Lecture Outlines
Natural Disasters, 7th edition
Patrick L. Abbott
Fire
Natural Disasters, 7th edition, Chapter 15
Fire
• Used by humans for hundreds of thousands of years
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–
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–
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Allowed migration into colder climates
Diverse successful civilizations
Increased number and quality of foods
Aid in hunting and in agriculture
Hardening properties  pottery, weapons, etc.  smelting,
metals
– Sterilization  public health
– Controlled inside machinery provides energy for civilization 
industry, domestic power, travel
Fire
• 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 humanmade): grasses, shrubs, trees, slash (organic debris left on
ground after logging or storms), houses
– Understory of slash and shrubs  ladder fuel allows fire to
spread up into tall trees  major wildfires
Figure 15.5
The Fire Triangle
• Firefighting:
– Water reduces heat
– Reddish-orange viscous fluids block oxygen from plants
– Bulldozing vegetation or setting backfires removes 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 during pyrolysis
– 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
Figure 15.9
The Spread of Fire
Figure 15.9
The Spread of Fire
Figure 15.9
The Spread of Fire
Figure 15.9
The Spread of Fire
Fuel
• Energy release depends on chemical composition of
plants and organic debris
• Eucalyptus: high oil content, ignites easily, burns very hot
Wind
• Continuous supply of fresh oxygen
• Distributes heat
• Pushes flames forward
• Transports flaming debris to start new fires
The Spread of Fire
Topography
• 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
Figure 15.11
tornadoes
The Fuels of Fire
Grasses
• 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
Shrubs
• 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
Forests
• 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 highpressure 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 wide crown fire raced 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
Figure 15.23
• October 29: Winds died down, some control gained
• 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
Figure 15.26
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
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
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 midSeptember 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
Australia
• 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
End of Chapter 15