fire triangle

STUDY
PLAY
fire
byproduct of combustion
______ fires have abundant supply of O in the air
wildland fuels
rapid oxidation occurs in 2 forms -
smoldering fires - no open flames, can be actively moving but not always (campfire when you wake up in am)
steady state fires - open flames, actively moving fires (what you want your campfire to look like)
components of fire triangle
oxygen sources
heat sources
fuels
% O required for combustion
16%
%O in normal air
21%
supply can be increased by wind
heat sources
causes fuels to reach ignition temperatures
heat is molecular motion - particles become excited & move around & create friction
heat sources may come from...
open flame, sun (dvd side up on road reflects sunlight), lightening, hot surfaces, sparks & arcs (highways & trains), friction (highways & trains?), chemical action, electrical energy, compression of gasses
fuel
may be solid liquid or gas
only gases burn - liquid & solid must be heated to gas to burn
initiation of combustion requires comversion to gaseous state by heating
ash
leftover material that didn't burn
part of fuel that didn't burn
gaseous fuels
natural gas, propane, butane, hydrogen, acetylene, carbon monoxide
drip torch
slow drip of fuel (fire) coming out
gives more control than something that puts out as much butane as a torch
liquid fuels
kerosene, turpentine, alcohol, cod liver oil, paint, varnish, lacquer, olive oil
solid fuels
dust, coal, wood, paper, cloth, leather, plastic, sugar, grain, hay, cork
heat energy
as HE is released, further chemical changes occur adding more fuel and producing a self-sustaining process
heat activates & sustains chemical reactions needed for continued combustion
amount of heat required to reduce moisture content of the fuel depends on physical and chemical make-up of fuel & % of atmospheric moisture
if the supply of O is available to combustion process...
combustion process increases, then combustion intensifies
energy release
heat and light
#1 cause of TX wildifre
lack of humidity
day time humidity almost always lower than that of night, so fires start & spread during the day
combustion
self-sustaining process
oxygen
supply can be increased by wind or rearranging fuels
heat transfer
allows sustained combustion
heat must transfer from involved fuels to those not involved
3 primary methods for heat transfer
conduction, convection, radiation
fire limiting/promoting factors
limiting - humidity
promoting - wind
conduction
when 2 objects of different temps contact (directly or thru medium) heat conducts from the warmer obj to the cooler obj until temps are equalized
ex. a burning log is sitting on a bed of dried leaves
heat conductors
heat conduction is the least important ignition of wildlife
metals like aluminum, copper & iron conduct heat rapidly & can play significant role in fire spread within structures
fibrous materials like plants & wood are poor conductors
heat transfer by conduction has limited effect on spread of wildifres
convection
Gases heated in fire expand, becoming lighter, and rise
Can cause local winds (that you didn't plan for)
As gases rise up the column, sparks & embers are carried aloft. These burning material can fall back to earth & start spotfires.
Hot convected gases moving up a slope can dry out fuels, lowering their ingnition temperatures. These fules also become preheated by the convection heat, increasing their susceptibility to ignition and more rapid fire spread (fire runs up a hill much quicker than down).
Convection columns aren't important regarding initial ignition of wildfires, but can be a big deal after the burn has started.
ex. wind is blowing heat from a grass fire into tree branches
radiation
Heat waves (infrared rays) radiate in all directions from the heat source. Heat waves travel through air until they are totally or partially absorbed by an opaque object. The opaque object gains heat and in turn radiates heat from its surface.
ex. fire is burning down one side of a steep forested canyon
fire triangle
oxygen, heat, fuel
Broken when one or more of these components is removed, interrupting the combustion process & extinguishing fire
removing fuel
clearing space of all surface fuels down to mineral soil
common way to control or extinguish fires
also called fire lines
mineral soil
pretty much just the dirt, no organic material
organic soils will burn
removing oxygen
smothering
flappers/swatters - inch of thick, rectangular rubber pads on a stick are used in the field
can be effective to put out a small spot fire & most common way to extinguish camp fires
removing heat
water
class A foam (surfactant added to water to increase travel distance)
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