Probably the best approach to fire hazard classification or zoning from the standpoints of both technically
correct theory and practical application by local planning department staffs is that developed in 1973 by the
California Department of Forestry. It rates fire hazard
based on three weighted values each of fuels, weather,
and topography (table 2).
In light of more recent information (Deeming and others 1977) the limits and factor
weights may be revised, and whether a "low" or "base
level" fire hazard classification should be recognized at
the lowest levels of all factors in the table should be
explored. Still the factors used and the approach to
combining and analyzing them are sound. Technically it
might be more correct to use up to 20 fuel types and five
slope classes as recognized by the National Fire Danger
Rating System (Deeming and others 1977) but this
would unnecessarily complicate analysis and mapping.
In any event, this system or a modification of it can.
identify those areas which present varying degrees of
fire hazard, including those so hazardous that no construction or development should be allowed. It can also
indicate which areas can be made reasonably safe
through the application of various levels of design, construction, and maintenance standards (Orange County
Bd. Sup. 1976, Task Force on California's Wildland
Fire Probl. 1972, San Bernardino County Bd. Sup.
1974, Helm and others 1973).
Any such system should provide for raising to the
next higher level of hazard those limited areas that are
in saddles above canyons on the windward side of
ridges or at the mouths of canyons on the lee side of
main ridges (Los Angeles County Fire Dep. 1970).
Zoning Ordinances
General plans and the various uniform codes (building, fire, etc. ) have no force or effect until adopted by
ordinances of local governing bodies (e.g., county
boards of supervisors, city councils, fire district boards
of directors) and provided with penalty sections (Task
Force on California's Wildland Fire Probl. 1972).
In California, general plans including safety elements
are mandated to counties and cities by State law
(California Government Code Sect. 65300 et seq.). The
standards set by the State to which these plans and
elements must be prepared, especially those having to
do with wildland fire, have been very weak. Consequently, an almost total lack of uniformity exists from
one local jurisdiction to another. The governmental
units that are larger, most heavily damaged in the past,
and more progressive have adopted enabling ordinances
containing rather comprehensive requirements relating
to fire safety. In contrast, some of the smaller units and
those that have not perceived or understood the severity of the problem have treated it in one sentence or one
paragraph (Task Force on California's Wildland Fire
Probl. 1972).
One important element of the General Plan is the
Land-Use Element. It establishes the areas that can be
devoted to different uses (e.g., residential, commercial,
manufacturing, agriculture, open space). This element
has great potential for enhancing structural fire safety in
wildland areas if wildland fire hazard severity classes
are accounted for during its development. So far this
potential has rarely been considered, and no case has
been found where the Land-Use Element of the General Plan was actually implemented in this manner. 3
The Uniform Building Code (UBC) published by the
International Conference of Building Officials has been
adopted by many counties and cities. Others have no
such code or ordinance. A major component of the
UBC is the establishment of Fire Zones 1, 11, 111.
These zones set standards by requiring decreasing degrees of fire safety to be built into structures of various
types of occupancy and prohibit certain occupancies in
Zones I and II. Zone 111 generally encompasses residential areas having the lowest (base level) fire danger
and requires minimal fire safety construction. In all
zones, the standards are designed to provide protection
from fires starting within the building or in another one
nearby (3 to 20 feet). The problem of fires approaching
through large expanses of vegetation is not addressed
anywhere in the UBC (Task Force on California's
Wildland Fire Probl. 1972, Int. Conf. Build. Off. 1976).
A few jurisdictions that have adopted the UBC by
reference in an ordinance have amended it in various
ways to attempt to cover the wildland fire problem.
Some have added fire zones and incorporated certain
restrictions and requirements for structures located in
them. Others have declared fire hazardous wildland
areas to be in Fire Zone II. In most cases the only
effective remedial measure is the requirement of fire-resistive roofing (Build. News, Inc. 1977, County Sup.
Assoc. Calif. 1966, San Bernardino County Bd. Sup.
1974).
Proposed Standards: Recognize varying degrees of
wildland fire hazard in local ordinances. Establish construction and spacing standards commensurate with
each degree, and make such standards applicable to residences and their appurtenant structures as well as to
other types of occupancy.
Spacing and Building Density
To provide a reasonable degree of fire safety, building
spacing and density must be different in mountainous
areas, wildlands, and rural areas than they are in urban
areas. This differentiation is needed because the usual
source of ignition of the structure in the wildland or
rural setting is external while in the more developed city
situation it is internal. Exceptions to this general rule do
occur, but they are relatively rare (Alger 1971, Los
Angeles City-County Fire Bd. Inquiry 1971).
The Uniform Building Code (UBC), Uniform Fire
Code (UFC), and most subdivision codes are based on
two assumptions: an internal ignition and a fire department response time of less than 15 minutes. These are
relatively safe assumptions in most cities and some fire
districts, but are valid only in very limited areas where
fire protection is provided by a county, State, or Federal agency. They are almost totally irrelevant in most
mountain and wildland areas where only seasonal resource fire protection is usually available (Alger 1971).
In addition to being subject to external ignition and up
to 2-hour response times, structures built on sloping
ground are affected by the same fire behavior phenomenon discussed earlier in relation to the wildland fuel.
The slope creates an effect similar to that of wind and
causes fire to spread faster uphill than downhill or on
the level. Buildings situated on slopes should be required, therefore, to be spaced farther apart than similar
buildings built on essentially level ground. On excessively steep slopes (more than 55 percent), all wood
frame construction probably should be prohibited 3a(Los
Angeles County Fire Dep. 1970, Oreg. St. Dep. For.
1978b, County Sup. Assoc. Calif. 1966, San Bernadino
County Bd. Sup. 1974, Helm and others 1973).
In recent years a new concept in residential development has been adopted in some areas. This is the cluster
development in which the population density limitations
of general land-use plans are met by placing individual
homes or multifamily residences (e.g., duplexes, apartments, condominiums) in small groups on smaller lots
than would otherwise be required. The land area thus
saved is reserved for community open space. This practice is esthetically pleasing to most people, and can also
improve the fire safety in rural or wildland areas as long
as certain minimum spacing standards are followed.
The space between-buildings, for instance, should not
be less than half that required between residences in
conventional subdivisions in similar areas. And the native vegetation should be modified at least to fuelbreak
standards of width and hazard reduction in the spaces
between clusters (Task Force on California's Wildland
Fire Probl. 1972, Colo. St. For. Serv. 1977).
Because of the close spacing commonly employed in
mobile home parks, those situated in wildland fire
hazardous areas are particularly susceptible to destruction or serious damage from conflagrations. Required
spacing between mobile homes in such parks should be
no less than that allowed between buildings in a cluster
development in a similar fire hazard classification zone
(Los Angeles County Fire Dep. 1970).
Most of the references on structure density and spacing base their recommendations primarily on slope.
Only rarely are the other primary factors contributing to
wildland conflagrations (i. e., fuels and weather) mentioned, mostly in work done in the late 1970's. The most
logical and defensible standard on which to base structure density and spacing requirements is fire hazard
severity classification and mapping (Colo. St. For.
Serv. 1977, Helm and others 1973).
Proposed Standards: Establish minimum standards
of building spacing and density, as shown below. Provide for the imposition of higher standards or the prohibition of building where local conditions (e.g., excessively steep slopes, ridge saddles, canyon mouths)
create critical fire hazards:
Individual Buildings Clusters
Prop.
Hazard Density Spacing line Between Between
class: setback bldgs. clusters
(feet)
Moderate 3 per 60 30 40 100
acre
High 1 per 80 40 40 150
acre
Extreme 1 per 100 50 50 200
4-5 acres
Previous Section
Back to Table of
Contents
Next Section
