USDA
United States
Department
of Agriculture
Southeastern Forest
Experiment Station
Macon, GA31208
6ER&
United States
Environmental Protection
Agency
Industrial Environmental Research
Laboratory
Research Triangle Park NC 27711
EPA-60O«-79-019h
NovemberSS79
Research and Development
Source Assessment
Prescribed Burning,
State of the Art
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into nine series. These nine broad cate-
gories were established to facilitate further development and application of en-
vironmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The nine series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
6. Scientific and Technical Assessment Reports (STAR)
7. Interagency Energy-Environment Research and Development
8. "Special" Reports
9. Miscellaneous Reports
This report has been assigned to the ENVIRONMENTAL PROTECTION TECH-
NOLOGY series. This series describes research performed to develop and dem-
onstrate instrumentation, equipment, and methodology to repair or prevent en-
vironmental degradation from point and non-point sources of pollution. This work
provides the new or improved technology required for the control and treatment
of pollution sources to meet environmental quality standards.
EPA REVIEW NOTICE
This report has been reviewed by the U.S. Environmental Protection Agency, and
approved for publication. Approval does not signify that the contents necessarily
reflect the views and policy of the Agency, nor does mention of trade names or
commercial products constitute endorsement or recommendation for use.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.
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EPA-600/2-79-019h
November 1979
Source Assessment:
Prescribed Burning, State of the Art
by
C.T. Chi, D.A. Horn, R.B. Reznik,
D.L. Zanders, R.E. Opferkuch, and J.M. Nyers
and J.M.'Pierovich, L.G. Lavdas, C.K. McMahon,
R.M. Nelson, R.W. Johansen, and P.W. Ryan
Monsanto Research Corporation
1515 Nicholas Road
Dayton, Ohio 45407
Southeastern Forest Experiment Station
P.O. Box 5106
Macon, Georgia 31208
Contract No. 68-02-1874
Program Element No. 1AB015
EPA Project Officer: Ronald A. Venezia
Industrial Environmental Research Laboratory
Office of Environmental Engineering and Technology
Research Triangle Park, NC 27711
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Research and Development
Washington, DC 20460
Prepared for
and
U.S. Department of Agriculture
Forest Service
Washington, D C 20013
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PREFACE
The Industrial Environmental Research Laboratory (IERL) of the
U.S. Environmental Protection Agency (EPA) has the responsibility
for insuring that pollution control technology is available for
stationary sources to meet the requirements of the Clean Air Act,
the Federal Water Pollution Control Act, and solid waste legisla-
tion. If control technology is unavailable, inadequate, or
uneconomical, then financial support is provided for the develop-
ment of the needed control techniques for industrial and extrac-
tive process industries. Approaches considered include process
modifications, feedstock modifications, add-on control devices,
and complete process substitution. The scale of the control
technology programs ranges from bench- to full-scale demonstra-
tion plants.
IERL has the responsibility for developing control technology for
a large number of operations (more than 500) in the chemical and
related industries. As in any technical program, the first step
is to identify the unsolved problems. Each of the industries is
to be xamined in detail to determine if there is sufficient
potential environmental risk to justify the development of con-
trol technology by IERL.
Monsanto Research Corporation (MRC) has contracted wtih EPA to
investigate the environmental impact of various industries that
represent sources of pollutants in accordance with EPA's respon-
sibility, as outlined above. Dr. Robert C. Binning serves as MRC
Program Manager in this overall program, entitled "Source Assess-
ment," which includes the investigation of sources in each of
four categories: combustion, organic materials, inorganic materi-
als, and open sources. Dr. Dale A. Denny of the Industrial
Processes Division at Research Triangle Park serves as EPA Proj-
ect Officer for this series. Reports prepared in this program
are of two types: Source Assessment Documents and State-of-the-
Art Reports.
Source Assessment Documents contain data on pollutants from
specific industries. Such data are gathered from the literature,
government agencies, and cooperating companies. Sampling and
analyses are also performed by the contractor when the available
information does not adequately characterize the source pollut-
ants. These documents contain all of the information necessary
for IERL to decide whether a need exists to develop additional
control technology for specific industries.
111
-------
State-of-the-Art Reports include data on pollutants from specific
industries which are also gathered from the literature, govern-
ment agencies, and cooperating companies. However, no extensive
sampling is conducted by the contractor for such industries.
Sources in this category are considered by EPA to be of insuffi-
cient priority to warrant complete assessment for control technol-
ogy decision making. Therefore, results from such studies are
published as State-of-the-Art Reports for potential utility by
the government, industry, and others having specific needs and
interests.
This study was undertaken to provide information on air emissions
from prescribed burning. In this project, Dr. Ronald A. Venezia
served as EPA Task Officer.
IV
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ABSTRACT
This report summarizes reported data on air emissions from pre-
scribed burning, which is defined as the skillful application of
fire in forest and range management under conditions that will
confine the fire to a predetermined area and accomplish certain
planned benefits.
Prescribed fire is used on a seasonal basis in all regions of the
United States. The total vegetative material burned annually in
prescribed fires (1978 survey) is estimated at 36.6 million
metric tons, dry weight. Thirty-four percent of this total is
burned in the Southern region, and the Pacific Northwest and
Northern regions each burn 24 percent. Major fuel categories
include piled or windrowed material (49%), naturally occurring
understory vegetation and litter (31%), and broadcast (unpiled)
material (20%).
Imperfect combustion in the natural environment of prescribed
fires results in emission products from pyrolysis and oxidation
similar to those expected from other carbonaceous fuels. Impor-
tant among emissions are particulate matter, gaseous hydrocar-
bons, and carbon monoxide. Nitrogen found within the fuel and
from the atmosphere enters the combustion product formation pro-
cess to result in nitrogen oxides. Polycyclic organic matter
and trace amounts of metal elements are also emitted. Production
of sulfur dioxide is negligible. Amounts of emissions produced
are highly varied due to variations in fuel moisture, arrange-
ment, and species, as well as to differences in preferences for
firing technique. By using smoothed emission factors derived for
all fuels, estimates have been made of the total national emis-
sions produced by prescribed fires each year. Estimated emis-
sions from prescribed fires constitute 0.5%, 2.0%, and 2.7% of
national emissions from all stationary sources of particulates,
carbon monoxide, and hydrocarbons, respectively. Nitrogen oxides
production was not estimated due to current uncertainties related
to the fuel-bound, versus atmospheric, contributions for differ-
ent fuels and fire types.
The emerging best-available control technology calls for quanti-
tative appraisals of prescribed fire and its alternatives, and
for specifying conditions that will limit air quality impacts in
areas of concern. In those land management and air management
communities where this technology is being developed, these
v
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functions are defined as smoke management. Among the most viable
of alternatives to burning is increased utilization of timber-
harvesting residues, but even this alternative is limited by
markets and energy costs. Other alternatives are also practised,
but these, too, are energy demanding, costly, and, in some cases,
will not take the place of fire as a natural component in eco-
system dynamics.
A net decrease of prescribed fire emissions concentrations in
receptor areas is foreseen despite an expectation that more
emmisions will be produced from this source during the next
decade. The receptor area decrease is based most upon continued
and foreseeable applications of smoke management technology. The
emission production increase is based upon several actions which
will offset use of alternatives to fire, such as restrictions on
the use of herbicides and recent Presidential direction to in-
crease timber supplied from federal lands.
This report was submitted under Contract No. 68-02-1874 by
Monsanto Research Corporation under the sponsorship of the U.S.
Environmental Protection Agency. This report covers the period
from August 1975 to September 1979 and the work was completed as
of September 1979.
VI
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CONTENTS
Preface iii
Abstract v
Figures viii
Tables ix
Abbreviations and Symbols xii
Acknowledgements xiii
1. Introduction 1
2. Summary 2
3. Source Description 6
General character 6
Fuels 13
Fire behavior 16
Fuel categories and preferred firing
techniques related to smoke production
and dispersal 22
4. Geographic Distribution of Fuels Burned by
Prescription 29
5. Emissions 40
Introduction 40
Types of emissions 40
Factors affecting emissions 42
Measurement techniques 44
Emissions data 47
Regional and national estimates of the
annual production of criteria pollutants
from prescribed fire 60
"Safe-sided" emission factors for
local use 64
6. Control Technology 68
Introduction 68
General considerations 69
Appraisals of prescribed fire 69
Operating plans for smoke management .... 78
7. Outlook 87
Trends 87
Applying the technology 89
Conclusions 90
References. 92
Glossary. . 102
Conversion Factors and Metric Prefixes 106
Vll
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FIGURES
Number
Principal components of surface fuels
and aerial fuels 14
Extent of burning by categories of fuel,
expressed as percents of national total fuel
consumed each year 23
Geographic regions used to summarize survey
data within the conterminous states. (Alaska
Region also used in summarization not
shown.) 30
Extent of prescribed burning programs by
geographic regions, expressed as percents of
national net total fuel consumed each year,
all ownerships . 32
Chromatogram of organic (Ci* to €12) vapors
in loblolly pine smoke. Each peak represents
a separate compound. 55
Family of curves showing Arithmetic Mean and
several "Safe-sided" statistics for determining
total suspended particulate matter emission
factors for different categories of fuel and
fire types. Starred numbers refer to examples
of use in accompanying text 67
Vlll
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TABLES
Number Page
1 Elemental Composition and Heating Value
of Various Trees 16
2 Trace Elements Measured in Bark From Tree
Branches of Different Species (Average
Values on a Dry Weight Basis) 17
3 Estimated Net Total Weights of Fuel Consumed
Annually in Prescription Burning on All
Ownerships 30
4a Series of Geographic Region Tables Showing the
Principal Species, National Fire Danger Rating
Fuel Models (NFDRS) Applied, and Burning
Seasons for Each Geographic Region... ALASKA
REGION 33
4b Series of Geographic Region Tables Showing the
Principal Species, National Fire Danger Rating
Fuel Models (NFDRS) Applied, and Burning
Seasons for Each Geographic Region... EASTERN
REGION 33
4c Series of Geographic Region Tables Showing the
Principal Species, National Fire Danger Rating
Fuel Models (NFDRS) Applied, and Burning
Seasons for Each Geographic Region... INTER-
MOUNTAIN REGION 34
4d Series of Geographic Region Tables Showing the
Principal Species, National Fire Danger Rating
Fuel Models (NFDRS) Applied, and Burning
Seasons for Each Geographic Region... NORTHERN
REGION 35
4e Series of Geographic Region Tables Showing the
Principal Species, National Fire Danger Rating
Fuel Models (NFDRS) Applied, and Burning
Seasons for Each Geographic Region... PACIFIC
NORTHWEST REGION 35
IX
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TABLES (continued)
Number Pag<
4f Series of Geographic Region Tables Showing the
Principal Species, National Fire Danger Rating
Fuel Models (NFDRS) Applied, and Burning
Seasons for Each Geographic Region... PACIFIC
SOUTHWEST REGION 36
4g Series of Geographic Region Tables Showing the
Principal Species, National Fire Danger Rating
Fuel Models (NFDRS) Applied, and Burning
Seasons for Each Geographic Region... ROCKY
MOUNTAIN REGION 36
4h Series of Geographic Region Tables Showing the
Principal Species, National Fire Danger Rating
Fuel Models (NFDRS) Applied, and Burning
Seasons for Each Geographic Region... SOUTHERN
REGION 37
4i Series of Geographic Region Tables Showing the
Principal Species, National Fire Danger Rating
Fuel Models (NFDRS) Applied, and Burning
Seasons for Each Geographic Region... SOUTH-
WESTERN REGION 37
5 Categories of Fuels Associated with National
Fire Danger Rating System Fuel Models 39
6 Summary of National Ambient Air Quality
Standards 41
7 Emission Factors for Prescribed Fires 49
8 Emission Factors from Residential Wood
Combustion 52
9 POM Emission Factors From Burning Pine Needles
by Fire Type, yg/kg of Fuel Burned; Dry
Weight Basis 57
10 POM Emission Factors From Burning Pine Needles
by Fire Type, yg/kg of Fuel Burned; Dry
Weight Basis 58
11 PPOM Content of Total Suspended Particulate
Matter (TSP) From Burning Pine Needles, TSP. . 59
12 Results of Analysis of National Criteria Pollu-
tant Emission Factor Data From Tables 7 and 8. 63
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TABLES (continued)
Number Page
13 Regional and National Estimates of Annual
Criteria Pollutant Production From Prescribed
Fire, Including Comparisons with National
Production From All Sources (103 metric
tons) 65
14 Illustration of Typical Short-Term Peak TSP
Concentrations Data with Utility for Air
Quality-Related Appraisals of Prescribed
Fires of Short Duration (i.e., <3 or 4
Hours). Adapted from Tables in Reference 9. . 71
15 Quick Reference to Specification Options
Related to Fuels Characteristics 80
16 Quick Reference to Specification Options
Related to Firing Technique 82
17 Quick Reference to Specification Options
Related to Meteorological Scheduling 84
18 Summary of Some of the More Important Actions
and Trends, the Underlying Reasons, and
Projected Net Consequence to Receptor Area
Emissions Concentrations 88
XI
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ABBREVIATIONS AND SYMBOLS
NFDRS
POM
PPOM
PSD
SX
sx/x
THC
TLLMC
TSP
X
X
*L95
U99
national fire danger rating system
polycyclic organic material
particulate polycyclic organic material
prevention of significant deterioration
standard deviation of the sample
coefficient of variation
total hydrocarbons
total litter layer moisture content
total suspended particulate matter
arithmetic mean
quadratic mean
lower limit of the mean at the 95% confidence level
upper limit of the mean at the 90% confidence level
upper limit of the mean at the 95% confidence level
upper limit of the mean at the 99% confidence level
xn
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ACKNOWLEDGEMENTS
The authors wish to acknowledge the following individuals who
carefully reviewed this report during its preparation. Their
comments and suggestions were invaluable in producing a final
document of highest quality.
Warren Harper, Weyerhaeuser Company, Tacoma, Washington
Dan Sjolseth, Weyerhaeuser Company, Tacoma, Washington
Mark Rey, National Forest Products Association, Washington,
D.C.
Dr. John Pinkerton, National Council for Air and Stream
Improvement, Inc., New York, New York
Ron Smith, Oregon State Department of Forestry, Salem,
Oregon
Stewart Wells, Oregon State Department of Forestry, Salem,
Oregon
Neil Paulson, U.S. Forest Service, Washington, D.C.
Hugh Mobley, U.S. Forest Service, Southeastern Area, State
and Private Forestry, Macon, Georgia
Xlll
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SECTION 1
INTRODUCTION
Prescribed burning is the term applied by wildland managers in
the United States to a form of open burning. The name is derived
from the required prescription of atmospheric, fuel, and fire
variables by which the burning is to be conducted under control
to meet specified land management objectives. These objectives
include fire hazard reduction, silviculture, disease control,
range forage production, wildlife habitat improvement, and vege-
tation management for other purposes such as the protection
and/or enhancement of rare and endangered plants and animals.
The objective of this report is to document the current state of
knowledge of (1) the prescribed fire emissions source, (2) the
geographic distribution of this source, (3) emissions produced,
(4) control technology, and (5) outlook. To meet this objective,
the Environmental Protection Agency and its contractor have been
joined by the Forest Service, U.S. Department of Agriculture.
The literature and specialists in the field have been heavily
drawn upon in its preparation.
As a state-of-the-art study covering a wide diversity of practice
and an extremely variable set of natural elements, no attempt is
made to arrive at a direct assessment of effect upon air quality.
Rather, regional emissions production estimates are made using
the limited emissions data available. Then, by examining how
concentrations of these emissions may be locally predicted for
individual fires under prescribed conditions, a view of the
effect in receptor areas has been afforded.
A similar open burning operation, namely, agricultural open
burning, which includes the burning of residues of field crops,
row crops, and fruit and nut crops for field sanitation, residue
removal, and residue disposal, is not covered in this report.
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SECTION 2
SUMMARY
The name "Prescribed Fire" implies more than open burning. Pre-
scription criteria are established by which fires are confined
to areas under treatment, and are employed as a means of meeting
specified land-management objectives, in all regions of the
United States. Even when only one objective is specified, multi-
ple benefits will usually accrue to the land. For example, when
fire is prescribed to reduce residues from timber harvesting,
introduction of this natural ecological element will tend to pro-
mote improved wildlife habitat. Thus, while used only intermit-
tently on the same tract of land, prescribed fire is regarded by
land managers to be an ecologically sound practice for preventing
and/or reducing intensity of wildfires, for maintaining site
productivity, and for meeting many other land management
objectives.
The total vegetative material burned annually in prescribed fires
(1978 survey) is estimated at 36.6 million metric tons,a dry
weight. Thirty-four percent of this total is burned in the
Southern region, and the Pacific Northwest and Northern regions
each burn 24 percent. Major fuel categories include piled or
windrowed material (49%), naturally occurring understory vegeta-
tion and litter (31%), and broadcast (unpiled) material (20%).
Unlike agricultural open burning, which has been covered in a
separate report, the fuels consumed in wildland prescribed fires
are very heterogeneous.
Imperfect combustion in the natural environment of these fires
results in emission products from pyrolysis and oxidation which
may include several thousand compounds similar to those expected
from other carbonaceous fuels. Important among emissions are
particulate matter, gaseous hydrocarbons, and carbon monoxide.
Nitrogen found within the fuel and from the atmosphere enters the
combustion product formation process to result in nitrogen oxides.
Polycyclic organic matter and trace amounts of metal elements are
also emitted. Production of sulfur dioxide is negligible.
a
1 metric ton equals 106 grams; conversion factors and metric
system prefixes are presented at the end of this report.
-------
Amounts of emissions produced are highly varied due to variations
in fuel moisture, arrangement, and species, as well as to differ-
ences in preferences for firing technique. This variability is
reflected in overall emission factor ranges such as 2.5 g/kg to
79 g/kg for total suspended particulate matter, where grams
emitted are per kilograms of fuel actually consumed, dry weight.
By using smoothed emission factors derived for all fuels, esti-
mates have been made of the national prescribed fire total emis-
sions production each year for pollutants covered by the National
Ambient Air Quality Standards. These production estimates are
included in the data which follows. Also shown are estimates of
the relative national contribution of the estimated annual aver-
age prescribed fir production to the total produced by all
sources,3 expressed as percentages.
Thousands of metric
tons produced Percents at
Lower Upper average
Criteria pollutant limit Average limit value
Total suspended particulate
matter 366 622 878 0.5
Carbon monoxide 1,464 2,049 2,634 2.0
Total hydrocarbons 183 329 476 2.7
Nitrogen oxides Not estimated
Sulfur dioxide Negligible
Nitrogen oxides production was not estimated due to current un-
certainties related to the fuel-bound, versus atmospheric, con-
tributions for different fuels and fire types.
Several studies have shown that a high percentage of the mass of
total suspended particulate matter emitted from prescribed fires
is in the submicron size range. On a number basis, the average
aerodynamic particle diameter has been shown to be about 0.1 ym.
The emerging best-available control technology calls for quanti-
tative appraisals of prescribed fire and its alternatives, and
for specifying conditions that will limit air quality impacts in
areas of concern. In those land management and air management
communities where this technology is being developed, these func-
tions are defined as smoke management.
Among the most viable of alternatives to burning is increased
utilization of timber-harvesting residues, but even this alter-
native is limited by markets and energy costs. Other alternatives
Including fugitive dust. See Section 5 for further definition
of sources.
-------
are also practiced, but these, too, are energy demanding, costly,
and in some cases, will not take the place of a fire as a natural
component in ecosystem dynamics.
Smoke management appraisals of prescribed fire are to include an
assessment of predicted downwind emissions concentrations for
specified fuels, fire, and atmospheric variables. A smoke manage-
ment operating plan is drawn up using those specified variables
found in the appraisal to maintain acceptable receptor area con-
centrations. The major control features of these operating plans
are those which limit amounts of fuel to be burned, the selection
of a best-firing technique, and meteorological scheduling. Each
of these control measures can be further specified in individual
fire prescriptions. Some operating plans need only be fairly
simple, while others must be sophisticated. In several areas
where large amounts of fuel are burned each year, and where main-
tenance of air quality is a challenge, forms of centralized smoke
management have been effected. There, the amount of burning to
be scheduled each day will vary, depending upon a prediction of
the downwind consequences of all proposed burns, individually and
in combination. The more advanced smoke management technology
being brought on line now utilizes automated data processing of
near-real-time observed and forecast weather variables in opera-
tional adaptations of EPA-recommended dispersion models.
A net decrease of prescribed fire emissions concentrations in
receptor areas is foreseen despite an expectation that more emis-
sions will be produced from this source during the next decade.
The receptor area decrease is based most upon continued and fore-
seeable applications of smoke management technology. The emis-
sion production increase is based upon several actions which will
offset use of alternatives to fire, such as restrictions on the
use of herbicides and recent Presidential direction to increase
timber supplied from federal lands. Much of this latter action
will occur in defective oldgrowth (i.e., virgin) stands. Addi-
tional actions bearing upon the outlook for an upward trend in
emissions production are those taken to meet the need to conserve
energy and to reduce economic demands; lessening of the fuel and
dollar expenses for wildfire suppression by trading off prescribed
fire and wildfire emissions is an important example.
Areas of major importance to further characterization of the pre-
scribed fire source are: (1) development of improved and interim
emission and heat-release factors; (2) completion of mathematical
models of the fuel and fire interactions affecting emission rate
and heat-release rate; (3) quantification of emissions of "non-
criteria pollutants", (4) continued systematization of the avail-
able and emerging control technology in an appropriate smoke
management format. Improved and additional interim emission and
heat-release factors are needed for a wide variety of fuels and
burning situations. These need to be developed as best-available
-------
estimates even though parallel work is in progress which it is
hoped will obviate their need in time. The longer-term parallel
work will complete models of fuel and fire interactions and is
targeted at solving the problem of natural variability which now
confronts experimenters attempting to derive factors from in situ
prescribed fires. As with other sources of emissions, prescribed
fire smoke contains important constituents for which National
Ambient Air Quality Standards have not been set; quantification
of these "non-criteria pollutants" should continue to be incor-
porated in current research in anticipation of future standards.
Even though control technology in the form of smoke management
is now mainly in an emerging status, it is sufficiently advanced
to call for emphasis upon systems by which land managers and air
quality personnel may bring about needed applications.
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SECTION 3
SOURCE DESCRIPTION
GENERAL CHARACTER
Source Definition
Prescribed burning is the skillful application and confinement of
fire in forest and range management under specified conditions of
weather, fuel moisture, and soil moisture that will accomplish
planned benefits such as fire hazard reduction, control of under-
story species, seedbed and site preparation, grazing enhancement,
wildlife habitat improvement, and forest tree disease control.
It differs from wildfire in that it is employed only under con-
trolled conditions and is managed so that beneficial effects
outweigh costs and detrimental effects.
Unlike most sources of emissions, prescribed fires are mostly
seasonal and, as individual fires, are transient. While a large
landowner may have an annual program of prescription burning, the
individual fires each year will usually be limited to those days
within a few months when prescription criteria are met. Fires
located within the same ownership are scheduled either following
timber harvesting, or on cycles ranging from every two to every
eight years, depending upon rates of natural vegetation regrowth
and litter accumulation.
Prescribed burning is a portion of the overall open burning seg-
ment of combustion sources of air pollution in the United States.
A similar open burning operation, namely, agricultural open burn-
ing, is covered in a separate report (1), and is not included in
this study. Agricultural open burning covered in that report
includes burning of residues of field crops, row crops, and fruit
and nut crops for purposes of field sanitation, residue removal,
and residue disposal.
(1) Chi, C. T., and D. L. Zanders. Source Assessment: Agricul-
tural Open Burning, State of the Art. EPA-600/2-77-107a, U.S.
Environmental Protection Agency, Research Triangle Park, North
Carolina, July 1977. 74 pp.
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Fire As A Natural Agent
Fire in the past was a major natural environmental factor in con-
trolling plant succession, species composition, and age structure
in forests (2, 3). In the wilderness state, fire tended to fol-
low natural fuel accumulations, with great conflagrations in
drought periods leading to the creation of extensive open grass
and brush areas. In the long intervals that followed, grass and
brush would gradually be replaced by the prevalent forest types
through the process of natural succession. Succession is defined
as the more or less orderly pattern of events and processes in
nature whereby plant and animal species replace each other as a
result of changing environment over time.
Some plant types are dependent upon fire for the maintenance of
their position in the ecosystem. Aspen and jack pine in the Lake
States, longleaf pine in the South, ponderosa pine in the South-
west, and lodgepole pine in the Rocky Mountains are just a few
of the species whose natural regeneration and survival are re-
lated to periodic fires. With the absence of natural disturban-
ces like fire, species such as pines tend to be succeeded by more
shade-tolerant species such as true firs and hardwoods. Dis-
turbances which man regards as "natural disasters" are frequently
localized and classed as relatively minor ecological factors
overall. Research during the last 40 years has shown that fire
is neither minor nor abnormal, but, rather, a major factor for
most of the terrestrial habitats of the world. Man's failure to
recognize ecosystem adaptations to fire has indeed been cited
as the source of a great deal of mismanagement of our natural
resources (4).
Many trees and other native plant and animal species in areas of
naturally high fire frequency are adapted to fire through the
process of natural selection. Adaptations to fire found in in-
digenous species include: serotinous cones of lodgepole pine in
the West, and of sand pine in the East, for both of which the
heat of fire induces release of seeds; light, wind-disseminated
seed of some species such as aspen, cottonwood, and western larch
(2) Fire in the Northern Environment - A Symposium. C. W.
Slaughter, R. J. Barney, and G. M. Hansen, editors. U.S.
Department of Agriculture, Forest Service, Pacific Northwest
Forest and Range Experiment Station, Portland, Oregon, 1971.
275 pp.
(3) Prescribed Burning Symposium Proceedings. U.S. Department
of Agriculture, Forest Service, Southeastern Forest Experi-
ment Station, Asheville, North Carolina, 1971. 160 pp.
(4) Odum, E. P. Fudamentals of Ecology, 3rd Edition. W. B.
Saunders Co., Philadelphia, Pennsylvania, 1971. 574 pp.
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that can blow from great distances, and fire-resistant bark of
ponderosa pine, longleaf pine, red pine, Douglas-fir, and redwood.
Chaparral is regarded as a fire-adapted plant community in which
recycling of the plant succession takes place each time enough
fuel accumulates and is ignited.
Use of Fire in Forest Management
Reduction of Hazardous Fuels—
A principal use of prescribed burning is that of hazard reduction •
a means of reducing fuel accumulations to levels which will sel-
dom support high-intensity wildfires. Fuel buildups composed of
vegetative growth and litter accumulations are an inherent part
of the forest environment, and they require some measure of con-
trol if eventual damage from wildfires is to be minimized. In
pine stands of the Coastal Plains and Piedmont areas of the South,
for example, heavy accumulations posing a serious threat from
wildfire may develop within 4 to 5 years (5,6).
Prescribed burning is also used to remove residue and nonmerchan-
table species remaining after a harvest cut of timber. In three
Pacific Coast states (California, Oregon, and Washington), the
annual logging residue (i.e., slash) has been estimated at
11 x 106 metric tons on a bone-dry basis (7). The removal of
these fuel concentrations is desirable because unburned slash has
been a primary fire control problem in the Pacific Northwest
since the late 1940's (8).
Fire exclusions in forested regions results in a gradual accumula-
tion of fuels - leading to the potential for a conflagration if
a wildfire does escape during extremely dry conditions. Property
loss, loss of life or injury, mortality of merchantable timber,
and other resource losses are examples of directly measurable,
or tangible, losses from such large, high-intensity fires, even
though prompt salvage of timber may reduce the overall net loss.
(5) Mobley, H. E., R. S. Jackson, W. E. Balmer, W. E. Ruziska,
and W. A. Hough. A Guide for Prescribed Fire in Southern
Forests. U.S. Department of Agriculture, Forest Service,
Atlanta, Georgia, May 1977. 40 pp.
(6) Davis, L. S. and R. W. Cooper. How Prescribed Burning
Affects Wildfire Occurrence. Journal of Forestry, 61(12):
915-917, 1963.
(7) Grantham, J. B. Forest Residue: A Forgotten Source of
Energy. Paper Processing, 10(2):17-20, 1974.
(8) Cramer, O. P. Disposal of Logging Residues Without Damage
to Air Quality. Technical Memorandum WBTM WR-37, U.S.
Department of Commerce, Salt Lake City, Utah, March 1969.
8 pp.
8
-------
An intense wildfire may consume the entire litter mat and expose
the mineral soil to erosion forces. In contrast, prescribed
burning is employed only under controlled conditions, when
temperature, wind, and fuel moisture meet prescribed criteria for
accomplishing land management objectives without damage to crop
trees and soil. In a proper prescribed fire, the soil is seldom
bared except possibly in the small areas adjacent to piled debris,
or to long-burning heavy fuels, where the surface litter will
become dried out and burn. This is illustrated by the estimated
litter fuel available to burn in southern prescribed fires. When
published tables are used in reverse, an indicated range of from
about 35 percent to about 98 percent is left unburned when the
total litter layer moisture content (TLLMC) varies from 10 percent
to 200 percent, respectively (9).
Site Preparation—
Prescribed burning is employed in preparing a proper site for tree
seeding or planting. Fire aids in the removal of litter and
debris which obstructs seed gemination; reduces upper organic
layers, thereby exposing adequate mineral soil for new seedlings;
and reduces competition for moisture, nutrients, heat, and light
by temporarily reducing or eliminating competing vegetation such
as shrubs, herbs, and grasses, as well as mosses and lichens. It
may also release quantities of essential mineral elements needed
for plant growth. These elements are present in the ash layer,
and represent a recycling of nutrients accumulated in the litter,
humus, wood, bark, and foilage of the old forest. Production of
some commercially important species of timber calls for clear
areas in which the seedlings can receive full light; hence clear-
cutting in small blocks has become a common practice in timber
management. Clearcutting deposits large amounts of residue on
the cut areas—cull logs, limbs, tops, foilage, and brush. Burn-
ing is used to remove the logging residue (i.e., slash) and kill
brush that would compete with the young trees of the next crop.
Control of Undesirable Species--
The pure pine stands of the South are a subclimax forest main-
tained largely by fires. In the absence of fire, most southern
pine sites succeed to a climax type of hardwood. If these species
are permitted to invade and develop, regeneration of pine is very
difficult.
In many grasslands, the gradual colonization by woody species is
retarded or reversed by fire because the brush stems are scorched
by fire, resulting in "dieback" even if new sprouts do gradually
reappear. Not all brush species resprout following scorching of
root crowns.
(9) Southern Forest Fire Laboratory Personnel. Southern Forest-
ry Smoke Management Guidebook. Forest Service General
Technical Report SE-10, U.S. Department of Agriculture,
Asheville, North Carolina, and Macon, Georgia, 1976. 140 pp.
-------
Wildlife Habitat Improvement—
Prescribed fire is used in wildland management for improving food
and cover conditions for certain threatened and endangered spe-
cies as well as the more common wildlife species. Quali, grouse,
deer, pheasant, turkeys, and other animals are supported best by
varied vegetative patterns which include open areas, and areas
where the early successional stages of the forest are found. As
the forest matures, open areas and the young trees, shrubs, and
herbs upon which animals depend disappear. Fire removes unpala-
table brush and litter, stimulates new shrub and sprout growth,
and increases yield and quality of herbage, legumes, and browse
from hardwood sprouts. Seeds and insects are also more plentiful
on burned areas.
Range Improvement—
Large areas of land in the United States support weed, brush,
woodland, or forest types where forage production can be greatly
increased by conversion to grassland or some other more desirable
forage cover. Prescribed fire is used in the conversion and re-
generation of these areas to improve the range for grazing. For
example, in mesquite-tobosa communities in west Texas, fire is
used to remove accumulated litter, increase yields and palatabil-
ity of tobosa, reduce mesquite canopy to acceptable levels, top-
kill misquite, kill mesquite, kill 40 percent to 80 percent of
three species of cactus, and kill undesirable broomweeds (10).
Where cattle are raised on forested ranges, fire is used to
improve forage production without affecting the pine overstory.
Wire-grasses and principal herbaceous plants of the pine wire-
grass type green up after burning. Periodic, low-intensity fires
control competition and maintain the grass species. In the
absence of fire, total herbaceous cover declines after 6 to 8
years, and the range becomes less desirable for animal use (5).
Disease Control—
Prescribed fire has a role in the control of forest tree diseases.
For years, fire has been recognized as the most practical means
of controlling brown spot disease (Scirrhia acicola) of long-leaf
pine seedlings. Brown spot is a fungal infection that defoliates
and weakens young plants, prevents height growth, and eventually
kills. As an example of the critical nature of some fire pre-
scriptions, temperatures in brown spot burning should be hot
enough to consume or scorch all infected needles, but should not
kill the terminal bud. Burning the infected needles reduces the
number of spores available to infect the seedlings the following
spring.
(10) Wright, H. A. Range Burning. Journal of Range Management,
27(1) :5-ll, 197.4.
10
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Insect Control—
The use of prescribed fire to control the red cone pine beetle
has been documented (11) as have other agriculture and forestry
applications, including both habitat changes and direct (heat)
dosages (12).
Access, Visibility, and Esthetics—
Both for public enjoyment and timber management operations, fire
is prescribed to improve access by reducing dense understory
vegetation. Diversity of cover also results from the mosaic of
different age classes that will be found in large tracts of land
treated in this way. Vegetative diversity further supports a
variety of birds and animals, and also provides greater oppor-
tunities for them to be seen in the park-like stands adjoining
age-classes of vegetation that are their optimum habitat (13).
Timing
A critical factor affecting characterization of prescribed burning
is timing. Prescribed fires are of comparatively short duration
and are mostly seasonal in nature. Individual fires may last
from a few hours to a day, except for larger pieces of wood, which
may sometimes smolder for weeks. The same tract of land is then
left unburned for a period of from one to ten years or even
longer. Annual or biannual burns may take place in areas subject
to wildlife habitat improvement, such as grasslands used for
quail cover. Understory burning in pine forests generally takes
place every five years, but may be longer in areas where growth
is slow.
In the prescribed burning of chapparal in the West, timing is very
important. Up to approximately seven years after the last burn,
litter is lacking and the new growth will not carry fire alone.
By about the tenth year, however, dead stems and twigs accumulate
and, in combination with the seasonally-dried living vegetation,
will burn explosively if set afire.
Prescribed fire used to dispose of timber-harvesting residues may
take place as infrequently as once every 25 to 100 years, depend-
ing on the cutting cycle.
(11) Miller, W. E. Use of Prescribed Burning in Seed Production
Areas to Control Red Pine Cone Beetle. Environmental Ento-
mology, 7:698-702, 1978.
(12) Miller, W. E. Fire as an Insect Management Tool. Bulletin
of the Entomology Society of America, 25:137-140, 1979.
(13) Mobley, H. E. Personal communication. U.S. Department of
Agriculture, Forest Service, Macon, Georgia, July 1979.
11
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The season of the year is also important in prescribed burning.
Both the moisture content of the fuel and the ambient temperature
must be within given limits for a good burn, and those parameters
vary on a seasonal basis. For example, late winter or early
spring are generally the best seasons for prescribed understory
fires in southern pine stands, but when the timber is clearcut in
the South, the burning may be done whenever fuel and weather con-
ditions permit.
Constraints on Burning
Smoke management is being increasingly applied to prescribed
fires. This response to the need to maintain air quality can it-
self be an important constraint on burning. A review of the
checklists and smoke management procedures reveals that the number
of days available for burning may become more limited as a result
(9). If burning is scheduled with fewer years between prescribed
fires in the same area, less fuel will accumulate, and, thus,
less emissions will be produced per unit area per burning year.
But, this too must be classed as a constraint on burning if the
result is to force other land-management compromises and/or
additional expenditures.
Other prescribed burning constraints are found in a differentia-
tion of the two broad categories of burning, (1) where a tree
overstory exists, and (2) where no tree overstory exists. The
success of the first type is dependent on conditions such as
steady winds, cooler temperatures, and proper burning techniques
that minimize damage to the crop trees. The main considerations
in the second case are optimum removal of debris or unwanted vege-
tation from an area, while keeping fires confined to areas being
treated. Different techniques are used for each situation.
When burning under a tree overstory, a forest manager must wait
for those days when temperatures are relatively low and when
winds are likely to remain steady for the burning period. He can
then ignite the downwind side of his area and allow the fire to
back slowly against the wind. If fuel loading is light, and the
overstory trees are old enough, a higher intensity heading fire
may be acceptable.
When burning areas free of an overstory, there is obviously no
need for concern about damage to an overstory. Precautions to
prevent fire escape, to minimize air pollution downwind, to avoid
soil damage and unwanted runoff of ash, etc., need to be con-
sidered. Because flames of high-intensity heading fires will
lean further, these are often used when fuel continuity is poor.
12
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FUELS
Surface Fuels
Surface fuels include all combustible material lying on or imme-
diately above the ground, as shown in Figure 1 (14). Because
roots or the lower layers of duff, and highly organic soils, will
on occasion also burn with these more obvious fuels, they are
sometimes also included in the surface fuel category, or may be
known as "ground fuels." In this report all such fuels are clas-
sified as "surface fuels." The principal fuel materials are duff,
surface litter, and low-lying vegetative growth.
Duff—
Duff is composed of matted layers of partially decomposed organic
matter and highly organic soils such as humus, peat, or muck on
the forest floor. Duff is normally moist and rather tightly com-
pressed and has little influence on the forward rate of spread of
a fire, supporting instead a slow, smoldering type of combustion.
A path for the fire to creep between patches of more flammable
material may, however, be found through duff. Normally, only the
uppermost layer of duff is consumed in the course of a fire.
During periods of drought, however, a severe wildfire may consume
all of the organic duff layers, exposing the mineral soil to
erosive forces.
Surface Litter—
Litter on the forest floor normally consists of fallen leaves or
needles, twigs, bark, cones, and small branches that have not
decayed sufficiently to lose their identity. It also includes
logs, stumps, and large limbs. Dry, dead leaves and needles are
highly flammable. Flammability depends on the physical charac-
teristics of the fuel element and on its arrangement. A litter
bed of ponderosa pine needles, for example, is more flammable
than one of spruce or Douglas-fir needles. Pine needles are much
larger in size and are shed in clusters of two-to-five needles to
form a loose, well-aerated mat. In contrast, spruce or Douglas-
fir needles are shed singly, are smaller in size, and form a
more compact moisture-retaining mat which ignites and burns more
slowly. Leaves or needles attached to fallen branches are par-
ticularly flammable because they are fully exposed to the air and
dry easily. Fine branches, small limbs, bark, and other similar
materials are important to influencing rate of spread and general
fire behavior. Fine dead wood in a dry condition ignites easily
and may act as kindling material for larger, heavier fuels. In
areas where there is a great accumulation of fine dead wood, an
extremely hot fire can develop. Large amounts of fine dead wood
accumulate on the ground in fire-killed, diseased, insect-damaged
(14) Intermediate Fire Behavior. U.S. Department of Agriculture,
Forest Service, August 1972. 59 pp.
13
-------
FUEL COMPONENTS
TREE BRANCHES
MOSS
SNAGS
LOW VEGETATION
LARGE LOGS
LEAVES GRASS
& LIMBWOOD
Figure 1. Principal components of surface fuels and aerial
fuels (14).
14
-------
or killed, wind-damaged, and ice-damaged timber stands, or in
areas containing logging slash. Under dry conditions, such areas
will burn violently with intense heat.
Heavy fuels, such as logs, stumps, and large limbs, require long
periods of hot, dry weather before they can become very flammable.
Usually this material is only partially consumed in short-lived
and less intense broadcast fires (i.e., fires which burn on a
broad front within a delineated area). Piling techniques are
commonly used in management programs to effect more complete con-
sumption. Extremely hot fires may develop in piles of logs and
large limbs because the various fuel components radiate heat to
each other.
Low-lying Vegetative Growth—
Surface growth includes grasses, low shrubs, ferns, seedlings,
and other small herbaceous plants. Flammability depends to a
large extent on species, moisture content, weather, and seasonal
variations. During the growing season, green and succulent new
growth can retard fire spread. However, when dry, the entire
plant will contribute to support of fast moving surface fires.
Open grass and brush types are an important fuel because of their
usual continuity and their complete exposure to the drying effects
of the sun and wind.
Aerial Fuels
Aerial fuels include all live and dead material located in the
upper forest canopy. The main aerial fuels are tree branches and
foilage, snags, high brush, mosses, lichens, and epiphytic plants.
Flammability of tree branches and foilage is dependent on type,
moisture content, and phenology of growth - volatile oils and
resins contained in pine needles make tree branches and crowns of
coniferous trees an important component in aerial fuels. Live
leaves of hardwood high-forest tree species will not normally
carry fire, but those of chaparral and related species do at times
when fuel moisture is low.
Dead branches and bark on trees and snags (dead standing trees)
are an important aerial fuel. Concentrations of dead branches
and foilage, such as found in insect- or disease-killed stands,
can even carry fire from tree to tree. Various species of moss,
lichens, and epiphytic plants hanging on trees are light and
flashy aerial fuels. These fuel elements react quickly to changes
in relative humidity and provide a means of spreading fires from
ground fuels to other aerial fuels, or from one aerial component
to another.
15
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FIRE BEHAVIOR
Fuel Properties
Materials consumed in prescribed fires consist of tree parts,
understory vegetation, ground litter, shrubs, and grasses. Ele-
mental analyses and heating values for common tree species are
shown in Table 1 (7). Carbon, hydrogen, and oxygen are the ele-
ments present in the largest amounts. The heating value of
resin-free, moisture-free wood is about 19.3 MJ/kg, while that of
resin is about 39.3 MJ/kg.. Thus, the woods containing resins or
oils (e.g., Douglas-fir and southern pines) have slightly higher
heating values than those that do not contain appreciable amounts
of these materials (e.g., hemlock, beech, or oak) (7). The com-
position of other materials besides wood (e.g., shrubs and
grasses) in general is similar to the composition of wood. A
typical ultimate analysis and heating value for straw (15) is
given in Table 1 for comparison.
TABLE 1. ELEMENTAL COMPOSITION AND HEATING
VALUE OF VARIOUS TREES (7)a
Heating
Composition, % value,
Species Carbon Hydrogen Oxygen Sulfur Nitrogen Ash MJ/kg
Douglas fir:
Wood
Bark
Western hemlock:
Wood
Bark
Yellow pine wood
Southern pine bark
Beech wood
Red oak wood
Strawb
52.3
53.0
50.4
51.2
52.6
56.5
51.6
49.5
42.7
6.3
6.2
5.8
5.8
7.0
5.5
6.3
6.6
5.9
40.5
39.3
41.4 0.1
39.2
40.0
37.0
41.5
43.7
45.1
0.1 0.8
1.5
2.2
0.1 3.7
1.3
0.4 0.6
0.6
0.2
0.6 5.6
21.0
22.8
21.6
21.6
22.3
, 21.8
20.4
20.2
14. 9C
Dry basis.
From Reference 15.
£
Heating value at 15.75% moisture content.
Note: Blanks indicate elements are below detection limit for species shown.
In addition to the major elements listed in Table 1, trace quan-
tities of numerous other elements have been identified in tree
(15) Johnson, A. J., and G. H. Auth. Fuels and Combustion Hand-
book. McGraw-Hill, New York, New York, 1951.
16
-------
parts. Table 2 contains a list of some of these elements and
their concentrations for various tree types as found in tree
bark (16).
TABLE 2. TRACE ELEMENTS MEASURED IN BARK FROM
TREE BRANCHES OF DIFFERENT SPECIES (16)
(AVERAGE VALUES ON A DRY WEIGHT BASIS)
Species
Red spruce
Balsam fir
Hemlock
White pine
Northern white cedar
White birch
Red maple
Aspen
Alumi-
num, ppm
89
154
130
157
85
24
23
15
Boron,
ppm
14
13
18
14
9
12
17
14
Calcium,
%
1.06
0.84
1.39
0.83
2.28
1.05
1.38
1.18
Copper,
ppm
14
9
9
7
1
7
8
12
Iron,
ppm
124
162
146
111
122
38
62
80
Magne-
sium, %
0.08
0.08
0.08
0.11
0.07
0.05
0.05
0.09
Manga-
nese, ppm
834
77
1,223
319
19
235
732
140
Molyb-
denum , ppm
6.7
5.5
8.7
5.1
16
6.3
7.5
6.4
Phos-
phorus , %
0.06
0.11
0.10
0.07
0.04
0.04
0.07
0.04
Potas-
sium, %
0.15
0.36
0.19
0.24
0.05
0.10
0.24
0.20
Zinc,
ppm
7:
66
41
94
21
100
70
97
Bone-dry wood is composed of cellulose, hemicellulose, lignin,
and extractables (oils, pigments, minerals). Cellulose, hemi-
cellulose, and lignin constitute 90 to 95 percent of the weight
of the wood. The proportions of these groups in the wood vary
from species to species, between trees of the same species, and
within parts of the same tree. The organic fraction of the ex-
tractables consists of many classes of compounds: aliphatic and
aromatic hydrocarbons, alcohols, aldehydes, gums, and sugars (17).
Combustion Process
The burning of wood is accomplished by a two-staged process of
pyrolysis and combustion, the relative proportions of which are
determined by burning conditions (16). Pyrolysis is generally
believed to be a heat-induced, endothermic chemical degradation
process in which virgin wood is transformed into charcoal, or-
ganic tars, and vapors. Combustion is the subsequent rapid oxi-
dation of the pyrolysate vapors escaping from the surface of the
fuel in the presence of oxygen. Although both pyrolysis and com-
bustion occur simultaneously in moving fires, the former is the
initiating stage of chemical decomposition. As wood is heated,
volatile components move to the fuel surface and are released to
the surrounding air. Initially, these volatiles contain large
amounts of water vapor and lower molecular weight organic com-
pounds. As temperature increases, the wood material undergoes
pyrolytic decomposition. The amount of resulting products depends
(16) Young, H. E. Preliminary Estimates of Bark Percentages and
Chemical Elements in Complete Trees of Eight Species in
Maine. Forest Products Journal, 21(5):56-59, 1971.
17
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upon heating temperatures, rate of heating, surrounding medium,
and wood species.
The order of decomposition of the wood components is: hemicellu-
lose, cellulose, lignin. Extractables evolve on the basis of
their volatility and reactivity at the higher temperatures. The
classic concept is one of initial heating resulting in an endo-
thermic reaction. Additional heating then results in an exother-
mic reaction (280°C to 300°C) with liberation of carbon dioxide,
carbon monoxide, and liquid distillate (acetic acid and its
homologs, methanol, and light tars). Further high-temperature
heating results in the production of hydrogen and heavy tars (17).
Hot gases and vapors, once released, mix with the oxygen in the
air and ignite - producing a second phase in the combustion pro-
cess. In this second phase, rapid oxidation, or flaming, of
these combustible vapors results in rapidly rising temperatures.
Pyrolysis continues during this period, along with the evolution
of high concentrations of organic compounds. Some of the pyro-
lytic proucts cool and condense without passing through the
flame zone; others pass through the flames but only partially
oxidize, producing a range of products.
Once the fire is started, it is propagated in a series of igni-
tions. Heating of the fuel ahead of the flame as it progresses
is the first step of the flame propagation mechanism. Heat sup-
plied to the potential fuel from the fire dehydrates the surface
of the fuel. Further heating results in pyrolysis and the re-
lease of combustible gases (as described above), which are then
ignited by the flame, and the fire advances to the new position.
Finally, a relatively constant rate of spread is achieved, a
rate that is the average of all the elemental rates (18).
The above discussion describes mechanisms involved in the active
burning phase or advancing front stage of the total prescribed
burning process. This phase of the burning process is associated
with the visible flame front moving through the fuel. After the
main flame front has passed over the fuel, the remaining un-
burned fuel smolders while dehydration, pyrolysis, solid oxida-
tion, and scattered flaming continue simultaneously. The
(17) Yamate, G. Development of Emission Factors for Estimating
Atmospheric Emissions from Forest Fires. EPA-450/3-73-009
(PB 230 889), U.S. Environmental Protection Agency, Research
Triangle Park, North Carolina, October 1973. 127 pp.
(18) Rothermel, R. C. A Mathematical Model for Predicting Fire
Spread in Wildland Fuels. Forest Service Research Paper
1NT-115 (PB 210 095), U.S. Department of Agriculture, Ogden,
Utah, January 1972. 40 pp.
18
-------
smoldering phase, often characterized by emissions of large
amounts of smoke, continues as long as temperatures remain
adequate.
Firing Techniques
The firing techniques employed in prescribed burning depend on
the kind of area to be burned and the burning conditions. There
are four major burning techniques: backing fire, heading fire,
ring- fire, and area-ignition (or sometimes, simultaneous area-
ignition) (9). Often, combinations of these categories are used
in a single burning operation. A fifth category is that of pile
and windrow fires.
Backing Fire—
Backing fires are ignited on the downwind side of an area and
permitted to spread against the wind. The advance of the active
burning zone is slow, and most of the fuel is consumed within
this zone. In this way, smoldering time for the fuel is reduced,
and total combustion efficiency of the fire is increased (i.e.,
for vegetative fuel, the greater the proportion of C02 and H20
produced by the fire, the greater is the combustion efficiency).
Since burning on slopes has an effect similar to wind on rate of
fire spread, daytime down-slope fires in hilly terrain behave
similarly to backing fires in flat country.3
The backing fire produces the least fire intensity of all tech-
niques - having slow spread rates, a narrow burning zone, and
short flames (5). It therefore lends itself to use in heavy fuel
accumulations and in removing understory growth and debris where
an overstory of crop trees exists.
Heading Fire—
Heading fires are ignited on the upwind side of an area and
spread with the wind. The active burning zone moves rapidly from
fuel element to fuel element. Under these conditions, many fuel
elements are not consumed completely in the active burning zone.
A rather large zone of smoldering.fuel .is left behind, producing
large quantities of products of incomplete combustion. This
technique is employed in lighter fuels if the amount of heat
produced will not scorch overstory tree crowns. Perennial grasses
are more apt to survive heading fires than backing fires. Head-
ing fires are also preferred for control of brownspot disease in
longleaf pine.
aFires set at the base of a slope, and with enough intensity to
partially overcome normal nighttime downslope winds, may be
made to spread upslope and behave like backing fires. When the
nighttime winds are fully overcome in these situations, fires
will spread upslope and behave like heading fires.
19
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Ring Fire—
Ring firing is accomplished by igniting the perimeter of the in-
tended burn area and allowing the fire to burn towards the center,
This technique results in a rapid, relatively hot fire and finds
particular application in reducing timber-harvesting residues in
clearcut areas.
Simultaneous Area Ignited Fire—
Area-ignited fires are set by igniting the intended burn area in
many individual spots and allowing individual fires to burn in
all directions as they come together.
This type of fire is frequently employed in clearcut areas when
a rapidly-developed and high-rising convection column is desired.
It will have high variability in burning intensity as junction
zones of increased intensity form.
Pile and Windrow Fire—
Piles and windrows are used in management programs to effect more
complete consumption of large pieces of material, such as logging
residue. When hand-piling is practiced (often where timber har-
vesting has taken place on fragile soils, as in many helicopter
logging operations), the objective is to dispose of only the fine
fuels and the smaller diameter branchwood. The preferred firing
technique calls for igniting the finer fuels around pile perime-
ters to obtain rapid heat buildup, permitting the larger fuel
elements to become ignited and consumed. The extreme fire inten-
sity may adversely affect the soil immediately beneath piles. In
occasional, poorly conducted operations, piles and windrows may
contain large amounts of soil when machine piled. This may
result in areas which burn and smolder for days.
Other Factors Affecting Emissions
In addition to the firing techniques mentioned above, other fac-
tors affecting the completeness of burning and emission of
pollutants can be separated into the two categories listed below;
the factors of major importance are indicated by an asterisk (5).
• Environmental factors
*wind speed and direction
*rainfall history
*relative humidity
cloud cover
temperature
air mass stability
slope of land
20
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« Fuel conditions
*fuel moisture content
*fuel loading
fuel arrangement
fuel species composition
Certain of these factors are discussed in more detail in Section
5.
Transport and Diffusion
Downwind concentrations of emissions from the prescribed fire
source are a result of the same transport and diffusion processes
modeled for other sources, but certain initiating factors require
special adaptations.
Because prescribed fires occur over a sizable area, receptor area
concentration patterns do not resemble those of stationary
sources (such as a stack) except after long travel distances.
The point source definition, thus, does not fit well. A better
overall definition is as a moving line or as an area source. It
must be emphasized, however, that unlike conventional line or
area sources, prescribed fires release sufficient heat during
initial stages to result in significant, though variable, plume
rise. This means that, aside from transport by winds, dispersion
of smoke from prescribed fires is a result of three separate
mechanisms. The first two mechanisms are entrainment by con-
vection into the rising plume, with subsequent dispersion in the
atmosphere. The third mechanism is diffusion of the unentrained
portion along the ground. All three mechanisms must be accounted
for in predicting the ground level concentrations of pollutants
downwind from the source (9).
Plume rise from prescribed fires depends upon the source heat
release rate and upon ambient meteorological conditions (chiefly,
wind speed and air mass stability). Heat release rate is a
function of the amount of fuel being consumed, and differs between
fire phases. A fire may be separated into two phases: convective-
lift phase and no-convective-lift phase. During the convective-
lift fire phase, most emissions are entrained into a definite
convective column as a result of the large quantities of heat
being released. The no-convective-lift fire phase occurs when
the heat release rate is not high enough to generate a significant
column. The advancing front, or active-burning stage, produces
the heat that is responsible for the convective column. Hence,
the emissions from this stage are generally contained within the
convection column. The residual, or smoldering, combustion stage
lacks the necessary heat to produce a significant convection col-
umn. As the flaming front of a fire advances, the heat of the
front exerts lessening influence on emissions from residual
21
-------
burning. These residual emissions are less and less drawn into
the column, and are increasingly left with no significant plume
rise.
There are still important knowledge gaps for the variety of fuel
and fire types concerning (1) differing emission rates for the
advancing-front fire stages and the residual, or smoldering
stages; and (2) heat release rates for these two stages. Thus, a
mathematical predictive model of the vertical profile of concen-
trations in the prescribed fire smoke column is not yet possible.
Estimated ratios of amounts of smoke lofted to amounts left un-
entrained are used instead for the convective lift fire phase.
In high-intensity fires, this ratio may attain 100 percent
lofted:0 percent unentrained. In low-intensity fires, such as
are used under tree canopies in the South, the ratio of 60 per-
cent lofted:40 percent unentrained has been suggested (9). This
implies a need to relate these ratios to the amounts of heat
released at different times in the life of a fire in order, to
predict downwind concentrations (19).
FUEL CATEGORIES AND PREFERRED FIRING TECHNIQUES RELATED TO SMOKE
PRODUCTION AND DISPERSAL
Percents of net fuel consumed on all ownerships, nationally, have
been determined for different categories of fuel in a recent U.S.
Forest Service survey (20), as shown in Figure 2. Preferences
for firing techniques were determined in the same survey. In
this section, major fuel categories and preferred firing tech-
niques are discussed in relation to smoke production and disper-
sal. Geographic distributions of these same major fuel catego-
ries are covered in Section 4.
Piled or Windrowed Timber Harvesting and Land-Clearing Residues
Net national total fuel consumption is 17.9 x 106 metric tons,
dry weight. Two subcategories of piled or windrowed timber har-
vesting and of landclearing residues have been combined due to
the relatively low amounts reported for all lesser categories of
landclearing (less than 3 percent of the national total net fuel
consumed in all, including rights-of-way, brushfields, and open
range). While practiced in the East, the greater extent of this
(19) Lavdas, L. G. Plume Rise from Prescribed Fire. In: Pro-
ceedings of the Society of American Foresters/American
Meteorological Society 5th Conference on Fire and Forest
Meteorology, Atlantic City, New Jersey, 1978. pp. 88-91.
(20) Pierovich, J. M. Office Report: A National Survey of Pre-
scribed Burning and Managed Natural Fires on All Ownerships,
Unpublished report on file, U.S. Department of Agriculture,
Forest Service, Southeastern Forest Experiment Station,
Asheville, North Carolina, 1978. 19 pp.
22
-------
31%
NATURALLY OCCURRING
UNDERSTORY
VEGETATIONS LI HER
49%
PILEDORWINDROWED
RESIDUES
20%
BROADCAST (UNPI LED)
RESIDUES
Figure 2. Extent of burning by categories of fuel, expressed as
percents of national total fuel consumed each year
(20).
type of burning is in the states west of the Mississippi River.
Investment in piling or windrowing treatment prior to burning is
for two main purposes: (1) to provide more unimpeded access for
subsequent revegetation or tree planting (usually by machines)
and use (as for grazing animals), and (2) to promote more effi-
cient combustion of larger materials. Stumps and root crowns are
included in some road right-of-way clearing, where forced air
blowers may even be employed to accelerate fuel consumption, and
in some range improvement where groups of dwarfed trees (frequent-
ly pifion and juniper) are uprooted by cabling as a means of
returning the landscape to a more open savannah type.
The firing technique preferred for this category is from the
base of the pile or windrow, and is obviously one which will pro-
vide as rapid ignition throughout as possible. In this way,
advantage is taken of radiant heat for more complete combustion
and greater convective lift of the smoke. As a general rule, the
dryer the material, the larger the pile dimensions, the greater
proportion of small sizes to be burned, and the less soil mixed
in with the fuel, the more complete will be the combustion. It
follows that the more rapid and complete the combustion, the less
unwanted emissions and the greater the convective lift of the
smoke plume.
23
-------
In partially-cut timber stands, piled harvesting residues are
confined to smaller quantities in each pile, but these are fre-
quently only limbwood and often are hand piled. Smaller piles
will be less likely to scorch tree crowns and are best suited to
the scattered residues being treated. Often, the piles are
covered to keep out rain, and then burned in late season when the
surrounding forest is wet or snow covered. Soil mixed with
material to be burned is usually minimal. An opportunity presents
itself with this treatment to schedule burning days for optimum
atmospheric dispersion and to limit amounts burned on any one day.
In areas where the entire stand has been harvested ("clear-cut"),
larger machine-constructed piles or windrows are employed. On
steep slopes (>30%), piles are frequently made using cable sys-
tems, and sometimes helicopters, to bring the material to the
collection and loading point ("landing") of the preceding harvest-
ing operation. This practice, which results in very little soil
disturbance, has come to be known as "YUM" for yarding (collec-
tion) of unmerchantable material. In the Northwest, where this
practice was undertaken by some land managers in an attempt to
better meet air quality requirements, the YUM piles are sometimes
sold for further utilization, depending upon markets, and are
looked upon as a potential new source of energy. This practice
is in itself energy-demanding, and the additional operating fuel
costs for loading, hauling, and further preprocessing can result
in a negative energy balance. Piles whdch are not further uti-
lized are available for burning late into the rainy season and
are sometimes even burned during precipitation as a means of
"washing out" the emissions.
In more gentle terrain, piling and windrowing in clearcut areas
are more likely to be done by bulldozers with brush-rake blades
(specially designed to minimize soil admixtures). This practice
is employed, rather than burning the material in place, where it
is desired to maximize the cleared area available for reforesta-
tion. The benefits are that on the flatter sites, machine plant-
ing is facilitated, and young trees are less subject to sustained
heat from large logs if wildfires later burn into planted areas.
The detriments are that greater soil disturbance may occur and
that more care must be taken to avoid soil admixtures with fuels
to be burned. As a consequence of windrowing, large dimension
material is afforded a greater opportunity to become better ig-
nited than if burned in place (broadcast treatment), but is not
afforded the desirable sustained heat of larger piles.
Naturally Occurring Understory Vegetation and Litter
Net national total fuel consumption is 11.5 x 106 metric tons,
dry weight. Understory burning may be for one land management
objective in particular, with fire prescriptions written to pro-
mote this benefit most, but other objectives are usually met as
24
-------
well. More common objectives are for fuel hazard reduction,
wildlife habitat improvement, forage improvement, disease control
(as discussed earlier in particular for control of brownspot
disease in longleaf pine during the "grass stage" of growth
development), and improved access. The practice is most common
in the coastal plain of the Southern States, but is being extended
north and west wherever natural fire dependence is recognized for
the desired dominant species. Common names of principal species
in fuel associations where this practice is employed are as
follows: in the East, in descending order of importance, south-
ern pine, southern pine/hardwood, jack pine/red pine, oak/pine;in
the West, in descending order of importance, ponderosa pine,
Douglas-fir/mixed conifer, mixed conifer, aspen.
Preference for firing technique varies widely with individual
dominant species and even within species as influenced by fuel
continuity, and probably as influenced by experience with an
established technique for a local area. Overall preferences,
based upon amounts of net fuel consumed, are backing fires in
multiple strips in both the East and West. General preferences
for other firing techniques, in descending order, are then as
follows: in the East, backing fires in a single line of fire,
heading fires in a single line of fire, heading fires in multiple
strips; in the West, heading fires in multiple strips, backing
fires in a single line of fire, heading fires in a single line of
fire. An increasing emphasis is being given to development of
ignition methods for closely-spaced simultaneous area ignition,
and a trend to this technique may be expected.
Because the foremost requirement of all understory burning is to
avoid scorched foliage in tree crowns (a general rule being the
less the better, but always to protect at least the upper two-
thirds of crown), fires in this fuel category are intentionally
of low intensity. Enough surface wind must also be present to
disperse the heat from under the timber stand.
Backing fires are less intense than other firing techniques.
Backing fires move slowly against the wind and/or downslope, and
will assure the most complete fuel consumption, but, as will be
discussed further in Section 5, they may result in a contrast of
emission products.
Heading fires are more intense, move rapidly with the wind and/or
upslope, and usually consume less fuel. Their combustion effi-
ciency is also less than backing >fires, and, thus, characteristi-
cally large smoldering areas are left behind the flaming front.
Plumes of heading fires are apt to be darker in appearance because
of a greater tendency toward "soot" production during the hotter
flaming period. Since heat is given off rapidly, the plume will
be lofted well during the convective-lift fire phase, but it is
25
-------
during the non-convective-lift phase that smoke from the remain-
ing smoldering fuel will not be well lofted because of a low
heat-release rate.
For maintenance of acceptable levels of fire intensity, simul-
taneous area ignition in underburning will depend upon numerous
small heading fires burning rapidly together. Because this
technique is still mainly under development, emissions and heat
release rates have not been studied to date. It can be expected,
however, that emissions will correspond to heading fires and
that the greater concurrent heat release during flaming combus-
tion will tend to add to plume height.
Broadcast (Unpiled) Timber-Harvesting and Land-Clearing Residues
Net national total fuel consumption is 7.2 x 106 metric tons, dry
weight. As with piled and windrowed fuels, broadcast (unpiled)
timber-harvesting and land-clearing residues have been combined
in one category because of the relatively low amounts reported
for brushfields and open-range treatments (less than 2 percent of
the reported national total net fuel consumed). Included in this
category of fuel is an unreported amount of residues which are
pretreated in place by a practice known as "chopping." When pre-
treated in this way (commonly using tractor-drawn bladed rollers),
tops and limbwood are broken and crushed into a more compact fuel
arrangement, which can be expected to result in less flashy com-
bustion, as well as in better fuel consumption (provided the
chopping is done when soil conditions resist burying and soil
admixtures with the fuel to be burned). No known emissions
studies have been conducted in this special fuel type which is
mostly limited to more gentle terrain in the East and to certain
brushfield and open-range treatments in the West.
As part of understanding treatment of this category of fuel, it
must be recognized that a substantial amount of timber-harvesting
residues are left broadcast but unburned. As examples, this may
occur when land managers determine that a fire risk is low or that
soils on fragile slopes will benefit most from permitting the
woody material to decay in place.3
aCriteria for such decisions are given in Reference 21, pp.
213-217.
(21) Pierovich, J. M., et al. Forest Residues Management Guide-
lines for the Pacific Northwest. Forest Service General
Technical Report PNW-33, U.S. Department of Agriculture,
Forest Service, Pacific Northwest Forest and Range Experiment
Station, Portland, Oregon, 1975. 273 pp.
26
-------
Areas of broadcast residue fuels designated for prescribed fire
treatment include those where there is an overstory of trees,
those where there has been no tree overstory (e.g., brushfields
or large areas of grassland) and those where all standing trees
have been harvested ("clearcut").
When an overstory is present, low-intensity fires are prescribed,
just as in the previously described treatment of naturally-
occurring understory vegetation and litter. Only an estimated
one percent of the national total net fuel consumed is in this
subcategory, mainly in the selectively harvested ponderosa pine,
mixed conifer, and lodgepole pine stands of the West. Preferred
treatments, when under a timber stand, are for strips of backing
fires, single lines of backing fires, and strip-heading fires,
in descending order of preference. Smoke production and disper-
sion relationships are similar to these same firing techniques
when applied to understory vegetation and litter, except that
harvesting residues result in longer times both for flaming com-
bustion and for smoldering combustion during the non-convective-
lift fire phase. Diurnal weather changes are, thus, of great
importance in planning this technique for disposal of harvesting
residues.
Preferred firing techniques for broadcast residues not under a
timber canopy favor more intense fires. The extent of larger
materials consumed depends upon fuel moisture and the extent to
which these have become accumulated in one place (or as popularly
described, "in jackpots") during previous harvesting operations.
Because aerial seeding and hand-planting or natural regeneration,
rather than machine operations, are practiced on most such areas,
burning is conducted mainly to reduce only branchwood and other
residues smaller than 2 inches in diameter. Frequently, larger
logs are consumed only when they are decayed, or when concentra-
tions of pitch are present. Where there is no overstory of trees,
firing techniques in descending order of reported preference for
broadcast residues treatment are: single lines of heading fires
(usually with a backing fire set first as a control measure at
the top of the slope or on the downwind boundary); strips of
backing fires; ring fires (where the order of firing calls for
progression from the upslope or downwind boundary, along both
flanks, and then across the base of the slope or upwind boundary);
simultaneous area ignition; strips of heading fires; single lines
of backing fires.
Correspondence to each of the firing techniques described
previously for other fuel categories are apparent. The ring fire
technique is most similar to several heading fires burning toward
a common central point and with a common well-defined smoke plume
27
-------
during the convective-lift fire phase. It has been postulated
(22) that the time relationships of emissions for a representa-
tive prescribed fire in this fuel category in Western Oregon and
Washington are constant for the first 6 hours, then undergo
exponential decay with a 4-hour time constant. Significant plume
rise has been further hypothesized to occur during the first 4
hours, with 100 percent lofting of emissions assumed for calcu-
lations covering this time period.
(22) Lavdas, L. G. A Statistical/Physical Estimate of the Effect
of Western Oregon Burning on Willamette Valley Air Quality.
Unpublished manuscript in progress, copy on file, U.S.
Department of Agriculture, Forest Service, Southeastern
Forest Experiment Station, Asheville, North Carolina, 1979.
15 pp.
28
-------
SECTION 4
GEOGRAPHIC DISTRIBUTION OF FUELS BURNED BY PRESCRIPTION
The U.S. Forest Service survey of all ownerships (20) referenced
in Section 3 was conducted among field offices, extending in some
cases to the district organizational level of the agency and its
cooperators. In other cases, estimates were made from available
data at regional levels only. Data have been summarized for the
geographic regions delineated in Figure 3, and for the Alaska
Region which is not shown.
Net total amounts of fuel consumed (i.e., "available fuel")
reported in each of the fuel categories described in Section 3
are shown by geographic regions in Table 3. The estimated total
annual fuel consumption of 3.66 x ip7 metric tons exceeds pre-
vious estimates by more than 100%. For example, a national
inventory of forest wildfires, forest managed burns, and agri-
cultural burns reported a fuel consumption for managed burns of
1.56 x 107 metric tons (23). An increase in amounts over pre-
vious estimates is perhaps most due to estimates of additional
acreages of burning done on private lands, but estimates of tons
of fuel burned per acre are also subject to variability. Methods
are available by which fairly exacting fuel estimates can be
made, but these are often expensive; in the present survey, most
estimates were limited by cost and time constraints to experi-
enced judgments. These judgments are likely least accurate for
the broadcast timber harvesting and land clearing fuel category.
(23) Yamate, G. Emissions Inventory from Forest Wildfires, Forest
Managed Burns, and Agricultural Burns. EPA-450/3-74-062
(PB 238 766), U.S. Environmental Protection Agency, Research
Triangle Park, North Carolina, November 1974. 34 pp.
29
-------
Figure 3. Geographic regions used to summarize survey data with-
in the conterminous states. (Alaska Region also used
in summarization not shown.)
TABLE 3. ESTIMATED NET TOTAL WEIGHTS OF FUEL
CONSUMED ANNUALLY IN PRESCRIPTION
BURNING ON ALL OWNERSHIPS (20)
Net annual consumption, 105 metric tons
(dry weight)
Timber harvesting and Naturally
land clearing occurring
residues understory
Geographic
region
Alaska
Eastern
Intermountain
Northern
Pacific
Northwest
Pacific
Southwest
Rocky Mountain
Southern
Southwestern
Total of all
regions
Piles or
windrows
0.
0.
6.
82.
50.
20.
4.
0.
12.
178.
5
1
9
7
4
2
9a
9
3
9
Broadcast
(unpiled)
0.
0.
6.
37.
8.
1.
9.
8.
71.
3
7
3
0
2a
0
9
3d
7
vegetation
and litter
0.
0.
0.
114.
0.
115.
1
5
2
2
3
3
Total
of all
categories
0
0
7
89
87
28
6
125
20
365
.5
.5
.6
.0
.4
.9
.1
.0
.9
.9
Includes precommercial thinning residues as follows: Pacific
Southwest and Rocky Mountain, each <0.1 x 105 metric tons;
Southwestern, 1.1 x 105 metric tons.
30
-------
Table 3 shows that prescribed fire treatment of the Naturally
Occurring Understory Vegetation and Litter fuel category is domi-
nant both nationally and regionally in the Southern Region.
While western regions are presently reporting relatively low
amounts in this fuel category, an expected upward trend will be
discussed later in Section 7 of this report. The conversion of
old growth (i.e., virgin) forests to managed forests accounts for
much of the relatively greater amounts of Timber Harvesting and
Land Clearing Residues categories of fuel consumed in the western
regions.
It is useful to examine the relative importance of prescribed
burning by regions of the Nation. Relative importance is shown
by regions in Figure 4 as percents of net national total fuel
consumed. Three regions are seen in Figure 4 to account for 82
percent of the national total net fuel consumed.
Prescription burning is possible only when both weather and fuel
moisture variables are within prespecified ranges. Increased
attention to optimizing atmospheric dispersion has placed a new
dimension on weather variables. As discussed in Section 3, piled
and windrowed fuels can often be burned when other fuels are too
moist, or even when the forest is blanketed by snow. No attempt
is made here to assess the days available to burning when all
variables are within prescribed ranges or at optimums, but infor-
mation from the referenced survey does make possible a statement
of the seasonal climatologies that are needed for this purpose,
as well as for the purpose of determining downwind impacts.
Seasons of burning for the principal species in each fuel associa-
tion are given in the series of Tables 4a through 4i, each of
which covers a specific geographic region. Fuel associations in
the Table 4 series are presented in descending order of importance
(on the basis of net total weight of fuel consumed) for each
region.
Many land managers routinely employ a National Fire Danger Rating
System (24) in planning their daily fire management activities.
A series of indices in this system provides needed information
about the day's predicted fire business. The system also affords
a now limited number of stylized fuel models with which many land
management personnel are familiar. Those NFDRS fuel models
reported to be applied within each fuel association are, thus,
also listed in descending order of importance (fuel consumed
basis) in the Table 4 series. With this information available,
(24) Deeming, J. E., R. E. Burgen, and J. D. Cohen. The National
Fire Danger Rating System. Forest Service General Technical
Report INT-39, U.S. Department of Agriculture, Forest Serv-
ice, Intermountain Forest and Range Experiment Station, Ogden,
Utah, 1978. 63 pp.
31
-------
ROCKY MOUNTAIN
2%
ALASKA& EASTERN
Figure 4. Extent of prescribed burning programs by geographic
regions, expressed as percents of national net total
fuel consumed each year, all ownerships (20).
32
-------
TABLE 4a. SERIES OF GEOGRAPHIC REGION TABLES SHOWING THE
PRINCIPAL SPECIES, NATIONAL FIRE DANGER RATING
FUEL MODELS (NFDRS) APPLIED, AND BURNING
SEASONS FOR EACH GEOGRAPHIC REGION... ALASKA
REGION (20)
Common names NFDRS Burning seasons
of principal species fuel
in fuel association model JA F MR AP MY JN JY At)
White spruce and I /• /
white spruce/birch
TABLE 4b. SERIES OF GEOGRAPHIC REGION TABLES SHOWING THE
- PRINCIPAL SPECIES, NATIONAL FIRE DANGER RATING
FUEL MODELS (NFDRS) APPLIED, AND BURNING
SEASONS FOR EACH GEOGRAPHIC REGION... EASTERN
REGION (20)
Common names NFDRS
of principal species fuel Burning seasons
in fuel association model . , JA F MR AP MY JN JY AU
Species comprising
^90% of reported
net total fuel
consumed
Jack pine K / /
J /-
Jack pine/red pine J /
Southern pine H & K / /
Oak E
Remaining species
comprising ^10% of
reported net total
fuel consumed
Aspen/balsam fir E / / /-
33
-------
TABLE 4c. SERIES OF GEOGRAPHIC REGION TABLES SHOWING THE
PRINCIPAL SPECIES, NATIONAL FIRE DANGER RATING
FUEL MODELS (NFDRS) APPLIED, AND BURNING
SEASONS FOR EACH GEOGRAPHIC REGION...
INTERMOUNTAIN REGION (20)
Common names NFDRS
of principal species fuel
in fuel association model
Burning seasons
JA
MR AP MY JN
JY
AU
Species comprising
^90% of reported
net total fuel
consumed
Lodgepole pine
Douglas-fir
Lodgepole pine/
mixed conifer
H
G
C
I
H & J
I
C
G
C
H
Mixed conifer
Engleman spruce/fir
Ponderosa pine
Remaining species
comprising ^10%
of reported net
total fuel
consumed
Ponderosa pine/
mixed conifer
Pinon/juniper
Aspen
Grass
Grass/sagebrush
Sagebrush/bitterbush/
greasewood
Sagebrush/pinon/
juniper
I
H
G
I
C
C
H
C
C
C
C
34
-------
TABLE 4d. SERIES OF GEOGRAPHIC REGION TABLES SHOWING THE
PRINCIPAL SPECIES, NATIONAL FIRE DANGER RATING
FUEL MODELS (NFDRS) APPLIED, AND BURNING SEASONS
FOR EACH GEOGRAPHIC REGION... NORTHERN REGION
(20)
Common names NFORS
of principal species fuel
in fuel association model
Burning seasons
JA
MR AP
MY
JN
JY
AU
Cedar/hemlock/grand
fir/lodgepole pine/
Douglas-fir/larch/
mixed conifer
TABLE 4e. SERIES OF GEOGRAPHIC REGION TABLES SHOWING THE
PRINCIPAL SPECIES, NATIONAL FIRE DANGER RATING
FUEL MODELS (NFDRS) APPLIED, AND BURNING SEASONS
FOR EACH GEOGRAPHIC REGION... PACIFIC NORTH-
WEST REGION (20)
Common names NFDRS
in fuel association model JA F MR AP
Doug las- fir/hemlock/
Ponderosa pine/
mixed conifer
Burning seasons
MY JN JY AU S 0 N D
/
Note:
Burning season, though year-long largely as a result of piling, usually peaks
for: Coast Range in late spring; Cascades and Eastern portions in fall.
35
-------
TABLE 4f. SERIES OF GEOGRAPHIC REGION TABLES SHOWING THE
PRINCIPAL SPECIES, NATIONAL FIRE DANGER RATING
FUEL MODELS (NFDRS) APPLIED, AND BURNING
SEASONS FOR EACH GEOGRAPHIC REGION... PACIFIC
SOUTHWEST REGION (20)
Common names NFDRS
of principal species fuel
in fuel association model
Burning seasons
JA
MR AP
MY
JN
JY
AU
Species comprising
•v-90% of reported
net total fuel
consumed
Mixed conifer
Not
specified
J&K comb. /-
I
C
K /-
J
-/
/ /
/
/
Mixed conifer/
Douglas-fir
Douglas-fir
Chaparral and
Chamise/chaparra1
Remaining species
comprising -v-10%
of reported net
total fuel
consumed
ISJ comb. /-
Not
specified
I
Not
specified /-
F /-
Ponderosa pine/
Douglas-fir J
Pinon/ juniper K
/
/
/
.,_, , _ . /
TABLE 4g. SERIES OF GEOGRAPHIC REGION TABLES SHOWING THE
PRINCIPAL SPECIES, NATIONAL FIRE DANGER RATING
FUEL MODELS (NFDRS) APPLIED, AND BURNING
SEASONS FOR EACH GEOGRAPHIC REGION... ROCKY
MOUNTAIN REGION (20)
Common names
of principal species
in fuel association
Ponderosa pine
Lodgepole pine
Eng Ionian spruce
"Brush"
NFDRS
fuel
model JA F MR AP
r /.
K /— /
J /
K / .
P /
Burning seasons
MY JN JY AU S 0 N D
/ tt
/ t
/ • • /
/
(spp. unspecified)
36
-------
TABLE 4h. SERIES OF GEOGRAPHIC REGION TABLES SHOWING THE
PRINCIPAL SPECIES, NATIONAL FIRE DANGER RATING
FUEL MODELS (NFDRS) APPLIED, AND BURNING
SEASONS FOR EACH GEOGRAPHIC REGION... SOUTHERN
REGION (20)
Common names
of principal species
in fuel association
Southern pine
Southern pine/
Hardwood
NFDRS
fuel
model
D
K
C
E
K
J
Burning seasons
JA F MR AP MY JN JY AU S 0 N D
/,.,. ,., / / /
/ / ' '
/ , / / /
/ / / /
fi it
/. / / /
/ / f /
TABLE 4i. SERIES OF GEOGRAPHIC REGION TABLES SHOWING THE
PRINCIPAL SPECIES, NATIONAL FIRE DANGER RATING
FUEL MODELS (NFDRS) APPLIED, AND BURNING
SEASONS FOR EACH GEOGRAPHIC REGION...
SOUTHWESTERN REGION (20)
Common names
of principal species
in fuel association
NFDRS Burning seasons
fuel
model JA F MR AP MY JN JY AU SON
Species comprising
i.90% of reported
net total fuel
consumed
Ponderosa pine
Remaining species
comprising ^10%
of reported net
total fuel
consumed
Mixed conifer
Pinon/juniper
J
K
J&K
comb.
C
G
K
C
/
/ •'
/
/
/
/
/
37
-------
current investigations (25, 26) may lead to ways that the famil-
iar NFDRS can in time be used in a new applied technology for
managing prescribed fire emissions. Categories of fuels included
in the Fuel Models are listed in Table 5 for additional reference.
Both the National Parks and National Forests are beginning to
include areas where fires are permitted to burn under prespeci-
fied conditions, in recognition of the natural role of fire in
fulfilling ecological requirements. Not included in the preceding
figures and tables, this type of "prescribed fire" is coming to
be known by several names: "Prescribed Natural Fire;" "Managed
Natural Fire;" "Fire by Unplanned Ignitions;" etc. The survey
shows that at present such fires account for less than 4/10 per-
cent of all fuel consumed nationally, with most of it being in
the western regions.
(25) McMahon, C. K. Combustion Processes in Wildland Fuels Re-
search Work Unit Description. Unpublished draft on file,
U.S. Department of Agriculture, Forest Service, Southeastern
Forest Experiment Station, Asheville, North Carolina, 1979.
10 pp.
(26) Ryan, P. W. Smoke Management Systems Research Work Unit
Description. Unpublished draft on file, U.S. Department of
Agriculture, Forest Service, Southeastern Forest Experiment
Station, Asheville, North Carolina, 1979. 9 pp.
38
-------
TABLE 5. CATEGORIES OF FUELS ASSOCIATED WITH
NATIONAL FIRE DANGER RATING SYSTEM
FUEL MODELS (24)
Fuel category NFDRS model
Grass and grass-like:
Western annual grasses L
Western perennial grasses A
Everglades sawgrass N
Tundra S
Savannah:
Open timber with grass C
Brush:
Mature California chaparral B
Intermediate chaparral F
High pocosin 0
Southern rough (palmetto-gallberry) D
Shrubs and grass T
Timber:
Short-needled conifer--heavy dead G
Short-needled conifer—normal dead H
Southern pine plantation P
Alaskan upland black spruce Q
Hardwoods—summer R
Hardwoods--winter E
Long-needled conifer—normal dead U
Slash (timber harvesting residues):
Heavy I
Medium J
Light K
39
-------
SECTION 5
EMISSIONS
INTRODUCTION
Although emissions from prescribed fires may be similar to those
from other combustion processes, their complete characterization
is much more complex. Many parameters affect the type of
emissions generated, the magnitude of emissions, and the emission
rate; these prameters vary widely from fire to fire. In addition,
the techniques used to measure emissions are still under develop-
ment and rely heavily on simulated fires. Emissions data for
prescribed fires are not extensive, especially in view of the
many types of prescribed fires, and much more work is needed in
the area of emissions measurement. This section discusses the
factors that affect emissions from prescribed fires, the tech-
niques used to measure emissions, and the emissions data that
have been reported to date. Data have been evaluated in terms of
representativeness and reliability by examining test conditions
and methods.
TYPES OF EMISSIONS
Emissions from prescribed fires include both criteria and non-
criteria pollutants. Criteria pollutants are those for which am-
bient air quality standards have been set as listed in Table 6
(27-29). Particulate matter includes any condensed phase that can
be trapped on a filter at standard conditions of temperature and
pressure, excluding water. In some cases, material collected in
impingers following the filter may be added into the total par-
ticulate loading. For many combustion sources such as utility
boilers, particulate emissions are an inorganic ash formed from
(27) Federal Register, 36:22384, November 25, 1971
(28) Federal Register, 43:46258, October 5, 1978.
(29) Federal Register, 44:8220, February 8, 1979.
40
-------
TABLE 6. SUMMARY OF NATIONAL AMBIENT AIR QUALITY STANDARDS (27-29)
Pollutant
Particulate matter
Sulfur Oxides
(measured as sulfur dioxide)
Carbon monoxide
Nitrogen dioxide
Ozone
Hydrocarbons (nonme thane)
Lead
Averaging
Annual (geometric mean)
24-hrb
Annual (arithmetic mean)
24-hrB
3-hrb
8-hrb
l-hrb
Annual (arithmetic mean)
l-hrb
3-hr (6 a.m. to 9 a.m.)
Quarterly
Primary
standards ,
yg/m3
75
260
80
365
c
10,000
40,000
100
235
160d
1.5
Secondary
standards ,
yg/m3
60a
150
c
c
1,300
10,000
40,000
100
235
160
1.5
The secondary annual standard (60 yg/m3) is a guide for assessing implementation
plans to achieve the 24-hr secondary standard.
Not to be exceeded more than once per year.
>
'No standard exists.
There is no primary ambient air quality standard for hydrocarbons. The value of
160 yg/m3 used for hydrocarbons in this report is an EPR-recommended guideline for
meeting the primary ambient air quality standard for ozone.
-------
minerals in the fuel. However, particles generated in prescribed
fires result from incomplete combustion and are primarily
carbonaceous material (30).
Carbon monoxide and hydrocarbons also result from incomplete
combustion. Hydrocarbons comprise a great number of individual
organic compounds; when used in the context of criteria pollu-
tants, the term denotes total nomethane hydrocarbons as measured
by a specified analysis method, namely a flame ionization detec-
tor (FID). "Hydrocarbon" is somewhat of a misnomer because
oxygenated organic species are measured as part of the total.
Sulfur oxides are formed during combustion by the oxidation of
sulfur in the fuel. They are not released to any great extent by
prescribed fires because the sulfur content of vegetation is low;
typical values are: <0.2% in foliage (30) and <0.1% in branches
and wood components (31). Nitrogen oxides arise from nitrogen in
the fuel and by reaction of atmospheric nitrogen in the flame
zone.
Non-criteria pollutants (i.e.: pollutants for which no ambient
air quality standards have been established) emitted from pre-
scribed fires are primarily organic species and trace elements
that are considered on an aggregate basis under the criteria
pollutant categories of hydrocarbons and particulate matter.
They are treated separately here to distinguish their specific
environmental effects. One class of organic compounds, the poly-
cyclic organic materials (POM's), includes recognized carcinogens.
Known to be formed in virtually all combustion processes involv-
ing carbonaceous fuel, their evaluation has been mandated by the
Clean Air Act Amendments of 1977.
FACTORS AFFECTING EMISSIONS
Because emissions from prescribed fires are produced during the
combustion process, variables that affect :combustion are the same
as those affecting emissions. This perspective is important in
understanding the variability in emissions from prescribed fires.
Particulate matter, hydrocarbons, and carbon monoxide emissions
from prescribed burning are a result of incomplete combustion. As
a simplification, it follows that those factors promoting better
combustion tend to reduce emissions of these constituents, and
(30) Ryan, P. W., and C. K. McMahon. Some Chemical and Physical
Characteristics of Emissions from Forest Fires. Presented
at the 69th Annual Meeting of the Air Pollution Control
Association, Portland, Oregon, June 27-July 1, 1976. 21 pp.
(31) Shriner, D. S., and G. S. Henderson. Sulfur Distribution and
Cycling in a Deciduous Forest Watershed. Journal of Envi-
ronmental Quality, 7(3):392-397, 1978.
42
-------
vice versa. The actual situation is more complex because some
parameters are interdependent, but the general principle applies.
For convenience, the variables affecting emissions can be grouped
into three categories: (1) firing techniques, (2) type and
condition of the fuel, and (3) environmental factors. Firing
techniques have been described in Section 3. One of the more im-
portant emissions effects of varying firing technique is between
heading fires and backing fires. Heading fires, for example,
result in more residual smoldering (a poor combustion situation)
and yield approximately three times more total suspended par-
ticulate matter than do backing fires (32). Fuel that is piled
for burning constitutes a distinct type of combustion situation
that has not been adequately characterized. Combustion condi-
tions (e.g., higher flame temperatures and longer burning times)
suggest that burning piles may resemble wood burned in fire-
places, but it must be noted that fuel and fire conditions would
be expected to be more ideal in fireplaces.
Fuel-related variables play a major role in determining emissions
and encompass such items as the type of fuel (this may be quite
complex), arrangement of fuel, fuel loading (i.e., amount of fuel
per unit area), and fuel moisture content. Fuel type signifies
the material burned (wood, brush, grass, leaves, or a combination
of these), the plant species, size of fuel pieces (i.e., the
length and diameter of pieces of wood), and age. Studies have
shown a difference in emissions not only between burning wood vs
burning leaves, but also between burning wood of different
species (9, 33-36).
(32) Ward, D. E., C. K. McMahon, and R. W. Johansen. An Update
on Particulate Emissions from Forest Fires. Presented at
the 69th Annual Meeting of the Air Pollution Control Associ-
ation, Portland, Oregon, June 27-July 1, 1976. 14 pp.
(33) Snowden, W. D., D. A. Alguard, G. A. Swanson, and W. E. Stol-
berg. Source Sampling Residential Fireplaces for Emission
Factor Development. EPA-450/3-76-010, U.S. Environmental
Protection Agency, Research Triangle Park, North Carolina,
November 1975. 173 pp.
(34) Clayton, L., G. Karels, C. Ong, and T. Ping. Emissions from
Residential Type Fireplaces. Source Tests 24C67, 26C, 29C67,
40C67, 41C67, 65C67, and 66C67, Bay Area Air Pollution Con-
trol District, San Francisco, California, January 31, 1968.
6 pp.
(35) Butcher, S. S., and D. I. Buckley. A Preliminary Study of
Particulate Emissions from Small Wood Stoves. Journal of
the Air Pollution Control Association, 27(4):346-347, 1977.
(36) Darley, E. F. Emission Factor Development for Leaf Burning.
EPA-450/3-76-004 (PB 263 660), U.S. Environmental Protection
Agency, Research Triangle Park, North Carolina, 1976. 43 pp.
43
-------
Environmental variables that influence emissions production in-
clude wind speed, wind direction with respect to the fire, rain-
fall history, relative humidity, air temperature, atmospheric
stability, and slope of land. Wind speed, wind direction, and
slope of land all determine how fast a heading fire or backing
fire will spread. In general, a faster moving fire front burns
less efficiently, produces more smoldering, and results in higher
emission levels. Rainfall history and relative humidity have a
direct bearing on the fuel moisture content.
Detailed consideration of some of the variables that affect emis-
sions is presented later under emission data for individual
pollutants. It must be emphasized again that the correlations
observed between emission levels and various parameters are only
generalizations, and can not be expected to apply in every
situation.
MEASUREMENT TECHNIQUES
Because prescribed fires are more nearly moving line or area
sources than point sources, and lack a convenient stack from
which to take samples, it is only with difficulty that emission
measurements taken in the field can be related to the actual
quantity of fuel consumed. Determining the total fuel consumed
in an individual burn is in itself a formidable task. Conse-
quently most emissions studies have relied on laboratory simula-
tion of field conditions. The major drawback to laboratory
studies is their inability to reproduce all of the factors pre-
sent in a field situation. As a result there is uncertainty
involved in applying measurements taken in the lab to field
conditions, with the degree of uncertainty depending on the fire
type being modeled.
Plumes from prescribed fires have been sampled using apparatus
on masts, in aircraft, and supported by tethered balloons (37-39)
(37) Ward, D. E., E. R. Elliott, C. K. McMahon, and D. D. Wade.
Particulate Source Strength Determination for Low-Intensity
Prescribed Fires. In: Proceedings, Control Technology of
Agricultural Air Pollutants Specialty Conference, Air Pollu-
tion Control Association, Pittsburgh, Pennsylvania, March
1974. pp. 39-55.
(38) Radke, L. F., J. L. Stith, D. A. Hegg, and P. V. Hobbs.
Airborne Studies of Particles and Gases from Forest Fires.
Journal of the Air Pollution Control Association, 28(1):30-
34, 1978.
(39) Ryan, P. W., C. D. Tangren, and C. K. McMahon. A Balloon
System for Profiling Smoke Plumes from Forest Fires. Paper
No. 79-6.1, Presented at the 72nd Annual Meeting of the Air
Pollution Control Association, Cincinnati, Ohio, June 24-29,
1979.
44
-------
A "window" is defined through which the windspeed (air flow) and
emissions concentrations are measured; these must then be related
back to the originating fire and its rate of fuel consumption at
the time of emissions production. Work in progress at the Forest
Service Southern Forest Fire Laboratory includes studies which
are pointed toward improving upon indirect methods for measure-
ment of combustion rate (39). A unique experiment has also pro-
vided results by which aerial and ground sampling systems have
been compared (40). Elusive plumes in a varying wind will, how-
ever, continue as a persistent field sampling problem best solved
by conducting field experiments only under a steady wind.
Quantitative field measurements of prescribed fire emissions im-
pacting in typically far-removed receptor areas are also difficult
to carry out due to frequent concurrent impacts from certain
other very similar vegetation sources, such as field burning,
wildfires, backyard burning, and home heating with wood. Charac-
terization of the prescribed burning aerosol is a continuing and
difficult task. Discovery of a reliable "signature" (i.e., iden-
tifying) compound would change this situation, but, until one is
found, it has been necessary to correlate measured air quality
monitoring samples with upwind burning activity.
Two studies in the Willamette Valley, Oregon, have reported upon
specialized methods employed to overcome the inherent sampling
problem. One, using gravimetric mass, particle size and upwind
activity methods shows the relative prescribed burning impact
upon ambient particulate matter levels to be greatest in rural
areas (due to absences of impacts from other sources); to be small
on a seasonal or annual basis when compared with geological im-
pacts (i.e., from soil); but to be substantial for a few hours
at a time (41). The other study utilized chemical mass balance,
carbon-14 analysis, and upwind activity methods, and showed that
all vegetation-burning sources together contribute the second
largest total suspended particulate matter (TSP) impact (geologic
sources being first). This study pointed to one sampling day
when upwind activity indicated about half of the TSP carbon to be
biogenic in origin, and primarily due to a slash fire. Fine par-
ticulate matter on this same day was largely attributed to the
(40) Ward, D. E., R. M. Nelson, Jr., and D. F. Adams. Forest
Fire Smoke Plume Documentation. Paper No. 79-6.3, Presented
at the 72nd Annual Meeting of the Air Pollution Control
Association, Cincinnati, Ohio, June 24-29, 1979.
(41) Lyons, C. E., et al. Relating Particulate Matter Sources
and Impacts in the Willamette Valley during Field and Slash
Burning. Paper No. 79-46.3, Presented at the 72nd Annual
Meeting of the Air Pollution Control Association, Cincinnati,
Ohio, June 24-29, 1979.
45
-------
slash burning source, but again, only through the usually less
certain method of determining what upwind activity had taken
place. Home heating with wood was described as the most sig-
nificant source of concern in the area (42).
Studies conducted in the laboratory have the advantage that both
the quantity of fuel burned and the amount of pollutants produced
can be monitored more accurately than in the field. Testing
apparatus has been described in the literature (36, 43, 44) and
generally consists of a platform on scales to hold the material
to be burned. A large cone over the platform collects combustion
products and funnels them to an exhaust stack where samples are
withdrawn for analysis. To simulate backing fires and heading
fires, the platform may be tilted at various angles. Particulate
matter samples are collected isokinetically on glass fiber fil-
ters; carbon monoxide (CO) and total hydrocarbons (THC) are mea-
sured by continuous on-line analysis (nondispersive infrared for
CO and flame ionization detection for THC). Grab samples are
also taken for analysis of individual hydrocarbon (i.e., organic)
species by gas chromatography and other methods. The stack gas
flow rate is monitored so that emission data, flow rate data, and
fuel consumption data can be combined to yield emission factors
(grams of emissions produced per kilogram of fuel burned, dry
weight basis).
Sampling and analysis procedures employed in laboratory studies
are generally proven, reliable methods, and can be expected to
yield good data. Analytical techniques for compounds classed
as polycyclic organic material (POM) are, however, very complex
and still subject to some debate. Three reported studies illus-
trate this point. One is a limited experimental series widely
cited in projections of certain POM compounds for the prescribed
fire source (often without the author's caution as to the limited
number of samples). In this case, results reported were restrict-
ed to the anthracene-to-coronene fraction, included in the so
called particulate polycyclic organic matter, intentionally avoid-
ing dispute due to possible errors from high vapor pressures of
(42) Cooper, J. A., J. G. Watson, and J. J. Huntzicker. Summary
of the Portland Aerosol Characterization Study (PACS).
Paper No. 79-24.4, Presented at the 72nd Annual Meeting of
the Air Pollution Control Association, Cincinnati, Ohio,
June 24-29, 1979.
(43) Darley, E. F., F. R. Burleson, E. H. Mateer, J. T. Middleton,
and V. P. Osterli. Contribution of Burning of Agricultural
Wastes to Photochemical Air Pollution. Journal of the Air
Pollution Control Association, 16(12):685-690, 1966.
(44) Gerstle, R. W., and D. A. Kemnitz. Atmospheric Emissions
from Open Burning. Journal of the Air Pollution Control
Association, 17(5):324-327, 1967.
46
-------
such POM compounds as those of the naphthalenes (45, 46).
Another study reports that the appreciable vapor pressures of a
number of POM compounds at ambient temperature can cause filter
samples to fail to include a significant portion of total mate-
rial (47). In the third example, a recent study employed cold
trap filters and reports the loss of benzo(a)pyrene from high
volume-collected glass fiber filters to be less than 0.008 ng/m3
(48)„ The procedure presently recommended by the EPA for sam-
pling of POM's is with a fiber filter followed by a solid porous
polymer sorbent trap (49).
The principal difficulty with laboratory studies lies in extrapo-
lating the data to field conditions that differ, almost inevi-
tably, from those in the laboratory. The present state of
knowledge offers little in the way of correlative experiments
that compare both lab and field emissions data for the same fuel
type and firing technique. An exception is found in tests on
southern pine understory which showed comparable results for both
lab and field (32, 37). Additional work is needed to better
establish the relationship between the two types of measurements.
EMISSIONS DATA
This subsection deals with results of published studies of emis-
sions data in detail. In the next subsection, these data are
(45) McMahon, C. K., and S. N. Tsoukalas. Polynuclear Aromatic
Hydrocarbons in Forest Fire Smoke. Presented at the Second
International Symposium on Polynuclear Aromatic Hydrocarbons,
Columbus, Ohio, September 28-30, 1977. 21 pp.
(46) McMahon, C. K. Personal communication. U.S. Department of
Agriculture, Forest Service, Macon, Georgia, March 29, 1979.
(47) Pupp, C., R. C. Lao, J. J. Murray, and R. F. Pottie. Equi-
librium Vapour Concentrations of Some Polycyclic Aromatic
Hydrocarbons, ASi+Oe and Se02 and the Collection Efficiencies
of these Air Pollutants. Atmospheric Environment, 8:915-925,
1974.
(48) Miguel, A. H., and S. K. Friedlander. Distribution of BaP
and Coronene...Submicron Range. Atmospheric Environment,
12(12):2407-2413, 1978.
(49) Lentzen, D. E., D. E. Wagoner, E. D. Estes, and W. F. Gut-
knecht. IERL-RTP Procedures Manual: Level 1 Environmental
Assessment (Second Edition). EPA-600/7-78-201, U.S. Environ-
mental Protection Agency, Research Triangle Park, North
Carolina, October 1978. 279 pp.
47
-------
summarized and an analyses of central tendencies is made by way
of arriving at estimates of regional and national total annual
criteria pollutant emissions production. The last subsection
covers emission factors for local use.
Emissions data are commonly reported in terms of emission factors,
i.e., the quantity of material emitted per unit of fuel burned.
Available data for emissions of criteria pollutants from pre-
scribed burning are compiled in Table 7 according to fuel type
and test conditions (9, 30, 32, 37, 43, 50-54). An examination
of Table 7 shows that most data are derived from laboratory
tests. Also, comparatively few of the many possible prescribed
burning conditions have been sampled. The wide spread in the
data is indicative of how greatly emissions vary with fuel type
and combustion conditions.
Some of the data for grassland in Table 7 resulted from studies
of agricultural open burning rather than prescribed burning. It
is beleived these best-available data may be cautiously used
due to some similarities in fuels. At the same time, it must be
recognized that agricultural fuels are usually many-fold more
homogeneous in species composition, texture, and arrangement than
are the similar fuels burned with prescribed fire.
(50) Sandberg, D. V. Measurements of Particulate Emissions from
Forest Residues in Open Burning Experiments. Ph.D. Thesis,
College of Forest Resources, University of Washington, 1974.
(51) Ryan, P. W. Quantity and Quality of Smoke Produced by
Southern Fuels in Prescribed Burning Operations. In:
Proceedings of the National Conference on Fire and Forest
Meteorology, American Meteorological Society and Society of
American Foresters, Lake Tahoe, California, April 2-4, 1974.
(52) Benner, W. H., P. Urone, C. K.'McMahon, and P. W. Ryan.
Photochemical Potential of Forest Fire Smoke. Presented at
the 70th Annual Meeting of the Air Pollution Control Asso-
ciation, Toronto, Ontario, Canada, June 20-24, 1977. 15 pp.
(53) Boubel, R. W., E. F. Darley, and E. A. Schuck. Emissions
from Burning Grass and Straw. Journal of the Air Pollution
Control Association, 19(7):497-500, 1969.
(54) Sandberg, D. V., S. G. Pickford, and E. F. Darley. Emissions
from Slash Burning and the Influence of Flame Retardant
Chemicals. Journal of the Air Pollution Control Association,
25(3):278-281, 1975.
48
-------
TABLE 7. EMISSION FACTORS FOR PRESCRIBED FIRES
Fuel category Fuel type
I. BROADCAST ARRANGEMENT
A. Understory live understory
(southern)
live understory
(southern)
pine needle litter
(southern)
pine needle litter
(southern)
pine needle litter
(southern)
pine needle litter
(southern)
pine needle litter
(southern)
slash pine needle
litter
slash pine needle
litter
Test
site
lab
field
lab
field
lab
lab
lab
lab
lab
Type fire
—
backfire
backfire
backfire
headfire
headfire
hoadfire
backfire
headfire
Other
test conditions
flaming combustion
phase
noldwring combustion
phase
50% slop*) 18%-27%
moisture content
50V slop* i 18%-27%
moisture content
Emission factors, gAg
P articulate
matter Hydrocarbons CO NOx Comments
12-48*
7.5-15*
8.5-14*
22-28*
20-79*
7-25*
32-90*
3-14
Reference
36
36
36
36
31,36
36
36
29
29
B. Brushfield
pine needles
(southern)
lab
native brush
San Joaquin
Valley, Cali-
fornia
native brush
San Francisco
Bay Area,
California, 1965
native brush
San Francisco
Bay Area,
California, 1966
lab
a small
(2 g)
sample
was ig-
nited on
a plat-
form
25* burned
on flat
platform
25* burned
on flat
platform
25* burned
on flat
platform
a. average for total 11-62
run
b. flaming phase 7-20
c. snoldaring phase 32-90
14% moisture content
8.7 ± 3
68 ± 28 4.3 1 1.0
a. dry brush
b. mixture of dry and
c. green brush
moisture content of
5% + 1%
moisture content of
13» ± 7%
2.4 ± 1.2 35 ± 4
7.6 ± 2.2e 40 ± 3
13.7 ± 4.46 67 ± 20
2.4 ± 1.0 32 ± 15
2.2 ± 1.1 28 ± 10
Averages and standard devi-
ation for best four ruos.
Data for all 16 runs are:
Hydrocarbons, 9.25±3 g/kgt
CO, 78±22 gAgi and NOx,
4.7±1.4 gAg. Data for
MO and NOa were also giveni
NO, 3.2±1.0 gAg: HOa, 1.6±
0.6 gAg (data for 16 runs).
Mixtures of 11 species of
brush were tested includ-
ing such types as chamise,
sagebrush, and manzanita.
Other test data for fruit
primings yielded similar
results.
51
(continued)
-------
TABLE 7 (continued)
t_n
o
Fuel category
C. Grassland
D. Logging debris
Fuel type
barley straw
rice straw
six types of
grass
six types of
grass
logging residue
(western)
logging residue
(western)
logging residue
(eastern)
Ponderosa pine
logging slash
Test
site Type fire
lab 25* burned
on flat
platform
lab 25* burned
on flat
platform
lab 25* burned
on flat
platform
lab 25* burned
on flat
platform
lab
field
lab
labf 30* burned
on flat
platform
Emission factors, g/kg
Other Particulate
test conditions matter Hydrocarbons CO NOx
7.2 ± 1.8e . 42 ± 12
4.6 1 1.2* 36 ± 8
moisture content ranged 5.2 to 8.2 3.5 to 9e 42 to 74
from 5% to 15%
'
moisture content ranged 4.5 to 13.0 2 to 9.5* 20 to 56
from 20% to 71%
3 to 12
14 to 54
—
a. untreated 6*1 5. 5*1 98 i 9
b. treated with di- 12 1 1.5 7.5 * 2 116 * 14
BjBBonium phosphate
(DAP) at 3 gal/100
ft»
c. treated with DAP 15 i 1 9*1 136 1 12
•t 6 gal/100 ft*
d. treated with DAP 18 t O.5 11 i 1.5 133 ± 20
at 12 gal/100 ft*
Comments
Moisture contents of
needles were 4%-ll%i of
twigs, 3%-8%i of branches
over 2 inches in dianetexr
3%-14%. Relative humidity
varied from 41% to 80%,
temperature from 70*F to
90 'F.
Reference
42
52
49
49
31
53
II. PILED OR WINDROHED ARRANGEMENT
A. Brushfields
B. Logging debris
C. Other
no data
no data
leaf piles from
15 species
leaf pile of
silver maple
lab 6* in a
conical
pile
lab 61 in a
conical
pile
dry leaves 4.7 to 38 1.3 to 32 26 to 95
mixture of dry and 82 23 73
green leaves
Moisture content ranged
from 6.4% to 26.6%. Wind-
rows were occasionally
ignited instead of piles.
Average moisture content
was 24.1%; 19.1% for dry
leaves and 41.9% for
green leaves.
42
42
Only particles less than 10 micron in diameter.
bCited in Reference 31 from Reference 50.
CBasically same data as in Reference 36.
Data are expected to be similar to those from grasslands.
eReported as total carbon.
^Emission factors for this series of tests are reported in terms g pollutantAg fuel actually consumed.
-------
Emissions data from the residential combustion of wood are given
for comparison in Table 8 (33-36, 55-57). It can be seen that
both sets of data are in general agreement. Emissions from resi-
dential wood combustion may be expected to resemble emissions
from wood and brush that is windrowed or piled for burning in the
field. However, caution is warranted due to the high variability
encountered, even in the contained environment of a stove or fire-
place, where fuels are again more homogeneous than in open burn-
ing of piles and windrows. (Note, for example, the range of 0.7
to 26 for particulate matter in Table 8.)
Sulfur Oxides
Little data have been reported on emissions of sulfur oxides from
prescribed fires, and they are considered a negligible emission
for the prescribed fire source. In a recent study, the plumes
from five prescribed fires were sampled from an airplane, and no
significant gaseous sulfur was found (38). A material balance
based on the sulfur content of vegetation (<0.2%) indicates that
emission factors must be less than 4 g/kg. Data for coal com-
bustion show that most of the sulfur in coal is released during
the combustion process (58). Recent work with burning of wood
bark (59) suggests a low conversion rate (approximately 5%) of
bark sulfur to S02, with the balance accounted for in the ash
combustion products. Another study on residential wood combus-
tion showed that most of the fuel sulfur was released as S02 (56).
(55) Source Testing for Fireplaces, Stoves, and Restaurant Grills
in Vail, Colorado. (Draft) PEDCo Environmental, Inc., Con-
tract 68-01-1999, U.S. Environmental Protection Agency,
Region VIII, Denver, Colorado, December 1977. 26 pp.
(56) DeAngelis, D. G., and D. S. Ruffin. Source Assessment:
Wood-Fired Residential Combustion Field Tests. Draft docu-
ment in preparation by Monsanto Research Corporation, Con-
tract 68-02-1874, for U.S. Environmental Protection Agency,
Research Triangle Park, North Carolina.
(57) Butcher, S. S., and E. M. Sorenson. A Study of Wood Stove
Particulate Emissions. Journal of the Air Pollution Con-
trol Association, 29(7):724-728, 1979.
(58) Compilation of Air Pollutant Emission Factors. Publication
AP-42-A, U.S. Environmental Protection Agency, Research
Triangle Park, North Carolina, February 1976. 216 pp.
(59) Oglesby, H. S., and R. 0. Blosser. Information on the Sul-
fur Content of Bark and Its Contributions to S02 Emissions
When Burned as Fuel. Paper 79-6.2, Presented at the 72nd
Annual Meeting of the Air Pollution Control Association,
Cincinnati, Ohio, June 24-29, 1979.
51
-------
TABLE 8. EMISSION FACTORS FROM RESIDENTIAL WOOD COMBUSTION
en
ro
Emission factor, g/kg
Test unit
Residential
fireplaces
(4 woods)
Residential
fireplaces
Wood stoves
Residential
fireplace
(4 woods)
Residential
fireplace
(4 woods)
Wood stoves
(2 stoves,
4 woods)
Wood stoves
(2 stoves,
2 woods)
Particulate
matter Hydrocarbons
5.9 to 15.3 2 to 3
(10)a (2.5)
5.2 to 24 2.7 to 41.4
(11.4) (20.6)
0.7 to 25
( 3.4)
15 to 26 10 to 390
(20) (120)
8 to 12
( 8.9)
5 to 18
( 9.2)
1.3 to 24.4
( 9.2)
CO N0x
43 to 87
(64)
12.9 to 219 0.8 to 7.8
(65) (2.1)
28 to 140
(94)
15 to 30 1.4 to 2.4
(22) (1.9)
91 to 370 0.2 to 0.8
(177) (0.5)
Reference
32
33
34
54
55
55
56
Values in parentheses are average emission factors for all measurements.
-------
Nitrogen Oxides
In addition to the data in Table 7, data have been reported on
NOX emissions from the burning of landscape refuse in a labora-
tory study (44). Emission factors ranged from 0.25 g/kg to
2 g/kg. Another laboratory study reported only the NOX concen-
tration at the temperature peak during the combustion of various
grass species (53). The concentration varied from 21 ppm to
72 ppm for dry grasses (20% to 71% moisture), showing that hotter
fires produce higher NOX levels. On the basis of these limited
data, it is impossible to determine what fraction of NOX emis-
sions arise from fuel nitrogen and what fraction from atmospheric
nitrogen. Progress toward this end has been made in a study
utilizing a thermogravimetric system and a chemiluminescence
nitrogen oxide analyzer to characterize production of nitrogen
oxides from fuel-bound nitrogen. Fuel nitrogen is reported from
that study to be an important source of NOX for low temperature
fires «1,000°C), but results were not expected to hold for high
intensity fires since thermal NO would be expected to dominate
(60). It is currently impossible to predict how NOX emissions
will vary under different field conditions, pointing to the need
for further experimentation.
Carbon Monoxide
Reported emission factors for carbon monoxide generally range from
20 g/kg to 100 g/kg, with the higher values associated with poor-
er combustion conditions such as green vegetation or higher mois-
ture content material. Logging slash treated with the fire
retardant chemical diammonium phosphate yielded CO emission fac-
tors in excess of 100 g/kg, presumably because the fire retar-
dant caused a longer period of smoldering (54).
Emission factors for CO have all been derived from laboratory
studies. Field studies have only measured CO concentrations
(60) Clements, H. B., and C. K. McMahon. Nitrogen Oxides from
Burning Forest Fuels Examined by Thermogravimetry and
Evolved Gas Analysis. Manuscript at press, copy on file,
U.S. Department of Agriculture, Forest Service, Southeastern
Forest Experiment Station, Asheville, North Carolina, 1979.
19 pp.
53
-------
near the fire zone (61, 62), and found that they decrease rapidly
with distance away from the fire. Further field studies are
needed to relate CO concentrations to the mass of fuel actually
consumed in a fire.
Hydrocarbons
Hydrocarbon emission factors for prescribed fires have been found
to vary from 2 g/kg to 32 g/kg in laboratory tests. Combustion
of green vegetation tended to yield higher emission factors,
although the highest values reported were for dry leaves. Only
one set of emission factors based on field studies was reported,
14 g/kg to 54 g/kg (50). Considering the extrapolations involved
in calculating emission factors from field measurements, both
lab and field data can be considered to be in good agreement.
A number of studies have characterized the hydrocarbons (i.e.,
organic compounds) emitted from prescribed fires (30, 43, 53,
54), and found a great number of species as illustrated in Figure
5 (30). The individual compounds observed, as well as the rela-
tive amount of different classes of compounds such as alkanes or
olefins, are strongly influenced by the type of fuel and combus-
tion conditions. In general, it has been found that the com-
pounds present in the highest concentrations are the low-molecular
weight hydrocarbons; methane, ethane, ethylene, propylene and
acetylene (54). Under good combustion conditions (i.e., no
smoldering), saturated and unsaturated hydrocarbons (alkanes,
alkenes, and alkynes) make up about 50% of total hydrocarbon
emissions (43, 53, 54).
The remaining carbonaceous material is composed of oxygenated
species such as aldehydes, ketones, and organic acids. During
poor combustion conditions, the relative percent of simple
alkanes, olefins, and alkynes decreases and the proportion of
other types of organic species increases (54). Additional stud-
ies are needed to correlate hydrocarbon emissions with combustion
conditions and to characterize the organic species emitted,
especially the oxygenated compounds.
(61) Countryman, C. M. Mass Fires and Fire Behavior. Pacific
Southwest Forest and Range Experiment Station Resource
Paper PSW-19, U.S. Department of Agriculture, Forest Service,
Berkeley, California, 1964.
(62) Fritschen, L., H. Bovee, K. Buettner, R. Charlson, L. Mon-
teith, S. G. Pickford, J. J. Murphy, and E. F. Darley.
Slash Fire Atmospheric Pollution. Forest Service Research
Paper PNW-97 (PB 192 342), U.S. Department of Agriculture,
Portland, Oregon, 1970. 42 pp.
54
-------
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One class of hydrocarbons that has received special attention is
the polycyclic organic materials, or POM's. A number of these
compounds (e.g., most widely referenced is benzo(a)pyrene) are
known to be carcinogenic, and they are formed during most carbo-
naceous fuel combustion processes. Data on POM emissions from
prescribed fires are sparse, and in fact there has been only one
study (45) performed to measure POM emissions from prescribed
fires, as that term is used in this report (i.e., in wildland
management). This investigation simulated backing fires and
heading fires using slash pine needle litter as the fuel, at three
different fuel loadings. Emissions were channeled through a
large stack where particulate matter samples were collected iso-
kinetically on a glass fiber filter in a modified high volume
sampler. Filters were extracted and the extract was analyzed
for POM's by gas chromatography-mass spectrometry. Test results
are shown in Tables 9, 10 and 11. Table 9 gives a breakdown of
emissions from heading fires into the active burning (or flaming)
phase and the smoldering phase.
As mentioned earlier in the discussion of measurement techniques,
the data in Tables 9, 10 and 11 must be interpreted with caution.
The limited amount of data also argues against coming to any
definite conclusion, but there is an indication that POM emissions
are higher under smoldering conditions than under flaming com-
bustion. More surprising is the finding that the highest POM
emissions occurred in a lightly loaded backing fire, while at the
same time particulate emissions were higher for heading fires.
Further studies are needed to explore this phenomenon before any
definite conclusions are drawn.
Particulate Matter
Currently under one standard as total suspended particulate matter
(TSP), this emission from prescribed fires has been studied much
more extensively than gaseous emissions because it visibly af-
fects air quality. TSP emission factors presented in Table 7
range from 2.5 g/kg to 90 g/kg, depending on fuel and combustion
conditions. Of the two fire types, backing fires have generally
lower emission factors than heading fires. This is believed to
be mainly due to the differences in combustion efficiency. Com-
bustion efficiency of smoldering fires, and of heading fires
which leave large smoldering areas behind the flaming front, is
less than for backing fires. TSP data from limited field experi-
ments are in general agreement with lab studies.
A number of investigators have provided characterizations of the
chemical and physical properties of particulate matter emissions.
Unlike many other combustion sources where particles consist of
inorganic ash, the particulate matter emissions from prescribed
fires are primarily organic in nature. This is commonly measured
by solvent extraction with benzene, with the benzene soluble
organic (BSO) fraction ranging from 40 percent to 75 percent (30).
56
-------
TABLE 9. POM EMISSION FACTORS FROM BURNING PINE NEEDLES
BY FIRE TYPE, yg/kg OF FUEL BURNED; DRY WEIGHT
BASIS3 (45)
Type fire and fuel loading
Backing fires Heading fires
anthracene/phenanthrene
Methyl anthracene
Fluoranthene
Pyrene
Methyl pyrene/fluoranthene
Benzo ( c ) phenanthrene
Chrysene/benz ( a ) anthracene
Methylchrysene
Benzofluoranthenes
Benzo(a)pyrene
Benzo(e)pyrene
Perylene
Me thy Ibenzopy rene s
Ideno( 1 , 2 , 3-cd)pyrene
Benzo(ghi)perylene
TOTAL PPO1T
Total suspended particulate
matter (TSP)
Benzene soluble organics
0.5 kg/rn2
12,181
9,400
14,563
20,407
18,580
8,845
"28,724
17,753
12,835
3,454
5,836
2,128
6,582
4,282
6,181
171,750
10 g/kg
55
percent
1.5 kg/mz
2,189
1,147
2,140
3,102
2,466
1,808
5,228
1,891
1.216
555
1,172
198
963
655
1,009
25,735
4.5 g/kg
50
percent
2.4 kg/in2
584
449
687
1,084
1,229
468
2,033
877
818
238
680
134
384
169
419
10,249
2.5 g/kg
45
percent
0.5 kg/mz
2.525
1,057
733
1,121
730
244
581
282
164
40
61
33
65
--
7,632
10 g/kg
44
percent
1.5 kg/mz
5,542
4,965
974
979
1,648
142
543
1,287
129
97
78
24
198
—
16 , 549
36 g/kg
73
percent
2.4 kg/mz
6,768
7,611
1,051
1,133
2,453
175
836
1,559
241
33
152
46
665
--
22,787
59 g/kg
75
percent
Heading fires by phase
Flaming Smoldering
0.5 kg/mz .
1,621
539
445
750
455
228
472
263
178
100
56
38
19
—
5,097
6.5 g/kg
39
percent
7,049
3,872
2,317
3.078
2.383
397
1,324
497
199
17
133
33
397
—
21,779
28 g/kg
48
percent
Flaming
TT5~
865
667
244
342
494
77
230
343
69
55
45
14
52
~"
3,456
5.5 g/kg
54
percent
Smoldering
kg/m*
9.046
8.193
1.516
1.454
2.501
189
769
1,989
174
36
102
32
304
~~
26,324
82 g/kg
76
percent
Flaming Smoldering
2.4 kg/m*
2,351
1,909
622
888
1,036
179
628
466
90
140
82
27
75
-"
8,389
16 g/kg
69
percent
8.791
11.447
1.331
1.291
3.396
173
980
2,290
347
203
61
1,069
~~
31,519
111 g/kg
76
percent
Sloisture content for all fires ranged between 18 to 27 percent
Particulate polycyclic organic material
-------
TABLE 10. POM EMISSION FACTORS FROM BURNING PINE NEEDLES BY
FIRE TYPE, pg/kg OF FUEL BURNED; DRY WEIGHT BASIS3 (45)
Anthracene/phenanthrene
Methyl anthracene
Fluoranthene
Pyrene
Methyl pyrene/fluoranthene
Benzo (c)plienanthrene
Chrysene/benz (a) anthracene
Methylchryaene
Ul
CO Benzofluoxanthenes
Benzo (a) pyrene
Benzo (e) pyrene
Perylene
Methylbenzopyrenes
Ideno (1,2, 3-cd) pyrene
Benzolghi Iperylene
Total suspended participate
matter (TSP)
Benzene soluble organics
12,181
9,400
14,563
20,407
18,580
8,845
28,724
17,753
12,835
3,454
5,836
2,'*128
6,582
4,282
6,181
171,750
10 gAg
55
percent
Type fire and fuel loading
Backing fires Heading fire
2,189
1,147
2,140
3,102
2,466
1,808
5,228
1,891
1,216
555
1.172
198
963
655
1,009
25,735
4.5 g/kg
50
percent
584
449
687
1,084
1,229
468
2,033
877
818
238
680
134
384
169
419
10,249
2.5 gAg
45
percent
2,525
1,057
733
1,121
730
244
581
282
164
38
61
33
65 '
—
7,632
10 gAg
44
percent
5,542
4,965
974
979
1,648
142
543
1,287
129
40
78
24
198
—
16,549
36 gAg'
73
percent
s
2.4 kg/a3
6,768
7,611
1,051
1,133
2,453
175
836
1,559
241
98
152
46
665
—
22,787
59 gAg
75
percent
Planing
0.5
1,621
539
445
750
455
228
472
263
178
33
56
38
19
—
5,097
6.5 gAg
39
percent
Heading fire by phase
SBOlderlna Flaming smoldering Flaming Smoldering
7,049
3,872
2.317
3.078
2.383
397
1,324
497
199
100
133
33
397
—
21,779
28 gAg
48
percent
1.5 h
865
667
244
342
494
77
230
343
69
17
45
14
52
~*
3,456
5.5 gAg
54
percent
9,046
8,193
1,516
1,454
2,501
189
769
1,989
174
55
102
32
304
;;
26,324
82 gAg
76
percent
2,351
1,909
622
888
1,036
179
628
466
90
36
82
27
75
I
8,389
16 gAg
69
percent
8.791
11,447
1.331
1,291
3,396
173
980
2,290
347
140
203
61
1,069
I
31,519
111 gAg
76
percent
dMoisture content for all fires ranged between 18 to 27 percent
Participate polycyciic organic material
-------
TABLE 11. PPOM CONTENT OF TOTAL SUSPENDED PARTICULATE
MATTER (TSP) FROM BURNING PINE NEEDLES,
TSP (45)
Fire type
Backing
Backing
Backing
Heading
Heading
Heading
Fuel loading,
kg/m2
(Ib/ft*)
0.5
(0.1)
1.5
(0.3)
2.4
(0.5)
0.5
(0.1)
1.5
(0.3)
2.4
(0.5)
Benzo (a)pyrene, yg/g
274
135
98
3
2
2
Total PPOMa, yg/g
13,982
6,254
4,084
873
399
392
Particulate polycyclic organic material
59
-------
The organic character of particulate matter results from incom-
plete combustion in the fire zone-. Organic species are volati-
lized by heat and, instead of being totally oxidized, are pyro-
lyzed or partially oxidized and escape to the air. Depending on
their molecular weight, they may subsequently condense as liquid
or solid particles in the submicron range. Some larger particles
are also generated by entrainment of fuel fragments in hot com-
bustion gases (30) .
A number of studies have shown that most of the particulate matter
released during prescribed fires is of submicron size. Tests on
slash pine fires gave 70 percent of the particle mass below
0.4 ym and 95 percent below 1 ym. For palmetto-gallberry fires,
the values are 51 percent below 0.4 ym and 91 percent below
1 ym (32). Studies in Australia (63) and England (64) reported
that most wood smoke is in the neighborhood of 0.1 ym in diameter.
In laboratory burning of Douglas fir logging slash, 82 percent
of the particulate mass was found to be under 1 ym and 69 percent
under 0.3 ym (65). Finally, a series of field experiments in
the southeastern United States showed that the average particle
diameter, on a number basis, was about 0.1 ym, independent of
fuel type (30).
REGIONAL AND NATIONAL ESTIMATES OF THE ANNUAL PRODUCTION OF
CRITERIA POLLUTANTS FROM PRESCRIBED FIRE
The preceding discussions have made it evident that there are
wide variations in results of prescribed fire emissions studies.
These variations are safely explained on the basis of natural
variability alone. Because of this variability, and because of
the many voids in knowledge regarding prescribed fire emissions,
wide ranges of national estimates of annual emissions production
from prescribed fire have resulted. In an examination of these
several previous estimates, fuel consumed data and emission
factors employed were seen to be causes for disagreement, and for
suggesting a new national total suspended particulate matter
(TSP) factor for prescribed fire (32). In suggesting a new
national TSP factor of 25 g/kg, existing data in combination were
weighed against the experience of the investigators with many
(63) MacArthur, D. A. Particle Sizes in Bush Fire Smoke. Aus-
tralian Forestry, 31:274-278, 1966.
(64) Foster, W. W. The Size of Wood Smoke Particles. Inter-
national Journal of Air Pollution, 3:89-96, 1960.
(65) Sandberg, D. V., and R. E. Martin. Particle Sizes in Slash
Fire Smoke. Pacific Northwest Forest and Range Experiment
Station Research Paper PNW-199, U.S. Department of Agricul-
ture, Portland, Oregon, 1975. 7 pp.
60
-------
field and experimental fires. Another approach to coping with
emission factor variability has been to express only the extremes,
or "reasonable extremes" of reported factors. Two examples of
this approach use a TSP emission factor range from 8 g/kg to
34 g/kg (66, 67), permitting the reviewer to recognize a real
value lies somewhere within this four-fold interval.
While the available data do not lend themselves well to statisti-
cal inference, investigators needing to reach a single value are
faced with the alternatives of: 1) arriving at either a judg-
mental approach (as in the 25 g/kg TSP example); 2) deriving
their own averages from results of published studies; and 3)
averaging the extremes of ranges (which for the 8-34 g/kg TSP
range example would yield an arithmetic mean of 21 g/kg).
In arriving at mean values from published emission factors, as in
alternative 2), above, there are some obvious risks. Important
among these are the risks that a subpopulation will be given
undue weight as a result of more studies in one area, or con-
versely, that another subpopulation will not be adequately
represented as a result of only few, or no, studies in the area
by which it is bounded. Some exhaustive studies may report only
a single factor which is the result of analysis of many data
points, while other studies may report several factors which are
each representative of only a few data points.
Despite these risks, as well as those which enter with all judg-
ments, the approach used for this report has been to follow a
combination of the above alternatives 1) and 2). The rationale
of this approach is to afford a measure of central tendency with-
in the data employed, and to express an average national factor
with an upper and lower limit, using as a basis what appear to be
the most representative published emission factors. As with all
other such estimates, it is necessary to caution that the above
risks have been taken, and that the derived emission factors
employed for regional and national estimates are not intended
for further local application.Factors for local application are
discussed in the next subsection.
Emission factors from preceding Tables 7 and 8 have been employed
in derivation of national factors with the following provisions.
(66) Cook, J. D., J. H. Himel, and R. H. Moyer. Impact of
Forestry Burning Upon Air Quality: A State-of-the-Knowledge
Characterization in Washington and Oregon. EPA-910/9-78-052,
U.S. Environmental Protection Agency, Region X, Seattle,
Washington, October 1978. 270 pp.
(67) Sandberg, D. V., et al. Effects of Fire on Air. Forest
Service. General Technical Report WO-9, U.S. Department of
Agriculture, Washington, D.C., 1978. 40 pp.
61
-------
In the case of understory values for TSP from Table 7, those
reported for only the smoldering combustion phase have been ex-
cluded since these do not represent the entire period of the fire,
as in other reported values. Table 7 values for piled leaves
were not used. Table 8 data for residential fireplaces are used
in part as a representation of the Piled and Windrowed fuel cate-
gory. Wood stove data are excluded due to the greater dissimilar-
ity of this type of combustion to prescribed fire. No attempt
has been made to arrive at emission factors for nitrogen oxides
due to the current uncertainty regarding fuel-bound versus atmos-
pheric contributions of nitrogen.
Sulfur dioxide has not been analyzed due to the negligible emis-
sions of this compound found in studies of the prescribed fire
source. The notable emission of several sulfurous compounds
found in studies of fire in organic soils of marshy areas (such
as the Florida Everglades) are associated with prescribed fire
only as proper prescriptions call for conditions which will pre-
vent ignition of the soil in these areas. A further relationship
to be expected is that an important tradeoff may, thus, be attrib-
uted to prescribed fires used to prevent subsequent wildfires
during seasons when the organic soils will burn.
Emission factor data for TSP, CO, and THC were examined for a
central tendency by calculating the arithmetic means and standard
deviations for each group of factors. Lower and upper limits
of the means were determined to n-1 degrees of freedom at the 95
percent confidence level. For this type of data, it is believed
an indicated error of less than a factor of two is reasonable.
Results of analysis showing the calculated values of statistical
terms and error comparisons are presented in Table 12. Not shown
in the table, but also of interest to the question of suitability
of the data, comparisons were made of the derived mean TSP emis-
sion factor to those TSP factors used as examples in the preceding
discussion. These comparisons show that the 25 g/kg example, and
that the arithmetic, geometric, and quadratic means of the 8-34
g/kg range example, all fall within less than a factor of two
error for the derived Table 12 TSP arithmetic mean of 17 g/kg.
The derived national mean emission factors, as well as their upper
and lower limits, from Table 12 were used with regional net fuel
consumed data from Table 3 to obtain estimates of regional and
national annual prescribed fire criteria pollutant emissions
production. The national estimates were then used to adjust
currently published (68) national all-sources totals. Estimates
(68) Eimutis, E. C., R. P. Quill, and G. M. Rinaldi. Source
Assessment: State by State Listing of Criteria Pollutant
Emissions (1978 Update). EPA-600/2-78-004s, U.S. Environ-
mental Protection Agency, Research Triangle Park, North
Carolina, July 1978. 155 pp.
62
-------
TABLE 12. RESULTS OF ANALYSIS OF NATIONAL CRITERIA POLLUTANT
EMISSION FACTOR DATA FROM TABLES 7 AND 8
Criteria
pollutant
Ranges of
Rounded emission factor emission
statistics,3 g/kg factors used
from Tables
C V .
bX AL95 X
U95 8 and 9
Error comparisons
results
X
X
L95
Total suspended
particulate matter,
TSP
Carbon monoxide,
CO
Total hydrocarbons,
THC
Nitrogen oxides,
NO
x
Sulfur dioxide.
18
43
12
12 17 23
2-79
42 56 69 12.9-21.9
12
1-54
Not estimated (see text)
Negligible
Symbols used:
Sv = standard deviation of the sample.
A
= lower limit of the mean at 95% confidence level.
X = arithmetic mean.
1.02 1.98
.78 1.64
1.30 2.36
U95 = upper limit of the mean at 95% confidence level.
= coefficient of variation.
63
-------
of the relative national production of prescribed fire to produc-
tion from all sources were then made as percentages. The cited
publication includes fugitive dust from certain defined sources
such as roads. The original reference should be consulted for
more detailed definitions of sources if needed for further analy-
ses. It should be noted that the national totals used from that
publication required some further corrections before used, due to
a few inconsistencies in state totals. Resulting estimates are
presented in Table 13.
"SAFE-SIDED" EMISSION FACTORS FOR LOCAL USE
The derived average emission factors used for regional and na-
tional estimates in the preceding subsection should not be used
for further localized estimates.
Only a portion of the important fuel types in the southern states
have been covered by studies which have permitted some suggested
TSP emission factors to be cautiously advanced for operational
smoke management (9). Procedures are published with these for
using the factors to make predictions of emissions at different
combustion stages and moisture levels, as well as for determining
appropriate emission rates. Current studies and proposals promise
to offer improved and interim factors and procedures for addi-
tional fuels and firing techniques (25, 26).
For use in the meantime, an attempt is herein made to provide
"safe-sided" emission factors. Prescribed burners may elect to
use these instead of national average emission factors for want
of any other values. This attempt draws upon the few available
data points for each of several prescribed fire categories in
preceding Tables 7 and 8. Of these categories, the largest sam-
ples are for backing fires in understory vegetation and litter
and for piled and windrowed residues (n = 8). The smallest
samples are for grass, understory heading fires, and broadcast
timber harvesting residues (n=4, each). Because this is a very
weak data base, a method has been devised by which users of pre-
scribed fire may select their own "safe-sided" value from any
array of values. Only the TSP data from preceding Tables 7 and
8 have been used in this approach, as a suggested starting point
for downwind concentrations predictions.
While the arithmetic mean of a sample population is ordinarily the
best single estimate of the overall population mean, the varia-
tions found in the limited number of samples available for this
approach result in several extremely wide limits of the means.
This implies that these calculated arithmetic mean values are not
apt to be adequate in themselves for the purpose of maintaining
local air quality to an acceptable level. The less frequently
used quadratic mean, because it employs an average of the squares
of all values in the sample distribution, is weighted toward the
64
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TABLE 13. REGIONAL AND NATIONAL ESTIMATES OF ANNUAL
CRITERIA POLLUTANT PRODUCTION FROM PRESCRIBED
FIRE, INCLUDING COMPARISONS WITH NATIONAL
PRODUCTION FROM ALL SOURCES'1 / b, c
(103 metric tons)
Estimate
of annual
fuel con-
sumed (all Total suspended
catego- particulate matter
Estimate type
Regional
Alaska
Eastern
Intermountain
Northern
Pacific N.W.
Pacific S.w.
Rocky Htn.
Southern
Southwestern
National and Comparisons
(1) Total of means
(all regions)
ries).
Tg
0.05
0.05
0.76
8.90
8.74
2.89
0.61
12.50
2.09
at
10 g/kg
0.5
0.5
7.6
89.0
87.4
28.9
6.1
125.0
20.9
365.9
at
17 g/kg
0.8
0.8
12.9
151.3
148.6
49.1
10.4
212.5
35.5
621.9
at
24 g/kg
1.2
1.2
18.2
213.6
209.8
69.4
14.6
300.0
50.2
878.2
Total hydrocarbons
at
5 gAg
0.2
0.2
3.8
44.5
43.7
14.4
3.1
62.5
10.5
182.9
at
9 gAg
0.4
0.4
6.8
80.1
78.6
26.0
5.5
112.5
18.8
329.1
at
13 g/kg
0.6
0.6
9.9
115.7
113.6
37.6
7.9
162.5
27.2
475.6
Carbon monoxide
at
40 g/kg
2.0
2.0
30.4
356.0
349.8
115.6
24.4
500.0
83.6
1,463.6
at
56 g/kg
2.8
2.8
42.6
498.4
489.4
161.8
34.2
700.0
117.0
2,049.0
at
72 g/kg
3.6
3.6
54.7
640.8
629.3
208.1
43.9
900.0
150.5
2,634.5
(2) Comparative totals
from 1978 Update Cri-
teria Pollutants (68)
(a) National total,
prescribed fire source
(b) National total,
all sources
(3) Adjusted national
total, all sources
(line 1 - line 2a +
line 2b)
(4) Percent prescribed
fire, this study com-
pared to adjusted na-
tional total, all
sources
(line 1 :- line 3)
377.8
123,010.2
123,254.3
98.2
11,818.6
12,049.5
2.7
740.4
89,192.4
90,501.0
2.0
^Derived national emission factors used in this table should not be applied locally; see Section 5 instead.
Nitrogen oxide emissions not estimated (see text).
Sulfur dioxide negligible.
65
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high side. By itself, however, the quadratic mean gives no
statement of confidence. By an examination of the trends of all
the derived arithmetic means, quadratic means, and each of
several upper limits of the means between categories, it is
believed likely that a user can select a "safe-sided" value more
representative of his local situation than by any other method
currently available.
Figure 6 has been prepared in an attempt to provide for such a
composite examination. In addition to comparisons within
categories (vertical axis), the same statistic for the separate
distributions in each of five prescribed fire categories may be
compared between categoriep (horizontal axis). It is of interest
to note that even with the limited data base available, the
previously reported (32) approximate 3:1 ratio of TSP emissions
between understory heading and backing fires holds for both the
arithmetic and quadratic means of these two distributions. The
principal utility of the semi-logarithmic plot (vertical axis)
of this family of curves is, however, in the ways it may be used
for "high-sided" estimates. These possible uses are illustrated
by a series of examples which follow.
In the following series of conjectural examples of possible uses
of Figure 6, each example is preceded by the same symbol which
appears on the figure.
1. Because of an unusually large amount of fresh pine needles
still readily available with the residues, and because of
uncertainty about the effect of fuel moisture in the larger
fuels, 50 mg/kg, the upper limit of the mean at the 99
percent confidence interval,3 is selected for conservatism.
2. Noting a seeming departure of the arithmetic mean from the
general shape of the family of curves, the apparently safer
quadratic mean value of 19.5 mg/kg is selected for use.
3. A selection of this moderately "safe-sided" 15.9 mg/kg value
might result from the belief that while the planned burn
is fairly typical, fuel moisture is not adequately known.
4. For the values presented, a combination of heading and
backing fires is assumed since neither is specified; since
only heading fires will be used, a high, "safe-sided"
16.5 mg/kg value is selected.
aStrictly, the confidence interval implies that for the popula-
tion represented by the sample, the average is expected to fall
between the upper and lower limits of the mean that percent of
the time. In this example, the upper limit of the mean, Xu99,
is read 50 mg/kg, and it is implied that the population average
should not be greater more than one percent of the time.
66
-------
o
o
j?
"Si
to
O*
o
l/l
UPPER LIMITS
OF THE MEAN
9 99 %. 95 %,
&90%COMF.
INTERVALS
QUADRATIC MEAN
ARITHMETIC MEAN
UNDERSTORY
VEGETATION
& UTTER
w/HEADING FIRES
BROADCAST
HARVEST
RESIDUES
UNDERSTORY
VEGETATION
& UTTER
w/BACKING FIRES
PILED HARVEST
RESIDUES
(FIREPLACE
DATA)
GRASS
Figure 6. Family of curves showing Arithmetic Mean and several
"Safe-sided" statistics for determining total sus-
pended particulate matter emission factors for dif-
ferent categories of fuel and fire types. Starred
numbers refer to examples of use in accompanying text,
67
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SECTION 6
CONTROL TECHNOLOGY
INTRODUCTION
As applied to prescribed burning, the term control technology may
be defined as either alternatives to burning in which prescribed
fires are no longer used, or use of best-available control tech-
nology whereby emissions from prescribed fires are reduced, dis-
persed, and directed away from critical areas. Both approaches
have certain advantages and disadvantages, and a careful evalua-
tion is needed before choosing an optimum mix of control tech-
niques for any given situation. In some cases (e.g., disease
control, meeting natural ecosystem requirements, or habitat
improvement), there may be no viable alternative to burning.
Consequently, the objectives for use of prescribed fire must be
well defined before a control technique is selected, and the
benefits must be weighed against the costs in terms of environ-
mental impact.
Within the land management community where prescribed fire is
used, "smoke management" is regarded as the means by which con-
trol technology can be effected. This section will, thus,
examine current and emerging smoke management technology for
parallels to the control technology statements of the preceding
paragraph. A recently advanced (69) definition of, and proposed
methods for, smoke management serves to initiate this examina-
tion. The definition is:
SMOKE MANAGEMENT: Procedures by which prescribed
fire and its alternatives are appraised and by
which conditions are specified for operating plans
prepared to maintain air quality to acceptable
levels in areas of importance.
Methods proposed for appraisals of prescribed fire call for deter-
mination of both net air quality impact and net benefit margins
for prescribed fire and its alternatives. Methods for specifying
conditions that limit air quality impacts call for development of
(69) Paulson, N. Personal communication in reference to internal
committee report NWAQ Team. U.S. Department of Agriculture,
Forest Service, Washington, D.C., 1979.
68
-------
an Operating Plan which is based upon the same fuels, atmospheric,
and fire criteria found acceptable in appraising the air quality
impact.
GENERAL CONSIDERATIONS
Factors that influence the application of control technology to
prescribed fires include the existing ambient air quality, the
air standards for the region, the contribution to ambient air
pollutant concentrations by prescribed fires, and the impact of
other sources, as well as national and local importance of the
prescribed burning source. The seasonal nature of prescribed
burning, the short duration of individual burns, the proximity of
designated nonattainment areas, and public safety will all affect
evolution of both voluntary and regulatory processes. This evo-
lution will be discussed further in Section 7.
The following subsections describe available and emerging control
technologies applicable to prescribed fire, relating these to
smoke management and summarizing their major advantages and dis-
advantages. It is impossible to cite any one method as the best
approach for all situations. To be successful, smoke management
planning under the above definition provides for sorting of these
many variables to arrive at locally appropriate control tech-
nology selections (69).
APPRAISALS OF PRESCRIBED FIRE
Appraisals in Terms of Effects on Air Quality
To make prescribed fire appraisals, emission factors are needed
for local use. These should be specifically tied to local fuels
and firing techniques. Field and laboratory measurements (de-
scribed in Section 5) are very expensive, and will still result
in wide ranges due to the highly variable natural relationships
involved. Previously referenced interim methods proposed for
emission and heat-release rate information (26) are deemed neces-
sary while more broadly applicable predictive equations are
developed and validated (25). Some "safe-sided" factors for TSP
have been provided in Section 5 of this report (Figure 6). Where
heat-release rates and emission factors are locally available
(9) , smoke management can now be effected with more certainty.
But, air quality and land management personnel, and in some cases
legislators, are faced with complex issues that are demanding air
quality appraisals now. To not make the best possible appraisals
means that risks must be taken and that promulgated regulations
may be difficult to replace even when better control technology
is brought to bear. Issues have had to be resolved under this
uncertainty already. For example, open burning is now specifi-
cally prohibited in one state for materials which are deliberately
69
-------
piled or bunched to prepare forest land for planting or seeding
(70).
Short-term peak concentrations are believed to be the main con-
cern for short-lived prescribed fires. For these fires, typical
case examples have been provided to southern land managers where
rate information is available and an operational adaptation
of EPA-approved models has been made (9). One such southern case
example is illustrated in Table 14. This approach has utility
for appraisals where emissions production is of short duration
(i.e., <3 or 4 hours).
In many areas of the country, air quality portions of prescribed
fire appraisals can be made through uses of simple case examples
like the one illustrated by Table 14. Another fairly simple
example is found in a smoke management plan now under preparation;
in the case study area covered, the greatest smoke management
concern appears to be only to maintain adequate visibility for
safe operations at an adjoining airstrip, and along traveled
roads (71). In appraising the air quality effects of the burning
program in this example, areas of local concern were delineated,
and local authorities were requested to supply air quality cri-
teria. Then, through one-time use of a relatively simple auto-
mated-data program known by the acronym PRESMOK (72), downwind
TSP concentrations of planned burns were predicted. (PRESMOK is
an adaptation of an EPA-recommended model validated for flat and
rolling terrain.) By carefully specifying wind directions, and
limiting the planned size of some areas to be burned, predicted
concentrations were maintained within the preset criteria.
Not all parts of the country can be handled this simply. In
some, "background" air pollution levels are already high from
other sources, heavily populated areas are nearby, complex ter-
rain and/or multiple fires are involved, and large amounts of
fuel must be treated. In cases combining elements like these,
(70) Virginia, Commonwealth of. Forest Management and Agricul-
tural Practices (from Appendix D). In: Regulations Concern-
ing Open Burning. Pamphlet, State Air Pollution Board,
Richmond, Virginia. Undated. 8 pp.
(71) Johansen, R. W., and R. A. Phernetton. Managing Smoke from
Prescription Burning on the Okefenokee National Wildlife
Refuge. Manuscript in progress, draft on file, U.S. Depart-
ment of Agriculture, Forest Service, Southeastern Forest
Experiment Station, Asheville, North Carolina, 1979. 15+ pp,
(72) Lavdas, L. G. PRESMOK, Operational Prescribed Fire Smoke
Dispersion Computer Program. Documentation on file, U.S.
Department of Agriculture, Forest Service, Southeastern
Forest Experiment Station, Asheville, North Carolina, 1978.
70
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TABLE 14. ILLUSTRATION OF TYPICAL SHORT-TERM PEAK TSP
CONCENTRATIONS DATA WITH UTILITY FOR AIR
QUALITY-RELATED APPRAISALS OF PRESCRIBED
FIRES OF SHORT DURATION (i.e., <3 or 4
HOURS). ADAPTED FROM TABLES IN REFERENCE 9
Type of fire
Pa Ime tto-gal Iber ry :
backing fire
Palmetto-gallberry:
heading fire in
2-year-old rough
Pasquill
stability
class
C
C
Distance
downwind,
km
0.10
.13
.16
.20
.25
.32
.40
.50
.63
.79
1.00
1.30
1.60
2.00
2.50
3.20
4.00
5.00
6.30
7.90
10.00
13.00
16.00
20.00
25.00
32.00
40.00
50.00
63.00
79.00
100.00
Mixing Heat release
height, rate,
tan megacal/sec
1.5 37.632
1.5 137.984
Particulate matter
Backing fire in
901
730
591
479
388
314
256
206
167
135
110
90
72
57
45
37
31
25
19
14
10
7
5
3
2
2
1
1
1
1
1
Length of
fired line Transport
or equiv. , windspeed,
m m/sec
800 8
800 8
concentrations at various
downwind, vig/m3
Heading fire
2-year-old roughs
3,302
2,675
2,167
1,756
1,422
1,152
933
756
612
496
402
325
261
206
157
116
83
59
43
32
25
20
15
10
8
7
6
5
4
3
3
Emission
rate,
mg/m-sec
168
616
distances
71
-------
differing levels of sophistication are needed. In the following
discussion, examples are drawn from currently active research and
development to illustrate how these needs are being met.
Quantitative determination of local air quality effects of pre-
scribed fire is dependent upon TSP and other criteria pollutant
background concentrations data for potential receptor areas.
Also needed are climatologies of atmospheric dispersion parameters
during the burning season. These data are generally available,
but often lack desired localization in land management areas
remote from monitoring and weather observation stations.
EPA designation of nonattainment areas has served to flag areas
where violations of National Ambient Air Quality Standards have
occurred or are expected. Though sometimes encompassing large
areas which may not be of entirely the same air quality, non-
attainment areas are useful to smoke management. These designa-
tions will serve to alert prescribed fire appriasers of the need
to be especially careful in examining background levels of cri-
teria pollutants in receptor areas designated nonattainment, and
to select optimum diffusion parameters if smoke is to be vectored
toward them.
A pilot test of supplying prescribed burners with information on
nonattainment area locations and the bases for designations is
now in progress using an experimental automated data processing
program known by the acronym "SMKLCR" (73). With this program,
the user merely enters the latitude and longitude ,of the loca-
tion where burning is to be done, and the azimuth(s) of expected
transport winds. He is then furnished with the approximate
centerpoint location, the name, and the type(s) of designation
for any EPA-designated nonattainment areas within 100 kilometers
that may be impacted by smoke from the location of the burning.
(More precisely, SMKLCR searches a file of nonattainment area
effective radii for any within 100 kilometers of a fire's center-
point location.)
A further use is made of this program by its automatic incorpora-
tion in operational smoke management procedures which are being
made available for verifying the real-time effects of meteorologi-
cally scheduled burning, discussed in the following section. One
of these is the program called "RXBURN" (74) , an adaptation of a
(73) Rodgers, S. L. SMKLCR. Computer Program Automatically Flag-
ging Nonattainment Areas Toward which Prescribed Fire Smoke
May be Advected. Documentation on file, Southeastern Forest
Experiment Station, Asheville, North Carolina.
(74) Paul, J. T., J. M. Pierovich, L. G. Lavdas, and S. L. Rodgers,
RXBURN Prescribed Burning/Smoke Management Decision Module
Computer Program. Documentation on file, U.S. Department of
Agriculture, Forest Service, Southeastern Forest Experiment
Station, Asheville, North Carolina.
72
-------
validated EPA-recommended model for flat and rolling terrain.
RXBURN can also be used for prescribed fire appraisals in flat
and rolling terrain by substituting climatological data in place
of the automated observed and forecast data used in operational
procedures on the day of burning.
In heavy fuels (which may burn for more than a day), it becomes
necessary to incorporate "decay rate" adjustments to emission
factors and heat release, and to allow for the times of constant
emissions duration, for the time of end of convective lift, and
for changing dispersion parameters with time. An experimental
program called "HRSMOK" (75) allows for making hourly adjustments
to these variables and affords the approach by which adapted
steady-state Gaussian dispersion models may be made usable for
heavy fuels. PRESMOK and RXBURN, mentioned above for flat and
rolling terrain, are now under examination for this further
adaptation.
Meteorology and smoke dispersion in .complex terrain are coming
under increased attention, both as the HRSMOK experimental pro-
gram will permit automated changes in emissions and heat-release
inputs for this need, and as the EPA-recommended RAM (76, 77) and
CDM (78, 79) models are proposed for adaptaion and validation
See also Section 3 for discussion of convective lift, constant
emissions duration, and decay rates.
(75) Lavdas, L. G. HRSMK Experimental Prescribed Fire Smoke Dis-
persion Computer Program. Documentation on file, U.S.
Department of Agriculture, Forest Service, Southeastern
Forest Experiment Station, Asheville, North Carolina, 1978.
(76) Turner, D. B., and J. H. Novak. User's Guide for RAM,
Volume I. EPA-600/8-78-016a, U.S. Environmental Protection
Agency, Research Triangle Park, North Carolina, 1978. 60 pp.
(77) Turner, D. B., and J. H. Novak. User's Guide for Ram,
Volume II. EPA-600/8-78-016b, U.S. Environmental Protection
Agency, Research Triangle Park, North Carolina, 1978. 222 pp.
(78) Burse, A. D., and J. R. Zimmerman. User's Guide for the
Climatological Dispersion Model. EPA-R4-73-024, U.S. Envi-
ronmental Protection Agency, Research Triangle Park, North
Carolina, 1973. 131 pp.
(79) Brubaker, K. L., P. Brown, and R. R. Cirillo. Addendum to
User's Guide for Climatological Dispersion Model.
EPA-450/3-77-015, U.S. Environmental Protection Agency,
Research Triangle Park, North Carolina, 1977. 134 pp.
73
-------
through new coefficients now under development (80). These
models will also accommodate more than one fire in the same area
and are similar in hour-by-hour accounting procedures used with
the Gaussian steady-state equation they employ.
Yet another approach under examination for complex terrain and
multiple fires would employ the most advanced technology by which
temporal and spatial changes are reflected in grids, or in air
parcels, to predict concentrations. With these methods, effects
of specific topographic features may be represented as has been
demonstrated for LIRAQ and other such models (81). A deterrent
to their use, however, has been the very high cost of the compu-
tational requirements for the involved equations. Now it is
suggested the power of the models warrants at least adaptations
for those specific mountain airsheds where air quality is cri-
tical and lesser approaches do not yield satisfactory results.
The approach under examination would overcome these costs by
uing typical combinations of weather, fuels, and fire variables
to create an area-specific "library" of expected results. The
"library" is then automatically searched for comparability to
actual situations (either on a climatological planning and apprai-
sed basis or possibly on a day-in-day-out operational basis),
with resulting predictions made available at a fraction of the
cost that would be otherwise incurred.
Appraisals in Terms of Alternatives to Burning
Alternatives to prescribed burning are being seriously pursued.
General categories of alternatives include mechanical treatment,
chemical treatment, improved utilization, and no treatment. The
feasibility of each alternative varies with the type of applica-
tion. For example, the use of acceptable herbicides to control
understory growth for reduction of fire hazard might adversely
affect wildlife habitat and would not be relevant at all to
treatment of harvesting residues in the Northwest. Conversely,
improved harvesting and utilization developed on the Pacific coast
would not be applicable to wildlife habitat improvement in the
South.
Relative advantages and disadvantages of different methods are
difficult to compare because net benefits cannot always be meas-
ured on the same basis. The factor that is generally the least
difficult to quantify is the direct economic cost (capital and
operating), in terms of dollars per ton or dollars per acre of
(80) Fosberg, M. A. Personal communication. U.S. Department of
Agriculture, Forest Service, Pacific Southwest Forest and
Range Experiment Station, Riverside, California, August 1979.
(81) Turner, D. B. Atmospheric Dispersion Modelling - A Critical
Review. Journal of the Air Pollution Control Association,
29(5):502-519, 1979.
74
-------
treatment. This type of information is available on several
alternatives and shows, as expected, that prescribed burning is
usually the least expensive form of land treatment (66). The
alternative of no treatment obviously involves no direct treat-
ment cost.
Unfortunately, the direct economic cost is only the tip of an
iceberg. Site variability has a profound effect on operating
costs, and the cost data are too limited and scattered to draw
anything more than general conclusions. Even more important, it
is impossible to quantify the indirect costs and benefits of dif-
ferent treatment alternatives. Some pertinent factors that can-
not be fully quantified from data available today are (9, 66):
• The net value of fire hazard reduction (an indirect cost
of no treatment)
• Net esthetic impact
• Net environmental impact of mechanical or chemical treatment
• Net air quality improvement as a result of no burning
(allowance must here be made for contributions of emissions
from wildfires that would result)
• Net silvicultural considerations (e.g., controlled disease/-
species optimization, optimum stocking)
• Net ecosystem response (affecting other net impacts)
In light of these considerations, the following descriptions of
treatment alternatives do not offer quantitative effect informa-
tion nor draw conclusions in terms of what method is best.
Qualitative advantages and disadvantages are given, as well as
the type of application each method may be suited for.
Mechanical Treatment—
Different types of mechanical treatment can be used to clear away
brush and trees, to prepare land for planting, to break up slash
into finer material, and to dispose of slash or brush by burial
in gentle terrain. These techniques are not effective for con-
trol of understory species without damage to the overstory, for
disease control, for reduction of fire hazard (except burial), or
for wildlife habitat improvement; nor can they be used on steep
slopes (9, 66). They are also energy demanding.
Brush and tree removal—Mechanical choppers and shredders can be
used to clear away brush and trees for tree planting in open
areas. Their cost of operation is high and limits their use to
smaller areas such as openings in forest tracts. Moreover, the
debris left behind may have to be disposed of to avoid a fire
hazard (9, 66).
Site preparation and scarification—In addition to choppers and
shredders, bulldozers or tractors may be used to clear land for
planting. However, this kind of. clearing has potential for soil
compaction and increased erosion. Scarification, or clearing
75
-------
away all vegetation to expose the soil, is used as an effective
method of preparing firebreaks in fire-prone areas (9, 66), but
is less applicable to the frequently preferred shaded fuel break.
Slash treatment—Slash can be reduced to finer material by various
types of choppers and shredders. Although slash material is not
eliminated, it may be easier to dispose of by other methods or
through natural decay. If a fire hazard still exists, some type
of prescribed burning may be needed (9, 66).
To reduce the cost of slash treatment and minimize land damage,
yarding techniques are often employed to gather slash into one
central location. Yarding is also used to gather slash for
burning (66).
Burying—In flat terrain, burial is a method of very limited ap-
plication for the disposal of logging slash. This method in-
volves digging trenches to push the slash into and then covering
the slash with dirt. Burial has the advantage that no flammable
material is left on the surface as a fire hazard. It cannot be
used in rocky soil and may leave barren soil exposed to erosion
(66). Tree diseases, such as Fames annosus and Armellaria mellea ,
are known to colonize buried harvesting residues, leading to
losses of desirable timber (82).
Chemical Treatments--
Chemical treatments, such as the application of herbicides, have
been used for specific purposes, e.g., seedbed preparation and
brush control. The development of selective herbicides (com-
pounds that are only toxic to certain species) has made this
technique useful in more applications. Such treatments, however,
can only be applied to live vegetation and do nothing to reduce
fire hazard; indeed the risk of fire may actually increase as the
dead vegetation dries. Recent suspension of the herbicide,
2,4,5-T has seriously limited this silvicultural treament alterna-
tive. Thus, chemical treatment is an alternative to prescribed
fires in only certain situations (9, 66).
Improved Utilization—
Improved utilization is an attractive alternative to prescribed
burning that encompasses both improved harvesting techniques
that generate less slash and new end uses for material that is
normally burned. Examples of improved harvesting methods that
are being used or under development include (66):
(82) Nelson, E. E., and G. M. Harvey. Diseases. In: Environ-
mental Effects of Forest Residues Management in the Pacific
Northwest, Compend. 0. P. Cramer, ed. U.S. Department of
Agriculture, Forest Service, Pacific Northwest Forest and
Range Experiment Station, Portland, Oregon, 1974. pp. S3-S5
76
-------
• Directional felling to reduce log breakage
• Prelogging or postlogging to recover small diameter timber
• Better handling techniques that will accept material normal-
ly discarded as slash
• Design of contractual agreements to encourage recovery of
small size material
Progress is also being made in using the entire logged tree, thus
eliminating any slash. In the South, merchantable pine trees are
often utilized down to diameters of 55 mm to 100 mm (9). Rising
demand (and prices) for wood fiber raw materials, and possible
uses of forest residues (including tops, branches, foliage, bark,
stumps, roots, small stems, and dead standing trees) as fuel and
as a source of chemicals, all contribute toward progress in
industrial use of the whole tree (83). A general guideline,
however, is to minimize the loss of fine textured residues since
these are a principal source of soil humus and many nutrients
needed for forest growth (84).
Whole-tree chipping, a new technique of harvesting forest pro-
ducts for complete utilization, looks promising. Large, trans-
portable chippers mounted on semitrailers accept whole trees and
cut them into chips which can be blown into a truck and hauled
to a pulp mill. No appreciable logging debris is left on areas
logged in this manner (9).
When slash must be transported to a processing site, physical and
economic limitations are imposed by material handling and trans-
portation systems. Advances in these areas include preprocessing
for optimum size grading of slash or for conversion of slash into
chips or pellets, and new and modified hauling systems for non-
standard size logs or wood chips (66).
In order for improved utilization to be an acceptable alternative,
there must be a market for timber-harvesting residues. At the
present time, the two primary outlets for harvesting residues are
in the pulp and paper industry and for boiler fuel. New pulp
digestion processes can accept substantial amounts of material
containing bark and leaves. Various forest industries can also
use hogged slash as fuel for industrial boilers (9, 66), and
(83) Quinney, D. N. Economics of Utilizing Residuals from Log-
ging - Problems and Opportunities. American Institute of
Chemical Engineers Symposium Series, 71(146):30-32, 1975.
(84) Miller, R. E., R. L. Williamson, and R. R. Silen. In:
Environmental Effects of Forest Residues Management in the
Pacific Northwest, Compend. 0. P. Cramer, ed. U.S. Depart-
ment of Agriculture, Forest Service, Pacific Northwest
Forest and Range Experiment Station, Portland, Oregon, 1974,
p. Jll.
77
-------
increased attention is being given to timber-harvesting and land-
clearing residues as sources of energy. Energy balance (i.e.,
the amount of energy expended for collection, hauling, storage,
and processing) must, however, be accounted for in assessing this
alternative.
Improved utilization cannot replace prescribed burning in range
management and in removal of understory growth and litter within
the timber stands. In these cases, volumes are too low and
scattered to justify the cost of harvesting the material, espe-
cially when the material has to be removed from among tree stems.
There is currently no developed market for most of this material
(9).
No Treatment—
Although the elimination of any form of treatment including pre-
scribed burning poses no immediate adverse effects to the en-
vironment, it does not accomplish any of the benefits for which
prescribed fires are used (see Section 3). Moreover, no treat-
ment for extended periods of time can lead to increased risks of
losses due to wildfire, to insect infestation, to losses of
species diversity and site productivity, as well as to other
undersirable effects. Thus, it cannot be considered a viable
alternative in most situations (9, 66).
OPERATING PLANS FOR SMOKE MANAGEMENT
Operating plans for smoke management are in effect to different
levels of sophistication in several states (85-89). Permit
(85) Kilian, L. Designated SF-FM, Practices, Coordination of
Prescribed Burning Activities. Unpublished memorandum with
enclosures, North Carolina Division of Forest Resources,
1974. 14 pp. w/encl.
(86) Montana, State of. State of Montana Cooperative Smoke
Management Plan. Unpublished agreement on file, State of
Montana, Division of Forestry, Helena, Montana, 1978.
6 pp. + exhibits.
(87) Oregon, State of. Directive 1-1-3-410, Smoke Management
Plan. Unpublished plan on file, Oregon State Board of
Forestry, 1972. 14 pp.
(88) Oregon, State of. Directive 1-1-3-411, Operational Details
for the Oregon Smoke Management Plan. Unpublished plan on
file, Oregon State Board of Forestry, 1978. 20 pp.
(89) Washington, State of. Smoke Management Program. State of
Washington, Department of Natural Resources, Olympia,
Washington, 1975. 17 pp. + exhibits.
78
-------
systems resulting in different levels of smoke management are
also in effect (9, 90). In many states, blanket air quality
regulations make avoidance of violation of the National Ambient
Air Quality Standards incumbent upon all sources of emissions.
In essence, a combination of voluntary and regulated control
technology is being applied.
This combination may work well today where applied. Questions
remain, however: how well will chosen control measures operate
in the light of new interpretations of existing regulations, or
of those yet to be promulgated; will they operate when the pre-
scribed burning practice may be extended to new areas, or are
requirements already too stringent in some areas? Unanswered
questions like these, originating in a lack of data about the
source and its emissions, tend to impede implementation of
available technology. Complete dependence upon subjectivity in
matters of this importance will beget indecision, advocacy, and
even adversary situations.
The appraisals discussed in preceding sections demonstrate tech-
niques for partial quantifications by which decision can be
reached and delays minimized. A major impediment is lack of
guidance, and/or of commitment to acceptance of those measures
which might be implemented, on the part of air quality regula-
tory agencies.
Each of the following sketches of operating plan components is
intended to summarize the available and emerging technology,
giving relative levels of sophistication, in order to facilitate
removal of these impediments. "Sophistication" relates only to
application of the technology, and has no relation to cost or to
difficulty of underlying research and development.
Specification of Fuels Characteristics
Fuel characteristics are obviously a prime factor affecting the
magnitude of emissions from prescribed burning. Important param-
eters include fuel amount, fuel loading, fuel moisture content,
and the physical arrangement of the fuel. Each of these items
should be addressed as part of a comprehensive smoke management
program. Table 15 provides a quick reference to specification
(90) New York, State of. Part 215, 121 CN, 5-31-71, Open Fires,
1972. 3 pp.
79
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TABLE 15. QUICK REFERENCE TO SPECIFICATION OPTIONS RELATED TO FUELS CHARACTERISTICS
Technology for effecting option
Specification option
Available
Relative level
of sophistication
Emerging
Relative level
of sophistication
00
O
Burn size
(limits total
emissions
production)
Fuel loading
(limits total
emissions
production)
Pysical Arrangement
(limits total
emissions, promotes
better convective
lift)
Fuel Moisture
(limits total
emissions, promotes
better convective
lift)
Fire control methods for
containing fire to an area
with an acceptable amount
of total available fuel
Simple
Providing for shorter
time intervals between
burning of naturally
occurring vegetation and
litter
Encouraging better
residues utilization
Mechanical pretreatments
(YUM, piling and
windrows, chopping)
Emission factors for
different treatments
(see Sec. 5, Figure 6)
Supplemental specifications
for limiting soil
admixtures
"Fuel stick" analog
Large fuels probes
Recommended fuel
moisture ranges
Drying curves for fuels
of different time lags
Simple
Moderate
Moderate
Moderate
Moderate
Simple
Simple
Simple
Simple
Typical case examples of
downwind impacts for specific
fuel types (9)
Improved low-cost fuel
inventory methods (91, 92)
Table of available fuel
at different fuel moisture
levels for specific fuel
types (9)
Simple
Simple
Moderate
Added and improved emission
and heat release rates for
different fuel treatments
(25, 26)
Moderate
Tables of available fuel at
different fuel moisture
levels for specific fuel
types (9)
Probable fuel moisture data
for specified locations
away from observation
stations (93)
Moderate
Simple
-------
options related to fuels characteristics (9, 25, 26, 91-93).
Brief amplifying discussions follow the table.
Barring a natural disaster, such as wind or ice damage, fuel
loading in naturally occurring vegetation and litter can be regu-
lated by timing between burns. In the area of timber-harvesting
residues, removal of the fuel through increased utilization will
reduce the fuel loading.
Emissions per unit of fuel burned generally increase as fuel mois-
ture content increases, so smoke management calls for burning at
lower moisture contents. However, the drier the fuel, the great-
er the chances for a prescribed burn to become damaging and to
escape. An example prescription recommendation is that prescrib-
ed burning be done 2 days to 3 days after 12 mm to 25 mm of rain
have fallen, thus insuring that the soil will be moist and that
the deep organic layers will not be burned. A preferred range
for fine fuel moisture, affected readily by the relative humidity
in the air, rainfall, and air temperature, is from 7 percent to
20 percent. For heavy fuel loadings, the moisture content should
be kept near 20 percent to keep the fire from becoming hot enough
to damage young growth, overstory crowns, and the soil (9).
Fuel arrangement can be influenced by various piling techniques
that are normally applied to the burning of logging debris.
Burning of piles also results in more rapid and complete combus-
tion. It can be performed during a greater portion of the year
because piles are less dependent on lower fuel moisture content
(66) .
Specification of Firing Technique
Firing technique options are limited by the type of fuel to be
burned and the objectives of the prescription. Table 16 pro-
vides a quick reference to options related to firing technique.
Brief amplifying discussions follow the table.
(91) Maxwell, W. G., and F. R. Ward. Photo Series for Quantify-
ing Forest Residues in the Coastal Douglas-Fir Hemlock Type,
Forest Service General Technical Report PNW-51, U.S. Depart-
ment of Agriculture, Forest Service, Pacific Northwest
Forest and Range Experiment Station, 1976.
(92) Schmidt, R. G. An Approach to Hazard Classification. Fire
Management Notes, 39(4):9-ll, 19, 1978.
(93) Paul, J. T. Forestry Weather Data Systems. Proposed Work
Unit Description, Draft on file, U.S. Department of Agri-
culture, Forest Service, Southeastern Forest Experiment
Station, Asheville, North Carolina, 1979. 10 pp.
81
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TABLE 16. QUICK REFERENCE TO SPECIFICATION OPTIONS
RELATED TO FIRING TECHNIQUE
oo
Specification option
Technology for effecting option
Available
Relative level
of sophistication
Emerging
Relative level
of sophistication
Backing fires
(relatively less
TSP emissions)
Timing of ignitions
(avoidance of late
afternoon and even-
ing lessened atmos-
pheric dispersion
capacity & of down-
slope downcanyon
night-time circulation)
Use of forced-air
methods (for collected
debris only, reduces
emission - limited
application)
Both application guides
and experienced personnel
Experienced personnel
with knowledge of time
for burnout
Air curtain devices
Simple
Simple
Decay-rate data for
specific fuels and
firing techniques (22)
Moderate
Moderate
-------
It has been shown quantitatively and qualitatively that firing
technique affects emissions from forest fuels. Backing fires
emit less total suspended particulate matter than heading fires
apparently because backing fires have more glowing combustion,
while heading fires have more flaming and smoldering combustion
(9, 20, 94). Backfiring requires steady winds of 1.8 m/s to 4.5
m/s (5).
A relatively new technique called air curtain combustion is spe-
cifically designed for the combustion of wood waste with minimal
smoke emissions. In this system, a blower directs an air curtain
diagonally across the burning pile of wood thereby promoting rapid
and complete combustion. Air quality evaluations show that the
air curtain combustion process will produce no visible smoke
emissions if combustion temperatures are maintained over 1,600°F
(95). This technique is not widely utilized at present because
of its high operating costs (66) and site disturbance.
Specification of Meteorological Scheduling
Prescribed fires can be set when meteorological conditions pro-
vide for the best dispersal of pollutants. "Best dispersal"
is both directing plumes away from receptor areas where unwanted
impacts are to be avoided, and obtaining maximum atmospheric
diffusion. This broad area of technology is known as meteorolo-
gical scheduling.
Meteorological scheduling options are many and may be combined.
The Table 17 quick reference to these options is, thus, an
(94) Yamate, G., J. Stockham, D. Becker, T. Waterman, P. Llewel-
len, and W. M. Vatavuk. Development of Emission Factors for
Estimating Atmospheric Emissions from Forest Fires. Pre-
sented at the 68th Annual Meeting of the Air Pollution
Control Association, Boston, Massachusetts, June 15-20, 1975,
15 pp.
(95) McLean, H. R., and F. R. Ward. Air Curtain Combustion
Device Evaluated for Burning Heavy Fuels. R-6 Fuel Manage-
ment Notes, 4(l):l-7, 1976.
83
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TABLE 17. QUICK REFERENCE TO SPECIFICATION OPTIONS RELATED TO METEOROLOGICAL SCHEDULING
oo
Specification option
Forecast wind
direction (avoids)
critical receptor
areas)
Available
Loco ; knowledge of areas
to be avoided and used
with National Weather
Service fire weather
Technology for effecting option
of sophistication Emerging
Simple ADP data for designated
nonattainment areas -
SMKLCR (73)
Relative level
of sophistication
Moderate
Forecast air
pollution alert
"stagnation index,"
mixing height and
stability class
limiters - include
time of day
(lessen.-rj.sks of
.inversion-trapped
smoke plumes)
Single fire pre-
dicted downwind
emission concentra-
tions (avoids
unacceptable con-
centration In down-
wind receptor areas)
Multiple-fire manage-
ment package for
categories of burn-
ing days
Multiple-fire manage-
ment package for
full examination of
each day's prescribed
burning capacity
National Weather Service
fire weather forecasts0
and smoke management
training for "simple
screening**
Predetermined burning day
categories (usig burning
season climatology) and
pre-allocated amounts
of burning* with manual
weather data comparisons
by competent meteorologist(s)
High
ADP weather observations and
forecast localizing techniques Moderate
for flat and rolling terrain
(97)
Same as above for mountainous
terrain (96) Moderate
ADP weather observations and
localizing techniques for
flat and rolling terrain Moderate
(97)
Same as above for /
mountainous terrain (96) Moderate
ADP-determined single fire
short-term peak concentra-
tions predictions - PBESMOK Moderate
(7, 30) and 24-hr, concentra-
tions - HRSMOK (75)
ADP-determined single fire
short-term peak and 24-hr.
average concentration pre-
dictions using automatically Moderate
interfaced nonattainment
areas as well as observed
and forecast weather variables
- RXBURN (74)
Fully automated predeter-
mined burning day categories Moderate
(using burning season
climatology) and pre-allo-
cated amounts of burning.
Utilizes accounting system
with automatic interfacing
of nonattainment area as
well as 36-h r. and shorter
term weather forecast and
observed data to provide
"burn/no-burn" advice (96)
Same as above, except makes
more thorough use of indivi-
dual fire prescriptions High
criteria to advise on best
mixes of individual fires
for maximized operation
(96)
aTrends away from one-on-one meteorological assistance by the National Weather Service will further limit this availability.
-------
abbreviation of the total technological capability possible
(73-75, 96, 97). It will be noted that automated-data processing
is shown with the more sophisticated levels of emerging smoke
management technology in Table 17. This critical need to best
use meteorological scheduling has been illustrated in Section 6
and is discussed again in Section 7.
Because prescribed fires are not bound to year-long, day-in-day-
out operations, as with stationary sources, and because the
better of atmospheric conditions can be used in scheduling their
execution, questions are raised regarding the fit of prescribed
fire to PSD provisions. These are related specifically to a need
for prescribed fire increments, and to the appropriateness of
using reduced prescribed burning as an offset for increments de-
sired by proposed new sources (96).
Prime considerations in scheduling are mixing height, atmospheric
stability, wind speed and wind direction. Atmospheric stability
indicates the degree of thermally and mechanically induced
turbulence in the atmosphere. Mixing height is that height to
which ground-based thermal eddies extend. Smoke dispersal is
best when the atmosphere is unstable and the mixing height is at
great distance from the earth's surface. This is because the
relative warmth of smoke plumes will cause them to continue to
rise rapidly under these conditions until plume and atmospheric
temperatures become equal; at that point, the smoke diffuses and
is carried along in the air of which it has become a part. When
high yields of heat are available, it is still possible to obtain
satisfactory dispersal of the plume, so long as the temperature
difference is present, even with less than these optimum atmos-
pheric conditions. It must be stressed, however, that under
extreme conditions of instability, the fire may burn out of
control.
A special stability situation occurs when there is an inversion
layer in which the air temperature increases with height. An
inversion layer acts as a lid that tends to trap rising smoke
(96) Pierovich, J. M. Current Activities and Future Plans for
Smoke Management Research and Development at the Southern
Forest Fire Laboratory. Manuscript at press, copy on file,
U.S. Department of Agriculture, Forest Service, Southeastern
Forest Experiment Station, Asheville, North Carolina, 1979.
6 pp. + appendices.
(97) Paul, J. T., and J. Clayton, et al. User Manual - Forestry
Weather Interpretations System...(FWIS). U.S. Department of
Agriculture, Forest Service, Southeastern Forest Experiment
Station, Asheville, North Carolina, and Southeastern Area
State and Private Forestry, Atlanta, Georgia, in cooperation
with the U.S. Department of Commerce, NOAA, NWS. U.S.
Government Printing Office, Washington, D.C., 1978. 83 pp.
85
-------
columns near the earth's surface. As a consequence, prescribed
burning is often precluded when an inversion layer is present
(9, 66). On the other hand, inversions lower in elevation than
the area where prescribed burning is being done tend to limit
smoke below the inversion height. For example, slash burning in
the Pacific Northwest frequently takes place in high, mountainous
areas, so that meteorological scheduling is designed to keep
pollutants from reaching population centers in the valleys.
Under certain meteorological patterns, an inversion layer is
desirable in helping to keep emissions above the valleys (8).
Wind direction during burning operations should be away from
populated areas. For fires in the Southeastern United States,
recommended optimum wind speeds are 2 mph to 10 mph near the
ground and 5 mph to 18 mph at the 20-foot level (9). Within this
range, the best wind speed depends upon the presence or absence
of a tree canopy, upon the firing technique used, and upon the
conditions of the fuel.
Meteorological scheduling is among the most viable of control
technologies for operational smoke management plans. Among the
tools of meteorological scheduling are EPA-recommended Gaussian
dispersion models adapted for prescribed fires and for use of
real-time weather data. This carries with it two elements of
chance. One is in the statistical basis (i.e., uncertainty) of
the Gaussian dispersion model. The other is in dependence upon
rapidly disseminated, and as locally correct as possible, weather
observations and forecasts. The probabalistic nature of model
predictions, and of weather forecasts which they incorporate, is
recognized by the land management community due to familiarity
with these same elements in controlling wildfires and in other
weather-affected operations. Rapid dissemination and localiza-
tion of weather data do not represent a new concept, but the
utility of these are being newly realized in a pilot test cur-
rently under way between the Forest Service and the National
Weather Service (97). Burning permit systems in several states
make this information vital to land managers, and smoke manage-
ment modules in the referenced test are automatically interfacing
localized near-real-time data with other inputs in decision aids
that would not be usable otherwise.
86
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SECTION 7
OUTLOOK
Prescribed fire is the major forest management method for reduc-
tion in intensity of wildfires and is also used to accomplish
other management objectives such as silviculture, disease con-
trol, range improvement, and vegetation management, such as pro-
tection and/or enhancement of rare and endangered plant and animal
species. At present, there is no satisfactory alternative to
prescribed burning for many applications. Alternative approaches
are generally more expensive, damaging to the environment, im-
practical, or unsuited for accomplishing needed land management
objectives.
TRENDS
Some of the more important actions and trends that bear upon an
outlook for prescribed fire are summarized in Table 18, along
with some of the underlying reasons for these actions and trends.
The projected net consequences to receptor areas from prescribed
fire during the next decade are also presented, showing results
of a subjective evaluation of the possible increases or decreases
in emisions concentrations in areas of concern.
Although a meaningful projection of tons of produced emissions
cannot be made from indicators in Table 18, the net effect in
receptor areas is predictable. To make such a prediction, we
must first examine the actions and trends that will decrease con-
centrations in receptor areas of concern. From these, it will be
seen that prescribed burners are expected to continue to adopt
available and emerging smoke management technology. Actions have
been taken to improve upon utilization of residues that would be
left behind in timber-harvesting operations. Work to encourange
energy production from biomass cleared for silvicultural reasons
is an example of how this trend may be continued. Smoke manage-
ment, though also encompassing alternates to burning, bears most
heavily upon reduced emission concentrations in receptor areas.
By taking advantage of the best-available control technology, the
land manager-burner may predict downwind concentrations, may
better direct smoke plumes away from areas of concern, and may
limit the amounts of fuel burned on any one day as necessary. He
may also apply burning and pretreatment measures that will promote
more complete combustion with attendant lessening of emissions.
87
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TABLE 18. SUMMARY OF SOME OF THE MORE IMPORTANT ACTIONS AND TRENDS,
THE UNDERLYING REASONS, AND PROJECTED NET CONSEQUENCE TO
RECEPTOR AREA EMISSIONS CONCENTRATIONS
oo
00
Underlying reasons
Projected net consequence to receptor
areas concentrations in next 10 years
Actions and Trends
Economic
Energy
Sources
supply
& demand
Responses
to Clean
Air Act
Increases
Decreases
Strong
Lesser
Strong
Lesser
Presidential decision to accelerate
cutting of Federal timber
Further changes from alternate methods
to use of prescribed fire
Further changes to alternate methods
from use of prescribed fire
Increased utilization
Other
Need to reduce expenditures for wild-
fire presuppression and suppression
Public safety
PSD visibility regulations
Loss of alternative treatment methods-
herbicides
State Implementation Planning
Transfer and adoption of smoke
management technology
Completion of conversions from old-
growth (virgin) to second growth
forests
Reintroduction of fire wildland
ecosystems0
No significance
alf pending PSD visibility regulations are applied to prescribed burning there will be a strong decrease of impacts
from prescribed fire emissions in this decade, but this is believed to be a precursor to a strong upward trend in
wildfire emissions in the last half of this decade and in subsequent decades.
Effect will not be felt in this decade, but will be substantial within 3 to 5 decades.
Also, to manage ecosystems in natural state in selected areas, i.e.. Wilderness and National Parks.
-------
Next, examining the actions and trends that will tend to increase
emissions, it can be seen from Table 18 that most will exert a
strong increase tendency. While the national timber supply is
roughly two-thirds from other lands, the recent Presidential
direction to increase timber supplies from federal lands will
have an effect of increasing emissions. This direction, reflect-
ing a determination to improve efficiency and management of the
Nation's federal timber reserves through a temporary departure
from a non-declining, even-flow policy, will be felt most in the
defective oldgrowth (i.e., virgin) stands of the West where more
residues will require treatment (98). Economic pressures are
expected to call for placing more land in full production of
commercial forests by preparing sites now occupied by brush and
commercially undesirable species. But, as costs climb and as
energy sources and herbicides are less available, it is inevitable
that some alternative treatment methods will be foregone in favor
of more use of prescribed fire. Except in the area of increased
utilization, as discussed already, any shift from prescribed
fire to alternate methods will be of no significance to decreases
in concentrations of emissions in receptor areas. Economic and
energy-related reasons, also underlie changes in wildfire pre-
suppression and suppression policies (99); among alternatives un-
der examination will be added installation of "fuel-free" corri-
dors, fuel breaks, uneven-aged vegetation mosaics created by the
use of fire, and general reduction of fuels which have accumulat-
ed under past fire exclusion policies. While these changes in
policy will have a strong emissions increase tendency, a related
policy change toward reintroduction of fire to wildland eco-
systems (especially in wilderness and in National Parks) will be
of generally lesser importance. Overall, the emissions increas-
ing actions and trends are expected to be of most importance in
the Western States. From this examination of the emissions de-
creasing and increasing trends and actions, it is predictable
that while more emissions will be produced, the overall net con-
sequence to concentrations of emissions in areas of concern will
be less during the next decade than at present.
APPLYING THE TECHNOLOGY
Questions that have tended to impede implementation of control
technology are daylighted in Section 6 of this report. A para-
mount question among these has been lack of guidance, or of
(98) Carter, President James. Memorandum for the Secretary of
Agriculture, The White House, Washington, D.C., June 13,
1979. 1 p.
(99) Gale, R. D. Evaluation of Fire Management Activities of
the National Forests. Policy Analysis Staff Report, U.S.
Department of Agriculture, Forest Service, Washington, D.C.,
1977. 127 pp.
89
-------
commitment, on the part of air quality regulatory agencies for
acceptance of those measures which might be implemented. It is
anticipated that during the next decade land managers and air
quality personnel at all levels will enhance air quality by
an increased sharing in this evolutionary process, in order that
the best-available control technology can be effected to appro-
priate levels.
The intermittent or temporary nature of prescribed fire has re-
sulted in mixed interpretations among land managers and air
quality personnel at the State level. Some believe that because
it is a temporary source, prescribed fire does not come under
the Clean Air Act PSD provisions at all. This is a question of
special importance where there is strong competition for PSD
increments or where prescribed burning activity is expected to
increase.
One balancing factor recently advanced (100) is based on the EPA
Offset Policy, whereby an increase in pollution from a new
source can be offset by a reduction in emissions from other exist-
ing sources. The rationale of this concept is that prescribed
fires will offset emissions from wildfires that would otherwise
take place and produce substantially higher emission levels.
The outlook for evolution of applications of control technology
will depend in many areas upon availability of data processing
systems which make near-real-time weather data, and automated
processing of interfaced weather data, prescribed fire data, and
operational dispersion modeling a reality. Even in areas where
simple screening procedures and checklists will serve prescribed
burners without further sophistication, the importance of reliable
local weather information cannot be minimized. Continuation of
the Forest Service and National Weather Service cooperative pilot
test referenced in Section 6 will be dependent upon conversion to
an operating system in the future, but this possibility cannot
be definitely assessed at this time.
CONCLUSIONS
A nonspeculative conclusion possible through the preceding dis-
cussions is that prescribed fire emissions will increase, but
that the net impact of this increase in production will not be
crucial, due largely to voluntary actions taken among land mana-
gers. Somewhat more speculatively, it is possible to conclude
(100) Pierovich, J. M. Resource Management-Smoke Management:
Some Common Operational Priorities. Informal paper pre-
sented at the Fall Section Meeting of the Society of Ameri-
can Foresters, Ocala, Florida, October 10-11, 1978.
90
-------
that land management and air quality personnel will have common
points of communication concerning an available and emerging
technology, and that this communication will result in a desir-
able evolution of both voluntary and regulated processes. The
net result should be a strong downward trend in concentrations
of emissions in receptor areas.
91
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REFERENCES
1. Chi, C. T., and D. L. Zanders. Source Assessment: Agricul-
tural Open Burning, State of the Art. EPA-600/2-77-107a,
U.S. Environmental Protection Agency, Research Triangle Park,
North Carolina, July 1977. 74 pp.
2. Fire in the Northern Environment - A Symposium. C. W.
Slaughter, R. J. Barney, and G. M. Hansen, editors. U.S.
Department of Agriculture, Forest Service, Pacific Northwest
Forest and Range Experiment Station, Portland, Oregon, 1971.
275 pp.
3. Prescribed Burning Symposium Proceedings. U.S. Department
of Agriculture, Forest Service, Southeastern Forest Experi-
ment Station, Asheville, North Carolina, 1971. 160 pp.
4. Odum, E. P. Fundamentals of Ecology, 3rd Edition. W. B.
Saunders Co., Philadelphia, Pennsylvania, 1971. 574 pp.
5. Mobley, H. E., R. S. Jackson, W. E. Balmer, W. E. Ruziska,
and W. A. Hough. A Guide for Prescribed Fire in Southern
Forests. U.S. Department of Agriculture, Forest Service,
Atlanta, Georgia, May 1977. 40 pp.
6. Davis, L. S., and R. W. Cooper. How Prescribed Burning
Affects Wildfire Occurrence. Journal of Forestry, 61(12):
915-917, 1963.
7. Grantham, J. B. Forest Residue: A Forgotten Source of
Energy. Paper Processing, 10(2):17-20, 1974.
8. Cramer, 0. P. Disposal of Logging Residues Without Damage
to Air Quality. Technical Memorandum WBTM WR-37, U.S.
Department of Commerce, Salt Lake City, Utah, March 1969.
8 pp.
9. Southern Forest Fire Laboratory Personnel. Southern Forest-
ry Smoke Management Guidebook. Forest Service General
Technical Report SE-10, U.S. Department of Agriculture,
Asheville, North Carolina, and Macon, Georgia, 1976. 140 pp.
10. Wright, H. A. Range Burning. Journal of Range Management,
27(1):5-11, 1974.
92
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11. Miller, W. E. Use of Prescribed Burning in Seed Production
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23. Yamate, G. Emissions Inventory from Forest Wildfires, Forest
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66. Cook, J. D., J. H. Himel, and R. H. Moyer. Impact of
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67. Sandberg, D. V., et al. Effects of Fire on Air. Forest
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68. Eimutis, E. C., R. P. Quill, and G. M. Rinaldi. Source
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69. Paulson, N. Personal communication in reference to internal
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70. Virginia, Commonwealth of. Forest Management and Agricul-
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Richmond, Virginia. Undated. 8 pp.
71. Johansen, R. W., and R. A. Phernetton. Managing Smoke from
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Experiment Station, Asheville, North Carolina, 1979. 15+ pp.
72. Lavdas, L. G. PRESMOK, Operational Prescribed Fire Smoke
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73. Rodgers, S. L. SMKLCR. Computer Program Automatically Flag-
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May be Advected. Documentation on file, Southeastern Forest
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74. Paul, J. T., J. M. Pierovich, L. G. Lavdas, and S. L. Rodgers,
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Computer Program. Documentation on file, U.S. Department of
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Station, Asheville, North Carolina.
75. Lavdas, L. G. HRSMK Experimental Prescribed Fire Smoke Dis-
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76. Turner, D. B., and J. H. Novak. User's Guide for RAM, Vol-
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77. Turner, D. B., and J. H. Novak. User's Guide for Ram, Vol-
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Agency, Research Triangle Park, North Carolina, 1978. 222 pp.
78. Burse, A. D., and J. R. Zimmerman. User's Guide for the
Climatological Dispersion Model. EPA-R4-73-024, U.S.
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North Carolina, 1973. 131 pp.
79. Brubaker, K. L. , P. Brown, and R. R. Cirillo. Addendum to
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80. Fosberg, M. A. Personal communication. U.S. Department of
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81. Turner, D. B. Atmospheric Dispersion Modelling - A Critical
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29(5):502-519, 1979.
82. Nelson, E. E., and G. M. Harvey. Diseases. In: Environ-
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85. Kilian, L. ' Designated SF-FM, Practices, Coordination of
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86. Montana, State of. State of Montana Cooperative Smoke
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87. Oregon, State of. Directive 1-1-3-410, Smoke Management
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88. Oregon, State of. Directive 1-1-3-411, Operational Details
for the Oregon Smoke Management Plan. Unpublished plan on
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89. Washington, State of. Smoke Management Program. State of
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97. Paul, J. T., and J. Clayton, et al. User Manual - Forestry
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101
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GLOSSARY
air quality: Atmospheric properties with respect to the presence
of pollutants which may impair health, visibility or general
welfare.
area ignition: Fires set in many places throughout an area
either simultaneously or in quick succession and spaced so
that the entire area is rapidly covered with fire.
available fuel load: The fuel load that will be consumed in a
fire under given conditions.
backing fire: A prescribed fire or wildfire burning into or
against the wind or down the slope without the aid of wind.
brush: Scrub vegetation and immature stands of tree species that
do not produce merchantable timber.
burying: A residue disposal treatment in which residue is col-
lected, placed in a large pit or trench, and covered with
soil; usually done with a tractor.
chapparal: A plant community comprised of stiff or thorny shrubs
widely distributed in Southern California.
chipping: (1) In residue treatment, the reduction of woody resi-
due by a portable chipper to chips that are left to decay on
the forest floor. (2) In utilization, the conversion of
usable wood to chips, often at the logging site, for use in
manufacture of pulp, hardboard, energy, etc.
clearcutting: A harvest and regeneration system, normally ap-
plied to an even-aged forest, whereby all trees are cut.
Regeneration may be artificial or natural, logging methods
may vary, and clearcut areas may be of any size.
convection: The transmission of heat by the mass movement of
heated particles, as circulation in air, gas, or liquid
currents. In meteorology, convection refers to the thermal-
ly induced, vertical motion of air.
convective plume height: The elevation a plume attains due to
buoyancy caused by its initial increased temperature over
ambient conditions.
102
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convective smoke column: The thermally produced ascending column
of hot gases and smoke over a fire.
call logs: Inferior or diseased logs removed from a forest, or
logs removed for thinning.
duff: Forest litter and other organic debris in various stages
of decomposition, on top of the mineral soil, typical of
coniferous forests in cool climates where rate of decomposi-
tion is low and litter accumulation exceeds decay.
emission factors: Statistical average of the amount of emissions
released to the atmosphere in relation to the amount of fuel
burned. It is generally expressed in g/kg.
criteria pollutants: Air pollutants for which national ambient
air quality standards have been set.
fine fuels: The complex of living and dead herbaceous plants and
dead woody plant materials less than 6 mm in diameter.
fuel loading: The amount of fuel present expressed quantitative-
ly in terms of weight of fuel per unit area. This may be
available fuel or total fuel and is usually dry weight.
fuel moisture content: The quantity of water in a fuel particle
expressed as a percent of the oven dry weight of the fuel
particle.
Gaussian plume: A plume in which the concentration of the pol-
lutant material is distributed according to the normal dis-
tribution (the fundamental frequency distribution of
statistical analysis) in the crosswind and vertical
directions.
heading fire: A fire spreading or set to spread with the wind
and/or upslope.
herbicide: A chemical compound that causes physiological plant
damage usually resulting in death.
humus: That more or less stable fraction of the soil organic
matter remaining after the major portion of plant and animal
residues have decomposed; usually dark colored.
landing: Anyplace on or adjacent to the logging site where logs
are assembled for further transport.
litter: The surface layer of the forest floor consisting of
freshly fallen leaves, needles, twigs, stems, bark, and
fruits. This layer may be very thin or absent during the
growing season.
103
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logging residue: Unmerchantable or otherwise unwanted woody
material remaining after a logging operation.
non-attainment area: Region of the country where national
ambient air quality standards are not being met.
old growth: Timber stands of age and stature so as to resemble
a virgin forest in which the mean annual growth is
declining.
plume: A cloud of pollutant material, containing emissions from
a particular source or group of sources, which is being
dispersed in the atmosphere.
prescribed burning: The skillful application of fire in forest
and range management under conditions of weather, fuel
moisture, and soil moisture that will confine the fire to a
predetermined area resulting in planned benefits such as
fire hazard reduction, control of understory species, seed-
bed and site preparation, grazing enhancement, wildlife
habitat improvement, and forest tree disease control.
pyrolysis: A heat-induced, endothermic chemical degradation.
ring fire: Fires started by simultaneous ignition around the
perimeter of an intended burn area, which burns toward the
center.
scarification: Clearing away all vegetation to expose the soil.
second growth: Natural or planted timber stands on areas, pre-
viously logged or cleared.
silviculture: A phase of forestry dealing with the care of
forest trees.
site preparation: Removal or killing of unwanted vegetation,
residue, etc., by use of fire, herbicides, or mechanical
treatments in preparation for reforestation and future
management.
slash: A complex of woody forest debris left on the ground after
logging, land clearing, thinning, pruning, brush removal, or
natural processes such as ice or snow breakage, wind and
fire. Slash includes logs, chunks, bark, branches, tops,
uprooted stumps and trees, intermixed understory vegetation,
and other fuels.
smoke management: Providing quantitative appraisals of pre-
scribed fire and specifying conditions that limit air
quality impacts in areas of concern.
104
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convective smoke column: The thermally produced ascending column
of hot gases and smoke over a fire.
call logs: Inferior or diseased logs removed from a forest, or
logs removed for thinning.
duff: Forest litter and other organic debris in various stages
of decomposition, on top of the mineral soil, typical of
coniferous forests in cool climates where rate of decomposi-
tion is low and litter accumulation exceeds decay.
emission factors: Statistical average of the amount of emissions
released to the atmosphere in relation to the amount of fuel
burned. It is generally expressed in g/kg.
criteria pollutants: Air pollutants for which national ambient
air quality standards have been set.
fine fuels: The complex of living and dead herbaceous plants and
dead woody plant materials less than 6 mm in diameter.
fuel loading: The amount of fuel present expressed quantitative-
ly in terms of weight of fuel per unit area. This may be
available fuel or total fuel and is usually dry weight.
fuel moisture content: The quantity of water in a fuel particle
expressed as a percent of the oven dry weight of the fuel
particle.
Gaussian plume: A plume in which the concentration of the pol-
lutant material is distributed according to the normal dis-
tribution (the fundamental frequency distribution of
statistical analysis) in the crosswind and vertical
directions.
heading fire: A fire spreading or set to spread with the wind
and/or upslope.
herbicide: A chemical compound that causes physiological plant
damage usually resulting in death.
humus: That more or less stable fraction of the soil organic
matter remaining after the major portion of plant and animal
residues have decomposed; usually dark colored.
landing: Anyplace on or adjacent to the logging site where logs
are assembled for further transport.
litter: The surface layer of the forest floor consisting of
freshly fallen leaves, needles, twigs, stems, bark, and
fruits. This layer may be very thin or absent during the
growing season.
103
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logging residue: Unmerchantable or otherwise unwanted woody
material remaining after a logging operation.
non-attainment area: Region of the country where national
ambient air quality standards are not being met.
old growth: Timber stands of age and stature so as to resemble
a virgin forest in which the mean annual growth is
declining.
plume: A cloud of pollutant material, containing emissions from
a particular source or group of sources, which is being
dispersed in the atmosphere.
prescribed burning: The skillful application of fire in forest
and range management under conditions of weather, fuel
moisture, and soil moisture that will confine the fire to a
predetermined area resulting in planned benefits such as
fire hazard reduction, control of understory species, seed-
bed and site preparation, grazing enhancement, wildlife
habitat improvement, and forest tree disease control.
pyrolysis: A heat-induced, endothermic chemical degradation.
ring fire: Fires started by simultaneous ignition around the
perimeter of an intended burn area, which burns toward the
center.
scarification: Clearing away all vegetation to expose the soil.
second growth: Natural or planted timber stands on areas pre-
viously logged or cleared.
silviculture: A phase of forestry dealing with the care of
forest trees.
site preparation: Removal or killing of unwanted vegetation,
residue, etc., by use of fire, herbicides, or mechanical
treatments in preparation for reforestation and future
management.
slash: A complex of woody forest debris left on the ground after
logging, land clearing, thinning, pruning, brush removal, or
natural processes such as ice or snow breakage, wind and
fire. Slash includes logs, chunks, bark, branches, tops,
uprooted stumps and trees, intermixed understory vegetation,
and other fuels.
smoke management: Providing quantitative appraisals of pre-
scribed fire and specifying conditions that limit air
quality impacts in areas of concern.
104
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smoldering combustion: Combustion of a solid fuel, generally
with incandescence and smoke but without flame.
succession: The sequence of identifiable ecological stages in
the biological population of an area.
yarding: Moving of logs from stump to roadside deck or landing.
YUM: Yarding unmerchantable material by cable techniques,
usually in areas inaccessible to tractors.
105
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CONVERSION FACTORS AND METRIC PREFIXES (101)
To convert from
Degree Celsius (°C)
Gram/kilogram (g/kg)
Joule (J)
Kilogram (kg)
Kilometer (km)
Meter (m)
Meter (m)
Meter2 (m2)
Metric ton
CONVERSION FACTORS
To
Degree Fahrenheit (°F)
Pound/ton
Btu
Pound-mass (avoirdupois)
Mile
Foot
Inch
Mile2
Ton (short, 2,000 pound
mass)
Multiply by
1.8 t0(; + 32
2.000
9.478 x 10-*
2.205
6.214 x 10-1
3.281
3.937 x 101
3.861 x 10~7
1.102
PREFIXES
Multiplication
Prefix Symbol factor
Tera T 1012
Giga G 109
Mega M 106
Kilo k 103
Milli m 10~3
Micro y 10~6
Example
1
1
1
1
1
1
Tg
Gg
Mg
km
mm
ym
=
1
1
1
1
1
1
x
x
X
X
X
X
1012
109
106
103
lO-3
10-6
grams
grams
grams
meters
meters
meters
(101) Standard for Metric Practice. ANSI/ASTM Designation
E 380-76e, IEEE Std 268-1976, American Society for Testing
and Materials, Philadelphia, Pennsylvania, February 1976.
37 pp.
106
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-600/2-79-019h
2.
3. RECIPIENT'S ACCESSION NO.
4. TITLE AND SUBTITLE
Source Assessment: Prescribed Burning, State of the
Art
5. REPORT DATE
November 1979
6. PERFORMING ORGANIZATION CODE
7.
c „ Chi , D. Horn , R. Reznik , D. Zanders , R. Op=
ferkuch,J. Nyers (MRC)- and J. PierovichjL.Lavdas ,
C . McMahon.R. Nelson .R. Johansen . P. Ryan (USFS)
8. PERFORMING ORGANIZATION REPORT NO.
MRC-DA-931
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Monsanto Research Corp. *
1515 Nicholas Road
Dayton, Ohio 45407
10. PROGRAM ELEMENT NO.
1AB015; ROAP 21AXM-071
11. CONTRACT/GRANT NO.
68-02-1874
12. SPONSORING AGENCY NAME AND ADDRESS
EPA, Office of Research and Development
Industrial Environmental Research Laboratory
Research Triangle Park, NC 27711
13. TYPE OF REPORT AND PERIOD C(
Task Final; 8/75 - 9/79
COVERED
14. SPONSORING AGENCY CODE
EPA/600/13
15. SUPPLEMENTARY NOTES
IERL-RTP project officer is Ronald A. Venezia. (*) Cooperating
in this project was the Forest Service's Southeastern Forest Experiment Station
(USDA). PO Box 5106, Macon. GA 31208.
16. ABSTRACT
repOrt summarizes reported data on air emissions from prescribed
burning. Prescribed fire is used seasonally in all U.S. regions. The total vegetative
material burned annually in prescribed fires (1978 survey) is estimated at 36. 6 mil-
lion metric tons , dry weight. Of this , 34% is burned in the South; the Pacific North-
west and the North each burns 24%. Major fuels include piled or windrowed mate-
rial (49%), naturally occurring understory vegetation and litter (31%), and broadcast
(unpiled) material (20%). Important air emissions from prescribed fires include
particulates , gaseous hydrocarbons, CO, and NOx. Amounts of emissions produced
are highly varied. Estimated total national emissions from prescribed fires consti-
tute 0. 5%, 2.0%, and 20 7% of national emissions from all stationary sources of par-
ticulates, CO, and hydrocarbons , respectively. NOx production was not estimated.
The emerging best available control technology calls for quantitative appraisals of
prescribed fire and its alternatives, and for specifying conditions that will limit air
quality impacts in areas of concern.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.IDENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
Pollution
Combustion
Vegetation
Dust
Aerosols
Hydrocarbons
Carbon Monoxide
Nitrogen Oxides
Pollution Control
Stationary Sources
Prescribed Burning
Parti culate
13B
2 IB
06C
11G
07D
07C
07B
8. DISTRIBUTION STATEMENT
Release to Public
19. SECURITY CLASS (This Report I
Unclassified
21. NO. OF PAGES
122
20. SECURITY CLASS (Thispage)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
107
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