Skip to main content

Active Crown Fire Behavior

  1. Definitions
  2. Active Crown Fire Rate of Spread and Flame Length
  3. Estimating Active Crown Fire Spread Rate With Surface Shrub Models

Definitions

Crown Fraction Burned (CFB) is a theoretical concept that is used to model and classify crown fire. It may be observable after the fact in burn severity assessments.

Image
This graph compares Crown Fire spread rates utilizing several surface shrub fuel models and compares them to the Rothermel Crown Fire Spread Model.

Passive Crown Fire (Intermittent or Persistent Torching) occurs where surface fire intensity is sufficient to ignite tree crowns, individually or in groups, but winds are not sufficient to support propagation from tree to tree. CFB between 0.10 and 0.90.

Active Crown Fire occurs where surface and crown fire energy are linked. Surface intensity is sufficient to ignite tree crowns, and fire spread and intensity in the tree crowns encourages surface fire spread and intensity. CFB at least 0.90.

Independent Crown Fire occurs (rarely) where tree crown loading and flammability is sufficient to carry fire without surface fire contribution under ambient weather and wind conditions. CFB generally approaching 1.0.

Isolated Tree Torching should not be considered crown fire, though it may be an indicator of potential later in the burn period. It usually occurs due to anomalies in surface fire behavior due to jackpots of surface fuel, isolated terrain features, or brief wind gusts. CFB is less than 0.10.

Return to Top

Active Crown Fire Rate of Spread and Flame Length

After the 1988 fire season, Rothermel (1991) developed an empirical model for estimating crown fire spread rates and fireline intensities, referencing several fires from the Rocky Mountains in its development. Based on fire behavior in Fuel Model 10 (FB10), the calculation is essentially:

ROSActiveCrownFire = 3.34*ROSFuelModel10

(Assuming MFWS = 20ft windspeed*0.4)

These graphs, using season, slope, and 20ft windspeed, provide rough estimates of active crown fire spread rates using the Rothermel Crown Fire Spread model.

No Slope

Image
Using the season of the year and the 20-ft windspeed, this graph helps the analyst estimate crown fire spread rate for fires on generally level or low slope landscapes.

50% Slope

Image
Using the season of the year and the 20-ft windspeed, this graph helps the analyst estimate crown fire spread rate for fires on steep slopes of approximately 50%.

100% Slope

Image
Using the season of the year and the 20-ft windspeed, this graph helps the analyst estimate crown fire spread rate for fires on steep slopes of approximately 100%.

Return to Top

Estimating Active Crown Fire Spread Rate with Surface Shrub Models

In fireline assessments, it may be necessary to make quick estimates of crown fire spread based on simple inputs.  Simple lookup tables or graphs like those above provide rough estimates. Anderson (1982), when describing the original 13 surface fuel models, identified several shrub models as representative of crown fire behavior in several classic types:

  • FM4 (Chaparral) for New Jersey Pine Barrens and Lake States Jack Pine.
  • FM6 (Dormant Brush) for Alaska Spruce Taiga.
  • FM7 (Southern Rough) for Alaska Black Spruce/Shrub Communities.

Bishop (2010), in developing the Fireline Assessment Method (FLAME), averaged spread rates for fuel models 5, 6, and 7 to estimate crown fire spread.

Fuel Models sh5 (145) and sh7 (147) have been used in the same manner in spatial modeling in different situations.

This graphic demonstrates the similarity in spread rates produced by the Rothermel Crown Fire Spread Rate (crown) and several surface shrub fuel models.  

Image
This graph compares Crown Fire spread rates utilizing several surface shrub fuel models and compares them to the Rothermel Crown Fire Spread Model.

Caution: Using surface fuel models to represent crown fire behavior may not accurately provide for the calculation of Crown Fraction Burned (CFB) or the modeling of increasing spread due to passive crown fire (torching and spotting) behavior in spatial fire analyses. It may also over-estimate fire spread and intensity under moderated environmental conditions.

Return to Top

Print PDF

NWCG Latest Announcements

NEW! S-219, Firing Operations (Blended) Now Available

Date: Sept 11, 2025
Questions? Please contact:
Fuels Management Committee 

The S-219, Firing Operations (Blended) course is now available on the Wildland Fire Learning Portal. Developed through the Incident Performance and Training Modernization (IPTM) effort, this training supports individuals working towards Firing Boss, Single Resource (FIRB) incident qualifications.

This blended course combines online and instructor-led training to provide students with the knowledge and skills required to perform the duties of the FIRB, as described in the NWCG Incident Position Standards for Firing Boss, Single Resource, PMS 350-105.

Any changes to qualification pathways will take effect with the next update of the NWCG Standards for Wildland Fire Position Qualifications, PMS 310-1, scheduled for January 2026.

References:

S-219, Firing Operations (Blended)

NWCG Firing Boss, Single Resource Position Page

Wildland Fire Learning Portal

NWCG Committees Observe Suicide Prevention Awareness Week: September 7-13, 2025

Date: Sep 5, 2025
Questions? Please contact:
Mental Health Subcommittee

The NWCG Mental Health Subcommittee (MHSC) and Risk Management Committee (RMC) recognize the unique challenges and demands faced by the wildland fire community. The MHSC and RMC know that we are all stronger together and believe in fostering a culture of support, understanding, and resilience.

Suicide Prevention Awareness encourages us to actively connect with and support each other. For more information that could make a difference for yourself or someone else please review the materials and resources provided for the 2025 Suicide Prevention Awareness Week.

References:

2025 Suicide Prevention Awareness Week Materials and Resources

NEW! Incident Performance and Training Modernization Story Map Now Available

Date: Aug 26, 2025
Questions? Please contact:
National Wildfire Coordinating Group

NWCG is excited to announce the launch of the Incident Performance and Training Modernization (IPTM) Story Map, a new interactive resource that showcases how NWCG is transforming wildland fire training and qualifications through a performance-based system.

Since its launch in 2023, IPTM has made major strides in updating how we manage incident positions:

  • 36 incident positions now have new Incident Position Standards and Next Generation Position Task Books available for field use
  • 6 more incident positions are nearing completion
  • 111 total incident positions are being analyzed through the IPTM initiative

The Story Map guides you through the IPTM process, highlights key accomplishments, and outlines what’s ahead. Whether you are a trainer or a trainee, this tool offers valuable insight into the modernization effort shaping the future of wildland fire training and qualifications.

This effort would not be possible without the contributions of NWCG staff, NWCG committees, and hundreds of subject matter experts across the wildland fire community.

References:

IPTM Story Map

Incident Performance and Training Modernization Webpage

NEW! S-290, Intermediate Wildland Fire Behavior (Blended) Available Now

Date: Aug 15, 2025
Questions? Please contact:
Fire Behavior Subcommittee

NWCG is excited to announce that the S-290, Intermediate Wildland Fire Behavior (Blended) training is now available on the Wildland Fire Learning Portal. S-290 (Blended) training combines online training and instructor-led training components that support individuals working towards any Single Resource Boss or Fire Effects Monitor incident qualifications.

This second course in the series collectively serves to develop fire behavior prediction knowledge and skills, and provides more detailed information on fuels, weather, and topography that affect wildland fire behavior for safety purposes.

Students are required to finish the prerequisite S-190, Introduction to Wildland Fire Behavior, before enrolling in S-290, Intermediate Wildland Fire Behavior (Blended).

References:

S-290, Intermediate Wildland Fire Behavior (Blended)

S-190, Introduction to Wildland Fire Behavior

Wildland Fire Learning Portal