Fuel moisture as measured and predicted during the 1988 fires in Yellowstone Park

10 Pages·1991·0.58 MB·English

by  Bartlette, Roberta A

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Historic, archived
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n
i i * J
United States Fuel Moisture as
Department
of Agriculture
Forest Service Measured and Predicted
Intermountain
Research Station During the 1988 Fires in
Research Note
INT-396
Yellowstone Park
February 1991
Roberta A. Hartford
Richard C. Rothermel1
C-3
~~
tr>
ABSTRACT
drought conditions and the repeated passage ofdry
cold fronts, which brought strong gusty winds and
Finefuel moisture content, relative humidity, air no appreciable precipitation, created the conditions
temperature, andfire behavior were observed hourly for fire growth beyond projections. Crown fires,
for48 hours on theNorth Fork Fire in Yellowstone which had previouslybeen limited to areas ofdeca-
NationalPark from August 25 toAugust 27, 1988. dent lodgepole pine (Pinus contorta Dougl.), contin-
Finefuel reached minimum moisture contents of ued to spread regardless offuel type or stand age.
3 to 5percent late in the afternoon, remained below In addition, the daily burningperiod was extending
8percent until after midnight, then rose toa maxi- as the season progressed so that by mid-August
mum of10 to 11percent around 9 a.m. At this time, fires wereburningactively, even crowning, well into
fires were burningactively well into the night, sub- the night. In late August a team was called in from
siding to low-intensity surface andgroundfire dur- the Intermountain Fire Sciences Laboratory (IFSL)
ing the morning, then entering the crowns in late by the GreaterYellowstone Area Command. The
afternoon. Livefoliage moisture contents were team monitored fine fuel moisture contenthourly
sampledpredawn and late afternoon. Standing for a 48-hour period to help explain the extended
dead boles, duff, and mineral soil were also active burningperiod. These data were used
sampled. Moisture contents were determined by promptly after collection to explain the persistence
Computrac moisture analyzer, ovendrying, and ofthe fires and why fire control actions taken at
Delmhorst wood moisture meter. Measuredfinefuel night were not effective. This paper discusses these
moisture contents were compared with thosepre- observations and compares the observed moisture
dicted byfire behavioranalysts'tables and the contents with predictions for those conditions.
BEHAVE
fireprediction system.
FUEL MOISTURE SAMPLING
KEYWORDS: wildfire, diurnal weather, Yellow-
stone National Park, weather, fire Three sites were sampled near the westflank of
behavior the North Fork Fire (fig. 1) within fuels representa-
tive ofthose consumed by the fire. They were situ-
In mid-Augustof1988, the behavior offires in the ated in the path ofthe North Fork Fire, near the
GreaterYellowstone Area surpassed that predicted road between WestYellowstone and Madison Junc-
in early Augustby a six-member team offire spe- tion, from 3 to 6 miles east ofWestYellowstone.
cialists (Rothermel 1990). Projected growth ofthe Fire activity in the area prevented the team from
fires was based on previously observed fire behavior remaining at one site for the duration ofthe study.
in specific fuel types within the park and most prob- The fire burned over all three sites within hours to
able expected weather for the season. Extended a few days after sampling. Though location differed,
canopy cover, aspect, elevation, and proximity to the
Madison River were essentially the same between
sites. All sites were flatbenches with 30 to 60 per-
foresterandProjectLeader, IntermountainResearchStation, cent canopy cover, primarily lodgepole pine, with
locatedatIntermountainFireSciencesLaboratory,Missoula, occasional Douglas-fir (Pseudotsuga menziesii
MT.
[Mirb.] Franco). The understory vegetation was
1
—
Figure 1 Westflankof the North Fork Fire indicating numbered sample sites and fire perimeters
just priorto, during, and immediatelyfollowing the study, and final perimeter.
sparse grass, withjuniper (Juniperus spp.), big by dryingin a convection oven at 217 °F (103 °C).
sagebrush (Artemesia tridentata), and grasses in Temperature, relative humidity (table 1), eye-level
the openings. windspeed, and currentfire behavior near the site
Three composite samplesfrom the loose upper were recorded at the time ofsample collection.
litter under lodgepole pine canopy were collected in Incidental samples were also taken to character-
4-inch-diameter soil cans approximately hourly for ize the moisture status ofotherfuels in the area.
48 hours. The litter consisted primarily oflodgepole Dead grass was not collectedhourly because it was
pine needles cast in the pastyear, but also con- a very minor component ofthe surface fuel complex
tainedbark flakes, twigs less than one-fourth inch within the forested sites that were burning, butwas
in diameter, and cones. After each samplingperiod, collected atpredawn and midafternoon to obtain
one sample was evaluated on site with a measurement ofthe approximate maximum and
Computrac2 moisture analyzer powered by a minimum values reached in this fine fuel. Duffand
portable generator. The other two samples were
mineral soil samples were collected as well as pre-
sealed and their moisture contents determined later
dawn and midafternoon live foliar moisture samples
from conifers and shrubs. The moisture contentof
dead standing and downed large-diameter (3+-inch)
2Theuseoftradeorfirmnamesinthispaperis forreader boles were measured using a Delmhorst wood
informationanddoesnotimplyendorsementbytheU.S. De- moisture meter.
partmentofAgricultureofanyproductorservice.
2
—
Table 1 Weather and litterfuel moisture observations
Fine fuel Fine fuel
Date Time RH Temp moisture Date Time RH Temp moisture
Pet orC Petovendry Pet F Petovendry
August 25 4:00 p.m. 9 88 3.2 August 26 4:00 p.m. 8 80 5.3
4:40 p.m. 10 82 3.5
5:00 p.m. 11 88 4.1 5:00 p.m. 9 77 5.2
5:20 p.m. 12 88 5.3
6:00 p.m. 10 89 5.4 6:0—0 p.m. 2—0 6—9 —4.8
6:20 p.m. 11 83 5.1
7:00 p.m. 12 81 5.5 7:10 p.m. 28 65 5.6
8:00 p.m. 20 67 5.6 8:00 p.m. 34 60 5.5
9:00 p.m. 21 78 5.7 9:00 p.m. 38 56 6.0
10:30 p.m. 32 68 6.3 10:30 p.m. 45 52 7.0
11:00 p.m. 30 68 6.4 11:00 p.m. 54 48 7.1
August 26 Midnight 42 59 6.1 August 27 Midnight 60 43 7.5
1:00 a.m. 46 54 6.8 1:00 a.m. 66 39 8.3
2:00 a.m. 49 53 6.8 2:00 a.m. 72 39 8.0
3:00 a.m. 48 50 7.5 3:15 a.m. 64 37 8.5
4:00 a.m. 56 42 7.8 4:00 a.m. 72 33 9.2
5:00 a.m. 62 38 8.1 5:00 a.m. 83 30 9.0
6:00 a.m. 64 35 7.9 6:00 a.m. 79 30 8.9
6:30 a.m. 74 43 9.6
7:00 a.m. 73 33 8.9
8:30 a.m. 48 60 10.5 8:40 a.m. 65 46 9.5
9:00 a.m. 46 59 10.7 9:00 a.m. 66 45 10.3
10:00 a.m. 36 63 9.3 10:15 a.m. 46 58 10.3
1I1I'.CU\CU\ ad.lmll. 1R 7fi 11'C\C\ a m JO Q Q
Noon 15 75 7.2 Noon 30 64 8.7
1:00 p.m. 12 78 7.0 1:00 p.m. 25 69 7.4
2:00 p.m. 12 78 6.1 2:00 p.m. 18 72 7.2
3:15 p.m. 9 81 5.5 3:00 p.m. 15 73 7.1
4:00 p.m. 8 80 5.3 4:00 p.m. 13 80 6.4
WEATHER AND FUEL MOISTURE
to partly cloudy throughout the period with cumulus
OBSERVATIONS buildups in the afternoons over the smoke columns
and up to 40 percent cloud cover for a fewhours the
The weather in the areahadbeen dominatedby night ofthe 25th.
a high pressure ridge duringthe week, with warm The litterfuels collected duringthe study were
afternoon temperatures in the upper 80's, extremely shaded most ofthe time by the lodgepole pine
low relative humidities, and morninginversions. canopy. Under the canopy, fuels received direct
On August 25, the high pressure ridge began to solar radiation only for relatively short periods of
weaken and move eastward allowing cooler air to time as the shadows and sunspots were continually
move in alongwith a slight increase in moisture. shifting. These fuels were also well sheltered from
Upper level winds were west to southwest at 10 to the wind. There was no wind at the surface while
15 mi/h during the afternoon. One thunderstorm the inversion was present. After the inversion
developed the evening ofthe 25th over the fuel lifted, eye-level windspeeds of3 to 5 mi/h, with occa-
moisture site delivering a trace ofrain. A smokey sional gusts to 7 to 10 mi/h in the afternoon, were
inversion persisted until around 11 a.m. on the observed. The wind subsided at dusk.
morning ofthe 26th. Late on the 26th a dry cold Both methods oflitter moisture analysis gave
frontbrushed the park bringing stronger northwest comparable results for the range ofmoisture con-
to north winds aloft at 15 to 25 mi/h and a slight tents observed. The Computrac proved to be a valu-
increase in relative humidity. Dense smoke re- able tool for rapidly evaluating dead fuel moisture
mained over the sample site into early afternoon on contents on site. Differences between paired
the 27th with cooler temperatures. Skies were clear samples dried in the oven were as great as
3
20 where the duffhad accumulated to a depth of
4 inches ormore. Duffin unshaded areas, and
areas with thin accumulations ofduff, had moisture
contents similar to that ofthe litter layer. Mineral
soil moisture content at the interface between soil
and duffwas only 3 to 4 percent.
Live coniferfoliar moisture contents were similar
to those observed in other conifer species at that
time ofyear. The measured moisture ofmature
conifer needles rangedfrom 96 to 118 percent and
new needles ranged from 117 to 148 percent.
Lodgepole pine foliage sampled in 1989 and 1990 in
Yellowstone National Park ranged from 95 to 146
1600 0000 0800 1600 0000 0800 1600 percent, averaging about 120 percent in late August
25Aug88 26Aug88 27Aug88
(unpublished data on file at IFSL). This compares
—
Figure 2 Diurnal trend of observed relative with mature needle moisture contents ofDouglas-fir
humidity and measured moisturecontent in and ponderosa pine (Pinusponderosa Laws.) of110
lodgepole pine litter, August 25to 27, 1988. to 120 percent in mid-August and new needle mois-
ture contents averaging 130 percent (Philpot and
Mutch 1971). Philpot and Mutch found thatthe
general trends in foliar moisture were similarfrom
differences between the ovendry and Computrac-
measured moisture. Avariability ofup to 2 percent one year to the next even though weather differed.
Johnson (1966) observed the seasonal trend offoliar
moisture content was observed both in the oven-
moisture content in red pine (Pinus resinosa Ait.)
dried pairs and between the two techniques, but the
andjack pine (Pinus banksiana Lamb.), reporting
average difference was only 0.5 and 0.75 percent
mature needle moisture contents in the range of110
moisture content, respectively. These differences
to 125 percent and new needle moisture contents
are within expectedvariability in field-collected
between 125 and 150 percentin late summer. Jack
samples.
An average moisture content (table 1), calculated pine foliar moisture contents were measured by
Crosciewicz (1986) over two seasons. Old foliage
for each samplingperiodfrom all litter samples, ranged from 95 to 110 percent, and new foliage was
was used for further analysis. All moisture contents
near 150 percent in late summer.
are expressed as a percentage ofthe dry weight.
Measured moisture contents ofshrub foliage were
Figure 2 displays the relative humidity andfine
considerably lower than those ofthe conifers, but
fuel moisture duringthe 48-hour samplingperiod.
were within the range expected for that time of
Moisture values under 4 percent were observed in
year. Moisture content in sagebrush ranged from
shaded litterfuels in late afternoon; unshadedfine
fuels reached this value by early afternoon. A ther- 78 to 106 percent. By comparison, Wyomingbig
sagebrush (Artemesia tridentata wyomingensis)
mocouple placedjust under the surface-mostneedle
moistures measured at the Dinosaur National
litter registered approximate surface fuel tempera- Monument in 1987 and 1989 ranged broadly in late
tures. Fuel temperatures as high as 128 °F were
Augustfrom 50 to 105 percent, averaging 60 to 80
measured in these unshaded fuels. The litter mois-
percent (Riedel and Petersburg 1989). Sagebrush
ture content remained low, between 5 to 7 percent
moisture contents measured in 1989 in southeast-
until after midnight. The highest moisture contents
ern Montana ranged from 67 to 110 percent, and
observed in the litter, around 11 percent, occurred
those measured in 1990 in Yellowstone National
about 9 a.m. This 11 percent moisture content is
Park (unpublished data on file at IFSL) averaged
well below the moisture ofextinction ofthese fuels,
around 110 percent in late August.
which would range from 18 to 25 percent. By com-
Observed fire behavior ranged to dramatic ex-
parison, standing cured grass moisture content
tremes throughout the diurnal samplingperiod. At
ranged from 4 to 7 percent in the afternoon to 13
2 p.m. on August 25 large smoke columns capped by
to 18 percentjust before dawn.
cumulus clouds were visible from WestYellowstone.
Moisture contents in longer response fuels were
At 4 p.m. the fire was observed movingthrough the
also very low. Large-diameter sound dead wood
surface fuels and the crowns from the south toward
ranged in moisture from 4 to 9 percent, with the v*> Madison River. A spot fire ignited on the hill-
higher moistures occurringin boles with bark.
side ^ ^oss the river, ajump ofat least one-fourth
Mostboles measured 6 to 7 percent. Duffmoisture
mile, and trees began torching within minutes.
content ranged from 8 to 12 percent in shaded areas
The team was requested to move back toward West
4
Yellowstone as the fire was approachingthe high-
way and would be crossing it. At 8 p.m. a crown
fire was observed approachingfrom the south with
flame heights to about 150 feet. The crown fire was
observed until 9:30 p.m. when it was again neces-
sary to relocate. At 11 p.m. surface fuels were burn-
ing, with flame heights of2 to 5 feet, in sagebrush
at an estimated 2 chains per hour rate ofspread.
Smaller lodgepole pine and pine near fueljackpots
continued to torch. Intense burningto the east was
noted by the smoke column and strong orange glow
on the horizon. By 2:30 a.m. August 26, flame
lengths through the needle litter were 3 to 4 inches
in a continuous front, 6 inches in dead grass, and 1600 0000 0800 1600 0000 0800 1600
25Aug88 26Aug88 27Aug88
2 feet in sagebrush. Burning was primarily limited
—
to the surface fuels. Flames climbed tree boles but Figure 3 Comparison of observed (points)
did not ignite the foliage. The surface fire burned and predicted (curve) fine fuel moistures.
through the bases ofthe standinglodgepole pine, Predictions obtained from the FBAtables.
with numerous trees fallingthroughout the night
and early morning at a rate ofone to two per minute
in the immediate area. Intensity increased and
EVALUATION OF PREDICTED
waned both to the north and to the east ofthe
MOISTURE CONTENTS
sample site, subsidingjustbefore dawn. Predawn
flame heights were 6 inches to 1 foot in litter and
small downed dead fuels, up to 4 feet in larger con- The weather parameters collected duringthe fuel
centrations offuel. moisture samplingperiod were used to calculate
From 6 to 8 a.m. the surface fireburned well in expected fine fuel moisture contents. Two methods
the litter, with flame heights of3 to 4 inches. The ofprediction were tested. The fire behavior analyst
fire continued to burn strongly at the bases oftrees, (FBA) tables, as described by Rothermel (1983),
climbingthe boles but not ignitingthe crowns. By allow moisture content calculation at any specified
9 a.m., flame heights were down to 2 to 4 inches in time based on observed relative humidity and tem-
the litter and by 9:30 a.m., the litter was only smol- perature. The MOISTURE module ofFIRE2 ofthe
dering. The sun began to feel effectively warm BEHAVE prediction system (Andrews and Chase
around 10 a.m., and the litterbegan flaming again 1989) incorporates the moisture model developed
with flame lengths up to 6 inches. Smoke columns by Rothermel and others (1986). This model pre-
began building east and south ofthe sample area. dicts hourly temperature, relativehumidity, and
By 11 a.m. flame lengths in litter were up to 1 foot, fuel moisture contentbased on the input ofweather
and flame lengths of3 feet were observed in downed conditions at specified times.
woody material. By noon, torching ofindividual Figure 3 includes observed moisture contents and
and small groups oftrees was observed. From 1 to those calculated using the FBA tables. Shaded day-
3 p.m., fire across the riverfrom the site was carried time conditions were assumed because ofthe combi-
through the lodgepole pine crowns, but adjacent to nation ofcanopy cover and smoke. Usingthe tables,
the sample site flames remained on the surface, each prediction is based on the actual relative hu-
with occasional torching within the heavily canopied midity and temperature observed at the time of
area. sampling. No provision is given for a time lagin
Aburnout operation at 8 p.m. produced frequent moisture recovery. Also, at 8 p.m., moisture predic-
torching and illuminated the sky until 4 a.m. the tion begins from the nighttime tables. The abrupt
morning ofAugust 27. At 4 a.m., flaming in the fine drop in predicted moisture content at this time is
fuels continued with lengths of4 to 6 inches. By due to differences between the daytime and night-
6 a.m., flame fronts were no longer continuous and time tables. The daytime minimum moisture con-
by 8 a.m. flaming was replaced by smoldering. The tents used to predict fire behavior duringnormal
inversion persisted throughout the morning, with burningtimes are very close to actual moisture con-
little increase in fire activity until around 2 p.m. tents. The predicted nighttime fuel moisture con-
By 3 p.m. cumulus clouds were building over smoke tents are higher than observed in lodgepole pine
columns to the east ofthe site. litter and peak moisture contents correspond with
peak relative humidity observations.
5
(fig. 5) were good duringthe afternoon and for the
period through the night ofAugust 25. On the night
ofthe 26th and morning ofthe 27th, however, the
moisture ofthe litter fuels recovered only to the
same level as on the previous night, though it was
predicted to recover an additional 4 percent due to
thehigher relativehumidity that second night.
Through both diurnal periods, the time atwhich
maximum and minimum moisture contents were
predicted corresponded with that observed. The
abrupt drop in predicted moisture at noon is caused
by the transition from one cycle ofweather data to
the next. The curves illustrate the difficulty ofpre-
1600 0000 0800 1600 0000 0800 1600 dictingmoisture duringthe night and morning.
25Aug88 26Aug88 27Aug88
—
Figure 4 Comparison of observed (points) and DISCUSSION AND CONCLUSIONS
predicted (curves) relative humidity and airtempera-
ture. Predictions obtained from MOISTURE module Although the litterfuel moisture content did re-
of FIRE2 in BEHAVE. spond to changes in relative humidity and air tem-
perature, two points are noteworthy. First, the
lodgepole pine litter responded differently to rising
20 20 and fallingrelative humidity. The fine fuel mois-
ture contentbegan to increase with risingrelative
humidity within an hour after reaching the after-
noon low point; however, its recovery rate was slow.
The maximum fuel moisture was reached 3 to 4
hours after the peak in relative humidity. There-
fore, the rate at which moisture was gained by the
fuel was slower than the rate at which it was lost.
Secondly, the litter fuels did not recover to their
moisture-of-extinction levels of18 to 25 percent.
The nighttime relative humidity reached 74 percent
by morning ofAugust 26 and 83 percent the follow-
1600 0000 0800 1600 0800 1600 ingmorning. Based on the temperature and rela-
25Aug88 26Aug88 27Aug8 tivehumidity atthe sample sites, fine fuel mois-
Figure 5—Comparison of observed (points) and tures were predicted to reach 13 to 14 percentby
early morningofthe 26th and 14 to 18 percent on
predicted (curve) fine fuel moisture. Predictions
obtained from MOISTURE module of FIRE2 in the 27th. Fine standingcured grass, sampled at
BEHAVE. dawn and at 4 p.m., had moisture contents of13
and 18 percent on the mornings ofthe 26th and
27th. But, the lodgepole pine litter moisture con-
tent reached only 10.7 and 10.3 percent, respec-
The MOISTURE module ofBEHAVE can be used tively, those two mornings. There was very little
to provide a diurnal cycle ofweather and fine fuel moisture in the system, either in the surrounding
moisture content predictions athourly intervals. air or from the underlying soil, to increase the litter
Temperature and relative humidity are input at fuel moisture content. The situation, however, was
2 p.m. (the day prior to burn day), sunset, sunrise, aggravated by the fuel itself. Anderson (1985)
and at burn time. For this comparison, burn time showed that the timelagofall fine fuels cannotbe
was set at 11:59 a.m. Hourly predictions were ob- assumed to be 1 hour. Conifer needles respond
tained from noon on burn day-1 through 11:59 a.m. much more slowly, and lodgepole pine was found to
on burn day. This procedure was followed to obtain be the slowest ofthe species tested, with a response
predictions for August 25, 26, and the morningof time of1.6 hours to more than 34 hours, depending
August 27. To obtain predictions for the balance of on the degree ofdecomposition. The needle litter
the 27th, weather conditions were inputfor 2 p.m. gained moisture atnight more slowly than was pre-
on burn day and at the burn time of4 p.m. The dictedby the models ormeasured in the grass.
BEHAVE prediction ofrelative humidity and air This minimal fine fuel moisture response in a
temperature was quite close to observed values drought situation is one key to the active nighttime
(fig. 4). The predictions offine fuel moisture content burning that was observed for the Yellowstone fires.
6
The sample sites were under the influence ofinver- Chrosciewicz, Z. 1986. Foliar moisture content
sions by dawn. Fuels on the slopes above the inver- variations in four coniferous tree species ofcentral
sion layer mayhave experienced even less night- Alberta. Canadian Journal ofForest Research. 16:
time moisture recovery. 157-162.
The active crown fire behavior cannotbe attrib- Johnson, Von J. 1966. Seasonal fluctuation in mois-
uted to unseasonably low foliar moistures. Dead ture content ofpine foliage. Res. Note NC-11. St.
fuels within the crown such as twigs and lichen, Paul, MN: U.S. Department ofAgriculture, Forest
however, would havehad low moistures similarto Service, North Central Forest Experiment Sta-
those measured in the litter. Also, standing dead tion. 4 p.
large fuels were as dry as the late afternoon values Philpot, Charles W.; Mutch, RobertW. 1971. The
for litter. Dry fuel was readily available to fire from seasonal trends in moisture content, ether extrac-
the ground through the crown throughoutmost of tives, and energy ofponderosa pine and Douglas-
the night and day. fir needles. Res. Pap. INT-102. Ogden, UT: U.S.
Predictions offine fuel moisture contentbased on Department ofAgriculture, Forest Service,
observed weatheryielded expected values in agree- Intermountain Forest and Range Experiment
ment with measured values in dead grass. But af- Station. 21 p.
ter midnight and early morningthe predictions Riedel, A. L.; Petersburg, S. J. 1989. Live fuel mois-
were considerablyhigher than were observed in ture in Wyomingbig sagebrush (Artemesia
the fine fuel that was carryingthe surface fire, the tridentata wyomingensis) in Dinosaur National
lodgepole pine needle litter. Observed fire behavior Monument. Draft report. Dinosaur, CO: U.S. De-
exceeded that expected, especially duringthe late partment ofthe Interior, National Park Service,
evening and at night. Fire behavior was consistent Dinosaur National Monument.
with thatexpectedbased on the measured fuel Rothermel, Richard C. 1983. How to predict the
moisture contents, which illustrates the value of spread and intensity offorest and range fires.
directly measuringfine fuel moisture content when Gen. Tech. Rep. INT-143. Ogden, UT: U.S. De-
possible. partment ofAgriculture, Forest Service, Inter-
mountain Forest and Range Experiment Station.
REFERENCES 161 p.
Rothermel, Richard C;Wilson, Ralph A; Morris,
Anderson, Hal E. 1985. M—oisture and fine forestfuel Glen A.; Sackett, Stephen S. 1986. Modelingmois-
response. In: Weather the drive-train connecting ture content offine dead wildland fuels: input to
the solar engine to forest ecosystems: Proceedings the BEHAVE fire prediction system. Res. Pap.
8th conference on fire and forest meteorology; INT-359. Ogden, UT: U.S. Department ofAgricul-
1985 April 29-May 2; Detroit, MI. Bethesda, MD: ture, Forest Service, Intermountain Research
Society ofAmerican Foresters: 192-199. Station. 61 p.
Andrews, Patricia L.; Chase, Carolyn H. 1989. Rothermel, Richard C. [In preparation]. Yellowstone
BEH—AVE: fire prediction and fuel modeling sys- Park longrange fire predictions in 1988.
tem BURN subsystem, Part 2. Gen. Tech. Rep. Missoula, MT: U.S. Department ofAgriculture,
INT-260. Ogden, UT: U.S. Department ofAgricul- Forest Service, Intermountain Research Station,
ture, Forest Service, Intermountain Research Intermountain Fire Sciences Laboratory.
Station. 93 p.
Intermountain Research Station
324 25th Street
Ogden, UT 84401
7
frU.S.GOVERNMENTPRINTINGOFFICE:1991-573-041/21021
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