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5.4 Perimeter and Area Estimation Charts

The perimeter and area of a fire can be determined by using estimation charts as shown below. These charts require knowledge of the spread distance in chains and the effective windspeed in miles per hour. A fire area/size worksheet is provided to be filled out with the data collected.

EFFECTIVE WINDSPEED

Effective windspeed is the midflame windspeed, corrected for the effects of slope on fire spread. Changes in slope affect how wind influences a fire and the overall fire spread. For slopes above 20%, each additional 20% increase in slope translates to an additional 1 mph increase in the effective equivalent “upslope” component of the wind. For slopes between 20% and 40%, for example, a 1-mph slope-equivalent upslope component would be added to the flame-level wind. Between 40% and 60%, a 2-mph slope-equivalent upslope component would be added, and above 60%, flame-level winds would increase by 3 mph.
 

screengrab of animation of flame heights increasing as slope increases
Click to view animation of slope effects on fire

Example 1 - A fire starts at point A. Given the following values, determine the fire perimeter. 
rate of spread = 5 ch/h, projection time = 3 h, effective windspeed = 10 mi/h

Step 1. Use the equation for determining the spread distance (see Section 5.3).
ROS × PT = 5 ch/h × 3 h = 15 chains spread distance.

Step 2.> Look at the perimeter estimation chart. Find a spread distance of 15 chains on the vertical axis. Move your gaze across horizontally.

Step 3. Find an effective windspeed of 10 miles/hour on the horizontal axis, which is between 9 miles/hour and 11 miles/hour. Follow the column down vertically.

Step 4. Where the two lines intersect, read the number. In this case there are two numbers.
34 chains and 33 chains

Step 5. Take an average of the two values.
34.0 chains + 33.0 chains / 2 = 33.5 chains

The perimeter of the fire is 33.5 chains.

Example 2 - Determine the area of the fire in Example 1 and complete the fire area/size worksheet. The spread distance is the same, 15 chains.

Step 1. Reference the area estimation chart for a spread distance of 15 chains. Follow the row across horizontally.

Step 2. Look for an effective windspeed of 10 miles/hour, which is between 9 miles/hour and 11 miles/hour. Follow the column down vertically and read the numbers from the two windspeeds.
4.9 acres and 5.7 acres

Step 3. Take an average of the two values.
4.9 acres + 5.7 acres / 2 = 5.3 acres

The area of the fire is 5.3 acres.

Perimeter estimation for point source fires.
Table showing Perimeter Estimation

Area estimation for point source fires.
point source fires

Fire Area/Size Worksheet

Line Input    
0 PP Projection point A
1 ROS Rate of spread, ch/h 5
2 EWS Effective windspeed, mi/h 10
3 PT Projection time, h 3
4 SDF Spread distance, ch 15
  Output    
  PER Perimeter, ch 33.5
  AC Area, ac 5.3

NWCG Latest Announcements

Updated NWCG Standards for Fire Unmanned Aircraft Systems Operations, PMS 515

Date: May 10, 2024
Contact: IFUASS Qualification and Curriculum Board (IFUASS) 

The 2024 revision of the NWCG Standards for Fire Unmanned Aircraft Systems Operations, PMS 515 is now available. PMS 515 standardizes the processes and procedures for interagency use of Unmanned Aircraft Systems (UAS), including pilot inspections and approvals. This publication is now available as a PDF for easy use offline.

References:

NWCG Standards for Fire Unmanned Aircraft Systems Operations, PMS 515

Memorandum 24-003: Removal of Type 1 Command and General Staff (C&G) Incident Position Qualification Pathways

Date: May 10, 2024
Contact: Aitor Bidaburu 

The purpose of this memorandum is to provide NWCG direction for removal of the Type 1 Command and General Staff (C&G) incident position qualification pathways to transition to Complex Incident Management (CIM). Responders may continue to utilize available NWCG pathways to attain Type 1 C&G qualifications until December 31, 2024.

References:

Memorandum 24-003

CIM Story Map

2024 Professional Reading Program

Date: April 26, 2024
Contact: Wildland Fire Leadership Development Program (WFLDP) 

The Wildland Fire Leadership Development Program is announcing the 2024 Professional Reading list! The intent of the Professional Reading Program is to promote the reading and discussion of these books throughout the year. Discussion guides are provided and the corresponding Wildland Fire Leadership Levels have been identified.

The five books chosen for this year are: Young Men and Fire by Norman Maclean, The Wisdom of the Bullfrog by William H. McRaven, The Art of Clear Thinking by Hasard Lee, Emotional Agility by Susan David, and Writing to Persuade by Trish Hall.

References:

Professional Reading Program

Wildland Fire Leadership Levels

NWCG Training Catalog now on Wildland Fire Learning Portal

Date: April 25, 2023
Contact: NWCG Training  

The National Wildfire Coordinating Group (NWCG) has migrated the training catalog from the NWCG website to the Wildland Fire Learning Portal (WFLP) as part of our ongoing efforts to streamline processes and improve efficiency. To facilitate this transition, the training catalog remains available on www.nwcg.gov through April 2024.

Starting May 2024, the training catalog will no longer be accessible on www.nwcg.gov. However, you can still access the complete training catalog by logging in as a guest to the WFLP.

References:

Wildland Fire Learning Portal