The Fire Factor An Introduction to Fire Behaviour

1
The Fire Factor??? An Introduction to Fire
Behaviour ?????

• Lucy/Guangzhi Yu
• China Program of The Nature Conservancy
• March 2009

2
The Fire Factor ???

• Fire Behaviour is the main factor that determines
  how people manage, respond to and live with fire.
• ?????????????????????????????
• A clear understanding of fire behaviour is a
  critical first step to making decisions regarding
  fire management.
• ?????????????????????????

3
Introduction ????

• Fire Science
• ???
• Fire Behaviour
• ???

4
Fire Science ???

• Combustion ??
• Fire Triangle ???
• Heat transfer ???
• Fire Types ????
• Parts of a fire ????

5
Combustion ??

• Chemical Reaction exothermic - generating heat,
  light seen as flames
• ?????????,???????
• Three elements to the reaction
• ??????????
• Oxygen ??
• Heat??
• Fuel???
• These form the Fire Triangle
• ????????????

6
Fire Triangle ???
Oxygen is the component of the air we breath. It
is essential for a fire to burn. ?????????????????
???????,????????? Heat, when great enough will
ignite fuel and sustain its burning ??,??????????
,???????,????????? Fuel is the combustible
material that burns. ??????????
7
Breaking the Fire Triangle ?????
Oxygen ?? Smothering a fire with soil can be used
to put out the flames. ??????????????? Foam
smothers the fire. ??????????? Both these reduce
the fires access to oxygen. ????????????????
8
Breaking the Fire Triangle ?????
Heat ?? To reduce heat the most common method is
to add water. ?????????????? Water removes heat
energy by absorbing it and dispersing it to the
atmosphere as steam. ????????????????????? Water
cools down the temperature of the fuel to below
its ignition temperature. ????????????????????????
????
9
Breaking the Fire Triangle ?????
Fuel ??? Removing fuel is often called dry fire
fighting. ???????????????? Use hand tools to
remove vegetation (rake hoe or shovel) in small
control lines. ?????????(??/?????)????????? Use
machinery to create larger control
lines. ???????????? Burn vegetation in front of a
fire leaving no fuel to burn ?????????????????????
??
10
Heat Transfer ???

• Three types of Heat Transfer ?????????
• Radiation
• ??
• Convection
• ??
• Conduction
• ??

11
Radiation ??
The heat energy that travels in straight lines
away from the heat source (light). It reduces in
energy further away from the source. ???????????(
?)??????????,?????
12
Convection ??
The transfer of energy through heating the
surrounding air. ????????????? The heated air
will rise creating a column of rising hot
air. ??????????????????
13
Conduction ??
The transfer of heat energy through a solid
object. ????????
14
Fire Types ????

• Ground fire (underground) ???
• Surface fire ???
• Crown fire ???
• Spot fire ??

15
Underground Fire ???
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16
Surface Fire ???
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Crown Fire ???????????,?????????????
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Spot Fire ??????????????,???????????????????,???
???
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Underground Surface
Crown??? ???
???
20
Spot??

21
Parts of a Fire ????
Back or rear ??
Flank or side ??????
Point of Origin ???
Head or front ?????
Flank or side ????
Spot fires ??
Un-burnt pockets or islands ?????????
Fingers ??
22
Fire Behaviour ???

• Fuel ???
• fuel type ?????
• Quantity and size ????????
• Moisture content ????
• Arrangement ?????
• Weather ??
• Temperature ??
• Relative Humidity ????
• Wind Speed ??

• - Topography ??
• Slope ??
• Aspect ??

23
Fuel Type ?????

• Affected by dominant vegetation
• ????????????????
• Grassland / Savannah
• ??/????
• Peat / duff / humus
• ????/??????/???
• Shrubs / thicket
• ??/???
• Forest / regeneration
• ??/???
• Slash
• (?)(?????)????
• Plantations
• ???

24
Fuel Type ?????
Grass Fuel Bark Fuel Shrub
Fuel ????? ????? ?????
25
Quantity and Size ?????

• The more fuel the greater a fires possible
  intensity.
• ?????,????????
• Fuel is measured in tons per hectare (t/ha)
• ?????????????????(t/ha)
• Fuel is primarily classified as fine and coarse
  where fine fuel determines fire behaviour
• ???????????????,????????????
• Fine fuel is less than 6mm in diameter(size of a
  pencil)
• ???????????6??????(????)
• Coarse fuel is greater than 6mm in diameter.
• ???????????6??????

26
Moisture Content ????

• Refers to how wet or dry a fuel is how much
  water it contains expressed as a of dry weight.
  
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• The higher the moisture content the wetter the
  fuel is and the less likely it is to burn.
• ??????,?????,?????
• The lower the moisture content the dryer the fuel
  is and the more likely it is to ignite and burn.
• ??????,??????,????
• Moisture content of fuel is related to
• ???????????????
• temperature and humidity ?????
• recent rainfall ?????
• soil dryness ??????
• exposure to sunlight ??????

27
Arrangement ?????

• Fire behaviour is affected by how a fuel is
  arranged
• ????????????
• A fuel that is tightly compacted together such as
  peat or heavy leaf litter will burn more slowly
• ??????,???????????????,?????
• A fuel that is loosely packed and aerated such as
  savannah or thickets will burn more quickly.
• ??????,???????????,?????

28
Weather ??

• Temperature
• ??
• Relative Humidity
• ????
• Wind
• ?
• Long term drought (El Nino)
• ????(??????)

29
Temperature ??

• Air temperature and direct sunlight influence
  fire behaviour by
• ?????????????????????
• Increasing the fuel temperature, meaning it is
  closer to its ignition point, but
• ???????,???????????,??
• More importantly decreases the fuel moisture
  content, drying the fuel and making it easier to
  ignite
• ???????????????,?????????????

30
Relative Humidity ????

• Relative Humidity indicates atmospheric moisture,
  expressed as a percentage of the maximum amount
  of water the air can hold.
• ???????????,???????????????????
• A high relative humidity (at 80) indicates a
  high level of water in the atmosphere
• ?????(?80)?????????
• A low relative humidity (at 30) indicates a low
  level of water in the atmosphere.
• ?????(?30)?????????
• Fuel will absorb or release water to balance its
  moisture content with the atmosphere.
• ???????,??????????????????
• The fuel moisture content then affects fire
  behaviour
• ?????????????

31
Wind ?

• Wind speed acts to push a fire forward.
• ?????????
• The greater the wind speed the greater the
  potential rate of fire spread.
• ????,???????
• Wind ?
• Increases supply of oxygen to the fire
• ??????????
• Causes the flame to tilt forward pre-heating the
  un-burnt fuel in front of the fire so it ignites
  more easily
• ??????????????????????????????
• Causes embers to be blown ahead of the fire and
  ignite as spot fires ahead of the fire front.
• ????????????????,?????????,??????

32
Long Term Drought (El Niño) ????(??????)

• Drought is a longer term climatic event, as
  compared to short term weather influences.
• ??????????,??????????
• Drought events can reduce the annual rainfall to
  a region creating drier fuels which are easier to
  ignite.
• ???????,???????????,???????????????
• During a drought event fire behaviour is
  increased due to reduced fuel moisture content
  leading to increased suppression difficulty
• ??????,??????,????????????????????

33
Topography ??

• Slope ??
• Aspect ??

34
Slope ??

• Slope affects a fires forward rate of spread.
• ???????????
• A fire travelling uphill will travel faster than
  a fire travelling downhill.
• ????????????
• For every 10o upslope the rate of spread doubles
• ??????,?????10?,??????
• For every 10o downslope the rate of spread halves
• ??????,?????10?,??????

35
Aspect ??

• Aspect is the direction that a slope faces. This
  influences the amount of sunlight received by the
  slope, in turn affecting the vegetation that
  grows there and the fuel moisture content.
• ????????????????????????,???????????????????
• This is important in temperate countries where
  aspect has a marked influence on vegetation
  patterns and fuel moisture dryness.
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