An Examination of the Summerhaven, Arizona Home Destruction Related to
the Local Wildland Fire Behavior during the June 2003 Aspen Fire

Jack D. Cohen

Research Physical Scientist

USDA Forest Service

Rocky Mountain Research Station

Missoula Fire Sciences Laboratory

406-329-4821 jcohen@fs.fed.us

August 1, 2003

# Summary

I examined the home destruction in Summerhaven associated with the 2003
Aspen Fire on July 31 and August 1. My examination was prompted by
questions regarding the wildfire behavior related to home destruction
and specifically whether homes could have survived the wildfire in the
Summerhaven area. **The evidence revealed by my examination indicates
that the wildfire in the Summerhaven area largely spread as a surface
fire not as a high intensity crown fire. The differences in the direct
flame and firebrand exposures related to the home characteristics
resulted in one house surviving next to its destroyed neighbor.**
Although the wildland fire largely spread on the surface, high intensity
burning occurred in several locations of high structure density. The
burn pattern suggests that high intensity fire spread occurred from
structure to tree canopy to structure.

# Examination

The Aspen Fire started on June 16, 2003 in the Santa Catalina Mountains
north of Tucson, Arizona. On June 19 the fire spread into the mountain
community of Summerhaven. Over 300 homes and cabins burned in
association with the wildfire. Photos 1 and 2 show the character of the
wildfire. Crown fire occurred in limited patches and on the slopes to
the west and above the residential area.

![](media/image1.jpeg){width="3.0076388888888888in"
height="2.2715277777777776in"}
![](media/image2.jpeg){width="3.0076388888888888in"
height="2.2715277777777776in"}

**Photos 1,2---active spreading crown fire occurred above and to the
west of Summerhaven**

**but did not spread into the residential area.**

High intensity crown fire spread did not occur in the bottom of the main
gulch where Summerhaven resides. Photo 3 shows the post burn situation
along the main road down slope and up-wind from structure locations.
Photo 4 shows surface fire spread that was typical under the conifer
canopy. Although the surface fire spread does not produce high intensity
burning, the intensities and durations produced significant canopy
needle kill.

![](media/image3.jpeg){width="3.0076388888888888in" height="2.4in"}
![](media/image4.jpeg){width="3.1354166666666665in" height="2.4in"}

**Photos 3,4---surface fire spread principally occurred within the
Summerhaven residential area**

> **without burning in the tree canopies (crown fire).**

The surface fire spread does not produce direct flame heating sufficient
to ignite the wood exteriors of structures beyond about 10-15 feet.
Photos 5-9 provide examples from various locations within Summerhaven
that represent the destruction of the entire area.

![](media/image5.jpeg){width="3.029166666666667in"
height="2.3194444444444446in"}
![](media/image6.jpeg){width="3.1145833333333335in"
height="2.3513888888888888in"}

**Photo 5,6---totally destroyed homes surrounded by unconsumed tree
canopies indicate that**

> **lower intensity surface fires burned in the structures' surrounding
> areas.**

![](media/image7.jpeg){width="3.05in" height="2.2715277777777776in"}
![](media/image8.jpeg){width="2.9652777777777777in"
height="2.2715277777777776in"}

![](media/image9.jpeg){width="3.1354166666666665in"
height="2.3513888888888888in"}

**Photos 7,8,9---totally destroyed homes surrounded by unconsumed tree
canopies indicate**

> **that lower intensity surface fires spread to the structures'
> surrounding areas.**

The evidence indicates that burning homes commonly burned the adjacent
and over-hanging trees. Tree canopy burning began at totally destroyed
structures. In several areas of higher structure density, the evidence
suggests that burning homes ignited the tree canopy that subsequently
carried into adjacent structures. As each structure ignited more canopy
ignited. The hillside burn pattern indicates that the ignited tree
crowns originated at burning home locations. Photo 10 shows the patched
pattern of destroyed homes and associated burned trees surrounded by
unconsumed tree canopy. The crown fire originates and ends in
association with home destruction. Photos 11-12 show the home
destruction and canopy consumption within such a patch. Photos 13-14
show evidence of decreasing consumption and the charring of tree trunks
and canopies as the distance away from a structure increases. Note the
mottled char pattern on the tree trunks. The mottled portion is where
all bark was consumed facing the burning house. The side away is charred
but bark remains. Without examining the large scale patterns of home
destruction associated with tree crowning and the small scale patterns
of consumption, one might get the impression that the high intensity
crown fire spread into the residential area and caused the destruction
rather than the likely sequence of a home or homes burning leading to
tree canopy fire involvement.

![](media/image10.jpeg){width="5.1194444444444445in"
height="3.8555555555555556in"}

**Photo 10---patches of burned trees that are associated with multiple
totally destroyed homes**

> **break the largely unconsumed forest canopy. The red ovals show 3
> examples of**
>
> **this burn pattern.**

![](media/image11.jpeg){width="3.1145833333333335in"
height="2.3354166666666667in"}
![](media/image12.jpeg){width="3.029166666666667in"
height="2.3354166666666667in"}

**Photos 11,12---burning homes commonly burn the trees in close
proximity. Where homes are**

> **close together, the trees burn around and between the homes
> producing areas**
>
> **of totally destroyed homes and associated burned tree canopies. Note
> the**
>
> **multiple homes present in each photo.**

![](media/image13.jpeg){width="5.098611111111111in"
height="3.839583333333333in"}

![](media/image14.jpeg){width="5.1194444444444445in"
height="3.8715277777777777in"}

**Photos 13,14---the red arrows indicate the complete bark consumption
(mottled) on the side**

**facing the burned home and char with remaining bark on the side facing
away.**

**The double ended arrow indicates the decreasing consumption and char
as the**

**distance from the burned home increases.**

That leaves the question of how one home can survive adjacent to total
home destruction. Photos 15-16 show such a situation. Fire does not
behave capriciously; it either meets the requirements for combustion or
not. If a high intensity crown fire had spread through the entire
residential area then the distances between structures would not have
made significant differences in the requirements for combustion. But
even crown fires do not have the ability to directly ignite wood at
distances greater than 100 feet. Thus, when surface fire principally
occurs, the ability to directly ignite a home must occur within a few
feet of or in contact with the flammable parts of the structure. A
structure may ignite directly from firebrands that have come from an
intense wildland fire at over ½ mile away, but these ignitions are
dependent on the materials and design of the structure. Thus,
significant differences in the requirements for combustion can occur
from one house to an adjacent house. These differences in the direct
flame and firebrand exposures related to the home characteristics result
in one house surviving next to its destroyed neighbor.

![](media/image15.jpeg){width="3.1145833333333335in" height="2.4in"}
![](media/image16.jpeg){width="3.1569444444444446in" height="2.4in"}

**Photos 15,16---homes destroyed adjacent to homes survived indicates
that significant**

**differences existed in the fire and home characteristics necessary
to**

**meet the requirements for home ignition.**