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Undergraduate Level Model Exam Answers
Question 1
The "Fire Tetrahedron" represents the essential elements or conditions necessary for the
development of a fire.
Identify each of these elements and for each one of these give suitable examples stating any
physio-chemical property variables so as to differentiate dissimilar circumstances that may
arise in a fire and its development, thereby contributing to any subsequent fire
investigation.
The essential elements which are necessary for a fire to take place comprising the fire
tetrahedron are fuel, oxidant, chemical chain reaction and heat.
Fuel
Fuel is the substance which is combustible/flammable in nature and can undergo a chemical
reaction with an oxidative agent like oxygen to release enormous amounts of energy in the form
of heat leading to a fire. Fuels can be in solid, liquid or gaseous forms. Flash point is the least
temperature at which the vapours of a flammable fuel can catch fire in the presence of an ignition
source. On the other hand, auto-ignition temperature of a flammable fuel is the lowest
temperature at which a fuel vaporizes into gaseous form and ignites in the absence of an external
source or flame.
The ignition temperature of paper is 233 degrees Celsius. Flammable solids have flash points of
less than 100 degrees Celsius. Extremely flammable liquids have flashpoints below 0 degrees
Celsius while highly flammable liquids have flash points below 21 degrees Celsius. Another
physio-chemical property variable of fuels is their lower and upper flammability limits. For
example methane gas has a lower flammability limit of 5% which is the lowest concentration of
methane on the air required to produce an ignition in the presence of an ignition source.
Similarly, the upper flammable limit of methane is 15% which is the highest concentration of
methane in the air which can ignite.

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Oxidant
Oxidant includes the oxygen in any form which is required for fire to take place. It includes 21%
of the oxygen in air, hydrogen peroxide, medical oxygen, chlorates and bromine.
Chemical Chain Reaction
Chemical chain reaction is initiated by the ignition source which mediated by the free radicals.
Heat
Heat is the energy input required to initiate and maintain the process of combustion/fire.
Question 2
Using relevant illustrations, diagrams and graphs, describe in detail the identifiable
sequence of phases and events associated with the development of a compartmental fire.
The compartmental fire development proceeds in the following four stages:
Incipient stage
In this first stage, a fuel, oxygen, heat and a chemical chain reaction interplay to result in a fire. It
is easiest to arrest the fire at this stage as it can be considered to be a mere ignition.
Growth stage
Various structures start to catch fire in this stage and these results in the spread (or growth) of
fire
Fully developed stage
It occurs when the growth stage reaches its climax and every flammable/combustible material is
on fire. This has the highest temperature and is the most dangerous one for victims.
Decay stage

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Undergraduate Level Model Exam Answers Question 1 The "Fire Tetrahedron" represents the essential elements or conditions necessary for the development of a fire. Identify each of these elements and for each one of these give suitable examples stating any physio-chemical property variables so as to differentiate dissimilar circumstances that may arise in a fire and its development, thereby contributing to any subsequent fire investigation. The essential elements which are necessary for a fire to take place comprising the fire tetrahedron are fuel, oxidant, chemical chain reaction and heat. Fuel Fuel is the substance which is combustible/flammable in nature and can undergo a chemical reaction with an oxidative agent like oxygen to release enormous amounts of energy in the form of heat leading to a fire. Fuels can be in solid, liquid or gaseous forms. Flash point is the least temperature at which the vapours of a flammable fuel can catch fire in the presence of an ignition source. On the other hand, auto-ignition temperature of a flammable fuel is the lowest temperature at which a fuel vaporizes into gaseous form and ignites in the absence of an external source or flame. The ignition temperature of paper is 233 degrees Celsius. Flammable solids have flash points of less than 100 degrees Celsius. Extremely flammable liquids have flashpoints below 0 degrees Celsius while highly flammable liquids have flash points below 21 degrees Celsius. Another physio-chemical property variable ...
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