Flank, Head, and Back Fire in Fire Management

Managing fire is a complex and critical task, particularly when it involves prescribed burns. Fire management professionals must have a thorough understanding of fire behavior under varying conditions to utilize it effectively and safely. This process relies on three key types of fire behavior essential to prescribed burns: flank fire, head fire, and back fire. Each serves a distinct purpose in meeting burn objectives while ensuring the process remains controlled and safe.

Head Fire

A head fire is what happens when flames are pushed forward by the wind. This type of fire is known for:

• Rapid Spread: Its movement accelerates as it’s carried by the wind.
• Long Flame Lengths: Flames can reach impressive heights, adding to its intensity.
• Higher Risk: This is the most dangerous type of fire behavior, making it essential to maintain strict control.

How It’s Used:

Despite its intensity, head fires are incredibly useful in prescribed burns. They are usually ignited last, after backing and flanking fires have secured the edges of the burn unit. Once ignited, the head fire pushes to meet the other fire lines in the center, extinguishing itself by consuming all available fuel. This strategic burn plan ensures the head fire does its job without spreading aggressively beyond the intended area.

Flank Fire

A flank fire spreads at a steady rate, moving parallel to the wind. Its characteristics fall somewhere between head and back fires.

Key Features of a Flank Fire:

• Moderate Spread Rate: Not as fast as a head fire, but faster than a back fire.
• Moderate Flame Lengths: Flames are neither too short nor excessively tall.
• Strategic Flexibility: Flank fires are highly maneuverable, allowing fire managers to adjust the burn dynamically.

How It’s Used:

Flank fires often act as “connectors” between backing and head fires. Fire managers use them to move along the perimeter of the burn unit and into the wind direction, ensuring a steady and complete burn. Their flexibility makes them a vital tool for controlling fire spread and achieving specific burn objectives.

Backing Fire

Unlike head fires, back fires work against the wind.

Characteristics of a Back Fire:

• Slow Spread: Back fires creep steadily into the wind, giving fire managers more control.
• Shorter Flame Lengths: Flames are smaller but burn closer to the ground.
• Hot Ground Temperatures: While the flames are smaller, the heat concentrates at the ground level, making this fire type ideal for consuming deeper layers of fuel.

How It’s Used:

Fire managers typically start prescribed burns by igniting back fires first. Their slow pace and high level of control make them perfect for creating safety buffers or “blacklines” on the edges of the burn unit. This approach ensures the fire stays within the intended boundaries as the other fire types are introduced.