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5.1 Burn Area and Perimeter

The perimeter is the distance around the fire or along the handline. Perimeter is determined by adding the lengths of the various lines that enclose the black area of a fire. Because fires often burned in unusual shapes such as fingers, the perimeter of a fire can be approximated by assembling a combination of known shapes and lines. 

Area is the amount of surface covered within a given perimeter and is useful in determining burnout acreage. Area is always in square units: for example, square feet (ft2), square yards (yd2), or acres, which represents a square distance. 

A square, rectangle, and triangle are shown in the following figures, with their formulas for area and perimeter. 

square, circle, and triangle

Determining perimeter and burn area after a fire is often necessary. Average dimensions for a sketch can be obtained by pacing or walking around and through the burn. This method is especially useful for small fires. Global Positioning Systems (GPS) are used for larger fires to determine their shape, area, and perimeter. 

Example 1 - John sketched the following burn shape in his firefighter's notebook. Use this information to determine the acreage of the fire. John's pace is 12 paces per chain.

burned area shape

Step 1. Set up the cancellation table so all units will cancel, except the desired unit, chains.

cancellation table

Step 2. Take the average of the two widths. The average width = 8.5 chains + 3.5 chains / 2 = 12 / 2 = 6 chains.

Step 3. Use the equation for determining the area of a rectangle.
Area of rectangle = length × average width

Area = 10 chains × 6 chains = 60 square chains.

Step 4. Set up the cancellation table so all units will cancel, except the desired unit, acres.

cancellation table

The area of the fire is 6 acres.
 

ACREAGE GRID

A clear acetate/plastic dot acreage grid can be placed over the mapped sketch of a burn area. It is important that the plastic grid overlay and burn map have the same scale. Burn area is determined by counting the number of dots inside the sketch of the burn. For dots that are on the border of the burn sketch, count every other dot. Multiply the number of dots counted by the dot conversion factor. This conversion factor is typically indicated on the bottom of the plastic overlay. 

Example 2 - Janie sketched out a burn area in the following shape on a 7.5 minute USGS quadrangle map. The U.S. Geological Survey (USGS) produces a series of standard maps to various scales. The 7.5 minute map series has a 1:24,000 scale. One inch on a 7.5 minute map represents 2,000 feet on the ground. (See Chapter 6, Latitude and Longitude, for more information.) Use the acreage grid overlay to determine the area of the fire.

acreage grid

Step 1. Count the number of dots within the shape. Count every other dot for dots on the borderline. There are 181 dots.

Step 2. Read the overlay scale to obtain the dot-grid conversion. In this case the conversion is 2.500 acres per dot. 

Step 3. Set up the cancellation table so all units will cancel, except the desired unit, acres.

cancellation table

The area of the above figure is about 453 acres.

schematic of burn area with paces marked

 

NWCG Latest Announcements

EMC Memo 25-001: Interim Rapid Extraction Module (REMS) Training and Qualification Requirements

Date: June 3, 2025
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Emergency Medical Committee

The Emergency Medical Committee has issued interim guidance for Rapid Extraction Module Support (REMS) teams. Until further notice, Type I and II REMS teams must designate a team leader qualified at Firefighter Type 1 Squad Boss (FFT1) or higher. This temporary change replaces the Single Resource Boss (SRB) requirement, which is currently not feasible due to administrative barriers.

This memorandum does not include any other changes to the NWCG Standards for Rapid Extraction Module Support, PMS 552. This interim change takes effect immediately and will remain in place until further notice.

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EMC Memo 25-001: Interim Rapid Extraction Module (REMS) Training and Qualification Requirements

NWCG Standards for Rapid Extraction Module Support, PMS 552

Equipment Bulletin 25-002: Chaps, Chain Saw, M-2020, Nonconformities Affecting Use, Appearance, and Serviceability

Date: June 2, 2025
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Equipment Technology Committee

The Equipment Technology Committee issued Equipment Bulletin: 25-002 to address a manufacturing nonconformity affecting Forest Service specification, 6170-4K Chain Saw Chaps. The issue applies to chaps manufactured in 2024 and 2025 and distributed through FedMall. These chaps may have incorrectly bound edges that expose inner protective layers.

Independent purchasers should inspect all chain saw chaps received from FedMall beginning in 2024, prior to use. Review the full Equipment Bulletin: 25-002 for inspection criteria and recommended actions.

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2024 Wildland Fire Emergency Medical Service Awards

Date: May 22, 2025
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The NWCG Emergency Medical Committee (EMC) is proud to announce the recipients of the 2024 Wildland Fire Emergency Medical Service Awards. Each year, EMC recognizes individuals and groups who have demonstrated exceptional actions or accomplishments that go above and beyond their normal mission or job duties.

Congratulations to all the awardees and nominees. Through leadership and initiative, they have made significant contributions to the safety and well-being of the wildland fire community. These honors are well deserved.

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NWCG Welcomes the Incident Management Teams Association as an Associate Member

Date: May 21, 2025
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The NWCG Executive Board is honored to announce that the Incident Management Teams Association (IMTA) has joined the National Wildfire Coordinating Group as an associate member.

IMTA is a dedicated group of incident management professionals committed to enhancing the profession by promoting standards and fostering collaboration across federal, state, local, Tribal, and private sector partners throughout all phases of incident management.

“Joining NWCG aligns with our mission to elevate incident management professionals nationwide,” said Dr. Randal Collins, President of IMTA. “This is a proud moment for all of us committed to advancing public safety.”

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