Current through Register Vol. 35, No. 18, September 24, 2024
Emissions reductions techniques (ERTs) are control strategies
that help reduce smoke from prescribed fires. ERTs are used in conjunction with
fire and do not replace fire. In addition to department-approved ERTs, other
ERTs are included below.
A. Reducing
the area burned.
(1) Burn concentrations -
Sometimes concentrations of fuels can be burned rather than using fire on 100
percent of an area requiring treatment. The fuel loading of the areas burned
using this technique tends to be high.
(2) Isolate fuels - Large logs, snags, deep
pockets of duff, sawdust piles, squirrel middens or other fuel concentrations
that have the potential to smolder for long periods of time can be isolated
from burning. Eliminating these fuels from burning is often faster, safer and
less costly than mop-up, and allows targeted fuels to remain following the
prescribed burn. This can be accomplished by several techniques including:
(a) constructing a fireline around fuels of
concern;
(b) not lighting
individual or concentrated fuels;
(c) using natural barriers or snow;
(d) scattering the fuels; and
(e) spraying with foam or other fire
retardant material.
(3)
Mosaic burning - Landscapes often contain a variety of fuel types that are
noncontinuous and vary in fuel moisture content. Prescribed fire prescriptions
and lighting patterns can be assigned to use this fuel and fuel moisture
non-homogeneity to mimic natural wildfire and create patches of burned and
non-burned areas or burn only selected fuels. Areas or fuels that do not burn
do not contribute to emissions.
B. Mechanical treatments - Mechanically
removing fuels from a site reduces emissions proportionally to the amount of
fuel removed. Treatments may include but are not limited to the following
methods.
(1) Firewood sales - Firewood sales
may result in sufficient removal of woody debris making on site burning
unnecessary. This technique is particularly effective for piled material where
the public has easy access.
(2)
Whole tree harvesting - Whole trees can be removed through harvesting or
thinning techniques and virtually eliminate the need for burning.
(3) Mulch/chips - Mechanical processing of
dead and live vegetation into wood chips or shredded biomass is effective in
reducing emissions if the material is removed from the site or biologically
decomposed.
(4) Fuel for power
generation - Vegetative biomass can be removed and used to provide electricity
in regions with cogeneration facilities.
(5) Biomass utilization - Vegetative material
can be used for many miscellaneous purposes including pulp for paper,
methanol/ethanol production, wood pellets, garden bedding, furniture, specialty
crafts, compost, mulch and fiberboard/particleboard.
C. Chemical pre-treatments - Broad spectrum
and selective herbicides can be used to reduce or remove live vegetation, or
alter species diversity respectively. Herbicides can be applied before burning
to kill vegetation, which can create a much drier fuel, which in turn burns
more efficiently.
D. Site
conversion - Natural site productively can be decreased by changing the
vegetation composition.
E. Land use
change - Changing wildlands / shrublands / rangelands / croplands to another
land use category may result in elimination of the need to burn and vice
versa.
F. Reduce fuel loading -
Some or all of the fuel can be permanently removed from the site, biologically
decomposed, or prevented from being produced. Overall, emissions can be reduced
when fuel is permanently excluded from burning.
(1) Mechanically removing fuel - Mechanically
removing fuels from a site reduces emissions proportionally to the amount of
fuel removed.
(2) Burn more
frequently at low intensity - This method prevents the fuels from building up
and causing greater emissions.
(3)
Schedule burning before green up - Burning in cover types with a grass or
herbaceous fuel bed component can produce fewer emissions if burning takes
place before these fuels green-up for the year.
(4) Under burn before fall leaf drop - When
deciduous trees and shrubs drop their leaves, this ground litter contributes
extra volume to the fuel bed.
(5)
Ungulates - Grazing and browsing live grassy or brushy fuels by sheep, cattle
or goats can reduce fuels prior to burning or reduce the burn
frequency.
(6) Isolating pockets of
fuel - See explanation under reducing the area burned.
G. Reduce fuel consumption - Emission
reductions can be achieved when significant amounts of fuel are at or above the
moisture of extinction, and therefore are unavailable for combustion.
(1) Having high moisture content in
non-target fuels - This can result in only the fuels targeted being dry enough
to burn.
(2) High moisture in large
woody fuels - Burning when large-diameter woody fuels (three- plus inch
diameter or greater) are wet can result in lower fuel consumption and less
smoldering.
(3) Moist litter or
duff - The organic layer that forms from decayed and partially decayed material
on the forest floor often burns during the inefficient smoldering phase.
Consequently, reducing the consumption of this material can be effective at
reducing emissions.
(4) Mass
ignition/shortened fire duration/aerial ignition - "Mass" ignition can occur
through a combination of dry fine-fuels and rapid ignition, which can be
achieved using a helitorch. The conditions necessary to create a true mass
ignition situation include rapid ignition of a large open area with continuous
dry fuels.
(5) Burn before large
fuels cure - Living trees contain very high internal fuel moistures, which take
a number of months to dry after harvest. If an area can be burned within 3-4
drying months of timber harvest, many of the large fuels will still contain a
significant amount of live fuel moisture.
(6) Rapid mop-up - Rapidly extinguishing a
fire can reduce fuel consumption and smoldering emissions somewhat, although
this technique is not particularly effective at reducing total emissions and
can be expensive.
(7) Burn before
precipitation - Scheduling a prescribed fire before a precipitation event will
often limit the consumption of large woody material, snags, stumps, and organic
ground matter, thus reducing the potential for a long smoldering period and
reducing the average emission actor.
H. Minimizing emissions by minimizing the
emission factor - Using burning techniques that create a more efficient burn.
(1) Burning fuels in piles or windrows -
Keeping piles dry and free of dirt and other debris generates greater heat and
therefore, the piles burn more efficiently. The piles or windrows can be made
mechanically or by hand.
(2)
Utilizing a backing fire - Flaming combustion is cleaner than smoldering
combustion. A backing fire takes advantage of this relationship by causing more
fuel consumption to take place in the flaming phase than would occur if a
heading fire were used.
(3) Rapid
mop-up - See above.
(4) Mass
ignition/shortened fire duration/aerial ignition - See above.
(5) Dry conditions - Burning under dry
conditions increases combustion efficiency and fewer emissions may be
produced.
I. Air curtain
incinerator (ACI) - Use of an air curtain incinerator improves combustion and
reduces emissions by introducing high velocity air into a combustion
environment. As the air continuously rotates in and over the environment, a
"curtain" is created over the fire thus trapping smoke and particulate matter.
Constant airflow into and over the combustion environment allows temperatures
to remain high, resulting in relatively complete combustion of all emission
products. ACIs can burn a wider variety of materials from green fuel to red
slash and produce lower smoke emissions as compared to pile or broadcast
burning. They also reduce risk of an escaped fire since the fire is contained
and can be quickly extinguished if necessary.
