NIST Technical Note 1796

A Case Study of a Community Affected by the 

Witch and Guejito Fires: Report #2 – Evaluating 

the Effects of Hazard Mitigation Actions on 

Structure Ignitions

Alexander Maranghides

Derek McNamara

William Mell

Jason Trook

Blaza Toman
NIST Technical Note 1796

A Case Study of a Community Affected by the 

Witch and Guejito Fires Report: #2 – Evaluating 

the Effects of Hazard Mitigation Actions on 

Structure Ignitions

Alexander Maranghides

Fire Research Division

Engineering Laboratory

Derek McNamara

McNamara Consulting

Golden, CO

William Mell

U.S. Forest Service

Seattle, WA

Jason Trook

850 Couer d’Alene Tribe

Coeur d’Alene, ID

Blaza Toman

Statistical Engineering Division

Engineering Laboratory

May 2013

U.S. Department of Commerce 

Rebecca Blank, Acting Secretary

National Institute of Standards and Technology 

Patrick D. Gallagher, Under Secretary of Commerce for Standards and Technology and Director
ii

Certain commercial entities, equipment, or materials may be identified in this

document in order to describe an experimental procedure or concept adequately. Such

identification is not intended to imply recommendation or endorsement by the

National Institute of Standards and Technology, nor is it intended to imply that the

entities, materials, or equipment are necessarily the best available for the purpose. 

National Institute of Standards and Technology Technical Note 1796

Natl. Inst. Stand. Technol. Technical Note 1796, 107 pages (May 2013)

This publication was a joint effort between the National Institute of Standards and 

Technology and the United States Forest Service (USFS).

Cover Page Photo: The Trails Monday 22 October 2007, Photo Courtesy of Michael Bunnell, Used by Permission
iii

Table of Contents

Abstract....................................................................................................................................... 1

1.0 Background........................................................................................................................... 2

2.0 Introduction........................................................................................................................... 3

3.0 Summary of Objectives and Findings in First Trails Report ................................................ 5

3.1 Defensive Actions, Fire Timeline and Fire Direction....................................................... 5

4.0 Objectives of this Report ...................................................................................................... 7

5.0 Materials and Methods.......................................................................................................... 8

5.1 Firewise Checklist Data Collection and Processing ......................................................... 8

5.2 Additional Data Processing............................................................................................. 12

5.3 Data Analysis Procedures............................................................................................... 15

6.0 Data Collection, Production and Analysis Limitations....................................................... 20

6.1 Field Data Collection ...................................................................................................... 21

6.2 Data Production .............................................................................................................. 22

6.3 Exposure Determinations................................................................................................ 23

6.4 Data Analysis Limitations............................................................................................... 24

7.0 Results................................................................................................................................. 25

7.1 Applicability of Firewise at the Trails (Zone Concept).................................................. 25

7.2 Presence of Firewise Treatments at the Trails................................................................ 27

7.3 Firewise Effectiveness (Individual Treatments)............................................................. 28

7.4 High Hazard Area Determination ................................................................................... 31

7.5 Exposure Method Evaluations........................................................................................ 31

7.6 Firewise Effectiveness (Two Exposure Methods).......................................................... 33

7.7 Defensive Actions as a Function of High/Low Hazard Exposure .................................. 38

8.0 Discussion........................................................................................................................... 40

8.1 Analyzing if Firewise treatments are applicable within the Trails................................. 40

8. 2 Determining if Firewise treatments were present at the Trails, prior to the Witch and 

Guejito Fires.......................................................................................................................... 42

8.3 Evaluating the effectiveness of Firewise treatments in reducing structure ignitions at the 

Trails. .................................................................................................................................... 43

8.4 Mapping fire exposure profiles within the Trails. .......................................................... 43

8.5 Evaluating the effectiveness of Firewise treatments in reducing structure ignitions in 

context of potential exposure................................................................................................ 44

8.6 Evaluating of defensive action in terms of Firewise treatments and as a function of 

exposure. ............................................................................................................................... 44

8.7 Future WUI post-fire case studies................................................................................... 44

9.0 Summary............................................................................................................................. 45

10.0 Conclusions/Recommendations........................................................................................ 46

11.0 Future Work...................................................................................................................... 47

12.0 Acknowledgements........................................................................................................... 48

Appendix A............................................................................................................................... 75

Appendix B............................................................................................................................... 79

Appendix C............................................................................................................................... 82

Appendix D............................................................................................................................... 85

Appendix E ............................................................................................................................... 88
iv

Appendix F................................................................................................................................ 90

Appendix G............................................................................................................................... 93

13.0 References......................................................................................................................... 98
v

List of Figures

Figure 1 Overview of the entire extent of the Witch and Guejito Fires in context with the United 

States. Also portrayed is the study area within the fire perimeter and the origins of the 

fires............................................................................................................................... 49

Figure 2 Fire approach to the Trails Community from the Witch and Guejito Fires. Back ground 

imagery is 1 foot horizontal resolution color imagery flown shortly after the fires.... 50

Figure 3 Trails community in relation to Witch fire perimeter with primary structures displayed 

by damaged status. Back ground imagery is 3 inch horizontal resolution color 

imagery from 2005. ...................................................................................................... 51

Figure 4 Hillshade portraying topography in and around the Trails. Hillshade created from 

Light Intensity Detection and Ranging (LIDAR) derived 1.5 meter digital elevation 

model obtained from the United States Geologic Survey (USGS). .............................. 52

Figure 5 Property lot types in the Trails Community. Back ground imagery is 3 inch horizontal 

resolution color imagery from 2005. ........................................................................... 53

Figure 6 Primary structure densities per square mile for the Witch and Guejito Fires. Derived 

using the ArcGISTM Point Density Tool with a circle window having a radius of 

approximately 200 meters (660 feet) and an output cell size of 3 meters (10 feet). .... 54

Figure 7 Residential structure density in and around the Trails. Derived using the ArcGISTM 

Point Density Tool with a circle window having a radius of approximately 200 meters 

(660 feet) and an output cell size of 3 meters (10 feet). ............................................... 55

Figure 8 Defensive actions on residential properties overlaid with primary structures displayed 

by damaged status. Back ground imagery is 1 foot horizontal resolution color 

imagery flown shortly after the fires. ........................................................................... 56

Figure 9 Fire direction in the Trails overlaid with primary structures displayed by damaged 

status. Back ground imagery is 1 foot horizontal resolution color imagery flown 

shortly after the fires. ................................................................................................... 57

Figure 10 Above ground residential vegetation in the Trails overlaid with the Fire perimeter. 

Back ground imagery is 1 foot horizontal resolution color imagery flown shortly after 

the fires......................................................................................................................... 58

Figure 11 Wildland vegetation community types in and around the Trails overlaid with primary 

structures displayed by damaged status. Back ground imagery is 3 inch horizontal 

resolution color imagery from 2005. ........................................................................... 59

Figure 12 Trails percent slope raster data set derived from LIDAR 5 foot DEM overlaid with 

residential structure damage and destruction.............................................................. 60

Figure 13 Trails aspect raster data set derived from LIDAR 5 foot DEM and reclassified to eight 

directions and overlaid with primary structures displayed by damaged status. ......... 61

Figure 14 Potential change in vegetation greenness (dNDVI) between 2005 and 10 days after the 

Witch and Guejito Fires............................................................................................... 62

Figure 15 Overview of data analysis steps................................................................................... 63

Figure 16 Example of directional sector employed on destroyed structure at the Trails. All 

sectors begin at zero and continue the specified distance. Sectors for 30, 100, 200 and 

300 foot (9, 30, 60 and 90 m) distances have portions excluded by the other sectors. 64

Figure 17 Geographic distribution of Firewise Zones assuming homeowner cooperation. ........ 65

Figure 18 Firewise Zones viewed at an individual property level. Back ground imagery is 3 inch 

horizontal resolution color imagery from 2005........................................................... 66
vi

Figure 19 Relationship between Firewise Zones 3 (100 to 200 feet) and Zones 4 (200 to 300 

feet), and dNDVI (surrogate for burned vegetation) overlaid with primary structures 

displayed by damaged status........................................................................................ 67

Figure 20 Frequency counts of structures by bins of percent of wildland vegetation found on the 

property for four zones................................................................................................. 68

Figure 21 Frequency counts of properties by bins of average percent slopes found on properties 

for all structures, undamaged structures and damaged/destroyed structures............. 69

Figure 22 Frequency counts of properties by bins of the majority of aspects found on properties 

for all structures, undamaged structures and damaged/destroyed structures............. 70

Figure 23 Frequency counts of properties by bins of percent of Firewise Treatments present on 

property for all structures, undamaged structures and damaged/destroyed structures 

where the presence of treatments on the property could be determined for greater than 

50% of the Firewise Treatments assessed.................................................................... 71

Figure 24 Areas with high slopes (>20%); northeast, north and east aspects; and vegetation 

(shown in yellow) overlaid on the modified dNDVI data set ....................................... 72

Figure 25 Bar graphs portraying percent primary structures destroyed by bins of percent of 

wildland vegetation present in the respective sector distance. A) Shows results for 0 

ft to 30 ft (0 m to 9 m) sector. B) Shows results for 0 ft to 100 ft (0 m to 30 m) sector. 

C) Shows results for 0 ft to 200 ft (0 m to 61 m) sector. D) Shows results for 0 ft to 

300 ft (0 m to 91 m) sector. .......................................................................................... 73

Figure 26 Boxplot showing 95% confidence interval for the interactions between individual 

treatments and perimeter/interior parcels and high/low exposure parcels. The 1st line 

(blue) represents perimeter; 2nd line (green) is interior; 3rd line (purple) is high 

exposure; 4th line (orange) is low exposure. ................................................................ 74
vii

List of Tables

Table 1 Defensive actions taken on 15 out of the 16 damaged residential structures.................... 6

Table 2 Firewise checklist treatments........................................................................................... 10

Table 3 Remote sensing data used in analysis.............................................................................. 12

Table 4 Additional data used in analysis...................................................................................... 13

Table 5 LIDAR point classification values. .................................................................................. 13

Table 6 Counts of properties with N/A and N/D values by treatment with percentage of 

residential structures destroyed by N/A and N/D. ....................................................... 25

Table 7 Descriptions of 21 fire jump locations identified in the Trails........................................ 26

Table 8 Treatment 1a contingency table with results of Chi-Square test. Treatment 1a is present 

(pass) if an irrigated area encircles the structure for 30 feet on all sides................... 28

Table 9 Treatment 7 contingency table with results of Chi-Square test. Treatment 7 is present 

(pass) if fuel breaks like driveways, gravel walkways and lawns are present............. 29

Table 10 Treatment 8 contingency table with results of Chi-Square test. Treatment 8 is present 

(pass) if vegetation on the property is pruned to 6 to 10 feet from the ground. .......... 29

Table 11 Treatment 9 contingency table with results of Chi-Square test. Treatment 9 is present 

(pass) if leaf clutter and dead and overhanging branches are removed from the 

property........................................................................................................................ 29

Table 12 Treatment 13 contingency table with results of Chi-Square test. Treatment 13 is 

present (pass) if there is no wood roof, wood siding, wood eave, wood deck, wood 

pergola, wood fence or wood pile on the property. ..................................................... 29

Table 13 Treatment 17 contingency table with results of Chi-Square test. Treatment 17 is 

present (pass) if there dead wood and dense vegetation is cleared at least 30 feet from 

the house. ..................................................................................................................... 29

Table 14 Treatment 19 contingency table with results of Chi-Square test. Treatment 19 is 

present (pass) if there is no wood fence attached to the house.................................... 30

Table 15 Treatment 10 contingency table with results of Chi-Square test. Treatment 10 is 

present (pass) if there is no Firewood within 30 feet of the structure. ........................ 30

Table 16 Treatment 14, roof construction type, classified by damage status............................... 30

Table 17 Roofing material example.............................................................................................. 31

Table 18 Frequency counts and percent destruction of structures by high hazard area for four 

sector distance (30, 100, 200, 300 feet). ...................................................................... 33

Table 19: Treatment 1a three-way contingency tables. First table shows counts by treatment, 

burn status and perimeter/interior designation. Second table shows counts by 

treatment, burn status and high/low hazard area. Treatment 1a is present (pass) if an 

irrigated area encircles the structure for at least 30 feet on all sides. ........................ 34

Table 20: Treatment 7 three-way contingency tables. First table shows counts by treatment, 

burn status and perimeter/interior designation. Second table shows counts by 

treatment, burn status and high/low hazard area. Treatment 7 is present (pass) if fuel 

breaks like driveways, gravel walkways and lawns are found on the property........... 34

Table 21 : Treatment 8 three-way contingency tables. First table shows counts by treatment, 

burn status and perimeter/interior designation. Second table shows counts by 

treatment, burn status and high/low hazard area. Treatment 8 is present (pass) if 

vegetation is pruned on the property. .......................................................................... 35
viii

Table 22: Treatment 9 three-way contingency tables. First table shows counts by treatment, 

burn status and perimeter/interior designation. Second table shows counts by 

treatment, burn status and high/low hazard area. Treatment 9 is present (pass) if leaf 

clutter and dead/overhanging branches are removed on the property........................ 35

Table 23: Treatment 17 three-way contingency tables. First table shows counts by treatment, 

burn status and perimeter/interior designation. Second table shows counts by 

treatment, burn status and high/low hazard area. Treatment 17 is present (pass) if 

dead wood and dense vegetation are cleared at least 30 feet from the house............. 36

Table 24: Treatment 19 three-way contingency tables. First table shows counts by treatment, 

burn status and perimeter/interior designation. Second table shows counts by 

treatment, burn status and high/low hazard area. Treatment 19 is present (pass) if a 

wood fence is not attached to the home. ...................................................................... 36

Table 25 Differences between percent damaged/destroyed when the respective Firewise 

Treatment is absent (i.e., fail) and present (i.e., pass), for Firewise Treatment 1a..... 37

Table 26 Differences between percent damaged/destroyed when the respective Firewise 

Treatment is absent, (i.e., fail) and present, (i.e., pass) for Firewise Treatment 7...... 37

Table 27 Differences between percent damaged/destroyed when the respective Firewise 

Treatment is absent (i.e., fail) and present (i.e., pass) for Firewise Treatment 8........ 37

Table 28 Differences between percent damaged/destroyed when the respective Firewise 

Treatment is absent (i.e., fail) and present (i.e., pass) for Firewise Treatment 9........ 37

Table 29 Differences between percent damaged/destroyed when the respective Firewise 

Treatment is absent (i.e., fail) and present (i.e., pass) for Firewise Treatment 17...... 37

Table 30 Differences between percent damaged/destroyed when the respective Firewise 

Treatment is absent (i.e., fail) and present (i.e., pass) for Firewise Treatment 19...... 38

Table 31 Distribution of defensive actions across high and low exposure properties. ................ 39

Table 32 Defensive actions types taken on the 19 defended high exposure properties................ 39

Table 33 Percent Structure Destroyed with and Without Wildland Vegetation in Zones 1 through 

4.................................................................................................................................... 42
1

A Case Study of a Community Affected by the Witch and Guejito Fires: Report #2 –

Evaluating the Effects of Hazard Mitigation Actions on Structure Ignitions

by

Alexander Maranghides, Derek McNamara, William Mell, Jason Trook and Blaza Toman

Abstract

The National Institute of Standards and Technology (NIST) has a suite of research 

projects addressing risk reduction in Wildland Urban Interface (WUI) communities. The 

NIST WUI Team was invited by California Department of Forestry and Fire Prevention 

(CAL FIRE) to collect post incident data from the California October 2007 fires. Early 

on, the NIST WUI Team initiated a case study within the Witch Fire perimeter. The case 

study is focused on the Trails development at Rancho Bernardo, north of the city of San 

Diego. There were 270 homes in the Trails community, with 242 within the fire 

perimeter. Of these, 74 homes were completely destroyed and 16 were partly damaged. 

Field measurements included structure particulars, specifically roof type, proximity of 

combustibles to the structure, and damage to wildland and residential vegetation.

Documentation included over 11 000 digital images. The data collected and the data 

analysis are divided into two papers. The first paper, NIST TN 1635 addressed the event 

timeline reconstruction and general fire behavior observations. This second paper 

investigates the effect of structure attributes, landscaping characteristics, topographical 

features and potential wildland fire exposure on structure survivability. 

This is the first case study that evaluates hazard mitigation technology effectiveness 

while accounting for fire and ember exposure and at the same time factoring in defensive 

actions. The majority of the hazard mitigation treatments evaluated at the Trails 

Community appeared to be applicable even if they were not all individually effective.

The level of fire and ember exposure was identified as having played a significant role in 

the survivability and destruction of structures with a pattern of increased destruction of

residential structures with increased exposure. Additionally, exposure was found to play 

a significant role in structure survivability with respect to the effectiveness of defensive 

actions. Defensive actions were over two times more effective in saving structures in low 

exposure areas compared to high exposure areas. While the Trails community, at the time 

of the Witch/Guejito fires, did not employ a community wide WUI hazard mitigation

plan this case study provides a detailed analysis of the primary hazard mitigation 

technologies that were present. 

KEY WORDS: Wildland Urban Interface, WUI, fire behavior, community, Witch fire, Guejito fire, 

Firewise, Firewise effectiveness
2

1.0 Background

In this paper, the term Wildland Urban Interface (WUI) refers to locations where 

topographical features, vegetation types, local weather conditions and prevailing winds 

result in potential for ignition of structures from flames and embers of a wildland fire.1

The WUI fire problem is gaining momentum across the southern continental US and is 

particularly severe across Southern California. Between 2003 and 2010, seven California 

WUI fires destroyed a total of 9582 structures,2 on average over 1000 structures per year. 

These fires resulted in 442 100 hectares (1 092 451 acres) burned. The October 2007 

Southern California fires displaced residents in over 300,000 homes. The Witch 

Creek/Guejito fire (hereafter referred to as the Witch fire), the largest of the fires that 

occurred during the 2007 California firestorm, burned 80 124 hectares (197 990 acres) 

and destroyed 1125 residential structures, 509 outbuildings and 239 vehicles; 

additionally, 77 residential structures and 25 outbuildings were damaged.3 Suppression 

costs were $18 million. The property damages for the 2007 California Fire Storm, 

dominated by the Witch fire, are estimated at $1.8 billion4. The Witch Fire resulted in 45 

firefighter injuries and two civilian fatalities. 

It was initially believed that the Trails community was impacted only by the Witch Fire. 

The After Action Report of the October 2007 Wildfires, City of San Diego Response5

identified the Guejito Fire as the main fire that hit the Trails. The Witch Fire6 was ignited 

in the Witch Creek area east of Ramona, California, about 27 km (17 miles) east of the 

Trails, at approximately 12:35 pm on October 21, 2007. The cause of ignition was 

determined as electrical line arcing. The Guejito Fire7 started twelve and a half hours 

later at 1:00 am October 22nd, 2007 at Guejito Creek drainage, on the south side of 

California State Route 78 and 0.4 km (1⁄4 mile) west of Bandy Canyon Rd, or 10 km (6 

miles) northeast of the Trails. The cause of ignition was identified as energized power 

lines contacting lashing wire. The following excerpt from the After Action Report 

described the general progression of the Guejito Fire: 

“The Guejito Fire spread rapidly along the river bottom area of the San Pasqual 

Valley and southwest toward Highland Valley Road. San Diego Fire Department 

(SDFD) strike teams engaged in numerous firefights along the Highland Valley 

Road and Bandy Canyon Road areas, but in many cases were forced to retreat by 

the wind-driven flames. It took just over two hours from the start of the Guejito 

Fire for the first homes in northeastern Rancho Bernardo to be destroyed by fire. 

The Guejito Fire spread west along Highland Valley Road, eventually spotting 

across Interstate 15 and ultimately destroying hundreds of structures in West 

Rancho Bernardo.” 

The combined perimeter of both the Witch and Guejito Fires along with the origins of 

each fire is shown in Figure 1. Figure 2 portrays the approach of the Witch and Guejito 

Fires to the Trails community. 

The National Institute of Standards and Technology (NIST) WUI Team was invited by the 

California Department of Forestry and Fire Prevention (CAL FIRE) to collect post 

incident data from the Witch and Guejito Fires. Early on, the NIST WUI Team initiated a 

case study within the Witch/Guejito Fire perimeter. The case study is focused on the Trails 

development at Rancho Bernardo, located 40 km (25 miles) north of San Diego City 

Center. There were 270 primary residences in the Trails, with 242 located within the fire 
3

perimeter (Figure 3). Seventy four homes were completely destroyed and 16 were partly 

damaged (Figure 3). 

The field data collection effort took approximately 1300 person hours over 14 months. 

Field data were collected by NIST personnel and CAL FIRE Fire Marshals with the 

support of residents, and the San Diego Fire and Rescue and Police Departments. Field 

measurements included structure particulars, fire direction and damage to vegetation 

adjacent to structures. Documentation included over 11 000 digital ground images. The 

data collected and the data analysis conducted are divided into three papers. The first 

NIST publication on this study, NIST TN16358 addressed the event timeline construction 

and general fire behavior observations. The current report explores the response of 

structures within the Trails to the WUI fire. Specifically, this report will attempt to 

determine the effectiveness of Firewise9 type actions in reducing structure ignitions at the 

Trails while considering exposure as well as defensive actions. A third paper will then be 

developed analyzing the use of fire models in the Trails. 

The NIST WUI research effort has three primary components: computer model 

development, experiments and field data collection. All three components are interlinked 

and work together towards enabling a reduction of losses at the WUI. This is achieved 

by the NIST WUI effort in codes and standards as well as work in economics aimed at 

ensuring the benefit cost effectiveness of hazard mitigation solutions. 

Fire behavior models are being developed to help characterize and predict fire behavior 

in the WUI. At the same time, experimental work is being conducted, with input from 

post-fire assessments, to characterize and quantify structure ignition vulnerabilities. 

Modeling and experiments are being used to assess the potential effectiveness of hazard 

reduction techniques. By implementing this comprehensive methodological approach to 

studying communities burned by wildfires, the effectiveness and reliability of WUI 

mitigation techniques might be better assessed.10

2.0 Introduction

The extent of the Trails community, at its greatest, is 1.8 km (1.1 miles) from east to west 

and 1.6 km (1 mile) from north to south. Average elevation of properties within the 

Trails range from 125 m to 205 m (405 feet to 670 feet) above sea level. The community 

rests on a knoll and is surrounded by valleys on the north, east and west with higher 

density residential communities to the south (Figure 3). Highland Valley is to the north at 

elevations above sea level ranging from 100 m to 110 m (330 feet to 365 feet). Sycamore 

Creek is to the east at similar elevations and an unnamed ravine is to the west with 

elevations ranging from 100 m to 135 m (330 feet to 445 feet). Figure 4 portrays 

topography in and around the Trails along with destroyed and damaged residential 

structures. There are numerous naturally occurring draws and chimneys present on and 

close to the western, northern and eastern properties in the Trails. Many of these 

topographic features extend into the interior of the Trails. Additionally, structures are 

present in various topographic positions throughout the Trails; some are close to 

chimneys/draws of various configurations, others are close to ridges and many are at the 

top of significant slopes. 

Figure 5 shows the distribution of property lots in and around the Trails. The Trails 

consists of 281 lots: 242 residential lots inside the fire perimeter, 28 residential lots 

outside the fire perimeter, 10 vacant lots and 1 small government owned utility lot. The 
4

Trails directly abuts two large property lots to the north, east and west. The property to 

the north and east contains wildlands, which are directly adjacent and continue into some 

Trails residential properties. There are also nurseries on these properties to the east and 

northwest that do not directly abut residential properties. The property to the east is all 

wildlands. There is a paved two-lane road to the north and unpaved roads to the east and 

west. Surrounding the Trails on the south are high density residential property lots. 

The housing density within the Trails is approximately 164 homes per km2 (422 homes 

per square mile), not considering structures in adjacent communities. Figure 6 portrays 

primary structurei

density across the Witch and Guejito Fires. The housing density 

within the Trails is generally lower than the densities seen to the west and south, but 

greater than the densities seen to the east. Structure density in the Trails, considering all 

residential properties surrounding the Trails community, is shown in Figure 7. Lower 

residential structure densities in eastern, northern and western portions of the Trails are 

caused by adjacent wildland properties containing no structures as well as the geometry 

of these residential property lots. As can be seen in Figure 7, these perimeter properties 

tend to have a different geometry compared to those in the interior portions of the 

community. The lots on the western, eastern and northern perimeter tend to be longer 

and thinner with most extending into the wildlands. This varied geometry is further 

demonstrated by the properties on the “perimeter”ii having an average area of 1.7 acres 

and those on the “interior” of the community having an average area of 1.1 acres. 

Wildland vegetation in and directly around the Trails was categorized as the following: 

Cismontane Alkali Marsh, Coast Live Oak Woodland, Coastal and Valley Freshwater 

Marsh, Diegan Coastal Sage Scrub, Valley and Foothill Grasslands, Southern Riparian 

Forest, Southern Cottonwood-willow Riparian Forest, Southern Willow Scrub, Disturbed 

Wetlands and Non-Native Grasslands. Wildland vegetation community types of Diegan 

Coastal Sage Scrub, Coast Live Oak Woodland, Valley and Foothill Grasslands and NonNative Grasslands directly abut or continue onto residential properties in the western, 

northern and eastern portions of the Trails. Vegetation community types found in 

Sycamore Creek to the east but not directly abutting residential properties consists of 

Southern Willow Scrub, Coastal and Valley Freshwater Marsh and Disturbed Wetlands 

as well as a plant nursery. Highland Valley to the north but not directly abutting 

residential properties contains Non-Native Grasslands, Southern Willow Scrub, 

Cismontane Alkali Marsh and different types of Southern Riparian Forest. The ravine to 

the east is dominated by Diegan Coastal Sage Scrub and Coast Live Oak Woodlandiii

with some Southern Cottonwood-Willow Riparian Forest and a plant nursery further 

away from residential properties. Other areas within the Trails contain an extremely 

diverse variety of vegetation with some being very flammable such as Mexican Palms 

(Washingtonia robusta) and Eucalyptus (Eucalyptus cinerea) and other residential 

vegetation also likely being flammable. The vegetation community types mapped are 

 i

Primary structures are considered to be a residential dwelling or a business facility, including Federal, 

State and local government facilities. The number of residences per dwelling is not considered in Figure 6

or Figure 7. ii In NIST TN 1635, the perimeter of the community is defined by the lots that have a portion of their 

perimeter adjacent to wildlands.

iii The southern areas in the ravine to the east of the Trails contain a more diverse group of vegetation 

communities compared to what is portrayed in Figure 11.
5

defined and described in the SanGISiv Vegetation Community Type data set.11

Vegetation community types within the Trails were not mapped due to this diversity and 

the fact that there was no mapping of residential vegetation in the SanGIS data set. 

Ornamental vegetation mapping of interior vegetation was, however, conducted as 

described in section 5.3.

The report outline is provided here for clarity. Section 3 provides a summary of the 

objectives and findings from the first Trails Report (NIST TN1635)8. Section 4 identifies 

the objectives of this report while section 5 covers materials and methods used. Section 6 

covers data collection, production and analysis limitations. Section 7 lists the results, 

while section 8 is a discussion of the findings. Section 9 provides a summary, and section 

10 offers conclusions and recommendations. Lastly section 11 addresses future work and 

acknowledgments are provided in section 12. Appendix A provides a complete list of the 

NIST TN1635 findings, and Appendix B includes the Firewise checklists used. 

Appendices C and D include the additional field data collection forms used. Appendix E 

provides information on the derivation of the Normalized Difference Vegetation Index 

(dNDVI) data set. Lastly Appendix F and G provide additional two and three-way 

contingency tables. 

3.0 Summary of Objectives and Findings in First Trails Report

In order to better understand the fundamentals of fire behavior at the WUI, NIST 

Technical Note 1635 addressed the following technical questions:

• How far within the Trails did the fire spread? 

• To what extent did embers contribute to ignition of structures?

• Why did the fire spread stop when it did?

• Did all the structures ignite from the passage of the wildland fire front, or were 

some structures ignited later and why?

A timeline was developed for the event and the damage that occurred to structures and 

some residential vegetation were identified. Additionally, the fire fighting and structure 

protection responses taken shortly before and during the fire event were documented. 

Detailed findings from NIST TN1635 are found in Appendix A.

3.1 Defensive Actions, Fire Timeline and Fire Direction

Information on defensive actions, fire timeline and fire direction were collected as

described in NIST TN1635. This fire timeline and human behavior information 

presented in TN1635 is used here to provide insights to fire behavior and structure 

vulnerabilities. Additionally, fire direction information provides a potential means to 

characterize exposure from burning features across the landscape. Finally, locations of 

fire jumps were used to characterize effective and ineffective property treatments. 

Defensive actions are defined here as actions taken by the San Diego Fire and Rescue

Department (SDFRD), San Diego Police Department (SDPD), and homeowners to slow 

down, redirect, control and extinguish any fires during the morning of October 22, 2007. 

 iv SanGIS is the joint City and County of San Diego Geographic Information system. Here San GIS is used 

to populate the database describing vegetation in and around the Trails community.
6

The focus is on all actions taken shortly before the approach of the Guejito fire and for 

approximately 12 hours after its arrival, or until 3:00 pm October 22. No structures were 

ignited after 1:30 pm and all major fire suppression activity was significantly reduced. A 

total of 85 defensive actions on 79 properties shown in Figure 8 were identified at the 

Trails, however, it is possible that a number of defensive actions were not identified. The 

actions ranged in complexity and scope from SDFRD fire engine crew defending a house 

with multiple fire hoses to a homeowner putting out a gutter fire with a garden hose. It is 

not possible to accurately estimate the total impact of all defensive actions; however, the 

effects of defensive actions on damaged structures are clearly seen as 15 out of the 16 

damaged structures were defended. Table 1 lists the specific defensive actions taken on 

these damaged structures.

Figure 9 portrays fire direction in the Trails. Fire direction was delineated in the field on 

hard copy data sheets portraying aerial imagery from GoogleTM Earth. Several different 

indicators were used to determine the direction that the fire spread within the Trails. In 

the wildlands, needle freeze, directional degree of damage to wildland vegetation and the

presence of partly damaged golf balls were all used to determine directionality of fire 

spread. Within the Trails, the extent of burned vegetation around destroyed homes was 

documented along with the locations that the fire jumped a road. This allowed for the 

identification of 21 locations representing spotting across the road. Needle freeze, the 

process of dehydrated foliage aligning or “freezing” parallel to the wind direction, was 

used to obtain wind direction.12 Directional scorching was also used to document fire 

direction within the Trails.

Table 1 Defensive actions taken on 15 out of the 16 damaged residential structures.

Damaged area/ ignition 

location

Defensive Action (party responsible)

decking and railroad ties Garden hose used to extinguish fires (resident or SDPD)

detached garage and corner of main 

house/ unknown

Fire contained in garage (SDFD)

detached garage/ unknown Fire contained in garage (SDFD)

Structure addition under 

construction

Water from suppression evident (SDFD)

main structure/ outside column 

(stucco over wood)

Fire contained to outside column (SDFD)

detached garage/ unknown Fire contained in garage (SDFD)

detached structure/ unknown Fire contained in detached structure (resident or SDPD)

main structure/ exposed wood beam Garden hose used to extinguish fires (resident)

decking Garden hose and bucket (resident)

main structure/ gutter Garden hose used to extinguish fires (resident)

decking Garden hoses used (unknown)

detached wood shed, wood fencing Fire contained (SDFD)

decking Fire contained to location of origin (SDFD)

roof top solar panels Spot fires extinguished (SDFD)

deck and main structure Fire contained to location of origin (unknown)
7

4.0 Objectives of this Report

There are many different types of guidance available to residential homeowners and 

builders regarding development and maintenance of properties in a WUI environment. 

There is, however, a lack of studies assessing the effectiveness of current WUI mitigation 

guidance for WUI homeowners and builders. Enforceable guidance is found in building 

codes and standards that are typically determined at the city or county level with some 

statewide standards existing in states such as California. WUI building codes and 

standards, however, vary both geographically and over time. Residential WUI mitigation 

guidance is also provided at the national level from organizations such as Firewise

Communities and the National Fire Protection Association (NFPA) 13. This national level 

guidance is often adopted or modified by state or local governments when providing 

recommendations for developing or treating WUI communities. In addition to codes and 

standards, WUI mitigation guidance for residential properties is typically presented to 

homeowners and builders in two forms:

1. Checklists: these types of guidance provide a set of pre-defined criteria which 

homeowners or builders can use to ensure the structure has been built or is being 

maintained to provide protection from wildland fires. 

2. Scored Evaluations: these types of guidance also provide a set of pre-defined 

criteria where each WUI treatment has a weighted value resulting in an overall 

score for the primary structure relating to protection from wildland fires.

The NFPA Firewise Communities program, at the time of the 2007 Witch Fire, had 

published landscape and construction checklists (Firewise checklists)13 providing 

guidance to homeowners and builders on WUI residential property development and 

maintenance. These checklists are provided in Appendix B. This report evaluates certain 

aspects of the Firewise Communities checklists in context of the Witch and Guejito Fire 

affected the Trails Community at Rancho Bernardo. Specifically, this report focuses on:

1. Analyzing if Firewise treatments are applicable within the Trails.

2. Determining if Firewise treatments were present at the Trails prior to the Witch 

and Guejito Fires.

3. Evaluating the effectiveness of Firewise treatments in reducing structure ignitions 

at the Trails individually and in context of exposure from flames and embers.

4. Examining the need to know defensive actions in order to determine Firewise 

treatment effectiveness. 

The Firewise checklists reflect Firewise type guidance at the time of the 2007 Witch and 

Guejito Fires. Additionally, the Firewise checklists are currently provided on websites of 

many state and local governments responsible for providing WUI mitigation guidance. 

Given the limited amount of resources available, the Firewise checklists represented a 

readily available format that could be recorded on paper forms. Finally, the data 

collection approach might provide an indication of factors to focus future WUI post-fire 

case studies.
8

5.0 Materials and Methods

The NIST data collection effort provided the necessary information to characterize the 

fire approach from the wildlands, the effects of fire within the community and the 

defensive actions taken. The intent of the effort was to collect sufficient information, not 

only to characterize overall fire behavior in the WUI but also to provide a foundation for 

future, more in depth, case studies. The following data collection methodology was 

developed and followed for the NIST data collection effort:

1. Immediately after the fire, the construction characteristics of the destroyed 

residences as well as damage to some residential vegetation were documented 

using the field forms shown in Appendix C. This was necessary in order to 

capture the information before it was lost during community reclamation efforts.

2. Emergency responder data logs were obtained and technical meetings were 

conducted with first responders to develop an event time line. At the same time, 

the Trails Homeowners Association (HOA) provided critical input to the timeline.

3. Homeowner technical discussion forms were sent to each homeowner within the 

Trails community by CAL FIRE and subsequently by the Trails HOA to 

determine information on structure particulars, vegetation around the structure, 

defensive actions, fire behavior timeline, weather, and other information.

4. The Trails was revisited by NIST Scientists and California Fire Marshalls to 

assess properties with non-destroyed structures as per the field form shown in 

Appendix D. The form was based on the Firewise Checklist in Appendix B.

5. Properties with destroyed structures were assessed as per the Firewise checklist 

using the data collected in step one above in conjunction with other sources of 

data as described in the sections below.

6. Responses to the Firewise checklist were normalized in an attempt to provide 

consistency between observers. 

7. Results of the Firewise checklist data collection were used with other data sources 

to determine the applicability of the WUI treatments, the presence of WUI 

treatments in the Trails, and the effectiveness of WUI treatments in reducing 

structure ignition in the Trails.

The data collection effort was conducted with support from CAL FIRE and San Diego 

Fire and Rescue and Police Department personnel. Additionally, critical support was 

provided by the Trails HOA. 

5.1 Firewise Checklist Data Collection and Processing

In April 2008, following the Witch and Guejito fires, 168 properties without destroyed 

primary structures but within the fire line were assessed for the presence of the respective 

Firewise treatments listed in Table 2v. Treatments 1a and 19 had clarification added or 

modifications made to the treatment description before the data collection event as shown 

in italics in Table 2. The modified Firewise treatments were transferred to a hard copy 

data sheet and the address, time of data collection, image documentation and team 

 v Some Firewise treatments present on the Firewise Checklist were not assessed because the determination 

of these treatments in a post-fire environment was believed to be too difficult to obtain reliable answers.
9

number for the respective property assessment were recorded. Each property received a 

rating for the respective treatment as follows:

• Yes: indicates the property received the respective treatment (i.e., passed/treated).

• No: indicates the property did not receive the respective treatment (i.e., 

failed/untreated).

• N/A: indicates a yes/no value is not applicable for the respective treatment. An 

example is treatment 22 where a property with no deck would receive a N/A.

• N/D: indicates that it could not be determined if the respective property was treated. 

An example is a completely burned property where the presence of firewood 

could not be determined.
10

After examining the initial data it was discovered that Firewise treatments 10, 13 and 18 

also required modification to the treatment description for consistent evaluation. These 

modifications to the Firewise treatment description are shown in bold in Table 2. 

 vi Treatment descriptions listed in italics were added at the time of data collection. Treatment descriptions 

listed in bold were added after the data collection. Treatments highlighted in grey were not analyzed.

vii The Firewise checklist indicates Zone 1 is closest to the structure; Zones 2-4 move progressively further away.

Table 2 Firewise checklist treatmentsvi.

Treatment 

Number

Treatment Description Treatment 

Number

Treatment Description

1a Zone 1vii. This well-irrigated area 

encircles the structure for at least 30' 

on all sides. (If one section does not 

meet this it is a “fail”)

12 Set your single-story structure at least 30 

feet back from any ridge or cliff; increase 

distance if your home will be higher than 

one story.

1b Zone 1. Provide space for fire 

suppression equipment in the event of 

an emergency. 

13 Use construction materials that are fireresistant or non-combustible whenever 

possible. (The presence of a wood roof, 

siding, eave, deck, pergola, fence or 

wood pile receives a “no”)

1c Zone 1. Plantings should be limited 

to carefully spaced low flammability 

species.

14 Roof construction from materials such as 

Class-A asphalt shingles, slate or clay tile, 

metal, cement and concrete products, or 

terra-cotta tiles.

2 Zone 2. Low flammability plant 

materials should be used. Plants 

should be low-growing, and irrigation 

should extend into this zone.

15 On exterior wall facing, fire resistive 

materials such as stucco or masonry are 

much better choices than vinyl which can 

soften and melt.

3 Zone 3. Place low-growing plants 

and well-spaced trees in this area, 

remembering to keep the volume of 

vegetation (fuel) low.

16 Driveway 12 feet wide with a vertical 

clearance of 15 feet and a slope that is less 

than 5 percent and include ample 

turnaround space near the house.

4 Zone 4. This furthest zone from the 

structure is a natural area. Selectively 

prune and thin all plants and remove 

highly flammable vegetation.

17 Periodically inspect your property, clearing 

dead wood and dense vegetation at distance 

of at least 30 feet from your house.

6 Take out the “ladder fuels” —

vegetation that serves as a link 

between grass and tree tops.

18 Move firewood away from the house or 

attachments like fences or decks. (30 feet 

is defined as a minimum distance)

7 Provide added protection with “fuel 

breaks” like driveways, gravel 

walkways, and lawns.

19 Is the structure free of an attached wood 

fence?

8 Keep vegetation pruned. Prune all 

trees so the lowest limbs are 6' to 10' 

from the ground.

20 Prevent combustible materials and debris 

from accumulating beneath patio decks or 

elevated porches.

9 Remove leaf clutter and dead and 

overhanging branches.

21 Screen or box-in areas below patios and 

decks with wire screen no larger than 1/8 

inch mesh.

10 Store firewood away from the house. 

(30 feet is defined as a minimum 

distance)

22 Elevated wooden deck not located at top of 

hill where in direct line of a fire.

11 Slope of terrain; build on the most 

level portion of the land.
11

Properties with destroyed primary structures were evaluated in the office using field and 

remote sensing data following the complete descriptions shown in Table 2.

Hard copy field forms representing the 168 properties assessed by NIST and CAL FIRE 

were scanned and entered into a digital format. Certain errors were encountered when 

reviewing these digital data as follows:

1. Systematic errors identified at a team level. Examples include flipping questions 

on a sheet, incomplete data sheets, or inconsistencies assigning a N/A value.

2. Ambiguity in the question. An example is question 13 examining combustibles 

around a structure. 

3. Diversity of expert opinion. For example, experts may disagree on what types of 

vegetation might be low in flammability.

While information was collected regarding the presence of treatments 1b and 16, it was 

decided not to assess attributes related to first responder access. Treatment 12 was also 

removed from the analysis due to confusion on what constituted a cliff or ridge. Finally,

treatments 2, 3 and 4 were removed from the analysis due to confusion in interpretation 

of these treatments as described in Section 6 of this paper.

The raw field data were converted into digital format and inspected back in the office in 

an attempt to provide consistency amongst observers and between evaluations of the 

destroyed and not destroyed primary structures. This was a difficult process and some 

treatments might not have been evaluated consistently. Inconsistent use of the value N/A 

might not have been corrected due to ambiguity in the field and office data. There was 

also difficulty in transferring the data and data integrity issues arose. An attempt was 

made to clean up the data but certain errors might remain. The new digital data collection 

methodology was designed, in part, to address these issues. 

Table 3 shows additional remote sensing data sources used for the analysis along with the 

specific use. All Firewise responses were also inspected using observer comments, 

homeowner technical discussion forms, first responder technical discussions, assistance 

from the Trails Home Owners Association (HOA), ground images and other data 

obtained from the initial Trails assessment. With the exception of treatment 1a and 11, 

spatial representations of property boundaries were not used in the data normalization 

process. Also note that there was no normalization process conducted on the destroyed 

primary structures as the methods used to assess these were the same methods used in the 

normalization process.viii

 viii Normalization consisted of reviewing the data and checking for consistency across the different data 

collection teams. As an example, one team misinterpreted one of the questions recoding “yes” when a 

combustible was present instead or recording “no”.
12

5.2 Additional Data Processing

In addition to the remote sensing data listed in Table 3, other vector GIS data was 

acquired and used in this paper as shown in Table 4. The raw LIDAR data listed in Table 

3 had points classified to the designations shown in Table 5.

14 These specifications 

follow the American Society of Photogrammetry and Remote Sensing (ASPRS) LIDAR 

Point Classes15 for those features with classification values less than 10. Those features 

with classification values greater than 10 represent features with no standard LIDAR 

Point class value and the ASPRS reserved values were assigned. The features extracted 

for this classification schema were based on potential needs for modeling and ability to 

delineate vegetation by structural stage. 

Polygons representing the horizontal extent of vegetation and building footprints were 

extracted across the study area from the LIDAR data and fire barrier locations were 

extracted from color imagery. Additionally, digital elevation models and derivatives 

were created from the LIDAR ground points. Extracted vegetation polygons were also 

classified by structural class, vegetation community type and other categorizations using 

a combination of remote sensing and GIS data sources. Finally, a change in greenness 

data set was developed from pre- and post-fire imagery (imagery dates listed in Table 3) 

to help portray, at a coarse level, fire damage to vegetation in and around the Trails 

community. 

Table 3 Remote sensing data used in analysis.

Data 

Source/Type

Type of 

Data

Spatial 

Resolution

Date Uses

PictometryTM Oblique 

Imagery

6 Inch 5/19/06 Verify presence of all Firewise 

treatments.

Pictometry Aerial 

Imagery

6 Inch 5/19/06 Verify presence of all Firewise 

treatments.

Ortho-rectified 

Imagery (USGS)

Aerial 

Imagery

1 Meter 6/2005 Verify presence of treatments 11 and 

13. Creation of pre-fire NDVI data 

set.

Ortho-rectified 

Imagery (USGS)

Aerial 

Imagery

3 Inch 3/2005 Verify presence of treatments 11 and 

13.

GoogleTM Imagery Aerial 

Imagery

1 Foot 1/2006 Verify presence of all Firewise 

treatments except treatments 11 and 

13.

Ortho-rectified 

Imagery (San 

Diego State 

University)

Aerial 

Imagery

1 Foot 11/2007 Verify presence of treatments 11 and 

13; cleanup LIDAR extracted building 

footprints; general fire behavior; 

creation of post-fire NDVI data set.

Light Intensity 

Detection and 

Ranging (LIDAR)

Point 

Measuremen

ts of Surface 

Elevation of 

All Features

5 Foot 

Nominal 

PostSpacing

3/2005 Verify presence of Firewise treatment 

11. Creation of various topographic 

products and derivates; extraction of 

building footprints; and creation of 

vegetation data set.
13

All LIDAR points except ground points were classified using automated and manual 

techniques found in the ArcGISTM extension LP360TMx

. Boulder and fire barrier features 

were extracted as polygons from the 2005 imagery using the ArcGIS extension Feature 

AnalystTM. The techniques used were similar to those described in McNamara et al., 

2009 16 except results were manually 

adjusted for misclassifications using 

the 2005 three inch imagery. 

Additionally, building footprints 

were derived from the classified 

LIDAR points, again using LP360

software. These building 

footprints were manually corrected 

for misclassifications, occlusions 

caused by vegetation and other 

errors as observed in various 

remote sensing data sources shown 

in Table 3. The building 

footprints are estimated to have a 

horizontal accuracy of about 1.5 m 

to 3 m (5 ft to 10 ft). LIDAR 

points representing vegetation 

were further classified as to the vegetation height categories shown in Table 5. This was

again accomplished using LP360 software to subtract the LIDAR recorded height above 

sea level of the respective vegetation point from the height above sea level of the 

interpolated ground points on which this LIDAR vegetation point falls. Thereby 

providing a measure of height above ground for the respective point and allowing for the 

automatic classification of the remaining unclassified points to the vegetation height 

categories shown in Table 5. Vegetation polygons representing above ground vegetation 

by structural stage were then derived from the classified LIDAR point cloud using LP360

software to group and trace LIDAR points in the height categories shown in Table 5. 

Following this a polygon representing the study areaxi was delineated. This study area 

polygon was then erased by polygons in the fire barrier and the building footprint data set 

 ix Property boundaries used in this analysis had a horizontal accuracy listed as 3 m to 4.5 m (10 ft to 15 ft). x LP360 for ArcGIS is an extension that provides the ability to create and manipulate LIDAR Layers 

directly from industry standard LAS files without any time consuming importing or converting processes. 

http://www.geocue.com/products/qcoherent.html

xi The study area consists of the Trails community, the Sycamore Creek water shed to the east, the adjacent 

western ravine and parts of Highland Valley as seen in Figure 3. 

Table 4 Additional data used in analysis.

Data Source/Type Type of 

Data

Uses

Property Boundaries (SanGISTM)

ix Vector 

GIS Data

Firewise Zone Concept Analysis; 

determining presence of Firewise 

treatments 1a and 11.

Vegetation Community Types 

(SanGIS)

Vector 

GIS Data

Conflated vegetation community types 

found in this data set to LIDAR derived 

vegetation polygons.

Feature Classification Value

Low Vegetation: ≤2m 3

Medium Vegetation: >2m ≤ 4m 4

High Vegetation: >4m 5

Building 6

Ground 8

Vehicle 15

Pole 16

Bridge 17

Boulder 18

Fire Barrier 19

Deck (material unknown) 20

Solar Panels 21

Tennis Courts 22

Playground Equipment 23

Table 5 LIDAR point classification values.
14

described above. The remainder of the polygons represented vegetated surfaces across 

the study area, excluding vegetation that covered buildings and fire barriers. Next, the 

remainders of these polygons were erased by the structural stage vegetation polygons 

traced from the LIDAR point cloud, leaving polygons with only ground vegetation. 

These ground vegetation polygons were then combined with the structural stage polygons 

to produce the final dataset portraying the horizontal extent of the top vegetation layer 

across the study area, including vegetation covering buildings and fire barriers. Areas 

representing nurseries or tree farms were classified as “agriculture”. The horizontal 

extent and structural stage of vegetation was not extracted in these areas. 

Many of the ground vegetation polygons created above represented large contiguous 

areas of species such as Manzanita (Arctostaphylos) and other shrubs species (broadly 

grouped here as Diegan Coastal Sage Scrub) with only sparsely scattered LIDAR 

vegetation returns. The scarcity of LIDAR vegetation returns was due to the high density 

of the, sometimes low growing but often highly flammable in this case, vegetation and 

the difficulty in distinguishing between shrub and ground returns in cases such as these. 

Using manual techniques described below these polygons were edited to reflect changes 

in vegetation community type and manually identified Diegan Coastal Sage Scrub 

polygons were re-classified with a height category ≤2m, unless portrayed to be of a 

greater structural stage class in the LIDAR data. The structural stage vegetation polygons 

are estimated to have a horizontal accuracy of about 1.5 to 3 meters (5 ft to10 ft). 

Other vegetation community types portrayed in the vegetation data set listed in Table 4

were also conflated or transferred to the LIDAR extracted vegetation polygons from the 

SanGIS vegetation data set. This conflation process was conducted due to the poor 

spatial representations of the SanGIS vegetation polygons when compared to the LIDAR 

extracted vegetation polygons. The vegetation community classifications present in the 

SanGIS data set, however, provide the best estimate of vegetation type available for the 

study area. Polygons in the wildland areas, generally greater than a quarter acre (less on 

the wildland edge) were edited to reflect changes in community types based off of aerial 

photo interpretation from the 2005 three inch spatial resolution imagery and PictometryTM 

oblique imagery. Vegetation community type mapping was conducted to help divide 

lands into wildland versus residential vegetation and as a potential means to prescribe the 

material properties of vegetation for future fire modeling in the Trails. 

Vegetation polygons mapped to a community type were also sub-classified as wildland 

vegetation with all other vegetation polygons being classified as residential vegetation. 

This sub-classification followed a conservative approach along the wildland edge only 

attempting to identify those vegetation community types shown in Figure 11 and there 

evident continuation into or occluded occurrence in the Trails Community. The exact 

edge where wildlands ended and residential vegetation began was in some cases quite 

clear and in other cases more difficult to delineate. Ground photos were coupled with 

aerial imagery to better discern these edges. Small patches of natural vegetation 

representing a single or small group of species in the interior of the community might 

have been missed in this mapping process (< 0.25 acres). 

The height class vegetation polygons for non-ground vegetation mapped in the Trails 

community are displayed in Figure 10. Wildland vegetation community type polygons 

mapped in and around the Trails are displayed in Figure 11. Vegetation polygons 

displayed in Figure 10 were not mapped to community types but vegetation polygons 
15

displayed in Figure 11 were mapped to structural stage. In fact, though not studied here, 

this initial mapping of height class greatly facilitated the manual delineation of vegetation 

community type in the Trails due to differences in structural stage among vegetation 

community types.

Other derivative products of the LIDAR point cloud included a digital elevation model 

(DEM) at a 1.5 meter (five foot) horizontal resolution derived from the LIDAR classified 

ground points using LP360. Ground points were converted to a triangulated irregular 

network (TIN) and the TIN was converted to a raster DEM using LP360. Again, using 

ArcGIS, percent slope and aspect grids were derived from the DEM and are shown in 

Figure 12 and Figure 13, respectively. 

In addition to the above derivative products, a change in greenness data set between the 

2005 National Agriculture Imagery Program (NAIP) color infrared (CIR) imagery and 

the post-fire four-band imagery was also created. This change in greenness data set is 

derived by differencing two Normalized Difference Vegetation Index (NDVI) data sets to 

produce what is termed a dNDVI data set as described in Appendix E. This data set was 

not developed for quantitative analysis but as a means to identify where the top 

vegetation layer burned or was scorched. This data set is used for various map figures 

and to help portray burned areas in combination with other data for visual data 

exploration. 

In the Trails, the dNDVI data product does not portray vegetation types that were 

senescent (i.e., no photosynthetically active vegetation) for both pre- and post-fire 

imagery. Field observations, however, indicated that several grassland areas were 

consumed by the fire. These areas were typically Diegan Coastal Sage Scrub, NonNative Grasslands and Valley and Foothill Grasslands. Most of these areas experienced 

stand replacing firesxii and appeared to have helped spread the fires into and through 

portions of the Trails. These burned areas are also displayed with the dNDVI product 

shown in Figure 14. All subsequent figures displaying the dNDVI data set have these 

manually delineated burned areas displayed as white with a transparency of 30%. It 

should also be noted that Figure 14 does not display areas where the vegetation understory burned and the vegetation over-story was not burned or scorched. 

5.3 Data Analysis Procedures

This section presents the methods used to assess the following items:

1. Applicability of Firewise treatments within the Trails,

2. Presence of Firewise Treatments within the Trails, prior to the Fire,

3. Effectiveness of Firewise treatments in reducing structure ignitions,

4. Effectiveness of Firewise treatments in reducing structure ignitions in context of 

potential exposure.

5. Effectiveness of Firewise treatments when considering defensive actions as well 

as locations of defensive actions in context of potential exposure. 

 xii A stand replacing fire kills all or most of the living upper canopy layer (in a forest or woodland, the 

overstory trees) and initiates succession or regrowth. National Wildfire Coordinating Group, Incident 

Operations Standards Working Team. 1996. Glossary of wildland fire terminology. PMS 205/NFES 1832. 

Boise, ID: National Interagency Fire Center, National Fire and Aviation Support Group, Training Standards 

Team.
16

Certain methods presented in this section do assess the presence of Firewise treatments 

collectively but this is not intended to be an analysis of the combined effectiveness of 

Firewise treatments. The precise integration and accurate analysis of the data collected 

and produced in this report to determine the factor or, more likely, the set of factors under 

various scenarios that result in a structure’s increased risk of ignition from wildland fire 

or embers is a complex process. A future report will attempt to address the feasibility of 

conducting such a task given the available data using various models (e.g. GIS, Logistic 

Regression, Fire Behavior Models) for demonstration. Nonetheless, an examination of 

the treatments presented below has been invaluable in the development of the NIST WUI 

Assessment System deployed at the Tanglewood Complex Fire (Amarillo, Texas 2011) 

and can be used to provide insight into the data in terms of data collection methodology 

for future post-fire assessments. More importantly, the NIST data collection 

methodology utilized in this report does facilitate the analysis of the Firewise treatments 

evaluated for this study, even if at a specific type of treatment level. The overall analysis 

framework for the assessment of the effectiveness of Firewise treatments is presented in 

Figure 15.

5.3.1 Firewise Applicability 

Assessing the effectiveness of individual Firewise treatments generally provides an 

indication of the applicability of the respective treatment. Certain treatments, however, 

might be exceptions. For example, recommending vegetation irrigation as a treatment 

might not be applicable in a desert regardless of the effectiveness of the treatment. 

Beyond this, a qualitative assessment of the applicability of the Firewise Zone Concept at 

the Trails is also conducted. This assessment involves cartographically displaying two 

different interpretations of the Firewise Zone Concept at the Trails in conjunction with 

residential structure damage. One interpretation of the Firewise Zone Concept involves 

community cooperation in implementing the landscape design principals portrayed in the 

Firewise Landscaping Checklist and is the approach recommended by the Firewise 

Program. The second approach involves individual landowners treating only their 

properties, regardless of their neighbor’s property condition and hazards; following the 

principals portrayed in the Firewise Landscaping Checklist. While this second approach 

is not recommended by Firewise explicitly a different approach is not presented for 

situations where community cooperation is not occurring. Consequently, even though 

data was lacking to completely assess the Firewise Zone Concept this qualitative 

assessment might provide insight on the appropriateness of the different implementation 

methods. 

5.3.2 Firewise Presence

After evaluation of the applicability of the Firewise treatments, an assessment of several 

general concepts portrayed in the Firewise Checklists is conducted. The presence of 

native or wildland vegetation across the Trails was assessed as well as general analyses of 

slope and aspect on Trails properties. Cartographic display of the various delineations 

conducted in the vegetation data set also help to portray the presence of various 

vegetation treatments across the Trails. Finally, the overall presence of assessed Firewise 

treatments is examined. There are, however, numerous Firewise treatments not assessed 

in this report such as the type of window present. These treatments were not assessed due 

to difficulties associated with collecting reliable field data. 
17

5.3.3 Firewise Effectiveness (Individual Treatments)

The effectiveness of assessed Firewise treatments is first analyzed using two-way 

contingency tables individually for each treatment. This type of analysis was standard 

when analysis of categorical data with more than one variable is being conducted. Each 

of the Firewise treatments assessed either had the respective treatment present on the 

property (i.e. pass) or absent on the property (i.e. fail). Properties where the respective 

treatment could not be determined or was not applicable were not included as part of the 

population examined. In this case, two-way contingency tables allow for the display of 

the frequency of the categorical data classified by the presence/absence of the treatment 

and the structure response to the Witch and Guejito Fires. Using the Chi-square test of 

independence the following hypotheses was tested for all assessed Firewise treatments 

with adequate response frequencies of n≥20.

Ho (null hypothesis): Properties in the Trails at Rancho Bernardo Community have 

no association between implementation of the respective Firewise Treatment and 

damage to the property’s primary structure from the 2007 Witch and Guejitio Fires.

Ha (alternative hypothesis): Properties in the Trails at Rancho Bernardo 

Community have an association between implementation of the respective Firewise 

Treatment and damage to the property’s primary structure from the 2007 Witch and 

Guejitio Fires.

Significant codes for p-values produced by the respective Chi-Square test are: p value < 

0.001 (***), p-value < 0.01 (**), and p-value < 0.05 (*). Some Firewise treatments could 

not be assessed due to their limited presence (low frequencies). It should also be

reiterated that this analysis, due to low sample numbers, does not account for the 

interdependence between treatments that is implied in the Firewise Checklist. 

5.3.4 Exposure Determinations

The contingency table analyses and Chi-Square tests described above examine all 

structures collectively that were determined to be within the combined perimeters of the 

Witch and Guejito Fires and found within the Trails Community. Traditional methods of 

quantifying exposure for post-fire assessments typically rely on assessing only the 

properties containing wildfire destroyed primary structures (USDA 2008 17). It is less 

common for WUI post-fire assessments to examine all structures within the fire 

perimeter, with some exceptions as evidenced by the Australian bushfires of 200918. 

Accurate assessment of the effectiveness of WUI treatment guidance might, however, 

require a more precise quantification of exposure to better understand potential structure 

vulnerabilities and ignition mechanisms. Exposure in this paper is defined as the fire and 

ember assault at a particular location in space and time. The concept of exposure 

discussed in this paper should be independent of the structure construction and ignition 

vulnerabilities. It is necessary to uncouple the exposure from the ignition vulnerabilities 

in order to effectively assess vulnerabilities under similar exposure conditions. This 

applies to both vegetative and structural ignitions. Ideally, the exposure measured for 

WUI post-fire assessments should be the sum of the fire and ember exposures over time. 

Coarse scale assessment of the spatial extent of ember exposures were conducted in this 

study based on various written and verbal discussions with homeowners and first 

responders. These assessments aided in characterizing properties as inside or outside the 
18

fire perimeter, but the fine scale variation that might have had consequences for structure 

response to the Fires was not conducted in terms of mapping embers and burned features 

across the study area. For example, while ember exposure in certain locations in the 

Trails on the edge of the fire perimeter might have been “significant”, the ember 

exposure in these areas was likely much less extreme compared to properties directly 

adjacent to wildlands on aspects facing the oncoming fires containing Manzanita. 

Consequently, the direct measurement of the sum of the fire exposures over time across 

the Trails could not be conducted in this study. Instead, two exposure methods were

examined that build on the results presented in NIST TN1635 and help to provide insight 

into quantifying exposure in a post-fire WUI environment when the precise measurement 

of the sum of the fire and ember exposures over time is not possible. Section 5.3.5 

contains a complete description of the exposure methods, while section 6.3 covers 

exposure determination and section 7.5 the exposure data analysis.

The first exposure method uses the concept of “perimeter” properties as detailed in NIST 

TN1635. This method defines “perimeter” properties as those that had a portion of their 

property boundary adjacent to wildlandsxiii, which might continue onto the respective 

property. The rationale behind this approach is that at the Trails, where the interface with 

the burning wildlands was often well defined, these structures, which occurred on the 

eastern, northern and western portions of the community, received a stronger assault from 

the wildland fire than structures on the southern and interior portions of the community. 

The approach, while simply implementable at the Trails may be harder to implement in 

other communities. Nonetheless, the approach is strongly supported by personal 

observations on fire intensity collected across the Trails. 

Due to the possible site specific nature of the first method, a second method is examined 

that combines high-resolution vegetation and topographic data to delineate the Trails into 

areas of high and low hazard areas as a potential surrogate for actual exposure. The 

second method begins by classifying slope and aspect grids into hazardous areas. This 

type of categorization is also likely site specific (fuels, topography and weather). 

Appropriate thresholds or categorizations were determined by examining the results of 

the general assessment of slope and aspect conducted when examining the structural 

response to the Witch and Guejito fires. Next, areas that meet the threshold for both the 

slope and aspect grids, as determined as described above, will be extracted. Slope and 

aspect were derived from 1.5 meter horizontal resolution DEM. These areas of 

potentially high hazard slope and aspect were used to clip out portions of the vegetation 

data set produced as described in Section 5.2 to create the high hazard data set. 

The theory behind this simple combination of data is displayed in the Fire Triangle where 

air heat and fuel and necessary for combustion. Areas of high slope (topography) on 

appropriate aspects facing the local wind (weather) with vegetation (fuels) might have 

high potential for conditions that could result in high exposure to structures at certain 

distances (i.e., high hazard areas). Conversely, areas with low slopes on sheltered aspects 

with no vegetation might result in low exposure to structures at certain distances (i.e., low 

hazard areas). The high hazard area criteria can be summarized in equation 1 below.

High hazard results from the combination of steep slope plus dangerous aspect plus 

vegetative fuel.

 xiii Wildlands defined in this study differ from those described in NIST TN1635, which did not include 

occluded wildlands found in the interior of the Trails.
19

High Hazard = (Slopes > Threshold) AND (Aspect =Thresholds) AND (Vegetative Fuel)

Equation 1

The validity of both exposure techniques are examined in terms of structure response to 

the Witch and Guejito Fires. For method 1, percent damage and destruction can be 

examined for both the “perimeter” (surrogate for high exposure) and “interior” (surrogate 

for low exposure) populations. Method 2 can be evaluated in a similar manner but more 

detailed characterization can be conducted. Examination of method 2 was conducted by 

determining the percentage of high hazard area present in the down fire direction of each 

residential structure at distances of 0 m to 9 m (0 ft to 30 ft), 0 m to 30 m (0 ft to 100 ft), 

0 m to 61 m (0 ft to 200 ft) and 0 m to 91 m (0 ft to 300 ft) from the structure edge. The 

down fire direction was manually assigned to each building footprint based on field 

observations made around destroyed structures. The remainder of the structures used a 

down fire direction opposite that of the prevailing wind (i.e., northeast). An example of 

this analysis for a single destroyed structure is shown in Figure 16. The sectors 

illustrated in Figure 16 point upwind. For each of the directional sector distances 

employed above, the percentage of high hazard area with respect to the whole area 

available in the respective sector was tabulated. Thresholds were then employed to each 

structure categorizing the potential exposure to high and low hazard areas, which were

used here as surrogates for high and low exposure. 

5.3.5 Firewise Effectiveness (Two Exposure Methods)

Firewise treatments will next be re-evaluated in the context of two different surrogates 

for exposure delineated at the Trails. This re-evaluation is conducted to determine if 

there is a difference in the effectiveness of the respective Firewise treatment in high or 

low exposed areas. For “perimeter” and “interior” classified properties the following 

hypotheses are tested:

Ho (null hypothesis): Properties in the Trails at Rancho Bernardo Community have 

no association between implementation of the respective Firewise Treatment coupled 

with perimeter/interior designations and damage to the property’s primary structure 

from the 2007 Witch and Guejitio Fires.

Ha (alternative hypothesis): Properties in the Trails at Rancho Bernardo 

Community have an association between implementation of the respective Firewise 

Treatment coupled with perimeter/interior designations and damage to the property’s 

primary structure from the 2007 Witch and Guejitio Fires.

For residential structures classified as high or low exposure using the high hazard method 

discussed above the following hypotheses are tested.

Ho (null hypothesis): Properties in the Trails at Rancho Bernardo Community have 

no association between implementation of the respective Firewise Treatment coupled 

with high/low hazard area designations and damage to the property’s primary 

structure from the 2007 Witch and Guejitio Fires.

Ha (alternative hypothesis): Properties in the Trails at Rancho Bernardo 

Community have an association between implementation of the respective Firewise 

Treatment coupled with high/low hazard area designations and damage to the 

property’s primary structure from the 2007 Witch and Guejitio Fires.
20

The hypotheses are tested by fitting a logistic regression with dependent variable 

structure response (i.e., undamaged and damaged/destroyed) and independent variables of 

the respective Firewise treatment and the exposure designation (i.e., “perimeter” versus 

“interior” or high versus low hazard area). The statistical tests are done using the Zstatistic computed on the coefficients of the regression model. To further demonstrate the 

effect of the respective Firewise treatment and exposure delineations on structure 

response three-way contingency tables (Section 7.5) showing the frequencies of Firewise 

treatments by burn status grouped by the respective exposure surrogate category 

(perimeter/interior; high/low hazard area) will be created. Percent values are also 

provided in these contingency tables to further illustrate the effect of the treatment. 

These table are created to help demonstrate the effect of a Firewise treatment and 

exposure designation on the structure response to the Witch and Guejito Fires. 

5.3.6 Defensive Actions

Including defensive actions in the above analysis might be a key to determining WUI 

mitigation effectiveness. Defensive actions are accounted for in the above analyses by 

grouping the damaged structures with destroyed. Fifteen of the 16 damaged structures 

were defended (and it is possible that San Diego Police defended the 16th house). It was, 

therefore, assumed that these damaged structures would have been destroyed without the 

defensive actions. There are likely cases where structure ignitions go out on their own 

but this is believed to be relatively rare. There was also one structure for which the first 

responders indicated that without their action this structure would have been destroyed. 

Ideally, this structure should also be included in the damaged/destroyed population; 

however, the authors could not confirm the effectiveness of the defensive action in this 

case. Other defensive actions involved some action on the property that could not always 

be determined and the effectiveness could not be evaluated. Due to this fact it was 

difficult to analyze defensive actions using the statistical methods described above. 

Instead, defensive actions will be used to examine ignition mechanisms in damaged 

structures; thereby providing clues as to the effectiveness of certain WUI treatments. 

Future studies might allow for the recording of defensive actions with the associated 

feature on which the action was taken; thereby facilitating the quantification of defensive 

actions at a higher resolution and, possibly, accounting for these actions in similar 

methods to those used for exposure. Also, an assessment of the location of potentially 

effective defensive actions is conducted in context of high/low hazard area. For this 

assessment structures that were listed as “contained” or “overhauled” were not included

as the action was not to protect the structure, but instead to mop-up the already burned 

structure.

6.0 Data Collection, Production and Analysis Limitations

WUI post-fire assessments present unique challenges in regards to data collection and 

analysis. Additionally, many of the data production techniques employed in this study on 

various geospatial data sources have limitations and shortcomings. The techniques used 

to delineate exposure across the Trails landscape also have limitations. Finally, the 

analysis procedures employed might suffer from limitations. Consequently, before 

presenting results of the analysis methods described above it is important to list 

limitations present in the various data products collected, produced and analyzed in this 

study in order to have a context for discussing and developing conclusions about the data. 
21

This section discusses these limitations for field data collection, data production, 

exposure delineation and analysis. 

6.1 Field Data Collection

Immediate assessment of the community after the fire is required for post-fire WUI field 

data collection because site corruption and data loss occurs soon after the fire due to 

reclamation/recovery efforts. Budget constraints only allowed for properties with 

destroyed primary structures in the Trails to be assessed immediately following the fire

and some of these had properties cleared before they could be assessed. Certain features 

in a fire damaged environment are also completely consumed leaving little evidence of 

what might have been there before the fire. Other limitations present in the NIST field 

data collection are as follows:

• lack of access to certain properties;

• lack of knowledge of property boundaries, for some treatments, to indicate to 

observers the extent of the property to be assessed; 

• inability to identify construction materials both on the ground and from images 

(e.g. material such as cement fiber board and others sometimes require touching 

to determine the material type);

• broad analysis of construction materials with more specific assessments lacking;

• incomplete mapping of burned features across the landscape; and

• inconsistencies between data collection and analysis of destroyed and nondestroyed structures.

The direct assessment of the Firewise checklist also presented problems. For instance the 

Firewise Checklists in their original form might have been interpreted differently 

compared to the Firewise treatments shown in Table 2. Additionally, even when viewed 

in its entirety, the Firewise checklist could be interpreted differently by different

observers. In short, the Firewise checklists are very difficult to interpret, in terms of 

effectiveness, in a scientific manner. This, however, might not be any reflection on the 

actual interpretation of these checklists for performance of WUI mitigation activities by 

builders and homeowners, which is not assessed in this paper. It is also important to note 

the potential bias present on properties with significant fire behavior. There is possibly a 

tendency, although not confirmed in this study, to fail a property for the presence of a 

particular treatment when there is significant fire damage, even if the treatment was 

present prior to the fire. 

In this study, some observers of undamaged properties did not have access to the entire 

property due to locked gates or other obstacles. More common was misinterpretation of 

the actual property boundary. For instance, one observer indicated that the property was 

“cleared to property line (100 ft)” as a comment for treatment 4 (i.e., Firewise Zone 4) 

This comment illustrates both the confusion regarding appropriate distances to use for 

Firewise zones as well as the issue with observers not having property boundaries. In this 

case the observer interpreted the property boundary to not extend past 100 ft from the 

structure as this is where the treatment ended. The property boundary, however, 

extended far past 100 ft and this portion of the property did not seem to be assessed. Due 

to the lack of property boundaries, care must be taken in interpretation of the presence of 

Firewise treatments 6, 7, 8 and 9 which correspond to vegetation treatments for the whole 
22

property. Ratings for these treatments might not reflect wildlands contained on the 

respective property in some cases. 

Inconsistent interpretation amongst observers regarding the Firewise Zone Concept was 

also a limitation. The Firewise checklists used in this report do not provide a distance for 

each zone except zone 1. Other Firewise literature lists zone 1 as 0 m to 9 m (0 ft to 30 

ft), zone 2 as 9 m to 30 m (30 ft to 100 ft), and zone 3 as 30 m to 61 m (100 ft to 200 ft)12. 

Firewise literature seems to indicate zone 4 extending from 200 ft to the end of the 

property when this zone is referenced at all. The exact distances used by observers for 

zones 2 thru 4 are not known. Additionally, the observer determining the presence of 

Firewise zone treatments for destroyed homes responded with a N/A when there was not 

sufficient space around the entire structure to encompass the respective zone. Not all 

observers for properties with undamaged structures interpreted the zone treatments in this 

manner but some did. Additionally, some observers of the undamaged structure 

population appeared to use different distances than those listed above and might have 

interpreted the zones as a relative measure with respect to their estimation of the 

particular property boundary. The discrepancy among different observers led to the 

inability to fully evaluate all Firewise zone treatments.

6.2 Data Production

The digital data also had certain limitations. Light Detection and Ranging (LIDAR) data 

contains high-resolution elevation data that allows for precise and high spatial resolution 

delineations of topography, man-made features and vegetation. This LIDAR data was 

examined for flight overlap issues and the LIDAR data within the extent of the study area 

was deemed acceptable. LIDAR data cannot, however, see through solid objects such as 

leaves and accurate assessment of vegetation under-story is lacking in the data products 

produced for this study, which might have consequences for accurate high/low hazard 

area delineations. For example, polygons delineated as Coast Live Oak Woodlandxiv

might have extreme differences in under-story vegetation cover where certain vegetation 

polygons might have had little flame or ember contribution yet were listed as high hazard 

areas. Additionally, LIDAR data can suffer from occlusions due to flight geometry that 

cause certain features to be missed. Both the building and vegetation data sets were 

manually corrected for these errors, when observed. DEM and derivative products 

produced from this study also suffer from occlusions in densely vegetated areas where 

the laser pulse could not reach the ground in large quantities. This could have 

consequences for underestimation or over-estimation of slopes and over generalization of 

aspects used in this study. Regardless of the above, the LIDAR data represented the best 

available topographic, building and vegetation structural stage data for the study area.

Multi-spectral imagery utilized in this project suffered from the inability to portray 

changes in the landscape between the time of pre-fire imagery and the 2007 Witch and 

Guejito Fires (the most recent pre-fire imagery for the Trails is from the Spring of 2006). 

The post-fire imagery also did not have the ability to see through solid objects and, 

consequently, locations with burned under-story vegetation and green over-story 

vegetation could not be identified. The sensors used to derive the dNDVI data product 

were not calibrated making quantitative change detection difficult. The dNDVI data 

product also has issues with shadows where certain areas might be falsely portrayed as 

 xiv Technical discussions have indicated extensive ember generation from ground litter under the Coast Live 

Oak Woodland fuel in the northern boundary of the Trails community.
23

being less green in the post-fire scenario. These areas are particularly prevalent along 

taller hedge rows. The dNDVI data product was only used for visual data exploration 

and to give the reader an idea of the extent of burned top of the layer vegetation.

It should also be noted that the wildland vegetation mapped in this paper represents an 

underestimation, in terms of flammability, of the vegetation species found within the 

Trails. A better distinction would be flammable versus non-flammable vegetation. IN 

terms of quantifying the underestimation, the two extremes are on one end that none of 

the residential vegetation is flammable and at the other end that all residential vegetation 

is non-flammable. The authors could not make this distinction based on available pre-fire 

data across the entire study area and the budget did not allow for the delineation of 

burned vegetation. Instead the categories of wildland and residential vegetation are used 

as a conservative surrogate for vegetation flammability. When there was difficulty in 

determining the precise line of demarcation between wildland and residential vegetation, 

the vegetation was classified as wildland only when there was evidence of fire behavior 

continuing from the adjacent known wildland polygons into the unknown vegetation 

polygons. If fire continued from the wildlands into clearly demarcated residential 

vegetation this line of demarcation would be represented in the final wildland versus 

residential vegetation categorization. 

6.3 Exposure Determinations

The exposure methods used both have the same limitation in that neither directly 

measures the integral of the fire and ember exposures over time. Additionally, the 

“perimeter/interior” method does not account for areas on the perimeter where wildland 

fuel was limited, such as the knoll at the north east corner of the Trails where the rock 

outcrop significantly reduced the fire intensity due to the reduced wildland fuel loading. 

Secondly the perimeter/interior approach does not address the intrusion of wildland fuels 

into the community and the method does not account for the additional exposure threat 

generated by burning vegetation and structures within the community. The method also 

does not account for changes in exposure caused by topography. Having listed the 

limitations, the approach is strongly supported by observations on fire intensity collected 

across the community. 

The second method does quantify certain aspects of fuel quantity in that fire barriers such 

as rock outcrops are not included, it still does not capture vegetation treatment, and 

structural stage or material properties of vegetation that might have had consequences for 

actual exposure. Additionally, this method does account for vegetative fuels (present or 

absent) in the interior of the community. Finally, the second method does, in a coarse 

manner, account for changes in exposure caused by topography. Nonetheless, this 

exposure method still contains additional limitations as follows, all of which are 

limitations of method 1 as well:

1. The method does not account for changes in fire behavior caused by smaller scale 

changes in wind (e.g. swirling wind) and topography (e.g. ravines).

2. The method does not account for vegetation quantity and quality (e.g. water 

content, crown bulk density, ignitability and other vegetation properties).

3. The method does not account for the heat and ember release from different 

vegetation types. 
24

4. The method does not account for the fact that low hazard areas directly adjacent 

to high hazard areas will continue to burn if fuel is present (i.e., fuel connectivity 

is not considered) regardless of slope or aspect.

5. The method does not account for the exposure from burning structures and other 

man-made features. There is evidence, though not studied in this paper that the 

burning of structures significantly contributed to the spread of fire within the 

Trails. This information, primarily in the form of visual observations, was 

collected both from first responders and residents. 

Other limitations are also likely present in each method.xv

6.4 Data Analysis Limitations

The post-fire analysis conducted in this paper suffers from a lack of sample populations 

for some treatments and as a result lacks the statistical analysis of some treatments. This 

is demonstrated in Table 6 showing the frequency counts of not applicable (N/A) and not 

determined (N/D) responses for Trails properties by Firewise treatments. Treatments 

with N/A values are not included as part of the population being analyzed and should not 

be considered missing. Treatments with N/D values, however, are missing from the 

population and it is important to determine if these values are missing at random. First, it 

can be seen from Table 6 that treatments with N/D values tend to be damaged or 

destroyed, with the exception of Firewise treatments 10, 18, 20, and 21. Firewise 

treatments 10 and 18 likely have a large number missing that were not damaged or 

destroyed because a distance was not originally provided in the field data collection sheet 

for firewood to be stored away from a structure or fence and during the normalization 

process, the location of firewood could not always be determined. Nonetheless, due to 

large numbers of missing values for Firewise treatments 10, 18, 20, 21 and 22, the results 

of the statistical analyses might not be valid and should be viewed with caution. 

Furthermore, 10 and 18 show discrepancies between the N/D values. The reason(s) for 

these discrepancies are not known. 

Additionally, certain analyses aggregate data at the parcel level. The parcel is a logical 

unit of analysis in many cases because the WUI problem is a land use problem at some 

level, and should be studied at the land use level (i.e., individual owner and hence the 

parcel) but other land units should also be explored such as watershed boundaries. The 

parcel level of aggregation, however, might not always be appropriate. For example, 

average values of slope and aspect at the parcel level might not reflect smaller scale 

changes in topography present on the parcel. Finally, the inability to analyze treatments 

collectively presents major short comings in regard to analysis of the Firewise treatments 

because Firewise is meant to be implemented in its entirety, not just selected treatments. 

xvi

 

xv As this is the first study attempting to quantify exposure in a post-fire environment, it was felt that these 

simplified approaches represented a good starting point. More quantitative assessments might be 

considered in future research.

xvi Collective analysis of hazard mitigation technologies will be explored in future research.
25

7.0 Results

This section contains results of the analyses conducted in this study. Before examining 

the effectiveness of Firewise treatments, this section provides an assessment of the 

applicability of the Firewise Zone Concept as applied to residential properties in the 

Trails. An assessment of the overall presence of Firewise treatments is also conducted. 

Next, all 242 residential structures found in the Trails and within the Witch and Guejito 

Fire perimeters are analyzed for effectiveness of Firewise treatments at an individual 

level. Then, assessments of the validity of the two exposure methods at the Trails will be 

presented allowing for analysis of individual Firewise treatments in conjunction with the 

two exposure methods. The identification of ignition mechanisms is assessed in context 

of Firewise treatments and defensive actions. Finally, the locations of defensive actions 

in terms of exposure will also be examined. 

7.1 Applicability of Firewise at the Trails (Zone Concept)

Ideal implementation of the Firewise Zone Concept 12 (assuming the distances listed 

below), particularly in zones two through four (Table 2), would not have been possible 

throughout the Trails without cooperation among land owners. The size and spatial 

arrangement of residential properties would result in the inability of property owners to 

implement each Firewise zone in all directions without overlap from neighbors. The 

ideal implementation of the Firewise Zone Concept for the Trails is shown in Figure 17. 

In this implementation the zone of lowest number takes precedence in landscape design 

considerations. There was no evidence that this type of inter-community cooperation 

took place within the Trails based on visual examination of pre- and post-fire aerial 

imagery and discussions with the Trails HOA. The Firewise Communities program 

recognizes the hazard an untreated property can have on a nearby property and lists a key 

component of the Firewise Zone Concept as community cooperation.ix The Firewise 

Checklists could, however, be interpreted by a homeowner or builder as not requiring 

Table 6 Counts of properties with N/A and N/D values by treatment with percentage of 

residential structures destroyed by N/A and N/D.

Treatment 

Number

Count 

Total 

N/A

Count 

Total 

N/D

Total 

N/A & 

N/D

Percent 

Damaged/

Destroyed 

(N/A)

Percent 

Damaged/

Destroyed 

(N/D)

Percent 

of Total 

NA & 

N/D

1A 0 10 10 - 80% 4%

1C 0 9 9 - 100% 4%

6 1 15 16 0% 73% 7%

7 3 11 14 33% 91% 6%

8 2 12 14 0% 83% 6%

9 1 18 19 0% 78% 8%

10 86 56 142 12 27% 59%

11 0 0 0 - - 0%

12 98 8 106 7% 100% 44%

13 0 7 7 - 100% 3%

14 0 0 0 - - 0%

15 0 7 7 - 100% 3%

17 2 16 18 0% 94% 7%

18 86 47 133 12% 21% 55%

19 45 14 59 0% 79% 24%

20 116 37 153 49% 49% 63%

21 129 32 161 38% 44% 67%

22 160 25 185 32% 60% 76%
26

cooperation with neighbors. This property centric approach to landscape design is shown 

in Figure 18. In this approach, the Firewise Zone Concept is implemented only on the 

space available on the individual landowner’s property. Figure 18 does not include rights 

of way, which are not delineated in the property boundary data set. The zone distances 

used in Figure 17 and Figure 18 are as follows: zone 1 as 0 m to 9 m (0 ft to 30 ft), zone 

2 as 9 m to 30 m (30 ft to 100 ft), and zone 3 as 30 m to 61 m (100 ft to 200 ft) and zone 

4 is 61m to 91m (200 ft to 300 ft)

xvii. 

A visual examination of Figure 17 and Figure 18 shows that the ideal implementation has 

less area in the interior of the Trails in zone 4 compared to the property centric approach. 

Additionally, the property centric approach of the Firewise Zone Concept sometimes 

results in zones 1 or 2 abutting a zone 4 or a wildland property but the ideal 

implementation of the Firewise Zone Concept does not create these potentially hazardous 

areas in the Trails. Nonetheless, islands of less treated vegetative fuels are created in 

both implementations of the Firewise Zone Concept. Additionally, implementation in 

either manner will result in paths of less treated vegetative fuels (i.e., zone 3 and zone 4) 

in and around the Trails. These islands of less treated vegetative fuels might have aided 

in spreading the fire within interior portions of the Trails. This is evidenced by the fact 

that 15 of the 21 fire jumps identified in TN1635 had a zone 3 or 4 involved in the fire 

jump as shown in Table 7. Twelve of these 15 fire jumps had a destroyed structure in the 

down fire direction of the jump. When both zones and structures are listed in Table 7 it is 

not clear exactly which feature contributed fire spread to which other feature, just that 

there was evidence of burning in both features. The relationship between Firewise Zones 

3 and 4 and the dNDVI data set (surrogate for burned vegetation) is shown in Figure 19. 

 xvii Even though Firewise literature indicates zone 4 extending to the end of the property, 300 feet is used in 

this analysis so that the effect of larger parcels is not exaggerated in the analysis.

Table 7 Descriptions of 21 fire jump locations identified in the Trails.

Fire Jump From Location Fire Jump To Location

Zone 3 Destroyed Structure

Zone 1, 2 Zone 3, 4 and Destroyed Structure

Zone 3 Occluded Wildlands (Continuous Path to Destroyed 

Structure)

Zone 1, 2 and Destroyed Structure Zone 3, 4 and Destroyed Structure

Zone 3, 4 Zone 3

Zone 3, Destroyed Structure Zone 1 

Zone 4 Zone 4

Zone 3 Zone 3 and Destroyed Structure

Zone 1, Destroyed Structure Zone 3 and Destroyed Structure

Zone 1, 2 Zone 1, 2 and Destroyed Structure

Zone 1 and Destroyed Structure Zone 1, 2

Zone 1 and Destroyed Structure Zone 1, 2

Zone 1 and Destroyed Structure Zone 1, 2 and Destroyed Structure

Zone 1 Zone 1, 2, 3

Destroyed Building Zone 3, 4 and Destroyed Structure

Zone 3, 4 Zone 3, 4 and Destroyed Structure

Zone 3 Zone 3 and Destroyed Structure

Zone 3 Zone 3 and Destroyed Structure

Zone 3 and Destroyed Structure Zone 3

Zone 1, 2 and Destroyed Structure Zone 1, 2 and Destroyed Structure

Zone 3 Zone 1,2 and Destroyed Structure
27

7.2 Presence of Firewise Treatments at the Trails

In addition to the specific mitigation activities present in the Firewise Checklists, various 

overall items to consider when designing and installing a Firewise landscape are 

presented in the checklist to be:

• Local area fire history.

• Site location and overall terrain.

• Prevailing winds and seasonal weather.

• Property contours and boundaries.

• Native vegetation.

• Plant characteristics and placement (duffage, water and salt retention ability, 

aromatic oils, fuel load per area and size).

• Irrigation requirements.

No assessment was done of specific residential plant characteristics throughout the Trails. 

However, as detailed below, about 60% of the properties in the Trails were found to be 

well irrigated for at least 9 m (30 ft) around the entire primary structure.

Native vegetation was also assessed across the Trails, but the distinction in this paper 

between wildland and residential vegetation is in some cases an arbitrary one in terms of 

plant flammability and ignitability. That is to say that fire in many cases continued 

uninterrupted from the wildlands into residential vegetation. The use of the LIDAR 

derived vegetation data set, however, can help to determine the presence of native 

vegetation in Firewise zones. Figure 20 shows the frequency counts of properties by bins 

of percent wildland vegetation grouped by all residential structures, residential structures 

with no damage, and residential structures that were damaged or destroyed for all four 

Firewise zones. Figure 20 uses the property centric Firewise Zones.

A visual assessment of overall vegetation placement by structural stage in the interior of 

the Trails is portrayed in Figure 10, originally presented in section 5.2. The extensive 

nature of this residential non-ground vegetation shown in Figure 10 displays the 

culmination of landscape design practices implemented at the Trails prior to the Fires. 

The result was numerous paths of connected above ground vegetation between the 

wildlands and residential vegetation, often only broken by roads or driveways. Also 

shown in Figure 10 are the many vegetation corridors found along property boundaries 

representing hedge rows or privacy barriers. 

A coarse assessment of slope and aspect on Trails properties within the fire perimeter was 

also conducted to ascertain if topographic considerations were taken into account when 

designing and installing landscapes and structures in the Trails. Figure 12 and Figure 13

display slope and aspect grids derived from the 1.5 m (5 ft) Digital Elevation Model 

(DEM) for the Trails community. The slope grid displayed in Figure 12 was used with 

the ArcGIS Zonal command to derive an average slope value for each property lot. A 

histogram displaying the distributions of average property slope across the Trails for 

damaged and destroyed structures, undamaged structures and all structures within the fire 

perimeter is shown in Figure 21. Taking the average aspect of a parcel, however, is not 

necessarily logical when grid values are stored as directions (values between 0° and 359°

degrees). For example, the average of 359° and 1° is 180°, which would result in an 

illogical value. In order to account for this in a simplified manner, the aspect grid was 
28

reclassified to categorical values displayed in Figure 13, representing the 8 cardinal 

directions. For each property in the Trails, the majority of pixels in the lot representing 

one of the 8 cardinal and intercardinal directions were determined using the ArcGIS

Zonal command. A histogram displaying the distributions of these data is shown in 

Figure 22. 

An overall assessment of the presence of Firewise treatments analyzed in this report is 

provided in Figure 23 showing frequency counts of properties by bins of percent of 

Firewise treatments present on the property. The data for Figure 23 has excluded from 

the population ten properties that were greater than 50% of the evaluated Firewise 

treatmentsand could not be assessed. All but one of these ten properties contained a 

damaged or destroyed primary structure. Finally, it is important to note that not all 

Firewise treatments were assessed in this analysis. 

7.3 Firewise Effectiveness (Individual Treatments)

This section presents the results for the evaluation of the individual Firewise treatments 

assessed in this study for their effectiveness in reducing damage or destruction to primary 

structures on residential properties in the Trails. Table 8 through Table 14 show two-way 

contingency tables and results of the Chi-Square tests for independence between Firewise 

treatment and structure response for those treatments determined to be statistically 

significant at a p-value of 0.05 or lower (see section 5.3.3). For each of the treatments, 

the null hypothesis presented in 5.3.3 is rejected indicating that Properties in the Trails at 

Rancho Bernardo Community have an association between implementation of the 

FIREWISE Treatments listed in Table 8 through Table 14 and damage to the property’s 

primary structure from the 2007 Witch and Guejito Fires. All of the individually 

tabulated attributes listed in Table 8 through Table 14 are statistically significant at a pvalue of 0.001 except Firewise treatment 8, which is statistically significant at a p-value 

of 0.01 and Firewise treatment 13 which is statistically significant at a p-value of 0.05. 

xviii

Table 8 Treatment 1a contingency table with results of Chi-Square test. Treatment 1a is present 

(pass) if an irrigated area encircles the structure for 9 m (30 ft) feet on all sides.

Undamaged

Structures

Damaged/ Destroyed

Structures

Total

Fail 35 (39% ± 10%)

xix 53 (61% ± 10%) 88

Pass 115 (80% ± 7%) 29 (20% ± 7%) 144

Total 150 82 232

p-value = 0.0000 (***)

 xviii The Z-statistic is used to assess the relationship between burn status and various independent variables in a logistic 

regression. The p-value is the probability of getting a Z-score of this particular magnitude or larger (in absolute value), 

simply by chance. A p-value of 0.05 or smaller means that the effect being observed is likely real and not chance 

variation

xix See section 5.3.3 for explanation of uncertainty
29

Table 9 Treatment 7 contingency table with results of Chi-Square test. Treatment 7 is present (pass) 

if fuel breaks like driveways, gravel walkways and lawns are present.

Undamaged

Structures

Damaged/ Destroyed

Structures

Total

Fail 59 (49% ± 9%) 61 (51% ± 9%) 120

Pass 90 (83% ± 7%) 18 (17% ± 7%) 108

Total 149 79 228

p-value = 0.0000 (***)

Table 10 Treatment 8 contingency table with results of Chi-Square test. Treatment 8 is present 

(pass) if vegetation on the property is pruned to 6 to 10 feet from the ground.

Undamaged

Structures

Damaged/ Destroyed

Structures

Total

Fail 106 (60% ± 7%) 71 (40% ± 7%) 177

Pass 42 (82% ± 10%) 9 (18% ± 10%) 51

Total 148 80 228

p-value = 0.003 (**)

Table 11 Treatment 9 contingency table with results of Chi-Square test. Treatment 9 is present 

(pass) if leaf clutter and dead and overhanging branches are removed from the property.

Undamaged

Structures

Damaged/ Destroyed

Structures

Total

Fail 61 (51% ± 9%) 58 (49% ± 9%) 119

Pass 86 (83% ± 7%) 18 (17% ± 7%) 104

Total 147 76 223

p-value = 0.0000 (***)

Table 12 Treatment 13 contingency table with results of Chi-Square test. Treatment 13 is present 

(pass) if there is no wood roof, wood siding, wood eave, wood deck, wood pergola, wood fence or 

wood pile on the property.

Undamaged

Structures

Damaged/ Destroyed

Structures

Total

Fail 133(62% ± 6%) 80 (38% ± 6%) 213

Pass 19(86% ± 14%) 3 (14% ± 14%) 22

Total 152 83 235

p-value = 0.025 (*)

Table 13 Treatment 17 contingency table with results of Chi-Square test. Treatment 17 is present 

(pass) if there dead wood and dense vegetation is cleared at least 30 feet from the house.

Undamaged

Structures

Damaged/ Destroyed

Structures

Total

Fail 76(53% ± 8%) 66 (47% ± 8%) 142

Pass 73 (89% ± 7%) 9 (11% ± 7%) 82

Total 149 75 224

p-value = 0.0000 (***)
30

Table 14 Treatment 19 contingency table with results of Chi-Square test. Treatment 19 is present 

(pass) if there is no wood fence attached to the house.

Undamaged

Structures

Damaged/ Destroyed

Structures

Total

Fail 51(45% ± 9%) 62 (55% ± 9%) 113

Pass 98 (85% ± 7%) 17 (15% ± 7%) 115

Total 149 79 228

p-value = 0.0000 (***)

For treatments 1C, 6, 11, 15, 18, 20, 21 and 22 the null hypothesis presented in section 

5.3.3 is not rejected indicating that there is no evidence that Properties in the Trails at 

Rancho Bernardo Community have an association between implementation of the 

respective FIREWISE Treatment and damage to the property’s primary structure from 

the 2007 Witch and Guejitio Fires for Firewise treatments 1C, 6, 11, 15, 18, 20 and 22. 

It should be pointed out; however, that Firewise treatments 18, 20, 21 and 22 had 

numerous properties where the presence of the treatment could not be determined as 

described in section 6.4. Proper determination of the presence of the respective treatment 

might provide the evidence needed to change the results of the hypothesis test for these 

treatments. Two-way Contingency tables for the treatments 1C, 6, 11, 14, 15, 18, 20, 21 

and 22 are shown in Appendix F.

The two-way contingency table for Firewise treatment 10 is shown in Table 15. This 

treatment was determined to be statistically significant at a p-value of 0.0008. As 

described in section 6.4 there were a large number of properties where the presence of 

this treatment could not be determined. It is impossible to tell if these treatments are 

missing at random or for some underlying reason and the results of this test are therefore 

questionable. Firewise treatment 14 could not be tested for statistical significance using 

the Chi-square test due to the fact that all the structures that failed were destroyed, 

thereby, making the use of the Chi-Square test statistic invalid (Table 16). Nonetheless, 

the effectiveness of this treatment is demonstrated. Table 17 illustrates further analysis 

on Firewise treatment 14, roofing construction. The table illustrates the need to collect 

and analyze data from the entire fire exposed dataset. 

Table 15 Treatment 10 contingency table with results of Chi-Square test. Treatment 10 is present 

(pass) if there is no Firewood within 30 feet of the structure.

Undamaged

Structures

Damaged/ Destroyed

Structures

Total

Fail 19 (26% ± 10%) 53 (74% ± 10%) 72

Pass 17 (61% ± 18%) 11 (39% ± 18%) 28

Total 36 64 100

p-value = 0.0008 (***)

Table 16 Treatment 14, roof construction type, classified by damage status.

Undamaged

Structures

Damaged/ Destroyed

Structures

Total

Fail 0(0%) 13 (100%) 13

Pass 152 (67%) 76 (33%) 228

Total 152 89 241
31

7.4 High Hazard Area Determination

The slope threshold was selected at 20%. While steeper slopes are expected to be more 

hazardous, the 20% was selected as a threshold for capturing the transition from very flat 

to steep slopes. The prevailing wind during the fires was from the NE, so the NE aspect 

was elected and was extended from North to East to account for wind fluctuations. 

Figures 21 and 22 illustrate how the selected slope and aspect thresholds correlate with 

destroyed, damaged and undamaged structures. Using these thresholds the data set shown 

in Figure 24 was created and used in the analysis below. Figure 24 is overlaid with the 

dNDVI data product (showing change in vegetation greenness between before to after the 

fire), showing the relationship between high hazard areas and burned vegetation. Also 

shown in Figure 24 is the fact that burned vegetation extends beyond these high hazard 

areas if fuel is present. Future developments of the exposure method will further exposure

the slope and aspect and vegetative fuel domains.

7.5 Exposure Method Evaluations

Evaluation of both exposure methods can be conducted through examination of the 

structure response differences for each method. For the “perimeter/interior” method, it 

can be shown that perimeter properties had 54% (43 of 80) of the residential structures 

damaged or destroyed. Interior properties had 29% (47 of 162) of the residential 

structures damaged or destroyed. These numbers can be compared to 37% (90 of 242) of 

the residential structures damaged or destroyed across the entire Trails. Parcels 

categorized as “perimeter” represented 48% (43 of 90) of the damaged and destroyed 

residential structures and “interior” parcels represented 52% (47 of 90) of the damaged 

and destroyed residential structures.

Table 17 Roofing material example.

Sample

Population

Destroyed 

Structures 

Wood 

Shake 

Roofs

Destroyed 

Structures 

Spanish 

Tile Roofs

Typical Comparisons

Typical (only 

destroyed 

homes)

74 12 37 16% of 

destroyed

homes

had wood 

shake roofs

50% of 

destroyed

homes has

Spanish tile

roofs

Complete 

(all 

structures 

within fire 

line)

242 12 154

Technically 

Valid 

Comparisons

100% of 

exposed

wood

shake roofs 

destroyed

24% of 

exposed

Spanish

tile roofs 

destroyed
32

Evaluation for the high/low hazard area method is portrayed in Figure 25 displaying bar 

graphs showing percent of residential structures damaged or destroyed grouped by bins of 

percent of high hazard area present between 0 and 200 feet from the structure in the 

upwind direction. Figure 25 displays the above described bar graph for the following 

sector distances: 0 to 30 feet (0 m to 9 m), 0 ft to 100 ft (0 m to 30 m), 0 ft to 200 ft (0 m 

to 61 m) and 0 ft to 300 ft (0 m to 91 m). Another portrayal of the data shown in Figure 

25 is presented in Table 18, displaying frequency counts of structure response with 

percent destruction by bins of percent high hazard area for four directional sectors from 

the structure. These losses, as described in Table 18, were for all structures independent 

of construction or landscaping hazard mitigation solutions. Aggregating the data further 

it can be seen that at the 30 foot sector and greater than 50% high hazard area in the down 

fire direction that 69% (20 of 29) of the structures were damaged or destroyed; 66% (25 

of 38) at the 30 m (100 ft) sector; 75% (33 of 44) at the 61 m (200 ft) sector; and 76% (34 

of 45) at the 91 m (300 ft) sector. As mentioned previously, the high/low method does 

not account for vegetation treatment and it is possible the lower average percent 

destruction in the 9 m to 30 m (30 ft and 100 ft) sector is due to this fact. 

The “perimeter/interior” method shows different percent destructions for each population 

with similar numbers of destroyed or damaged structures indicating different exposure 

might have occurred in these two environments. The high/low exposure method has an 

even greater percent destruction when looking at greater than 50% high hazard area in the 

upwind direction of each structure, accompanied by a decrease in sample size, compared 

to the “perimeter/interior” method. Furthermore, the slope and aspect thresholds 

employed for this study in the high/low method are verified in Figure 21 and Figure 22. 

These figures show increased percent damage and destruction to primary structures with 

slopes greater than 20% and north, northeast and east aspects; the thresholds employed in 

this analysis. Due to the high/low exposure method first capturing all the structures (242) 

in the study area at the 200 foot sector distance and the increased percentage of losses for 

all sector distances at the above 50% high hazard area these thresholds were used to 

categorize structure exposure into high potential exposure (>50% high hazard area) and 

low potential exposure (=<50% high hazard area). Additionally, at 61 m (200 ft) any 

consequence of not accounting for vegetation treatment in the 0 m to 9 m (0 ft to 30 ft)

area would be reduced due to the sector increase in size with distance. The purpose of 

the analysis is to demonstrate how the Firewise attributes affected structure survivability 

while using a preliminary exposure framework to bin the data into a quantified two tiered 

exposure system. This exposure framework is being jointly developed by NIST and 

USFS. 
33

7.6 Firewise Effectiveness (Two Exposure Methods)

This section presents the results of the evaluation of individual Firewise treatments 

assessed in this study for their effectiveness in reducing damage or destruction to primary 

structures on residential properties in the various exposure categories analyzed in this 

paper. Table 19 through Table 24 show three-way contingency tables of percent of 

damaged or destroyed structures by treatment and results of the statistical test employed. 

The following tables for the statistically significant treatments, show the results of the ZTable 18 Frequency counts and percent destruction of structures by high hazard area for four 

sector distance (30, 100, 200, 300 feet).

30 Foot Sector Percent 

High Hazard Area

Damaged 

or 

Destroyed

Total

(damaged, destroyed and 

undamaged)

Percent Damaged or 

Destroyed

Any high exposure area 85 213 40%

0% 5 29 17% 

> 0% And =<25% 43 140 31% 

> 25% And =<50% 26 49 53% 

> 50% And =<75% 12 19 63% 

> 75% And =<100% 4 5 80% 

100 Foot Sector

Percent High Hazard 

Area

Damaged 

or 

Destroyed

Total 

(damaged destroyed and 

undamaged)

Percent Damaged or 

Destroyed

Any high exposure area 87 230 38%

0% 3 12 25% 

> 0% And =<25% 34 143 24% 

> 25% And =<50% 28 49 57% 

> 50% And =<75% 19 32 59% 

> 75% And =<100% 6 6 100% 

200 Foot Sector

Percent High Hazard 

Area

Damaged 

or 

Destroyed

Total 

(damaged destroyed and 

undamaged))

Percent Damaged or 

Destroyed

Any high exposure area 90 242 37%

0% 0 0 0% 

> 0% And =<25% 39 153 25% 

> 25% And =<50% 18 46 39% 

> 50% And =<75% 25 34 74% 

> 75% And =<100% 8 9 89% 

300 Foot Sector

Percent High Hazard 

Area

Damaged 

or 

Destroyed

Total 

(damaged destroyed and 

undamaged)

Percent Damaged or 

Destroyed

Any high exposure area 90 242 37%

0% 0 0 0% 

> 0% And =<25% 39 146 27% 

> 25% And =<50% 17 51 33% 

> 50% And =<75% 28 37 76% 

> 75% And =<100% 6 8 75% 
34

tests on the regression parameters and also the 95% confidence intervals for the percent 

damaged or destroyed in each category. The first table in each set of two displays the 

treatment counts and percentages for perimeter and interior structures. The second 

contingency table displays the treatment values for the high and low exposures as 

previously defined. For each of the treatments shown in Table 19 through Table 24 the 

null hypothesis presented in 5.3.5 is rejected indicating that properties in the Trails at 

Rancho Bernardo Community have an association between implementation of the 

respective Firewise Treatment coupled with both exposure designations and damage to

the property’s primary structure from the 2007 Witch and Guejitio Fires.

 

Table 19: Treatment 1a three-way contingency tables. First table shows counts by treatment, 

burn status and perimeter/interior designation. Second table shows counts by treatment, burn 

status and high/low hazard area. Treatment 1a is present (pass) if an irrigated area encircles 

the structure for at least 30 feet on all sides.

Property on Perimeter Property in Interior

Undamaged Damaged & 

Destroyed

Total Undamaged Damaged & 

Destroyed

Total

Fail 6 (18 ± 12%) 27 (82 ± 12%) 33 Fail 29 (53 ± 13%) 26 (47 ± 13%) 55

Pass 31 (72 ± 14%) 12 (28 ± 14%) 43 Pass 84 (84 ± 8%) 17 (16 ± 8%) 101

Total 37 (49 ± 12%) 39 (51 ± 12%) 76 Total 113 (72%±7%) 43 (28±7%) 156

Firewise Treatment 1a: p-value = 0.0000 (***), perimeter: p-value = 0.001 (**)

High Hazard Area Exposed Structure Low Hazard Area Exposed Structure

Undamaged Damaged & 

Destroyed

Total Undamaged Damaged & 

Destroyed

Total

Fail 2 (8 ± 11%) 22 (92 ± 11%) 24 Fail 33 (52± 12%) 31 (48 ± 12%) 64

Pass 8 (53 ± 26%) 7 (47 ± 26%) 15 Pass 107 (83 ± 8%) 22 (17 ± 8%) 129

Total 10 (26 ± 14%) 29 (74 ± 14%) 39 Total 140 (73%±6%) 53 (27± 6%) 193

Firewise Treatment 1a: p-value = 0.0000 (***), exposure: p-value = 0.0000 (***)

Table 20: Treatment 7 three-way contingency tables. First table shows counts by treatment, 

burn status and perimeter/interior designation. Second table shows counts by treatment, burn 

status and high/low hazard area. Treatment 7 is present (pass) if fuel breaks like driveways, 

gravel walkways and lawns are found on the property.

Property on Perimeter Property in Interior

Undamaged Damaged & 

Destroyed

Total Undamaged Damaged & 

Destroyed

Total

Fail 10 (27 ± 14%) 27 (73 ± 14%) 37 Fail 49 (59 ± 11%) 34 (41 ± 11%) 83

Pass 27(73 ± 14%) 10 (27 ± 14%) 37 Pass 63 (89 ± 8%) 8 (11 ± 8%) 71

Total 37 (50 ± 12%) 37 (50 ± 12%) 74 Total 112 (72%±7%) 42 (28±7%) 154

Firewise Treatment 7: p-value = 0.0000 (***), perimeter: p-value = 0.0001 (***)

Property with High Hazard Area Property with Low Hazard Area

Undamaged Damaged & 

Destroyed

Total Undamaged Damaged & 

Destroyed

Total

Fail 2 (8 ± 11%) 22 (92 ± 11%) 24 Fail 57 (59 ± 10%) 39 (41 ± 10%) 96

Pass 8(57 ± 26%) 6 (43 ± 26%) 14 Pass 82 (87± 7%) 12 (13 ± 7%) 94

Total 10 (26 ± 14%) 28 (74 ± 14%) 38 Total 139 (73%±6%) 51 (27±6%) 190

Firewise Treatment 7: p-value = 0.0000 (***), exposure: p-value = 0.0000 (***)
35

Table 21 : Treatment 8 three-way contingency tables. First table shows counts by treatment, 

burn status and perimeter/interior designation. Second table shows counts by treatment, burn 

status and high/low hazard area. Treatment 8 is present (pass) if vegetation is pruned on the 

property.

Property on Perimeter Property in Interior

Undamaged Damaged & 

Destroyed

Total Undamaged Damaged & 

Destroyed

Total

Fail 26 (44 ± 12%) 33 (56 ± 12%) 59 Fail 80 (68 ± 7%) 38 (32 ± 7%) 118

Pass 11 (73 ± 22%) 4 (27 ± 22%) 15 Pass 31 (86 ± 11%) 5 (14 ± 11%) 36

Total 37 (50 ± 12%) 37 (50 ± 12%) 74 Total 111 (72%±7%) 43 (28±7%) 154

Firewise Treatment 8: p-value = 0.005 (**), perimeter: p-value = 0.001 (**)

Property with High Hazard Area Property with Low Hazard Area

Undamaged Damaged & 

Destroyed

Total Undamaged Damaged & 

Destroyed

Total

Fail 6 (18 ± 13%) 26 (82 ± 13%) 34 Fail 100 (69 ± 8%) 45 (31 ± 8%) 145

Pass 4 (67 ± 38%) 2 (33 ± 38%) 6 Pass 38 (84 ± 11%) 7 (16 ± 11%) 45

Total 10 (25 ± 13%) 28 (75 ± 13%) 40 Total 138 (73%±6%) 52 (27±6%) 190

Firewise Treatment 8: p-value = 0.007 (**), exposure: p-value = 0.0000 (***)

Table 22: Treatment 9 three-way contingency tables. First table shows counts by treatment, 

burn status and perimeter/interior designation. Second table shows counts by treatment, burn 

status and high/low hazard area. Treatment 9 is present (pass) if leaf clutter and 

dead/overhanging branches are removed on the property.

Property on Perimeter Property in Interior

Undamaged Damaged & 

Destroyed

Total Undamaged Damaged & 

Destroyed

Total

Fail 20 (43 ± 14%) 27 (57 ± 14%) 47 Fail 41 (57 ± 14%) 31 (43 ± 14%) 72

Pass 17 (68 ± 18%) 8 (32 ± 18%) 25 Pass 69 (87 ± 8%) 10 (13 ± 8%) 79

Total 37 (51 ± 12%) 35 (49 ± 12%) 72 Total 110 (73 ± 7%) 41 (27 ± 7%) 151

Firewise Treatment 9: p-value = 0.0000 (***), perimeter: p-value = 0.01 (*)

Property with High Hazard Area Property with Low Hazard Area

Undamaged Damaged & 

Destroyed

Total Undamaged Damaged & 

Destroyed

Total

Fail 4 (17 ± 15%) 20 (83 ± 15%) 24 Fail 57 (60 ± 10%) 38 (40 ± 10%) 95

Pass 6 (46 ± 28%) 7 (54 ± 28%) 13 Pass 80 (88 ± 7%) 11 (12 ± 7%) 91

Total 10 (27 ± 14%) 27 (73 ± 14%) 37 Total 137 (74 ± 6%) 49 (26 ± 6%) 186

Firewise Treatment 9: p-value = 0.0000 (***), exposure: p-value = 0.0000 (***)
36

For Firewise treatments 1a, 7, 8, 9, 17 and 19 listed in the tables above the improved 

effectiveness of the treatment in one exposure environment compared to the other is 

examined. This examination is conducted by computing the difference between the 

percent damaged/destroyed when the respective Firewise treatment is absent (i.e., fail) 

and present (i.e., pass) for each exposure category. Additionally, the 95% confidence 

interval for this difference is derived. These computations are displayed in Table 25 

through Table 30. In all cases the interaction is not statistically significant, due to the 

relatively low sample sizes in some of the groups. Nonetheless, a pattern is shown and 

further demonstrated in Box Plots displayed in Figure 27. 

Table 23: Treatment 17 three-way contingency tables. First table shows counts by treatment, 

burn status and perimeter/interior designation. Second table shows counts by treatment, burn 

status and high/low hazard area. Treatment 17 is present (pass) if dead wood and dense 

vegetation are cleared at least 30 feet from the house.

Property on Perimeter Property in Interior

Undamaged Damaged & 

Destroyed

Total Undamaged Damaged & 

Destroyed

Total

Fail 21 (41 ± 12%) 30 (59 ± 12%) 51 Fail 55 (60 ± 10%) 36 (40 ± 10%) 91

Pass 16 (76 ± 18%) 5 (24 ± 18%) 21 Pass 57 (93 ± 6%) 4 (7 ± 6%) 61

Total 37 (51 ± 12%) 35 (49 ± 12%) 72 Total 112 (74 ± 7%) 40 (26 ± 7%) 152

Firewise Treatment 17: p-value = 0.0000 (***), perimeter: p-value = 0.004(**)

Property with High Hazard Area Property with Low Hazard Area

Undamaged Damaged & 

Destroyed

Total Undamaged Damaged & 

Destroyed

Total

Fail 7 (23 ± 15%) 23 (77 ± 15%) 30 Fail 69 (62 ± 9%) 43 (38 ± 9%) 112

Pass 3 (43 ± 35%) 4 (57 ± 35%) 7 Pass 70 (93 ± 6%) 5 (7 ± 6%) 75

Total 10 (27 ± 14%) 27 (73 ± 14%) 37 Total 139 (74 ± 6%) 48 (26 ± 6%) 187

Firewise Treatment 17: p-value = 0.0000 (***), exposure: p-value = 0.0000(***)

Table 24: Treatment 19 three-way contingency tables. First table shows counts by treatment, 

burn status and perimeter/interior designation. Second table shows counts by treatment, burn 

status and high/low hazard area. Treatment 19 is present (pass) if a wood fence is not attached 

to the home.

Property on Perimeter Property in Interior

Undamaged Damaged & 

Destroyed

Total Undamaged Damaged & 

Destroyed

Total

Fail 10 (26 ± 14%) 29 (74 ± 14%) 39 Fail 41 (55 ± 11%) 33 (45 ± 11%) 74

Pass 27 (77 ± 14%) 8 (23 ± 14%) 35 Pass 71 (88 ± 7%) 9 (12 ± 7%) 80

Total 37 (50 ± 12%) 37 (50 ± 12%) 74 Total 112 (73 ± 7%) 42 (27 ± 7%) 154

Firewise Treatment 19: p-value = 0.0000 (***), perimeter: p-value = 0.0008(***)

Property with High Hazard Area Property with Low Hazard Area

Undamaged Damaged & 

Destroyed

Total Undamaged Damaged & 

Destroyed

Total

Fail 3 (11 ± 12%) 24 (89 ± 12%) 27 Fail 48 (56 ± 10%) 38 (44 ± 10%) 86

Pass 7 (58 ± 24%) 5 (42 ± 24%) 12 Pass 91 (88 ± 6%) 12 (12 ± 6%) 103

Total 10 (26 ± 14%) 29 (74 ± 14%) 39 Total 139 (74 ± 6%) 50 (26 ± 6%) 189

Firewise Treatment 19: p-value = 0.0000 (***), exposure: p-value = 0.0000(***)
37

Table 25 Differences between percent damaged/destroyed when the respective Firewise 

Treatment is absent (i.e., fail) and present (i.e., pass), for Firewise Treatment 1a. 

Difference in % of destroyed between pass and fail

Perimeter 0.54 ±0.18

Interior 0.31± 0.14

High Exposure 0.45 ±0.28

Low Exposure 0.31± 0.14

Table 26 Differences between percent damaged/destroyed when the respective Firewise 

Treatment is absent, (i.e., fail) and present, (i.e., pass) for Firewise Treatment 7. 

Difference in % of destroyed between pass and fail

Perimeter 0.46 ±0.20

Interior 0.30± 0.12

High Exposure 0.49 ±0.28

Low Exposure 0.28± 0.12

Table 27 Differences between percent damaged/destroyed when the respective Firewise 

Treatment is absent (i.e., fail) and present (i.e., pass) for Firewise Treatment 8. 

Difference in % of destroyed between pass and fail

Perimeter 0.29 ±0.26

Interior 0.18± 0.14

High Exposure 0.49 ±0.40

Low Exposure 0.15± 0.12

Table 28 Differences between percent damaged/destroyed when the respective Firewise 

Treatment is absent (i.e., fail) and present (i.e., pass) for Firewise Treatment 9. 

Difference in % of destroyed between pass and fail

Perimeter 0.25 ±0.22

Interior 0.3 ± 0.13

High Exposure 0.29 ±0.30

Low Exposure 0.28± 0.12

Table 29 Differences between percent damaged/destroyed when the respective Firewise 

Treatment is absent (i.e., fail) and present (i.e., pass) for Firewise Treatment 17. 

Difference in % of destroyed between pass and fail

Perimeter 0.35 ±0.22

Interior 0.33 ± 0.12

High Exposure 0.20 ±0.40

Low Exposure 0.31± 0.10
38

Examination of this data, though not statistically significant, might indicate that for 

treatments 1a, 7, 8 and 19 the positive effect of having the treatment in the trails for high 

exposure environments (i.e., “perimeter” or high hazard area exposed structures) is more 

pronounced compared to low exposure environments (i.e., “interior” or low hazard area 

exposed structures) in terms of structure response from the Witch and Guejito Fires. For 

treatments 9 and 17 the effect is similar across all exposure groups examined. 

Firewise treatments found to be not statistically significant are shown in Appendix F. In 

some cases, there is insufficient data to generate reliable statistics. Firewise treatment 10 

and 1c are of note in the treatments shown in Appendix F. Firewise treatment 10 was 

statistically significant in the high/low hazard area exposed population but it was not 

significant in the “perimeter/interior” method. Again, the large number of properties 

where this treatment could not be determined made this result questionable. Firewise 

treatment 1c is not significant individually, coupled with the “perimeter/interior” method, 

or coupled with the high/low hazard area method. Treatment 1c, however, when 

evaluated only for high hazard area exposed structures shows that 79% of the structures 

were destroyed (26 of 33) when this treatment was absent and 6% (2 of 31) were 

damaged or destroyed when this treatment was present.

7.7 Defensive Actions as a Function of High/Low Hazard Exposure

Before examining locations of defensive action as a function of high/low exposure, it is 

useful to re-examine Table 1 for various ignition mechanisms on damaged structures in

the context of Firewise treatment effectiveness. As can be seen in Table 1, there were 5 

damaged structures where the ignition mechanism was, at least in part, the deck. This 

provides evidence of the effectiveness of Firewise treatment 12 as all five of these 

structures failed Firewise treatment 12 and the ignition mechanism is known. Table 1

also shows one ignition mechanism of a main structure gutter. This also provides 

evidence for the effectiveness of the Firewise treatment recommending to “Keep gutters, 

eaves, and roofs clear of leaves and other debris”, which was not assessed in this paper 

due to the impossibility of determining this for a destroyed structure. Additionally, there 

was one damaged structure where the ignition mechanism was an exposed wood beam, 

thereby providing more evidence for the importance of the Firewise treatment 

recommending to “Use construction materials that are fire-resistant or non-combustible 

whenever possible”, which was also not assessed in this paper. Finally, one of the 

damaged structures had wood fencing, combined with a damaged out building, providing 

further evidence for the importance of the Firewise treatment 19. There are, however, 

ignition mechanisms shown in Table 1 that are not addressed in the Firewise checklist. 

These include detached structures and roof top solar panels. Roof top solar panels are 

Table 30 Differences between percent damaged/destroyed when the respective Firewise 

Treatment is absent (i.e., fail) and present (i.e., pass) for Firewise Treatment 19. 

Difference in % of destroyed between pass and fail

Perimeter 0.51 ±0.20

Interior 0.33 ± 0.12

High Exposure 0.47 ±0.30

Low Exposure 0.32± 0.12
39

less common but detached structures are a common occurrence in the WUI and are not 

addressed at all in the Firewise Checklists or in this report.

Next, an examination of defensive action locations in context of high/low hazard area 

using the 50% threshold and 61 m (200 ft) distance as defined in section 7.4. The data 

was sorted to determine the distribution of defensive actions across high and low 

exposure properties. The information is summarized in Table 31.

Table 31 Distribution of defensive actions across high and low exposure properties.

High Exposure Defended Undefended

Total 43 19 (44%) 24 (56%)

Damaged/Destroyed 33 14 (42%) 19 (58%)

Undamaged 10 5 (50%) 5 (50%)

Low Exposure Defended Undefended

Total 199 66 (33%) 137 (67%)

Damaged/Destroyed 57 22 (39%) 35 (61%)

Undamaged 142 40 (28%) 102 (72%)

In high exposure, 14 out of 19 (74%) of defended were damaged or destroyed compared 

to 22 out of 66 (33%) in low exposure. Additionally, in high exposure, out of the 19 

defended 10 were destroyed and 4 damaged, where as in low exposure, out of the 66 

defended 10 were destroyed and 12 were damaged. Defensive actions were over twice as 

effective in low exposure compared to high exposure. 

Table 32 Defensive actions types taken on the 19 defended high exposure properties.

Burn Status Defensive Action Type Ignition

Destroyed defensive action taken to save structure unknown

Destroyed defensive action taken to save structure unknown

Destroyed defensive action taken to save structure

deck ignited three separate 

times

Destroyed defensive action taken to save structure ember in house

Destroyed defensive action taken to save structure ember in attic

Destroyed fire containment - house already destroyed unknown

Destroyed fire containment - house already destroyed unknown

Destroyed fire containment - house already destroyed Deck

Destroyed fire containment - house already destroyed unknown

Destroyed fire containment - house already destroyed unknown

Damaged defensive action taken to save structure deck and main structure

Damaged defensive action taken to save structure Gutter

Damaged defensive action taken to save structure Deck

Damaged defensive action taken to save structure Deck

Unburned defensive action taken to protect structure vegetation

Unburned defensive action taken to protect structure vegetation

Unburned defensive action taken to protect structure vegetation

Unburned defensive action taken to protect structure vegetation

Unburned defensive action taken to protect structure vegetation
40

The 19 defensive actions in the high exposure areas are further divided into two 

categories; actions that were taken to protect the primary structure and actions taken to 

contain the fire and limit spread to surrounding parcels and structures. Table 32 lists

these actions. It should be noted that even in the cases where suppression actions were 

taken on the structure or origin or primary structure, additional actions could have been 

taken to also prevent fire spread to adjacent properties. Out of the 19 defended structures 

in high exposure, there were eight deck ignitions (on five structures) and five suppression 

actions on burning vegetation. It should also be noted that burning vegetation likely was 

present on other defended structures in high exposure areas. The defensive actions 

provide significant insight to structure and landscaping vulnerabilities in different 

exposure conditions and are essential in documenting the successes and failures of hazard 

reduction solutions.

8.0 Discussion

The sections above present results attempting to analyze the applicability, presence and 

effectiveness of Firewise treatments. Confounding this task was the need to quantify the 

extent of radiant heat and embers across the study area coupled with defensive actions 

performed during the fire in the community. This is believed to be the first post-fire WUI 

assessment study attempting to account for all these factors and to attempt to fully 

quantify the exposure. As expected, numerous difficulties and obstacles were present as 

detailed in section 6.0 above. The following discussion is formatted around the primary 

objectives of this report:

8.1 Analyzing if Firewise treatments are applicable within the Trails

Beginning with applicability of Firewise Treatments, two factors should be noted. The 

first is the need for irrigation requirements and the statistical significance of this with

regards to structure survivability at the Trails. Given this, the applicability of irrigation 

treatments must be questioned as a sustainable treatment where water shortage is a 

problem. The second item considered with regards to applicability is the Firewise Zone 

Concept. First, visual examination of Figure 18 shows that there are certain properties in 

the Trails Community where if the Firewise Zone Concept is implemented using the 

property centric approach, there will be Zone 4 areas in one property directly abutting a 

Zone 1 or 2 in another property. Consequently, it might be concluded that a different 

treatment is required where community cooperation is not occurring. The research 

conducted for this paper could not discover any WUI mitigation advice that presents such 

a treatment alternative. Again, Firewise does recognize the hazard an untreated property 

can have on an adjacent property12 but a different treatment option is not presented, based 

on the research conducted for this paper. Nonetheless, community cooperation appears to 

be the ideal treatment based on visual examination of Figure 17 and Figure 18 because it 

will result in less zone 3 and zone 4 areas in interior portions of the Trails and not create 

disjointed zones. 

While it was not quantitatively shown in this study, visual examination of pre-fire aerial 

imagery coupled with discussions with the Trails HOA indicate that the property centric 

approach to treatment was the approach implemented in the Trails. It should also be 

noted that if the Firewise Zone Concept listed in the Firewise checklist (see Appendix B)

was followed strictly, that is, if zones would have been proportioned evenly based on the 
41

property size, there would have been even more areas of zones 3 and 4 and more 

potential paths for the fire to travel from the wildlands into the community. These less 

treated areas further from the house were typically wildlands, hedgerows or vegetative 

privacy barriers, and appeared to be main paths of fire through the Trails as shown in 

Figure 19. Examination of the homeowner technical discussion forms also indicates 

many areas of fire behavior in these hedge row areas or along property boundaries. 

Given the above, there are two concepts regarding the Firewise Zone Concept that might 

be questioned in an Interface Community such as the Trails. First, the concept of less 

treatment further from the structure, at least as portrayed in the Firewise Checklist might 

not be applicable given that no distances are provided. For structures close together this 

concept might not be appropriate and complete removal of flammable fuels might be 

required. The second concept that is being questioned in regards to the Firewise Zone 

Concept relates to the Interface nature of interior at least, portions of the Trails 

Community. It is possible the Firewise Zone Concept was developed as a result of 

studying fires that are in Intermix Communities where structure spacing is much greater 

than the Trails. In these areas a concept of less treatment as you move away from the 

structure is logical because it is impractical to treat all spaces between structures. In 

these cases, it is believed by the authors, that the Firewise Zone Concept intends for the 

fire to burn through the zones 3 and 4, ideally at lower intensities compared to wildlands 

adjacent to these zones. These low intensity burns combined with treatments that 

essentially result in nothing burning in Zone 1 and 2 are the essence of the Firewise Zone 

Concept, in the opinion of the authors who welcome correction from the research 

community and Firewise in general in this regard. Consequently, the question for an 

interface type community such as the Trails, again at least in the interior is as follows:

Is it desirable for a wildland fire to burn through sections of the community, even if 

these sections are greater than 100 feet from a structure? 

In fact, this might be the question every WUI Community should ask. When the spacing 

between structures and/or the property size is of a certain distance or area, not studied in 

this paper, such that complete treatment (i.e., treatment such that nothing in the zone 

burns) is not possible, the Firewise Zone Concept is the only logical conclusion. Exact 

distances, however, for all scenarios are not known by the Fire Science field. This is 

evident from the wide range of treatment distances recommended at a state level across 

the United Statesxx and the complete lack of reference to any scientific study (except for 

30 Feet International Crown Fire Experiment19) to justify these various distances. For 

interface type communities, however, a concept of less treatment further from the house 

might not be appropriate, except for properties on the perimeter. For example, properties 

in the interior portions of the Trails would ideally have no natural areas present. Yet, this 

is suggested in the Firewise Zone Concept (see Appendix B) as portrayed in the Firewise 

Checklist. Nonetheless, the effectiveness of actual Firewise treatments in zones 2, 3 and 

4 were not assessed in this paper. More importantly, there is no evidence to indicate that 

 xxIn Utah the furthest zone is Zone 3, which starts 100 ft from the structure. Source: Firewise Landscaping 

for Utah, Utah State University Extention, 

www.ffsl.utah.gov/firemgt/wui/educationalmaterials/firewiselanscaping..pdf

In Arizona Zones are given different distances from home as a function of uphill and downhill slope and 

zone 2 can extend beyond 200ft. www.azfireinfo.az.gov/userfiles/file/firewise-8%205x11_4_11_web.pdf
42

Firewise treatments recommended in zones 2, 3 and 4 were ineffective. Additional 

research is needed on the effectiveness of treatments as a function of distance away from 

the structure. Strict implementation of these treatments at the Trails, assuming zones were 

not proportioned evenly based on property size, might have significantly reduced 

destruction. Nonetheless, it is believed that the Ideal Firewise Zone implementation (see 

section 5.3.1) is the only implementation of the Firewise Zone Concept applicable at the 

Trails, with exact distances not being known. Furthermore, when implementing the Ideal 

Firewise Zone Concept, it is recommended that homeowners consider relatively small, 

but potentially significant Zones 3 and 4 that might be in dangerous topographic positions 

and potentially contribute to fire spread into the community. For these situations,

extending zone 1 and 2 type treatments into these areas should be considered. 

8. 2 Determining if Firewise treatments were present at the Trails, 

prior to the Witch and Guejito Fires.

There was no community wide effort to implement the Fire Zone Concept at the Trails. 

While the Firewise Zone Concept at the Trails could not be quantitatively assessed, the 

assessment of wildland vegetation across the Trails was undertaken. The data presented 

in Figure 20 can be aggregated to show that 67% (26 of 39) of the structures with 

wildland vegetation in zone 1 were damaged or destroyed while 32% (64 of 203) with no 

wildland vegetation were damaged or destroyed. There were 59% (46 of 78) of the 

structures with wildland vegetation in zone 2 damaged or destroyed and 27% (44 of 164) 

with no wildland vegetation damaged or destroyed. There were 54% (42 of 92) of the

structures with wildland vegetation in zone 3 damaged or destroyed and 27% (40 of 150) 

with no wildland vegetation damaged or destroyed. Finally, 69% (64 of 93) of residential 

structures with wildland vegetation present in zone 4 were destroyed, while 17% (26 of 

149) of structures with no wildland vegetation present in zone 4 were destroyed. In every 

zone, the presence of wildland vegetation, as mapped in this study, on an individual 

property resulted in an increased percentage of damaged or destroyed structures. The data 

is summarized in Table 33.

Table 33 Percent Structure Destroyed with and Without Wildland Vegetation in Zones 1 through 4 

Zone With Wildland Vegetation Without Wildland Vegetation

1 67% 32%

2 59% 27%

3 54% 27%

4 64% 17%

Expanding on the assessment of the presence of certain general recommendations made 

by Firewise, there is no evidence that local fire history was taken into consideration when 

designing the Trails Community. Additionally, assuming that the prevailing winds at the 
43

time of the Fires was similar to prevailing winds generally found during such wind events 

at the Trails, it could be said that consideration of prevailing winds and seasonal weather 

was not conducted. For example, examination of Figure 13, shows how the Trails 

Community is essentially oriented directly in line of the prevailing winds resulting in a 

large number of structures being oriented to face these prevailing winds. Forty-three 

percent (105 of 242) of the structures in the Trails were constructed on lots where the 

majority of aspects found on the property were facing the prevailing winds at the time of 

the Fires (i.e., northeast, north, east). Fifty-four percent (57 of 105) of the structures on 

property lots where the majority aspect was determined to be in the direction of these 

prevailing winds were destroyed. These destroyed structures represented 63% (57 of 90) 

of the total structures destroyed in the Trails. 

Discussion of the presence of considering site location, overall terrain and property 

contours can be conducted through examination of the data shown in Figure 21, 

representing average property slopes. This data shows that 46% (113 of 242) of the 

structures in the Trails were built on lots where the average of the slopes found on the 

property was greater than 20%. Fifty-three percent (60 of 113) of the structures on 

properties with slopes greater than 20% were destroyed or damaged representing 66% (60 

of 90) of the total structures destroyed or damaged in the Trails. Finally, examination of 

the overall presence of Firewise treatments can be discussed in context of Figure 23

where it can be seen that 58% (141 of 242) of residential properties in the Trails had less 

than 50% of the evaluated Firewise treatment present. 

8.3 Evaluating the effectiveness of Firewise treatments in reducing 

structure ignitions at the Trails.

Evaluation of the effectiveness of individual Firewise treatments found that treatments 

1a, 7, 8, 9, 13 , 17 and 19 (section 7.6) all showed an association between implementation 

of the respective Firewise treatment on the property and damage or destruction to the 

property’s primary structure. While Treatment 14 could not be tested statistically, all 

structures(16/16) with wood shake roofs in the Trails were destroyed. This provides 

some evidence of the effectiveness of this Firewise treatment. Firewise treatment 10 was 

also found to show an association between implementation of the respective Firewise 

treatment on the property and damage or destruction to the property’s primary structure. 

The large number of properties where the presence of firewood could not be determined, 

however, makes this conclusion questionable. The lack of statistical significance for 

other treatments does not indicate that the treatments are ineffective or would not be 

effective in different environments.

8.4 Mapping fire exposure profiles within the Trails.

An attempt was made to evaluate two distinct exposure determination methods. The first, 

perimeter interior method was introduced in the NIST TN 1635. The second, based on 

slope, aspect and vegetative fuels was defined in this paper. The mapping of exposure 

conducted in this paper emphasizes the importance of topography, fuels and weather but 

is limited in that fuel type and quantity is not considered. Additionally the exposure 

associated with burning structures, a significant source of flames and embers, was not 

factored into the exposure calculation. Also, assessment of topography, though conducted 

from high resolution elevation data, is likely too coarse and does not encompass micro-
44

scale effects caused by topographical features such as chimneys, canyons, ridges and 

other features. Vegetation treatment is also not considered in this exposure mapping and 

the mapping does not account for the fact that fuels adjacent to these high hazard areas 

will and did burn. Finally, distance is not directly considered and utilization of methods

similar to those discussed in the Australian Bushfire Study20 coupled with enhancement 

of the remote sensing derived vegetation data based on field data might be beneficial in 

quantifying the distance required for treatments to be effective. 

Nonetheless, a visual examination of Figure 24 indicates potential association between 

burned vegetation areas and the mapped high potential exposure areas. Also seen in 

Figure 24 is the extension of burned vegetated areas, often from and between highly 

exposed areas. Areas of potential high exposure with changes in greenness highlighted in 

white outside the fire perimeter shown in Figure 24 are in most cases shadow areas or 

areas with man-induced vegetation changes between pre and post-fire imagery. 

Also, clearly portrayed in Figure 25 is the concept of increased destruction with increased 

exposure. This is further specified in Figure 20 showing the increase in destruction with 

increased wildland vegetation present on the property. Other relationships not explored 

include calculation of the distance to steep slopes, percentage area of fire breaks, 

vegetation structural stage and numerous others. Future research will examine some of 

these factors in greater detail using fire behavior models, more complex GIS models, 

logistic regression and/or other modeling techniques as appropriate. 

8.5 Evaluating the effectiveness of Firewise treatments in reducing 

structure ignitions in context of potential exposure. 

Evaluation of the effectiveness of individual Firewise treatments combined with the 

various exposure designations indicates that treatments 1a, 7, 8, 9, 17 and 19 all showed 

an association between implementation of the respective Firewise treatment on the 

property and damage or destruction to the respective Firewise treatment in all exposure 

environments. It is possible that for Firewise treatments 1a, 7, 8 and 19, the effect of 

having the treatment in a high exposure environment is more pronounced compared to 

the effect of having the treatment in a low exposure environment.

8.6 Evaluating of defensive action in terms of Firewise treatments and 

as a function of exposure.

Analysis of the effectiveness of the defensive actions provide significant insight to 

structure and landscaping vulnerabilities in different exposure conditions and are 

essential in documenting the successes and failures of hazard reduction solutions. 

8.7 Future WUI post-fire case studies.

While not all obstacles could be overcome in this first analysis they did provide 

enormous assistance in the design of a new data collection system as employed in the 

Amarillo Texas Fires of 201121, the development of an exposure scale and the ongoing 

enhancement of NIST’s data collection system and associated training. Despite the high 

spatial, spectral and temporal resolution of the remote sensing data available and the 

extensive field surveys, more timely and extensive data collection is required for 

complete accounting of all the potential factors. Nonetheless, the results presented above 

provide valuable insight into the WUI problem. 
45

9.0 Summary

First, the applicability and presence of Firewise attributes within the Trails was assessed. 

Next, treatments were evaluated across the parts of the community that were within the 

fire line. The exposure concept was introduced and two different approaches were 

evaluated. The perimeter, interior exposure model was first introduced in NIST TN1635, 

the first Witch/Guejito report. The second approach computed high and low exposures as 

a function of slope, aspect and vegetative fuel. Firewise effectiveness was further 

evaluated using both exposure approaches. Lastly, defensive actions were evaluated in 

the context of ignition mechanism and Firewise treatment, and the locations of these 

defensive actions with respect to high/low hazard areas were assessed. The following 

statements summarize the findings from this study of the Witch and Guejito Fires:

• The majority of the Firewise treatments evaluated at the Trails Community 

appeared to be applicable even if each of them were not fully effective.

• Firewise irrigation treatments might not be applicable in a desert environment 

such as the Trails for long-term effective mitigation if water shortages occur.

• The Firewise Zone Concept, as described in the Firewise Landscaping Checklist

(see Table 2), if not implemented with community cooperation when there are 

overlapping zones from different owners might result in the creation of hazardous 

areas.

• Vegetative fuel removal and not fuel displacement is necessary for housing 

densities such as at the Trails. This is necessary as fuels distant from the primary 

structure can be very close to a neighboring structure. 

• WUI mitigation advice, such as provided by Firewise, that is designed to allow a

wildland fire to burn through a community might not be appropriate for interface 

type WUI communities or where structures are closely spaced and lot sizes are 

relatively small.

• Fifty eight percent (141 of 242) of the structures in the Trails had less than 50% of 

the evaluated Firewise treatments present.

• Fire vulnerabilities such as local area fire history, site location, overall terrain, 

prevailing winds, seasonal weather, property contours and native vegetation did 

not appear to be considered in design of the Trails community.

• There is a pattern of increased destruction to residential structures with increased 

exposure to slopes greater than 20%, for northeast, north and east aspects, and for 

vegetated surfaces at the Trails. Vegetation treatment was not considered in this 

analysis.

• Individually, implementation of Firewise treatment numbers 1, 7, 8, 9, 13, 17 and 

19 were associated with a reduction in damage and destruction to residential 

structures at the Trails. 

• Individually, implementation of Firewise treatment numbers 1, 7, 8, 9, 17 and 19 

were associated with a reduction in damage and destruction to residential 

structures in both low and high exposure environments as evaluated at the Trails. 

• Individually, implementation of Firewise treatment numbers 1, 7, 8, and 19 in a 

high exposure environment might show a more pronounced effect in terms of 
46

structure response compared to implementation in low exposure environments at 

the Trails.

• Defensive actions showed treatment 22 to be effective as well as Firewise 

treatments to “Keep gutters, eaves, and roofs clear of leaves and other debris” 

and to “Use construction materials that are fire-resistant or non-combustible 

whenever possible”; both of which were not assessed in this paper due to the 

impossibility of determining treatment presence for a destroyed structure. 

• For structures in high exposure areas, 74% of the defended structures were 

damaged or destroyed compared to 33% in low exposure. 

• For the 19 defended properties, 10 contained destroyed structures and 4 damaged, 

whereas in low exposure, of the 66 defended properties, 10 were destroyed and 12 

were damaged. 

• Defensive actions were over two times more effective in saving structures in low 

exposure areas compared to high exposure areas.

Again, it must be remembered that any correlation among the various treatments was not 

assessed in the above analyses. Additionally, more precise methods of quantifying 

exposure might be required such as delineation of burned features across the area and 

mapping of ember assault. Finally, it is important to note that this study was based on an 

uncoupled analysis of exposure and structure ignition. The more these mechanisms can 

be uncoupled, the more fully quantifiable structure response to WUI fires might become. 

10.0 Conclusions/Recommendations

This study emphasizes the importance of conducting specific actions when performing 

WUI post-fire assessments. WUI post-fire assessments aimed at determining the 

effectiveness of hazard mitigation technologies should involve:

1. Evaluating all structures exposed and their characteristics, not just what was

destroyed.

2. Quantifying the fire and ember assault on a structure at a particular location in 

space and time as practical or researching exposure surrogates for simpler 

quantification.

3. Measuring and recording the type, location and effectiveness of defensive actions. 

The above activities, particularly when combined, can provide critical insight into 

structural response. For example, the statistical analyses performed above all require data 

related to the entire population of data, both destroyed and undamaged. Additionally, 

combining defensive actions with the identification of damaged structures leads to a clear 

evaluation of ignition mechanisms and consequences in regard to treatment effectiveness. 

This is apparent in the case of elevated wood decks on top of a hill, which were not 

statistically significant due to the lack of data, but assessment of the damage coupled 

with defensive action associations allowed for the identification of these features as 

ignition mechanisms. This also demonstrates the effectiveness of this treatment, at least 

in some instances at the Trails. Nonetheless, performing the above activities to precisely 

measure and record the complex set of variables involved in full quantification of a postfire environment is a challenging endeavor. As this study represented the first attempt at 

such a task, certain activities were conducted at coarser scales than what might ultimately 
47

be necessary to fully evaluate the effectiveness of Firewise treatments. This approach 

also allowed for a framework to build and enhance the data collection methodology for 

more refined and/or variable data collection activities. Most importantly, this approach 

allowed for an assessment of certain aspects of current WUI mitigation advice. 

No Firewise treatments were found to be ineffective in this study, although not all 

treatments were evaluated, while many had different levels of effectiveness. 

Additionally, many of the treatments analyzed at an individual basis were found to be 

effective in all exposure environments assessed for this paper. There was, however, some 

evidence that structure response to treatment might be different in different environments. 

This might suggest the need for different treatment options depending on the scenario. 

Given the findings of this study, it is recommended that:

1. Additional field data collection studies are conducted to provide insight into structural 

response in both high and low exposure environments.

2. The exposure concept is further developed to enable valid comparisons of structural 

response within and across incidents.

3. Research is conduced to provide the technical foundation for improving the current 

Firewise Checklist (see Table2). Specifically, the detailed relationship of exposure 

and structure vulnerability needs to be developed. This will lead to improved testing 

standards for new construction and improved guidance for retrofit.

4. An unambiguous checklist should be developed to facilitate the implementation of 

hazard reduction techniques by homeowners. The authors have concluded that new 

checklists are required for different scenarios (e.g. intermix versus interface 

communities; existing construction versus new construction).

5. The concept of structure vulnerability should be further developed. When coupled 

with exposure, this approach should yield improved tools for predicting structure 

destruction.

11.0 Future Work

Future work using post fire data will explore the capabilities and limitations of using 

different fire behavior models to simulate and predict fire behavior at the Trails 

Community. 

The data collection methodology developed from the work at the Trails has already been 

implemented in other field post-fire studies21. Future work will involve analyzing the 

Amarillo data22 using the lessons learned from this report as well as improving the 

methodology for future deployments. 

This first case study has identified a need for additional high and low exposure data. 

While the benefits of Firewise type attributes are significant in low exposure 

environments, additional post-fire field data collections in high exposure areas will 

provide insight into the effectiveness of these treatments under more severe exposure 

conditions. 

The development of exposure characterization will continue and the introduction of 

burning structures into the exposure determination will be explored using GIS and 

WFDS. Additionally, vegetation characterization will be explored as well as the potential 
48

for introducing the effects of dangerous topographical features such as chimneys or 

ravines.

A structure destruction potential method may be fruitfull and future work will consider its 

development. A simple framework will be initially developed as outlined below for 

coupling exposure and vulnerabilities. Initial focus will be on determining the potential 

reliability of such a framework. The proposed destruction potential concept is outlined in 

equations 3 and 4, where a, b, c and d are constants for the four classes of attributes that 

represent the structure and landscaping vulnerabilities and access for defensive actions on 

and around the structure. The exposure characterization used will initially be the high/low 

concept presented here. Additional refinements in the exposure characterization will be 

introduced as they become available.

Vulnerability = a(Combustibles near home) – b(Fuel break/irrigation) + c(Combustible 

construction)- d(Access for defensive actions) equation 3

Structure Destruction Potential = Vulnerability x Exposure equation 4

12.0 Acknowledgements

This work would not have been possible without the contributions of, CAL FIRE, San 

Diego Fire and Rescue and Police Departments and the residents of the Trails, including 

Mr. Steve Arnold. Additionally, this work would not have been possible without Carol 

Ostergren of the United States Geological Survey (USGS) and the USGS geospatial data 

services, who provided most of the remote sensing data used in this analysis. This work is 

in part funded by the Joint Fire Science Program Project 11-1-3-29, “Evaluating the 

Effectiveness of Mitigations Activities in the Wildland Urban Interface”.
49

Figure 1 Overview of the entire extent of the Witch and Guejito Fires in context with the United States. Also portrayed is the 

study area within the fire perimeter and the origins of the fires.
50

Figure 2 Fire approach to the Trails Community from the Witch and Guejito Fires. Back ground imagery is 1 ft (0.3 m) horizontal 

resolution color imagery flown shortly after the fires.
51

Figure 3 Trails community in relation to Witch fire perimeter with primary structures displayed by damaged status. Back ground 

imagery is 3 inch (8 cm) horizontal resolution color imagery from 2005.
52

Figure 4 Hillshade portraying topography in and around the Trails. Hillshade created from Light Intensity Detection and Ranging 

(LIDAR) derived 1.5 m (4.9 ft) digital elevation model obtained from the United States Geologic Survey (USGS).
53

Figure 5 Property lot types in the Trails Community. Back ground imagery is 3 inch (8 cm) horizontal resolution color imagery from 

2005.
54

Figure 6 Primary structure densities per square mile for the Witch and Guejito Fires. Derived using the ArcGISTM Point Density Tool 

with a circle window having a radius of approximately 200 meters (660 feet) and an output cell size of 3 m (10 ft).
55

Figure 7 Residential structure density in and around the Trails. Derived using the ArcGISTM Point Density Tool with a circle window 

having a radius of approximately 200 m (660 ft) and an output cell size of 3 m (10 ft).
56

Figure 8 Defensive actions on residential properties overlaid with primary structures displayed by damaged status. Back ground imagery 

is 1 ft (0.3 m) horizontal resolution color imagery flown shortly after the fires.
57

Figure 9 Fire direction in the Trails overlaid with primary structures displayed by damaged status. Back ground imagery is 1 ft (0.3 m) 

horizontal resolution color imagery flown shortly after the fires.
58

Figure 10 Above ground residential vegetation in the Trails overlaid with the Fire perimeter. Back ground imagery is 1 ft (0.3 m ) 

horizontal resolution color imagery flown shortly after the fires.
59

Figure 11 Wildland vegetation community types in and around the Trails overlaid with primary structures displayed by damaged 

status. Back ground imagery is 3 inch (8 cm) horizontal resolution color imagery from 2005.
60

Figure 12 Trails percent slope raster data set derived from LIDAR 5 foot DEM overlaid with residential structure damage and 

destruction.
61

Figure 13 Trails aspect raster data set derived from LIDAR 5 ft (1.5 m ) DEM and reclassified to eight directions and overlaid with 

primary structures displayed by damaged status.
62

Figure 14 Potential change in vegetation greenness (dNDVI) between 2005 and 10 days after the Witch and Guejito Fires.
63

Figure 15 Overview of data analysis steps
64

Figure 16 Example of directional sector employed on destroyed structure at the Trails. All sectors begin at zero and continue the specified 

distance. Sectors for 30 ft, 100 ft, 200 ft and 300 ft (9 m, 30 m, 60 m and 90 m) distances have portions excluded by the other sectors.
65

Figure 17 Geographic distribution of Firewise Zones assuming homeowner cooperation.
66

Figure 18 Firewise Zones viewed at an individual property level. Back ground imagery is 3 inch (8 cm) horizontal resolution color imagery 

from 2005.
67

Figure 19 Relationship between Firewise Zones 3 100 ft to 200 ft (30 m to 61 m) and Zones 4 200 ft to 300 feet (61 m to 91 m), and dNDVI 

(surrogate for burned vegetation) overlaid with primary structures displayed by damaged status.
68

203

36

1 2 0

64

23

1 2 0

139

13

0 0 0

0

50

100

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Percent Wildland Vegetation in Zone 1

Property Count

All Structures

Damaged/Destroyed Structures

Undamaged Structures

164

43

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44

14

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26

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123

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51

0

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Percent Wildland Vegetation in Zone 4

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Undamaged Structures

Figure 20 Frequency counts of structures by bins of percent of wildland vegetation found on the property for four zones.
69

12

117

74

37

2

11

88

43

10

1 0

29 31 27

2

0

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40

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0-10% 10-20% 20-30% 30-40% 40-50%

Percent Slope Categories

Property Count

All Residential Structures

Damaged/Destroyed Structures

Undamaged Structures

Figure 21 Frequency counts of properties by bins of average percent slopes found on properties for all structures, undamaged structures and 

damaged/destroyed structures.
70

49

33

23

20 21

31 30

35

10 12

18

15

25 24 22

13

6 6 6

2

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23 26

0

10

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North Northeast East Southeast South Southwest West Northwest

Majority Aspect

Property Count

All Residential Structures

Damaged/Destroyed

Undamaged Structures

Figure 22 Frequency counts of properties by bins of the majority of aspects found on properties for all structures, undamaged structures and 

damaged/destroyed structures.
71

1

44

96

63

28

1

34

7 6

0

62

56

22

33

11

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40

60

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0% 25% 50% 75% 100%

Percent of Firewise Treatments Present

Property Count

All Structures

Damaged/Destroyed Structures

Undamaged Structures

Figure 23 Frequency counts of properties by bins of percent of Firewise Treatments present on property for all structures, undamaged structures and 

damaged/destroyed structures where the presence of treatments on the property could be determined for greater than 50% of the Firewise Treatments 

assessed.
72

Figure 24 Areas with high slopes (>20%); northeast, north and east aspects; and vegetation (shown in yellow) overlaid on the modified dNDVI 

data set
73

39 of 153

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17 of 51

28 of 37 6 of 8

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

0% 25% 50% 75% 100%

Percent High Hazard Area (300 ft Directional Buffer)

Percent of Structures Destroyed

Figure 25 Bar graphs portraying percent primary structures destroyed by bins of percent of wildland vegetation present in the 

respective sector distance. A) Shows results for 0 ft to 30 ft (0 m to 9 m) sector. B) Shows results for 0 ft to 100 ft (0 m to 30 m) 

sector. C) Shows results for 0 ft to 200 ft (0 m to 61 m) sector. D) Shows results for 0 ft to 300 ft (0 m to 91 m) sector.

A) B)

C) D)
74

Figure 26 Boxplot showing 95% confidence interval for the interactions between individual treatments and perimeter/interior parcels and high/low 

exposure parcels. The 1st line (blue) represents perimeter; 2nd line (green) is interior; 3rd line (purple) is high exposure; 4th line (orange) is low exposure.
75

Appendix A

NIST TN1635 Findings
76

The Witch fire was spreading towards the Rancho Bernardo area of San Diego, CA when 

the Guejito fire ignited. The proximity of the Guejito fire origin to the Rancho Bernardo 

area dramatically reduced the available time for resident evacuation and resource 

deployment. The net result was that in The Trails, resident evacuation was conducted as 

the fire reached the community. Additionally, half of the fire fighting resources available 

were involved in resident evacuation. The impact of the Guejito fire from embers 

(spotting ignitions) before the main fire front reached the community was very limited 

with only three home ignitions and six reported vegetative fires. The arrival of the front at 

approximately 3:45 am resulted in a very rapid increase in structure ignitions, exceeding 

20 per hour at its peak. As the structure ignitions continued, however the rate decreased 

to nine per hour by 5:30 am then to eight per hour by 6:30 am. After the Witch fire 

reached the community, shortly after 6:00 am, the ignitions of structures dropped to one 

or two per hour. 

The rapid ignition of structures after the main fire attack demonstrates that, with the 

limited available resources, effective fire prevention is essential to reducing losses. 

Tested and implementable guidance for homeowners, communities and land use officials 

are essential to reducing losses in the future. 

The contributions of the SDFD, SDPD and homeowners significantly reduced the losses 

from these fires. Thirty percent of structures within the fireline were defended. Actions 

by the SDFD saved a number of homes as did actions from homeowners. Even though 

structures were saved by residents, in the case of The Trails, smoke inhalation, egress 

considerations, and limited visibility all contributed to generating a very high risk 

environment. Many additional actions were taken that limited fire spread, however, their 

effects are not traceable.

The development of a timeline for fire spread through the wildland fuels and then through 

The Trails has been able to provide insights on fire behavior at the WUI. Figure 30 

summarizes much of the spatial and temporal information. The findings to date are 

divided into two categories; general fire behavior, and defensive actions and structural 

losses.

General Fire Behavior

- The Guejito fire approached The Trails at a fire spread rate of 9 km/h.

- Fire spread rate within the community dropped to 0.35 km/h.

- Embers from the approaching wildland fire front started arriving at the 

community an hour before the main fire front, traveling a distance of 9.0 km.

- The ignitions generated by embers prior to the arrival of the main fire front were 

limited to three homes and several patches of ornamental vegetation. These 

ignitions occurred 9.0 km ahead of the main front.

- Fire spread up to 500 m into the interior of the community.

Structural Losses and Defensive Actions
77

- The arrival of the wildland fire front, not the preceding embers, caused the 

majority of the damage and overwhelmed the first responder resources.

- 70 % of the destroyed homes were not defended.

- 60 % of defended structures on fire were saved.

- Over 50 % of the structures were ignited within 3 hours after the main front of the 

Guejito fire hit the community.

- At its peak; right when the wildland fire front reached the community, structure 

ignitions reached 21 per hour.

- It is estimated that 29 of the destroyed structures (40 %) were burning at the same 

time.

- Two out of every three destroyed homes were ignited directly or indirectly by 

embers.

- Direct embers ignitions occurred from the arrival of the wildland fire front and for 

the next nine hours.

- Direct ember ignitions accounted for one out of every three destroyed homes.

- Embers were responsible for the ignitions of structures on the perimeter and in the 

interior of the community.

- 40% of structures on the perimeter were destroyed compared to 20 % in the 

interior of the community.

- Defensive actions were taken on one out of every three homes in The Trails.

- Fifteen out the sixteen damaged homes were successfully defended. No defensive 

actions have been identified on the sixteenth damage home.

- Impact of defensive actions was significant, and probably reduced losses from 

over 37% down to 30 %.

Unanswered Questions

Despite the extensive data collection and analysis, there are several questions that remain 

unanswered. The information available has not been sufficient to determine how many 

home ignitions were a direct result of the wildland fire and how many resulted from 

structure to structure fire spread via structure generated embers. Additionally, the full 

impact of all the defensive actions was not quantified. Even though it is likely that most 

of the 15 damaged structures would have burned without intervention, over 60 

documented actions were taken with potentially significant yet unquantifiable 

ramifications to fire spread and structure ignitions. To provide implementable risk 

reduction technologies, the fire and ember exposure needs to be characterized. Post fire 

studies, laboratory and field experiments and fire modeling are needed to capture the true 

flame and embers exposures and structure vulnerabilities.

The reach of the wildland fire into the community was not determined. The limited data 

available shows that in the vicinity of fire jumps from the perimeter to the interior of the 

community, there are two cases were structures in the interior ignited before structures on 

the perimeter. It is therefore possible that the wildland fire front ignited structures 0.2 km 
78

in from the perimeter. This hypothesis, however, cannot be confirmed because of the 

limited spatial/temporal resolution of the currently available data. Additional information 

to answer this question should be collected in the future in the form of highly temporally 

resolved structure burning. This may be accomplished by ground observations or remote 

sensing platforms such as unmanned aerial systems. 
79

Appendix B

Firewise Checklists
80
81
82

Appendix C

NIST Field Data Collection Used for Assessing 

74 Destroyed Structures
83
84
85

Appendix D

NIST Field Data Collection Used for Assessing 

168 Non-Destroyed Structures
86

ADDRESS: ________________________ DATE: _______ TEAM #:_____ 

Pictures

First to Last

Issue Yes, No, N/A Comments

Zone 1 is closest to the structure; Zones 2-4 move progressively further away

Zone 1. This well-irrigated area encircles the structure for at 

least 30' on all sides. (If one side or section does not meet this it 

is a “No”)

Yes, No, N/A

Zone 1. Provide space for fire suppression equipment in the 

event of an emergency.

Yes, No, N/A

Zone 1. Plantings should be limited to carefully spaced low 

flammability species.

Yes, No, N/A

Zone 2. Low flammability plant materials should be used here. 

Plants should be low-growing, and the irrigation system should 

extend into this section.

Yes, No, N/A

Zone 3. Place low-growing plants and well-spaced trees in this 

area, remembering to keep the volume of vegetation (fuel) low.

Yes, No, N/A

Zone 4. This furthest zone from the structure is a natural area.

Selectively prune and thin all plants and remove highly 

flammable vegetation.

Yes, No, N/A

Take out the “ladder fuels” — vegetation that serves as a link 

between grass and tree tops.

Yes, No, N/A

Provide added protection with “fuel breaks” like driveways, 

gravel walkways, and lawns.

Yes, No, N/A

Maintaining a landscape:

Keep trees and shrubs properly pruned. Prune all trees so the 

lowest limbs are 6' to 10' from the ground.

Yes, No, N/A

Remove leaf clutter and dead and overhanging branches. Yes, No, N/A

Store firewood away from the house. Yes, No, N/A
87

NIST FIELD DATA COLLECTION FORM (PAGE 2)

Selecting a firewise location:

Slope of terrain; be sure to build on the most level portion of the 

land

Yes, No, N/A

Set your single-story structure at least 30 feet back from any 

ridge or cliff; increase distance if your home will be higher than 

one story. 

Yes, No, N/A

If Yes Specify 

Setback:___ 

ft

In designing and building your firewise structure, the primary goals are fuel and exposure reduction

Use construction materials that are fire-resistant or noncombustible whenever possible. (Any wood (deck/pergola, 

fence) within 30 ft is a “No”)

For roof construction, consider using materials such as Class-A 

asphalt shingles, slate or clay tile, metal, cement and concrete 

products, or terra-cotta tiles.

On exterior wall facing, fire resistive materials such as stucco or 

masonry are much better choices than vinyl which can soften 

and melt.

Driveway that is 12 feet wide with a vertical clearance of 15 feet 

and a slope that is less than 5 percent and include ample 

turnaround space near the house.

Any structures attached to the house, such as decks, porches, fences, and outbuildings should be considered part of the house. These structures can 

act as fuel bridges, particularly if constructed from flammable materials.

Periodically inspect your property, clearing dead wood and 

dense vegetation at distance of at least 30 feet from your house. 

Move firewood away from the house or attachments like fences 

or decks.

If you wish to attach an all-wood fence to your house, use 

masonry or metal as protective barriers between the fence and 

house.

Prevent combustible materials and debris from accumulating 

beneath patio decks or elevated porches.

Screen or box-in areas below patios and decks with wire screen 

no larger than 1/8 inch mesh.

Make sure an elevated wooden deck is not located at the top of 

a hill where it will be in direct line of a fire moving up slope.
88

Appendix E

Derivation of dNDVI Data Set
89

Change in greenness can be derived from the remote sensing image sources listed above 

by exploiting the difference between the spectral response of healthy green vegetation in 

the near infrared and red portions of the electromagnetic spectrum. The individual bands 

of imagery collected in the NAIP and post-fire imagery can be manipulated through the 

derivation of the Normalized Difference Vegetation Index (NDVI) as shown in equation 

A.

) Near Infrared Band Red Band

Near Infrared Band - Red Band NDVI

+ = ( Equation A

Near Infrared Band is the spectral response in the near infrared portion of the 

electromagnetic spectrum as recorded by the respective sensor. Red Band is the spectral 

response in the red portion of the electromagnetic spectrum as recorded by the respective 

sensor. 

The NDVI equation produces a range of values between -1 and 1. Generally speaking, 

values below zero represent areas where there is little photosynthetically active 

vegetation. Values above 0.2 typically represent areas with photosynthetically active 

vegetation. Values between -0.1 and 0.2 might represent features such as soil, rock and 

water. Assuming that the near infrared reflectance of burned vegetation decreases after a 

fire; pre- and post-fire NDVI data sets can be differenced to derive a change in NDVI 

product (dNDVI). The NDVI also helps to compensate for both in scene variations in 

imagery based on topography and between scene variation based on differences in flight 

season and time of day. The assumption of near infrared reflectance decreasing after a 

vegetation fire, however, is not always true when complete combustion occurs and is 

evidenced by white ash (Smith et al. 2005) xxiii. The wildlands surrounding the Trails also 

contained alkaline areas that experienced stand replacing fires where white areas might 

have been white ash but could have been exposed mineral soils. NDVI can also be 

influenced by shadows and/or clouds. Phenological differences in vegetation between 

image acquisition dates can also affect changes in NDVI. Finally, image differencing 

and calibration techniques might introduce errors.
90

Appendix F

Two-way Contingency Tables for Firewise Treatments with No 

Association Between Structure Survivability and Treatment 

Presence
91

Treatment 1c: Plantings should be limited to carefully spaced low flammability species

for at least 30’.

Undamaged

Structures

Damaged/ Destroyed

Structures

Total

Fail 121 70 191

Pass 31 11 42

Total 152 81 233

Firewise Treatment 1c: p-value = 0.1975

Treatment 6: Take out the “ladder fuels” — vegetation that serves as a link between grass 

and tree tops.

Undamaged

Structures

Damaged/ Destroyed

Structures

Total

Fail 114 67 181

Pass 33 12 45

Total 147 79 226

Firewise Treatment 6: p-value = 0.224

Treatment 11: Slope of terrain; be sure to build on the most level portion of the land.

Undamaged

Structures

Damaged/ Destroyed

Structures

Total

Fail 9 1 10

Pass 144 90 234

Total 153 91 244

Firewise Treatment 11: p-value = 0.096

Treatment 14: For roof construction, consider using materials such as Class-A asphalt 

shingles, slate or clay tile, metal, cement and concrete products, or terra-cotta tiles.

Undamaged

Structures

Damaged/ Destroyed

Structures

Total

Fail 0 13 13

Pass 152 77 229

Total 152 90 242

Firewise Treatment 11: No p-value exists

Treatment 15: On exterior wall facing, fire resistive materials such as stucco or masonry 

are much better choices than vinyl which can soften and melt.

Undamaged

Structures

Damaged/ Destroyed

Structures

Total

Fail 30 16 46

Pass 122 67 189

Total 152 83 235

Firewise Treatment 15: p-value = 0.9323
92

Treatment 18: Move firewood away from the house or attachments like fences or decks.

Undamaged

Structures

Damaged/ Destroyed

Structures

Total

Fail 20 39 59

Pass 21 31 52

Total 41 70 111

Firewise Treatment 18: p-value = 0.556

Treatment 20: Prevent combustible materials and debris from accumulating beneath patio 

decks or elevated porches.

Undamaged

Structures

Damaged/ Destroyed

Structures

Total

Fail 27 9 36

Pass 47 6 53

Total 74 15 89

Firewise Treatment 20: p-value = 0.0906

Treatment 21: Screen or box-in areas below patios and decks with wire screen no larger 

than 1/8 inch mesh.

Undamaged

Structures

Damaged/ Destroyed

Structures

Total

Fail 48 23 71

Pass 6 4 10

Total 54 27 81

Firewise Treatment 21: p-value = 0.6329

Treatment 22: Make sure an elevated wooden deck is not located at the top of a hill 

where it will be in direct line of a fire moving up slope.

Undamaged

Structures

Damaged/ Destroyed

Structures

Total

Fail 22 22 44

Pass 11 2 13

Total 33 24 57

Firewise Treatment 22: p-value = 0.02635
93

Appendix G

Three-way Contingency Tables for Firewise Treatments with No 

Association between Structure Survivability and Exposure 

Delineation, and Treatment Presence 
94

Treatment 1c: Plantings should be limited to carefully spaced low flammability species

for at least 30’.

Property on Perimeter Property in Interior

Undamaged Damaged & 

Destroyed

Total Undamaged Damaged & 

Destroyed

Total

Fail 27 (46%) 32 (54%) 59 Fail 94 (71%) 38 (29%) 132

Pass 31 (84%) 6 (16%) 37 Pass 31 (86%) 5 (14%) 36

Total 58 (60%) 38 (40%) 96 Total 125 (74%) 43 (26%) 168

Property with High Hazard Area Property with Low Hazard Area

Undamaged Damaged & 

Destroyed

Total Undamaged Damaged & 

Destroyed

Total

Fail 7 (21%) 26 (79%) 33 Fail 114 (72%) 44 (28%) 158

Pass 31 (94%) 2 (6%) 33 Pass 31 (78%) 9 (23%) 40

Total 31 (58%) 28 (42%) 66 Total 145 (73%) 53 (27%) 198

Treatment 6: Take out the “ladder fuels” — vegetation that serves as a link between grass 

and tree tops.

Property on Perimeter Property in Interior

Undamaged Damaged & 

Destroyed

Total Undamaged Damaged & 

Destroyed

Total

Fail 114 (78%) 32 (22%) 146 Fail 114 (77%) 35 (23%) 149

Pass 33 (73%) 12 (27%) 45 Pass 33 (73%) 12 (27%) 45

Total 147 (77%) 44 (23%) 191 Total 147 (76%) 47 (24%) 194

Property with High Hazard Area Property with Low Hazard Area

Undamaged Damaged & 

Destroyed

Total Undamaged Damaged & 

Destroyed

Total

Fail 114 (83%) 24 (17%) 138 Fail 114 (72%) 44 (28%) 158

Pass 33 (73%) 12 (27%) 45 Pass 33 (73%) 12 (27%) 45

Total 147 (80%) 36 (20%) 183 Total 147 (72%) 56 (28%) 203

Treatment 10: Storing firewood away from the house a minimum of 30 ft.

Property on Perimeter Property in Interior

Undamaged Damaged & 

Destroyed

Total Undamaged Damaged & 

Destroyed

Total

Fail 5 (16 ± 12%) 27 (84 ± 12%) 32 Fail 14 (35 ± 14%) 26 (65 ± 14%) 40

Pass 5 (63 ± 35%) 3 (37 ± 35%) 8 Pass 12 (60 ± 20%) 8 (40 ± 20%) 20

Total 10 (25 ± 13%) 30 (75 ± 13%) 40 Total 26 (42 ± 12%) 34 (58 ± 12%) 60

FW10: p-value = 0.003 (**), perimeter: p-value = 0.14 – The perimeter is not significant for this attribute

Property with High Hazard Area Property with Low Hazard Area

Undamaged Damaged & 

Destroyed

Total Undamaged Damaged & 

Destroyed

Total

Fail 0 19 19 Fail 19 (36 ± 13%) 34 (64 ± 13%) 53

Pass 1 (20 ± 35%) 4 (80± 35%) 5 Pass 16 (70 ± 18%) 7 (30 ± 18%) 23

Total 1 (4 ± 8%) 23 (96 ± 8%) 24 Total 35 (46 ± 11%) 41 (54 ± 11%) 76

FW10: p-value = 0.002 (**), exposure: p-value = 0.004(**)
95

Treatment 11: Slope of terrain; be sure to build on the most level portion of the land.

Property on Perimeter Property in Interior

Undamaged Damaged & 

Destroyed

Total Undamaged Damaged & 

Destroyed

Total

Fail 2 (100%) 0 (0%) 2 Fail 7 (88%) 1 (13%) 8

Pass 35 (45%) 43 (55%) 78 Pass 108 (70%) 46 (30%) 154

Total 37 (46%) 43 (54%) 180 Total 115 (71%) 47 (29%) 162

Property with High Hazard Area Property with Low Hazard Area

Undamaged Damaged & 

Destroyed

Total Undamaged Damaged & 

Destroyed

Total

Fail 0 (--%) 0 (--%) 0 Fail 9 (90%) 1 (10%) 10

Pass 10 (77%) 33 (23%) 43 Pass 133 (70%) 56 (30%) 189

Total 10 (77%) 33 (23%) 43 Total 142 (71%) 57 (29%) 199

Treatment 13: Use construction materials that are fire-resistant or non-combustible 

whenever possible.

Property on Perimeter Property in Interior

Undamaged Damaged & 

Destroyed

Total Undamaged Damaged & 

Destroyed

Total

Fail 34 (45%) 41 (55%) 75 Fail 99 (72%) 39 (28%) 138

Pass 3 (60%) 2 (40%) 5 Pass 16 (94%) 1 (6%) 17

Total 37 (46%) 43 (54%) 80 Total 115 (74%) 40 (26%) 155

Property with High Hazard Area Property with Low Hazard Area

Undamaged Damaged & 

Destroyed

Total Undamaged Damaged & 

Destroyed

Total

Fail 10 (24%) 31 (76%) 41 Fail 3 (50%) 3 (50%) 64

Pass 0 (0%) 1 (100%) 1 Pass 7 (78%) 2 (22%) 129

Total 10 (24%) 32 (76%) 42 Total 4 (44%) 5 (56%) 193

Treatment 14: For roof construction, consider using materials such as Class-A asphalt 

shingles, slate or clay tile, metal, cement and concrete products, or terra-cotta tiles.

Property on Perimeter Property in Interior

Undamaged Damaged & 

Destroyed

Total Undamaged Damaged & 

Destroyed

Total

Fail 0 (0%) 3 (100%) 3 Fail 0 (0%) 10 (100%) 10

Pass 37 (48%) 40 (52%) 77 Pass 115 (76%) 37 (24%) 152

Total 37 (46%) 43 (54%) 80 Total 115 (71%) 47 (29%) 162

Property with High Hazard Area Property with Low Hazard Area

Undamaged Damaged & 

Destroyed

Total Undamaged Damaged & 

Destroyed

Total

Fail 0 (0%) 4 (100%) 4 Fail 0 (0%) 9 (100%) 9

Pass 10 (26%) 29 (74%) 39 Pass 142 (75%) 48 (25%) 190

Total 10 (23%) 33 (77%) 43 Total 142 (71%) 57 (29%) 199
96

Treatment 15: On exterior wall facing, fire resistive materials such as stucco or masonry 

are much better choices than vinyl which can soften and melt.

Property on Perimeter Property in Interior

Undamaged Damaged & 

Destroyed

Total Undamaged Damaged & 

Destroyed

Total

Fail 4 (50%) 4 (50%) 8 Fail 25 (66%) 13 (34%) 38

Pass 33 (49%) 35 (51%) 68 Pass 90 (74%) 31 (26%) 121

Total 37 (49%) 39 (51%) 76 Total 115 (72%) 44 (28%) 159

Property with High Hazard Area Property with Low Hazard Area

Undamaged Damaged & 

Destroyed

Total Undamaged Damaged & 

Destroyed

Total

Fail 2 (33%) 4 (67%) 6 Fail 28 (70%) 12 (30%) 40

Pass 8 (24%) 25 (76%) 33 Pass 114 (73%) 42 (27%) 156

Total 10 (26%) 29 (74%) 39 Total 142 (72%) 54 (28%) 196

Treatment 20: Prevent combustible materials and debris from accumulating beneath patio 

decks or elevated porches.

Property on Perimeter Property in Interior

Undamaged Damaged & 

Destroyed

Total Undamaged Damaged & 

Destroyed

Total

Fail 7 (64%) 4 (36%) 11 Fail 20 (80%) 5 (20%) 25

Pass 18 (82%) 4 (18%) 22 Pass 30 (97%) 1 (3%) 31

Total 25 (76%) 8 (24%) 33 Total 50 (89%) 6 (11%) 56

Property with High Hazard Area Property with Low Hazard Area

Undamaged

Structures

Damaged & 

Destroyed

Total Undamaged

Structures

Damaged & 

Destroyed

Total

Fail 2 (40%) 3 (60%) 5 Fail 25 (81%) 6 (19%) 31

Pass 6 (75%) 2 (25%) 8 Pass 41 (91%) 4 (9%) 45

Total 8 (62%) 5 (38%) 13 Total 66 (87%) 10 (13%) 76

Treatment 21: Screen or box-in areas below patios and decks with wire screen no larger 

than 1/8 inch mesh.

Property on Perimeter Property in Interior

Undamaged Damaged & 

Destroyed

Total Undamaged Damaged & 

Destroyed

Total

Fail 18 (55%) 15 (45%) 33 Fail 30 (79%) 8 (21%) 38

Pass 1 (25%) 3 (75%) 4 Pass 5 (83%) 1 (17%) 6

Total 19 (51%) 18 (49%) 37 Total 35 (80%) 44 (20%) 44

Property with High Hazard Area Property with Low Hazard Area

Undamaged Damaged & 

Destroyed

Total Undamaged Damaged & 

Destroyed

Total

Fail 8 (38%) 13 (62%) 21 Fail 40 (80%) 10 (20%) 50

Pass 0 (0%) 2 (100%) 2 Pass 6 (75%) 2 (25%) 8

Total 8 (35%) 15 (65%) 23 Total 46 (79%) 12 (21%) 58
97

Treatment 22: Make sure an elevated wooden deck is not located at the top of a hill 

where it will be in direct line of a fire moving up slope.

Property on Perimeter Property in Interior

Undamaged Damaged & 

Destroyed

Total Undamaged Damaged & 

Destroyed

Total

Fail 12 (43%) 16 (57%) 28 Fail 10 (63%) 6 (38%) 5

Pass 6 (75%) 2 (25%) 8 Pass 5 (100%) 0 (0%) 1

Total 18 (50%) 18 (50%) 36 Total 15 (71%) 6 (29%) 6

Property with High Hazard Area Property with Low Hazard Area

Undamaged Damaged & 

Destroyed

Total Undamaged Damaged & 

Destroyed

Total

Fail 6 (29%) 15 (71%) 21 Fail 16 (70%) 7 (30%) 23

Pass 2 (67%) 1 (33%) 3 Pass 9 (90%) 1 (10%) 10

Total 8 (33%) 16 (67%) 24 Total 25 (76%) 8 (24%) 33
98

13.0 References 

 1 National Fire Protection Association. “ NFPA 1144, Standard for Reducing Structure 

Ignition Hazards from Wildland Fire 2008 Edition.” Quincy, MA 02169, 2007.

2 The 20 Largest California Wildland Fires (By Structures Destroyed), CALFIRE 

Communication, January 12, 2009 

http://www.fire.ca.gov/communications/downloads/fact_sheets/20LSTRUCTURES.pdf

3 Witch Fire – General Information, CALFIRE

http://bof.fire.ca.gov/incidents/incidents_details_info?incident_id=225

4 Karter, Jr., M. J. “NFPA Reports: U.S. Fire Loss for 2007”, NFPA ,www.nfpa.org

5 After Action Report, October 2007 Wildfires City of San Diego Response 

http://www.sandiego.gov/mayor/pdf/fireafteraction.pdf

6 CALFIRE Investigation Report, CA-CDF-010432 (Witch Fire), 

http://www.fire.ca.gov/fire_protection/downloads/redsheet/CA-MVU010432_Complete.pdf

7 CALFIRE Investigation Report, CA-CDF-010484(Guejito Fire), 

http://www.fire.ca.gov/fire_protection/downloads/redsheet/CA-MVU010484_Complete.pdf

8 Maranghides, A., and Mell, W., “ A Case Study of a Community Affected by the Witch 

and Guejito Fires”, NIST TN1635, April 2009

9 http://www.firewise.org/

10 Mell, W.E., Manzello, S.L., Maranghides, A., Butry, D., Rehm, R.G., “The wildlandurban interface fire problem – current approaches and research needs”, International J. 

of Wildland Fire, March 31 2010.

11 San Diego Geographic Information Source, A Joint Powers Authority of the City and 

County of San Diego, http://www.sangis.org/

12 Glossary of Wildland Fire Terminology, PMS 205, November 2008, A publication of 

the National Wildfire Coordinating Group

13 National Fire Protection Association and USDA Forest Service. “Safer from the Start: 

A Guide to Firewise-Friendly Developments.” 1 Battery Park, Quincy, MA 02169. 

2009.
99

 14 American Society of Photogrammetry and Remote Sensing, ASPRS LAS 1.1 Format 

Standard. May 07, 2005. Accessed August 01, 2012: 

http://www.asprs.org/a/society/committees/standards/asprs_las_format_v11.pdf.

15 American Society of Photogrammetry and Remote Sensing, LAS Specification Version 

1.2, Approved by the ASPRS Board 09/02/2008, 

www.asprs.org/a/society/committees/standards/asprs_las_format_v12.pdf

16 McNamara, D., Trook, J., Hu, J., Roberts, F., “Deriving Data Inputs for the Wildland 

Fire Dynamics Simulator” Report for NIST, Grant #60NANB5D1204, 2009.

17 USDA, Home Destruction Examination Grass Valley Fire, Lake Arrowhead, CA, 

http://www.fs.fed.us/rm/pubs_other/rmrs_2008_cohen_j001.pdf

18 bushfire CRC, Victorian 2009 Bushfire Research Response Interim Report, June 2009.

19 Firewise at NFPA: A brief history, www.firewise.org/abpout/history.aspx

20 Australian Bushfire Study, www.bushfirecrc.com/research/vicfires-taskforce/researchreports

21 Maranghides, A., Mell, W., Ridenour, K., McNamara, D., “Initial Reconnaissance of 

the 2011 Wildland-Urban Intreface Fires in Amarillo, Texas”, NIST TN 1708, July 

2011.

22 NIST Technical Note, Report in Preparation, 2013