The first Chad

What is Combustion

Combustion is the rapid combination of oxygen and fuel in the presence of heat resulting in an exothermic reaction (the release of heat), light and various reaction products (often called emissions).

Exothermic reaction

releases energy in the form of heat or light

Endothermic reaction

absorbs energy from its soundings

what are the three sides of the fire triangle

Fuel, oxygen, and heat

Sensible heat

is the amount of energy associated with a change in temperature of an object

Latent heat

is energy in hidden form, it is energy supplied or extracted to change the state of on object (e.g., melting ice) without changing the objects temperature.

What are the mechanics of fire

how a fire burns

Pre-ignition

– Dehydration

– Pyrolysis

• Ignition

• Combustion

– Flaming combustion

– Smoldering combustion

• Extinction

pre-ignition phase

As heat from the pilot source is transferred to

the fuel the energy is initially absorbed by the

fuel and any water within the fuel.

• As the temperature raises the water is

converted to steam (called dehydration) and

the fuel is decomposed and evaporated into

flammable vapors (called pyrolysis)

Dehydration

the temperature of the fuel is raised to the point

where the water molecules are converted to gas

drying out of the fuel, water is leaving

Pyrolysis

converts the fuel into combustible gasses

thermal breakdown of the fuel particles. These

gasses form a cloud above the fuel

What are the Combustion types

Flaming

Smoldering

Flaming combustion

occurs in the gas phase

visible flame

Smoldering combustion

occurs in the solid phase

slow, low-temperature, flameless form of combustion that occurs on the surface of the solid rather than above the solid.

Ignition

transition point between the pre-ignition process (dehydration and pyrolysis) and combustion.

What needs to happen for ignition to occur

fuel particles need to be heated at a rate high enough to produce enough pyrolysis gases, which must mix with enough oxygen and be heated to a minimum temperature

Extinction

termination of the combustion process

not enough heat available to sustain the combustion process, or a lack of oxygen, or a lack of fuel, something is removed from the fire triangle asshole

Piloted ignition

occurs when a flame or spark is

applied to the fuel and oxygen vapor mixture

(e.g., flame contact)

–593.15 K (320-350°C)

Autoignition

occurs without a spark or flame

–873.15 K (600°C)

What is the Qig equation

The energy required for the pre-ignition phase

Qig=Hd+Hw

The heat required to raise the dry fuel from its current temperature to the

ignition temperature (Hd)

• The heat required to raise the temperature of the water from its current

temperature to the ignition temperature (Hw)

specific heat (heat capacity)

amount of heat per unit mass to raise the temperature by 1 degree Kelvin

What are the three stages of the Hw - heat energy associated with water

1) heat required to raise water from temperature t0 (initial

temperature) to boiling temperature tb,

2) heat required to vaporize the water, and

3) heat required to raise the water vapor to the ignition

temperature

What type of lightning is the most likely to start a fire

Positive lightning strikes

What is the origin in a fire

the ignition point

Headfire

The portion of the fire that is spreading upslope and with the wind

most active part of the fire

Backfire

Fire spreading

against the wind and/or

slope refereed to as the

back, heel, or rear of the

fire

Flankfire

part of fire moving perpendicular to the wind

Rate of fire spread is in units of

m/s

Mass consumed is?

This is the amount of biomass consumed in a fire

in units of (kg/m2 or tons/acre)

high heat of combustion

maximum amount of energy that is released during combustion

The Low Heat of Combustion

Amount of heat released per unit mass of fuel consumed minus the latent heat of vaporization of the water produced during combustion

Assumes that the water produced during combustion

remains a gas rather than condensing back to a liquid

fireline intensity

the amount of heat energy (kW) per meter length of fireline regardless of the depth

mathematically I = HWR

I = the fireline intensity (kW/m)

H = the low heat of combustion (kW/kg)

W = the amount of fuel consumed (kg/m2)

R = the rate of spread (m/s)

Flame length

is the distance from the base of the flaming zone to the tip of the continuous flame

Flame height

the vertical distance that continuous flames extend above the fuel bed

the fire behavior triangle is composed of

Weather, topography, and fuel

What was fons’s theory, that old fuck

Focused on the head of the fire

• Fire spread can be visualized as a series of

successive ignitions

• Rate of spread primarily controlled by the ignition time

and the distance between particles

What are the three modes of heat transfer, describe them as well pls

Conduction: dominos

Radiation: throwing a pass

Convection: I’ll just come over to you. the transfer of heat due to the mass movement of fluids (gases and liquids).

Thermal Conductivity k

the property of a material to conduct heat

Heat transfer across materials with high thermal conductivity occurs at a

higher rate than across materials with a low thermal conductivity

What is turbulent flow and its effects on fire

Turbulence increases

bulk flow and effects

temp gradient by

bringing cool air

from above down to

the hot surface

fuel layers

fuelbeds are often stratified into vertical layers

(i.e. ground, surface, canopy)

Fuel Component

are fuel types that are qualitatively and

quantitatively defined for specific purposes such as fire

behavior prediction

What is the time lag

the time it takes for a fuel particle to

lose/gain 63% of the difference between its initial

moisture content and its equilibrium moisture content

Equilibrium moisture content

the moisture content that a fuel would reach if exposed to a constant external

moisture level (atmospheric temperature & humidity).

Timelag size classes

defined based on the midpoint of the class

1 hr. = <0.6 cm or 0-1/4” diameter

(1 hr. is midpoint of 0-2 hr. class)

– 10 hr. = 0.6 – 2.5 cm or ¼-1”

– 100 hr. = 2.5 – 8 cm or 1-3”

– 1000 hr. = 8+cm or 3”+

What is the crown

defined as the portion of a tree’s biomass that is

composed of branches that support live foliage

What is the canopy

summation of all the crowns in some area (typically

done to support fire behavior modeling)

Canopy bulk density (kg/m3)

Estimated as the amount of burnable biomass in the

canopy fuel layer by canopy volume

• Used to represent how close the canopy fuel particles are to

each other

Canopy base height (m)

Defined as the lowest

height above the ground

at which

there is sufficient canopy

fuel to propagate fire

vertically through the

canopy

What in the world are the 4 D’s, tell me

Development – living biomass production (+ live)

– Deposition – live fuels become dead fuels and fall

onto surface (+ dead, - live)

– Decomposition – chemical and physical break down of

dead fuels (- dead)

– Disturbance – an event that cause mortality, changes

ecosystems (+/- live and dead)

What are the major topographic parameters that

impact wildland fire?

Slope

– Aspect

– Elevation

– Shape of the land

How does slope affect fire

Increasing the radiant and convective heat

transfer between fuels thus contributing to

preheating and ignition

How does aspect affect fire behavior?

South facing slopes drier, less fuel

North facing slopes wetter, more fuel

What are the major meteorological parameters that

impact wildland fire are

1. temperature and dew point

2. Moisture - relative humidity, precip

3. Wind, direction and velocity