The team’s first contact was Andrea Rodriguez, a United State Forest Service Cartographer with the Geospatial Service and Technology Center. Andrea attempted to help by finding real forest-contour data derived from satellite data which could be incorporated into the program, but the program is not yet advanced enough to use the data. In the continuation next year, the program may become advanced enough for it to be possible to incorporate the available forest-contour data next year.


The next contact made was Nestor Pena who works as a battalion chief at the Rio Rancho Department of Public Safety. Nestor pointed out many of the assumptions made by the team and explained how firefighters battle large-scale forest fires. From Nestor, the team learned that because of the select few variables used in the program, the program can not yet be used as is for fire prevention and containment, but indicated the program showed promise.

 

The FARSITE Program is a fire perimeter expansion program developed by the United States Forest Service for fire path prediction. The most important thing learned from the FARSITE Program was Huygen’s elliptical expansion principles. Huygen’s Principles state that a fire will always expand in an elliptical pattern from a central ignition point. A fire’s perimeter was further expanded by creating new ignition points along the original elliptical expansion to complete a circular pattern. This pattern of expansion can be seen in this picture. A new ignition points are created along the original elliptical pattern further expanding the fire.
The limitations of the FARSITE program include the limited factors which are taken into account by the program. These few factors include wind vectoring and elevation. Since it is believed by the team that the burned fuel type plays a significant role, the team does not agree that FARSITE is an all-inclusive model even though it is widely accepted by the scientific community. Another difficulty with the FARSITE program is the very complex differential equations that made it hard to utilize in this project’s program.


From FARSITE, the team further expanded upon the fire perimeter expansion concept by using an original ignition point and creating numerous rays which each expand depending upon the factors in the path of the ray. Basically, a fire flow process was developed that borrowed from Huygen’s concept, but was altogether different.

 

From their research, the team was able to deduce several of the key factors which effect a fire. A key component in creating a successful fire model was first to differentiate between the heat flow of a fire and the actual fire spread. Fire cannot be explicitly defined and must be broken down into its component elements. When broken down, fire follows many known characteristics. Incorporated into this project’s model are several of these characteristics. In order to break apart the fire phenomena and gain insight into these characteristics, fire must be broken down to its intrinsic nature by starting with as basic an assumption as possible. In order for fire to exist three factors must be present: heat, oxygen, and fuel. Differing amounts of these variables effect the ability of a fire to exist within a certain area, the spread speed of the fire, and the damage inflicted upon the environment.

 

Elliptical Fire Theory
The basis of this project is the concept that under perfect conditions, fire grows in the form of a perfect circle. Even in space, fire maintains the shape of a sphere. This is the Elliptical Fire Theory. The theory suggests that fire growth is circular and is only acted upon by external forces. While not proven, the Elliptical Fire Theory is the underlying assumption of this project. Once this basis has been determined it opens the door to incorporating many other characteristics.

 

Heat
If a wildfire is burning in the winter, it will not have the same ability to spread as a fire in the summer. This is due to heat’s effect upon fire spread. There are three basic forms of heat flow: conduction, convection, and radiation. Heat flow in the atmosphere occurs everyday and has highs and lows as the day passes but is very different when a fire produces heat.

Convection
Convection is relevant to this project because of heat flow and loss to the atmosphere and has been incorporated with Newton’s Law of Cooling which states:


T(1) = ambient temperature + (T(0) – ambient temperature) x ekt

Whereas:
T(1) = New temperature *temperature units are interchangeable
T(0) = Old temperature
K = Negative variable constant dependent on the object’s heat retaining rate
T = Time elapsed in minutes

 

Conduction
Conduction is the heat flow into and from solid objects and integrated using Fourier’s Law of Conduction

 



Whereas:
Temp(2) > Temp(1)
dh/dt is the amount of heat flow from Temp(2) to Temp(1)
k is the thermal conductivity of the material of transfer
A is the area^2 of the two materials in meters
Pos(2)-Pos(1) is the difference in meters between the two Temp()
Note: Air has been treated as a solid for conduction object with k=.026 (Wikipedia.com)


Radiation
Radiation is the chief transport of heat flow from a fire. Radiation is the flow of heat from rays through space whether matter is present or not. Radiation has been defined with the Stephan Boltzmann Law of Radiation


E = KsAT4


Whereas
K = Stefan-Boltzmann Constant=5.67*10^(-8)
S = Emissivity
A = surface area (meters)
T = Kelvin Temperature of object
E = heat transfer in joules that is emitted

 

Note: This law doesn’t account for radiation emitted from fire only from an object


Fuel
The heat fire produces is developed from rapidly oxidizing the fuel in a chemical reaction, and fire needs fuel to produce heat. This chemical reaction is a self-perpetuating reaction that breaks off the oxygen atoms from its fuel. Yet, before this reaction can take place, the water contained in the fuel must be evaporated. Once the moisture content is evaporated, fire needs only to attain the piloted flashpoint or combustion temperature to combust the fuel and begin to spread.

 

Fuel types
In a forest there are many types of fuels. For example, the Russian olive tree and the cottonwood tree possess distinctive properties. When burned, the Russian olive produces a higher heat value and is consumed much faster than the cottonwood. There are thousands, if not millions, of varying kinds of fuels ranging from low grass to, piñon, and other deciduous hardwoods. Each fuel type governs different characteristics of fire flow when they are aflame and radically change the flow of fire. Also, some fuel types like oak are very thick and slow to burn. Others like redwoods have fire-retardant bark which prevents a crown fire. Depending on the forest, different fuel types must be defined empirically and entered into the program.

Wet and Dry Fuels
Each of these above fuels can be further generalized into two groups: wet fuels and dry fuels. Wet fuels are living fuels, which contain a moisture content that must be evaporated before igniting. Dry fuels consist of the dead underbrush that has lower flashpoints due to the minimal moisture.

Piloted Flash Point
The basic flash point, or piloted flashpoint, is the temperature the fire must attain to ignite the fuel and, with a fire present burst into flames. This flashpoint value is dependent upon the atomic structure of the material being burned and varies depending on the fuel source.

Unpiloted Flashpoint
The unpiloted flashpoint of a fuel is the temperature at which the fuel will be combusted, whether fire is present or not. Examples of such ignition without fire radiation include using friction to start a fire, a match on fire, rubbing two twigs together, or even focusing light under a magnifying glass to ignite a fire. This means the temperature of the heated area becomes hot enough to begin a fire without a fire present.

Crown Fires
The crown of a tree is the height at which its leaves or needles are located. The fire cannot burn the crown if it cannot reach that height. Tree trunks are generally too high for the heat of a ground fire to reach. Many forest fires behave in a pattern as if they were two separate fires a fast-moving crown fire and slow-moving ground fire. Crown fires constitute a major danger to forests and inhabitants because if a crown fire ignites a tree, it will likely determine whether the tree will survive the fire.

 

Oxygen
In order for the chemical reaction of rapid oxidization to take place, oxygen must be present. If there is no oxygen, then there is no fuel and thus no fire. As fire burns, it consumes the oxygen and produces carbon dioxide. The rate at which fire consumes oxygen can be partially attributed to convection movement of the oxygen-containing wind that fire produces. This is caused by the fact that when fire burns, it produces wind from convection, which further stimulates the fire because it brings in air rich in oxygen.

 

Environmental Factors
In addition to the heat, fuel, and oxygen factors, environmental factors also affect fire. They are named environmental factors because they are derived from the forest conditions.

Wind speed and angle
Wind speed and wind angle will ultimately determine the prevailing path and intensity of the fire. Sometimes fire can travel much faster than a human can run because of the result of wind. To firefighters, this is known as a bad day.

Ambient Temperature
Temperature plays a large role in determining fire flow. A fire burning in cold temperatures will have a lower intensity than a fire burning in the hot temperatures of the afternoon, which is why a fire’s intensity decreases after nightfall and increases in the afternoon. This suggests that heat has an affect upon fire flow.

Humidity
Humidity slows fire flow by increasing the moisture content of all fuels. The higher the moisture content, the longer and hotter a fire must burn to remove the moisture.

Elevation
Elevation plays a big role in fire flow. Fire will spread uphill faster than downhill to gain access to oxygen-rich air. Fire acts as a force that will oppose gravity. Therefore it affects fire flow in the third dimension and when elevation changes with slopes and cliffs, fire is also affected on the two-dimensional plane.

 

Fire is not totally inexplicable in its nature. This is because there are many variables acting upon fire that are yet to be defined. Those variables which have been defined and incorporated however, allow for a fire model to be constructed.

 

Fire Flow/Spread
As stated earlier, fire spread is something that, to date, can only be approximated. A commonly used approximation is based on Huygen’s Principle. In accordance with the Elliptical Fire Theory, fire will spread in all directions as fast as it possibly can while still maintaining its three fundamental bases: heat, oxygen, and fuel. However, the exact determination of fire spread is still not as simple as that. There are so many factors bearing upon fire that it is currently impossible to incorporate them all into some finite formula. To determine basic fire flow one must look at the basic intrinsic parts and develop an approximation. This is the goal of this year’s project.