The Behaviour of Fire
Causes of Fire
Fires have four main causes: accidental, deliberate, natural, and undetermined. It takes
intensive investigations to determine the causes of a fire; with the aim is to find what has
caused the fire and who is responsible.
Accidental
Accidental fires are defined as fires that started by chance and where, if a human was at
fault, there was no specific intent to inflict property damage or significant injury to another
person. Accidental fires in domestic settings are mostly caused by broken/faulty appliances,
fuel leaks, electrical item misuse, and having combustible materials too close to a potential
heat source. According to Mead, 2020, there were around "300 house fires started by home
appliances every week" in 2019, although this figure has now dropped by 3.2 percent in
2020. Accidental fires are most common in
residential areas such as homes. The Grenfell Tower
fire in 2017 was one of the most tragic incidents of
unintentional fires resulting in mass casualties. The
original cause of the fire, according to the BBC 2019,
was a faulty fridge freezer. Excluding all the
aggravating circumstances, such as the flammable
cladding on the building's exterior, the fire was
ignited accidentally by a domestic appliance and
resulted in the untimely deaths of 72 innocent
people.
Figure 1.1 – (BBC, 2019) Grenfell Tower
Deliberate
The deliberate initiation of a fire with the clear intent of inflicting substantial injury to
property or another person is referred to as arson. Arson falls under the Criminal Damage
Act of 1971. One of the key reasons that offenders commit arson is to erase evidence of
previous crimes. However, by purposefully igniting a fire, they are generating more evidence
with which to trace them. The features of a planned fire differ greatly from those of an
accidental fire. In an arson investigation, there is frequently more than one 'seat' of a fire
(the seat of a fire is its origination site within the scene). Furthermore, in cases of arson,
flammable items known as streamers may be detected, these facilitate the spread of fires
throughout all sections of the room more rapidly. There will also appear to be no viable
explanation for how the fire started, for instance, there being no electrical equipment
destroyed that could have caused the room to be enveloped in flames. The odours of the
fuel sources used may also lead the investigator to suspect that the fire was a product of
foul play. Moreover, intentionally started fires may behave differently from accidentally
caused fires. This is because the fuel sources selected were most likely chosen with the sole
intention of igniting and maintaining the fire for a prolonged period of time. As the offender
attempted to ignite as much flammable material as possible, there may be a more widely
distributed fuel sources discovered within an area. As a result, the fire may be more
, persistent in the environment than one caused by natural or unintentional circumstances
making its extinction harder.
Natural
Another potential cause of a fire is naturally caused. These are fires caused by
environmental incidents such as lightning strikes or excessively dry weather. The Australian
bushfires are a prime example of how the weather can cause devastating fires. According to
Kramer, 2020 the effects of climate change saw Australia face the driest conditions on
record. This is conjunction with lighting strikes initiated the fires and cause multiple
fatalities, lasting impacts on wildlife and the destruction of “11 million hectares” of land.
Natural fires, as evidenced in the case of the Australian bushfires, are often among most
tough to extinguish. This is due to the abundance of material being ignited in a short period
of time, as well as the possibility for weather conditions such as wind to rapidly spread the
fire. As a consequence, the damage may be significantly greater than that of an accidental
localised fire, such as an appliance fire.
Undetermined
An undetermined fire occurs when the cause of a fire cannot be determined. A fire may be
classified as undetermined if the damage to the property is too extensive, evidence cannot
be recovered, or a hypothesis of the cause cannot be supported/there’s still some
uncertainty.
Phases of a Fire
The incipient phase is the first phase of a fire. This occurs instantly after the ignition and is
when the fire begins. The fire then immediately enters the growth phase, in which it begins
to take possession of the combusting object/material and begins to burn self-sustainably. At
this stage, the fire has become established and will continue to generate temperature and
heat emission. Following the growth phase, we enter the free burning phase, during which
the fire reaches its peak temperature and releases its maximum amount of energy (the heat
release rate/HRR reaches its highest potential). It is also the stage at which the majority of
the chemical by-products of the incompletely combusting substances are emitted in the
form of smoke. Finally, the fire begins to deteriorate
in the decaying phase, where it begins to die due to a
lack of fuel sources and oxygen, meaning that the fire
can no longer self-sustain itself and will eventually
become extinct. This is often the longest phase of the
fire as the temperature slowly declines.
Heat Release rate
The heat release rate or HRR is the “rate at which fire
releases energy” (Thompson, 2010), usually
measured in Watts or Kilowatts depending on the
fuel source ignited. When the fire reaches its heat
Figure 1.2 (Josh, 2010) Heat Release Rate and Phases of
release rate the fire is at its maximum potential; this a Fire Correlation
also coincides with the when the fire has reached the
