wildfires

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1

what are wildfires?

  • self-sustaining fires that start and spread out of control; often move into populated or agricultural areas

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2

what are the diff causes of fires?

  • number 1 natural cause → lightning

  • arson

  • campfires, smoking, playing

  • transport

  • elec power

  • machinery

  • debris burning

  • unknown

  • other anthropogenic causes

  • 90% forest firest in US caused by human activity

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3

what is at risk with fires?

  • humans

  • ecosystem

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4

fires in Canada

  • numb of fires each yr in Canada n total burned

  • there is no correlation between the total area and the num of fires, as a few individual large fires account for most of the area

  • there r many small fires

  • less big ones

<ul><li><p>numb of fires each yr in Canada n total burned</p></li><li><p>there is no correlation between the total area and the num of fires, as a few individual large fires account for most of the area</p></li><li><p>there r many small fires</p></li><li><p>less big ones</p></li></ul>
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5

what is fire?

  • when gases react w/ oxygen to produce heat and light

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6

what are flames?

  • superheated gases (carbon dioxide, carbon monoxide, nitrogen, oxygen, water vapour and organic chemicals)

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7

what produces gases which fuel the fore?

  • breakdown of cellulose, fats, oils and sugar in plant walls and cells produces gases which fuel the fire

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8

what burns at relatively low temp?

  • cellulose and hemicellulose

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9

when does lignin burn?

  • burn at higher temperature than cellulose

  • tree species high in lignin (e.g., oak) will not burn as readily

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10

when does extractable burn?

  • flame suddenly when exposed to heat

  • contribute to the violence of wildfire in many conifer forest

  • ex. resins, fats, oils

  • unpredictable

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11

what is necessary to keep fire burning?

  • oxygen

  • heat

  • fuel

  • known as the fire triangle

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12

what is the preheating stage?

  • heat source raises a fuel’s temperature; water evaporates

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13

what is the pyrolysis stage?

  • molecs in fuel decompose to produce gases that rise in the air

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14

what is the combustion stage?

  • gases ignite and react with oxygen → produce fire

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15

what is flaming combustion?

  • dominates early fire

  • produces large flames and little smoke

  • initiated by ignition of volatile gases at 260ÂșC -450ÂșC

  • temperatures can rise to 1,500ÂșC; high enough to melt metal and glass

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16

what is smoldering combustion?

  • produces the most smoke

  • lack flames - associated w/ conditions where oxygen is lim

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17

combustion

knowt flashcard image
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18

where do ground fires occur?

  • within roots and buried organic matter

  • creep along under ground surface

  • little flaming, more smoldering; limited oxygen

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19

where do surface fires occur?

  • burn low-lying vegetation (undergrowth and forest litter ex. grasses and dead leaves)

  • burn slowly with smoldering, limited flaming

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20

what do ladder fires burn?

  • undergrowth and medium-sized trees (below the forest crown)

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21

crown fires?

  • flaming is carried via tree canopies

  • driven by strong winds and steep slopes

  • can jump from crown to crown without burning undergrowth

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22

what is fire severity?

  • percent biomass that burns during a fire

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23

what is fire intensity?

  • measure of energy released during burning

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24

what is flame length?

  • distance from the base to the end of the flame

  • more intense fire = longer flame length

<ul><li><p>distance from the base to the end of the flame</p></li><li><p>more intense fire = longer flame length</p></li></ul>
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25

what is conduction?

  • transfer of heart directly from molec to molec

<ul><li><p>transfer of heart directly from molec to molec</p></li></ul>
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26

what is convection?

  • transfer of heat by the movement of heated air

  • hot gases are less dense and rise; pulls in fresh air to sustain combustion

<ul><li><p>transfer of heat by the movement of heated air</p></li><li><p>hot gases are less dense and rise; pulls in fresh air to sustain combustion</p></li></ul>
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27

what is radiation?

  • radiant energy heats fuel within 10-35m of a wildfire

<ul><li><p>radiant energy heats fuel within 10-35m of a wildfire</p></li></ul>
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28

what are firebrands?

  • sparks and embers can land on fresh fuel beyond the wildlife; start new fires

<ul><li><p>sparks and embers can land on fresh fuel beyond the wildlife; start new fires</p></li></ul>
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29

how do wildfires spread?

  • start most often when a small heat source (spark from campfire, cigarette) comes into contact with dry grasses, leaves, small sticks

  • heat from this small fire pre-heats surrounding fuel

<ul><li><p>start most often when a small heat source (spark from campfire, cigarette) comes into contact with dry grasses, leaves, small sticks</p></li><li><p>heat from this small fire pre-heats surrounding fuel</p></li></ul>
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30

what does spread depend on?

  • fuel

  • weather (wind)

  • terrain

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31

what do sparse or wet fuels result in?

  • less intense wildfires

  • seasonal changes dictate moisture lvls in fuel

<ul><li><p>less intense wildfires</p></li><li><p>seasonal changes dictate moisture lvls in fuel</p></li></ul>
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32

what does wind replace during burning?

  • oxygen consumption

  • also tilts flames causing preheating and spreading firebrands

<ul><li><p>oxygen consumption</p></li><li><p>also tilts flames causing preheating and spreading firebrands</p></li></ul>
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33

what do flaming gases and hot rise via?

  • convection

  • allows for fires migrate faster up slopes than down slopes

<ul><li><p>convection</p></li><li><p>allows for fires migrate faster up slopes than down slopes</p></li></ul>
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34

what are ways enviro has adapted to fire?

  • trees like cork oak have adapted to fire

    • their sponge bark does not burn

  • Jack pine are well adapted to fire, as the heat of the fire opens their cones liberating the seeds

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35

what are primary disaster of wildfires?

  • injury and death

  • property, agricultural, and forest losses

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36

what are secondary disaster of wildfires?

  • health effects from smoke inhalation

  • increased soil erosion

  • destabilizes slopes - can lead to landslides

  • longer impact

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37

Australia Bushfires 2020

  • known as the “black summer”

  • 5,900 buildings destroyed

  • 34 deaths

  • affected ~3 billion animals

  • some endangered species believed to have been driven to extinction

  • air quality hazardous in all southern and eastern states of Australia

  • estimated to cost upwards of $100B

  • Australia costliest natural disaster to date

  • biggest concern was wildlife

    • millions animals killed

  • no ele, water, phone service in some areas

  • not much govern help

  • strong winds

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38

fire suppression methods

  • firebreak construction

  • plane dropping retardant

  • create break + start new fire

<ul><li><p>firebreak construction</p></li><li><p>plane dropping retardant</p></li><li><p>create break + start new fire</p></li></ul>
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39

forest management

  • total fire suppression (1940’s-1980s) results in large fuel accumulations and larger fires

  • increased knowledge in forest ecology demonstrated the importance of fire for forest renewal

  • policy has shifted toward prescribed burns in some areas to reduce large fuel accumulations

  • natural lightning-caused fires were allowed to burn unless they posed threats to people, commercial timber lands or scenic attractions

<ul><li><p>total fire suppression (1940’s-1980s) results in large fuel accumulations and larger fires</p></li><li><p>increased knowledge in forest ecology demonstrated the importance of fire for forest renewal</p></li><li><p>policy has shifted toward prescribed burns in some areas to reduce large fuel accumulations</p></li><li><p>natural lightning-caused fires were allowed to burn unless they posed threats to people, commercial timber lands or scenic attractions</p></li></ul>
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40

there is a growing num of ____________ ______________________ bringing humans closer to fire risk

  • interface communities

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41

how to reduce risk?

  • homes should be constructed from flame resistant material

  • area around homes should be clear of brush

  • a clear emergency plan and response should be in place

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