United States

Department

of Agriculture

Forest Service

Rocky Mountain

Research Station

General Technical Report 

RMRS-GTR-253

March 2011

How to Generate and Interpret 

Fire Characteristics Charts for 

Surface and Crown Fire Behavior

Patricia L. Andrews, Faith Ann Heinsch, and Luke Schelvan 
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Andrews, Patricia L.; Heinsch, Faith Ann; Schelvan, Luke. 2011. How to generate and interpret 

fire characteristics charts for surface and crown fire behavior. Gen. Tech. Rep. RMRSGTR-253. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain 

Research Station. 40 p. 

Abstract

A fire characteristics chart is a graph that presents primary related fire behavior characteristics—rate 

of spread, flame length, fireline intensity, and heat per unit area. It helps communicate and interpret 

modeled or observed fire behavior. The Fire Characteristics Chart computer program plots either 

observed fire behavior or values that have been calculated by another computer program such as 

the BehavePlus fire modeling system. Program operation is described in this report, and its flexibility 

in format, color, and labeling is demonstrated for use in a variety of reports. A chart produced by the 

program is suitable for inclusion in briefings, reports, and presentations. Example applications are 

given for fire model understanding, observed crown fire behavior, ignition pattern effect on fire behavior, 

prescribed fire planning, briefings, and case studies. The mathematical foundation for the charts is 

also described. Separate charts are available for surface fire and crown fire because of differences 

in the flame length model used for each. 

Keywords: wildland fire, fire behavior, fire modeling, fire spread, fire intensity, computer program

Cover Photos: Surface fire, Wayne Cook, U.S. Forest Service; Backing 

Fire Operation, NWCG S-390 course; Torching fire, NWCG S-290 course; 

Airtanker, NAFRI Images CD-ROM; Crown fire, NWCG S-290 course.

The use of trade or firm names in this publication is for reader information and does 

not imply endorsement by the U.S. Department of Agriculture of any product or service
Authors

Patricia L. Andrews is a Research Physical Scientist with the Fire, Fuel, and Smoke 

Science Program at the Fire Sciences Laboratory in Missoula, Montana. She has 

been at the Fire Lab since 1973, serving as Project Leader of the Fire Behavior 

Research Work Unit from 1991 to 1996. Her research focus is fire behavior prediction and fire danger rating.

Faith Ann Heinsch is a post-doctoral Research Ecologist with the Fire, Fuel, and 

Smoke Science Program at the Fire Sciences Laboratory in Missoula, Montana, 

where she has focused on improving fire behavior and fire danger modeling systems 

as well as on climate change. From 2002 to 2008, she worked at the University of 

Montana with the Numerical Terradynamic Simulation Group (NTSG) in the College of Forestry and Conservation, where she analyzed vegetation productivity in 

response to current changes in climate and collaborated in climate change research, 

education, and outreach.

Luke Schelvan is a Software Engineer with Systems for Environmental Management 

(SEM) in Missoula, Montana. He received a B.S. degree in Computer Science from 

the University of Montana in 1993. He has been involved in a number of projects 

related to fire behavior with SEM since 2003.

Preface

The electronic version of this publication can be obtained though the Rocky 

Mountain Research Station publications web page: http://www.fs.fed.us/rm/pubs/

rmrs_gtr253.html. The publication and the program can be downloaded from the 

BehavePlus section of the website http://www.FireModels.org. This publication 

is also bundled with the program as the Help system.

Funding for development of the Fire Characteristics Chart program was provided by 

the USDA Forest Service, Fire and Aviation Management, Washington, DC, and the 

Rocky Mountain Research Station, Fire, Fuel, and Smoke Program. Programming 

was done through a contract with Systems for Environmental Management (SEM).

We thank the following reviewers for providing helpful comments on this document 

and the computer program: William Aney (U.S. Forest Service), Kelly Close (City 

of Fort Collins, Colorado), Louisa Evers (USDOI Bureau of Land Management), 

Valentijn Hoff (University of Montana), Tobin Kelley (U.S. Forest Service), Joe Scott 

(Pyrologix), and Deb Tirmenstein (SEM).
Contents

1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

2 Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

2.1 Fire Model Understanding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

2.1.1 Surface Fire—Effect of Live Fuel Moisture . . . . . . . . . . . . . . . . . . . . . . . . 6

2.1.2 Crown Fire—Effect of Canopy Base Height, Canopy Bulk Density, 

and Wind Speed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

2.2 Observed Crown Fire Behavior . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

2.3 Ignition Pattern Effect on Fire Behavior . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

2.4 Prescribed Fire Plan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

2.5 Briefings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

2.6 Case Studies and After Action Reviews . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

3 Program Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

3.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

3.1.1 Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

3.1.2 Opening and Closing the Program . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

3.1.3 The Fire Characteristics Chart Window . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

3.1.4 Worksheet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

3.1.5 Docking and Undocking the Worksheet . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

3.1.6 Menu Items . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

3.2 Chart Format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

3.2.1 Units . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

3.2.2 Graph Scale and Tick Marks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

3.2.3 Flame Length Curves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

3.2.4 Flame Length Images . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

3.2.5 Graph Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

3.2.6 Grid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

3.2.7 Graph Color . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

3.2.8 Legend . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

3.2.9 Font . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

3.2.10 Restore Settings to Default . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

3.3 Entering Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

3.3.1 Caption Lines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

3.3.2 Data Points . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

3.3.3 Graph Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

3.3.4 Point Icons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

3.3.5 Point Label . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

3.3.6 Legend Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

3.3.7 Clear Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
3.4 Saved Files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

3.4.1 Saving a Fire Characteristics Chart File . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

3.4.2 Opening a Fire Characteristics Chart File . . . . . . . . . . . . . . . . . . . . . . . . . 30

3.4.3 Save Image File . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

3.4.4 Saving Data as HTML . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

3.5 Printing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

3.6 Adding Custom Labels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

3.7 Help . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

4 Modeling Foundation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

4.1 Surface Fire Behavior . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

4.2 Crown Fire Behavior . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

4.3 Surface and Crown Fire Flame Length and Fireline Intensity . . . . . . . . . . . . . 34

4.4 Other Forms of the Fire Characteristics Chart . . . . . . . . . . . . . . . . . . . . . . . . . . 34

5 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

Appendix A. Fire Intensity Levels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

USDA Forest Service Gen. Tech. Rep. RMRS-GTR-253. 2011 1

1 Introduction___________________

	 A fire characteristics chart is a graph that illustrates

primary fire behavior values—spread rate and intensity.

The location of a plotted point represents the character

of a fire, which can range from a fast spreading, low

intensity fire to a slow spreading, high intensity fire. The

chart is a visual aid for displaying both observed fire

behavior and values calculated by computer programs

such as the BehavePlus fire modeling system (Andrews

2007; Andrews and others 2008).

	 Graphic presentation of quantitative fire behavior values can support a number of applications. A scientist or

student can use the fire characteristics chart to compare

predicted and observed fire behavior. A Fire Behavior

Analyst can use it to describe potential fire behavior in

a briefing to a wildfire management overhead team. A

prescribed fire planner can use it to illustrate acceptable

fire behaviorin a fire prescription document.Anyone can

use the fire characteristics chart to better understand fire

models by showing the effect of a change in fuel model,

fuel moisture, wind speed, or slope on calculated rate

of spread, heat per unit area, flame length, and fireline

intensity.

	 Mathematical relationships among rate ofspread, heat

per unit area, fireline intensity, and flame length are the

basisforthe surface and crown fire behavior characteristics charts. The surface fire characteristics chart includes

curvesforseveralflame length values asrelated to rate of

spread and heat per unit area (Figure 1) with symbolsfor

fire suppressioninterpretationsrangingfromfiresthat can

be attacked by persons with hand toolsto firesfor which

control efforts are ineffective. The fire characteristics

chart is, therefore, also known as the “hauling chart”—

haul in crews, haul in equipment,

haul in aircraft, or haul everything

out of there. The fire characteristics

chart was developed for surface fire

behavior by Andrews and Rothermel

(1982). Rothermel (1991) later used

the concept to develop a crown fire

characteristics chart (Figure 2).

	 The BehavePlus fire modeling system includes an option for

producing a fire characteristics chart

output for surface fire, with limited

capabilities for plotting and labeling. There is not a similar output

option for crown fire. The chart that

is produced in BehavePlus is only

for calculated values and cannot be

used to plot observed fire behavior

or adjusted calculated values. The

computer program described in this

report offers plotting flexibility and

produces a chart that is suitable for

inclusion in briefings, reports, and

presentations.

Figure 1—The surface fire behavior fire 

characteristics chart is used to plot rate 

of spread, heat per unit area, and flame 

length for calculated or observed fire 

behavior (Andrews and Rothermel 1982). 

Figures on the chart are an indication of 

fire suppression effectiveness related to 

flame length.
2 USDA Forest Service Gen. Tech. Rep. RMRS-GTR-253. 2011

	 Four variables are represented by a single point on

the chart: rate of spread, heat per unit area, fireline

intensity, and flame length. The relationship among

these variables is used to produce the surface and

crown fire charts; equations are given in the Modeling

Foundation section. While four values are represented

by a given point, only two values are specified to locate the plotted point: rate of spread (ROS) and either

flame length (FL) or heat per unit area (HPUA). When

plotting was done with a pencil on a paper chart, it was

easiest to enter values for the X- and Y-axes, HPUA

and ROS, because it is difficult to estimate the correct

location of a flame length value between the curves. A

computer can easily plot a point given ROS and FL,

which are the more likely available values for fire

behavior observations.

Figure 2—The crown fire behavior fire 

characteristics chart is used to plot rate 

of spread, heat per unit area, and flame 

length for calculated or observed crown 

fire behavior (Rothermel 1991). The 

crown fire flame length model is different 

from that used for surface fire.

	 Figure 3 illustrates the relationship between flame length and

fireline intensity.The flame length

of a spreading surface fire is the

distance between the average tip of

the flame and the ground (orsurface

of the remaining fuel) midway in

the active flaming zone. Fireline

intensity is the heat energy release

per unit time per unit length of fire

front. Fireline intensity relates to a

foot (or meter) wide section of the

fuel bed that extends from the front

to the rear ofthe active flaming zone

(Figure 3). Unlike fireline intensity,

flamelengthisanobservablecharacteristicoffirebehavior.However, as

stated byRothermel(1991): “Flame

length is an elusive parameter that

exists in the eye of the beholder. It

is a poor quantity to use in a scientific or engineering

sense, but it is so readily apparent to fireline personnel

and so readily conveys a sense of fire intensity that it is

worth featuring as a primary fire variable.”

	 While there is a direct (non-linear) mathematical

relationship between fireline intensity and flame length

(although different for surface and crown fire), we have

chosentolabel chart curveswithonlyflame lengthvalues.

	 Flame length and fireline intensity are related to the

heat felt by a person standing next to the flames and have

been interpreted in terms of suppression capabilities.

Figures on the chart aid general interpretation. Table 1

was developed for the advanced fire behavior training

course (S-590; Rothermel 1983) and was derived from a

more detailed table prepared byRoussopoulos(1974)for

a National Fuel Management Workshop (Appendix A).

The fireline intensity values in Table 1 are rounded because they are general guidelines.
USDA Forest Service Gen. Tech. Rep. RMRS-GTR-253. 2011 3

Figure 3—The diagrams illustrate the relationship between flame length and fireline intensity. A side 

view of a wind-driven fire shows that flame length is measured from midway in the active flaming zone 

to the average tip of the flames. The overhead view illustrates that fireline intensity is the heat energy 

release per unit time from a foot (or meter) wide section of the fuel bed extending from the front to the 

rear of the active flaming zone.

Table 1—Relationship of surface fire flame length and fireline intensity to suppression interpretations. 

Flame length Fireline intensity Interpretation

ft m Btu/ft/s kJ/m/s

< 4 < 1.2 < 100 <350 • Fires can generally be attacked at the head or flanks by 

persons using hand tools. 

• Hand line should hold the fire.

4 – 8 1.2 – 2.4 100 – 500 350 – 1700 • Fires are too intense for direct attack on the head by persons using hand tools. 

• Hand line cannot be relied on to hold the fire. 

• Equipment such as dozers, pumpers, and retardant aircraft 

can be effective.

8 – 11 2.4 – 3.4 500 – 1000 1700 – 3500 • Fires may present serious control problems—torching out, 

crowning, and spotting. 

• Control efforts at the fire head will probably be ineffective

> 11 > 3.4 > 1000 > 3500 • Crowning, spotting, and major fire runs are probable. 

• Control efforts at head of fire are ineffective.
4 USDA Forest Service Gen. Tech. Rep. RMRS-GTR-253. 2011

	 In simplified terms, heat per unit area is equal to the

fireline intensity divided by rate of spread. Heat per unit

area is the heat release for an area. Fireline intensity is a

heat release rate. For any given fireline intensity (flame

length), the faster the rate of spread, the less heat will

be directed to the site. Conversely, a slow-moving fire

with the same fireline intensity as a fast-moving fire will

concentrate considerable heat on the site (Rothermel and

Deeming 1980).

	 The surface fire characteristics chart has a much lower

range of spread rate and intensity than the crown fire

characteristics chart. The surface fire chart depicts the

limits of fire control as well as general guidelines for

torching and crown fire development. These limits are

all exceeded by active crown fires. A crown fire should

always be considered uncontrollable by direct attack at

the head of the fire.

	 Because themodelfor crown fire flame length is differentfromthat used forsurface fire flame length, we do not

combine the two fire types on a single fire characteristics

chart. A fireline intensity of 1000 Btu/ft/s produced by a

surface fire gives a flame length of approximately 11 ft,

whereas that same intensity generates a flame length of

approximately 20 ftfor a crown fire. Details are provided

in the Modeling Foundation section. A common chart

could be used ifthe curveswere labeled onlywith fireline

intensity andwere notlabeled as orinterpreted in terms of

flame length. We do not offer that option in our program

because it would be contrary to the primary purpose of

the chart—a visual comparison offire characteristics.As

noted earlier, it is easier to visualize the character of a

fire in terms of flame length rather than fireline intensity.

	 As an example of the information that can be gained

from viewing plotted values on a fire characteristics

chart, we compare calculated fire behavior for four

fuel models under the same environmental conditions.

A BehavePlus run was produced for fuel models 1, 10,

8, and 4 for 5 percent dead fuel moisture, 100 percent

live fuel moisture, midflame wind speed of 7 mi/h, and

10 percent slope (Figure 4). As described by Anderson

(1982), fuel model 1 can represent continuous stands

of arid western grass; fuel model 10—the litter and

Figure 4—A BehavePlus run with values for four fuel models to be plotted on the surface 

fire characteristics chart.
USDA Forest Service Gen. Tech. Rep. RMRS-GTR-253. 2011 5

Figure 5—Outputs from the BehavePlus run in Figure 4 are plotted on the fire 

characteristics chart.

understory of a timber stand with heavy accumulations

of deadfall; fuel model 8—short needle litter; and fuel

model 4—chaparral. Fuel models 1 and 8 include only

dead fuel. A look at the BehavePlus table output shows

a significant difference in calculated rate of spread, heat

per unit area, fireline intensity, and flame length for the

four fuel models.

	 Plotting calculated values on the fire characteristics

chart (Figure 5) provides a visual display of fire characteristics and the relationship among the fire behavior

values for the four modeled fires. The flame length is

roughly 6.5 ft for both fuel models 1 and 10 under the

stated moisture, wind, and slope conditions. According

to the interpretations in Table 1, both fires may be too

intense for direct attack at the head by persons using hand

tools. The character of the two fires is, however, very

different. The fire in fuel model 1 (short grass) is fast

spreading with a low heat per unit area, while the fire

in fuel model 10 (timber litter and understory) is slow

spreading with a high heat per unit area.While the fireline

intensity is nearly identical (about 340 Btu/ft/s) for fuel

models 1 and 10 under these conditions, the large difference in heat per unit area (32 Btu/ft2 and 1330 Btu/ft2

)

results from the much faster fire rate of spread in fuel

model 1, which produces much less heat at any given

point on the ground.
6 USDA Forest Service Gen. Tech. Rep. RMRS-GTR-253. 2011

	 A fire in fuel model 8 (short needle litter) under the

same environmental conditions has both a low spread

rate and low heat per unit area. The calculated flame

length is 1.5 ft, indicating that it may be controlled by

hand crews. The other extreme is the fire in fuel model

4 (chaparral), which has a high spread rate and a high

heat per unit area. The calculated flame length of more

than 25 ft means control efforts at the fire head would

be ineffective.

	 The plotted points in Figure 5 are circled for emphasis

(added to the chart produced by our program, using other

software). The circles might also serve as a reminder of

the inherent variability of wildland fire, as well as the

limitations of fire modeling—of the fire models; of the

fuel description; and ofthe fuelmoisture,wind, and slope

values. Keep in mind that the guidance given in training courses that use nomograms to predict fire behavior

(Albini 1976b) has been to use a fat crayon rather than a

sharp pencil (Rothermel 2009). This also applies to the

fire characteristics chart.

	 We have described what a fire characteristics chart

is and have given an example of how the character of

four modeled fires can be compared using the chart. The

remainder of this paper is organized into three sections.

	 •	 Applications.Examplesofuseofthe chart aregiven,

with focus on application rather than on methods of

producing the charts.

	 •	 Program Operation. Program use and available

options are detailed in the form of a reference guide.

	 •	 Modeling Foundation. The mathematical relationships that form the foundation of the fire characteristics charts are described. Other forms of the fire

characteristics chart are briefly described.

2 Applications __________________

	 Using the fire characteristics chart to visually display

quantitative fire behavior values (observations, calculations, or adjusted calculations) can be useful for many

applications.

	 Wepresentexampleapplicationsof a firecharacteristics

chart for the following:

	 •	 Fire model understanding

	 •	 Documentation of observed fire behavior

	 •	 Illustration of the effect of ignition pattern on prescribed fire behavior

	 •	 Comparison of fire behavior within and outside of

a prescribed fire unit

	 •	 Briefings to a fire management overhead team

	 •	 Case studies and after action reviews

	 These examples demonstrate various format options

that are offered by the program. In some cases, we have

used additional software to add text and figures to the

charts.

2.1 Fire Model Understanding

	 The fire characteristics chart program does not include

fire model calculations; observed values or values that

are calculated using any fire behavior modeling software

can be entered and plotted. The display of relationships

among calculated values can aid fire model understanding. In addition to personal use, the fire characteristics

chart can help in formal training sessions that describe

relationshipsofinputvariablestocalculatedfirebehavior.

	 In the Introduction, we compared surface fire behavior for four fuel models under the same environmental

conditions. In the following examples, we first compare

the effect of live fuel moisture for two fuel models. We

then compare crown fire behavior for two values of

canopy bulk density and wind speed. In both examples,

we display calculations from BehavePlus.

2.1.1 Surface Fire—Effect of Live Fuel 

Moisture

	 The BehavePlus run in Figure 6 is for two grass fuel

models and two values of live fuel moisture. Figure 7

shows the four points plotted on a fire characteristics

chart.Thisis a simple comparison ofmodeled fire behavior for fuel models 2 and GR2 with 50 percent and 100

percent live fuel moisture, 5 percent dead fuel moisture,

midflame wind speed of 5mi/h, and 0 percentslope. Fuel

model 2 (timber grass and understory) is one of the 13

fuel models described by Anderson (1982). Fuel model

GR2 (low load, dry climate grass) is one of the 40 fuel

models developed by Scott and Burgan (2005).

	 The fire characteristics chart illustratesthat the change

in live fuel moisture results in a greater change in fire

behavior for fuel model 2 than for fuel model GR2. This

is in large part because fuel model 2 is static and GR2

is dynamic. The parameters of a static fuel model do

not change. A dynamic fuel model, on the other hand,

is designed to reflect seasonal changes in fuel loading

due to curing. The fuel model parameters of a dynamic

fuel model change as a function of live herbaceous fuel

moisture;fuel load istransferred fromthe live to the dead

category. At 100 percent, most of the live herbaceous

fuel is not cured (in other words, it isstill considered live

fuel).At a fuel moisture of 50 percent, most of the fuel is

cured, meaning most of the live herbaceousfuel load has

been transferred to the dead category. Live herbaceous
USDA Forest Service Gen. Tech. Rep. RMRS-GTR-253. 2011 7

Figure 6—BehavePlus input and table output. The same live moisture value is used for live woody 

and herbaceous fuel. Fuel model 2 is static and GR2 is dynamic.

fuelmoisture influences calculated fire behaviorfor both

fuel model 2 and GR2. There is an additional influence

on GR2 due to the load transfer function, resulting in the

differences shown in Figures 6 and 7.

	 The purpose of this example is to compare changes in

fire behavior that result from a change in input. Because

the objective is not fire suppression interpretation, the

suppression icons were removed and the flame length

curves were changed, (compare with the basic chart in

Figure 1). Chart scales were changed to better display

plotted points, and we used othersoftware to add dashed

lines to emphasize relationships.
8 USDA Forest Service Gen. Tech. Rep. RMRS-GTR-253. 2011

Figure 7—Plotted points compare fuel models 2 and GR2 for live fuel moistures of 50% 

and 100%. Other conditions are constant. BehavePlus calculations are shown in Figure 6.

2.1.2 Crown Fire—Effect of Canopy Base 

Height, Canopy Bulk Density, and Wind Speed

	 Results of BehavePlus runs (Figure 8) show an example ofthe effect of canopy base height(CBH), canopy

bulk density (CBD), and 10-m wind speed on crown

fire behavior. The associated fire characteristics chart

is in Figure 9. Metric units were selected for both the

BehavePlus calculations and the chart.

	 Because we are demonstrating an application of model

understanding rather than a complete analysis of fire

behavior, the BehavePlus run was limited to calculation

of crown fire rate of spread, heat per unit area, flame

length, and fireline intensity. We did not model surface

fire behavior orfire type based on transition to crown fire

and potential for active crown fire. Heat per unit area for

the surface fire is, therefore, a user input,selected from a

table of values from Rothermel (1991) to represent fuel

model 9 (long needle litter) with additional fuel load, as

described in the Modeling Foundation section.

	 Notice that crown rate of spread is influenced by

wind speed but not by canopy bulk density or canopy

base height. The opposite is the case for heat per unit

area, which is influenced by canopy bulk density and

canopy base height and not by wind speed. Flame length

and fireline intensity are affected by all three variables

included in the calculations. Relationships among all

crown fire model variables in BehavePlus are available

in flowcharts in the Help window.
USDA Forest Service Gen. Tech. Rep. RMRS-GTR-253. 2011 9

Figure 8—BehavePlus runs producing crown fire behavior values that are plotted on the fire 

characteristics chart in Figure 9.

(continued)
10 USDA Forest Service Gen. Tech. Rep. RMRS-GTR-253. 2011

Figure 8—(continued)
USDA Forest Service Gen. Tech. Rep. RMRS-GTR-253. 2011 11

Figure 9—Plotted points from BehavePlus calculations (Figure 8) show difference in fire 

characteristics resulting from varying wind speeds and canopy bulk density.

2.2 Observed Crown Fire Behavior

	 Anderson (1968) documented the Sundance Fire

that burned across northern Idaho in 1967. It burned in

mixed conifers, was driven by winds of up to 45 mi/h,

and reached spread rates of 6 mi/h. The magnitude of the

fire resulted from a prolonged dry period, persistent high

temperatures,sustained winds during the fire run, and an

uncontrolled 4-mile fire front. In a period of 9 hours, the

fire traveled 16miles and burnedmore than 50,000 acres.

The major fire run occurred on September 1, 1967, from

approximately 1400 to 2300. Observed rates of spread

and calculated fireline intensity values were taken from

Anderson (1968) and are given in Table 2. Flame length

values were calculated for this table using the Thomas

(1963) model (equation 10). Rate of spread and flame

length values were plotted on the fire characteristics

chart (Figure 10). Other software was used to connect

the points to show the envelope of fire behavior during

the run.
12 USDA Forest Service Gen. Tech. Rep. RMRS-GTR-253. 2011

Table 2—Hourly rate of spread and fireline intensity of the Sundance Fire on September 1, 

1967, from Anderson (1968). Flame length values were calculated for this table 

based on Thomas (1963).

Time

Rate of 

spread,

mi/h

Fireline intensity, 

Btu/ft/s

Flame 

length,

ft

1400 0.75 1000 20

1500 1.25 5400 62

1600 1.6 6900 72

1700 <1.0 3150 43

1800 2.5 11,300 101

1900 1 3400 45

2000 6 22,500 159

2100 2.5 8250 82

2200 1.5 3800 49

2300 0.5 735 16

Figure 10—Envelope of the observed behavior of the Sundance Fire by time of day for 

September 1, 1967. Plotted values (rate of spread and flame length) are from Table 2.
USDA Forest Service Gen. Tech. Rep. RMRS-GTR-253. 2011 13

2.3 Ignition Pattern Effect on Fire 

Behavior

	 The Rothermel surface fire spread model is based on

the assumption that fire is steady-state, burning under

uniform conditions. This is not the case for prescribed

fire where the pattern of ignition is used to affect fire

behavior.Rothermel(1984)discussedapplyingfiremodel

predictions to this situation, stating that “Prediction of

fire behavior is difficult, but careful and selected use of

availablemethods can aid planning and execution of prescribed fire by aerial ignition or other ignition methods.”

He used the fire characteristics chart to illustrate differences between the steady-state fire behavior calculated

by the model and fire with (1) lesser fire behavior that

had notreached steady-state, and (2) greaterfire behavior

driven by induced winds.

	 Fire characteristics charts might be included in a burn

plan to show the calculated steady-state behavior and

the behavior that is planned via ignition pattern. Calculated values using ambient conditions can be plotted,

illustrating expected behavior if the fire were allowed

to reach steady-state, without induced winds on the fire.

In addition, a calculation with no wind can represent a

lower limit for fire behavior. If narrow strips are used

and ignition of successive strips is delayed until the fine

fuel has burned, the expected rate of spread and flame

length should lie somewhere between the two points.

Faster spread rates and larger flames can be achieved by

more rapid ignition ofstripsthat are spread wide enough

to allow flames to fully develop but not so wide as to

get beyond the indraft influence. The upper limit of fire

behavioris unknown since itis determined by the amount

of induced wind that is generated by the ignition system

and the heat generation of the fire. However, the effect

of induced wind can be indicated on the chart above the

calculated values.

	 The following two examples are based on those presented by Rothermel (1984). BehavePlus was used to

do the calculations. We used other software to highlight

plotted points and to add labels.

	 Suppose there is a scheduled burn in sagebrush. A

high pressure system is stagnant over the area, producing warm weather but no wind. From experience and/or

test fires, it is known that the fuel is too sparse to burn

without an 8- to 10-mi/h wind. The calculated no-wind

behavior and the value plotted on the fire characteristics

chart are shown in Figure 11. Even though the heat per

unit area is considerable (656 Btu/ft2

), the rate of spread

is very low (1.2 ch/h) and, as noted, the fire won’t actually spread under no-wind conditions. If induced winds

of 8 to 10 mi/h can be generated using rapid, aerial

ignition, the fire would plot as shown on the chart. The

fireline intensity would increase significantly and the

flame lengths would range between 8 and 10 ft.

	 As a second example, suppose there is an area on a

30 percentslope with fuelsrepresented by fuel model 12

(medium slash). The dead and down fuel load could be a

result of logging or of blow-down following beetle kill.

The burn is planned for the afternoon, when dead fuel

moisture nears 7 percent. Upslope winds are predicted to

be about 5 mi/h at eye level (midflame). A helitorch will

be used for strip ignition, and we would like to assess

expected fire behavior.

	 The effect of induced wind can be illustrated on the

fire characteristics chart by calculating fire behavior for a

no-wind condition and for a 5 mi/h midflame wind. Both

of these conditions are plotted on the chart in Figure 12.

The ambient wind condition indicates the expected

behavior if there are no induced winds on the fire. The

no-wind condition indicates behavior if the fire were

backing down the slope.

	 If the strips are kept narrow and ignition of successive

strips is delayed until the fine fuel has burned out, the

expected rate of spread and flame length should lie in

the bracketed area marked “narrow strips” between the

two points. The effect of induced wind is located above

the other two points on the chart, as shown by the arrow.

2.4 Prescribed Fire Plan

	 The Interagency Prescribed Fire Guide (USDA and

USDOI 2008) defines prescription as “the measureable

criteria that define a range of conditions during which a

prescribed fire may be ignited and held as a prescribed

fire.” In addition to specifying acceptable fire behavior

within the burn unit, the guide states: “Holding and

contingency plans must be developed with the consideration of the predicted fire behavior outside the project

boundary(s). Fire behavior characteristics for fuel

models within the maximum spotting distance and/or

adjacent to the project boundaries must be considered

and modeled.”

	 While the fire behavior within a prescribed fire burn

unit may be controlled by the pattern of ignition, a spot

fire outside of the unit would better meet the steady-state

assumptions of the fire model. The fire characteristics

chart can illustrate differencesin fire behavior that result

from different conditions inside and outside of the unit.

Surface fuel models and slope may differ; dead fuel

moisture will depend on aspect and overstory shading;

live fuel moisture will depend on aspect and vegetation

type; and midflame wind speed will depend on overstory

sheltering.
14 USDA Forest Service Gen. Tech. Rep. RMRS-GTR-253. 2011

Figure 11—Effect of induced winds on sagebrush fire characteristics (based on 

Rothermel 1984).
USDA Forest Service Gen. Tech. Rep. RMRS-GTR-253. 2011 15

Figure 12—Effect of narrow strips and of induced winds on logging slash fire 

characteristics (based on Rothermel 1984).
16 USDA Forest Service Gen. Tech. Rep. RMRS-GTR-253. 2011

	 Figure 13 is a map of a burn unit with labeled fuel

modelsforthe surroundingarea andcalculatedmaximum

spotting distance. Table 3 gives calculated rate ofspread

and flame length of fire within the unit and of potential

spot fires outside the unit. Calculations for fire within

the unit are done for fuel model 11 (light logging slash)

with a 20-ft wind speed of 25 mi/h and zero wind. The

ignition planwill not allowthe fire to reach themaximum

steady-state spread rate.

	 Fire behavior is calculated for litter fuel models TL2

and TL6 in addition to fuel model 9 (long needle litter),

which is shown on the map.

Figure 13—Map showing the relationship of the burn unit (fuel model 11) to areas and associated fuel models 

outside of the unit. The calculated maximum spotting distance is indicated (developed by Tobin Kelley, U.S. 

Forest Service).

Table 3—Conditions and calculated fire behavior for within the burn unit (fuel model 11) and for potential spot 

fires outside of the burn unit.

Fuel 

model

Max 

slope,

%

20-ft 

wind,

mi/h

Wind 

adj. factor

Midflame 

wind,

mi/h

Dead 

moist.,*

%

Live 

moist.,

%

Rate of 

spread,

ch/h

Flame 

length,

ft

11 35 25 0.4 10 5,8,10 — 14.8 5.2

11 35 0 0.4 0.0 5,8,10 — 1.9 2.0

9 45 25 0.3 7.5 7,8,10 — 18.0 4.0

TL2 45 25 0.3 7.5 7,8,10 — 1.9 0.9

TL6 45 25 0.3 7.5 7,8,10 — 11.6 3.6

8 20 25 0.2 5.0 7,8,10 — 2.0 1.1

10 45 25 0.2 5.0 7,8,10 100 10.9 5.0

*1-h, 10-h, 100-h moisture
USDA Forest Service Gen. Tech. Rep. RMRS-GTR-253. 2011 17

	 Figure 14 is a fire characteristics chart that might be

included in the prescribed fire planwith themap, description of conditions, and assumptions used in themodeling.

Lines were added to the chart to highlight the range of

potential fire behavior inside and outside the unit. The

scale was changed to better display the plotted points.

Because fire suppression interpretation isrelevant to this

application, the flame length curves and icons were not

changed.

2.5 Briefings

	 Wildland fire behavior information is needed in a

variety of settings and is often presented in the form of

briefings. The following is taken from a lesson in the

S-590 Advanced Fire Behavior Interpretations course:

“High quality visual aids help increase the interest of

the audience, increase the understanding and retention

of information, and can greatly increase the amount of

information presented and understood in a shorter

Figure 14—Plot of potential fire behavior of a spot fire outside the burn area and the 

range of fire behavior in the unit. The ignition method will not allow the prescribed fire 

to reach steady-state. The planned fire behavior is indicated by the large red dot. The 

range of potential fire behavior inside and outside the unit is indicated by the shaded 

envelope.
18 USDA Forest Service Gen. Tech. Rep. RMRS-GTR-253. 2011

period of time. Good visual aids also help present a

professional image.”

	 Expected fire behavior by time and location can be

illustrated on a fire characteristics chart. A fire behavior

forecast can include calculations from a system such

as BehavePlus, but the Fire Behavior Analyst also uses

observed fire behavior and personal experience to make

predictions.

	 Figure 15 is a portion of a written fire behavior forecast that describes expected fire behavior for the head

and flanking fire. Figure 16 shows those values on a fire

characteristics chart.

2.6 Case Studies and After Action 

Reviews

	 Post-fire documentation, case studies of wildfire behavior, and after action reviews (AAR) of planned and

unplanned fires can include a fire characteristics chart.

We present an example fromthe report on the 1989Black

Tiger Fire near Boulder, Colorado (National Fire ProtectionAssociation 1990). Rates ofspread were determined

from the timed progress of the fire as noted from aerial

observation. The term “energy density” in that report is

equivalent to “heat per unit area” (HPUA) used here.

HPUAwas estimated for ponderosa pine, mixed conifer,

anddrymeadowandthenfireline intensitywascalculated.

Figure 15—Portion of a Fire Behavior Forecast prepared by a Fire Behavior Analyst on a wildfire. Expected fire 

behavior is plotted on the fire characteristics chart in Figure 16.
USDA Forest Service Gen. Tech. Rep. RMRS-GTR-253. 2011 19

The authors noted: “Calculation of fireline intensity for

specific areas of this fire demonstrates that two different

types offire can have the same resistance to control: a fire

spreading rapidly through fuels with low energy density,

and a fire spreading more slowly but through fuel with

higher energy densities.”

	 Figure 17 showsthe differentfireline intensitieswithin

the Black Tiger Fire. Area labels are shown on the associated fire characteristics chart in Figure 18.

3 Program Operation_____________

3.1 Overview

	 TheFireCharacteristicsChartprogramis a stand-alone

program that provides a means for plotting fire behavior

valuesthat areobtainedelsewhere.BehavePlusor another

program can be used to calculate values, or fire behavior

values can be obtained from the field observations.

Figure 16—Fire characteristics chart illustrating expected fire behavior from the 

Fire Behavior Forecast in Figure 15.
20 USDA Forest Service Gen. Tech. Rep. RMRS-GTR-253. 2011

Figure 17—From NFPA (1990), Black Tiger Fire. Relative fireline intensity by area. These areas are referenced in 

Figure 18.

	 The charts are based on mathematical relationships

among four variables: Rate of spread (ROS), heat per

unit area (HPUA), flame length (FL), and fireline intensity (FLI). There are separate charts for surface and

crown fire behavior because of the different relationship

between fireline intensity and flame length for each (see

Modeling Foundation section).Aplotted point is defined

by two values, either ROS and HPUA or ROS and FL.

A toggle in the program lets you switch from one input

option to the other, and values are typed directly into the

worksheets.

	 Data and chart format settings can be saved for later

use. The program opens with default settings, but you

can open a saved file to use as a template. Chart default

settings can be restored without deleting the data, and

data can be deleted without altering chart settings.

	 The followingare amongmanyoptionsfor customizing

the chart:

	 •	 Graph limits can be changed.

	 •	 Colors on the chart can be shades of red, rainbow

colors, orshades of grey.Alternatively,flame length

lines can be drawn without color or shading.

	 •	 Images can be added to the surface fire chart or left

off. Custom images can be developed and used.

	 •	 Flame length values used to define curves can be

changed.

	 •	 Units can be changed.

	 •	 Font type and size on the chart can be changed.

	 •	 Point icons, labels, and the legend can be changed.

	 Although the program offers many optionsfor display,

it certainly will not meet all needs.Additional labels can
USDA Forest Service Gen. Tech. Rep. RMRS-GTR-253. 2011 21

Figure 18—From NFPA (1990), Black Tiger Fire, fire characteristics chart showing the character of the 

fire for locations shown in Figure 17.

be added to a basic chart using other software, as was

done for many of the Application section figures.

	 The following sections provide a detailed description

of program operation. This document is included as the

Help system for the program. Bookmarks help you find

the appropriate section to answer your question.

3.1.1 Installation

	 The Fire Characteristics Chart installation program

(FireChart.msi)canbedownloadedfromtheBehavePlus

website. Once you have saved the program, double-click

onFireChart.msitoinstallthe executable andassociated

files.The FireCharacteristicsChart operates on computers running Microsoft® Windows 2000, XP, Vista, or

Windows 7. You will be prompted to save the program

to the location of your choice. The program will default

to the folder C:/BehavePlus/FireChart. You can save

the program files anywhere on your computer by

simply changing the location at the prompt. However,

we recommend that you not save the program to the

folder C:/Program Filessince administrative privileges

associatedwith thisfoldermay affect programoperation.
22 USDA Forest Service Gen. Tech. Rep. RMRS-GTR-253. 2011

3.1.2 Opening and Closing the Program

	 Each time you open the program, it opens the surface

fire chart with default settings (Figure 19). You can then

open a saved file with the settings that you prefer to use

as a template. The command File > Exit allows the user

to exit the program; however, any data and settings that

are not saved will be lost. For more information on saving data and settings, see Section 3.4.1.

3.1.3 The Fire Characteristics Chart Window

	 The header shows the program name and version

number. Beneath the header are three menu items: File,

Options, and Help (described in Section 3.1.6). The

left-hand side of the program window is the worksheet;

the right-hand side is the chart (Figure 19). You change

between the Surface Fire Behavior and Crown Fire Behavior worksheets by clicking on the appropriate tab.

3.1.4 Worksheet

	 The worksheet is the form in which data are entered.

There are separate worksheetsforsurface and crown fire

behavior, identified by separate tabs. Each worksheet

contains three sections: Caption Lines, the Data Table,

andGraphDefinitions(Figure20).The surface andcrown

fire behavior worksheets are similar, with differences in

units selection. Also, the crown fire behavior worksheet

does not offer images for curve labels.

3.1.5 Docking and Undocking the Worksheet

Increase graph size by removing the worksheet from

the program window, clicking anywhere on the Double

click to dock/undock menu bar (Figure 21). This option

allows the user to move the worksheet to a different area

on the computer monitor, thereby enlarging the graph.

To re-attach the worksheet, simply double-click on it; it

Figure 19—The Fire Characteristics Chart window contains both Surface Fire Behavior and Crown Fire Behavior worksheets 

(left-hand side) and a chart (right-hand side).
USDA Forest Service Gen. Tech. Rep. RMRS-GTR-253. 2011 23

Figure 20—The Fire Characteristics Chart worksheet is divided into three sections: Caption Lines, 

Data Table, and Graph Definitions.

Figure 21—The worksheet can be removed from the graph by double-clicking anywhere 

on the Double click to dock/undock menu bar or on the icon circled in red. Double-click on 

the worksheet again to return it to the program window.
24 USDA Forest Service Gen. Tech. Rep. RMRS-GTR-253. 2011

will always attach to the left-hand side of the program

window. If the worksheet is detached when the program

is closed, the worksheet will return to the left-hand side

of the program window when it is re-opened.

3.1.6 Menu Items

Themainmenu items areFile,Options, andHelp.These

itemswillguideyoutorelevant operationswithintheFire

Characteristics Chart. File offers a means of opening,

saving, and printing files(Figure 22).Filesthat have been

previously saved can be accessed using the command

Open Fire Characteristics Chart data (.fcd) file. The

program is closed using the File > Exit command.

	 Files can be saved in three ways:

•	 All data and settings(Save data and settingsto .fcd

file)

•	 The chart itself (Save image file...)

•	 The worksheet, including all of the data (Save data

as HTML...)

	 In addition, the program allows you to print just the

chart (Print Chart) or the entire window, including

both the worksheet and the chart(PrintWindow). Printing options can be modified using the Page setup...

command.

	 The Options menu (Figure 23) provides access to the

Graph options..., where you can modify chart settings.

To restore the chart to the program default settings without deleting data, select Restore settings to default....

To clear the worksheet and return worksheet settings

to default without changing the chart, choose Clear

data.... To clear everything, select both options or exit

the program and re-open it.

	 The Help menu (Figure 24) gives information about

the program and links to this report.

Figure 22—The File menu offers a means of opening, 

saving, and printing files.

3.2 Chart Format

	 Options for defining chart format are found on the

Graph Definitions portion of the worksheet (Figure 20)

and under Options > Graph options... (Figure 25). In

theworksheet’sGraphDefinitionssection, youcanselect

data units, the graph scale, and tick mark intervals, as

well as define flame length curves. Graph options...

allows you to show/hide gridlines, choose colors, or use

and format the legend. Changes affect only the graph

in the active tab (Surface Fire Behavior or Crown Fire

Behavior). All of the chart format options described in

this section are reset to default settings for the active tab

using Options > Restore settings to default....

3.2.1 Units

	 Both English and metric units are available and are

set in the Graph Definitions section of both worksheets

using drop-down menus beside ROS units and HPUA

units. Surface fire English units are: ROS—ch/h, ft/min,

or mi/h; HPUA—Btu/ft2; and FL—feet. Metric units

are: ROS—km/h, m/s, or m/min; HPUA—kJ/m2; and

FL—meters.

	 There are fewer unit selections for the Crown Fire

Behaviorworksheet, buttheworksheet behavesthe same

way.Crown fireROS is expressed as eithermi/h or km/h;

HPUA is either Btu/ft2or kJ/m2; and FL is either feet or

meters.

Figure 23—The Options menu provides access to graph 

options and settings.

Figure 24—The Help menu gives information about 

the program and opens this report.
USDA Forest Service Gen. Tech. Rep. RMRS-GTR-253. 2011 25

	 When the userswitchesfromEnglish tometric units(or

vice versa), the graph updates automatically, converting

all valuesfor ROS, HPUA, and FLto metric values. This

switch also applies to the maximum values on the graph.

If the user changes units within a given measurement

system, the units and settings of the other axis and the

curves may or may not change, depending upon the units

selected. For example, changing from ch/h to ft/min will

not change the maximum Y-Axis value, while changing

from ch/h to mi/h will change it.

3.2.2 Graph Scale and Tick Marks

	 Graph scales are modified by setting the maximum

values; minimum values are always zero. The Y-Axis

represents the ROS, and the maximum value can be

changed by typing a number into the Y-Axis max box.

The upper limit for the Surface Fire Behavior Y-Axis

Figure 25—The Graph Options window controls the look 

of the chart.

(ROS) is 500 ch/h. The upper limit for the Crown Fire

Behavior Y-Axisis 20 mi/h. If you type in a larger value,

the program will automatically reset it to the upper limit.

Similarly,theX-Axis(HPUA)maximumcanbe changed.

The upper limit for the Surface Fire Behavior X-Axis is

5000Btu/ft2.TheupperlimitfortheCrownFireBehavior

X-Axis is 10,000 Btu/ft2.

	 The program will automatically estimate a tick mark

interval, which, in most cases, is appropriate. The tick

mark intervals can be changed by typing a new tick mark

interval in theMajor tick interval box on the worksheet.

If you reset the graph scale, the program will estimate

a new tick mark interval. Gridlines can be removed by

unchecking the Show grid on graph box in the Graph

Options menu (Section 3.2.6).

3.2.3 Flame Length Curves

	 As many asseven flame length curves are available on

both the Surface and Crown Fire Behavior charts. Each

curve can be denoted by a change in color on the graph.

The colorway can be changed using the Curve shading

options in the Graph Options menu. Values for flame

length curves must appear sequentially from smallest to

largest for the program to draw curves correctly. If they

are entered in a different order, the program will sort

them automatically. Curves with a flame length of zero

will be moved to the end of the list automatically and

will not appear on the graph. A change from English to

metric units may result in valuesthat need to be changed

to more reasonable, rounded values.

	 The default Surface Fire Behavior chartsetup contains

four curves with FL of 4, 8, 11, and 15 ft. These curves

can be interpreted as ranging from fires that can easily

be controlled by hand crews, to fires for which tractors

or bulldozers are required, to fires on which control efforts at the head of the fire will be ineffective (Table 1;

Andrews and Rothermel 1982). The images provide a

roughgraphicalindicationofthe intensityofthe fire (Section 3.2.4). Icons are associated with the curve number,

not the flame length value, and it is your responsibility to

ensure that the icons are correct when modifying flame

length curve values.

	 The default Crown Fire Behavior chart setup contains

seven curves with FL values of 20, 50, 100, 150, 200,

250, and 300 ft. Icons are not available for the crown fire

chart.

3.2.4 Flame Length Images

	 Images related to the Surface Fire Behavior worksheet flame length curves are located in a folder titled

ChartImagesin the program folder (Figure 26) and can
26 USDA Forest Service Gen. Tech. Rep. RMRS-GTR-253. 2011

be shown by placing a checkmark in the Show Image?

box next to the image. The images can be changed by

using the Change image button next to each curve. We

have created a series of default images for the surface

fire behavior curves (Table 1), and we have included

two additional images of a standing firefighter carrying

a shovel(representing, perhaps, FL<1 ft) and of a tractor.

	 You can easily develop your own images. The images

used in this program are black and white X Pixmap

files. Custom images can be created using any graphics

software. Your image should be saved in bitmap (.bmp)

format and then converted to X Pixmap (.xpm) files using a converter program. We recommend that you store

your images in the ChartImages folder located in the

program folder. However, if you have saved a custom

image elsewhere, you can easily navigate to it.

3.2.5 Graph Options

	 Manyofthegraph’s appearance settings aremadeusing

the Options > Graph options... window (Figure 25).

Gridlines can be added to the graph, and changes can

be made to curve shading, the legend, and graph fonts.

Clicking on the Apply button will apply your changesto

the graph without closing the Graph Options window.

You can undo applied changes using the Undo button.

Cancel will close the window without making any

changes that have not yet been applied. Click on OK to

apply changes and close the Graph Options window. If

a file is opened that contains different graph optionsthan

those currently selected, the settings associated with the

file will override the current graph options. Files can be

saved and used as templates (3.4.1).

Figure 26—Flame length curve images are stored in the ChartImages folder.

3.2.6 Grid

	 Gridlines for both the X- and Y-Axes are visible by

default. They can be removed (turned off) by removing

the checkmark next to Show grid on graph in the

Graph Options window (Figure 25). The tick mark

interval is specified on the worksheet. This interval will

be calculated automatically, but it can easily be changed

(Section 3.2.2).

3.2.7 Graph Color

	 Select the graph’s colorway by selecting the FLcurve

shading options (Figure 25). These options include:

None (black lines on a white background), Greyscale,

Green-Blue-Yellow-Orange-Red, or Shades of PinkRed (default).Colors are associatedwith curve numbers,

not flame length values.

3.2.8 Legend

	 A legend is available for identifying points on the

graph. Within the legend, there are optionsto show point

labels and/or the legend description.This may be helpful

when the same point icon is used for more than one point

(Sections 3.3.5 and 3.3.6).

	 Theplacementandformatofthelegendcanbechangedin

Options > Graph Options.... The legend is placed inside

the graph, either at the center(Top center) orin the upper

right-hand corner (Upper right). You can also remove

the legend by selecting No legend. At times, the legend

may hide plotted data points.Ifthisis a problem, you can

change the axis scales to reveal the data point, remove

the legend, or add a legend later using other software.
USDA Forest Service Gen. Tech. Rep. RMRS-GTR-253. 2011 27

3.2.9 Font

	 Graph fonts can be changed using Options > Graph

Options > Graph label font. There are three available

fonts: Arial, Helvetica, and Times New Roman, which

can be selected using radio dial buttons(Figure 25). Font

size may be an issue in crowded graphs,so there are five

optionsthatrange fromVerySmalltoVeryLarge,which

can be selected using a drop-downmenu.The defaultfont

is Arial, and the default font size is Large. Changes to

the graph font will affect all text on the graph, including

axis labels, point labels, and the legend.

3.2.10 Restore Settings to Default

	 To startoverwhencustomizingthegraphformat,select

Options > Restore settings to default... (Figure 27).

This action will revert to the default graph settings on

the active tab for both the graph definition portion of

the worksheet (Figure 20) and the Options > Graph

options... window (Figure 25). Data are not deleted.

However, if metric units are used, the data will be converted to the default English units (Section 3.2.1).

3.3 Entering Data

	 In the following sections, we describe worksheet data

entry (Figure 28). This includes not just the data values

but all entries on the worksheet. All entries described in

this section are cleared for the active tab using Options

> Cleardata.Clearing the data does not change the chart

settings (Section 3.2.10).

3.3.1 Caption Lines

	 AsmanyasthreeCaptionlinescanbeaddedtothegraph

for clarity (Figure 20). Caption line 1 is automatically

generated to properly identify the graph as SURFACE

FIRE BEHAVIOR or CROWN FIRE BEHAVIOR.

The second and third caption lines are optional and can

be customized to provide more detailed information

about the graph. For example, Caption line 2 could be

“Burn Plan X” or the name of the fire. Caption line 3

may providemore specific information aboutthe project,

such as the date the worksheet was created or the date of

the fire. Caption lines are limited to 50 characters.

3.3.2 Data Points

	 Before entering any data values, it is important to

decide whether you will be entering ROS and HPUA or

ROS and FL. Use the toggle button to ensure the correct

variable (HPUA or FL) is active. Make certain that the

Figure 27—Selecting Options > Restore settings 

to default... will set the graph options to the default 

values.

Figure 28—The third column of the Data Table of the worksheet toggles between (a) Heat per Unit Area, HPUA, and (b) Flame 

Length, FL.
28 USDA Forest Service Gen. Tech. Rep. RMRS-GTR-253. 2011

units in the Graph Definitions section of the worksheet

(Figure 20) are correctly set. Remember, a change in

units after data entry will change data values.

	 The ROS is entered in column 2, while HPUA and FL

share the third column. Toggling on the box at the top of

column 3 will switch between the two variables. Values

for ROS and either HPUA or FL must be entered. The

other term will be calculated as described in the Modeling Foundation section. The program will not check

for illogical values for ROS, HPUA, or FL. It is your

responsibility to ensure that the values entered on the

graph make sense.

	 If you enter a value for either HPUA or FL and toggle

back and forth between the two variables several times,

the values may “drift” because of round-off issues in the

calculations.However, enteringvaluesonce andtoggling

to the other variable should not cause a problem. Zero

is a valid input for all three variables and will appear on

the graph and in the legend if the Graph Data? box is

checked (Section 3.3.3). Entering values outside the plot

scale limits (Section 3.2.2) is possible, but the values

will not appear on the graph. If a point label or legend

description has been entered for that value, however, the

point will appear in the legend.

3.3.3 Graph Data

	 If the box in the Graph Data? column is checked, a

point corresponding to the data in thatrow will be plotted

on the graph and create a line in the legend. If the Graph

Data? box is not checked, the data are ignored. However,

these datawill be saved in both FireCharacteristicsChart

data files(Section 3.4.1) and HTMLfiles(Section 3.4.4).

3.3.4 Point Icons

	 The icon and color for the plotted point

areselectedfromdrop-downmenusforIcon

and Color. There are 10 possible icons in

column6thatthat canbeusedtodistinguish

among data points and 10 possible colors

to select in column 7 (Figure 29).

3.3.5 Point Label

	 Up to six characters can be entered in the

Point Label column to label a point on the

chart. If you leave it blank, the point will

appear on the graph, but there will be no

label marking the point, and the point will not appear

in the legend unless there is a Legend Description. By

default, the label will appear both on the graph and in

the legend. The user can change the legend settings if

desired (Section 3.2.8). At times, point labels may appear above the chart, interfering with the chart title. To

fix this, simply increase the Y-Axis maximum value.

3.3.6 Legend Description

	 A longer description can be entered for each point in

theoptionalLegendDescriptioncolumn,providingmore

information for the legend (Figure 30). By default, it appears at the end of the legend, although legend settings

can be changed if desired (Section 3.2.8). The Legend

Description can be 35 characters in length.

3.3.7 Clear Data

	 ThemenuitemOptions>Cleardataclears everything

in theworksheet data table (Figures 20 and 31),including

thedatavalues, pointlabels,legenddescription, andicon/

color selections. It will not, however, affect the graph

settings (Section 3.2.10). This command applies only to

data in the current tab.

3.4 Saved Files

	 The program opens with the default graph settings and

a blank worksheet. Data and graph format settings can

be saved to a file for later use. Data values and the graph

can be saved separately for documentation purposes.The

default location forsaving all filesisthe program folder,

but files can be saved in any location on your computer.

Figure 29—There are 10 possible point icons and colors for use in the Fire 

Characteristics Chart program.
USDA Forest Service Gen. Tech. Rep. RMRS-GTR-253. 2011 29

Figure 30—The Point Label and Legend Description from the data table are 

used to identify the points in the graph and/or the legend.
30 USDA Forest Service Gen. Tech. Rep. RMRS-GTR-253. 2011

Figure 32—A worksheet can be saved as an HTML file for documenting the data 

used in creating the fire characteristics chart. 

3.4.1 Saving a Fire Characteristics Chart File

	 Data and settings can be saved to a Fire Characteristics Chart data file (.fcd) by selecting File > Save data

and settings to .fcd file (Figure 22). These files contain

both data values and graph settings for a given chart and

can only be used within the Fire Characteristics Chart

program. You may wish to clear the data and save the

file as a template of personal preferences to use in place

of default settings. Data and settings are

saved only for the active worksheet; if

there are data in both tabs, they must be

saved separately.

3.4.2 Opening a Fire 

Characteristics Chart File

	 The File > Open Fire Characteristics

Chart data (.fcd) file command is used

to open a Fire Characteristics Chart file

that was previously saved. The Surface

Fire Behavior and Crown Fire Behavior

worksheets operate independently, but

the program will ensure the correct tab is

active when a file is opened.

3.4.3 Save Image File

	 Graphs can be saved as images in the

followingformats:JPEG(.jpg),Windows

bitmap (.bmp), and Portable Network

Graphics (.png). Once the graph is complete, click on File > Save image file...,

select the desired location and file format,

and save the graph. The resulting image

can be easily used in documentation or

can be edited using other software.

3.4.4 Saving Data as HTML

	 When you print a chart or save it as an image, you

should document the information needed to reproduce it,

including data values represented on the chart. To assist

in documentation, the worksheet can be exported as an

HTML file that contains all of the data points, including

those that do not appear on the screen (Figure 32). This

file can be included in reports with the chart so that others can recreate your chart if desired.

3.5 Printing

	 The Fire Characteristics Chart can be printed using the

File > Print command (Figure 22). The program will

send the graph to the selected printer. Only the graph

can be printed, not the worksheet. It is a good idea to

use caption lines (Section 3.3.1) to clearly describe the

graph.

	 Use the File > Page setup...command to modify print

settingsfortheprogram(Figure33).Selectthepapersize,

source, orientation (either Portrait or Landscape), and

Figure 31—Selecting Options > Clear data... will 

delete all data in the active worksheet.
USDA Forest Service Gen. Tech. Rep. RMRS-GTR-253. 2011 31

program. Printer settings are only valid for the current

session of the Fire Characteristics Chart.

3.6 Adding Custom Labels

	 The Fire Characteristics Chart program will not meet

all user needs.In particular, users may want to emphasize

certain portions of the graph (e.g., Figure 30) by adding

custom labels. To add custom labels, you should make a

screen capture of the chart or save it as an image file and

use other software to add additional lines, circles, or text

to the graph.

3.7 Help

	 The Help button on the Menu Bar (Help > About this

program...) provides information about the program,

including the version number (Figure 34) and contact

information for the developers.

	 Clicking onHelp >Help opensthis document.You can

navigate to the section of interest using the bookmarks.

4 Modeling Foundation ___________

	 In this section, we describe the relationship among the

variables used to produce the fire characteristics charts

described in this paper. A person whose application is

not satisfied by the options offered in our program can

use these equations to develop their own chart. We do

not provide complete details of the calculation of values

plotted on the chart (ROS, HPUA, FL, FLI) since points

plotted on the chart are calculated elsewhere.

Figure 33—The Page Setup option window allows the 

user to define page margins and orientation for the current 

session. 

Figure 34—Information about this program can be found in the Help > About this 

program... box.

printer margins to customize print settings. The default

printer margins are set by your printer. The printer can

be identified (File > Page Setup > Printer...) before

clicking OK to save the selections. Selecting Cancel

will cancel the current selections and return to the main
32 USDA Forest Service Gen. Tech. Rep. RMRS-GTR-253. 2011

4.1 Surface Fire Behavior

	 Themathematical basisforthe surface fire characteristics chartincludesRothermel’s(1972)surface fire spread

model,Byram’s(1959)fireline intensityandflame length

models, Anderson’s (1969) residence time model, and

the linkages among them. These models address only

the flaming front of the surface fire, which is influenced

primarily by fine fuels. The surface fire model describes

fire spreading through fuels that include litter, grass,

brush, and other dead and live vegetation within about 6

ft of the ground. It does not include organic ground fuel

(duff) or large fuel that burns after the flaming front has

passed.

	 Surface fire rate of spread is calculated using Rothermel’s model from a description of the fuel (often a fuel

model), fuel moisture, wind speed, and slope. Heat per

unit area is available from intermediate calculations in

the spreadmodel.Byram’sfireline intensity is calculated

from rate of spread and heat per unit area, forming the

basis for the fire characteristics chart.

IB = HAR	 (1)

where

	 IB = Byram’s fireline intensity (Btu/ft/s),

	 HA = heat per unit area (Btu/ ft2

), and

	 R = rate of spread (ft/s).

	 Changing units to match those used for the fire characteristic charts in Andrews and Rothermel (1982) and

rearranging equation (1) to plot the curves for specified

values of fireline intensity gives:

R = 55 IB / HA	 (2)

where

	 R = rate of spread (ch/h),

	 IB = Byram’s fireline intensity (Btu/ft/s), and

	 HA = heat per unit area (Btu/ ft2

).

	 Flame length is calculated from fireline intensity, according to Byram’s (1959) equation.

FB = 0.45 IB

0.46	 (3)

where

	 FB = Byram’s flame length (ft) and

	 IB = Byram’s fireline intensity (Btu/ft/s).

	 Byram(1959) presented hismodelforfireline intensity

as:

IB = Hw R	 (4)

where

IB = Byram’s fireline intensity (Btu/ft/s),

	 H = heat yield (Btu/lb of fuel),

	 w = weight of the available fuel (lb/ft2

), and

	 R = rate of spread (ft/s).

	 Heat per unit area (HA) is used to estimate Hw, leading to equation (1). Heat per unit area is the heat energy

release per unit area within the flaming front. “Available

fuel,” therefore, includes only the fuel that burns in the

flaming front and not the total fuel consumed.

	 Heat per unit area is derived from Rothermel’s model.

Reaction intensity is the rate of energy release per unit

area within the flaming front and is an intermediate value

in Rothermel’s calculation of rate of spread. Heat per

unit area is reaction intensity multiplied by the flame

residence time, such that

HA = IR tr	 (5)

where

	 HA = heat per unit area (Btu/ft2

),

	 IR = reaction intensity (Btu/ft2

/min), and

	 tr = residence time (min).

	 Residence time is the length of time that it takes the

fire front to pass a given point. It does not include the

indefinite trailingedgeofthe fire.Anderson (1969)found

that a good approximation of the flaming time of fuel

particles burning in a uniformfuel array can be calculated

from fuel particle size.

tr = 8 d	 (6)

where

	 tr = residence time (min) and

	 d = fuel particle diameter (inches).

	 Rothermel’s surface fire spread model uses surfacearea-to-volume ratio as a measure of fuel particle size.

The relationship to diameter is:

d = 48 / σ (7)

where

	 d = fuel particle diameter (inches) and

	 σ=surface-area-to-volume ratio(inches2

/inches3).

	 Substituting equation (7) into equation (6) gives:

tr = 384 / σ (8)

	 Heat per unit area can then be calculated from factors

available in the calculation of rate of spread using

Rothermel’s (1972) model.

HA = 384 IR / σ (9)
USDA Forest Service Gen. Tech. Rep. RMRS-GTR-253. 2011 33

4.2 Crown Fire Behavior

Rothermel (1991) provided methods for predicting

the spread rate, intensity, and size of crown fires. He

developed a model for crown fire rate of spread based

on his surface fire spread model (Rothermel 1972). He

usedByram’s(1959)modelforfireline intensity,Thomas’

(1963) model for flame length, and Albini’s (1976a)

burnout model in estimating surface heat per unit area.

He presented a crown fire characteristics chart to display

observed and modeled crown fire behavior.

	 Byram’s model for fireline intensity,stated in terms of

heat per unit area and rate of spread, is used as the basis

for the crown fire characteristics chart as well as for the

surface fire chart (equation 1).

	 Rothermel (1991) presented a simple model for crown

fire rate of spread. He developed a correlation between

observed crown fire rate ofspread and a calculated value

using hissurface fire spread model. Observed crown fire

spread rate was determined using spread distance and

elapsed time forseven crown fires.The length oftime for

the crownfire runsinRothermel’sstudyrangedfrom0.83

to 5 hours, over which time conditions certainly varied

significantly, with fire spread being strongly influenced

by spotting.

	 The model for average crown fire spread rate issimply

3.34 times the spread rate calculated for a surface fire

in fuel model 10 with a midflame wind speed equal to

0.4 of the 20-ft wind speed. Crown fire spread rate is

calculated in BehavePlus from 20-ft wind speed and the

moisture content of the dead and live surface fuels (the

same moisture values used in the surface fire spread

model).The crownfire spreadratemodeldoesnotinclude

a description of either the surface or the crown fuel.

	 While Byram’s flame length model is used for surface

fire (equation 3), it underpredicts the flame length of

crown fires. Rothermel (1991) used Thomas’ (1963)

model because it produces flame lengths that “appear to

be reasonable except at low intensity; no exact values

for such a phenomenon can be fixed, but the numbers

serve as useful guides to the intensity of the fire.”

	 Crown fire flame length is calculated from fireline

intensity, according to Thomas (1963), as:

FT = 0.2 IB

2/3	 (10)

where

	 FT = Thomas’ flame length (ft) and

	 IB = Byram’s fireline intensity (Btu/ft/s).

	 Calculation of heat per unit area for crown fire requires

estimationoftheproportionofthe fuel contributingto the

development of the convection column. This includes

both the surface fuel and canopy (overstory)fuel loads.

	 Crown fire heat per unit area is the sum of surface fire

heat per unit area and canopy heat per unit area.

	 HA,crown = HA,surface + HA,canopy	 (11)

where

	 HA,crown = heat per unit area of the crown fire,

	 HA,surface = heat per unit area contributed by the

surface fuel, and

	 HA,canopy= heat per unit area contributed by the

overstory canopy.

	 Surface fire heat per unit area can be calculated in

BehavePlus using Rothermel’s surface fire model, as

described in Section 4.1, based on the fine fuelsthat carry

the fire at the fire front. There is, however, an important

contribution to fire intensity by accumulations of larger

sizes of dead and downed fuel. Rothermel (1991) used

Albini’s (1976a) burnout model to estimate an alternate

value for several of the standard fuel models, including

two with additional heavy fuel. BehavePlus allows userspecified valuesforsurface heat per unit area, which can

be selected fromthose calculated byRothermel(Table 4).

	 Rothermel assumed the contribution of canopy fuel

to be the total energy release to be produced by the consumption of the conifer needles, assuming heat from the

needlesis 8000Btu/lb (18,622 kJ/kg) of dry needles.The

canopy contribution is:

HA,canopy = Hw	 (12)

where

HA,canopy = heat per unit area of the canopy fuel

(Btu/ft2

),

	 H = heat content (Btu/lb), and

	 w = crown load (lb/ft2

).

	 InBehavePlus, crown load is estimated bymultiplying

canopy bulk density by the difference between canopy

height and canopy base height.

Table 4—Surface heat per unit area values calculated using 

Albini’s burnout model (from Rothermel 1991). 

Fuel model

Additional 1000-h 

fuel,

tons/ac

Heat per 

unit area,

Btu/ft2

8 580

2 760

9 1050

9 30 1325

10 1325

10 30 1570

12 3430
34 USDA Forest Service Gen. Tech. Rep. RMRS-GTR-253. 2011

4.3 Surface and Crown Fire Flame 

Length and Fireline Intensity

	 While both the surface and crown fire characteristics

charts are based on the relationship of fireline intensity

to rate ofspread and heat per unit area, they use different

models to calculate flame length from fireline intensity.

Figure 35 shows a plot of Byram’s flame length (equation 3, used for surface fire) and Thomas’ flame length

(equation 10, used for crown fire) as a function offireline

intensity. Note the significant difference.

	 Afire characteristics chartwithcurvesbasedonfireline

intensity and that is labeled with surface and crown fire

flame lengths illustrates the issue of misinterpretation

of the chart (Figure 36). A comparison of the surface

and crown fire charts with the same flame length curves

shows the difference between the flame length models

(Figure 37).

	 Table5showsfireline intensityassociatedwithselected

surface flame length based on Byram (1959) for English

andmetricunits.Similarly,Table6showsthe relationship

between crown fire flame length and fireline intensity

based on Thomas (1963). Note that surface fire flame

length of 20 ft is associated with fireline intensity of

3821 Btu/ft/s, while a crown fire flame length of 20 ft is

associated with fireline intensity of 1000 Btu/ft/s. Given

that the curves on the fire characteristics charts produced

by our program are labeled with flame length, Tables 5

and 6 can be used as quick references for conversion to

fireline intensity.

4.4 Other Forms of the Fire 

Characteristics Chart

	 In this report, we described surface and crown fire

characteristics charts along with the mathematical relationships that form the basis for these charts. In this

section, we provide a brief review of other forms of the

fire characteristics chart. Each version of the chart depends onmathematicalrelationships among themodeled

variables and its intended use.

	 Rothermel and Anderson (1966) presented results of

laboratory experiments that led to development of the

Rothermel (1972) surface fire spread model. They plotted data on what they called a fire characteristics chart,

which related rate of spread and equivalent unit energy

release rate, later called reaction intensity.

Figure 35—Flame length as a function of fireline intensity using Byram (1959) for surface 

fire and Thomas (1963) for crown fire.
USDA Forest Service Gen. Tech. Rep. RMRS-GTR-253. 2011 35

Figure 36—Fire characteristics chart with fireline intensity curves. The associated 

surface and crown fire flame lengths are given for each curve. To avoid potential 

misinterpretation, we do not offer this option in our program.

Figure 37—Comparison of the surface and crown fire characteristics charts with the same flame length curves. The difference is 

due to the difference in flame length equations.
36 USDA Forest Service Gen. Tech. Rep. RMRS-GTR-253. 2011

Table 6—Relationship between selected values of crown fire flame length (Thomas 1963) 

and fireline intensity for English and metric units. (FLI values are rounded.) 

Crown 

flame length,

ft

Fireline intensity, 

Btu/ft/s

20 1000

30 1840

40 2830

50 3950

75 7260

100 11,200

125 15,600

150 20,500

175 25,900

200 31,600

225 37,700

250 44,200

275 51,000

300 58,100

Table 5—Relationship between selected values of surface fire flame length (Byram 

1959) and fireline intensity for English and metric units.

Surface 

flame length,

ft

Fireline intensity, 

Btu/ft/s

1 6

2 26

3 62

4 116

5 188

6 279

7 390

8 521

9 673

10 847

11 1042

13 1498

15 2045

20 3821

Surface

flame length,

m

Fireline intensity, 

kJ/m/s 

0.5 1

1.0 6

1.5 14

2.0 26

2.5 42

3.0 62

3.5 86

4.0 116

4.5 149

5.0 188

5.5 231

6.0 279

Crown 

flame length,

m

Fireline intensity, 

kJ/m/s 

5 2570

10 7280

15 13,400

20 20,600

25 29,800

30 37,800

40 58,200

50 81,400

60 107,000

70 135,000

80 165,000

90 197,000

100 230,000
USDA Forest Service Gen. Tech. Rep. RMRS-GTR-253. 2011 37

	 Nomograms (or nomographs) are a graphical means

of calculating fire behavior. The upper right quadrant of

somenomogramsisbasedonthe same relationships asthe

fire characteristics chart.Theoriginalnomograms(Albini

1976b) graphed rate of spread versus reaction intensity,

with flame length curves. Those nomograms were later

reproducedinRothermel(1983),withtheX-axisrescaled

to be heat per unit area to facilitate obtaining values to

plot on a fire characteristics chart. Rothermel’s (1991)

crown fire nomogramsinclude a similar plot, with flame

length curves also labeled with values for unit power of

the fire (which is compared to unit power of the wind).

Nomographs developed by Scott (2007) do not produce

intermediate values such as heat per unit area, so they

do not include a fire characteristics chart graph.

	 Andrews and Rothermel (1982) provided fire characteristics charts in a form suitable for copying. The fire

behavior chartwas producedwith two scales, one labeled

“Scale forHeavyFuels”withhigherheatperunit area and

lower rate of spread. Neither version covered the entire

range of possible values. To overcome that limitation,

they also provided a form of the chart that used logarithmic scales on the axes. They cautioned that “Because

a primary purpose of the fire characteristics chart is to

visually illustrate changes in fire behavior, care should

be taken in interpretation of relative location of points

plotted on the logarithmic chart.” Given the difficulty in

interpreting plotted values using a logarithmic scale and

the fact that the program allows the scale to be set to a

wide range of possible values, this option is not offered

in our program.

	 The FARSITE programuses a fire characteristics chart

to display fire front characteristics during a simulation of

fire growth (Finney 1998). For each time step,surface or

crown fire rate ofspread and heat per unit area are plotted

for each pixel. The curves on the chart are labeled with

Byram’s flame length values regardless of fire type. The

changing cloud of points provides a general representation of changes in fire behavior with space and time.

	 Cruz and others (2008) plotted observed head fire

rate of spread and fuel consumed in relation to type of

fire (surface or crown) and six levels of Byram’s (1959)

fireline intensity, assuming a constant heat of combustion. This relationship is based on calculation of fireline

intensity from total fuel consumed rather than the fuel

consumed in the flaming front.

	 The Canadian system of fire danger rating has been

used to produce “fire intensity class graphs.” Head fireline intensity for a Canadian Fire Behavior Prediction

(FBP) System fuel type is based on the Initial Spread

Index (ISI) and Buildup Index (BUI) components of the

Canadian Forest FireWeatherIndex (FWI) System (e.g.,

Alexander andCole1995;Cole andAlexander1995).The

relationships require that a separate graph be produced

for each FBP System fuel type.

	 A fire characteristics chart was developed for the U.S.

National Fire Danger Rating System (NFDRS) based on

the relationship among SpreadComponent(SC), Energy

Release Component (ERC), and Burning Index (BI)

(Andrews and Rothermel 1982). BI is a function of SC

and ERC, allowing BI curves to be plotted on a chart.

The program described in this paper will be expanded

to include the option of plotting U.S. NFDRS indices.

5 References ___________________

Albini, Frank A. 1976a. Computer-based models of wildland fire

behavior: a user’s manual. Gen. Tech. Rep. Ogden, UT: U.S.

Department of Agriculture, Forest Service, Intermountain Forest

and Range Experiment Station. 68 p.

Albini, Frank A. 1976b. Estimating wildfire behavior and effects.

Gen. Tech. Rep. INT-30. Ogden, UT: U.S. Department ofAgriculture, Forest Service, Intermountain Forest and Range Experiment

Station. 92 p.

Alexander, M. E.; Cole, F. V. 1995. Predicting and interpreting fire

intensitiesinAlaskan black spruce forests using the Canadian system of fire danger rating. In: Managing Forests to Meet People’s

Needs: Proceedings of 1994 Society of American Foresters/

Canadian Institute of Forestery Convention; 18-22 September,

1994; Anchorage, Alaska. 95-02. Bethesda, Maryland: Society of

American Foresters: 185-192.

Anderson, HalE. 1968. Sundance fire: an analysis offire phenomena.

Res. Pap. INT-56. Ogden, UT: U.S. Department of Agriculture,

Forest Service, Intermountain Forest and Range Experiment Station. 37 p.

Anderson, Hal E. 1969. Heat transfer and fire spread. Res. Pap. INT69. Ogden, UT: U.S. Department of Agriculture, Forest Service,

Intermountain Forest and Range Experiment Station. 20 p.

Anderson, Hal E. 1982. Aids to determining fuel models for estimating fire behavior. Gen. Tech. Rep. INT-122. Ogden, UT: U.S.

Department of Agriculture, Forest Service, Intermountain Forest

and Range Experiment Station. 22 p.

Andrews, Patricia L. 2007. BehavePlus fire modeling system: past,

present, and future. In: Proceedings of 7th Symposium on Fire and

Forest Meteorology; 2007 October 23-25; Bar Harbor, Maine: 13.

Andrews, Patricia L.; Bevins, Collin D.; Seli, Robert C. 2008. BehavePlus fire modeling system, version 4.0: User’s guide. Gen.

Tech. Rep. RMRS-GTR-106WWW [Revised]. Fort Collins, CO:

U.S. Department of Agriculture, Forest Service, Rocky Mountain

Research Station. 116 p.

Andrews, Patricia L.; Rothermel, Richard C. 1982. Charts for interpreting wildland fire behavior characteristics. Gen. Tech. Rep.

INT-131. Ogden, UT: U.S. Department of Agriculture, Forest

Service,IntermountainForest andRangeExperimentStation. 21 p.

Brown, A. A.; Davis, K. P. 1973. Fire Effects. In: Forest Fire Control

and Use, 2nd Edition. New York, NY: McGraw-Hill Book Co.,

Inc.: Chap. 3.

Byram, George M. 1959. Combustion of forest fuels. In: Davis, Kenneth P. Forest Fire Control and Use. New York, NY: McGraw-Hill

Book Co.: Chap. 3.
38 USDA Forest Service Gen. Tech. Rep. RMRS-GTR-253. 2011

Cole, F. V.; Alexander, M. E. 1995. Head fire intensity class graph

for FBP system fuel type C-2 (Boreal Spruce).Alaska Department

of Natural Resources, Division of Forestry, Fairbanks, AK, and

Canadian Forest Service, Northern Forestry Centre, Edmonton,

AB. Poster (with text).

Cruz, Miguel G.;Alexander, Martin E.; Fernandes, PauloA. M. 2008.

Development of a model system to predict wildfire behaviour in

pine plantations. Australian Forestry. 71(2): 113-121.

Finney, Mark A. 1998. FARSITE: Fire Area Simulator-model development and evaluation. Res. Pap. RMRS-RP-4. Ogden, UT:

U.S. Department of Agriculture, Forest Service, Rocky Mountain

Research Station. 47 p.

Hodgson,Athol. 1968.Control burning in eucalyptforestsinVictoria,

Australia. Journal of Forestry. 66(8): 601-605.

Hough, W. A. 1968. Fuel consumption and fire behavior of hazard

reduction burns.Res. Pap. SE-36.Asheville, NC: U.S. Department

of Agriculture, Forest Service, Southeastern Forest Experiment

Station. 7 p.

Kiil,A. D. 1975. Fire spread in a black spruce stand. Canadian Forest

Service Bi-Monthly Research Notes. 31(1): 2-3.

Kilgore,Bruce M.; Sando,RodneyW. 1975.Crown-fire potential in a

sequoiaforestafterprescribedburning.ForestScience.21(1):83-87.

Mann, Jim. 1974. [Personal Communication]. U.S. Department of

Agriculture, Forest Service, Region 3.

McArthur,A.G.1967.FirebehaviourinEucalyptforests.Leaflet 107.

Canberra, Australia: Commonwealth of Australia, Department of

National Development, Forest andTimberBureau,Canberra. 36 p.

Methven,IanR.;Murray,W.G.1974.Usingfiretoeliminateunderstory

balsamfirin pinemanagement.The ForestryChronicle. 50(2): 1-3.

National Fire Protection Association. 1990. Black Tiger Fire: Case

study of the wildland/urban interface fire that destroyed 44 homes

and otherstructures near Boulder, Colorado,July 9, 1989. Quincy,

MA: Fire Investigations Division, National Fire Protection Association. 40 p.

Rothermel, Richard C. 1972. A mathematical model for predicting

fire spread in wildland fuels. Res. Pap. INT-115. Ogden, UT: U.S.

Department of Agriculture, Forest Service, Intermountain Forest

and Range Experiment Station. 40 p.

Rothermel, Richard C. 1983. How to predict the spread and intensity

of forest and range fires. Gen. Tech. Rep. INT-143. Ogden, UT:

U.S. Department of Agriculture, Forest Service, Intermountain

Forest and Range Experiment Station. 161 p.

Rothermel,RichardC.1984.Firebehavior considerationof aerialignition. Workshop: Prescribed Fire by Aerial Ignition. Intermountain

Fire Council, Missoula, MT: 143-158.

Rothermel, Richard C. 1991. Predicting behavior and size of crown

firesin the northern Rocky Mountains. Res. Pap. INT-438. Ogden,

UT:U.S.Department ofAgriculture,ForestService,Intermountain

Research Station. 46 p.

Rothermel, Richard C. 2009. Use a crayon to model fire behavior.

Learning from the experts. Wildland Fire Lessons Learned Center,

Tucson, Arizona. Available: http://MyFireVideos.net.

Rothermel, Richard C.; Anderson, Hal E. 1966. Fire spread characteristics determined in the laboratory. Res. Pap. INT-30. Ogden,

UT:U.S.Department ofAgriculture,ForestService,Intermountain

Forest and Range Experiment Station. 34 p.

Rothermel, Richard C.; Deeming, John E. 1980. Measuring and interpreting fire behavior for correlation with fire effects. Gen. Tech.

Rep. INT-93. Ogden, UT: U.S. Department of Agriculture, Forest

Service, Intermountain Forest and Range Experiment Station. 4 p.

Roussopoulos, Peter J. 1974. Fire intensity levels. National Fuel

Management Workshop. 3 p.

Scott, Joe H. 2007. Nomographs for estimating surface fire behavior

characteristics.Gen.Tech.Rep.RMRS-GTR-192.FortCollins,CO:

U.S. Department of Agriculture, Forest Service, Rocky Mountain

Research Station. 119 p.

Scott, Joe H.; Burgan, Robert E. 2005. Standard fire behavior fuel

models: a comprehensive set for use with Rothermel’s surface fire

spread model. RMRS-GTR-153. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research

Station. 72 p.

Thomas,P.H. 1963.The size offlamesfromnaturalfires.In:Proceedings, 9th International Symposium on Combustion; 1962; Ithaca,

NY: Academic Press: 844-859.

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Interior [USDOI]. 2008. Interagency prescribed fire: planning

and implementation procedure guide. Boise, ID: NationalWildfire

Coordinating Group. 50 p.

Van Wagner, C. E. 1968. Fire behavior mechanisms in a red pine

plantation: field and laboratory evidence. Departmental Publication. No. 1229. Ottawa, Ontario, Canada: Canada Department of

Forestry and Rural Development, Forestry Branch. 30 p.

Van Wagner, C. E. 1975. Conditions and criteria for the spread of

crown fire. Draft. Unpublished copy, Canadian Forestry Service,

Petawawa Forest Experiment Station. 20 p.

Walker, J. D.; Stocks, B. J. 1972. Analysis of two 1971 wildfires in

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Canadian Forestry Service, Great Lakes Research Centre. 13 p.
USDA Forest Service Gen. Tech. Rep. RMRS-GTR-253. 2011 39

Appendix A. Fire Intensity Levels __________________________

Fire Intensity Levels

Initial Summary used at National Fuel Management Workshop (Roussopoulos 1974).*

Fireline Calculated

intensity flame length

(Btu/ft/s) (ft) Fire descriptions and control actions

Level I:

2-3 <1 Few fires exist at this low intensity. (Byram 1959)

Level II:

19-58 2-3 Most prescribed fires are backing into the wind in surface fuels. The 

depth of the flaming zone is less than 1 foot and the flame length is 

about 2 feet. (Brown and Davis 1973)

20-100 2-4 Prescribed backfires in slash-longleaf pine with palmetto-gallberry 

understory reduced surface fuels and did little damage to the overstory. 

Higher intensities resulted in stand damage, especially with low winds; 

rates of spread between 1.5 and 3 ft/min. (Hough 1968)

24 2 A test fire in a balsam fir understory with a tree height of 13 feet and a 

crown base height of 3 feet. The crown bulk density was moderate to 

light at 0.0087 lb/ft3

. The fire would not sustain crowning, only occasional torching. The surface fire is below the critical level. (Methven and 

Murray 1974)

27 2 The fire was in the surface fuels of a eucalypt forest with a fuel load of 

3.4 tons/acre of fuels less than 1

⁄

4 inch in diameter. The surface rate of 

spread is about 1.1 ft/min, and the flame length was about 12-15 inches. 

(McArthur 1967)

100 4 In eucalypt forests, this level of intensity generally represents the limit 

of control for manual ground attack. Flame lengths exceed 3 feet and 

the surface rate of spread is about 4 ft/min. This is the maximum prescribed intensity for controlled burning activities. (Hodgson 1968)

Level III:

100-1000 4-11 Prescribed and wildfires are burning with the wind in surface fuels. 

Most fires are controlled by direct attack with conventional firefighting 

methods and are considered to be two-dimensional fires. At the upper 

end of the range, flame lengths will be about 9 feet and heat from fire 

will be intense at a distance of 30-40 feet from fire. (Brown and Davis 

1973)

112 4 Fire was in the surface fuels of a eucalypt forest. The fuel load was 

6.5 tons/acre fuels for fuels less than 1⁄4 inch in diameter. The surface 

rate of spread was 2.4 ft/min. Flame lengths were as much as 5 feet but 

averaged 3-4 feet. (McArthur 1967)

210 5 This was a prescribed fire under a three-storied sequoia-mixed conifer 

stand: white fir saplings (10-50 feet), ponderosa pine/incense cedar 

(100-180 feet), and sequoia (180-250 feet). The rate of spread was 

about 7.5 ft/min with a combustion rate of 6367 Btu/min/ft2

. The live 

crown base changed from 3 feet to 16 feet, and the live crown load was 

reduced from 7.2 to 3.1 tons/acre. (Kilgore and Sando 1975)

500 8 This fireline intensity represents the upper limit for good control. Serious spotting limits attack. In a eucalypt forest, flame heights reach 

8 feet. (Hodgson 1968)
40 USDA Forest Service Gen. Tech. Rep. RMRS-GTR-253. 2011

Level III:

700 9 This intensity represents the limit for fires in ponderosa pine stands of 

Region 3 (U.S. Forest Service) that can be contained by initial attack 

forces. It was used to set slash residue limits. (Mann 1974, personal 

communication)

725 9 These test fires were monitored in a red pine plantation with a tree

surface height of 46 feet and a crown base height of 23 feet. Crown bulk density 

was moderate at 0.0162 lb/ft3

. Crowning occurred for up to 2 minutes

23 with flame lengths 20-23 feet above the crown. The crown fire was

crowning dependent upon the surface fire. (Van Wagner 1968)

Level IV:

>1000 11 This represents the intensity above which spotting, torching, and crowning activities contribute significantly to fire spread and resistance to 

suppression.

1209 12 This test fire was in a Canadian black spruce stand 14 feet high with a 

total load of about 15 tons/acre. About 54% of the crowns were burned, 

mainly by torching of clumps. Spotting was experienced up to 200 feet 

ahead of the front in a wind of 12 mi/h. (Kiil 1975)

1148-1390 11-13 This intensity was experienced in a test fire in a jack pine stand 66 feet high 

with crown base of 39 feet. Crown bulk density was light at 0.0062 lb/ft3

. 

No crowning occurred. (Van Wagner 1975)

2900 18 In a stand with about 50% crown closure, fire achieved crowning but 

was dependent on ground fire. (Van Wagner 1975)

2000-6500 15-26 Crown fires in standing pine were observed with rates of spread from 

35 to 90 ft/min. Flame lengths were observed to be 49-69 feet, exceeding about 26 feet above the tree canopy. (Van Wagner 1968)

10,500 32 These conditions were found at the 1971 Thackary Fire in Ontario. 

(Walker and Stocks 1972)

13,500 36 These conditions were found at the 1971 Whistle Lake Fire in Ontario. 

(Walker and Stocks 1972)

22,500 45 Extensive crowning, long-range spotting, tree breakage and blowdown 

all occurred during high-intensity portions of the 1967 Sundance Fire. 

(Anderson 1968)

30,000 52 This level of intensity represents a major fast-spreading fire with flame 

depth to 0-0.25 mile or more and flame heights from 50 to 150 feet. 

A change in fuels and/or weather is needed to suppress such a fire. 

(Brown and Davis 1973)

*Minor editorial changes have been made to the original text.

Fireline Calculated

intensity flame length

(Btu/ft/s) (ft) Fire descriptions and control actions

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