Managing 

Smoke at the 

Wildland-Urban 

Interface

Dale Wade and Hugh Mobley

United States

Department of

Agriculture

Forest Service

Southern Research 

Station

General Technical

Report SRS–103
Authors

Dale Wade, Research Forester (now retired), U.S. 

Department of Agriculture Forest Service, Southern 

Research Station, Athens, GA 30602 (www.rxfire@

ix.netcom.com); and Hugh Mobley, Forester (now 

retired), U.S. Department of Agriculture Forest 

Service, Southern Region and Alabama Forestry

Commission, Montgomery, AL 30309. 

Cover photos: Top by Steven R Miller, Saint John’s 

Water Management District, Palatka, FL. Bottom 

left by Larry Kohrman, University of Florida. 

Bottom right courtesy of Dale Wade.

June 2007

Southern Research Station

200 W.T. Weaver Blvd.

Asheville, NC 28804
i

Managing 

Smoke at the 

Wildland-Urban 

Interface 

Dale Wade and Hugh Mobley

Abstract

When prescribed burning is conducted at the wildland-urban interface (WUI),

the smoke that is produced can sometimes inconvenience people, but it can

also cause more serious health and safety problems. The public is unlikely to 

continue to tolerate the use of prescribed fire, regardless of the benefits, if burn 

managers cannot keep smoke out of smoke-sensitive areas. In the South, forest

management organizations commonly require that plans for prescribed burns

pass a smoke screening review and some States require such a review before they 

will authorize a burn. Current screening systems, however, do not incorporate

criteria for use at the WUI. This guide describes modifications to the Southern

Smoke Screening System for burns at the WUI. These modifications couple new 

research findings with the collective experience of burners who have extensively 

used the 1976 Southern Smoke Screening System. This new smoke screening

system is designed for use on burns less than 50 acres in size and has undergone 

several years of successful field testing in Florida.

Keywords: Fire management, prescribed fire, smoke management, smoke

screening, wildland urban interface.

iii

i Abstract

 iv List of Figures

v List of Tables

1 Introduction

2 Smoke Management Basics

2 Smoke Production and Significance

3 Firing Technique

3 Smoke Transport and Dispersion

4 Residual Smoke

5 Tools

5 Lavdas Dispersion Index (DI)

6 Low Visibility Occurrence Risk Index (LVORI)

6 Southern Smoke Screening Systems

8 Smoke and Nighttime Burns

8 Gaining Experience in Smoke Management

9 The Wildland-Urban Interface Smoke Screening System

9 Step 1—Plot Distance and Direction of Probable Smoke Plume

14 Step 2—Identify Smoke Sensitive Areas

14 Step 3—Dealing with Smoke Sensitive Areas within the 500-foot 

Buffer and/or First One-Fourth of the Impact Distance

16 Step 4—Dealing with Smoke Sensitive Areas within the Last 

Three-Fourths of the Impact Distance

17 Step 5—Interpreting Screening System Results

19 Acknowledgments

19 Literature Cited

21 Appendix A: Some Federal and Florida Air Quality Laws and Rules 

23 Appendix B: How to Reduce the Smoke Impact from 

Prescribed Burns

27 Appendix C: Suggested Reading

Contents
iv

List of Figures

10 Figure 1—Flowchart of the Wildland-Urban Interface Smoke 

Screening System.

12 Figure 2—Plot of the probable smoke impact area when a point

represents the burn. 

12 Figure 3—Plot of the probable smoke impact area when a figure other 

than a point represents the burn.

13 Figure 4—Plot of probable nighttime smoke impact area.
v

List of Tables

5 Table 1—Lavdas Dispersion Index, revised on the basis of extensive 

use by field practitioners

6 Table 2—Description of Low Visibility Occurence Risk Index 

(LVORI) values

7 Table 3—Low Visibility Occurrence Risk Index (stable conditions such 

as at night)

11 Table 4—Greatest distance of probable smoke impact from burns 

smaller than 50 acres

1

Managing Smoke at the Wildland-Urban Interface

Introduction

Periodic prescribed fire is an integral part of 

the management of fire-adapted ecosystems,

where it is a requisite to ecosystem health. At

the wildland-urban interface (WUI), it is also

used to reduce hazardous fuel accumulations

and to produce recreational benefits. Fire

managers would like to conduct these burns

without alarming nearby residents and without

having smoke intrude into smoke-sensitive

areas (SSAs), but smoke will likely affect people 

whenever fire occurs at the WUI. Smoke effects

include increased anxiety because a fire is

burning nearby, minor nuisances such as ash 

in swimming pools, temporary inconveniences

such as disrupted or detoured traffic flow, and

potentially serious public health and safety issues

such as aggravation of respiratory aliments and

reduction of roadway visibility. Smoke consists 

of a great many combustion products, some of 

which are designated as pollutants and, as such,

are regulated by various Federal and State statutes

(see appendix A). Readers desiring an indepth

discussion of air quality regulations and the

pollution caused by fire are referred to Hardy and 

others (2001) and Sandberg and others (2002). 

The three general strategies used to manage 

smoke from prescribed burns, including those

at the WUI are: (1) avoid SSAs, (2) disperse and

dilute smoke before it reaches SSAs, and (3)

reduce production of undesirable combustion

products. Managing smoke at the WUI is one of 

the most difficult tasks a burn manager faces. 

This is because SSAs are within or adjacent to

the burn rather than some distance away. Smoke

intrusions into SSAs cause the vast majority of

public complaints related to prescribed burning

at the WUI. If prescribed fire is to continue to be 

a viable resource management option, we must

make sure the public understands that fire is

necessary to perpetuate fire-adapted ecosystems 

and that attempting to exclude this natural force

has untenable long-term consequences. If the

public recognizes the dramatically different

long-term outcomes between these two fire

management strategies, and burn managers 

demonstrate they can skillfully and safely apply

fire, the public is likely to allow the continued use

of prescribed fire.

The purpose of this publication is to build upon

the knowledge of experienced prescribed burners

by describing tools that have proven helpful in

reducing smoke problems . For the purposes 

of this publication we define “experienced” 

prescribed burners as those who have completed

the Florida Interagency Basic Prescribed Fire 

Course or its equivalent. Users of this guide are

encouraged to review the slide presentation for

the smoke management unit of that course by 

going to the Florida Division of Forestry Web site 

http://www.fl-dof.com/ wildfire/rx_training.html 

and clicking on “Chapter 6: Smoke Management.” 

Alabama also has an excellent smoke management 

Web site; to access it, go to www.pfmt.org/fire and 

click on “Fire Management.”

Smoke management basics are briefly reviewed

below and tools to help manage smoke at the

WUI are discussed. A major modification of the

Southern Smoke Screening System is introduced,

which can help minimize the likelihood of smoke

problems when burning in the WUI. This smoke 

screening system for use at the WUI has been 

successfully used for the past 3 years by graduates

of an advanced Florida fire management training

course. Concepts to keep in mind and important

rules for reducing smoke impacts are reviewed in

appendix B. A list of suggested reading for those 

interested in a more detailed treatment of various

smoke related topics is provided in appendix C. 
2

Gen. Tech. Rep. SRS–103

Smoke Management Basics

The key to the effective use of prescription 

fire is to combine appropriate firing techniques 

and ignition patterns with favorable weather and

fuel moisture conditions to produce the desired

fire intensity and severity, which will, in turn,

achieve the burn objectives. The prescription

should, however, also consider offsite effects 

caused by the byproducts of combustion. Smoke 

management concerns usually override all other 

aspects of prescribed fire planning when burning

at the WUI because of the proximity of SSAs.

The amount of smoke that will be generated by 

flaming and residual combustion, coupled with the

distance to SSAs, will dictate acceptable burning

conditions and ignition plans. Manipulation of fuel

moisture, wind direction, firing technique, and

ignition pattern can usually, but not always, result 

in an acceptable prescription.

Smoke Production and Significance

The primary components of wildland fire

combustion are water vapor and carbon dioxide,

especially during the flaming phase when 

combustion is most efficient. Combustion is much

less efficient during the smoldering and residual 

phases and this inefficiency results in increased

particulate emissions (at least double those 

produced during flaming combustion). Particulate

emissions are usually the pollutant of concern in

wildland fires because of their impact on visibility

and human health. Because most particulates are

very small, they:

• Absorb and scatter light which washes

out contrast and decreases visibility

• Act as nuclei to facilitate the formation 

of fog

• Remain suspended in the atmosphere for 

relatively long periods

• Enter deep into human airways where 

they exacerbate respiratory problems

The amount of smoke produced is directly

related to the amount of fuel consumed; when fuel 

consumption is doubled, the amount of smoke

produced will roughly double, assuming other

factors remain constant. Fuel moisture is the

most important determinant of the proportion

of the total fuel load that will be available during 

a particular combustion phase. As fuel moisture

increases, more heat energy has to be used

to convert the moisture to steam; this slows 

the combustion process and increases smoke 

production because more of the fuel will be

consumed during the residual and smoldering

phases. The combustion of damp fuels generates

smoke that contains a large amount of water vapor, 

which, although not a pollutant, has a substantial

adverse affect on visibility. Remember that live

green fuels and damp fuels, whether live or dead,

will significantly increase the amount of moisture

in smoke. Burning when fine fuel moisture is

fairly low is recommended because less energy is

needed to drive off moisture, which means: 

• More heat energy is available to preheat 

additional fuels

• Fuels reach ignition temperature quicker

• More fuel is available

• Combustion efficiency is increased

• Rate of spread and flame length increase

resulting in higher fire line intensity

• More of the emissions will be entrained

into the smoke plume

• The plume will be lofted higher into

the atmosphere

The shape, size, arrangement, stage of

decomposition, and chemistry of fuel particles all

influence the proportion of the total fuel bed that

will be available, as well as combustion efficiency, 

which in turn influences smoke production. A

discussion of fuels can be found on the Florida

Division of Forestry prescribed fire training and 

education Web site at http://www.fl-dof.com/

wildfire/rx_training.html. Click on “Chapter 8: 

Fire Behavior.”
3

Managing Smoke at the Wildland-Urban Interface

Firing Technique

Backing fires have the highest combustion

efficiency because the flaming front progresses

through the fuel bed relatively slowly, allowing

more complete oxidation of the fuel and, thus,

fewer intermediate products such as volatile

organic hydrocarbons, oxides of nitrogen, and

other gaseous emissions of concern. Backing 

fires generally consume about the same

proportion of the forest floor as do heading fires, 

but in backing fires most of the available fuel is

consumed in the flaming front so smoldering after 

the front has passed is substantially reduced. This

significantly decreases the amount of particulate

matter generated. 

Even though headfires are characterized by 

incomplete combustion, they still produce only

about half as much particulate matter as does

smoldering combustion. A typical headfire in 

southern rough consumes about 60 percent of

the available fuel in the flaming phase and 40 

percent in the smoldering and residual phases 

(Southern Forest Fire Laboratory Staff 1976). 

The bottom line is that headfires produce about

three times as much particulate matter as backing 

fires. Backing fires have two major drawbacks 

from a smoke management standpoint. Firstly

they take more time than other firing techniques

to cover a given area, which means smoke will

be produced over a longer time period. Secondly,

when the distance between upwind and downwind

control lines exceeds about 300 feet, less of the

area will be burned during the middle of the

day when atmospheric dispersion is normally 

best. For these reasons, the increased intensity

of spot fires or a flanking fire is often accepted 

whenever prudent even though more smoke will

be produced, because the smoke will be generated

over a shorter time span and be lofted higher 

into the atmosphere. The only caveat here is that

increased fire line intensity may involve more 

of the understory, which will result in additional 

emissions. As the age of rough increases, the

proportion of the available dead fuel consumed

in the flaming front typically decreases; this has 

important implications when burning at the WUI

where fuel loads are usually very high.

Smoke Transport and Dispersion

Explanation of two terms will facilitate

discussion of atmospheric stability and its

influence over smoke transport and dispersion. 

Mixing height (MH) is the height to which 

vigorous mixing due to convection occurs and is

a good indicator of the approximate maximum

height to which smoke from a low-intensity

fire can rise. More intense fires, however, can 

loft smoke above the mixed layer because it is

the temperature of a smoke parcel relative to

the environmental temperature that actually

determines how high the smoke will rise. As

a general rule, do not burn at the WUI unless 

the MH is at least 1,700 feet. MH becomes 

less important when very small acreages of 

short grasses (small quantity of available fuel)

are involved, but if the 1,700-foot minimum is

violated and a smoke problem occurs, the burner 

will be held responsible. On the other hand,

very intense fires that quickly consume a large

amount of fuel can generate enough smoke to

exceed the capacity of the air to disperse the 

smoke efficiently, resulting in reduced visibility

at ground level. When burning heavy fuel 

loads, such as those created when harvesting 

old-growth stands where much of the material

is unmerchantable and thus left on site or by 

natural events such as high winds or severe pest 

infestations, increasing the MH will help mitigate

potential smoke problems. MH is part of the daily

fire weather forecast in many Southern States.

Transport wind velocity (TWV) is another 

atmospheric parameter given in the daily forecast

issued by many State forestry agencies. TWV is

the average horizontal wind speed and direction 

from the surface up to the MH and should be 

at least 9 miles per hour (mph) when burning 

is conducted at the WUI. Wind speed is usually
4

Gen. Tech. Rep. SRS–103

greatest in the afternoon and increases with

height. This means that as long as surface winds

are at least 9 mph, transport winds should be

adequate. Keep in mind that it is possible for the

wind direction to vary within the mixed layer, so 

the direction that smoke will be carried depends 

upon the height that is reached by the plume. 

Atmospheric stability indicates how rapidly

vertical mixing is taking place in the atmosphere.

The more unstable the atmosphere, the quicker 

and higher the smoke can rise. When burning

takes place under marginally unstable conditions,

the smoke plume may drop back to ground

level miles downwind even though the plume

was initially lifted well into the atmosphere by 

the heat of the fire. Atmospheric instability 

normally peaks during the afternoon due to

solar heating of the Earth’s surface and ebbs at

night as the surface cools. One can bypass the 

task of estimating stability on a given day by

using the Dispersion Index (DI) developed by 

Lee Lavdas (Lavdas 1986) which is part of the

daily fire weather forecast in many Southern 

States. This numerical index provides an estimate 

of the atmosphere’s ability to disperse smoke 

and is conceptually similar to the Ventilation

Index but should be a better predictor of smoke

dispersion (Lavdas 1986). A doubling of the DI 

implies a doubling of the atmosphere’s capacity

to disperse smoke. The DI can be computed 

for any time period. Daytime and nighttime DI 

numbers are interpreted differently because

different stability classes are used in calculating

the estimate. For example, a daytime DI of 40 is

the commonly accepted threshold for conducting

daytime burns. Nighttime values are, on the other 

hand, typically very low so a nighttime DI of 12 

suggests unusually good dispersion, whereas a 

daytime value of 12 would be interpreted as poor.

Fire managers also want to know the likelihood

of reduced nighttime visibility when smoke 

mixes with higher nighttime relative humidities.

Use of the Low Visibility Occurrence Risk Index 

(LVORI) (Lavdas 1996) in conjunction with the DI

provides them with such a predictor. Both of these

tools are described below.

A more indepth discussion of meteorological

variables that affect emissions can be found by

going to the Florida Division of Forestry Web site

at http://www.fl-dof.com/wildfire/rx_training.

html and clicking on “Chapter 7: Fire Weather.”

Both Florida and Georgia have full-time fire

meteorologists on their forest protection staffs;

these meteorologists can answer weather-related 

questions and, upon request, provide a timely spot 

weather forecast for your intended burn unit.

Residual Smoke

Smoke produced after the flame front passes 

is a major concern when burns are conducted

at the WUI. Where dead fuel loads are heavy, 

particularly when a heavy duff layer and/or 

numerous partially decayed logs are present, 

smoldering can continue for days, resulting in

overstory tree mortality (from root damage) as 

well as significant smoke problems. This residual

smoke remains near the ground where it is moved

by eye-level wind flow (not to be confused with 20-

foot surface winds). As the ground cools at night, 

much of this smoke will move down-drainage 

where it can reduce visibility to near zero 

at bridges.

Extensive study of archived wind data and

field studies conducted by Southern Forest Fire

Laboratory staff showed that in Southern States,

winds are likely to blow from every direction at 

some point in time on any given night. For this

reason, WUI burn prescriptions usually include

more stringent mopup standards, often specifying

mopup at least several hundred feet in from 

all edges. 

A guideline used by some fire managers who

routinely burn adjacent to homes in Florida is

to allow a 12-person crew 12 hours to burn and

completely mop up a 5-acre unit in a 5-plus year

palmetto/gallberry rough once the prep work has
5

Table 1—Lavdas Dispersion Index,a revised on the basis of extensive use by field practitioners

Lavdas 

Dispersion 

Index

Smoke 

dispersion Interpretation of daytime values

70 + Very good Burning conditions are so good that fires generally present control

problems. Reassess decision to burn unless escape, particularly as a

result of spotting, is not a problem, e.g., burn unit is surrounded by

plowed fields. DI is generally too high for a WUI burn.

50–69 Good Preferred range for prescription burns, but fire control becomes

more difficult as values get higher.

41–49 Generally 

good

Especially when the planned burn is smaller than 50 acres. Afternoon

values in most inland forested areas typically reach this range.

Reassess decision to burn at WUI if daytime DI < 41

21–40 Fair Stagnation may be indicated if DI is in this range and windspeed is

low. Reassess decision to burn, especially if heavy rough or large 

dead fuels are present, or unit is larger than 15 acres.

Below 20 Poor to

very poor

Do not burn at the WUI.

DI = Dispersion Index; WUI = wildland-urban interface. a Lavdas (1986).

Managing Smoke at the Wildland-Urban Interface

been completed. They have found that for units

up to at least 25 acres in size, the total amount of 

time they spend burning and mopping up will be 

about the same whether they burn the whole unit 

in 1 day and come back several days in a row to

handle smoke complaints, or whether they break

the block into roughly 5-acre blocks and burn 

and completely mop up one each day with no

complaints. Water-and-foam is often the method of

choice for mopup at the WUI, and use of smaller

burn units facilitates reaching all parts of the burn. 

Florida statutes allow authorized fires to

actively spread between 0900 and 1 hour before 

sunset (1 hour after sunset for certified burners),

and under certain weather conditions, a burn 

authorization can be obtained for a nighttime

burn. We recommend that all burns at the WUI be

started as soon after 0900 as conditions warrant

so they can be completed early enough to allow 

sufficient time for mopup before sunset. Nighttime

burns at the WUI should only be considered

immediately after passage of a cold front, when 

the lower ambient temperatures will help

minimize overstory crown scorch, and only

when the predicted wind velocity will not result in 

other fire or smoke management concerns. 

Tools

Many models and tools have been developed

to aid in managing smoke and additional ones 

are under development. A discussion of available 

and emerging tools can be found in Sandberg and 

others (2002) and at http://www.fire.org/. Tools

introduced or reviewed in this publication include:

• The DI for assessing the atmosphere’s

capacity to disperse a smoke plume

• The LVORI for assessing the likelihood

of a vehicle accident caused by poor 

visibility resulting from residual smoke

• A smoke screening system for managing

smoke at the WUI

Lavdas Dispersion Index (DI)

The relation of the DI to burning conditions

is shown in table 1. The DI is part of the 
6

Table 2—Description of Low Visibility Occurence Risk Index (LVORI) values

LVORI

values Description

1 Lowest proportion of accidents with smoke and/or fog reported (130 of 127,604 

accidents, or just over 0.0010 of all accidents)

2 Physical or statistical reasons for not including in LVORI class 1, but proportion of

accidents not significantly higher

3 Higher proportion of accidents than LVORI class 1, by about 30 to 50 percent, marginal 

significance (between 1 and 5 percent)

4 Proportion of accidents significantly higher than LVORI class 1 (by a factor of about 2)

5 Proportion of accidents significantly higher than LVORI class 1 (by a factor of 3 to 10)

6 Proportion of accidents significantly higher than LVORI class 1 (by a factor of 10 to 20)

7 Proportion of accidents significantly higher than LVORI class 1 (by a factor of 20 to 40)

8 Proportion of accidents significantly higher than LVORI class 1 (by a factor of 40 to 75)

9 Proportion of accidents significantly higher than LVORI class 1 (by a factor of 75 to 125)

10 Proportion of accidents significantly higher than LVORI class 1 (by a factor of about 150)

Gen. Tech. Rep. SRS–103

daily fire weather forecast produced by many 

Southern States. 

Low Visibility Occurrence Risk 

Index (LVORI)

The LVORI (Lavdas 1996) shown in table 2

was developed to rank the relative likelihood

of a fog and/or smoke-related accident on the 

southern Coastal Plain. LVORI is a function of 

relative humidity and the DI (table 3) based on 

the proportion of accidents involving fog and/or

smoke, as reported by the Florida Highway Patrol

from 1979–81. The LVORI is a scale from 1 to 10 

with 1 indicating a low likelihood of poor visibility

and 10 indicating an extremely high likelihood

of poor visibility. The LVORI is a valuable tool

for assessing the probability of low visibility in 

down-drainage areas at night or under stable 

atmospheric conditions. Caution should be used

when contemplating WUI burns with a LVORI

of 5 or higher, and WUI burns should not be 

conducted when the LVORI is predicted to be 7

or higher unless the fire will be completely

mopped up (out—no smokes) by dusk. 

Southern Smoke Screening Systems

Smoke management at the WUI is one of the

most difficult parts of the burn prescription to

prepare because SSAs often occur within a short

distance on all sides of the intended burn unit. 

There will not be enough information available

in the foreseeable future, nor can a burning 

prescription integrate all the variables necessary,

to predict how much the visibility will be reduced

at a given distance from a burn, or the effects it 

could have on human health and welfare. In fact,

many of the interactions between these variables

are not yet well understood. Nevertheless, most 

Southern States have voluntary or mandatory

smoke management guidelines that should or

must be followed when planning a prescribed fire.

Many Southern State forestry agencies have Web

sites that provide recommended and/or required

procedures. State forestry Web sites can be

accessed through the National Association of State 

Foresters Web site at www.stateforesters.org/.
7

Table 3—Low Visibility Occurrence Risk Index (stable conditions such as at night)

Relative

humidity

Dispersion Index

> 40 40–31 30–26 25–17 16–13 12–11 10–9 8–7 6–5 4–3 2 1

< 55 1 1 2 2 2 2 2 2 2 2 2 2

55–59 1 1 2 2 2 2 2 3 3 3 3 3

60–64 1 1 2 2 2 2 3 3 3 3 3 3

65–69 1 3 3 3 3 3 3 3 3 3 3 4

70–74 3 3 3 3 3 3 3 3 3 3 3 4

75–79 3 3 3 3 4 4 4 4 4 4 4 4

80–82 3 3 3 3 4 4 4 4 4 5 5 6

83–85 4 4 4 4 4 4 4 4 5 5 5 6

86–88 4 4 4 4 4 5 5 5 5 6 6 6

89–91 4 4 4 4 5 5 5 5 6 6 7 7

92–94 4 4 4 5 5 5 6 6 6 6 7 8

95–97 4 4 4 5 5 6 6 6 7 8 89

> 97 4 4 4 5 5 7 8 8 9 9 10 10

Managing Smoke at the Wildland-Urban Interface

Few WUI prescribed fire projects can pass

any smoke screening system now in use, but 

prescribed burning is necessary to perpetuate firedependent plant communities in the WUI. For this

reason, the Southern Smoke Screening System 

(Southern Forest Fire Laboratory Staff 1976) 

has been modified to facilitate successful smoke 

management when burning is conducted at the

WUI. The new system, the WUI Smoke Screening 

System, is described herein. It is based largely on 

extensive fieldwork conducted by Hugh Mobley, 

which he used to modify the original version of the

Southern Forestry Smoke Management Guide.

(To see the guide as modified by Mobley, go to 

www.pfmt.org/fire, click on “Fire Management,”

then click on “Smoke Management.”) Dale Wade 

further modified the Southern Forestry Smoke

Management Guide; the resulting WUI Smoke 

Screening System is intended specifically for WUI

burns smaller than 50 acres. 

For larger units, the original screening

system found in The Southern Forestry Smoke

Management Guidebook (Southern Forest Fire

Laboratory Staff 1976) should be used. It can be 

found on the Web at http://www.srs. us.usda.

gov/pubs/viewpub.jsp?index=683. If the intended

burn does not pass that system, consider breaking 

it into smaller units and using the WUI Smoke

Screening System.

The latter system is straightforward and is

designed for use in the initial planning phase as

part of the written burn prescription. It should

also be used just before the burn to suggest 

alternatives when weather conditions are not as

described in the plan. This system should not 

be used without a working knowledge of fire 

behavior and smoke management. The better 

one’s understanding of the factors that affect 

smoke, the more fully and safely one will be able

to interpret the results provided by this WUI

screening system. Both smoke screening systems

utilize many, but not all, of the major variables 

that affect smoke. Values are based on “worst 

average” weather and fuel conditions and worst

case events. In some cases, indices are based on

very limited research and field verification. The 

total amount and rate at which smoke will be 

produced are crucial elements in developing a 

burn prescription, but are at best only indirectly

addressed in current smoke screening systems

(including this one). For example, the effects of 

fuel loading by size class, fuel moisture, and fuel
8

Gen. Tech. Rep. SRS–103

compaction on smoke production have only been 

studied on a very coarse scale. Therefore, current 

smoke screening systems can only suggest 

whether a smoke problem is likely, marginally 

likely, or not likely. They are a starting place to get

a feel for managing smoke.

The burn manager must make the final

decision. Experience and knowledge must be 

coupled with familiarity with the locale so the 

burn manager can judge whether the burn in

question is likely to cause a smoke intrusion given

the weather conditions and firing techniques 

spelled out in the burn prescription. The more

experienced and knowledgeable that person is

about prescription fire and smoke management,

the better the decision will be.

Smoke and Nighttime Burns

As a general rule, nighttime burns should

not be conducted in the WUI. The nighttime

atmosphere is usually stable, surface winds are

near calm and the direction of light breezes is

generally variable and difficult to predict, fine fuel 

moisture content is higher, and inversions are

common. More combustion products, particularly

water vapor, are thus produced and plume rise is

limited, so the smoke tends to remain much closer

to the ground where it reduces visibility, especially

when combined with fog. Nonetheless, nighttime

burns are sometimes advocated, e.g., in young

pine stands because ambient temperature tends to

be lower at night. If such a situation arises at the

WUI, a nighttime burn should only be considered

when the weather forecast predicts steady winds

lasting all night. Such conditions are usually

associated with passage of a cold front. The fire 

and smoke should be monitored continuously 

and a tractor-plow unit should be onsite so that

the burn can be terminated if necessary. Have

lighted “smoke” signs available and make sure 

local law enforcement personnel are alerted. A 

nighttime DI forecast can be obtained in Florida,

Georgia, and several other Southern States. 

Interpretation of nighttime DI is entirely different

from interpretation of daytime DI. At night a value 

of 8 or higher is generally acceptable (in selected

rural areas of Florida, a nighttime DI value of 3 is

permissible). Note that the WUI Smoke Screening

System detailed below is not applicable for 

nighttime burns.

Gaining Experience in Smoke Management

To increase your understanding of how much

smoke is produced and what happens to it in

various plant communities under different 

weather and topographic conditions we suggest 

the following:

• Observe—Observe and document the

production, transport, and dispersion of 

smoke on prescribed burns, even when 

no SSAs are identified. Check downwind

and down-drainage to observe the smoke 

during the day, at dusk, before midnight,

and at dawn the next morning. Document

the distance to which the smoke is

a visibility problem. Include all the

above information in your written burn

evaluation. This information can be used

later when burns are conducted in the

same fuel type under the same general

conditions and you have SSAs to consider.

• At dusk—Always check your burn for 

smoke at dusk. If there is residual smoke, 

monitor all night unless there is very 

little, in which case, check again just 

before daylight the next morning.

• Fog-prone areas—Learn where and at 

what time fog generally occurs in your

area. Locate and mark fog-prone areas on

your administrative map.
9

Managing Smoke at the Wildland-Urban Interface

When developing a burn prescription, check to

see if the smoke plume might reach a fog-prone 

area. If the plume will likely reach such an area,

make sure photos are taken to document the burn

and smoke dispersion. If fog forms in the potential

impact area the evening after a burn, monitor all

roads in the area throughout the night. Be aware

that conditions can deteriorate from relatively

good visibility to zero visibility within a matter of

minutes. Consider developing a smoke patrol plan

with thresholds for specified levels of activation;

Bill Twomey developed such a plan for the Francis

Marion National Forest in South Carolina in the 

1990s and has found it very useful. 

The WUI Smoke Screening System includes

estimates of minimum distances that burns 

should be from SSAs to minimize the impacts of

smoke on these SSAs. Because data are limited,

the WUI Smoke Screening System tends to be 

conservative. For example, prescribed burns

may be smaller in size, or for some other reason

produce less smoke than the system suggests. If 

you take the time to record and catalog the smoke

results of your WUI burns, this accumulating data 

will allow better estimation of potential impacts of

smoke on SSAs in your area.

If following any of the guidelines in the WUI 

Smoke Screening System results in smoke

intrusion into an SSA, mitigate the intrusion and

then please do all the following:

• Estimate the downwind extent of 

the problem

• Try to determine the exact cause of 

the problem

• Think about how you can adjust 

the screening system so it will not

happen again

• Notify others of the problem you 

encountered, e.g., your local fire 

council, and get word back to Scott

Goodrick with the Southern Research

Station, Disturbance Work Unit, Smoke

Management Team located in Athens, GA 

(http://www.srs.fs.fed. us/smoke)

The Wildland-Urban Interface 

Smoke Screening System

This system has five steps. Figure 1 

diagrams the process.

• Step 1—Plot distance and direction

of probable smoke plume and

residual smoke

• Step 2—Identify SSAs

• Step 3—Deal with SSAs within the first 

one-fourth of the downwind and downdrainage impact distance

• Step 4—Deal with SSAs within the last

three-fourths of the downwind and downdrainage impact distance

• Step 5—Interpret screening system 

results

Step 1—Plot Distance and Direction 

of Probable Smoke Plume

Step 1A

Use a map on which the locations of all SSAs

can be identified and plot the footprint of the

planned burn. Then draw another line around the

burn 500 feet out from the edge of the burn area.

This 500-foot buffer zone indicates the minimum 

area that is likely to be impacted regardless of 

wind direction. If the intended burn unit is larger 

than 50 acres, divide it into subunits that are less

than 50 acres in size. Go to step 1B. 
10

Gen. Tech. Rep. SRS–103

igure 1—Flowchart of the Wildland-Urban Interface Smoke Screening System.
11

Table 4—Greatest distance of probable smoke impact from burns smaller than 50 acres

Dispersion Index

41–50 51–60 61–70

Fuel category Firing technique Impact distance in miles

A Grass, light understory (< 2-year

rough) with no humus layer

Any firing technique 0.75 0.5 0.25

B Nonwoody marsh fuels—rush, 

cattail, or sawgrass

Any firing technique 1.5 1.25 1

C Palmetto/gallberry or waxmyrtle 

understory regardless of height

Backing fire 1.25 1 0.75

Da bPalmetto/gallberry or waxmyrtle 

understory regardless of height

Head, flank, 

or spot fires

4 32

E Any other native understory fuel

type regardless of height

Backing fire 1 0.75 0.5

F Any other native understory fuel

type under 3 feet high

Head, flank,

or spot fires

1.5 1 0.75

G Any other native understory fuel

type over 3 feet high

Head, flank. or spot fires2 1.5 1

Ha bMelaleuca Backing, flank, or spot fires3 21

I Exotic fuelbeds such as Casuarina

without much understory 

Any firing technique 2.5 2 1.5

J

a

Scattered logging debris Any firing technique 2.5 1.5 1

KaSmall dry piles Any firing technique 3 2 1.5

Lc

Large, wet, piled debris

or windrows

Using any firing

technique

Do not burn

a Firing should be completed at least 2 hours before sunset because dispersion will rapidly deteriorate at dusk. b Line headfires in 4- to 5-foot high palmetto, gallberry, waxmyrtle, or Melaleuca are very likely to result in

severe overstory crown scorch. cWindrows are the most polluting of all southern fuel types. They contain large fuels and dirt, and are compact 

which makes them very slow to dry and severely limits the amount of oxygen available for the combustion 

process. Dirt in piles or windrows will drastically increase the amount of smoke produced, and debris piles

containing substantial amounts of dirt can smolder for weeks. To pass this screening system, any large piles of 

debris or windrows will have to be reconfigured into small round piles and allowed to dry with stumps removed

or fireproofed.

Managing Smoke at the Wildland-Urban Interface

Step 1B

Choose the DI under which you plan to burn. 

Lower DIs (< 41) are not recommended because 

of poor smoke dispersion and DIs above 70 are

not recommended because of the likelihood of

fire control problems. Note that in Florida, the DI 

threshold for red-flag conditions is 75. Consider 

the DI chosen to be a tentative selection at this

point. Go to Table 4 and use the tentatively

selected DI to determine the maximum distance

to which smoke is likely to be a problem based

on the fuel category and firing technique chosen.

Visible smoke may be present for this distance,

although smoke can be smelled at much greater

distances. Go to step 1C. 
12

Gen. Tech. Rep. SRS–103

Step 1C

Draw a line representing the centerline of

the planned path of the smoke plume (transport

wind direction) from the burn. Draw this line 

for the length of the impact distance determined

from table 4. To allow for horizontal dispersion of

smoke as well as shifts in wind direction, draw two 

additional lines out the same distance from the

burn unit at 30-degree angles from the centerline

of the transport wind direction. Connect the ends

of the lines with arcs as in figures 2 and 3. Note 

that the transport wind direction and surface 

wind direction may differ on the day of the burn, 

e.g., if a seabreeze is present. In this case, plan 

for the change in smoke plume direction. When

burning on a seabreeze, keep in mind that once

the smoke plume is over water, it will likely drop 

to the surface and be blown back inland; the firing

technique and pattern used should, thus, assure

that the plume has dissipated by the time it might

be blown back across the shoreline so that people 

will not be adversely impacted. When rechecking

winds on the day of the burn, if forecast or actual

surface winds are light (< 5 mph), replot the

impact area using 45-degree angles.

If the planned burn is represented as a spot on 

the map you are using, draw as in figure 2 with

a protractor and straight edge. If the map scale 

allows the burn dimensions to be drawn on the

Figure 2— Plot of the probable smoke impact area when 

a point represents the burn.

Figure 3— Plot of the probable smoke 

impact area when a figure other than a 

point represents the burn.
13

Managing Smoke at the Wildland-Urban Interface

map, do so and draw as in figure 3. The result is

the probable daytime smoke impact area. The 

heaviest smoke concentration will be along

the centerline.

Figure 4 shows the application of step 1C to

an example area. If the fuels present are grass,

nonwoody marsh fuels, or less than a 2-year rough 

(fuel categories A and B), go to step 2, otherwise

go to step 1D.

Step 1D

Next, go down-drainage the same distance

determined from table 4 in step 1B. Draw a narrow 

area covering only the “bottom” or width of the

drainage area. This area may or may not lie wholly 

within the daytime smoke impact area. The result 

is your probable nighttime impact area due to the 

residual (smoldering) smoke produced. Note that

the probable down-drainage nighttime smoke 

impact area shown in figure 4 can extend further 

than the distance suggested in table 4 because the

smoke will be concentrated within this relatively

narrow area and will seek the lowest elevation.

If the smoke encounters heavy vegetation in the

drainage, it will build up at that point. If an open 

area such as a pasture or field is also adjacent to 

the drainage at that point, the smoke will tend to

spill over into this area if the terrain is fairly level.

Figure 4— Plot of probable 

nighttime smoke impact area.
14

Gen. Tech. Rep. SRS–103

If your preburn site inspection suggests this 

could happen, monitor that area for smoke buildup

after the burn, especially if an SSA is near the

other end of the open area. Complete step 1D even 

if you plan to have the burn completely mopped 

up (out) at least 2 hours before dusk. Then, if for

some reason residual smoke is present at dusk, 

you will know where it is likely to concentrate. Go

to step 2.

Step 2—Identify Smoke Sensitive Areas

Step 2A

If the area to be burned contains organic soils

that are likely to ignite, go to step 5B, otherwise

go to step 2B.

Step 2B

Identify and mark any SSAs within 500 feet of

the perimeter of the planned burn, regardless of

direction from the fire as determined in step 1A

above. Add these to the contact list in your written 

prescription. Make sure these SSAs are also

discussed in the public relations section of your 

prescription. Go to step 2C.

Step 2C

Identify and list any SSAs located within the

probable downwind impact area determined in 

step 1C. Go to step 2D.

Step 2D

Identify and list any SSAs located within the

down-drainage impact area determined in step 1D. 

Go to step 2E.

Step 2E

If any SSAs were identified in 2B through 2D,

mitigation is necessary as suggested in steps 3

and 4. Go to step 3.

If no SSAs are found, as described in steps 2A

through 2D, then it is not likely you will have a

smoke management problem. Go to step 5A.

Step 3—Dealing with Smoke Sensitive 

Areas within the 500-foot Buffer and/or

First One-Fourth of the Impact Distance

Step 3A

Consider felling snags. If their retention is

spelled out in the land management plan, follow 

standard procedures to keep them from igniting.

Go to step 3B.

Step 3B

If the predicted or actual LVORI is 7, 8, 9, or 10,

go to step 5B.

Step 3C

For fuel categories A through I: If any homes

are within the 500-foot buffer, each homeowner 

must be personally contacted and informed that

his or her home will likely be impacted by smoke. 

The landowner responses, e.g., that there are

severe respiratory problems or fears that homes

will be lost, should guide what actions are taken 

(include in the public relations plan).

Use the same fuel category selected in step 1B

(table 4). Fuel category selections follow:

• Fuel category A or B: Go to step 3D

• Fuel category C, D, E, F, G, H, or I: Go to 

step 3E

• Fuel category J or K: Go to step 3F

Step 3D—Fuel Categories A and B

If no SSAs are within the 500-foot buffer zone

or first one-fourth of the downwind smoke impact

distance, go to step 4.

If any SSAs are within the buffer zone or first

one-fourth of the predicted downwind smoke

impact distance, a smoke problem resulting

from the burn is a distinct possibility. First,

try changing the prescribed wind direction or

increasing the prescribed DI to minimize the

number of SSAs that are within the smoke

impact area. 
15

Managing Smoke at the Wildland-Urban Interface

If changing the wind direction or increasing the 

DI removes all SSAs from the buffer and first onefourth of the downwind smoke impact distance,

go to step 4. Otherwise, it is unavoidable that an

SSA will be within the buffer zone or first onefourth of the impact distance and mitigation will

be necessary. Either mop up the burn completely

(all smokes out) at least 1 hour before sunset or

complete active burning at least 3 hours before 

sunset under one or more of the conditions listed

below and mop up until dark:

• DI above 50

• MH above 2,500 feet

• Surface winds < 8 mph and transport 

wind speeds > 15 mph

• If the SSA is a road, mitigate by 

controlling or rerouting traffic during

the burn

Continue by going to step 4.

Step 3E—Fuel Category C, D, E, F, G, H, or I

If an SSA is within 500 feet of the fire perimeter,

regardless of the direction from the fire, divide

the unit into two or more subunits, the smaller of

which faces the SSA. An exception to creation of

subunits can occur where smoke corridors are

already established by county ordinance.

• The smaller subunit should have a depth

such that the distance from the closest 

SSA to the back of the subunit is at least

500 feet on the edge of the burn facing

the SSA. This edge should be delineated

with a hard (plowed or raked) line or

drainage ditch containing standing water.

The burn manager may select a shorter

distance in some specific situations, but 

much caution should be used. If the SSA

is a road, closing the road during the burn 

removes this distance restriction. If the 

SSAs are homes, all homeowners must

agree to the reduced distance with the

full understanding that their residences

could be impacted by drift smoke. In 

some uncommon situations, a Federal

or State statute such as the Hawkins 

Law in Florida may allow you to ignore

these guidelines, but we urge you to first

carefully consider the potential public

relations ramifications of such a decision.

• Burn this smaller subunit first toward the 

middle of the day, preferably when steady

eye-level winds are blowing away from 

the SSA at speeds > 2 mph. If you desire

to burn this subunit when eye-level winds

are blowing toward the SSAs, consider 

specifying weather conditions and a firing

technique that will facilitate lofting the

smoke plume over the SSAs.

• If an SSA is down-drainage, make sure 

the subunit can be burned and completely

mopped up (out) by dusk. This may

require breaking the subunit into smaller

(about 5-acre) blocks.

• If the SSA is a road, mitigate either by

rerouting traffic during the burn or by

stationing flaggers strategically. Be ready

to extinguish the fire if necessary.

Once the smaller subunit is burned out, if

no other SSAs are within 500 feet of the burn, 

address any SSAs within the first one-fourth of the

impact area.

When multiple SSAs are within 500 feet of the 

burn unit on more than one side, your options

are further constrained. If roads are present,

control traffic flow; if homes are present, contact

all residents and make sure they understand that

their residences may be impacted by residual

smoke. As a general rule, a residence should not 

be directly impacted by the plume, or impacted by

residual smoke throughout the night. If you are 
16

Gen. Tech. Rep. SRS–103

not sure that all smoke will be pulled away from

the SSAs as the remaining subunits are burned,

divide the remaining subunits further.

If no SSAs are within the first one-fourth of the

downwind smoke impact distance, go to step 4.

If any SSAs are within the first one-fourth of

the downwind smoke impact distance, a smoke 

problem resulting from the burn is a distinct 

possibility. Change prescribed wind direction or

increase DI to minimize the number of SSAs that

lie within the first one-fourth of the downwind

smoke impact distance.

If changing the prescribed wind direction or

increasing the DI removes all SSAs from the 

first one-fourth of the downwind smoke impact

distance impact area, go to step 4. If one or more

SSAs remain within the first one-fourth of the

impact distance, you must mitigate the problem. 

Burn and mop up completely (all smokes out)

at least 1 hour before sunset, or complete active

burning at least 3 hours (2 hours if using a 

backfire as described in the fourth bullet below)

before sunset under one or more of the conditions

listed below and mop up until dusk.

• DI above 50

• Divide unit into roughly 5-acre blocks and

burn them separately

• Surface winds < 8 mph and transport

wind speeds above 15 mph

• Use a backing fire and complete burn at 

least 2 hours before sunset. Begin mopup

as soon as practicable after the flame

front has passed.

• MH above 2,500 feet

• Keep stumps from igniting

• If the SSA is a road, mitigate by

controlling or rerouting traffic during 

the burn

Continue by going to step 4.

Step 3F—Fuel Categories J and K

If any SSAs are within the 500-foot buffer zone,

go to step 5B. 

If no SSAs are within the first one-fourth of the

downwind smoke impact distance, go to step 4.

If any SSAs are within the first one-fourth of

the downwind smoke impact distance, a smoke 

problem resulting from the burn is a distinct

possibility. Change prescribed wind direction or 

increase DI to minimize the number of SSAs that

lie within the first one-fourth of the downwind 

smoke impact distance.

If changing the prescribed wind direction or 

increasing the DI removes all SSAs from the 

first one-fourth of the downwind smoke impact

distance, go to step 4. If an SSA is unavoidable

within the first one-fourth of the impact distance,

you must mitigate the problem. Burn and mop up 

completely (all smokes out) at least 1 hour before 

sunset. The following conditions will facilitate 

smoke dispersal: 

• DI above 50

• Keep stumps from igniting

• Divide the unit into roughly 5-acre blocks 

and burn these subunits separately

• Burn when the MH is above 2,500 feet

• Surface winds < 8 mph and transport 

wind speeds > 15 mph

• If the SSA is a road, control or reroute

traffic during the burn

Continue by going to step 4.

Step 4—Dealing with Smoke Sensitive 

Areas within the Last Three-Fourths of the 

Impact Distance

Step 4A

Select the same fuel category used in step 3. 

Selections are grouped by fuel category as follows:

• Fuel category A or B: Go to step 5A
17

Managing Smoke at the Wildland-Urban Interface

Step 5—Interpreting Screening 

System Results

Step 5A—All Requirements Met

If all the requirements in the smoke screening 

system have been met to this point, it is not

likely that the prescribed fire will result in a

smoke problem if the maximum burn unit size

is < 50 acres. Keep in mind that as the DI class

under which the burn is conducted increases,

fire intensity and suppression become more

challenging. In order to use this WUI screening

system for burn units > 50 acres, you must

subdivide the unit into blocks of 50 acres or less to

conform with the underlying assumptions used in

developing this system.

If you proceed and a smoke problem is

encountered, please notify others of the problem 

you encountered, e.g., your prescribed fire 

council, and get word back to Scott Goodrick

with the Southern Research Station, Disturbance

Work Unit, Smoke Management Team located in 

Athens, GA, at the following Web address: http://

www.srs.fs.fed.us/smoke/contacts.htm so that 

the situation can be examined and changes to the

screening system can be made as appropriate.

Step 5B—Not All Requirements Met

If not all smoke screening system requirements 

have been met, consider the following options:

• Do not burn. Use a mechanical, chemical,

or biotic alternative instead

• Change the prescription to meet the

requirements

• Reduce the burn unit size to roughly 2-

acre blocks, burn with low surface winds,

and mop up completely by dark

There may be rare situations where a proposed 

burn will not pass any smoke screening system 

under the best dispersion conditions, but the use

of fire is still the preferred alternative (e.g., see 

• Fuel category C, D, E, F, G, H, or I: Go 

to step 4B

• Fuel category J or K: Go to step 4C

Step 4B—Fuel Category C, D, E, F, G, H, or I

Either:

• Complete firing at least 3 hours before 

sunset and mop up a minimum of 500 feet

in from the downwind edge of the burned

area, or

• Use a backing fire and completely mop 

up the burn at least 1 hour before sunset. 

Begin mopup soon after the flame front 

has passed and continue until dusk

If residual smoke is present at dusk, monitor 

all night and be prepared to act if a roadway is

impacted.

Continue by going to step 5A.

Step 4C—Fuel Category J or K 

If no interstate or major highways are within 2

miles down-drainage, consider the list of potential

measures below. Implement as many as practical

to mitigate potential smoke problems.

• Burn when the DI is above 50

• Reduce the size of the area to be burned

• Complete firing at least 3 hours before 

sunset

• Mop up as needed

• Burn when surface winds are < 8 mph and 

transport wind speeds are > 15 mph

• Monitor smoke all night and be prepared

to act if a roadway is impacted

• Keep stumps from igniting

• Burn when MH is above 2,500 feet

If interstate or other major highways are

within 2 miles down-drainage, divide the unit into

subunits and implement as many of the above

measures as practical.

Continue by going to step 5A.
18

Gen. Tech. Rep. SRS–103

Miller and Wade 2003). In such cases, the burn 

manager should take all the extra steps listed

below and then proceed with extreme caution:

• All homeowners within the potential

impact area agree to tolerate any 

temporary inconveniences associated

with the intended burn [unless burning

within a legalized smoke corridor or under

a state statute such as the Hawkins Law

(Florida Statute 590.125)]

• Local law enforcement and government 

officials are kept informed and agree with

the necessity of the burn

• All homeowners are contacted within

several weeks of the burn and informed

of the planned burn date, anticipated 

ignition time, burn duration, and mopup

time. Homeowners should be given the

address of a Web site where any schedule 

changes will be posted

• In the above situations, it is still

recommended that:

– Photos be taken before, during and after the

fire including any residual smoke indicating 

time of photo.

– The burn be completely mopped up and 

declared out before burn personnel leave

– If residual smoke is present at dusk, monitor 

it throughout the night

If some conditions are marginal, smoke could

still be a problem; consider reducing the size of 

the burn. On the other hand, it may be possible

to burn without causing a smoke intrusion even

though this screening system indicates otherwise.

Situations where this is likely the case include:

• The distance to the SSA is close to the

maximum impact distance

• The amount of available fuel is less 

than average

• The fuel is very dry and the fuel bed is

loosely arranged

• The only downwind SSA is close to

the end of the arc constructed in step

1C. Note that the heaviest smoke

concentration will be along the centerline

The decision to proceed with the burn or to

delay it until another time is up to the manager

of the prescribed burn. Remember that ideal

conditions at ignition time can change during 

the burn. This will most likely happen to every 

prescribed fire manager as a result of conditions

that are not anticipated or not as forecasted. 

When such a situation occurs, follow three 

guiding principles:

1. Use common sense—Do what a prudent

individual would do

2. Use integrity—Do the right thing

3. Keep good records—Have and follow a 

written plan and document all changes to

it as they are made

Hot Tip

This smoke screening system does not take into account other 

sources of smoke that may already be reducing visibility in the area.

Minimum background visibility around the intended burn site

should be at least 5 miles.
19

Managing Smoke at the Wildland-Urban Interface

the Florida Division of Forestry, Scott Goodrick

with the USDA Forest Service, and Paul Watts 

with the South Carolina Forestry Commission 

who reviewed this manuscript and made valuable

contributions. Rick Henion with the Maine Forest 

Service produced clip art used in this report.

Literature Cited

Hardy, C.C.; Ottmar, R.D.; Peterson, J.L.

[and others], comps., eds. 2001. Smoke

management guide for prescribed burning and 

wildland fire: 2001 edition. PMS 420–2. Boise, 

ID: National Wildfire Coordinating Group. 

226 p.

Lavdas, L.G. 1986. An atmospheric dispersion

index for prescribed burning. Research Pap.

SE–256. Asheville, NC: U.S. Department of

Agriculture Forest Service, Southeastern

Forest Experiment Station. 33 p.

Lavdas, L.G. 1996. Improving control of 

smoke from prescribed fire using low visibility

occurrence risk index. Southern Journal of 

Applied Forestry. 20(1): 10-14. 

Miller, S.R.; Wade, D. 2003. Re-introducing

fire at the urban/wild-land interface: planning 

for success. Forestry. 76 (2): 253-260.

Sandberg, D.V.; Ottmar, R.D.; Peterson, J.L.;

Core, J. 2002. Wildland fire in ecosystems: 

effects of fire on air. Gen. Tech. Rep. RMRS–

GTR–42. Ogden, UT: U.S. Department of

Agriculture Forest Service, Rocky Mountain

Research Station. 79 p. Vol. 5.

Southern Forest Fire Laboratory Staff.

1976. Southern forestry smoke management 

guidebook. Gen. Tech. Rep. SE–10. Asheville,

NC: U.S. Department of Agriculture Forest

Service, Southeastern Forest Experiment 

Station. 140 p. Available on the Web at:

http://www.srs.fs.usda.gov/pubs/viewpub.

jsp?index=683. [Date accessed: March 2007].

Acknowledgments

This screening system is based on the

screening system developed by the Southern 

Forest Fire Laboratory Staff (1976) and

revisions to it as dictated by extensive field 

use over the next several decades which can 

be accessed at www.pfmt.org/fire, a Web site

maintained by Auburn University. The lead author

modified this revised product at the request 

of the Florida Division of Forestry to develop 

a smoke management unit to be taught at an

advanced training course for certified prescribed

burners. Development of this course entitled

“Implementing Prescribed Fire in the Wildland

Urban Interface” was facilitated by Don Carlton 

with the Washington Institute. The first draft of 

this unit was critically reviewed by the course 

faculty and suggested modifications hammered

out in discussion with faculty members, notably 

Jim Brenner, Barry Coulliette, Rich Gordon, John

Kern, and Judy Turner with the Florida Division 

of Forestry; Steven Miller with the St. Johns Water

Management District; Caroline Noble with the

National Park Service; and Walt Thomson with 

The Nature Conservancy. Don Carlton produced 

original electronic versions of figures 1 and 4. This

and all other evolving units were then presented in

a dry run to a group of hand picked experienced

burners and further modified in light of their 

comments. In February 2003, the smoke unit was 

distributed to the faculty and participants of the

dry run as well as to remaining Florida Division of

Forestry Forest Area Supervisors and Prescribed

Burn Team Leaders; these people were asked to

use and evaluate the screening system. Based on

the positive feedback from those who used and

evaluated this screening system over the next 2

years and the lack of any reported problems, it

was decided to formalize and publish this WUI

screening system for use throughout the South.

The authors also wish to thank Jim Brenner with 

21

Managing Smoke at the Wildland-Urban Interface

Appendix A

Some Federal and Florida Air Quality Laws and Rules 

Federal Clean Air Act

• The Clean Air Act (as amended in 1987 and 1997) is a legal system designed to protect human 

health and welfare.

• Several sections of the Clean Air Act have smoke management implications.

• The Clean Air Act establishes minimum requirements, which must be met nationwide, but 

States may establish additional requirements.

• The various acts, amendments, and regulations can be found on the U.S. Environmental

Protection Agency (EPA) Web site at http://www.epa.gov/epahome/laws.htm.

National Ambient Air Quality Standards

• EPA has established National Ambient Air Quality Standards (NAAQS) for the following air

pollutants that are produced in wildland fires:

– Particulate matter

– Nitrogen dioxide

– Ozone

– Carbon monoxide

• Air quality monitors are located throughout Florida and maintained by the Florida Department

of Environmental Protection, Division of Air Quality

• These monitors are often located at the wildland-urban interface, so they are much more likely

to be impacted by smoke at levels exceeding the NAAQS

Florida Statutes and Rules Pertaining to Smoke Management

• Burn authorization is required from Florida Division of Forestry.

• Florida Division of Forestry may restrict or cancel authorizations if burning under rule 5I–2 

of the Florida Administrative Code creates a condition that is deleterious to health, safety, or

general welfare.

continued
22

Gen. Tech. Rep. SRS–103

Appendix A (continued)

Florida Statutes and Rules Pertaining to Smoke Management (continued)

• Florida Division of Forestry authorizations require burning to be done between 9 a.m. and 1

hour before sunset or at other times when conditions warrant. For certified burners, this time

period is extended to 1 hour after sunset.

• Smoke from a burn must not reduce visibility on public roadways to < 500 feet.

• A burn must not violate local laws, rules, regulations, or ordinances.

• An updated synopsis of current Florida statutes and rules governing fire management can 

be found on the Florida Division of Forestry wildland fire Web site at http://www.fl-dof.com/

wildfire/index.
23

Managing Smoke at the Wildland-Urban Interface

Appendix B

How to Reduce the Smoke Impact from Prescribed Burns

7. Don’t burn during pollution alerts or 

stagnant conditions. Smoke tends to

stay near the ground at such times, will 

not disperse readily, and will exacerbate

existing conditions. Many fire weather

meteorologists include pollution alerts

and stagnation information in their daily 

forecasts. The mixing height should be at

least 1,700 feet and transport windspeed

should be at least 9 miles per hour (mph)

when prescribed burns are conducted.

8. Comply with air pollution control

regulations. Know the regulations that

apply at the proposed burn site when you

write the prescription. Check with your 

State fire control agency if in doubt.

9. Burn when conditions are good for rapid

dispersion. Ideally, the atmosphere should

be slightly unstable so smoke will rise

and dissipate, but not so unstable as to

cause a control problem. Again, your local 

forestry agency can help. Some States

use category day based on the ventilation

rate to describe smoke transport and

dispersion conditions, but the Dispersion

Index (DI) is a better indicator.

10. Reassess a decision to burn at the WUI 

when the daytime DI is forecast to be

below 41 and use increasing caution as it

approaches 70.

11. Use caution when within 500 feet of 

smoke-sensitive areas (SSAs) or upwind

of them. Burning should be done when

wind will carry smoke away from public

roads, airports, hospitals, schools, and

Prescribed burning can be used to achieve

many resource objectives, but it pollutes the air.

Burn managers have an obligation to minimize 

this pollution. If this obligation is ignored, 

prescribed burners can be held liable for smokerelated damage if smoke causes accidents or

other problems. To reduce the impact of smoke

at the wildland-urban interface (WUI), heed the 

following advice:

1. Smoke management should be based on 

common sense and integrity.

2. Prepare a written burn plan well in

advance of the burn.

3. Define objectives. Be sure you have 

clear resource objectives and have

considered both onsite and offsite

environmental impacts.

4. Develop a smoke management plan and

attach it (along with any calculations) to

the written burn prescription.

5. Fire weather and smoke management

forecasts are available through State

forestry agencies. Be sure to use them.

Such information is necessary to predict 

smoke production and movement as well

as fire behavior. If the forestry weather

outlook does not agree reasonably well

with the radio or television forecast, find

out why before proceeding.

6. In States that have a forestry agency

fire meteorologist, such as Florida and

Georgia, consider asking for a spot

weather forecast. Contact information 

can be obtained by calling your local 

forestry unit. continued
24

Gen. Tech. Rep. SRS–103

populated areas. This is often not possible

at the WUI so extreme care must be

exercised to minimize the impact on

SSAs. Do not burn if a hospital, school (in

session), or airport (unless departures 

and arrivals can be temporarily

suspended) is within one-half mile

downwind of the proposed burn. 

12. Work with local law enforcement

personnel to manage or reroute traffic

on downwind roads. Avoid heavy traffic 

periods such as noontime and late

afternoon. Monitor for residual smoke

on roads within 1 mile of the burn in all

directions until the fire is declared out.

13. Develop and implement a public relations

plan that includes personal contact 

with all homeowners and businesses

within one-half mile of the burn unit. 

Check for any health issues, especially

respiratory problems, and schedule the 

burn when any residents with relevent

health problems will be gone overnight;

work with such residents to find a place 

to stay or consider paying to put them in 

a motel at least the first night postburn. 

Use firing techniques and ignition

patterns that minimize offsite fly ash, 

make sure windows in all houses likely to 

be impacted are closed on the day of the

burn. Make sure inside pets are removed

during the burn. Make sure all potentially

affected residents understand that

prescribed fire reduces the hazardous

accumulation of fuels as well as air

pollution from wildfires.

14. When burn units have adjacent SSAs 

on three or more sides or when they are 

down-drainage, try to keep burn units 

smaller than 5 acres so they can be 

burned and completely mopped up within

a single day. It is much better to divide a

20-acre block into four 5-acre blocks and

burn and mop up each on a separate day 

than to burn all 20 acres as a single unit

and impact adjacent homes over the next

several days until mopup is complete. 

15. If the unit has homes on all sides (no 

smoke corridor), do not burn when DI is < 

41. The larger the area being burned, the 

greater the amount of particulate matter

put into the air, and the longer visibility is

reduced downwind. However, if weather 

conditions are good for rapid smoke

dispersion, as when the DI is above 50, it

is often better from a smoke management

standpoint to burn the whole area at

one time using a firing technique that

creates a convection column to loft the 

smoke over nearby structures and roads. 

Remember that creation of a convection

column during the flaming phase does

little to mitigate production, dilution, or

dispersion of residual smoke.

16. Fine fuels carry a fire. Removal of large 

(100- and 1000-hr) dead, down fuels will

have little effect on reducing the fire

hazard at the WUI. Once they are ignited, 

however, large fuels generate smoke

for extended periods. Choose burning

conditions that will minimize ignition of

Appendix B (continued)

How to Reduce the Smoke Impact from Prescribed Burns (continued)
25

Managing Smoke at the Wildland-Urban Interface

large fuels. Ideally, burn when they are

wet and fine fuels are dry. Headfires are 

less likely to ignite larger fuels because

they have a shorter residence time. If

large fuels present are sound, consider 

the practicability of physically removing 

them prior to the burn.

17. Check moisture content of fine fuels and

lower litter by feeling with your hands. 

Upper litter should be fairly dry and lower 

litter too wet to burn.

18. Use the Keetch-Byram Drought Index

(also called the Cumulative Severity

Index). If large-diameter fuels are 

present, reconsider a decision to burn

when it is above 400 or use a moisture

meter to make sure the moisture content

of large dead fuels is above 20 percent.

19. If snags or stumps are present, take 

measures to keep them from igniting. 

20. Use a test fire to confirm smoke behavior.

Set it in or adjacent to (if fuel conditions

are comparable) the area proposed for 

burning, away from roads or other edge

effects, and make sure it is large enough

for you to assess smoke behavior.

21. Consider using a backfire at least near

homes. Although slower and more

expensive, a backing fire produces

less smoke (only about one-third of

the particulate emissions generated

by a heading fire). Substantially less 

smoldering combustion takes place in 

backing fires, and smoldering combustion 

emits about five times as much particulate

matter as flaming combustion emits.

22. Burn during the middle of the day when 

possible. Atmospheric conditions are

generally most favorable for smoke

dispersion at this time.

23. Do not ignite organic soils. If they are 

present at the WUI, use another method

to reduce hazardous fuel accumulations.

The only exception is if the organic soil is

confined to depressional ponds, in which

case burn only when they are full (no

organic soil above water). It is virtually 

impossible to put out an organic soil fire 

without submerging it in water. It will 

smoke for weeks despite control efforts,

creating severe smoke problems for miles

around. Such fires can also re-ignite

unconsumed surface fuels days or weeks 

later, resulting in a wildfire.

24. As a rule of thumb, do not burn at the 

WUI after sunset because smoke drift is

almost impossible to predict when surface 

winds die down. One exception is the

night after a frontal passage when surface

winds will be above 4 mph and relative

humidity will stay below 70 percent.

25. Never burn at the WUI under an

inversion, no matter how small the unit.

26. A nighttime smoke patrol is

recommended when a burn at the WUI is

still smoking at sundown.

27. Anticipate down-drainage smoke flow. 

Atmospheric conditions tend to become 

Appendix B (continued)

How to Reduce the Smoke Impact from Prescribed Burns (continued)

continued
26

Gen. Tech. Rep. SRS–103

Appendix B (continued)

How to Reduce the Smoke Impact from Prescribed Burns (continued)

stable at night. Stable conditions tend to

keep smoke near the ground. In addition,

downslope winds generally prevail at 

night even on gradual slopes unless

surface winds are stronger. Thus, smoke 

will flow down-drainage and concentrate 

in low areas. When relative humidity 

rises above 80 percent and smoke is

present, the formation of fog becomes 

increasingly likely as moisture condenses 

on the smoke particles. There are few

satisfactory solutions to these problems,

so try to avoid burning at the WUI late in

the day.

28. Start mopup soon after the flame

front passes to reduce the impact on

visibility. Use water, ideally with foam, to

extinguish duff around tree stems, and all

stumps, snags, and logs.

29. Have an emergency plan. Be prepared 

to extinguish a prescribed burn if it

is not burning according to plan, or if

weather conditions change. Have warning 

signs on site. If wind direction changes, 

be prepared to quickly direct traffic 

on affected roads until traffic control 

personnel arrive.
27

Managing Smoke at the Wildland-Urban Interface

Appendix C

Suggested Reading

Lavdas, L.G; Hauck, C.A. 1991. Climatology

of selected prescribed fire highway safety 

parameters for Florida. In: Proceedings, 11th

conference on fire and forest meteorology.

SAF Publ. 91–04. Bethesda, MD: Society of

American Foresters: 564-571.

Laverty, L.; Williams, J. 2000. Protecting

people and sustaining resources in fire-adapted

ecosystems: a cohesive strategy. Washington, 

DC: U.S. Department of Agriculture Forest 

Service. 85 p.

Malm, W.C. 2000. Introduction to visibility. 

CA–2350–97. Ft. Collins, CO: Colorado State

University, Cooperative Institute for Research

in the Atmosphere: T097-04, T098-06.

Mobley, H.E. 1989. Summary of smoke-related

accidents in the South from prescribed fire

(1979–1988). Tech. Release 90–R–11. American 

Pulpwood Association.

U.S. Department of the Interior; U.S.

Department of Agriculture. 1995. Federal

wildland fire management policy and program

review. Final Rep. Boise, ID: Bureau of Land

Management. 45 p.

U.S. Department of the Interior; U.S. 

Department of Agriculture; U.S. 

Department of Energy [and others]. 

2001. Review and update of the 1995 Federal

wildland fire management policy. Boise, ID: 

Bureau of Land Management. 78 p.

Achtemeier, G.L. 2001. Simulating nocturnal

smoke movement. Fire Management Today. 61:

28-33.

Battye, R.; Bauer, B.; MacDonald, G.

1999. Features of prescribed fire and

smoke management rules for Western and

Southern States. Chapel Hill, NC: EC/R Inc.

Contract 68–D–98–026. Prepared for: U.S. 

Environmental Protection Agency

Breyfogle, S.; Ferguson, S.A. 1996. User 

assessment of smoke dispersion models

for wildland biomass burning. Gen. Tech. 

Rep. PNW–GTR–379. Portland, OR: U.S. 

Department of Agriculture Forest Service,

Pacific Northwest Research Station. 30 p.

Bryan, D.C., ed. 1997. Conference

proceedings: environmental regulation & 

prescribed fire: legal and social challenges. 

Tallahassee, FL: Florida State University,

Center for Professional Development. 246 p.

Eshee, W.D. 1997. Legal implications of using

prescribed fire. In: Environmental regulation

& prescribed fire: legal and social challenges.

Tallahassee, FL: Florida State University,

Center for Professional Development: 126-130.

Harms, M.F.; Lavdas, L.G. 1997. Draft user’s 

guide to VSMOKE–GIS for workstations. 

Research Pap. SRS–6. Asheville, NC: U.S. 

Department of Agriculture Forest Service,

Southern Research Station. 41 p.

Lavdas, L.G. 1996. Program VSMOKE – user 

manual. Gen. Tech. Rep. SRS–6. Asheville, NC: 

U.S. Department of Agriculture Forest Service,

Southern Research Station. 147 p.

continued
28

Gen. Tech. Rep. SRS–103

U.S. Environmental Protection Agency. 

1998. Interim air quality policy on wildland

and prescribed fires. [Place of publication

unknown]: U.S. Environmental Protection

Agency, Office of Air Quality Planning and

Standards. 29 p.

U.S. Environmental Protection Agency.

2000. National ambient air quality standards 

(NAAQS). http://www.epa.gov/air/criteria.

html. [Date accessed: March 2007].

U.S. Environmental Protection Agency.

2000. Wildland fire issues group. http://www.

epa.gov/ttncaaa1/faca/fa08.html. [Date

accessed: March 2007].

Wade, D.D.; Lunsford, J.D. 1989. A guide

for prescribed fire in southern forests. Tech.

Publ. R8–TP11. Atlanta: U.S. Department 

of Agriculture Forest Service, Southern 

Region. 56 p. [Reprinted by National Wildfire

Coordinating Group. Available from National

Interagency Fire Center, Boise, ID.]

Appendix C (continued)

Suggested Reading (continued)


Wade, Dale and Mobley, Hugh, 2007. Managing smoke at the wildlandurban interface, Gen. Tech. Rep. SRS-103. Asheville, NC: U.S. Department 

of Agriculture, Forest Service, Southern Research Station. 28 p.

When prescribed burning is conducted at the wildland-urban interface (WUI), 

the smoke that is produced can sometimes inconvenience people, but it can 

also cause more serious health and safety problems. The public is unlikely

to continue to tolerate the use of prescribed fire, regardless of the benefits, if

burn managers cannot keep smoke out of smoke-sensitive areas. In the South, 

forest management organizations commonly require that plans for prescribed 

burns pass a smoke screening review and some States require such a review

before they will authorize a burn. Current screening systems, however, do not

incorporate criteria for use at the WUI. This guide describes modifications 

to the Southern Smoke Screening System for burns at the WUI. These

modifications couple new research findings with the collective experience 

of burners who have extensively used the 1976 Southern Smoke Screening 

System. This new smoke screening system is designed for use on burns less 

than 50 acres in size and has undergone several years of successful field 

testing in Florida.

Keywords: Fire management, prescribed fire, smoke management, smoke

screening, wildland urban interface.
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