# Presentation: 019301

## Effects of Weather on      Fire Behavior

- Chief Louis Johnson,
- Assistant Chief of Training
- Shreveport Fire Department

## Does Weather have anything to do with Firefighting?

## Yes, Only One Thing...............Everything

## Objectives (1 of 3)

- Define the terms wildland and ground fires.
- Define light fuels, heavy fuels, subsurface fuels, surface fuels, and aerial fuels.
- Describe how weather factors and topography influence the growth of wildland fires.

## Objectives (2 of 3)

- Define the parts of a wildland and ground fire.
- Describe how wildland and ground fires can be suppressed.
- List the hazards associated with wildland and ground firefighting.

## Objectives (3 of 3)

- Describe the personal protective equipment needed for wildland firefighting.
- Explain the problems created by the wildland urban interface.

## What are Wildland Fires? (1 of 3) 

- Defined by NFPA:
- Unplanned and uncontrolled fires burning in vegetative fuel that sometimes includes structures.
- Can consume grasslands, brush, and trees of all sizes
- Incidence varies from season to season.
- Referred to by different terminology

## What are Wildland Fires? (2 of 3)

- Ground cover fires burn loose debris on the surface of the ground.
- Some fire departments respond to more wildland and ground fires than to structural fires.
- Many structural fire fighters are called on to extinguish wildland and ground fires at some point.
- Must have proper training

## What are Wildland Fires? (3 of 3)

- Large wildland fires are handled by specialized agencies.
- Each state has an agency designated to coordinate wildland firefighting.
- There are federal agencies that are responsible for coordinating firefighting activities at large incidents.

## Wildland and Ground Fires and the Fire Triangle

- Wildland and ground fires require the same three elements as structural fires.
- Fuel, oxygen, and heat
- In wildland and ground fires the conditions under which fuel, oxygen, and heat come together to produce a fire are different.
- Weather conditions have a great impact on wildland fire behavior .
- Weather Plays a often overlooked role in ALL Firefighting Task

## The Wildland Fire Triangle

**The Wildland Fire Triangle**

## Fuel (1 of 2)

- Primary fuel is area vegetation.
- Amount of fuel in an area ranges from sparse grass to heavy underbrush and large trees.
- Some fuels ignite readily and burn rapidly when dry.
- Others are harder to ignite and burn more slowly.

## Fuel (2 of 2)

- Vegetative fuels can be located:
- Under the ground (roots)
- On the surface (grass and fallen leaves)
- Above the ground (tree branches)

## Fine Fuels

- Includes dried vegetation such as twigs, leaves, needles, grass, moss, and light brush
- Ground duff
- Partly decomposed organic material on a forest floor
- Main type of fuel in ground cover fires
- Aid the ignition of heavier fuels

## Heavy Fuels

- Includes large brush, heavy timber, stumps, branches, and dead timber on the ground
- Slash
- Consists of the leftovers of a logging operation
- Do not spread a fire as rapidly as fine fuels
- Can burn with a high intensity

## Subsurface Fuels

- Located under the ground
- Roots, moss, duff, and decomposed stumps
- Fires involving subsurface fuels are hard to locate and extinguish.

## Surface Fuels

- Located close to the surface of the ground
- Include grass, leaves, twigs, needles, small trees, and slash
- Brush less than 6' above the ground
- Sometimes called ground fuels
- Involved in ground cover fires

## Aerial Fuels

- Also called canopy fuels
- Located more than 6’ above the ground
- Usually trees
- Includes tree limbs, leaves and needles on limbs, and moss attached to the tree limbs

## Other Fuel Characteristics

- May determine how quickly the fuel ignites, how rapidly it burns, and how readily it spreads to other areas

## Size and Shape of Fuel

- Size and shape of a fuel influences how it burns.
- Fine fuels burn more quickly than heavy fuels.
- Requires less heat to reach their ignition temperature

## Fuel Compactness 

- Influences the rate at which a fuel will burn
- Air cannot circulate in and around fuels that are tightly compacted.
- Subsurface fuels burn more slowly than aerial fuels.

## Fuel Continuity 

- Refers to the relative closeness of wildland fuels
- Are close together or touch each other
- Allows fire to spread from one area of fuel to the next
- Have a sufficient supply of air to support rapid combustion
- Burn much more rapidly than fuels that are compact

## Fuel Volume 

- Refers to the quantity of fuel available in a specific area
- Amount of fuel in a given area influences the growth and intensity of the fire.

## Fuel Moisture

- Refers to the amount of moisture contained in a fuel
- Amount of moisture in a fuel influences the speed of ignition, the rate of spread, and the intensity of the fire.
- Fuels with high moisture content will not ignite and burn as readily.
- Fuel moisture varies with the amount of rain that has fallen.

## Oxygen

- Oxygen is needed.
- Not usually an important variable in the ignition or spread of the fire.
- Air movement influences the speed with which a fire moves.
- Wind speeds the process of combustion and influences the direction the fire travels.

## Heat

- Sufficient heat must be applied to fuel in the presence of adequate oxygen to produce a fire.
- Three categories of factors may ignite wildland and ground fires:
- Natural causes
- Unintentional causes
- Intentional causes

## Weather

- Weather conditions have a large impact on the course of a wildland fire.
- Moisture
- Wind
- Temperature

## Moisture (1 of 2)

- Relative humidity
- Ratio of the amount of water vapor present in the air compared to the maximum amount the air can hold at a given temperature
- A major factor in the behavior of wildland and ground fires
- Varies with the time of day and year

## Moisture (2 of 2)

- Precipitation
- Moisture falling from the sky helps to increase the relative humidity.
- Absorbed by plants
- Makes them less susceptible to combustion
- When there is adequate precipitation, fire risk is lower.

## Wind 

- Has the ability to move a fire at great speed
- Effect of wind on a wildland and ground fire is similar to fanning a fire to help it burn more rapidly
- Has the ability to Dry the fuel

## Topography (1 of 2)

- Refers to the changes of elevation in the land, the position of natural, and manmade features
- Has a great impact on the fire behavior
- When fires burn on flat land, much of the fire heat will rise into the air.
- When the elevation rises in the direction the fire is traveling, the fire heat ignites a greater quantity of fuel and increases the speed of fire spread.

## Topography (2 of 2)

- Natural barriers, such as streams and lakes, may help contain fires.
- Manmade barriers such as highways also make it easier to contain a fire.

## Anatomy of a Wildland Fire (1 of 4)

- Area of origin
- Location where fires begin
- Head of the fire
- Main or running edge of a fire
- Part of the fire that spreads with the greatest speed

## Anatomy of a Wildland Fire (2 of 4)

- Heel of the fire or the rear of the fire
- Side opposite the head of the fire, often close to the area of origin
- Finger
- Narrow point of fire caused by a shift in wind or a change in topography
- Can grow and produce a secondary direction of travel for the fire

## Anatomy of a Wildland Fire (3 of 4)

- Pocket
- A dangerous place for fire fighters because it is an area of unburned fuel surrounded on three sides by fire
- Island
- An unburned area surrounded by fire

## Anatomy of a Wildland Fire (4 of 4)

- Spot fire
- New fire that starts outside areas of the main fire
- Green
- Area of unburned fuels
- Black
- Areas that have already been burned

## Methods of Extinguishment

- Cooling the fuel
- Removing the fuel
- Smothering

## Cooling a Wildland Fire

- Water is used to cool.
- Backpack pump extinguishers
- Booster tanks from apparatus
- Aircraft

## Removing Fuel (1 of 2)

- Removal of fine fuels can be accomplished with:
- Fire broom
- Steel fire rakes
- McLeod fire tool
- Removal of heavier brush:
- Adze
- Pulaski axe

## Removing Fuel (2 of 2)

- Sometimes saws are used to remove heavy brush and trees from the fire.
- Hand saws to gasoline powered chainsaws
- Tractors, plows, and bulldozers
- Backfiring
- When properly set can burn an area of vegetation in front of the fire, thereby creating an area devoid of vegetation

## Removing the Oxygen (1 of 2)

- Smothering
- Most commonly used when overhauling the last remnants of a wildland and ground fire
- Earth is often thrown on smoldering vegetation to prevent flare-ups.
- Not as useful during the more active phases of a fire

## Removing the Oxygen (2 of 2)

- Compressed air foam systems (CAFS)
- Combines foam concentrate, water, and compressed air to produce a foam
- Sticks to vegetation and structures in the fire’s path
- When the heat of the fire reaches the foam, it absorbs the heat and breaks down the foam.
- This cools the fuel.

## Safety in Wildland Firefighting 

- Fighting wildland and ground fires is hazardous duty.
- Shares many of the hazards of structural firefighting plus additional hazards:
- Driving, falls, smoke and fire, and falling trees

## Personal Protective Equipment

- One-piece jumpsuit, or a coat, shirt, and trousers
- Meet the requirements of NFPA 1977
- Garments should be constructed of a fire-resistant material like Nomex®
- Wear an approved helmet with a protective shroud, eye protection, gloves, and protective footwear.
- Respiratory protection
- Filter mask

## Fire Shelters

- Lifesaving piece of equipment
- Thin reflective foil layer attached to a layer of fiberglass
- Designed to reflect about 95% of a fire’s radiant heat for a short period of time
- Fire fighters use their fire shelters when unable to reach safety in time.

## Wildland Urban Interface (1 of 2)

- The mixing of wildland with developed areas
- Creates a massive problem for fire departments in many parts of the country
- Wildland fires regularly ignite buildings and become structure fires.

## Wildland Urban Interface (2 of 2)

- Wildland urban interface
- Explain the mixing of wildland with developed areas
- Area where undeveloped land with vegetative fuels is mixed with manmade structures
- Fires in this zone present a significant life safety hazard.
- Many areas do not have adequate municipal water systems.

## Questions ?OrComments ?