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Lecture Outlines Natural Disasters, 7 th edition Patrick L. Abbott Fire Natural Disasters, 7 th edition, Chapter 15 Fire Used by humans for hundreds of thousands of years Allowed migration into colder climates Diverse successful civilizations Increased number and quality of foods

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  • Used by humans for hundreds of thousands of years
    • Allowed migrationinto colder climates
    • Diverse successfulcivilizations
    • Increased number and quality of foods
    • Aid inhuntingand inagriculture
    • Hardeningproperties  pottery, weapons, etc.  smelting, metals
    • Sterilization public health
    • Controlled inside machinery provides energy for civilization industry, domestic power, travel


  • Destructive powers of fire:
    • Destruction of enemies – obliteration of Troy
    • Denying enemies their prize – scorched earth policy
    • Bombs creating firestorms in World War II
  • Natural world
    • 1,800 thunderstorms active on Earth each hour
    • Lightning starts 15% of U.S. fires
    • Most fires started by humans

What is Fire?

  • Rapid combination of oxygen with carbon, hydrogen, and other elements of organic nature in reaction that produces flame, heat and light
  • Fire reaction:
    • C6H12O6 + 6 O2  6 CO2 + 6 H2O + released heat
  • Is reverse of photosynthesis reaction:
    • 6 CO2 + 6 H2O + heat from Sun  C6H12O6 + 6 O2
  • Solar energy stored by plants during growth is returned to atmosphere during fire

The Need for Fire

  • Organic material produced by plants is recycled by slow decomposition and rapid burning
  • Decomposition requires heat and moisture efficient in humid climates
    • Sparse vegetation of deserts  little material to decompose
  • Mediterranean climates:
    • Wet winters too cold for decomposition to occur efficiently, but still produce abundant vegetation
    • Fire (during dry summers) necessary for recycling of plant material, release of stored chemical potential energy
    • Necessary for health of some plant communities: germinates seeds, controls parasites, influences insect behavior

The Burning of Rome, 64 C.E.

  • Fire broke out in Circus Maximus and spread to cramped neighborhoods (Emperor Nero returned from Antium to Rome)
  • Six days: fire spread through 10 of 14 districts
  • Nero played lyre and sang own composition “The Fall of Troy” while fire raged
  • After fire, Nero rebuilt Circus Maximus and other areas, paid to remove debris, ordered safe reconstruction measures (wider streets, stone buildings, etc.)

The Fire Triangle

  • Fire may begin only when fuel, oxygen and heat are present in the right combination
  • Oxygen is 21% of atmosphere  steady supply of air
  • Heat warms up and dries out vegetation
  • Fire mostly limited by amount of fuel available

Figure 15.2


The Fire Triangle

  • Any combustible material can be fuel (organic or human-made): grasses, shrubs, trees, slash (organic debris left on ground after logging or storms), houses
    • Understoryof slash and shrubs ladder fuelallows fire to spread up into tall trees  major wildfires

Figure 15.5


The Fire Triangle

  • Firefighting:
    • Waterreduces heat
    • Reddish-orange viscous fluidsblock oxygen from plants
    • Bulldozing vegetation or setting backfiresremoves fuel

Figure 15.3


An Ancient View of Fire

Aristotle’s synthesis in 4th century B.C.E.: all matter composed of varying proportions of four elements, each with varying qualities of hot and cold, wet and dry

  • Air: hotness and wetness
  • Earth: coldness and dryness
  • Fire: hotness and dryness
  • Water: coldness and wetness

Figure 15.4


The Stages of Fire

  • Preheating: water expelled from fuel by nearby flames, drought, hot summer day
    • Wood needs to be dry and hot to burn
    • Cellulose is stable up to 250oC, breaks down quickly at 325oC
  • Cellulose begins to degrade duringpyrolysis
    • Chemical structure breaks apart, yielding flammable hydrocarbon vapors, water vapor, tar, mineral residues
    • If oxygen present, temperature raised  pyrolized gases ignite  combustion begins

Figure 15.6


The Stages of Fire

  • Flaming combustion: stage of greatest energy release, through convection, radiation, conduction, diffusion, as gases released by pyrolysis combustion
  • Glowing combustion: wood itself burns slowly, at lower temperature, without flames (oxidation)

Figure 15.8


The Spread of Fire

  • Wildfire styles:
    • Move slowly along ground mostly by glowing combustion
    • Wall of fire with flaming combustion front
    • Race through treetops as crown fire
  • Depends on:
    • Types of fuel
    • Weather and strength of winds
    • Topography of land
    • Behavior within fire itself

The Spread of Fire


  • Energy release depends on chemical composition of plants and organic debris
  • Eucalyptus: high oil content, ignites easily, burns very hot


  • Continuous supply of fresh oxygen
  • Distributes heat
  • Pushes flames forward
  • Transports flaming debris to start new fires

The Spread of Fire


  • Microclimates of different plant communities
  • Turbulence of winds blowing through rugged topography
  • Steep canyon slopes have high levels of radiant heat
  • Fire burns faster upslope than downslope – rising heat preheats slope above and creates chimney effect

Figure 15.10


The Spread of Fire

Fire Behavior

  • Heat given off creates unstable air and convection columns  fire tornadoes

Figure 15.11


The Fuels of Fire


  • Cover much of prairies of central U.S. and Canada
  • Late summer, early fall: dry grasses ignite easily, lightweight fuels
  • Fast, tall grass fires can kill and destroy property


  • Loose layering allows easy burning
  • High content of natural oils (palmetto, snowberry, chaparral) promote fires
  • Florida: 1998 wildfires after warm weather, heavy rainfall, excess plant growth, record-breaking drought, lightning without rain
  • California: scarce rain reduces plant growth except chaparral (rich in flammable oil) and inhibits decomposition chaparral plants respond by “sprouting” or “seeding”

The Fuels of Fire


  • Affected by amount of slash on ground beneath
  • Scarce litter: fires pass through quickly, little harm to trees
  • Abundant, dry litter: fires kill trees by burning hot and slow, or slash is ladder to treetops, becomes crown fire

Figure 15.16


Fire Weather

  • Fire hazards greatest where biggest differences between wet and dry seasons
    • Rainy season promotes plant growth
    • Dry season or drought dehydrates living and dead plants  easier to burn
    • Dry, windy patterns affect large region  major fires break out in bunches
    • More than 95% of burned area caused by 2-3% of fires

Winds of Fire

  • Large-scale movements of air-mass fronts
  • Small-scale local winds (temperature and topography differences)

Cold-front Winds

  • Cold fronts move at 30 to 50 km/hr with gusty conditions for hours
  • Dry in summer

Foehn Winds

  • High-pressure air mass spills over mountain range at up to 160 km/hr and descends as warm, dry wind toward low-pressure zone – caused by pressure gradient, warms adiabatically

Winds of Fire

Foehn Winds

  • Occur in September through April in western U.S. when high-pressure air sits over Great Basin and Rocky Mountains
  • Different names for foehn winds in different places

Figure 15.17


Fire Weather

  • Local Winds
    • Sea breezes, land breezes: temperature differences between land and ocean surfaces
    • Slope winds, valley winds: temperature differences between valley and ridge

Figure 15.19


Fire Weather

Great Lakes Region

  • Late 1800s: heavy logging left abundant slash, farmers used fire to clear land for agriculture
  • 1871: summer, early autumn drought followed by strong winds blew farmers’ small fires out of control

Peshtigo, Wisconsin: deadliest forest fire in U.S. history

  • 24 km widecrown fireraced forward with fire tornadoes
  • Covered 65 km and killed 1,152 people

Chicago, Illinois: fire broke out in O’Leary’s barn

  • Spread northeast through flammable businesses to river
  • Jumped Chicago River to burn tenements and spread downtown
  • In 27 hours: burned most of downtown, 300 people killed (O’Leary’s house undamaged)

Fire Weather

  • Four seasons: flood, drought, fire and earthquake
  • Winter rains send plants into fast-growth mode
  • Months of heat and drought kill and dehydrate plants

Oakland and Berkeley Hills (1991)

  • Expensive homes and decorative plants
  • Late 1980s five-year drought dried plants
  • 1990 freeze killed more plants
  • 1991 rainy spring spurred rapid grass growth
  • Rest of 1991 drought killed grasses
  • Dangerously high volume of dead and dry vegetation

Fire Weather

Oakland and Berkeley Hills (1991)

  • October 19: fire of suspicious origin started near hilltop
    • Fire extinguished Saturday evening
    • Planned return Sunday morning to control smoldering duff
    • Sunday morning Diablo winds blew sparks from duff into crown fire, blown in changing directions
  • October 20: fire burned out of control
    • Flames reached 1,000oC  firestorm
    • Consumed 790 homes in one hour
    • Continued all day throughout Oakland and Berkeley Hills, until early evening winds changed direction

Fire Weather

  • Oakland and Berkeley Hills (1991)
  • Never reached much more densely populated flatlands – desperate evacuation plans in place but not implemented
  • 25 people killed, about 3,000 dwellings destroyed, $1.5 billion in damages

Figure 15.20


Fire Weather

Southern California

  • Long dry season, chaparral vegetation, foehn winds
  • October 27, 1993: Santa Ana winds spread fires from downed power lines, transient’s campfire, arsonists’ fires
  • October 29: Winds died down, some control gained

Figure 15.23

  • November 2:
    • Winds hit up to 80 km/hr
    • Fires burned out of control, stopped only at ocean
    • Firestorms spun off tornadoes, starting new blazes
    • 3 people killed, 1,150 homes destroyed, $1 billion in damages, 215,000 acres burned

Home Design and Fire

  • Poor decisions:
    • Home of wood or roofed with wooden shake shingles
    • Wooden decks extending over steep slopes (concentrate heat)
    • Natural or planted vegetation from yard right up to house or draping over roof
  • House can ignite by:
    • Flames traveling through vegetation or along wooden fence
    • Flames generating enough radiant heat to ignite exterior
    • Firebrands carried by wind dropped on or next to house

Home Design and Fire

  • Safer decisions:
    • Clay- or concrete-tile roofs, stucco exterior walls, double-pane windows, few overhanging roofs or decks

Figure 15.28


Home Design and Fire

  • Safer decisions:
    • Fire breaks of cleared vegetation extending at least 9 m from house, farther if on a slope

Figure 15.29


Home Design and Fire

How Well Have Californians Learned?

  • 1923: firestorm destroyed 584 houses in Oakland, Berkeley Hills
  • Committee identified six factors that led to building loss
  • After 2003 San Diego wildfires, task force identified six factors that led to building loss
  • Five of six factors are identical on two lists

Fire Weather: The Winds of Madness

Santa Ana winds of southern California

  • Push firestorms
  • Affect people’s moods and behaviors
  • High wind speeds, extra low humidity, electrically charged air with 7 to 9 times normal level of positive ions
  • Described as ‘winds of madness’
  • Increases in domestic violence, household mishaps, allergic reactions, migraine headaches, suicides

Fire Suppression

  • 1910 Big Blowup: over 3 million acres in Idaho and Montana burned, destroying towns and killing 85 people
  • Forests with 30 big trees per acre  typical ground fires burnt grasses and thin litter without harming trees
  • Congress appropriated federal money to fight forest fires  policy of suppressing forest fires with professional fire fighters
  • 20th century fire suppression tactics and equipment improved  dramatic reductions in number of acres burned
  • After limiting fires, forests have 300 – 3,000 big trees per acre and shrub understory  slow, hot fires kill big trees

Fire Suppression

Yellowstone National Park

  • Oldest national park, about 15 lightning fires per year
  • Policy from 1880s to 1970s:
    • Extinguish all fires as soon as possible
  • Shift in 1970s to natural management changed policy to:
    • Extinguish human-made fires, let lightning fires burn
    • Between 1976-1987: 235 lightning fires, about 100 acres each
    • Policy judged successful
  • Winter of 1987-88 was dry
    • Many trees had been killed by mountain pine beetles
    • 90 years of fire suppression built up dead wood on ground
    • Moisture levels in wood dropped from 15-20% to 2-7%

Fire Suppression

Yellowstone National Park

  • Summer of 1988:
    • Lightning fires began as usual
    • Not followed by usual June-July rains
    • By late July, over 17,000 acres had burned
    • New policy enacted to extinguish all fires
    • High temperatures and high winds of August allowed fires to burn out of control until mid-September snows weakened them, then November winter conditions extinguished fires

Fire Suppression

    • At fire’s conclusion: 1.4 million acres burned, almost half of Yellowstone
    • In previous 116 years, only 146,000 acres burned
  • Ten years later:
    • Opened land to increased sunlight and nutrients  grasses, wildflowers, shrubs, tree seedlings, enriched soil

Figure 15.31


Fire Suppression

California vs. Baja California: Pay Now or Pay Later

  • Long-term effect of short-term fire suppression: in U.S., fires fought energetically and expensively, to not let fire interfere with human activities
    • Chaparral allowed to grow older, more flammable
    • Hot, dry Santa Ana winds unleash unstoppable firestorms
    • Fewer fires, but more large ones
  • In Baja California, Mexico: fires allowed to burn with little or no interference
    • Older chaparral surrounded by younger, less-flammable plants
    • More numerous fires, but smaller

Fire Suppression

  • Between 1972-80, percentage of chaparral acreage burned in U.S. and Mexico was about the same

Fire Suppression

  • U.S. fire-fighting reduced number of fires, not acreage burned
  • Santa Ana firestorms burn huge areas, kill people, destroy thousands of buildings

Figure 15.33


Fire Suppression

The Cedar Fire in San Diego County, October 2003

  • Huge areas of old chaparral fuel, dried by five years of drought
  • Lost hunter started signal fire, flames pushed westward by Santa Ana winds  burned 282,000 acres, destroyed 2,232 buildings, killed 15 people
  • Fire stopped when it encountered areas recently burned in 2001 Viejas fire and 2001, 2002 and 2003 prescribed Tragedy burns  would have burned more than 400,000 acres otherwise

Fire Suppression

The Western and Southern United States in 2000

  • Fires in 2000 burned almost three times more acreage than average year, with 20% more fires
  • On busiest day:
    • 84 large fires on 1.6 million acres in 16 states
  • Cool La Nina ocean water in eastern Pacific in 1999, 2000  drier than average weather in southern states

Fire Suppression

Prescribed Fires

  • Solution to problem of dense forests and shrublands: deliberately set prescribed fires at times of low wind speeds, low temperatures, high humidity, good soil moisture, approaching rain, etc.
  • 1995 to 2000: more than 31,000 prescribed fires

Los Alamos, New Mexico, May 2000

  • Controlled fire set at Bandelier National Monument to clear understory of brush
  • Following day, high winds blew prescribed fire into wildfire:
    • Consumed 50,000 acres of national forest, 235 Los Alamos houses, 115 buildings at Los Alamos National Laboratory, close to nuclear weapons research facility

Fire Suppression


  • Abundant eucalyptus trees: catch fire easily and burn very hot
  • Drought and high winds occur when El Nino-Southern Oscillation (ENSO) brings cool water off Australia
  • 60 km/hr winds descend from central deserts as foehns, bringing heavily populated coastal regions 40oC temperatures, low humidity
  • ENSO of 1982-3 was particularly strong  Australian summer driest on record
  • Foehn winds from interior were reinforced by jet stream until Adelaide and Melbourne were ringed by fires
  • Cold front came through dropping temperatures 10oC, but only changed direction of fire movement and increased speed of fire movement  winds 70 km/hr, gusts up to 170 km/hr, fire front advanced at 20 km/hr

The Similarities of Fire and Flood

Floods serve as metaphor for fire:

  • Both closely related to weather, plant cover and topography
  • Both at their strongest when atmospheric conditions are extreme (fire: fast dry winds; floods: heavy rains)
  • Both move across landscape and through human developments as waves of energy (fire: wave of chemical energy released from organic matter; flood: wave of mechanical energy unleashed when potential energy of high water is converted to kinetic energy of motion)
  • Both become more turbulent as they move faster and grow bigger
  • Both can be described by their size and frequency (inverse relationship)
  • Both aggravated by human activity