Chapter 14

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Chapter 14


Fire

Lecture PowerPoint


Copyright © The McGraw
-
Hill Companies, Inc. Permission required for reproduction or display.

Fire


Used by humans for many thousands of years


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

Insert Table 14.1

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:


C
6
H
12
O
6

+ 6 O
2


6 CO
2

+ 6 H
2
O + released heat


Is reverse of photosynthesis reaction:


6 CO
2

+ 6 H
2
O + heat from Sun


C
6
H
12
O
6

+ 6 O
2


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

Figure 14.2


Heat warms up and
dries out vegetation


Fire mostly limited
by amount of fuel
available


Any combustible material can be fuel (organic or human
-
made): 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

The Fire Triangle

Figure 14.5

The Fire Triangle


Firefighting
:


Water

reduces heat


Reddish
-
orange viscous fluids

block oxygen from plants


Bulldozing vegetation
or

setting backfires

removes fuel

Figure 14.3

An Ancient View of Fire

Aristotle’s

synthesis in 4
th

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 14.4

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 250
o
C, breaks down quickly at 325
o
C


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 14.6

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 14.8


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

The Spread of Fire

Figure 14.9

The Spread of Fire

Figure 14.9

The Spread of Fire

Figure 14.9

The Spread of Fire

Figure 14.9

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 14.10

The Spread of Fire

Fire Behavior


Heat given off creates unstable air and convection columns


fire
tornadoes

Figure 14.11

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 14.16

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 14.17

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 14.19

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

It is said that
California has 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 1,000
o
C


firestorm


Consumed 790 homes in one hour


Continued all day throughout Oakland and Berkeley Hills, until
early evening winds changed direction

Fire Weather

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 14.20

Southern California


Long dry season, chaparral vegetation, foehn winds


A land that was “born to burn”


Witch Creek fire of 2007:

197,900 acres burned, 1125 homes
destroyed, 239 vehicles burned, 45
firefighters injured, two deaths

More than 11,000 pictures
documented the
minute
-
by
-
minute
advancement

of the fire

Showed the importance of
flying
embers

Fire Weather

Figure 14.22

Insert Figure 14.22

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 14.26

Home Design and Fire


Safer decisions
:


Clay
-

or concrete
-
tile roofs, stucco exterior walls, double
-
pane
windows, few overhanging roofs or decks

Figure 14.28

Home Design and Fire


Safer decisions
:


Fire breaks of cleared vegetation extending at least 9 m (30 ft)
from house, farther if on a slope

Figure 14.29

Home Design and Fire

Insert Table 14.6

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

Insert Table 14.7

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


20
th

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

Insert Table 14.8

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

Fire Suppression

Figure 14.32

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

Insert Table 14.9


U.S. fire
-
fighting
reduced number of
fires, not acreage
burned


Santa Ana
firestorms burn
huge areas, kill
people, destroy
thousands of
buildings

Fire Suppression

Figure 14.34

Insert Figure 14.34

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 40
o
C 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 10
o
C, 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

Fire Suppression

Leave Early or Stay and Defend


Shelter
-
in
-
place

strategies


Build with
fire resistant materials
and have
landscaping with low fuel content


Modified vegetation
zones and
wide roads
for
firefighting equipment


Able
-
bodied
adults remain
to help firefighters


The debate continues


leave early or stay and defend

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

14