10.3.1 - 1 

Base Year: 1999 By: S. Claire 

SOURCE INVENTORY 

CATEGORY #750 

MISCELLANEOUS EMISSION SOURCES 

ACCIDENTAL FIRES - STRUCTURAL 

1999 EMISSIONS 

Introduction 

This category covers emissions from structural accidental fires, including building and 

mobile home fires. The method used to calculate emissions for this category conforms to 

the method used by ARB. 

Methodology 

The number of structural accidental fires was acquired from the state fire marshal’s 

office. The throughput data for this base year was obtained by multiplying base year 

1996 throughput by population growth. 

For building and mobile home fires, an average percent structural loss per fire was 

calculated by dividing the total monetary damage due to fires by the product of the 

average value of a residence in California and the number of residential fires. The result 

is an average loss of 12.4% per fire. To determine the amount of material burned in a 

fire, the ARB staff contacted the National Association of Home Builders and Mr. Larson, 

Chief Building Inspector, City of Sacramento. According to the National Association of 

Home Builders, the average residence has approximately 1200 to 1500 square feet of 

floor space and an average of 10,000 to 12,000 board feet of lumber in its structure. 

Assuming an average of one ton of material per 1000 board feet, an average residence 

would have approximately 11 tons of combustible material. With a rate of loss of 12.4%, 

the structural loss would be 1.36 tons per fire. 

The National Bureau of Standards lists the combustible contents per square foot of the 

areas of the average home. These figures were multiplied by the percent of fires 

originally estimated to occur within each of these areas, and the products were then 

added to give a weighted average of 7.91 pounds per square foot as shown in the 

following table. 
10.3.1 - 2 

 Origin of Combustible Weighted Ave. 

Area Fires (%) (lbs./sq.ft.) (Lbs./sq.ft.) 

Bedroom 28.96 10.4 3.012 

Sleeping Area 0.20 10.4 .021 

Dining Area 2.20 7.2 .159 

Kitchen 53.92 6.8 3.667 

Bathroom 6.32 7.0 .443 

Laundry 8.08 7.2 .582 

Office 0.17 7.9 .013 

Other 0.13 9.6 .012 

Sum of weighted averages 7.909 

With a 12.4% loss rate and a factor of 7.91 pounds of combustible contents per square 

foot, and assuming an average floor space of 1300 square feet, the content loss for the 

average residential fire would be: 

[(1300) x (0.124) x (7.91)] / 2000 = 0.63 tons/fire 

The amount burned per residential fire = 

Structural loss + Content loss 

= 1.36 + 0.63 = 2.0 tons/fire 

Structural fires were apportioned among counties based on total housing units. 

Structural fire emission factors in pounds per ton of material burned for TOG, CO and 

PM were obtained from the results of tests on the burning of model wood buildings. The 

emission factor for NOx was assumed to be similar to that listed in AP-42 for municipal 

refuse. These emission factors were converted to units of pounds per fire using the factor 

1.95 tons/fire. 

The emission factors are: 

 PM Organic NOx SOx CO 

Pounds/fire 21.1 27.1 7.8 0 327.6 

Monthly Variation 

The monthly distribution was taken to be the same as the monthly variation used in the 

BY87 Methodology calculation. 
10.3.1 - 3 

County Distribution 

The number of fires was broken down by household population by county. This was 

used directly in the county distribution except for Solano and Sonoma which were 

adjusted to include only areas inside the District using household population. 

TRENDS 

Historical and future county projection were estimated using county household 

population.