Assignment includes a practice write-up of extinction practical, heat transfer and combustion, information oof sources of ignition, the fire tetrahedron, and extinction methods. This assignment was graded as a distinction.
Investigating the Chemistry of Fire
Practical Investigation into the Difference in Heat Transfer Between Different
Metals
Introduction
Heat transfer is the “exchange of thermal energy” (Green Spec, 2021) usually from a high to
low temperature. Heat transfer can occur in three ways, conduction, convection, and
radiation. Conduction is when heat transfers through a solid object due to thermal contact,
meaning the solids are touching and the heat is passed through the molecules vibrating next
to one another. Convection transfers heat through heated fluids such as gasses or liquids, as
the hot liquid rises the colder sinks causing a convection current. The convection current
helps circulate the water ensure it is heated evenly. Lastly, thermal radiation transfers heat by
emitting electromagnetic radiation generated by a heated surface. By understanding how heat
can travel through different types of surfaces, fire investigators can begin to determine how a
fire has continued to spread or cause damage to certain materials such as the world trade
centre. The steel support structure that fell was found to have been weakened due to
convection that led to the steel reaching its melting point causing the structural failure. The
aim of this practical is to see how different metals conduct heat better than others and to
determine the rate of heat transfer.
Hypothesis
Copper will be the best conductor, shown by taking the least amount of time for the metal
drawing pin to drop. Lead will be the worst conductor, shown by taking the most amount of
time for the metal drawing pin to drop.
Equipment
The equipment used to conduct
this practical are as follows:
Conducting chamber
1100ml water
Measuring jug
Kettle
Thermometer
Stop watches
Vaseline
Metal thumb tacks Figure 1.1 – All equipment required for Figure 1.2 – Conduction Chamber
Heat proof mat practical Overview
Health and Safety
WHAT IS THE WHAT ARE THE WHAT IS THE HOW AND DOES
HAZARD? RISKS? PRECAUTIONARY THIS LOWER THE
MEASURE IN RISKS?
PLACE?
Injury through burns Personal protective By wearing personal
to exposed skin equipment. protective equipment
, throughout the
BOILING WATER practical investigation,
we created a sufficient
barrier between any
expose skin and the
boiling water. Lowing
the chances for any
accidental spilling of
the water causing
severe injury/burns
Injury through Emptying hot water By removing the
TEMPERATURE touching the heated after the investigation constant heat source
OF THE metal conduction was completed (the boiling water) we
CONDUCTION chamber can being to cool
CHAMBER down the chamber
reducing the chance
for significant injury if
then touched
Variables
Independent Variables Dependant Variables Control Variables
The metal rods being The time taken for the The amount of water used to
investigated drawing pin to drop fill the conduction chamber
The temperature of the water
in the conduction chamber
Method
To carry out this practical use the following method:
1. Gather the equipment, place the conduction chamber on the heat proof mat
2. Apply a small amount of Vaseline onto the ends of each metal rod protruding towards
you from the conduction chamber
3. Place one drawing pin at the end of each rod, trying to centre them in the same place
for each rod
4. Place the thermometer inside the conduction chamber ensuring it’s not touching any
of the rod
5. Fill the kettle with water and turn on
6. Once boiled measure 1100ml of water into the measuring jug
7. Pour the boiling water into the conduction chamber and start the stopwatch
8. Observe each drawing pin and record the time when they drop along with the
temperature
9. Record all the time and temperature of the drawing pins drop for each metal rod
Results and Findings
Metal Time (Minutes and Temperature (°C) Starting
Seconds) Temperature (°C)
Lead 7min 45s 71 89
Zinc 23s 89 89
Copper 42s 89 89
Our results found that the worst conductor based on time was lead and that the best conductor
based on time was zinc. The results also found that the starting temperature was not that of
boiling water (100°C) but rather 89°C. Additionally the results were measured in minutes and
seconds showing the drastic difference between how well some metals conduct heat
compared to others.
Discussion
Our investigation was partially successful as we correctly hypothesised that lead would be the
worst conductor. However, our results reflect that zinc was the best conductor, not copper
like we have hypothesised. There are many reasons which could have influenced the results
we obtained such as the amount of Vaseline we placed onto the ends of the rods was not
measured. Therefore, zinc could have had less Vaseline and thus less heat was required to
melt it and drop the drawing pin. Additionally, the placement of the drawing pin was not
precise and could have made our results inaccurate and unreliable. Lastly, the temperature of
the water we used was not boiling but rather 89°C this could have affected the times recorded
as some metals need higher temperature to conduct at their best. We could have repeated this
practical for an average but to replicate the investigation we would have to wait for the rods
to be fully cooled, to have the exact same temperature water, the same placement of the pins
and the same amount of Vaseline. This was not possible due to time constraints.
Conclusion
In conclusion, we proved that the different metals conduct heat at varying rates and that lead
was the worst and zinc was the best. Despite our hypothesis being partially incorrect, copper
was the second-best conductor that we tested. Being able to understand how different metals
conduct heat and how much heat is required to transfer the heat energy we can determine
what materials would not be sufficient in a fire. A real-life example of how fires heat metals
to the point of melting through conduction is the world trade centre collapse. Along with
various other factors it was found that “the collapse was caused by heating and failure of
structural steel beams in the centre of the buildings” (Science Daily, 2011). Using the
building flaws in the twin towers builders can now make better, more educated, decisions on
what fire-resistant materials to construct buildings from and hopefully prevent such incidents
from happening again.
Practical Investigation into the Correlation of Oxygen and Extinction
Introduction
Understanding the combination of elements that create and accelerate the spread of fire is
essential to comprehend how to extinguish said fire. Three major components that are crucial
for the formation are oxygen, heat, and a fuel source; an acceleration/spread of fire is a result
of chain reactions causing the fire to” become self-sustaining” (Carruthers 2017) or the
increase of any of the three components. When any of the three elements are removed, the
fire cannot continue to burn. For example, the use of water to extinguish fires is effective as it
removes the heat required to burn the fuel source and thus the by-product of the fire, the
flames/light, ceases and the fire is ‘out’. This practical investigation aims to determine if
oxygen is a factor in combustion and extinction.
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