Essay
Unit 36 - Forensic Fire Investigation Assignment 1 (Distinction)
- Institution
- PEARSON (PEARSON)
This is quite a lengthy distinction. This achieved the distinction criteria.
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Assignment 1Distinction
When a fire is spreading, it will typically spread in the direction
where the most abundant supply of the three main key
elements (oxygen, heat, and fuel) are situated. Typically, the fire
will follow where the heat is. A fires combustion rate tends to
be limited by one out of the three elements. In regard to fire
spreading, there are four various ways heat can transfer. Heat is
able to be transferred by the following; Conduction, Radiation ,
Convection , and Direct Flame Impingement (Direct Contact)
these four various heat transfer methods will be explained in
more detail below.
Conduction
Conduction is when heat energy has the ability to move through a substance when it comes into
contact with a good heat source. This is mostly seen by metals as they have closely bonded atoms
that allow for easy transfer of heat and objects such as non-metals and gases are poor heat
conductors and are more commonly referred to as insulators. The transfer of heat energy along an
object is always from the hot end to the cold end. With regards to the electrons in a metal, there is a
sea of free electrons which allow for easy transfer of heat and the closely packed molecules vibrate
as a result of this close packing and the hotter that the metal gets the more intense the vibrations
get as a result. The free electrons in the metal are responsible for transferring the energy by kinetic
energy from the hot end of the metal to the cold end of the metal.
In more depth conduction takes place when two objects which both have different temperatures
become into contact with one another. Heat will flow to the cooler object from the warmer object
until they are both at the same temperature. The scientific term for conduction is known as the
movement of heat through a substance by the collision of molecules. At the place where the two
objects come into contact with one another, the warmer objects faster-moving molecules will collide
with the cooler objects slower moving molecules. Through this colliding, the molecules which are
faster moving will give up some of their energy to the slower molecules, through this the slower
molecules gain more thermal energy and collide with other molecules within the cooler object. This
process will continue until heat energy from the object which is warm spreads throughout the object
which is cooler. Its important to note that some substances conduct heat a lot more easily in
comparison to others. Solids are more efficient conductors compared to liquids, and liquids are more
efficient conductors compared to gases. For example; good heat conductors are metals whereas a
poor heat conductor is air. An individual will experience heat transfer via conduction when they
touch something which is either colder or hotter than what their skin is, such as; when an individual
washes their hands in water which is either cold or warm.
Conduction is able to aid in fire spread through the following reasons. A fire will typically follow the
heat or occasionally the heat from conduction may cause an ignition of a fire elsewhere. Heat from
the fire is passed from molecule-to-molecule along the length of the material. As certain materials
are much better at conducting heat in comparison to others e.g. metals they are known as
conductors whereby material which are poor conductors e.g. plastic they are known as insulators. In
regard to houses, the walls which are between rooms are built from certain materials that are good
insulators therefore, on a winter’s night they are able to keep heat in a room, this can also be seen in
relation to fire as it helps to slow the rate at which the fire will spread through the house as it will
contain as much heat as possible. For example; in a commercial property a fire which is spreading
via conduction might involve heat being transferred through structural materials e.g. steel beams.
Therefore, combustible elements that come in to contact with these beams can ignite and the fire is
able to spread from there. Conduction can be responsible for the spread of fire between rooms
within larger buildings. Basically conduction is the transfer of heat through a solid and it takes place
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, Assignment 1
when matter conveys heat without visible movement of the matter. Through cooling the burning
material and the removal of fuel is how conduction can be controlled.
Radiation
Every type of object has the ability to take in and give out thermal radiation. Thermal radiation is
also referred to as infrared radiation. Some surfaces are better at reflecting and absorbing infrared
radiation in comparison to other surfaces. For example; matte black is a good absorber whilst shiny
silver is a good reflector. Essentially the hotter an object is, it will emit more infrared radiation.
Infrared radiation is known as a type of electromagnetic radiation which has the involvement of
waves. Within radiation there isn’t any molecule involvement unlike conduction and convection. It is
through this reason that radiation is able to work through the vacuum of space and why individuals
are able to feel the heat which the sun emits, even though the sun is 150 million km away from earth
itself. In regard to a fire, if a fires radiation is that intense it has the ability to cause objects which are
on the other side of rooms to heat up and have the potential to combust causing a larger fire.
Its known that conduction and convection both need matter for heat to be transferred, but radiation
is different to these two processes as it is a method of heat transfer which doesn’t rely upon any
contact between the heated object and heat source. By thermal radiation heat is able to be
transmitted through empty space. Basically radiation can be seen as a form of energy transport
which consists of electromagnetic waves which travel at the speed of light. During radiation no
medium is required, and no mass becomes exchanged. An object will emit radiation when their high
energy electrons within a higher atomic level fall down to energy levels which are lower. This energy
which is lost is emitted as electromagnetic or light radiation. Any energy which becomes absorbed by
an atom causes its electrons to ‘jump’ to energy levels which are higher. When the energy
absorption balances the emission of energy, the objects temperature will remain constant. However,
if the energy absorption is greater than the emission of energy, then the objects temperature will
rise. Whereas, if the energy absorption is less than the emission of energy, the objects temperature
will fall.
Radiation is able to aid the spreading of fire through the following reasons; Radiation simply travels
in rays which are similar to that of sun rays, in straight lines away from the fire. The rays heat is able
to be absorbed by materials which are combustible, and this causes them to heat up before possibly
igniting. The major principle of radiation is as follows; the more closer the material is to a fire the
more radiated heat it will obtain. Certain material e.g. concreate doesn’t allow for radiation to pass
through them. Due to this reason certain materials like concrete are very good construction
materials as they are able to help in preventing the spread of fire through houses or to buildings
which are nearby. A burning building sometimes is able to radiate enough heat that it can give rise
to a fire in a building which is nearby. Heat will transmit in all directions until it comes into contact
with an object which has the ability to absorb it. Although radiation can spread fire from buildings to
buildings and ignite nearby combustible material it can also penetrate windows and by doing so gain
access to the interior of properties which are adjacent to the burning building. Radiation is able to be
controlled through applying a shield of water fog.
Convection
Convection takes place in liquids and gases. Convection is when a liquid or gas becomes heated and
this heat then becomes transferred from one thing to another when it comes into contact with
something which is cooler than it. When a gas or liquid becomes heated, they expand this is because
the particles have the ability to move faster to places when they become heated compared to when
they’re cold, meaning they have more kinetic energy. This implies that particles will take up a larger
volumes as the gap which separates each molecule grows increasingly as the object is heated
however the particles themselves stay the same size. Due to the increase within heat energy the
liquid or gas’ density would’ve decreased, whereas, the density of liquid or gas will be higher in areas
which are cooler, thus causing the convection current. Cooler areas fall into a hotter areas which
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