Irregular pattern
When dealing with irregular patterns, we must keep one more important thing in
mind. There could have been objects on the floor in a regular fire scene, which
may protect the floor from burning. This can also lead to a floor which resembles
irregular fire pattern, but it is actually not an irregular pattern fire. It is key to always
ask what was present on the floor when encountered with irregular patterns. Also
fire investigators should wait for laboratory results before interpreting the cause
and origin of fire.
58. Spalling
Spalling refers to damages that happen on cement and concrete surfaces due to
fire. The changes can be either chipping or pitting. The area of damage can range
from few square centimeters to few square meters. Fire forms pitting / puddle
shaped damages on walls. The earlier understanding was that only intense fire can
cause spalling. And intense fire means use of fuel. Therefore, spalling meant
arson. Though it is still considered true, spalling may occur even with non-intense
heat. Heat causes differential expansion in the cement surface, drinks up all the
water in the surface and therefore causes pitting. So spalling does not require
intense heat always.
60. Electrical damages
Electrical damage can happen in fires due to electric short-circuits or other fires
could damage electrical parts - like wires, appliances etc. Electrical damage
patterns help fire investigators to rule our electrical fires and also to identify the
nature of fire in other fires. When fire damages electrical wires, it causes the
insulation to first melt and then with more heat it causes carbonization of the
insulation (ashing). This can cause short circuit as the live and neutral wires get in
touch with each other. These short circuits will not trip a circuit breaker or melt the
fuse. This is an important finding during a fire investigation.
In short circuit fire, fire investigators look for changes in the electrical wires or
appliances. 'Arcing through char' is the phenomenon examined for in electrical
fires. Arcing through char happens when electrical short circuit starts the fire and
the wire at the point of origin has globules of melted copper (or the wire's material).
62. Electrical damages
This seen under and demonstrated using the electron microscope for greater
detail.
In cases where wire is burnt and does not include a short circuit incident, the
melted copper globules are not observed. Therefore, during a fire investigation,
when electrical damage is there the fire investigator goes on a trail called 'the
mapping of arcs' to fix the origin of fire.
63. This seen under and demonstrated using the electron microscope for greater
detail.
In cases where wire is burnt and does not include a short circuit incident, the
melted copper globules are not observed. Therefore, during a fire investigation,
when electrical damage is there the fire investigator goes on a trail called 'the
mapping of arcs' to fix the origin of fire.
65. The major challenge to the fire investigator is to identify the origin of fire. It was
earlier said that the point of maximum damage is always mostly the origin of fire.
But the key word here is 'mostly' - not always. Therefore, to identify the origin of
fire, the fire investigator needs to understand the chemistry of fire. Heat effects /
patterns produce different physical changes at different places. There will usually
be proper difference in physical changes in one part of the scene and another. This
could be dependent on presence of air, fuel etc. This is known as intensity
patterns. Fire causes different patterns at different places due to its different
intensity at different places. It is a confusing task to understand intensity patterns,
but it is a useful step in fire investigation. Attributing more damage to the point of
origin of fire can be erroneous. We need to take a proper decision based on other
factors also.
66.
67. Ventilation generated pattern
This type of pattern is seen in many indoor fire cases and mostly misunderstood as
explosions (eg. LPG burst, electric appliance explosion etc.). When fire occurs in an
indoor closed scenario, the plumes of the fire start producing smoke and other gasses.
These gasses quickly deplete the oxygen present in the room. Fire requires oxygen to
continue. At the same time, the heat due to the existing fire reaches a point where the
combustible material in the room get burnt completely, generating more heat and
depleting more oxygen. This causes the room to become one big explosive, literally.
The fire searches for oxygen source and gets transferred toward the point of ventilation
- it could be a window, ventilator or the slit under a door etc. There is intense fire
buildup in the area close to the ventilation. Fire patterns are concentrated at this region,
confusing fire investigators to think that, this was the point of origin of fire. This
phenomenon also known as flashover, is the cause of the ventilation generated fire
pattern.
69. Origin of Fire
One of the important question that fire investigators need to answer is where did
the fire originate from. The point of origin of fire or the seat of fire is the point where
the fire initiated.
In accidental fires, there is a rare chance of multiple points catching fire at the
same time- electrical fires, LPG leak fire etc. But its more common in cases of
arson, there could be multiple places where fuel is poured and multiple sites may
be set on fire by the perpetuator. So the fire investigator has to keep the chance
open to see multiple points of origin of fire.
The most common sign of the point of origin of fire is maximum damage. Being the
first point of fire, the point of origin is obviously the point where the maximum
damage may have occurred. But it need not be true always. So fire investigators
must s tart looking for the point of maximum damage with this intuition in mind.
71. Origin of Fire
Fire tends to burn upwards and outwards in a ‘V’ pattern. This is another cue the
fire investigator must keep in mind. In cases where fire has occurred at multiple
heights / layers / floors, the point of maximum damage at the lowest altitude must
be suspected to be the point of origin.
76. Origin of Fire
Fire effects (damages caused to material) can be another clue in identifying point of
origin of fire.
Smoke patterns, burn patterns and damage patterns on material need to be looked
at. Commonly a V shaped pattern of smoke or damage can be noticed on materials,
but that need not be so always.
Ventilation needs to be considered when reading smoke patterns. Smoke travels
towards the ventilation. This needs to be kept in mind.
80. Origin of Fire
Glass and plastic melt under heat of fire. The melting takes a direction of tailing
along the direction of fire.
Structural damage to the building can also be used to locate the seat of the fire. In
some instances, buildings may collapse in such a way that the area first weakened
by the fire is obvious, suggesting this is where fire damage first occurred and thus is
the origin.
Similarly, windows and ceiling structures are likely to fail in areas close to the seat of
the fire first. However, this is by no means an accurate method of locating the seat
of the fire, as the collapse and damage of a building is affected by numerous
factors, not just the fire only.
85. Origin of Fire
It may also be possible to determine the area in which a fire began based on the
operation of smoke and fire alarms. There may be some form of record of which
alarm was triggered first, suggesting the fire is likely to have started in that room.
The order in which alarms were triggered can be used further to establish the path
of propagation of the fire. However, such information is not available for all
premises.
86. Origin of Fire
Due to the range of factors affecting the origin of a fire, it may not be possible to
specify the exact point of ignition of a fire. Therefore, investigators generally define a
confidence perimeter or radius of error. This is an extended section somewhere
within which is the seat of the fire, with the most probable origin placed in the center
of the circle. Generally, the radius of this circle will decrease as the investigator
becomes more confident in establishing the origin.
87. Origin of Fire
The best practice to ascertain origin of fire is to first rule out common causes of
accidental fire. Examine the wiring, fuse boards, main boards, external power line
from the service pole etc. Also examine the electrical appliances like AC, heater,
refrigerator etc. Also examine the kitchen stove, gas tubing, LPG cylinder etc. Once
those are examined and fire origin is ruled out, the scene can be searched for area /
areas of maximum damage. The area of maximum damage is next searched for
possible fuel, inflammable material, heat producing sources etc.
One more important point to keep in mind is the fact that laboratory examination is
required to confirm the origin of fire. Therefore, the findings in the fire scene is only
a preliminary marker. Presence of fuel, globules of melted copper in wires, short
circuit etc. needs to be examined and proved in laboratory for confirming the origin
of fire.
97. Type of Fire
The investigating officer’s first doubt would be origin of the fire.
Next would be type of fire.
It is important on his/her point of view to rule out arson in every fire case.
The common types of fire are accidental fire, arson, electrical fire, outdoor fire,
vehicular fires and flashover burns.
98. Arson vs. accidental fire
The major question in an investigator’s mind is whether the fire was intentionally set or
accidental.
Arson is intentional setting of fire. It can be done for vengeance, jealousy, insurance
frauds, homicide, to cover up homicide, terrorism and sometimes also as part of a mental
problem (pyromania).
Whenever there is a lack of evidence to suggest accidental or natural fire, arson has to
be ruled out by the investigation. But the fact that fire occurred itself removes the
chances of any evidence of arson from being left behind. Therefore, a thorough, patient
and careful search is necessary n cases when arson is suspected.
Signs of forced entry – CCTV footage, eye witness reports, broken windows, doors,
presence of tools, disabled intruder alarms, matchsticks, fuel bottles etc. can point
towards arson.
100. Arson vs. accidental fire
Flammable liquids are commonly used by arsonists to accelerate a fire, particularly
petrol, diesel, kerosene and turpentine. These are known as fire accelerants. When
accelerants are used, fire patterns and effects are distributed unevenly. There will
be burnt and unburnt parts next to each other. These signs need to be looked at
with care. Trailing marks may be present when accelerants have been splashed on
material.
102. Arson vs. accidental fire
The odor in a fire scene is another important finding. Sniffer dogs and hand-held
hydrocarbon detectors are available for this purpose, but the fire investigator gets
more information using his/her own sense of smell. Flammable liquids may be
present naturally in fire scenes and they too may cause the odor. But in cases of
arson flammable liquids would have been used in more quantity and also in places
where flammable liquids will not be seen under normal circumstances. Sometimes
incendiary devices like matches, lighters, piles of newspapers etc. will be signs of
arson.
104. Arson vs. accidental fire
Investigators should attempt to ascertain the contents of the building prior to the fire.
The removal of items from the premises, such as business stock or objects of
sentimental or monetary value, is another strong indication of arson, commonly
linked to cases of insurance fraud. The owner of the premises should be
investigated and any possible financial or business problems searched for, which
would provide further evidence in the form of a motive.
105. Arson vs. accidental fire
Fires are occasionally started to conceal a previously committed offence. However,
if the fire was ignited to conceal a murder, it is extremely unlikely that the victim’s
body will actually be completely destroyed, as this would require temperatures of
hundreds of degrees Celsius for 2-3 hours.
An autopsy is necessary for victims of fire incidents to rule out possible concealment
of previous crime.
Pugilistic attitude is a important marker to differentiate between antemortem and
post mortem burning.
106. Arson vs. accidental fire
Another important finding in cases suspected of arson is the eye witness reports
and the fire extinguisher team’s reports. The color of the flame, the amount of
smoke, the nature of doors and windows – whether they were open / closed etc. are
important findings to rule out arson. When accelerants are used the smoke is less
and the flames are concentrated on one side of the scene in the initial stages of the
fire. The flames are also blue and later change to orange when accelerants are
used.
107. Arson vs. accidental fire
It is also important to note that arsonists (pyromaniacs) like to stay in the
neighborhood of the scene to watch the fire. Eye witnesses should be treated as
possible suspects and unnecessary detail need not be shared to them. All of them
must be documented and interviewed.
108. Accidental Electrical Fires
Electrical fires are caused by many reasons. It could be due to the heat generated
by higher voltage of current than the wire is meant to conduct. It could be due to
short circuit due to a malfunctioning appliance. It could be due to a wire being
damages. It could be due to a wire being loosely connected and sending out sparks.
Usually electrical fires are accidental and arsonists don’t use electricity to cause fire.
Electrical fires cause more damage at the point of origin. Usually the wires snap and
the fire stops spreading. But sometimes the wire holds on leading to spread of fire
through the insulation of the wires. Electrical fires cause damage to all appliances
connected through the wires. This is an important sign in electrical fires. AC’s,
ceiling fans, kitchen appliances are all damaged whereas nearby areas in living
room or kitchen will have lesser damage.
111. Accidental Electrical Fires
Electrical fires need laboratory examination before confirming the nature of fire.
Scanning Electron Microscopy is a useful tool in physically examining the wires,
fuse carriers, appliance terminals etc. for initiation of fire.
112. Flashover fire
Flashover is a phenomenon known to occur in compartment fires following a series
of events, eventually resulting in the compartment’s full involvement in the fire.
Flashover can be radiation-induced or ventilation-generated.
Radiation induced flashover occurs when a compartment / closed room is on fire.
There is sufficient fuel and heat to keep the fire burning. Oxygen shortage causes
the formation of hot gasses and increase in temperature in the room. The hot
gasses get accumulated in the ceiling of the room. At a certain point, the fire has
enough heat to consume the entire material in the compartment. The heat radiation
suddenly burns up all available combustible material in the room. They all reach
their auto-ignition temperature and burst into flames in a flash of a moment and are
turned to ashes.
113. Flashover fire
Ventilation generated flashover occurs in a similar scenario – there is a
compartment on fire, where oxygen shortage ensues. Hot gasses build up in the
ceiling of the room. In search of oxygen, the fire breaches the window or door or
ventilator and causes a structural collapse. The flashover causes a sudden influx of
oxygen. The increased heat causes the fire to ‘flashover’. This could resemble an
explosion. You can expect eye witnesses and victims to claim that there was an
explosion – LPG cylinder or electrical appliance blast in ventilation generated
flashover incidents.
However, flashover will not occur if there is insufficient fuel, inadequate heat
production, too little ventilation or too great a flow of heat out of the compartment.
115. Outdoor Fires
When investigating an outdoor fire, there are various differences from compartment
fires that must be taken into consideration. A fire burning on a flat, open surface will
move outwards towards any available fuel whilst producing hot gases above the fire.
Assuming the fire is surrounded by a similar fuel source and there is no wind to take
into account, the fire will most likely spread in a circular pattern. A fire on a sloped
surface will most likely spread in an uphill direction, provided there is a fuel source,
producing a fan-shaped spread.
Wildfires are very difficult to investigate owing to the large area and the possibility of
every inch of the scene to resemble the origin of fire. The nature of fire to burn
outwards and upwards plays a major role in understanding wildfires. The wind data
and the witness reports are also equally important to arrive at the right conclusion.
117. Vehicular fires
Vehicular fires can occur due to fuel leakage, electrical short circuits, overheating of
engine, lamp filament sparking or battery leakage or sparking. It is a major mode of
insurance frauds as well. Therefore, it is important to examine vehicular fires with
caution.
The burn / damage pattern on vehicle body panels are important markers for the
cause of fire. As fuel (accelerant) is already present in a vehicle, the idea of
identifying fuel to prove arson is out of context. Therefore, interpretation has to be
made carefully in vehicular fires.
Service records, insurance history, electrical systems in the vehicle and witness
reports serve as important pointers in the investigation. The major causes of
accidental vehicular fires are overheating in engine, overloaded wiring, leaking
battery etc. These must be ruled out by carefully studying the burnt debris.
119. Vehicular fires
Causes
Fuel leakage
Accidental fires due to an open fire nearby
Electrical short circuit
Electric overloading
Over heating of engine
Lamp filament & spark plug over heating
Battery leakage / sparking
120. Vehicular fires
Vehicles have lot of dry and easily inflammable parts, thus making interpretation
difficult.
It was once thought that quick and rapid fire from vehicle certainly means arson. But
now that need not be the case.
Witness evidence, Lab analysis, factory examination, service history etc. include
steps of investigation.
121. Vehicular fires
Indicators of accidental fire
Service history indicating mechanical / electrical fault
The heat indicator stuck at high
Occupants complaining of a burning smell before the fire
Witness reporting that the car was in motion
Factory recall notice for that specific model
Improper service schedule
122. Vehicular fires
Common causes of vehicular fires
Open flame fires close to car or in car
Electrical sources
Overloaded wiring
Lamp filament heating
External electrical sources used in cars
Hot surfaces in vehicles
Mechanical sparks
123. Vehicular fires
Open flame fires close to car or in car
Backfire of carborator
When air filter is malfunctioning creating a block
Lighted matchstick in car / ash tray
Heaters & geysers installed in caravans.
124. Vehicular fires
Electrical sources
Battery is the source of electricity
Sparking or lose contact in terminals
Fuse blown producing a spark
Circuit breakers over heated and melted
Improper installation
125. Vehicular fires
Overloaded wiring
Wiring under dashboards produce heat. Heat cannot be dissipated there
Power seat & windows & steering have some heating issues
Electric arcing is another cause of heating. Wires can spark and burn
126. Vehicular fires
Lamp filament heating
Gas & vapours are present in certain cars.
Present day usage of LED bulbs reduce this risk
The lamps can get overheated, blown and finally burn
127. Vehicular fires
External electrical sources used in cars
Jumper cables connected to higher powered batteries
Unsuitable batteries installed to support heavy electrical equipment fixed in vehicles
128. Vehicular fires
Hot surfaces in vehicles
Engine oil, fuel oils etc when they drip on hot surfaces can catch fire.
Hot surfaces are silencers, engine, outer side of radiators etc.
130. Searching the crime scene
Fire scenes are as dynamic as crime scenes. Therefore, caution to not lose evidentiary
value of physical evidences is a matter of priority. But that should not lead to the
temptation to rush without personal protection.
Fire scenes could pose danger to the forensic examiner. Therefore, care needs to be
taken to protect oneself. Search should start only after getting the ‘go ahead’ from fire
service personnel. Forensic personnel should never attempt to rescue victims or remove
debris until the fire personnel complete their job.
It must be noted here that fire personnel are trained to assess fire scenes, document
changes that are made during the rescue mission to the scene etc. Therefore, the
integrity of the fire scene is actually not lost due to this due patience.
Fire cases also come with contamination with water, dry powder or sand on the
evidences during the fire relief work. This can be a challenge and must be kept in mind
before assessing the fire scene.
135. Searching the crime scene
Preliminary assessment
The investigator should first make a preliminary scene assessment (an overall tour
of the fire scene to determine the extent of the damage, proceeding from areas of
least damage to areas of greater damage) to identify areas that warrant further
examination, being careful not to disturb evidence.
Inspect and protect adjacent areas that may include non-fire evidence (e.g., bodies,
bloodstains, latent prints or tool marks) or additional fire-related evidence (e.g.,
unsuccessful ignition sources, fuel containers and ignitable liquids).
136. Searching the crime scene
Interview
Interview is an important part of search in the fire scene. The investigator must:
Contact the incident commander, identify first responders and first-in firefighters,
and arrange to document their observations either in writing or through recorded
interviews.
Determine who reported the fire. Secure a tape or transcript of the report if
available.
Identify the owner of the building/scene, any occupants, and the person responsible
for property management.
Identify who was last to leave the building/scene and what occurred immediately
before they left.
137. Searching the crime scene
Identify and interview other witnesses (e.g., neighbors and bystanders) and record their
statements.
Ask first responders where an entry was made, what steps were taken to gain entry to
the building or vehicle, and whether any systems had been activated when they arrived
at the scene.
Observe and document the condition of doors, windows, other openings, and fire
separations (e.g., fire doors). Attempt to determine whether they were open, closed or
compromised at the time of the fire.
Observe and document the position of timers, switches, valves, and control units for
utilities, detection systems, and suppression systems, as well as any alterations to those
positions by first responders.
Contact security and suppression system monitoring agencies to obtain information and
available documentation about the design and function of the systems.
138. Searching the crime scene
Documentation
The investigator must:
Photograph and/or videotape the assembled crowd and the fire in progress.
Remove all non-essential personnel from the background when photographing the scene and evidence.
Photograph the exterior and interior of the fire scene (consider walls, doors, windows, ceilings, floors) in a
systematic and consistent manner. (Videotaping may serve as an additional record but not as a replacement
for still photography.)
Photograph any points or areas of origin, ignition sources and first material ignited.
Photograph any physical reconstruction of the scene.
Maintain photo and video logs. Record the date, the name of the photographer and the subject.
Determine whether additional photographic resources are necessary (e.g., aerial photography, infrared
photography or stereo photography).
A detailed preliminary write-up / description of the scene also can be used for documentation.
139. Searching the crime scene
Search
The search must be done using standard existing crime scene search methods – grid,
zone, strip etc.
Search must be careful and elaborate – taking into account both burnt and unburnt
material.
All the dimensions of the evidences need to be looked at – not only the facing side of the
evidence.
Evidence must be handled with gloved hands and metal forceps.
Evidence may be numbered and documented as photographs.
Collection can follow later.
Evidences which can ascertain origin and cause need to be given importance during
search.
140. Collection of evidence
We usually tend to start collection from the origin of fire.
Select productive sampling area. It could be places where you notice stains of
ignitable liquid indicators - pour pattern.
Sometimes only the edge of the pour pattern may be visible.
Look in junctions where furniture and walls meet the floor.
Stair ends - joint between riser and tread.
Use chisels, mallets to break debris.
Use spatulas to collect the broken debris.
Collection must be made in a new clean metal container with lid.
141. Collection of evidence
Photograph sampling area, measure it and record the measurements of the place
you are choosing for collection.
Wear nitrile or woolen gloves to collect debris.
Have at least 1/3rd headspace in container.
142. Collection of evidence
Burnt cardboard is usually found.
photograph the cardboard which is partially unburnt.
It may contain adsorbed accelerant.
Use gloved hands to lift and pack in metal container.
Sometimes we may require a shovel to move burnt paper and cardboard which is
stuck to each other or walls or floors.
143. Collection of evidence
Carpets and flooring material are other common evidence.
Photograph
Select the suitable area.
Look for pour patterns or fire effects which are inconsistent with other parts.
Wear gloves
Use knife to cut portions of flooring material.
Pack in metal containers
144. Collection of evidence
Ceramic tiles are usually glazed and non porous substances.
They are made without baking (unlike bricks).
They tend to get damaged with extreme heat.
Look for extreme damage
Phtoograph
Break tile floors using hammer and chisel
Weareye protective equipment.
Gloved hands to collect
Metal container
145. Collection of evidence
Concrete is also regular evidence
Expansion joints need to be checked.
Spalling is a evidence of possible arson
Photograph
Break using hammer & chisel or concrete breakers.
Wear eye protection
Use gloved hands
Metal containers
146. Collection of evidence
Concrete is also regular evidence
Expansion joints need to be checked.
Spalling is a evidence of possible arson
Photograph
Break using hammer & chisel or concrete breakers.
Wear eye protection
Use gloved hands
Metal containers
147. Collection of evidence
Fire debris must be collected at random points
Depending on total area of fire damage, investigator can choose 3 /5 or more spots
for collection
Wear gloves
Photograph
Collect using spatula
Metal container
148. Collection of evidence
Sometimes we may see liquid evidence on floor or in bottles
Usually ignitable liquids evapourate quickly.
But there are scenarios where we may tend to find it
It is best to swab it on gauze cloth and perform spot tests in the scene using the fire
investigation kit.
It is also mandatory in such cases, to request the judge for a immediate forensic lab
test.
Bottles which are found with ignitable liquids must be emptied in front of witnesses
in to air tight bottles (glass) or metal conatiners
149. Collection of evidence
Other common evidences include burnt wood, burnt glass, plastics and fibres.
We need to choose if entire object or part of the object needs to be forwarded.
Use metal containers for collecrtion.
