Unit 2 – Fire Behavior

Unit 2 Objectives Define a fire triangle Affects of fire by: 1. Fuel volume 2. Fuel size 3. Fuel arrangement 4. Topography Define rating system used for media/news

Unit 2 – Fire Behavior Unit 2 Objectives -Continued List actions your department can do to promote fire prevention in relation to fire danger ratings

Unit 2 – Fire Behavior Fire Behavior Defined The manner in which fuel ignites, flame develops, fire spreads and exhibits other phenomena. The magnitude, direction and intensity of fire spread.

Unit 2 – Fire Behavior 9:00 pm Feb 2008 Johnson Road Fire – NE Mason, TX Mason County. Footage taken by Kimble County Fire Chief Cecil M. Conner.

Unit 2 – Fire Behavior How a fire burns 3 Elements of burning: 1. Heat 2. Oxygen 3. Fuel Historically, the fire triangle has been used for understanding the ingredients necessary for most fires. Removal of any element results in the fire going out.

Unit 2 – Fire Behavior How a fire burns 4 Elements of burning: 1. Heat 2. Oxygen 3. Fuel 4. Chemical Chain Reaction. The fire triangle has largely been replaced in the industry by the tetrahedron, which provides a more complete understanding of the required elements to make a fire burn. Removal of any element results in the fire going out.

Unit 2 – Fire Behavior How a fire burns Burning or combustion is a complex sequence of chemical reactions between a fuel and an oxidant accompanied by the production of heat or both heat and light in the form of either a glow or flames.

Unit 2 – Fire Behavior Fire Spread Conduction Radiation Convection Fire commonly spreads due to heat transfer. The three most common types of heat transfer associated with wildfires are:

Heat conduction, or thermal conduction, is the spontaneous transfer of thermal energy through matter, from a region of higher temperature to a region of lower temperature, and acts to equalize temperature differences. It is also described as heat energy transferred from one material to another by direct contact. Unit 2 – Fire Behavior Conduction

Radiant heat, or thermal radiation, is heat emitted from the surface of an object which is due to the object's temperature. Radiant heat is what you can feel from a distance. Unit 2 – Fire Behavior Radiation

Convective heat transfer is a mechanism of heat transfer occurring because of bulk motion (observable movement) of fluids. Unit 2 – Fire Behavior Convection Heat is transferred by the movement of hot air and smoke rising and heating the fuels above.

Unit 2 – Fire Behavior Factors that influence ignition and spread. Fuel Weather Topography

Unit 2 – Fire Behavior Fuel Characteristics Fuel size Fuel moisture Fuel continuity

Unit 2 – Fire Behavior Fuel Size Smaller fuels ignite and burn easier and faster. Small fuel size contributes to a faster spreading fire that has a shorter duration. Larger fuels ignite and burn slower. Small fuel size contributes to a slower spreading, longer duration fire. This in why you use kindling to start a camp fire.

Unit 2 – Fire Behavior Fuel Moisture Fuel moisture is the amount of moisture in the fuel. The higher the moisture content, the more heat is needed to burn the fuel. Live fuels typically have more moisture than dead fuels, thus dead fuels burn more easily. Photo by Eric Kamp

Unit 2 – Fire Behavior Fuel Continuity Another factor which influences the spread of a fire is continuity of fuels. This is though of as horizontal and vertical spacing.

Unit 2 – Fire Behavior Fuel Continuity Horizontal The spacing of the fuel, or the distance between burnable fuel as it lies on the ground

Unit 2 – Fire Behavior Fuel Continuity Vertical When fuels are closely spaced vertically, fire will spread rapidly as convective heat preheats and ignites fuels above

Unit 2 – Fire Behavior Volume or Quantity of Fuel How much fuel is burning or will burn is also important. The amount of fuel available to burn is usually referred to as volume or quantity. The more fuel to burn the more intense the fire can be.

Unit 2 – Fire Behavior Weather Influences One of the most important factors affecting the behavior of a fire is Weather. In fire control, we usually break weather into three parts. These are: Temperature Relative Humidity Wind

Unit 2 – Fire Behavior Weather Influences Temperature: The effects of temperature is important because fuels that are preheated by the sun burn more rapidly than cold fuels. Air is also preheated raising up during the day, cooling at night and reverse direction

Unit 2 – Fire Behavior Weather Influences RELATIVE HUMIDITY: It is expressed in (%). It is the amount of moisture present in a parcel of air compared to the total amount the air could hold at that temperature As air is heated the (RH) decreases

Unit 2 – Fire Behavior Weather Influences Night Lower winds Higher humidity Lower temps Fire easier to suppress Day Higher winds Lower humidity Higher temps Fire harder to suppress

Unit 2 – Fire Behavior Weather Influences Wind: Of all influences on a fire’s behavior, wind has the greatest influence on both the rate and direction of spread Wind generally blows upslope during the day and down slope at night. Up and down slope winds are sometimes overcome by the stronger prevailing winds.

Unit 2 – Fire Behavior Topography Influences Where the fire is burning, whether it be in steep mountainous terrain or on the coastal plain, the lay of the land is an important factor in the rate and direction of fire spread.

Unit 2 – Fire Behavior Topography Influences Topography is broken into (3) parts: SLOPE - how steep it is ASPECT - The direction it faces TERRAIN - The local features of the land

Unit 2 – Fire Behavior Topography Influences SLOPE - Greatest influences of fire spread Flames are closer to the fuels Wind currents are normally uphill Heat rises along the slope increasing ROS (rate of spread) Burning embers can roll down hill, setting new fires

Unit 2 – Fire Behavior Terrain Terrain is special land features or obstructions. Wind will take the path of least resistance. Which can cause turbulence or eddies on the low side of obstructions. Critical areas are chutes and steep “v”s.

Unit 2 – Fire Behavior Video Presentation NFES FWC DVD Part 1 Fire Behavior in the Wildland/Urban Interface

Unit 2 – Fire Behavior Fire Behavior in the Wildland Urban Interface

Unit 2 – Fire Prevention Fire Danger A state wide fire danger report has been implemented. An effort to alert citizens of a weekly fire danger rating is sent to the news media, showing a rating of low, moderate, high and extreme.

Unit 2 – Fire Prevention KBDI The Keetch-Byram Drought Index (KBDI) is basically a mathematical system for relating current and recent weather conditions to potential or expected fire behavior. This system was originally developed for the southeastern United States and is based primarily on recent rainfall patterns Soil and fuel moisture are high. Most fuels will not readily ignite or burn. However, with sufficient sunlight and wind, cured grasses and some light surface fuels will burn in spots and patches Fires more readily burn and will carry across an area with no gaps. Heavier fuels will still not readily ignite and burn. Also, expect smoldering and the resulting smoke to carry into and possibly through the night Fire intensity begins to significantly increase. Fires will readily burn in all directions exposing mineral soils in some locations. Larger fuels may burn or smolder for several days creating possible smoke and control problems Fires will burn to mineral soil. Stumps will burn to the end of underground roots and spotting will be a major problem. Fires will burn thorough the night and heavier fuels will actively burn and contribute to fire intensity.

Unit 2 – Fire Prevention KBDI Statewide Map

Unit 2 – Fire Prevention For more fire prevention information in your community you can contact your fire prevention specialist or get information at:

Unit 2 – Fire Prevention Unit #2 Review

Unit 2 – Fire Prevention Unit #2 Review Combustion can occur only when ____, ____, ____, and a ____ are present. Fuel, Air (oxygen), Heat, Chemical chain reaction The four wildfire danger rating levels are : Low, moderate, high and extreme Convection from a forest fire results in more oxygen being available for a fire. True or False? True

Unit 2 – Fire Prevention Unit #2 Review The likely hood of a fire starting is dependant on the temperature of the fuel. True or False True Weather differences during the night time usually aid firefighters because of: Lower temperatures, higher humidity, lower wind speeds.