Residential Developments
Because of the congestion and pollution of major metropolitan areas, subdivisions, individual homes, and
mobile home parks continue to proliferate year after
year. Many are in or close to wildland fuels, subjecting
them to the danger of being burned (Harvey 1974; Hulbert 1972; Orange County Bd. Sup. 1976; Oreg. St.
Dep. For. 1978a). This development has usually proceeded faster than has the enactment of effective laws
and ordinances to alleviate the problem. Because of
financial, social and political pressures, even those efforts previously made to require firesafe construction
and occupancy have been only partially enforced, and,
therefore largely ineffective (Hulburt 1972).
Within commuting distance (40 to 60 miles) of metropolitan areas, development most often takes the form
of relatively expensive residences on medium-to-large
lots. Unless prohibited by well designed and effectively
enforced ordinances, developers tend to leave as much
native vegetation as possible to maintain and promote
the rural effect that the buyers seek. Similarly, developers usually provide wood shingle or shake roofs, picture windows, and sun decks. Water and other utilities
are usually provided only in amounts adequate for normal use unless fire codes are strictly enforced. Because
of high land values, road rights-of-way tend to be narrow and, if in mountainous areas, steep. In such circumstances, residents often have only one route of ingress
and egress (Orange County Bd. Sup. 1976; Los Angeles
County 1973).
In addition to suburban subdivisions, hundreds of
thousands of residences and their outbuildings have
been built in the past few years beyond practical commuting range from cities. Such buildings can be found in
any of several arrangements. One is the rural subdivision composed of second (weekend or vacation) and/or
retirement homes. Except for location and the inclusion
of some recreation and light commercial development,
these subdivisions appear similar and present fire problems similar to those posed by suburban subdivisions.
Although fewer than those in subdivisions, the structures that individually cause the greatest fire protection
problems are ones built by or for their occupants on
individual parcels of land, each usually with its own
water system. The most dangerous of these problems
result from so-called lot splitting. Lot splits tend to
create densities approaching those of subdivisions
without any of the inherent advantages of subdivisions
(e.g., access to a public thoroughfare, water system,
refuse disposal, sewage system). All individually developed residences, whether on large farms or small parcels of land, are difficult to protect from fire. Their
water supply is seldom adequate. Access is usually
long, narrow, and slow. Electric power, if available, is
subject to interruption, often by the fire itself.
A relatively new structural fire problem is the mobile
home, which presents all the fire problems of the conventional home and several more. Because the structure
itself is more susceptible to flash fire, occupants find it
more difficult to escape. If the structure is not fitted
with adequate skirting, wildfire will run quickly under
the floor. A mobile home is easier than a conventional
house to set up with little or no clearing of native vegetation. And when it is placed in a mobile home park, the
spacing between structures normally is insufficient to
prevent a fire from spreading by radiation or convection
(Los Angeles County Fire Dep. 1970; Org. St. Dep.
For. 1978a).
Fire Hazards and Risks
Fire hazards are those elements in the combustion
process that actually burn or that cause the fire to burn
faster or hotter than normal. Fire risks are those factors
that cause fires to be ignited. To protect residences and
other structures from damage by wildland fire, both fire
hazards and fire risks must be understood and dealt
with. Fire hazards fall into three broad categories: fuels,
weather, and topography. Fuels, in turn, are composed
of two types: vegetation and structures.
Composed of cellulosic materials, all vegetation is
flammable to some degree. Some types (e.g., chaparral)
are much more flammable than others (e.g., irrigated
landscaping plants). All vegetation is more flammable at
certain times than at others. Vegetation in its wild state
consists of both living and dead materials. The dead
materials and the fine living materials (leaves or needles
and twigs) represent the bulk of the "available" wildland fuel.
Figure 2 shows how fuels increase with time.
In timber stands and heavy brush fields, this available
fuel may reach 50 tons per acre. In areas of 1- to
2-year-old logging slash, fuel loading may run up to 200
tons per acre. When hundreds or thousands of acres of
such volumes of fuel are burned in short periods of
time-as often happens under conflagration
conditions-the amount of heat and energy released
approaches that of an atomic bomb. Flame lengths can
exceed 100 feet. Radiated heat can ignite exposed
flammable materials at distances of 100 or more feet.
Convection columns carrying flaming leaves and other
fire brands often extend many thousands of feet into the
atmosphere and have been known to drop such firebrands several miles downwind. Thousands of homes
can be exposed to these conditions (Task Force on
California's Wildland Fire Probl. 1972, Helm-and
others 1973, Nerd and Countryman 1972).
Of particular concern is the wildland fuel known as
chaparral, because so much of it is in or near metropolitan areas. Chaparral also represents an unusually
dangerous fire hazard because of its inherent qualities.
As a "fire climax plant community, ' chaparral has for
thousands of years not only survived repeated fires but
has adapted itself to depend on fire for regeneration and
survival. Thus wherever chaparral exists large-scale fire
can be predicted with great certainty to occur sooner or
later, and the longer between fires the larger they are
(fig. 3).
In southern California, the average time between fires in any given area (cycle time) is about 30
years (Hanes 1974, Nerd and Countryman 1972, Philpot 1974, Wright 1972).
Structures built in wildlands can also be hazardous
fuel. They are mostly of wood frame construction, often
with wood siding. Wood shingle or shake roofs are
common, particularly in suburban and rural subdivisions. Attic and floor vents are often left unscreened.
Picture windows and stilt or cantilever balconies facing
directly into or over heavy wildland fuels are common.
Many roofs and rain gutters hold large quantities of dry
leaves or needles. Dooryards often are not kept clear of
flammable vegetation. Any or all of these qualities contribute to make these structures one of the most hazardous fuels in the urban, suburban, rural or wildland setting (Alger 1971, Task Force on California's Wildland
Fire Probl. 1972).
Weather, or more specifically "fire weather," can
properly be termed a fire hazard because it aids ignition
and accelerates combustion. Almost all conflagrations
have occurred during periods of extreme fire weather.
We can do little about the weather except to understand
it and its interactions with the other hazards. Yet
weather is at least as important as fuels in the urban/
wildland interface fire problem.
The weather elements responsible for very high or
extreme fire danger are strong winds, high temperatures, low humidities, and low fuel moisture contents.
This combination can happen, and has, at almost any
time of the year, including the middle of winter. In areas
with Mediterranean climates, such as most of California, extreme fire weather is actually quite common during late summer and fall, and should be expected to be
present one or more times at any point in the State
during the period from mid-June to mid-November
(Alger 1971, Task Force on California's Wildland Fire
Probl. 1972, Deeming and others 1977, Phillips 1971).
By far the most critical factor in fire weather is wind.
A study of fires 5000 acres or larger during the period
1961-70 revealed that at the time of start of 66 fires for
which weather records were available, the average wind
speed was about 30 mph; in some it went as high as 75
mph (Los Angeles County Fire Dep. 1970, Task Force
on California's Wildland Fire Probl. 1972).
The most dangerous wind is the foehn (subsidence)
wind, the most notorious being the Santa Ana of southern California
(table 1).
In other parts of the world this
wind is known by other local names, such as mono,
north wind, mistral, chinook, tramontana, and williwa.
The foehn wind produces the usual effects of winds:
fanning and supplying oxygen, preheating fuels by bending flames from the vertical, and carrying burning firebrands ahead of the fire front. But it also brings dry air
from continental high pressure areas, then heats and
dries it further by compression as it flows to lower elevations at a velocity of up to 100 mph (Alger 1971,
Orange County Bd. Sup. 1976, Task Force on California's Wildland Fire Probl. 1972, Phillips 1971).
High temperatures bring the fuels, both vegetative
and structural, closer to their ignition temperatures.
Low humidities dry the moisture from the fuels. Low
fuel moistures, by reducing the amount of heat used in
vaporizing moisture, reduce the total amount of heat
needed to raise the fuel to ignition temperature. Even
green fuels, particularly chaparral, can have remarkably
low moisture contents after long dry summers or under
adverse fire weather conditions (Deeming and others
1977, Hanes 1974, Nerd and Countryman 1972, Philpot
1974, Wright 1972).
The third major hazard contributing to wildland and
structural fire danger is mountainous topography. Although it increases the costs of construction and development, such topography attracts thousands of
homeowners with its feeling of openness, an attractive
view, and the possibility of getting above or away from
the smog. Sidehill construction often makes structures
more ignitable (e. g., stilts, cantilevers). Topography affects fires in some of the same ways that wind does as
well as modifying, and often intensifying, the effects of
the wind. Generally fires run faster uphill than down.
Higher elevation fuels (e.g., houses on ridgetops) are
preheated by flames and convection columns even in
the absence of wind. Canyons act as chimneys trapping
heat and intensifying combustion. Canyons, saddles
and ridgelines deflect, and often intensify, winds. Thus
the mouths of canyons on the lee side of main ridges
often become raging infernos during a Santa Ana.
Roadbuilding is difficult and expensive in mountainous
terrain, often making ingress for firefighting manpower
and equipment and egress for residents slow and difficult.
1
The fire risks involved in the structural/wildland fire
problem are almost all man-caused. In the populated
portions of California, 90 percent or more of the fires
involving vegetation are caused either by people directly or by their developments (e.g., arson, various
types of machines, power lines); only 4.2 percent of the
conflagration fires are caused by lightning. The mere
acts of developing, constructing and occupying structures in formerly wildland areas, therefore, expose both
the wildlands and the structures to increased risk of
destruction by fire (Alger 1971, Task Force on California's Wildland Fire Probl. 1972, Moore 1977).
The risk of structural ignition during wildland fires
comes from any of three sources: direct exposure to
flame, radiated heat, or firebrands carried by winds or
convection columns or both. The first two of these
sources can be fairly easily guarded against by proper
clearance of native vegetation, landscaping, and maintenance. The last (most common) is much more complex and requires a combination of defenses, including
all those described in the chapters on Land-Use Planning and Zoning; Property Development; Structural
Design and Construction; Maintenance; and Undeveloped Areas. The most usual structural fuel bed for
ignition by these flying firebrands, which are often carried from one-quarter mile to 2 miles ahead of the fire
front, is the roof. Therefore, roofing materials and
cleanliness are of prime importance as protective measures (Alger 1971, Los Angeles County Fire Dep. 1970,
Orange County Bd. Sup. 1976, Task Force on California's Wildland Fire Probl. 1972, Helm and others 1973).
Fire Suppression Difficulty, Costs, and Limitations
The owners of structures in or near wildland fuels
cannot depend on the fire suppression efforts of public
agencies to protect their buildings from destruction.
The use of tax funds to pay for enough firefighters and
equipment to contain every fire that starts on the few
days of very high and extreme fire weather conditions is
both economically and politically infeasible. It is, in
fact, also physically impossible under typical conflagration conditions of very strong, hot, dry winds. Therefore, each owner or resident must assume his or her
share of the responsibility for preventive measures
(Alger 1971, Los Angeles City-County Fire Bd. Inquiry
1971, Green 1977, Howard and others 1973).
Firefighting is at best one of the most hazardous activities of man. Under conflagration conditions, the
risks of entrapment, asphyxiation, heat exhaustion, falling, and other injuries become so great that chief officers and other leaders will usually not allow their men to
be at the head of the fire. Also under these conditions
smoke and air turbulence often preclude the use of air
tankers or helicopters. The only effective perimeter
control, therefore, is on the flanks of the fire until it
reaches some barrier or the weather changes (Los
Angeles County Fire Dep. 1970, Los Angeles CityCounty Fire Bd. Inquiry 1971, Howard and other 1973).
The strategy of wildland fire control requires perimeter control, containment of spread, and eventual extinguishment. Due to the scarcity of water, the tactics of
wildland fire control usually consist of constructing fire
lines, either by hand or with machines, burning out prepared or preexisting control lines, cooling limited areas
by air drops of fire retardants, and similar measures.
Such work cannot be carried out safely or effectively on
steep hillsides or in close proximity to a high intensity
fire in heavy fuels. It must usually be done at some
natural or artificial barrier, e.g., a ridgetop or interstate
freeway. If the wind is very strong, even these barriers
often will not hold because of spot fires caused by flying
firebrands (Alger 1971, Los Angeles County Fire Dep.
1970, Los Angeles City-County Bd. Inquiry 1971,
Howard and others 1973). Consequently wildland fire
control is basically incompatible with the aim of protecting structures.
Most wildland fire protection agencies consider their
primary statutory mission to be resource protection,
and have budgeted accordingly. In spite of this limitation, wildland firefighters normally react to human
moral values when faced with a choice of either saving
life or improved property, or saving several hundred
acres of brush or timber. Therefore, even though their
equipment and training are often poorly designed for
structural firefighting and adequate water is usually
lacking, firefighters tend to let the fire spread while they
do the best they can to save lives and structures (Alger
1971, Los Angeles County Fire Dep. 1970, Oreg. St.
Dep. For. 1978b).
Mountainous terrain complicates fire suppression in
several ways. The combined effects often make it impossible to save houses from burning during major wildland conflagrations, and, as discussed earlier, steep
slopes, canyons and ridges complicate and intensify the
effects of wind. Even in the absence of wind, fires race
much faster up a steep slope than they do on the level. It
is difficult, slow and dangerous to fight fire on steep,
rocky side hills. The combined effects of terrain and
wind often create smoke and air turbulence conditions
which preclude the use of aircraft. Mountain roads
make access and response time slow and difficult for
firefighters and for heavy fire trucks and other equipment. Sometimes access becomes impossible when
roads are blocked by debris, other vehicles, or the fire
itself or if construction of the roads themselves has
made them too steep or with curves too tight to be
traversed by fire engines or bulldozer transports (Alger
1971, Los Angeles County Fire Dep. 1970, Green 1977,
Howard and others 1973).
The control of major wildland fires, usually involving
structures, is further complicated by the communication
and coordination problems inherent when the fire is
being fought by multiple agencies, which is usual for
two reasons. First, wildland fires do not respect political, jurisdictional, administrative, or ownership boundaries. A fire of any appreciable size will usually spread
from the protection jurisdiction of one agency to those
of several other agencies. Secondly, no single agency,
even the largest, has the resources to handle a major
conflagration alone. Aid from other agencies, often
from considerable distance, must be called in. As a result, differences in training, equipment, and radio channels regularly exist. The effects of these differences are
usually minimized before a fire through joint planning
and coordination between adjoining agencies. But if
agencies are responding from a distance in emergency
situations, coordination of the efforts can be a serious
problem (Alger 1971, Los Angeles County Fire Dep.
1970, Los Angeles City-County Fire Bd. Inquiry 1971,
Oreg. St. Dep. For. 1978b, Lowden and Degenkolb
1972).
The fire protection available to structures in
mountainous areas in or near rural or wildland fuels is
often 1imited in certain other ways not usual for similar
structures located in cities. Federal and State wildland fire
protection agencies are funded only during the wildland fire season.
At other times of the year, manpower
is sharply reduced, outlying stations are closed, and
24-hour service is terminated. In some areas, a local
agency (county or fire district) can make up this deficiency by entering into a contract with the State for
firefighting services. Other areas receive structural protection from low-budget volunteer fire departments
funded by counties, fire districts, or informal donations
from private citizens. Their equipment may be old,
training inadequate, and response time excessive. Even
when professionally manned and well equipped, county
or district fire departments generally have longer response times than do city departments and water is not
as easily available. Thus the fire protection for structures in rural and wildland areas is at a somewhat lower
standard (Alger 1971, Oreg. St. Dep. For. 1978 b).
That hillside soil bared to the elements by fire is susceptible to accelerated erosion is rather self-evident and
has been noted by many researchers and fire officials.
What is not so widely known is that many soil types are
made hydrophobic (water-repellent) by fire. The overland flow of water during rainstorms is increased by 10
to 40 times the normal (unburned) amount because of
this phenomenon. This tremendously accelerated runoff
not only creates high flood waters, but provides the
force needed to move soil, gravel, and boulders
downslope and downstream and to transport
deposits accumulated largely by dry erosion between
fires (Houts 1974, Rice 1974, Zivnuska 1974.)
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