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What does a fire need to start?
List both natural and human ignition sources.
- natural: lightning, firebrands from existing fires, volcanic eruptions
- human: prescribed burns out of hand, campers
What are the kinds of natural fuel?
- ground: roots, duff and peat
- surface: leaves, needles, twigs, logs and low brush
- aerial: branches, crowns, hanging moss, leaves and snags
describe heavy fuel -vs- fine fuel and different fires of each and how they spread
- heavy fuel: longer to heat & ignite
- burns slowly
- flames at higher temperature
- tree trunks and large branches
- fine fuel: fast-drying
- easy to ignite
- rapidly consumed
- grass, leaves and sticks less than 1/4 inch diameter
How are fires classified?
- by location
- 1) ground fire in ground fuel
- 2) surface fire in surface fuel
- 3) crown fire in aerial fuel
What are the phases of a wildfire?
- preignition - absorbs energy
- combustion - energy released as heat and light
- extinction - insufficient heat and fuel to sustain combustion
What is pyrolysis?
- when volatile organic chemical compounds form fuel gas clouds
- long-chain organic carbon molecules are broken into smaller
- 3 products: fuel gases, tar smoke, and char residue
What are the stages of combustion?
- glowing and smoldering
What are some factors that influence fire behavior?
How does weather effect wildfire conditions?
- humidity: ignition @ low humidity
- fires move faster in afternoon
- influences moisture content of fuel
- temperature: effects ignition point of fuel
- peak intensity in afternoon
- wind: supplies oxygen, dries fuel and controls direction of burn
- transports firebrands (embers) to ignite spot fires
List primary effects of wildfires
- destabilization of slopes
- death of plants and animals
- mineral ash enriches soil
- pyrocumulus clouds can form
- air pollution
List secondary effects of wildfires.
- soil erosion and surface runoff
- debris flows and landslides
- propagation of some plants
How do you mitigate for wildfires both for the public and private home?
- public: flexible fire management
- prescribed burns
- fuel treatment
- red flag watches and warnings
- homeowner: defensible space
- fire-resistant exterior construction
- disaster plan
- emergency access
- wet down house and surrounding areas
How has Forest Service policy regarding fires changed?
they used to put out all wildfires, but now they are picking and choosing to prevent a huge uncontrollable fire down the road