AnAn AnalysisAnalysis ofof DodgeDodge’’ss EscapeEscape FireFire onon thethe 19491949 MannMann GulchGulch FireFire inin TermsTerms ofof aa SurvivalSurvival ZoneZone forfor WildlandWildland FirefightersFirefighters Marty Alexander Department of Renewable Resources Mark Ackerman Department of Mechanical Engineering University of Alberta, Edmonton, Alberta Greg Baxter FPInnovations – Feric Division, Wildland Fire Operations Research Group, Hinton, Alberta

10th Wildland Fire Safety Summit – April 27-30, 2009 – Phoenix, AZ MannMann GulchGulch FireFire FatalitiesFatalities MannMann GulchGulch FireFire SurvivorsSurvivors

Smokejumpers Smokejumper Foreman Bob Sallee and Walt Rumsey Wag Dodge Smokejumper Pioneer Earl Cooley publishes book in 1984 and includes a chapter on Mann Gulch Fire

Earl Cooley Norman Maclean Dick Rothermel

Fire Management Today summary TheThe storystory ofof thethe MannMann GulchGulch FireFire hashas beenbeen chronicledchronicled inin aa varietyvariety ofof formsforms WebsitesWebsites onon MannMann GulchGulch FireFire Dodge’s Escape Fire: was it a spur of the moment thing? QuestionsQuestions toto bebe answeredanswered regardingregarding DodgeDodge’’ss escapeescape firefire asas aa survivalsurvival zone:zone: How big an area did the escape fire burn out? How tall were the flames of the main advancing fire front?

from Useem (1998) GeneralGeneral ApproachApproach toto thethe ProblemProblem Primary & Secondary Sources Photographic evidence

Fire Behavior Science Review and Consultation

Dave Turner: Helena NF Historian Q1:Q1: HowHow bigbig anan areaarea diddid thethe escapeescape firefire burnburn out?out? TheThe FireFire Environment:Environment: Plentiful supply of critically dry, fully-cured grass fuels on a 76% slope Immediately downwind of the main advancing fire front, there would have been a zone of still, smoke-free air in which the ambient wind would be blocked by the fire and its convection column TheThe ““PowerPower ofof thethe SlopeSlope”” WalterWalter RumseyRumsey’’ss EstimateEstimate ofof FireFire SizeSize

In February 1961 he prepared a written statement on the Mann Gulch Fire.

Rumsey indicated that Dodge lit his escape fire “with his cigarette 1949 lighter quickly burning out an area several hundred feet long”.

Article entitled “Walter Rumsey’s Statement Twelve Years After Mann Gulch” published posthumously in the Smokejumper magazine in 2006.

1980 Starr Jenkins was a Missoula smokejumper in 1949.

Published book on his experiences in 1995, including two chapters related to the Mann Gulch Fire.

Indicates that Dodge’s escape fire burned “a half acre in 30 seconds”.

Primary sources were Cooley (1984) and “recollections of what survivors Walt Rumsey and Bob Sallee said around camp”. Starr Jenkins Butler and Cohen (1998): “Rothermel (1993) indicates that the escape fire burned around 90 m [~295 ft] ... Assuming an elliptical shape ... with its width approximately half the length ... the escape fire would have been about 45 m wide [~148 ft].”

This equates to an area of about 0.8 acre. RothermelRothermel (1993)(1993) onon DodgeDodge’’ss escapeescape fire:fire:

“... The main fire was only 50 yds away when he stopped to light the escape fire.

The main fire would cover 50 yds in 15 to 30 s if it were spreading from 360- 610 ft/min ...” 19521952 topographictopographic mapmap ofof thethe MannMann GulchGulch FireFire

* On a 76% slope this equates to a horizontal or slant distance of 79 feet.

*Maclean (1992) noted that the points where “Dodge set escape fire” and “Dodge survived here” are separated by three 20-ft contour intervals (i.e, 60 ft). WagWag DodgeDodge’’ss BoardBoard ofof ReviewReview TestimonyTestimony

Wag Dodge

“After setting a clump of bunch grass on fire, I made an attempt to start another one, but the match had gone out and upon looking up, I had an area of 100 feet square that ablaze*. I told the man nearest to me that we would wait a few seconds to give it a chance to burn out inside, and then we would cross through the flames into the burned area ...”.

* Dodge technically meant to say “100 feet squared (i.e., 10 x 10 ft). BoardBoard ofof ReviewReview Report:Report: AfterAfter lightinglighting thethe escapeescape firefire

“Dodge then walked around to the north [upslope] side of the fire he had started as an avenue of escape. He called to the men to go into the burned area, but was unsuccessful in getting them to do so. He then walked through the flames into the burned area for about 30 feet, lay down, and continued to call the men to join him. (The identical spot Foreman Dodge occupied has been definitely located and marked. As this time, the main fire was very close to the spot Dodge has fire to provide a retreat area ...”

Forward spread distance: 79 + 30 = 109 ft ForwardForward SpreadSpread DistanceDistance basedbased DodgeDodge’’ss observationsobservations andand presumedpresumed elapsedelapsed timetime ofof 3030 secondsseconds 10 ft in say 2-3 or 2.5 seconds (estimate of time span between lighting the first and second matches).

Forward Spread Distance = 4 ft/sec x 30 sec = 120 ft

Good agreement with previous estimate of 109 ft.

On the basis of these calculations, Dodge would have entered his escape fire with about 3 seconds left before the area burned by his escape fire was overrun by the main advancing fire front.

This time could be off by a couple of seconds but probably not much more. LengthLength--toto--BreadthBreadth (L/B)(L/B) RatioRatio ofof EscapeEscape FireFire

Based on Canadian and Australian research, a 76% slope is deemed to be the equivalent to a wind speed of ~44 mph and a L/B ratio of 8:1 in grass fuels. LengthLength--toto--BreadthBreadth (L/B)(L/B) RatioRatio vs.vs. ElapsedElapsed TimeTime SinceSince IgnitionIgnition

L/B = 1.4 @ 30 seconds

120 ft divided by 1.4 = 86 feet wide at its maximum point EstimatesEstimates ofof DodgeDodge’’ss EscapeEscape Fire:Fire:

120 ft long x 86 wide at maximum breadth = 0.2 acre

Assuming a flame front residence time (flame depth/rate of fire spread) of 5-15 seconds, the soonest any burned area would have begun to appear, would have been after the fire had advanced about 20 ft (i.e., after 5 seconds or so). Q2:Q2: HowHow talltall werewere thethe flamesflames ofof thethe mainmain advancingadvancing firefire front?front? CalculationsCalculations ofof FlameFlame FrontFront DimensionsDimensions

Flame front residence time: 5-15 seconds for grass Rate of fire spread: 360360 ft/minft/min oror 66 ft/secft/sec Available fuel load: 1.56 tons/acre or 0.072 lb/ft2 Mid-flame wind speeds: 15-20 mph

Flame depth = 5 sec x 6 ft/sec = 30 ft to 15 sec x 6 ft/sec = 90 ft

Byram’s (1959) Fireline Intensity = Fuel Heat Content (7444 Btu/lb) x 0.072 lb/ft2 x 6 ft/sec = 3333 Btu/sec-ft Equivalent to a Flame Length of 19 ft

Nelson & Adkins (1986) Flame Height vs. Flame Length and Mid-flame Wind Speed model prediction: 12.5 ft Maclean (1992): Flames “would have been thirty feet tall”.

Butler & Cohen (1998): “Flames were 10 m [33 ft] high (Rothermel 1993)”.

Rothermel (1993): Flames would have “ranged from 10 to 40 ft long”

Rothermel & Brown (2000): “flame lengths might have reached 40 feet” Flames 30-40 feet tall seems implausible given the visual evidence seen in the immediate post-fire photography.

Cohen (1983): “Dodge started a fire here that saved his life. Photo from Jack Nash collection.” Other photos from NWCG website convey same impression Wag Dodge, Walter Rumsey & Bob Sallee: No mention of flame heights of main advancing fire front in their Board of Review Testimony or in other documents

Jenkins (1995): “The wall of flame is solid and higher than a man’s head”

“.... an eight-foot wall of flame” Cheney and Sullivan (2008) Empirical Relationship for Predicting Flame Height from Rate of Forward Spread in Grasslands

Rate of Forward Spread of 360 ft/min or 6.5 km/h = ~3 m or 10 ft Flame Height

Butler and Cohen (1998) 4X Flame Height Safety Zone Guideline SimulationSimulation ofof thethe thermalthermal environmentenvironment inin DodgeDodge’’ss escapeescape firefire

• Lying prone on the

Path of Flame Center ground Elliptical Clearing • Flame depth – 30 ft Xc,Yc • Flame height – 10 ft

Xf,Yf Flame Width 300 ft

Planar Flame Front • Flame front Flame Angle residence time – 10 sec

Flame Depth 30 ft Critical Radiant Heat Flux for a Flame Front Residence Time of 10 seconds is 30 kW/m2 for a clothed firefighter

90

80

70 Proban T = 466.7Q-1.1374 60 Endura Nomex III 50 PK 40

Degree Burn, seconds Burn, Degree 30 nd

20

10 Time to 2 to Time 0 0 5 10 15 20 25 30 Heat Flux (kW/m2) Maximum Heat Flux During Flame Front Passage

kW/m2 Maximum Heat Flux During Flame Front Passage

kW/m2 Maximum Heat Flux During Flame Front Passage

kW/m2 Maximum Heat Flux During Flame Front Passage

kW/m2 EPILOGUE:EPILOGUE: DidDid DodgeDodge reallyreally getget liftedlifted offoff thethe ground?ground?

“Dodge later told Earl Cooley that, when the fire went over him, he was lifted off the ground two or three times” (Maclean 1992).

“Dodge said fierce winds lifted him off the ground three times during the few minutes it took the fire to pass over him ...” (Rothermel 1993).

“Wag suddenly felt buoyant, as if he were in a big vacuum, and the extreme gusts of hot air lifted him from the ground three separate times” (Matthews 2007). TheThe CounterCounter ViewView

“There were extreme gusts of hot air that almost lifted me from the ground as the fire passed over me” – Wag Dodge (statement in Cooley 1984).

“Three violent gusts of superheated air nearly lifted him from the ground” – The Missoulian newspaper, 14 August 1949 (cited in Lillquist 2006).

It’s estimated that winds >87 mph would have been required to physically lift Dodge off the ground.

While this is certainly within the range of entrainment winds observed on fires involving large quantities of fuel, such winds have not been measured on grass fires. InIn SummarySummary

 It’s estimated that the Dodge’s escape fire burned out an area of about 0.2 acre in size (i.e., ~120 feet in length and 86 feet in breadth) before being overrun.

 It’s estimated that the flames of the main advancing fire front were around 10 feet high or tall when they met the escape fire.

 It’s concluded that Dodge’s escape fire was large enough to safely accommodate all 16 firefighters (i.e., the 15 smokejumpers and one fire guard) lying down.

 It seems highly unlikely that Dodge was physically lifted off the ground as the main fire passed around his escape fire.