Level of Service

The Level of Service (LOS) is an assessment that focuses on identifying areas with the potential of unacceptable loss and high-cost fires. For this assessment, the department created a new model.

There are several components that define an unacceptable loss and high suppression cost fire. The department narrowed down four components that are common factors with damaging-costly fires. They are potential loss, travel times to the fire, historical occurrence, and resistance to control.

Mt. Vision Fire- October 1995

The defining factor for fire suppression cost and fire loss is the number of structures involved or threatened by fire. Every summer, hundreds of local government engines are dispatched to protect structures. With the cost of local government equipment and the sheer number of fire apparatus needed to protect neighborhoods, it is quite easy to expend a million dollars a day.

Loss figures are also compounded by structures destroyed by wildland fire. Historically, most large dollar loss fires involved numerous homes.

Topographic maps were divided into 81 cells called Quad 81^st. Each Q81^st is approximately 450 acres.

To model structure losses and protection cost potential, parcel information was queried to indicate parcels with at least one living unit. The entire state was divided into 450 acre cells called Quad 81^st. Quad 81^st cells (Q81) were overlaid and combined with the parcel information to indicate how many living units per Q81. Ranks were established for the Q81 based on the number of living units per cell.

For each of the Q81^st the following formula was used:

Living Unit Ranking Map  

Wildland fires became large, thus costly, due to response time. Using the Behave fire model, a fire burning in annual grasses, under a 10-mph wind, with a ten-percent slope, will grow to over 10 acres in five minutes. In ten minutes, the fire will be over 50 acres.

To model response times throughout the county, every fire station regardless of jurisdiction was mapped. Response times were modeled from the fire station to the center of each Q81. The Q81 with a majority of the area covered by ocean were not ranked.

For each of the Q81^st the following formula was used:

Response Time Ranking Map  

The probability of a wildland fire can be based on past ignitions. Over 880 fires were mapped to the nearest address. The dates of the wildfires were between May 1, 1990, and December 31, 1997. The fire location was mapped from the California Fire Information Reporting System reports. The total number of fires per Q81 was calculated. There is a strong correlation to population density, travel corridors, and ignition density.

Probability of Ignition Ranking Map  

The last factor used in the department’s Level of Service model is resistance of control potential. There are several factors that influence a fire’s ability to overwhelm suppression forces. The focus is to determine the resistance of fire control in each Q81.

How fast and how hot a fire burns determines the success rate of fire suppression. How fast (or a fire’s rate of spread) is measured in feet per minute. Fuel models 1 and 2 (with a high percent of annual grass) have the highest rates of spread.

How hot a fire burns is a measurement of intensity rates. Intensity rates are highest for brush or timber types of vegetation. Fuel models 4, 9, and 10 were used to determine areas with high intensity rates.

Access to fires is determined by the road system in place. Streets, both paved and in the county’s fire road system, were used to determine access. Areas more than 500 feet from a road were identified.

The last criteria used to determine the resistance of fire control is slope. Slope restricts fire engine use, slows down fireline production, and increases the rate of spread for wildfires. Slopes with a 40 percent grade are beyond the driving capability of fire engines. Areas with more than a 40 percent slope were identified.

	The equation for resistance to control is:
Areas more than 500 feet from a road	+
Slopes over 40% Details about Slope Models can be found here	+
Fuel models 1,2,4,9,10 Details about Fuel Models can be found here	+
=	Resistance of Control Ranking (RTC).

Percent of RTC Area Within a Q81	Rank	Rank Value
0	Not Ranked	0
1-10%	Low	1
11-30%	Moderate	2
31-50%	High	3
Over 50%	Very High	4

The rank values for all four models are added together to determine the areas with the highest probability for a large, costly, and damaging fire.

Click on the following map to display the level of service:

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