orce ange re

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USDA F orest Service Research Paper S E - 105 February 1973
orce ange re
e D. wade
and
d E. Ward
U. S. Department sf Agr i cuitura - Forest Servi ce
Southeastern FOWSB Experiment Station
Ashevi I le, North Carol i na
ACKNOWLEDGMENT
The authors wish to thank the
following people a n d organizations
for their various contributions: Dane
Roten and other employees of the
North Carolina Forest Service for
providing m a p s, photographs, fire
reports, interviews, and other infor-
mation concerning the area, fuels,
and subsequent fire b e ha vi o r and
control; Dale N. Ellis, Fire Weather
Forecaster for North Carolina, for
providing weather data, charts, and
related information; Quentin Bell and
other pe rs onne 1 of the Westvaco
Corporation for maps, photographs,
and other pertinent information; and
personnel of the U. S. Army Corps
of Engineers and U. S. Air Force
for an appraisal of fire damage
and photographs.
CONTENTS
Page
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Introduction 1
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Background 2
. . . . . . . . . . . . . . . . . . . .
Fire Development and Control 2
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Fuels 5
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Weather 10
. . . . . . . . . . . . . . . . . . . . . . . . . . . .
Fire Behavior 13
. . . . . . . . . . . . . . . . . . . . . . . . .
Convection Numbers 16
. . . . . . . . . . . . . . . . . . . .
Patterns of Fuel Consumption 20
. . . . . . . . . . . . . . . . . . . . . .
Particulates and Visibility 27
. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Fire Effects 29
. . . . . . . .
Fire Management in the Pocosins.. Research Needs 33
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Summary 35
. . . . . . . . . . . . . . . . . . . . . . . . . . .
Literature Cited 37
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Appendix 38
A
ANALVS S
of the
Air Force Bomb Range Fire
by
Dale D. Wade and Darold E. Ward
Associate Fire Behavior Scientists
Southern Forest Fire Laboratory
&lacon, Georgia
INTRODUCTION
There are few places in the world where wildfire behavior can be
studied strictly as it is affected by weather variables, both ambient and
fire-induced. Eastern North Carolina offers this opportunity. Large,
homogeneous expanses of highly combustible fuel exist on land that has a
maximum elevation of 10 ft. (3 m. ) above mean sea level.' Fine fuel
weights of 15 tonslacre (33.6 M.T./ha. ) are common, and under extreme
drought conditions these fuel weights may more than double as the
peat soils, characteristic of this region, dry to depths of 1 to 2 ft.
(0.3 to 0.6 m. ).
Wildfires occurring in eastern North Carolina frequently become
dangerously explosive, blowup fires. The 29,3 00-acre (11 ,860-ha. ) Air
Force Bomb Range Fire of March 22-26, 1971, was such a fire; it was
studied by a fire documentation team from the Southern Forest Fire
Laboratory. The fire exhibited several blowup features including high-
density, short-distance spotting, a well-developed convection column,
and rates of spread exceeding 2 rn.p.h. (0.9 rn./sec.) during a &hour
period with a maximum of almost 5 m.p.h. (2.2 m. /sec. ) during one
4-mile (6.4-km. ) run, The fire traveled 14 miles (22.5 km. ) prior to
the passage of a cold front, then changed direction, and ran an additional
6 miles (9.7 km, ) as a post cold-frontal Eire. A record of fire behavior
was imprinted on the area vegetation in the form of concentric bands of
unconsumed fuel that outlined the fire during the first 4 hours after igni-
tion. Fire suppression was hampered by the pwr trafficability of the
soils, the heavy fuels, and the rapid rate of fire spread.
';inetric equivalents appear in parentheses, See Appendix for conversion factors.
BACKGROUND
The inaccessibility of pocosins2 contributes to the development of
tremendously large fires such as the Lake Phelps Fire that burned
250,000 acres (301,"t5 ha.) during March and April 1955 and the Hyde-
Tyrrell Fire that burned 100,000 acres (40,470 ha, 9 during April 1963.
Other blowup fires have occurred during the summer (Bluff Point Fire--
July 1952), fall (Hales Lake Fire--October 1952), wet periods (Pungo
Lake Fire- -Apr"i 19593, and drought periods (Dare County Fire--August
195~9,
The area burned by the Air Force Bomb Range Fire contained a
well-stocked natural stand of 13-year-old pond pine (Pinus serotina
>
Michx. and a dense poeosin mderstory, both of which developed after
the lightning-caused 195'7 Dare County Fire that denuded some '75,000
acres (30,350 ha. 9.
Dare County itself is a sparsely populated peninsula comprised pri-
marily of pocosins and marshland. Most of the area is managed for for-
est production, A network of drainage canals and woods roads offers the
only interruption in an otherwise unbroken expanse of fuel. Fire can
travel. in a truly uninhibited fashion,
Two military bomb ranges are located in the heart of the county,
and both have a fire history because of the ordnance used, Several pre-
suppression measures are taken to insure that any fires started will be
confined to the target areas. A system of roads and canals acts as a
fuel break and gives access (fig, 29, Fuel modification involving herbi-
cides and prescribed fire and a suppression force composed of a heli-
copter and several tracked, cross-country vehicles have resulted in
direct control of 137 of the 138 fires that occurred on the Air Force
Bomb Range from 1965 through 1970. The average area burned was
0.5 acre (0.2 ha. ).3 The sole exception, prior to 1971, was a 3,600-
acre (1,460-ha. ) fire in April 1966.
FIRE DE\%LOPMENT AND CONTROL
The stage was already set for a conflagration on March 22, 19'71.
During four of the preceding five days, the dead and cured fine fuels on
the Air Force Bomb Range had been subjected to the desiccating effects
of low humidities, moderate-to-fresh winds, and full sunshine. The Air
Force Bomb Range Fire was ignited by a practice bomb dropped at 1028
2 ' in general, pocosins may be described as those areas, rnclud~ngs wsmps and bays, with
soil.: having 20 percent or more organic matter content, fair to peas internal drainage, and support-
ing stsn 3s oi povtc"pln~. Also, these arcas na-v~-a medium to heax-y density understory composed
princlpal1.v of ii:oociv shrubs and reeds. The pocosins constitute roughly 2 mrlllon acres in coastal
(3,
Xurth Carolina ' p. 3). See frgtire I for drstrihutlon of the principal areas of organic soil. in
easrern 'ZY'orth Carolrna.
3 ~ r e ~fni. ,J . Noten, ilane, and Plotkin, H. 5. illr Force BoII-,: Range Fire. 17 pp. 197 1.
(Xl;rneogr. rep. of ti:^ Roard I+\-. , 3. C. For, Serv., Dep. Conser:~. Iliev, 1
Figure 1. --Principal areas of or-
ganic soil in eastern North Car-
olina. The Air Force Bomb
Range Fire and nearby weather
stations are shown. [Soil map Figure 2. --The system of roads and
adapted from We n d e 1, Storey, canals used for access and fire con-
and Byram (-12) .] trol at the Dare County Air Force
Bomb Range. Fire origin is marked
by an "x."
e.s.t, and immediately became dominated by surface winds blowing at
20 m.p.h. (9 m./sec. ). The fire was beyond control before the standby
crew stationed on the range reached it.
The fire crowned through more than 15,000 acres (6,070 ha. ) of
pond pine during the next 20 hours and eventually burned 29,300 acres
(11 ,860 ha. ) of timber and nonforested watershed (fig. 3). The initial
14-mile (22.5-km. ) run from the Air Force Bomb Range northeast to
Croatan Sound produced a narrow, elongated shape typical of fires pushed
by high winds. Rate of spread averaged over 2 m.p.h. (0.9 m./sec. ) for
4 hours and nearly reached 5 m.p.h. (2.2 m./sec, ) during a l-hour
period. The flanks remained active throughout the night of the 22nd until
a cold front passed over the area before dawn on the 23rd. The resulting
shift in wind direction from southwest to north created two heads from
the southeast flank, one of which was pushed rapidly toward the town of
Stumpy Point.
This sequence of events is typical of blowup fires in the South.
They must be contained within a comparatively short time after ignition
or suppression efforts become ineffectual. The fire will then remain un-
controllable until either fuel o r weather conditions ameliorate, with a
resultant decrease in fire intensity. In the case of the Air Force Bomb
Range Fire, it was a change in fuel conditions that initially checked fire
spread, One head lost its momentum in a wet, marshy area about 100
Figure 3. --Photo mosaic of tho burned area. Outer solid line shows final perimeter of
fire. Inner lines show fire perimeter at various times. The fire was controlled on
. March 26, 1911, at 29,300 acres (11 ,860 ha, ).
yards (90 m,) north of Stumpy Point. The other also encountered wet
conditions and was dissipated. Some flareups occurred along the north-
west flank Tuesday and Wednesday, but, in general, the fire remained
quiet until Friday, &4arch 26, when a general rain occurred,
Even after the fire calmed dof~non Tuesday- morning, the control
force could not take full advantage of the situation. Because the water
table was near the surface, the organic soils would not support tractor-
plow units, and line building became an exceedingly difficult task,
Lightweight, full-tracked, off-road vehicles such as ~odwells' equipped
with portable pumps were used to trample down the brush along the fire
perimeter. Then water was used to extinguish the active fire edge. At
points where the vehicles did not proceed directly along the fire perirn-
eter, their path of crushed brush was used as a baseline from which
burning-out operations were initiated,
Fire development, behavior, and control, together with information
on fuel and weather conditions between March 22 and March 26, are surn-
marized in table 1.
FUELS
Pond pine, a fire-adapted species,' was the dominant overstory
tree on the burn, averaging 1,250 stems /acre (3,100/ha. ). About 64 per-
cent of the forested area was covered with well-stocked, 13-year-old
pond pine that came in after the 1957 burn (fig. 4). Another 13 percent
contained poorly or medium-stocked, 13 -year-old pond pine. The re-
mainder was comprised of reproduction from the 1966 burn and older
trees that survived the 1957 burn. In addition, 5,000 acres (2,025 ha.)
of marsh, 5,000 acres (2,025 ha. ) of low, open pocosin, and 1,200 acres
(490 ha. ) planted to species other than pond pine also burned,
The 13-year-old pond pine averaged 16 ft. (4.9 rn. ) in height and
2.9 inches (7.4 em. ) d.b.h. Its principal associates were redbay (Persea
borbonia (L. ) Spreng. ) and sweetbay (Magnolia virginima (L. )), which,
together, averaged 13 ft. (4.0 rn. ) in height, 1.6 inches (4.1 cm. ) d.b.h.,
and 220 stemslacre (5501ha. ).
Species composition of the understory was variable, Wendel et al.
(12) categorized poeosin fuels into 16 broad types on the basis of species
composition of the understory, density, height, and age of rough. At
least five of the tgppes occurred on the burn area (table 2). The weight of
fuel samples taken of types R-14, RB-10, and P-14 in the vicinity of the
-
burn compared favorably with those given by Wendel et al, (12).
'%lention of trade names throughout this Paper does not constitute endors~mentb y the !'. S.
Department of Agriculture.
"Among the f i x adaptallons of pond plne are rts ability to produce viable seed at an 6larl-y
age, rts serotrnous CORF"S, and ~ t sah l'lrty to sprout from both the root collar and the bole following
defoliation by fire.
Table 1. --Tile Atr Force Romh Range Ftre 17evclopment, hehav~ar,c ontrol, fuels, and weatlier between March 22 and 26, 1971
-- MONI>AY, MARCH 22, 1971 ----
B~irniargp errod (e.q.t. ) Ftre status and cantral actlvltlcs Fire stze, fuel, uc?tt~cr,c in(l ftrc behnvlor
-1028-1100 .
1028 Ftre ignlted in tlead bru~lra nd cured grass by practree iromb. [pire sszr 8 acres (7 ha. )
1043 Bomb range closed. -Fuels Type1 --GB-7
1047 Two cross-country vehiclcs mannetl by 5 me11 and eijuippeil wlth portable Eclght--6.2 tonsjarre (13 9 M.T./ha.)
pilnlps arrlve at f~re. Vi eather at 1100
1100 F~recr osses ('enter Roaii. %+tnd--W20, @st 30 r1i.p.h. (U9, q,ri15t I? m./sec.)
Temp. --70' F. (21' C. ), ItTI--34 percent
Ipire bchav~or
Rate of spread--0.4 n1.p.h. (0.5 krn.jhr.1
1ntrnsity3--875 I3.t,u./ft./sec. (6,0"7 cal./crn./ 3er. )
Total ~ntensity'--0.07 x lo7 ~.t.u./%c. (7.6 X lo7 enl.isec. )
-I.- -..1- 01-1226
1130-1150 Two tractor-plow unlts arrive along Center Road and attack Flanks. I'xre slre 155 acres (63 ha.)
North flanl: soon ibecomes too hot far cisrect attack. Fuels Type1 --GB-7
1215 Crew starts suppression ftre along Per~meterR oad. Atr observer Weight--6.2 tons/acre (13.3 ~.T./ha.
arrives ovrr hrc. meather at 1200
1226 F~rcer osses Perlrneter Road and beg~nsc rownmi?; through young Wind--f&SWZO, gust 70 n1.p.h. (TGS'VC9, guiust 18 rn./see. )
pond plne. Temp. --?lo f. (22" C. 1, RH--28 percent
Flre behavior
Rate of spread--0.5 rn.p.h. (0.8 krn, /hr, )
1ntenslty3--1,042 Il.t.u./ft./srr. (8,606 cal./crn./sec. )
Total intensity3--0.18 X lo7 tl.t.u./.;ec. (45.4 x 10' cal./sec. )
1227-141")
1230 Formation of an lnter~n~ttencot nvection column heglns. Fire size 2,094 acres (847 ha.
1245 Two Snow antankers arrlve and hegln dropplng retardant along Fuels Type1 --RB-10, R-14, G13-7
the north flank. Retardant appllcatlon dlseontinued because Welsht--11.6 tonslacre (25.9 hl.T.lha. )
tneffecttve, and retardant plane.; placed In a hold pattern to Weather at 1200
be used for emergency drops. Wind--SW15, gust 20 m.p.h. (STV7, gust 9 m./sec. )
1479 Suppresslan frrtng crew reports from Jackson Road that f~re Temp. --72' I". (22" C. 1, Ill%--2'7 perrent
has crossetf Road. Ftre hehamor
Rate of spread--1.8 m.p.h. (2.9 krn./hr.)
Intensity3--7,006 F.:.t.1i./ft./8ee. (57,870 cal./crn./sre. )
Total intens1ty~--2.81 x lo7 R.~.EI./sP~(7. 08 X cal./sec.)
1440-15'37
1440 F~reco ntlnut%st o crown through 13-year-old pond plna. P'lre s17e 2,975 acres (1,204 ha.)
1 500 F~recr osses wet area between Jackson and Navy Shell Roads. -I'uels Type' --F-14, RT3-10, R-14, GB-7
1577 Sufplprree hssaiso nc rfolsrlsnegd cRroeawd .r eports from Navy Shell Road that Weather Uate i1g5h0t0-- '1 0.8 tons/acrr (24.3 iVI.T./ha. )
Wind--SW15, gust 20 m.p h. 1SW7, gust Ci w./sec. )
Temp. --71' f. (22" C. ), RF-I--25 percent
Fire behavior
Rate of spread--0.8 m p.h. (1.3 km./hr.
Intensity3--2,918 R.t.u./ft. /see. (24,102 cal. /crn./see.)
Total intensity3--2.74 x lo7 B.t.u./~ec. (690 x lo7 cal./sec. )
'F'uc.1 types are lrsled in the table by descending amounts of acreage. GR-7 = grass--low brush, RR-10 - medium reedq--brush, R-14 = very high reeds, P-14 = high
porosln, P-5 = low pacos~n--open.
aOn-slte reatling.
3i[nt~nsit>1s drfined as the rate of energy release per foot of flre front. Total ~ntenslty1 s tleflned as the total energy released per second by the flue durtng a given
trme perlod.
4~ealhepra rameters estlrnated from rt*adings at nearby weather stations.
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