An Analysis of Dodge's Escape Fire on the 1949 Mann Gulch Fire in ...

<strong>An</strong> <strong>An</strong>alysis <strong>of</strong>
Dodge’s s <strong>Escape</strong> <strong>Fire</strong> on the
1949 Mann Gulch <strong>Fire</strong>
in Terms <strong>of</strong> a Survival Zone for
Wildland <strong>Fire</strong>fighters
Marty Alexander
Department <strong>of</strong> Renewable Resources
Mark Ackerman
Department <strong>of</strong> Mechanical Engineering
University <strong>of</strong> Alberta, Edmonton, Alberta
Greg Baxter
FPInnovations – Feric Division,
Wildland <strong>Fire</strong> Operations Research Group, Hinton, Alberta
10th Wildland <strong>Fire</strong> Safety Summit – April 27-30, 2009 – Phoenix, AZ

Mann Gulch <strong>Fire</strong> Fatalities

Mann Gulch <strong>Fire</strong> Survivors
Smokejumpers
Bob Sallee and Walt Rumsey
Smokejumper Foreman
Wag Dodge

Smokejumper Pioneer
Earl Cooley publishes
book in 1984 and
includes a chapter on
Mann Gulch <strong>Fire</strong>
Earl Cooley

Norman Maclean

Dick Rothermel
<strong>Fire</strong> Management Today summary

The story <strong>of</strong> the Mann
Gulch <strong>Fire</strong> has been
chronicled in a variety
<strong>of</strong> forms

Websites on Mann Gulch <strong>Fire</strong>

Dodge’s s <strong>Escape</strong> <strong>Fire</strong>: was it a spur <strong>of</strong> the moment thing

Questions to be answered regarding
Dodge’s s escape fire as a survival zone:
How big an area did the escape fire burn out
How tall were the flames <strong>of</strong> the main advancing fire front
from Useem (1998)

General Approach to the Problem
Primary & Secondary Sources
Photographic evidence
<strong>Fire</strong> Behavior Science
Review and Consultation
Dave Turner: Helena NF Historian

Q1: How big an area did the escape
fire burn out

The <strong>Fire</strong> Environment:
Plentiful supply <strong>of</strong> critically dry,
fully-cured grass fuels on a 76% slope

Immediately downwind <strong>of</strong> the main advancing fire front,
there would have been a zone <strong>of</strong> still, smoke-free air in
which the ambient wind would be blocked by the fire
and its convection column

The “Power <strong>of</strong> the Slope”

Walter Rumsey’s s Estimate <strong>of</strong> <strong>Fire</strong> Size
In February 1961 he prepared a
written statement on the Mann
Gulch <strong>Fire</strong>.
1949
Rumsey indicated that Dodge lit
his escape fire “with his cigarette
lighter quickly burning out an
area several hundred feet long”.
1980
Article entitled “Walter Rumsey’s
Statement Twelve Years After
Mann Gulch” published
posthumously in the
Smokejumper magazine in 2006.

Starr Jenkins was a Missoula
smokejumper in 1949.
Published book on his
experiences in 1995, including
two chapters related to the
Mann Gulch <strong>Fire</strong>.
Indicates that Dodge’s s escape
fire burned “a a half acre in 30
seconds”.
Starr Jenkins
Primary sources were Cooley
(1984) and “recollections <strong>of</strong>
what survivors Walt Rumsey
and Bob Sallee said around
camp”.

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 <strong>of</strong> about 0.8
acre.

Rothermel
(1993) on
Dodge’s s escape
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 ...”

1952 topographic map <strong>of</strong> the Mann Gulch <strong>Fire</strong>
*
On a 76%
slope this
equates
to a
horizontal
or slant
distance
<strong>of</strong> 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).

Wag Dodge’s s Board <strong>of</strong> Review Testimony
Wag Dodge
“After setting a clump <strong>of</strong> 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 <strong>of</strong> 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).

Board <strong>of</strong> Review Report:
After lighting the escape fire
“Dodge then walked around to the north [upslope] side <strong>of</strong>
the fire he had started as an avenue <strong>of</strong> 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

Forward Spread Distance based
Dodge’s s observations and presumed
elapsed time <strong>of</strong> 30 seconds
10 ft in say 2-32
3 or 2.5 seconds (estimate <strong>of</strong> 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 <strong>of</strong> 109 ft.
On the basis <strong>of</strong> 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 <strong>of</strong>f by a couple <strong>of</strong> seconds but
probably not much more.

Length-to
to-Breadth (L/B) Ratio <strong>of</strong> <strong>Escape</strong> <strong>Fire</strong>
Based on Canadian and Australian
research, a 76% slope is deemed to be
the equivalent to a wind speed <strong>of</strong> ~44
mph and a L/B ratio <strong>of</strong> 8:1 in grass fuels.

Length-to
to-Breadth (L/B) Ratio vs.
Elapsed Time Since Ignition
L/B = 1.4
@ 30
seconds
120 ft divided by 1.4 = 86 feet wide at its maximum point

Estimates <strong>of</strong> Dodge’s s <strong>Escape</strong> <strong>Fire</strong>:
120 ft long x 86 wide at maximum breadth = 0.2 acre
Assuming a flame front residence time (flame
depth/rate <strong>of</strong> fire spread) <strong>of</strong> 5-155
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: How tall were the flames <strong>of</strong> the
main advancing fire front

Calculations <strong>of</strong> Flame Front Dimensions
Flame front residence time: 5-155
seconds for grass
Rate <strong>of</strong> fire spread: 360 ft/min or 6 ft/sec
Available fuel load: 1.56 tons/acre or 0.072 lb/ft 2
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 s (1959) <strong>Fire</strong>line 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 <strong>of</strong> 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 <strong>of</strong> flame heights <strong>of</strong> main advancing fire front
in their Board <strong>of</strong> Review Testimony or in other documents
Jenkins (1995):
“The wall <strong>of</strong> flame is solid and higher than a man’s s head”
“.... an eight-foot wall <strong>of</strong> flame”

Cheney and Sullivan (2008)
Empirical Relationship for Predicting Flame Height
from Rate <strong>of</strong> Forward Spread in Grasslands
Rate <strong>of</strong> Forward Spread <strong>of</strong> 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

Simulation <strong>of</strong> the thermal environment in
Dodge’s s escape fire
Path <strong>of</strong> Flame Center
Elliptical Clearing
Xc,Yc
• Lying prone on the
ground
• Flame depth – 30 ft
• Flame height – 10 ft
Planar Flame Front
Xf,Yf
Flame Width 300 ft
Flame <strong>An</strong>gle
• Flame front
residence time –
10 sec
Flame Depth 30 ft

Critical Radiant Heat Flux for a
Flame Front Residence Time <strong>of</strong> 10 seconds
is 30 kW/m 2 for a clothed firefighter
90
Time to 2 nd Degree Burn, seconds
80
70
60
50
40
30
20
10
T = 466.7Q -1.1374
Proban
Endura
Nomex III
PK
0
0 5 10 15 20 25 30
Heat Flux (kW/m 2 )

Maximum Heat Flux During Flame Front Passage
kW/m 2

Maximum Heat Flux During Flame Front Passage
kW/m 2

Maximum Heat Flux During Flame Front Passage
kW/m 2

Maximum Heat Flux During Flame Front Passage
kW/m 2

EPILOGUE:
Did Dodge really get lifted <strong>of</strong>f the ground
“Dodge later told Earl Cooley that, when the fire went over
him, he was lifted <strong>of</strong>f the ground two or three times”
(Maclean 1992).
“Dodge said fierce winds lifted him <strong>of</strong>f 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 <strong>of</strong> hot air lifted him from the ground
three separate times” (Matthews 2007).

The Counter View
“There were extreme gusts <strong>of</strong> hot air that almost
lifted me from the ground as the fire passed over me”
– Wag Dodge (statement in Cooley 1984).
“Three violent gusts <strong>of</strong> superheated air nearly lifted
him from the ground” – The Missoulian newspaper,
14 August 1949 (cited in Lillquist 2006).
It’s s estimated that winds >87 mph would have been
required to physically lift Dodge <strong>of</strong>f the ground.
While this is certainly within the range <strong>of</strong> entrainment
winds observed on fires involving large quantities <strong>of</strong>
fuel, such winds have not been measured on grass
fires.

In Summary
It’s s estimated that the Dodge’s s escape fire burned
out an area <strong>of</strong> about 0.2 acre in size (i.e., ~120 feet in
length and 86 feet in breadth) before being overrun.
It’s s estimated that the flames <strong>of</strong> the main advancing
fire front were around 10 feet high or tall when they
met the escape fire.
It’s s concluded that Dodge’s 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 <strong>of</strong>f the ground as the main fire passed around
his escape fire.