Built to Burn - Design with the Desert: Conservation and Sustainable Development - page 216

are, after all, a reconstituted forest and burn according to similar principles. This collision
can occur in chaparral, desert, and grassland, but granted the availability of land and the
relative attractiveness of second- or retirement-home sites, it happens mostly in montane
forests, particularly those dominated by ponderosa pine ( Pinus ponderosa ).
11.4 Wildfire Management
This is a dumb problem to have because technical solutions exist. They begin with the
house itself. Banning wood-shingle roofs, attention to simple yard maintenance around
structures, installing hydrants, the application of some basic codes for construction and
zoning—such measures would eliminate the worst of the situation. The resulting land-
scape would be less that of a cabin in the woods than of woods in fragmented city. Such
places require the techniques—modified, adapted—of urban fire protection.*
A similar logic applies also to the flame-threatened fringe of communities, where an
evolving compromise is pointing to thinning-driven fuelbreaks as a means of protection. Is
this sensible? It is, if it addresses the particulars of how a house actually burns. Conduction
burns structures when flame makes contact. Clearing away the space immediately around
a house will break the continuity that allows this transfer. Radiation kindles by immersing
combustible material in heat. The distance needed to shield a structure depends on how
intense the source flame is and how readily the object ignites. (The intensity varies with
the square of the distance, such that small changes can yield big differences, which is why
it is so hard to find the right seating distance around a campfire.) Crown fire experiments
in Canada recommend 100-200 ft as a minimum distance, which is probably a maximum
anywhere. This refers to a tree-enveloping sheet of flame blasting its heat against a wooden
structure. Radiant heat from smaller caches of fuel will shrink the zone of danger. Planting
weakly flammable vegetation, and eliminating flaky decoration or needle-drenched roofs
will expand the zone of safety. Similarly, the proximity of structures one to another mat-
ters. As lots fill up with big houses, detached garages, and assorted sheds, one structure
can radiate against its too-proximate others, spreading the fire directly from one erected
lumber pile to another. 7
The greater problem is convection, and more broadly, wind, because it carries sparks.
Over short stretches, ember showers can saturate a site with new starts. But firebrands can
also travel long distances, which argues for protection not only at the house but over broad
areas, and they blow about well after the flaming front has passed, which means someone
has to be there to swat them out. Studies in both the United States and Australia have
shown that many houses have burned not in the thermal wave of a fire tsunami, but later,
from small flames that crept to a flammable deck or porch or from windblown sparks that
found tiny points of tinder. Had someone been on the scene they could have stopped them
with a squirt gun and a whisk broom.
All parties agree that house protection begins with the house itself. A wooden roof is
lethal (this particular threat has been known for more than 10,000 years). Other features
like eaves can either cache or discourage combustibles and sparks. The arrangement of
houses matters, the fire flaming from one to another, or from roof to roof without resort
of ground vegetation, leading to the curious spectacle of burned houses amid green
* http://www.firewise.org (accessed July 15, 2009).