Professionals - Wildfires - Prevention part 2

1. E-Learning for Wildfires
Professionals

2. Wildfire Prevention – Part 2:
Understanding fire behaviour
and extreme fire behaviour
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3. Fire Behaviour
This is the second part of the module on wildfire prevention . It will
explain the following topics:
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• Combustion
• Methods of heat transfer
• Fire behaviour and how
wildfires spread and develop
Source: Northumberland Fire and Rescue Service (UK)

4. Fire Behaviour
Combustion
Combustion is the chemical reaction
that emerges from a process of
combining fuel, oxygen and
temperature to produce fire. The
reaction changes the composition of the
materials, consumes oxygen and
generates high temperatures which in
turns ignites new materials.
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*Ignition: The act of initiating the combustion of a material.

5. Fire Behaviour
• Combustion Process
How well a fuel will ignite and burn is largely dependant on its
moisture content. Before a wet fuel can burn, the moisture it contains
must evaporate.
This process requires heat.
As fuel moisture increases, the amount of heat required to ignite and
burn the fuel also increases.
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6. Fire Behaviour
Combustion Process
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Stage 1:
Ignition
Stage 2: Flaming
Stage
Stage 3: Extinction
1. Dehydration 2. pyrolysis 3. Combustion
The first heat
brought to the
process of ignition is
used to evaporate
water (humidity)
which the fuel may
contain. This process
takes place at
temperatures around
100ºC
Once the water has
evaporated, the heat
brought is used for
the thermic
decomposition of the
fuel and the
evaporation of the
volatile elements.
This process takes
place at
temperatures around
200ºC and 500ºC
When there is
enough fuel in
vapour state mixed
with air, the heat
brought will allow the
ignition of this
mixture, activating
the reaction of
combustion. This
process takes place
at temperatures
around 350ºC and
600ºC
Once the combustion
has started, it will
continue for as long
as there is enough
fuel and oxygen, and
while the heat
supplied for the
combustion reaction
is sufficient in order
to continue with the
evaporation of the
fuel
The extinction takes
place once there is
no fuel o no oxygen,
o when the heat
coming out of the
combustion is no
longer sufficient for
the fuel to evaporate.

7. Fire Behaviour
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8. Fire Behaviour
The Fire Triangle
Three elements must be present before
combustion can occur and continue
• Fuel - In wildfires it is mainly vegetation dry enough to
burn. The fire will stop when fuel runs out, is eliminated
or too wet for combustion to continue.
• Oxygen - In the countryside, air is an unlimited source
of oxygen. Being in the open air, oxygen will always be
present . You can only remove it momentarily to stop the
reaction by tactics such as smothering.
• Heat - the heat from combustion ignites near by fuel. If
the heat transmitted is reduced sufficiently, the fuel will
not burn. In order to reduce the heat flow, it is important
to know how it is transferred.
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OXYGEN HEAT
FUEL

9. The videos on the following page provide further information about the
combustion process.
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Fire Behaviour
Find out more about Combustion

10. Fire Behaviour
Physical mechanisms of Heat Transfer
When burning, fuel produces heat energy that spreads to the surrounding area. Physically
three forms of heat transfer are recognized:
• CONVECTION
• CONDUCTION
• RADIATION
In wildfires, there is one more heat transfer mechanism known as spotting. This is when
sparks, firebrands and/or embers (small pieces of burning fuel) are transported ahead of the
main fire by wind.
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11. Fire Behaviour
Convection
Heat is transferred through the
air, moving up slopes and
pushed by the wind. It is the
most common heat transfer for
forest fires.
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12. Fire Behaviour
Convection
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13. Fire Behaviour
Conduction
Heat transfer through a solid
material by contact. Vegetation
and soil are poor heat
conductors , so this has little
effect on wildfires.
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14. Fire Behaviour
Radiation
Heat transfer by waves through
space in all directions equally
and with the same intensity.
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15. Fire Behaviour
Radiation
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16. Fire Behaviour
Fire behaviour
This is the term used to refer to the physical characteristics of a fire and
they in turn control the potential development of its propagation.
Key factors are:
Temperature distribution
Structure of a flaming front
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17. Fire Behaviour
Temperature distribution
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18. Fire Behaviour
Structure of a flaming front
Height and length of the flames:
The height is the vertical measure
of the flame from the ground to its
highest point and the length is
measured from the base to the top
of the flame following its
inclination. The length of the
flame serves as an indicator of the
intensity of the fire.
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19. Fire Behaviour
Parts and forms of a wildfire
Wildfires, according to their behaviour, have different parts and forms of
propagation.
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20. Fire Behaviour
Parts and forms of a wildfire
Wildfires take many forms, but
their shape at the beginning is
often circular or elliptic and it
can be distinguished in different
areas.
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21. Fire Behaviour
Parts and forms of a wildfire
Head – Part of the fire which
moves forward, progressing
faster, and usually where the
flames are the largest.
Tail – This is the part of the fire
which spreads the slowest. It
has minor flames and it often
extinguishes itself.
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22. Fire Behaviour
Parts and forms of a wildfire
Flank – The flanks are the part
of the fire on both sides of the
head. They are called right and
left as viewed from the tail
towards the head.
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23. Fire Behaviour
Parts and forms of a wildfire
Spot Fires – These are fires
ignited outside the perimeter of
the main fire caused by burning
brands or embers
Fronts – The zone of a moving
fire where the combustion is
primarily flaming.
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24. Fire Environment
Fire Environment components:
The main factors that influence
how a fire develops are:
Weather
Topography
Fuel
The Fire Environment Triangle
provides an excellent tool to
understand fire behaviour.
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25. Fire Environment
An understanding of how these three factors, along with the type, condition
and continuity of the fuel, influence fire behaviour and firespread is of vital
importance for developing safe and effective tactical plans at wildfire
incidents.
By analysing the fire environment we can determine if and when fire
behaviour will change.
The next few slides explain how weather, topography and fuel affect fire
behaviour, fire intensity and rate of firespread.
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Fire Environment components:

26. Fire Environment
WEATHER
Among the factors that influence fire behaviour, the weather is the most
important and the most changeable . Weather conditions are the most
likely cause of an unpredictable change in the fire. Meteorological
variables influence the speed and direction of wind, temperature,
relative humidity and precipitation.
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27. Fire Environment
WEATHER
The key factors influencing fire behaviour include:
Wind speed
Wind direction
Temperature
Relative Humidity
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28. Fire Environment
Weather factors – Wind
Wind has a major influence on wildfire behaviour due to its ability to vary
greatly in speed and direction. The direction of fire spread is determined
mostly by wind. Unexpected wind change is the major causes of fatalities and
injuries at wildfires.
Wind can:
Carry away moist laden air drying out vegetation
Increase the supply of oxygen giving the fire more intensity
Influence smoke distribution and impair visibility
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29. Fire Environment
Influence the amount of fuel consumed
Bend flames closer to unburned fuels pre heating them closer to their
ignition temperature
Bend convection columns through new fuels, drying them out and
encouraging fire spread
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Weather factors – Wind

30. Fire Behaviour
Weather factors – Wind
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31. Fire Environment
The following illustrations show how wind affects firespread and the
shape of the area burned (the fire footprint).
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No wind

32. Fire Environment
The following illustrations show how wind affects firespread and the
shape of the area burned (the fire footprint).
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No wind Moderate
wind

33. Fire Environment
The following illustrations show how wind affects firespread and the
shape of the area burned (the fire footprint).
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No wind Moderate
wind
Strong
wind

34. Fire Environment
Weather factors – Wind
GENERAL WIND: This is the wind caused by the motion of the
atmosphere
LOCAL WINDS: All of these special winds are caused by land surfaces
heating during the day and cooling at night
TOPOGRAPHICAL WINDS: Winds that change direction and speed
due to topographical features such as valleys and saddles
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35. Fire Environment
Weather factors – General Winds
General winds are large scale upper level winds caused by high and low
pressure systems
They are usually modified in the lower atmosphere by terrain
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36. Fire Environment
Weather factors – Local Winds
ANABATIC WINDS (upslope daytime winds): They begin during the
mid-morning and get more intense as the sun warms the slopes.
Depending on the orientation of the slope it will be stronger at
different times of the afternoon (from 2pm to 6pm).
KATABATIC WINDS (downslope night time winds): They start when
the sun sets and they increase in intensity during the night until about
two hours before dawn
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37. Fire Environment
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38. Fire Environment
Weather factors - Local Winds
 SEABREEZES: A sea breeze is a wind that moves from the sea onto the
land and is caused by the imbalance between the temperature of the
air covering the land and the sea.
When the surface of the land is
heated by the sun the air above it
rises and is replaced by the cooler
air from above the sea, creating an
onshore wind.
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39. Fire Environment
LAND BREEZES: A wind that moves from the land towards the sea at
night, caused by the imbalance of temperature between the air above
the land and the air above the sea.
When land is no longer being heated
by the sun, the surface loses
temperature and the air becomes
colder and denser. The relatively warm
air above the sea rises and the air
covering the land moves to replace
it, creating an offshore wind.
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40. If you would like further information about how land and sea breezes
are caused, watch the short video on the next slide.
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Fire Environment
Find out more about Combustion

41. Fire Environment
Weather Factors – Topographical Winds
As the wind pushes air horizontally across the landscape, its direction and
speed can be altered by physical, topographical features.
Features such as valleys and spurs can alter wind direction as much as 90°
Wind blowing through a feature such as a re-entrants or a saddles can
increase speed as it passes through the constricted area
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42. Fire Environment
Weather Factors -Air Temperatures
The sun warms solid objects, such as fuels/vegetation and the surface of
the land. This in turn raises the temperature of the fuel and the air
surroundings them.
High temperatures heat the fuels, they become warmer, dryer and more
easily ignited (even more so in fine dead vegetation)
Fires ignite and spread more easily when the weather conditions are
hot and dry. Hot weather is normally accompanied by low relative
humidity which supports and encourages combustion.
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43. FireEnvironment
Weather Factors – Relative Humidity
Relative Humidly (RH) is defined as the amount of water vapour present in
the atmosphere. RH is expressed as a percentage i.e 1% would indicate that
there is only 1% water present in the air and is very dry where 100% would
be saturated and very moist.
In the absence of rain, fuel moisture is directly affected by RH:
 The amount of moisture fuels can absorb or release to the air depends on
RH
 Fuels and air are constantly exchanging moisture, trying to maintain
equilibrium moisture content
 Low RH conditions allow fuel to dry
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44. Fire Environment
 High RH conditions inhibit drying or moisten fuels
Warm air has the ability to hold more water vapour than cold air before
becoming saturated. As temperature increase the amount of water
vapour required to reach saturation also increases.
 Temperature and RH have an inverse relationship
 Increase in temperature, decrease in RH
 Decrease in temperature, increase in RH
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Weather Factors – Relative Humidity

45. Fire Environment
The diagram on the
right illustrates the
typical relationship
between time of day,
temperature, relative
humidity and fire
intensity.
It shows that maximum
fire intensity will often
occur during the early
to mid afternoon period
of the day.

46. Fire Environment
TOPOGRAPHY
Topography is the configuration of the earths surface
including natural and man-made features.
The topography of an area affects the fire in
different ways, including increasing or
decreasing the rate of spread of a fire or
altering wind speed and direction.
Its much easier to predict the influence of
topography on a fire than that of fuel and weather.
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47. Fire Environment
Topographical Factors
The main factors of topography that affect fire behaviour include:
 Aspect
 Slope
 Type of slope
 Elevation
 The interaction between topography and wind
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48. Fire Environment
Topographical Factors –Aspect
Aspect is the direction a slope is facing i.e. North or South Easterly Aspect
has therefore a direct affect on the levels of exposure to the sun the land
receives.
South facing slope receive more solar radiation during the day than
North facing slopes. East facing slopes receive solar radiation earlier in
the day and West facing later in the afternoon.
The amount of solar radiation will determine the degree of pre heating
and the moisture content of fuels.
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49. Fire Behaviour
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We use the term in or out of aspect to
describe whether the land is receiving
solar radiation or not

50. Fire Behaviour
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We use the term in or out of aspect to
describe whether the land is receiving
solar radiation or not

51. Fire Behaviour
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We use the term in or out of aspect to
describe whether the land is receiving
solar radiation or not

52. Fire Behaviour
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In Aspect Out of Aspect
We use the term in or out of aspect to
describe whether the land is receiving
solar radiation or not

53. Fire Environment
Topographical Factors –slope
The degree of incline or steepness of the land
Fires burn more rapidly upslope than downslope . This is due to the
fuels being in closer contact to the upward moving flames
 The radiant heat and convection currents produced by the fire
preheat the fuel and lower its moisture content
Fires moving upslope can therefore significantly increase the fires
rate of spread
With every 10° increase in slope, the rate of spread is likely to double
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54. e-Learning for the Prevention, Preparedness and Response to
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Fire Environment
Topographical Factors –slope

55. Fire Environment
Topographical Factors –slope- Diagram illustrating how every 10°
increase in slope, the rate of spread will double

56. Fire Environment
Topographical Factors –Type of Slope
There are three main types of slope:
Straight slope – The rate of a fire will be even from the bottom
to top
Concave slope – The rate of spread will be slow at beginning
and increase as the slope increases
Convex slope – The rate of spread will be more extreme at the
base and decrease as it moves upslope
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57. TYPES OF SLOPE
Fire Environment

58. Fire Environment
Topographical Factors –Elevation
Elevation refers to the height of the land above sea level. Its usually
measured in metres and is depicted on maps using contour lines and
spot heights.
Temperatures decrease with a rise in elevation. In general
temperature drops approx. 1° for every 150m increase in height
Normally when temperature decreases, relative humidly increases.
Higher relative humidity increases fuel moisture content and may
reduce the fires intensity and rate of spread
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59. Fire Environment
Topographical Factors –Elevation
 At higher elevations fuel loading will normally be reduced due to the
decrease in temperature. In extremely high elevations the land may be
devoid of fuel.
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60. Fire Environment
Topographical Factors –The interaction between Topography and Wind
Features such as valleys may change the direction of winds
 Saddles and re-entrants may increase the speed of wind, which can
significantly increase the fires rate of spread and intensity
These characteristics may compromise the safety fire crews working in the
area
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61. FUEL
In wildfire terminology, fuel is identified as live or dead plant material that
exists across the landscape. Fuels are the source of energy necessary for
combustion.
The fire behaviour in a fuel source is dependant on the following criteria:
The size of the fuel
The fuel loading
How the fuel is arranged
The type of the fuel
The moisture content of the fuel
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Fire Environment

62. Fuel factors – Size
Within the wildfire environment fuel exists in various lengths, thickness and
diameters. A simplified way of classifying fuel according to their size is to
refer them as being either fine or course.
Fine fuels – Fuels < 6mm in diameter
Coarse fuels – Fuels > 6mm in diameter
Fine fuels drive the forward spread of a fire while the coarse fuels are
consumed in the smoulder zone behind the main fire front.
The fine fuels are ignited first , this in turn heats and ignites the coarse fuels.
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Fire Environment

63. Fire Environment
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64. Fine Fuels Fine Fuels <6mm diameter
Grasses
Twiglets
Leafs
Coniferous needles
Coarse Fuels >6mm diameter
Sticks
Branches
Logs
Tree trunks
Tree stumps
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Fire Environment

65. Fire Environment
Fuel Factors – Fine Fuels
Fine fuels give the characteristic flame length at the fire perimeter
Fine fuels are responsible for most of the extreme fire behaviour:
torching, crowning and spotting (see extreme fire behaviour section)
Fine fuels are ignited first in the combustion process and burn readily
The rate of fire spread is greater in fine fuels than in coarse fuels
Fine fuels dry out quickly and ignite easily
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66. Fire Environment
Fuel Factors – Course Fuels
Course fuels normally burn inside the fire perimeter behind the
flaming front
Coarse fuels , once ignited , are more difficult to extinguish than fine
fuels
Coarse fuels dry slowly proportionally to their diameter
Coarse fuels depend on fine fuels for their ignition source
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67. Fire Environment
Fuel Factors – Fuel loading
Fuel loading is the amount of available fuel present expressed in terms
of weight of fuel per unit area. This could equate to tonnes per hectare
or tons per acre.
The term “available fuel” refers to the actual amount of fuel that is
capable of igniting and sustaining combustion under its present
conditions.
The presence of high fuel loading indicates a greater potential for
intense prolonged fires.
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68. Fire Environment
Fuel Factors – Fuel Arrangement
The way fuel is arranged plays an important role in fire development .
Within the fire environment fuels are arranged horizontally and
vertically and it is important to understand how they interact.
Horizontal arrangement – The distribution of continuous vegetation
across the landscape.
Vertical arrangement – The way fuel is arranged between ground
level and aerial fuels
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69. Fire Environment
Fuel Factors – Types of Fuel
Common fuel types found in the wildfire environment include:
 Grass
 Crops
 Deciduous woodland
 Coniferous plantations
 Heath and moorland
 Scrubland
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70. Fire Environment
Fuel Factors- Re-burn
The ability of a fuel to burn
again when the fire has already
passed through it without
burning it all out. These areas
cannot be considered safe.
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71. Fire Environment
Fuel Factors – Fuel Moisture
The amount of moisture available in a fuel will directly affect how easily it
will ignite and how intensely it will burn . The amount of fuel moisture is
dependant upon a number of factors namely:
 Relativity and humidity and precipitation
 Wind
 Size of the fuels
 Compactness of the fuel
 The proximity of the fuel to damp soil
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72. If you would like further information about fuel at wildfire incidents,
watch the short video on the next slide.
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Fire Environment
Find out more about fuel

73. Types of wildfire
Classifications of wildfires
There are 3 main different types of wildfire:
 Surface Fire
 Ground Fire
 Crown Fire
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74. Types of wildfires
Classification of fuels according to where they are found
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75. Types of wildfire
Surface Fire
This is the most common type of
wild fire, spreading in surface
fuels including grass, leaves,
shrubs , needles. and litter.
Most crown fires and ground
fires begin as surface fires.
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76. Types of wildfires
Surface Fire
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77. Types of wildfire
Ground Fire
Ground fires consume the organic
and combustible material beneath the
surface, such as stumps, roots, duff
and peat .
These fires usually spread slowly and
may go undetected, making them
difficult to extinguish due the
accessibility.
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78. Types of wildfires
Ground Fire
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79. Types of wildfire
Crown Fire
Crown fires burn through the
crowns or the canopy of trees or
shrubs.
They can advance in conjunction
with or be independent of a
surface fire.
They mainly occur in forest fires,
due to the continuity of the
crowns, passing from one to
another. They are difficult to
control and extinguish.
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80. Types of wildfires
Passive Crown Fire
A fire that travels from
surface fuels into aerial
fuels without sustained
Crowning.
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81. Types of wildfires
Active Crown Fire
A fire that advances as a
wall of flame engulfing all
surface and aerial fuels
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82. Fire Development
All wildfires usually start with a small surface fire which is then
influenced by the interaction of the environmental factors of Weather,
Topography and Fuel. The information from the previous sections will
enable us to understand how a fire will develop and spread.
The following section will look more closely at how the fire develops
and how to identify potential extreme fire behaviour.
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83. Fire Development
Wildfires will burn uniformly in
all directions when they are
burning within uniform fuel (i.e.
one type of fuel with the same
characteristics), on flat ground and
in the absence of wind.
This is illustrated on the right.
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84. Fire Development
However, it is unusual to
experience wildfires under these
conditions.
Typically, wildfires will spread in
an elliptical shape because one or
more environmental factors act as
a dominant force that increases the
rate of fire spread in a particular
direction.
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85. Fire Development
The fire behaviour observed at the majority of wildfires can be classified
according to the following:
Wind-driven wildfire – where the rate and direction of firespread is
predominantly influenced by the speed and direction of the wind
Topography-driven wildfire – where the rate and direction of
firespread is predominantly influenced by the topography
Fuel-driven wildfire – where the rate and direction of firespread is
predominantly influenced by the amount, condition and
arrangement of the fuel the wildfire is burning within
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86. Fire Development
Some wildfires may be significantly influenced by more than one of the
above factors. Different parts of the same wildfire may also be
predominantly influenced by different factors.
Fire and rescue personnel need to understand and predict fire behaviour
at wildfires. Wildfire Prediction Systems are tools that can be used to
help understand and predict future fire behaviour and fire spread.
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87. Fire Development
The key principle behind an appropriate wildfire prediction system is
that fire behaviour within any given fuel is influenced predominantly
by three major forces:
• Wind
• Slope
• Aspect
These three factors can be referred to as the ‘forces of alignment’.
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88. Fire Development
Summary
• Whenever a wildfire is supported by either the wind, slope or aspect it
will burn with greater intensity and spread more rapidly.
• If the fire loses the support of the wind, slope or aspect the intensity
and rate of spread will decrease.
• An understanding of how these three factors, along with the type,
condition and continuity of the fuel, influence fire behaviour and
firespread is of vital importance for developing safe and effective
tactical plans for wildfires.
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89. Try watching the videos on the next slides – they provide a useful
overview to help consolidate and further develop your
understanding of fire behaviour at wildfires.
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Further information about fire behaviour at wildfires
Fire Development

90. Extreme fire behaviour is defined as “fire
behaviour that becomes erratic or difficult
to predict”.
Extreme fire behaviour can lead to rapid
and/or unpredictable firespread and
behaviour, and can be sporadic or
sustained over longer periods of time.
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Extreme fire behaviour

91. There are a number of conditions which can increase the likelihood of extreme fire
behaviour, including:
High fuel loading – particularly in fine dead fuels
The existence of ladder fuels – particularly if there are large quantities of fine
fuels
Fire aligned with a strong wind
Fire aligned with a steep slope
High temperatures
Low humidity
Drought conditions
Availability of combustible fuels (particularly dead fuels)
Multiple seats of fire
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Extreme fire behaviour

92. There are also some common indicators of extreme fire behaviour:
A surge in fire intensity
Long flame lengths
Pulsating flames
Large quantities of smoke
Separate fires occurring outside the fire edge (spotting)
Ignition of aerial fuels in the canopy
An increase in surrounding air movement
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Extreme fire behaviour

93. There are also some common indicators of extreme fire behaviour:
A surge in fire intensity
Long flame lengths
Pulsating flames
Large quantities of smoke
Separate fires occurring outside the fire edge (spotting)
Ignition of aerial fuels in the canopy
An increase in surrounding air movement
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IMPORTANT: If
you can spot these
indicators early
then you can keep
yourself and
others away from
danger.
Extreme fire behaviour

94. The most extreme examples of fire behaviour are caused by a
combination of some or all of these factors. Extreme fire behaviour can
represent a significant hazard to members of the public and to fire
suppression personnel.
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Extreme fire behaviour

95. The most extreme examples of fire behaviour are caused by a
combination of some or all of these factors. Extreme fire behaviour can
represent a significant hazard to members of the public and to fire
suppression personnel.
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IMPORTANT: If you can spot the indicators of
extreme fire behaviour early then you can keep
yourself and others safer.
Extreme fire behaviour

96. Extreme fire behaviour can occur under varying parameters, however, a
general rule of thumb is that extreme fire behaviour is highly likely
when one or more conditions approach the 30-30-30 rule:
• Relative humidity is at or below 30%
• Wind speed is at or above 30 kilometres per hour
• Temperature is at or above 30 degrees Celsius
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Extreme fire behaviour

97. Extreme fire behaviour can occur under varying parameters, however, a
general rule of thumb is that extreme fire behaviour is highly likely
when one or more conditions approach the 30-30-30 rule:
• Relative humidity is at or below 30%
• Wind speed is at or above 30 kilometres per hour
• Temperature is at or above 30 degrees Celsius
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IMPORTANT:
Remember the
30-30-30 rule.
But also be
aware that
extreme fire
behaviour can
also occur
under other
conditions
Extreme fire behaviour

98. Extreme fire behaviour is divided into a number of categories. The
names of these categories describe the behaviour that is observed:
Spot fires
Torching
Crown fires
Junction zone effect
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Extreme fire behaviour

99. Extreme fire behaviour is divided into a number of categories. The
names of these categories describe the behaviour that is observed:
Spot fires
Torching
Crown fires
Junction zone effect
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Extreme fire behaviour
Each of these categories
of extreme fire behaviour
will now be explained in
turn.

100. Spot Fires:
The process that causes
spot fires is referred to as
“spotting”.
During spotting, burning
material can be carried
considerable distances by
strong convection currents
and wind .
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Extreme fire behaviour

101. An example of spot
fires igniting new fires
outside the main fire
perimeter.
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Extreme fire behaviour

102. The key danger of spotting is that spot fires can
breach control lines and threaten access, egress
and escape routes for personnel, vehicles and
members of the public.
It is therefore vitally important that fire
suppression personnel are tasked with
monitoring the fire and reporting any signs of
spotting as soon as possible to other personnel.
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Extreme fire behaviour

103. The key danger of spotting is that spot fires can
breach control lines and threaten access, egress
and escape routes for personnel, vehicles and
members of the public.
It is therefore vitally important that fire
suppression personnel are tasked with
monitoring the fire and reporting any signs of
spotting as soon as possible to other personnel.
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Extreme fire behaviour
Please note…
guidance on
developing an
effective response
wildfires is explained
in more detail within
the final module of
this unit on wildfire
response and
recovery prevention.

104. Torching
Torching is a term used to describe a fire that spreads from a surface
fire into aerial fuels
Torching usually occurs in areas where there are sufficent ladder
fuels that can support fire spread
Torching is normally localised and restricted to single trees or small
groups of trees
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Extreme fire behaviour

105. Crown fires
Crown fires are fires that burn within the upper canopy of trees or
shrubs. Their intensity is usually dependent on the amount and
condition of the fuel. Some shrubs and trees are more susceptible to
crown fires than others.
For crown fires to occur, there usually needs to be sufficient available
surface fuels and continuous aerial fine fuels.
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Extreme fire behaviour

106. Junction zone effect
The junction zone effect is an increase in fire activity caused by two
fires, or two parts of a fire, burning into one another. It is created by the
convection column generating in drafts, causing both fires to draw
towards one another. This increases the speed at which the fuel is
consumed and the subsequent intensity and rate of spread. The junction
zone effect can also increase the likelihood of spotting and spot fires.
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Extreme fire behaviour

107. Summary
It must be noted that it is not just extreme fire behaviour conditions that threaten life and
cause injury
Four recognised common denominators for fatalities at wildfires have been identified as:
 Fires burn surprisingly fast upslope especially in re-entrants, chimneys and saddle
features
Unexpected changes in wind strength and direction
Most accidents occur on smaller fires or isolated areas at larger incidents
Flare ups generally occur in deceptively light fuels such as grass and light scrubland
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Extreme Fire Behaviour

108. Summary
It must be noted that it is not just extreme fire behaviour conditions that threaten life and
cause injury
Four recognised common denominators for fatalities at wildfires have been identified as:
 Fires burn surprisingly fast upslope especially in re-entrants, chimneys and saddle
features
Unexpected changes in wind strength and direction
Most accidents occur on smaller fires or isolated areas at larger incidents
Flare ups generally occur in deceptively light fuels such as grass and light scrubland
Communication failures have also been regarded as a key contributing factor to a number
of previous firefighter fatalities.
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Extreme Fire Behaviour

109. To learn more about extreme fire behaviour:
• Refer to the sub-section on “extreme fire behaviour” within the Scottish
Government’s Wildfire Operational Guidance
• Refer to the UK Fire and Rescue Service’s National Operational Guidance
for Wildfires
• The video on the following page shows extreme fire behaviour at a
wildfire in Alaska.
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Extreme fire behaviour
Further information about extreme fire behaviour

110. We hope you enjoyed this
part of the module!
Please visit the next part
which explains more about
the potential impacts of
wildfires and how to prevent
and reduce the impact of
wildfires.
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End of Wildfire Prevention: Part 2
Source: Junta de Andalucía (Spain)

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Unless otherwise stated, this educational resource is licensed under a Creative Commons Attribution-ShareAlike 4.0 International
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