Flashcards in GHC Ch 14: Fire Deck (70):
What is the relationship between photosynthesis and fire?
Fire is the photosynthesis reaction in reverse.
What is the difference between a fuel driven fire and a wind driven fire?
Fuel-driven fires are small and moderate and can be extinguished when deprived of it's heat, fuel, or oxygen. Catastrophic firestorms are wind-driven fires. When the winds blow, the fire goes, and only a change in the weather will stop them.
What is the relationship between atmospheric high-pressure systems and the spread of fire?
What is the significance of flying embers?
Strong, gusty winds pick up flaming debris and burning embers called firebrands and drop them onto unburned areas, starting new blazes.
A fire deliberately set to consume fuel in front of an advancing wildfire in order to stop it.
How would one protect their house from a wildfire?
Make defensible space (Fire breaks of cleared vegetation extending at least 9 m (30 ft) from house, farther if on a slope), remove combustibles, and remember the embers. 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.
A dense, impenetrable thicket of stiff shrubs especially adapted to a dry season about six months long; abundant in California and Baja California. Fire is part of the lifecycle of these plants.
Act of burning.
Transfer of heat downward or inward through material by communication of kinetic energy from particle to particle.
A process of heat transfer whereby hot material at depth rises upward due to its lower density while cooler material above sinks because of its higher density.
Intermingling movement caused by thermal agitation with flow of particles from hotter to cooler zones.
A mat of organic debris in which fire can smolder for days.
A small, glowing piece of burning material.
The rapid combination of oxygen with organic material to produce flame, heat, and light.
Burning debris such as branches and embers that are lifted above a fire and carried away to possibly start new fires.
A fire large enough to disturb the atmosphere with excess heat, thus creating its own winds.
Any substance that produces heat by combustion.
Fire burning on calm weather days that advances slowly through the fuel, giving firefighters opportunities to stop the fire.
The capacity to raise the temperature of a mass, expressed in calories.
Vegetation of varying heights in an area that allows fire to move easily from the ground the treetops.
Combination with oxygen. In fire, oxygen combines with organic matter; in rust, oxygen combines with iron.
The process whereby plants produce organic compounds from water and carbon dioxide using the energy of the sun.
Heat emitted as rays.
Chemical decomposition by the action of heat. 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.
Debris such as logs, branches, and needles left on the ground by logging or high winds.
Wind-driven fire fronts that move fast. The wind carries firebrands forward, starting spot fires several miles ahead. Firefighter scramble to put out spot fires but can do little against the flame front.
How many people die on average each year in fires in the United States?
What is the fire triangle? What are its components?
The three components needed to generate fire: fuel, oxygen, and heat.
Compare the conduction of heat in wood versus metal.
What is an equation that describes fire?
C6H12O6 + 6 O2 -> 6 CO2 + 6 H2O + released heat
How does setting a backfire help fight a major wildfire?
The fire draws in oxygen which causes the backfire to be drawn in as well. When the two meet, there is no more fuel for the main fire to consume as it moves forward.
What is the difference between flaming combustion and glowing combustion?
The flaming combustion stage involves a flaming front that passes by and leaves behind glowing combustion, where the wood itself burns slowly, at lower temperature, and without flames (oxidation).
Will a typical that wildfire burn faster upslope or downslope? Why?
A typical fire burns faster upslope because the convective heat rising from and above the fire front dries out the upslope vegetation and in an intense preheating phase; in effect, a chimney is created up the slope, allowing fire to move quickly.
Explain how a wildfire can create its own winds.
In a firestorm, a fire is large enough to disturb the atmosphere with excess heat, thus creating its own winds.
How does a fire tornado form?
The vast quantities of heat given off by fire create unstable air. Heat-expanded air is less dense and more buoyant; thus, it rises upward in billowing convection columns. The rising columns of hot, unstable air may spin off fire tornadoes or firewalls.
How does the daily cycle work for sea breezes and land breezes?
Sea breezes are a daily condition in which warm air over the land rises, and cooler air over the ocean flows in to replace the risen air. Land breezes on the opposite. During the night, the cooler air over the land flows seaward.
How do you downslope winds form? Why are they typically hot and dry?
Downslope winds form when a high-pressure air mass flows down slope from a mountain range or high plateau and descends as warm, dry wind toward a low-pressure zone. The air is high from being at such a high elevation, and warms adiabatically as it descends.
What difficulties are presented when duff catches fire?
Duff burns on top but smolders below the surface, where oxygen is in short supply. Water extinguishes the surface flames, but water can also combine with ash to form a crust over smoldering combustion.
What is the relationship between a La Niña condition in the Pacific Ocean and wildfires in the southern states from California to Florida?
La Niña brings a pool of cool ocean water to the Americas, leading to dryer than average weather in the southern tier of states from Florida to California.
What is the relationship between El Niño and large wildfires in Australia?
El Niño cools the oceans. When the ocean waters off Australia are cooler, and evaporation and precipitation are reduced. The lessoned rainfall creates a drought that can extend through an entire southern hemisphere winter.
What is a preheating phase?
Before a fire breaks out, when water is expelled from plants, wood, or fossil fuels by nearby flames, drought, or even a long summer day.
What are the four ways that heat can be transferred in a fire?
Convection, radiation, conduction, and diffusion.
What is flaming combustion?
The process in which the pyrolized surface of the wood burns fast and hot. It is is the stage of greatest energy release.
What effects fire's spread?
Fuel, wind, typography, and fire behavior.
What are the main fuels of fire?
Grasses (Cover much of prairies of central U.S. and Canada, late summer, early fall: dry grasses ignite easily), shrubs (Loose layering allows easy burning, high content of natural oils), and forests.
How often do big fires occur?
Major fires are of great significance; more than 95% of all burned area is caused by only 2-3% of fires.
How many fires are caused by lightning strikes?
What starts most fires?
2011 Los Conchas fire
How is fire related to the Carbon Cycle?
Solar energy stored by plants during growth is returned to atmosphere during fire
What climates are fire-dependent for recycling?
How is fire necessary for the health of some plant communities?
germinates seeds, controls parasites, influences insect behavior, recycles plant material
What are some methods used by firefighters to combat forest fires?
Water reduces heat, reddish-orange viscous fluids block oxygen from plants, bulldozing vegetation or setting backfires removes fuel
What does the strength of a fire depend on?
Types of fuel, weather and strength of winds, topography of land, and behavior within fire itself
What are some styles of wildfires?
Moves slowly along ground mostly by glowing combustion, as a wall of fire with flaming combustion front, or racing through treetops as crown fire
What makes Eucalyptus especially flammable?
high oil content, ignites easily, burns very hot
Where are fire hazards greatest?
Fire hazard is greatest where there is the biggest difference between wet and dry seasons.
Cold fronts move at 30 to 50 km/hr with gusty conditions for hours, dry in summer.
High-pressure air mass flows downslope from a mountain range at up to 160 km/hr and descends as warm, dry wind toward low-pressure zone – caused by pressure gradient, warms adiabatically. Different names for downslope winds in different places.
Sea breezes, land breezes; slope winds, valley wind. Temperature differences between one and the other.
Peshtigo, Wisconsin fire
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.
Oakland and Berkeley Hills (1991)
Winter rains send plants into fast-growth mode. Months of heat and drought kill and dehydrate plants. Dangerously high volume of dead and dry vegetation. Consumed 790 homes in one hour. Continued all day throughout Oakland and Berkeley Hills, until early evening winds changed direction.
Witch Creek fire of 2007
Southern California. More than 11,000 pictures documented the minute-by-minute advancement of the fire. Showed the importance of flying embers = DATA!
Santa Ana winds of southern California
Push firestorms in southern California. Described as ‘winds of madness.’
How does fire suppression affect future fires?
After limiting fires, forests have 300 – 3,000 big trees per acre and shrub understory ->slow, hot fires kill big trees.
Yellowstone National Park Summer of 1988
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. At fire’s conclusion: 1.4 million acres burned, almost half of Yellowstone.
California vs. Baja California
In California: Long-term effect of short-term fire suppression. Fewer fires, but more large ones. In Baja California: fires allowed to burn with little or no interference. More numerous fires, but smaller.
The Cedar Fire in San Diego County, October 2003
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.
Leave Early or Stay and Defend
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