Forestry Science I Unit 4: Wildfires Lesson 2: Fire Behavior Prepared by Chad Bass December 5, 2001 To accompany Georgia Agriculture Education Curriculum Lesson

Objectives 1. Explain the fire triangle. 2. Explain how air movement affects fire behavior. 3. Explain how topography affects fire behavior. 4. Explain how fuel types affect fire behavior. 5. Analyze the factors affecting a prescribed fire.

The Fire Triangle To produce fire, three things must be present at the same time- fuel, heat, and oxygen. FUELHEAT OXYGEN

The Fire Triangle The fire triangle is like a three-legged stool. If you remove one leg, the fire goes out. fuel heat oxygen

How is the triangle broken? Some of the ways used to break the fire triangle are: –fire rake –fire flap or pine top –backpack water pump –tractor with a fire plow –backfire torch –airplane water bomb –prescribed burning Substance Eliminated FUEL OXYGEN HEAT FUEL HEAT FUEL

What is fire behavior? When we talk about fire behavior, we are thinking in terms of the intensity of the fire itself, and the rate of spread or speed of the fire.

What determines fire behavior? Fire behavior is affected by a wide range of conditions. Three important factors of fire behavior are: –Time of occurrence of the fire season –air movements –topography (slope of the land, presence of roads, fields, streams, etc.)

Fire Seasons In the south, fire seasons occur primarily in the fall and spring of the year. In the north and western part of the U.S., fire season occurs in the summer. During fire seasons, there is a buildup of fuel, and extended dry periods.

Fire Seasons The hottest wildfires generally burn in the middle of the day on sunny days. However, when humidities remain extremely low along with steady winds, a hot wildfire can burn all night.

Air Movement Affects Fire Behavior Horizontal and vertical air movements determine the duration and speed of a fire. Wind is an important factor in drying out vegetation.

Air Movement Affects Fire Behavior Since hot air rises, fires tend to create their own winds. This “up draft” type wind carries sparks up into the air. Then, upper winds scatter the sparks over unburned areas and cause spot fires. These spot fires increase the spread and intensity of the fire.

Topography Affects Fire Behavior Steep slopes help put fuel in contact with the fire more quickly. This causes the fire to spread faster. These slopes also increase the updraft winds created by the fire. Highways, fields, streams, and other areas act as barriers that help control the spread of fires.

Topography Affects Fire Behavior Some weather conditions can also reduce the rate of spread and help with fire control: –Rain on the fire. –Wind reversal blowing the fire back over the burned area. –An increase in relative humidity (the amount of moisture in the air).

Fuel Types Affect Fire Behavior There are two basic types of wildfire fuels. They are: 1. Ground fuels 2. Aerial fuels

Fuel Types Affect Fire Behavior Ground fuels include: 1. Peat 6. Low shrubs 2. Duff 7. Tree seedlings 3. Tree roots 8. Dead limbs 4. Leaves 9. Weeds 5. Dead grass 10. Bushes

Fuel Types Affect Fire Behavior Aerial fuels include all burnable material located in the trees’ canopies above six feet from the ground.

Summary/Review Identify the parts of the fire triangle. Identify the fuels available in the forest. Review the weather information available from the Georgia Forestry Commission.

Credits International Paper corporation. International Paper School Forestry Guide. Georgia Forestry Commission Georgia Ag. Ed. Curriculum Resource CD