HomeMy WebLinkAbout2020-03-11- 190306- Westmont TTM 3157 FIRE PROJames A. Neumann
Roger Maggio, Fire Marshall
San Luis Obispo City Fire Department
2180 Santa Barbara
San Luis Obispo, CA
February 27, 2020
Regarding: Westmont Subdivision Wildland Fire Protect Report
Dear Mr. Maggio,
I have been asked to review the above noted project and to make comments on the fire
threat and to propose wildfire mitigation measures. I am very familiar with the area, as I
was a CAL FIRE firefighter for 29 years, 12 of those years working at the adjacent CAL
FIRE headquarters as a Battalion Chief.
Fire History
Historically, wildland fires in San Luis Obispo County have burned thousands of acres and
caused considerable property loss with an occasional life loss. Most of these large fires
have occurred in the northern and central portions of the County. Past large fires that have
threatened the City of San Luis Obispo include, the Los Pilitas Fire (75,000 acres) and
Hwy. 41 Fire (45,000 acres). Every summer wildfires, usually quickly contained, occur in
the Camp San Luis area just to the north of the proposed project site. In December of
2001 an approximately 400-acre fire burned on southeast aspect of Bishops Peak, just off
O’Connor way. The fuels and topography were similar to the those found at the project
site. The fire was quickly contained with no damage to the structures in the area.
Fire Factors
Three factors contribute to wildland fire spread and threat:
Topography: Canyons, hillsides, ridges and other “lay of the land” features will
have a dramatic effect on fire spread. Aspect or orientation of the fuel beds also
plays an important role, in general south facing slopes are subject to greater solar
radiation, making them drier and thereby intensifying wildland fire behavior. Slope
is a critical factor in fire spread, in general fire burns 16 times faster up hill.
Weather: In this coastal region weather plays a key factor in the wildland fire
potential. Rain fall occurs primarily between the months of November and April,
and ranges between 20 to 25 inches per year. Summers are typically cool with fog
and or high humidity the norm. Wind in the area, a key factor in spread, is quite
predictable. It typically flows from the north, down the Chorro Valley, and is
moisture laden due to the proximity of the ocean, minimizing the fire danger. The
fall season will see dryer and warmer days, with occasional east to west wind flows
offshore). This, in combination of the lack of rainfall, will see the fire hazard threat
increase. It should be noted that these winds do not have the intensity of the
Southern California “Santa Ana’s” and do not meet typically meet “Red Flag”
warning criteria.
Fuel: The arrangement of the fuel on the land is an important consideration. By
breaking up or thinning fuel beds one can slow the rapid spread rates of wildfires.
In addition, the removal of certain fuels in the horizontal plane can prevent fires
from “laddering” into the tops of trees where it may burn hotter and be more difficult
to contain.
Site Specifics
Topography: The project site is slightly sloped and located near the base of
Bishops Peak on the north and northwest aspect. The topography does not
negatively impact fire spread or fire protection efforts. In fact, it is favorable as
fire, if not driven by wind, will burn upslope away from the site. The slope to the
north, behind the project site, increases slightly but not enough to subject the
mosaic of fuels to preheating.
Weather: The generally mild coastal climate keeps the wildland fire threat to the
site at a minimum. As noted above, the normal wind flow is from the north and it is
cool and moisture laden, approaching the site flowing downhill. In the fall
moderate east to west offshore wind flows do occasionally occur. The wind
direction will then flow around Bishops Peak to the north away from the project
site, down the Chorro Valley to the coast at Morro Bay.
Fuels: There are very limited or no fire fuels on the east and south sides of the
project, these areas being fully developed residential areas. The area to the west
is vegetated in a riparian habit. The remaining north - northeast side is vegetated
in light flashy fuels (grass) that has traditionally been grazed by either sheep or
cattle. The pine trees surrounding the CAL FIRE station to the northeast are
widely spaced and do not present a crowning potential, however, should they be
ignited the ember cast would be of concern. The distance to the steeper portions
of Bishops Peak where denser brush fields and an oak woodland fuel model is
found is considerable; therefore, these fuels do not present a hazard to the project
based on distance.
Mitigation Measures
The proposed structures in this project are not adequately set back (100 feet) from
unmanaged wildland vegetation and riparian areas.
The existing City requirements of fire sprinklers, non-combustible roofs, dual window
glazing, fire department access, and water supply issues are sufficient.
The following additional requirements are necessary:
Rain gutters, when not adequately maintained, will collected leaf material which
becomes a receptive fuel bed for embers and sparks and can then transmit fire
underneath the non-combustible roof materials. I recommend that rain gutters be
protected by non-combustible leaf shields or not allowed.
Record on all lots a deed restriction that allows for only non-combustible fences and
decks are in the subdivision.
Record on all lots a deed restriction that allows for fire resistant landscaping in the
back yards of the subdivision.
Require enclosed eves on all structures within the subdivision
Install fireproof vents on all structures (Fire-rated, flame and ember resistant)
Working with the biologist, remove the non-native vegetation in the creek, riparian
area, reducing the fuel load.
Install a non-combustible wall (block or steel stud /stucco) wall 36 inches in height
all around the northern perimeter of the subdivision. (Installed from the riparian
area/ creek on the west side of the project terminating at the property line of the
CAL FIRE Station. The purpose of this wall is to interrupt fire progression from the
north onto the proposed lots without obstruct the very desirable view of the open
space.
Conclusion
The area fire history and weather patterns, indicate that should a fire occur it will either
move slowly onto the proposed subdivision, pushed downhill through the light fuels by the
prevailing north wind. Or, move away from the site, up the gentle slope, potential pushed
along by an offshore wind flow. In either situation, the construction type and proposed
mitigation measures will allow a wildfire fire to pass from or onto the site with little or no
damage to the improvements.
While the unmanaged wildland fuels located on the north/northeast side of the project do
present a threat, the combination of the favorable topography, the strong coastal weather
influence, the current fire department standard for fire sprinklers, coupled with the required
mitigation measures diminishes this hazard to an acceptable level.
James A. Neumann