Studied by 3 peoplewhat are wildfires?
self-sustaining fires that start and spread out of control; often move into populated or agricultural areas
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
what is at risk with fires?
humans
ecosystem
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
what is fire?
when gases react w/ oxygen to produce heat and light
what are flames?
superheated gases (carbon dioxide, carbon monoxide, nitrogen, oxygen, water vapour and organic chemicals)
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
what burns at relatively low temp?
cellulose and hemicellulose
when does lignin burn?
burn at higher temperature than cellulose
tree species high in lignin (e.g., oak) will not burn as readily
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
what is necessary to keep fire burning?
oxygen
heat
fuel
known as the fire triangle
what is the preheating stage?
heat source raises a fuel’s temperature; water evaporates
what is the pyrolysis stage?
molecs in fuel decompose to produce gases that rise in the air
what is the combustion stage?
gases ignite and react with oxygen → produce fire
what is flaming combustion?
dominates early fire
produces large flames and little smoke
initiated by ignition of volatile gases at 260ºC -450ºC
temperatures can rise to 1,500ºC; high enough to melt metal and glass
what is smoldering combustion?
produces the most smoke
lack flames - associated w/ conditions where oxygen is lim
combustion
where do ground fires occur?
within roots and buried organic matter
creep along under ground surface
little flaming, more smoldering; limited oxygen
where do surface fires occur?
burn low-lying vegetation (undergrowth and forest litter ex. grasses and dead leaves)
burn slowly with smoldering, limited flaming
what do ladder fires burn?
undergrowth and medium-sized trees (below the forest crown)
crown fires?
flaming is carried via tree canopies
driven by strong winds and steep slopes
can jump from crown to crown without burning undergrowth
what is fire severity?
percent biomass that burns during a fire
what is fire intensity?
measure of energy released during burning
what is flame length?
distance from the base to the end of the flame
more intense fire = longer flame length
what is conduction?
transfer of heart directly from molec to molec
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
what is radiation?
radiant energy heats fuel within 10-35m of a wildfire
what are firebrands?
sparks and embers can land on fresh fuel beyond the wildlife; start new fires
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
what does spread depend on?
fuel
weather (wind)
terrain
what do sparse or wet fuels result in?
less intense wildfires
seasonal changes dictate moisture lvls in fuel
what does wind replace during burning?
oxygen consumption
also tilts flames causing preheating and spreading firebrands
what do flaming gases and hot rise via?
convection
allows for fires migrate faster up slopes than down slopes
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
what are primary disaster of wildfires?
injury and death
property, agricultural, and forest losses
what are secondary disaster of wildfires?
health effects from smoke inhalation
increased soil erosion
destabilizes slopes - can lead to landslides
longer impact
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
fire suppression methods
firebreak construction
plane dropping retardant
create break + start new fire
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
there is a growing num of ____________ ______________________ bringing humans closer to fire risk
interface communities
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
