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Defensible Space and Inspection Activities Reducing Substation Wildfire Ignitions

Presented By:
Justin Flores, Principal Specialist

Substation Asset Management
Pacific Gas and Electric Company
TechCon 2024

Abstract

As wildland fires across the western US and beyond have recently increased in frequency and intensity, new strategies, and methods to detect ignition related failure risks are becoming increasingly critical to reduce the likelihood of utility caused catastrophic wildfires. Following a series of California wildland fires from 2017-2019, PG&E updated its approach to conventional substation maintenance and inspection strategies to also account for wildfire risk detection and other hardening activities designed to reduce ignition probabilities and to mitigate consequences following an ignition event within or near electric substations.

Introduction

This paper provides background of PG&E’s electric substations located within areas of elevated or increased wildfire risk and informs on the differences between conventional substation maintenance and inspection practices compared to new methods recently implemented to mitigate substation ignition events that could lead to catastrophic wildland fires which take into account, High Fire Risk Areas (HFRA), High Fire Threat Districts (HFTD), asset health, failure modes, and available fuel loads and vegetation.

References

  1. Dr. T. Wall, G. McDonald, C. Enquist and S. Leroy, International Association of Wildland Fire “Drivers of California’s Changing Wildfires” “State Has Potential to Be a Model for Change”
  2. J.E. Keeley, J. Guzman-Morales, A. Gershunov, A.D. Syphard, D. Cayan, D.W. Pierce, M. Flannigan, and T.J. Brown, “Science Advances, Ignitions Explain More Than Temperature or Precipitation in Driving Santa Ana wind Fires” 21 Jul 2021 Vol 7, Issue 30.

Wildfire Impacts and Background

PG&E is a combined electric and gas transmission, distribution and electric generation utility serving over 16 million Californians across the central valley, bay area and northern regions of the state. The company owns, operates and maintains 18,000 miles of electric transmission lines with nearly 1,000 electric substations, switching stations and switch yards within its portfolio.

Wildfires across California are increasing in frequency and intensity and are causing more devastation due to a variety of drivers. Wildfires represent broad societal and environmental impacts and consequences. Many of the most common drivers for wildfires include ignitions sources; natural or human related, weather, and available fuels.

Figure 1 and Figure 2 include data sourced from the CAL-Fire website showing the 20 largest and most destructive California wildfires measured by acres and structures burned predominantly occurring in the last 6 years.

Figure 1, Largest Wildfires Measured by Acres Burned

Figure 1, Largest Wildfires Measured by Acres Burned table

Figure 2, Most Destructive Measured by Structures Burned

Figure 2, Most Destructive Measured by Structures Burned table

Ignitions: Eight of the 20 largest wildfires recorded in California history are attributed or partially attributed to human activity. Human-ignited fires are also responsible for at least 12 of the 20 most destructive fires in terms of structures and lives lost1. Wildfires can be ignited due to a variety of causes that include lightning, man-made ignitions such as campfires or arson, and industry related ignitions such as powerlines and other electric utility infrastructure. This paper focuses on the mitigation of fuel sources in and around utility owned electrical substations as a proven and effective means by which the probability of a substation ignited wildfire could be significantly reduced. Although PG&E has recorded approximately 30 substation fire ignition events since 2017, fortunately, none of those events resulted in a catastrophic wildland fire.

Figure 3, PG&E Substation Ignition Data

Figure 3, PG&E Substation Ignition Data graph

Weather: Dry and hot conditions lend themselves to an increased likelihood of ignition events due to the absence of moisture. The U.S Drought Monitor has tracked an increasing percentage of California’s geography located within the five categories of drought from 2000-2020 with data showing 85-90% of California experiencing some level of drought during the same period. Many of those areas experiencing drought are within HFTD and HFRA boundaries. High winds can also contribute to an increased likelihood of impacting utility infrastructure such as downing of power lines and the acceleration of flames during fires, burning more acres at increased velocities. These events have driven electric utility companies such as PG&E to develop and implement Public Safety Power Shutoff (PSPS) strategies ahead of weather events to prevent utility infrastructure from creating ignitions.

Figure 4, California HFTD Boundaries by County and Tier

Figure 4 California HFTD Boundaries by County and Tier map

Figure 5, Percentage of California Experiencing Drought

Figure 5, Percentage of California Experiencing Drought graph

Data for increased offshore Santa Ana winds increasing powerline-induced wildfire ignitions from 1984-2018.2

Figure 6, Ignitions by Type

Figure 6, Ignitions by Type graph

Fuel: Available fuels also play a major part in the continuation and propagation of ignitions that evolve into wildland fires. In a 2009 report, Chris Dicus, Ph.D., professor of wildland fire and fuels management at the California Polytechnic State University, San Luis Obispo, wrote that before the Gold Rush, there were approximately 50 to 70 trees per acre in California’s forestlands. Today, there are more than 400 trees per acre. Also contributing to the propagation of wildland fires after ignition are the volume of dead or dying trees within forests due to insect infestations such as the bark beetle. These insects, along with drought, are responsible for killing approximately 129 million trees across California since 2010. The result is that the forests are more fire prone due to high volumes of abundantly dry and woody fuel sources. Until 2019, PG&E mitigated vegetation on a “passive” or as-needed basis but did not implement an intentional substation inspection and maintenance program to address vegetation and other fuels within and around electric substations to prevent the risk of wildland fires. Since 2019, the substation Utility Defensible Space Inspection and Mitigation program has been successfully implemented.

Discussion

For decades, PG&E has performed routine-based inspections and time or condition-based maintenance at all ~975 electrical substations within its fleet. However, the inspection methods did not directly focus on the detection of failure modes and failure mode accelerators that could result in an ignition event propagating beyond the substation fence line. Although electric substations do not have a historical track record of being the direct cause of wildfires, following the wildfires caused by electric distribution and electric transmission lines occurring in 2017-2018, in 2019 PG&E dove deeply into the unique failure mode drivers and accelerators that could cause a potential substation induced wildfire in the future.

Answering the question of how a substation could be the cause of a wildland fire became tricky as there was no tangible evidence or historical references to inform the discussion therefore the solution to help answer the question came through Failure Modes and Effects Analysis (FMEA) aided by a cross-industry panel of internal and external subject matter experts.

Through the FMEA exercise, the team learned that ignition events from within a substation could propagate outward and beyond the fence line, but the likelihood would be largely dependent on distance between the ignition source and available fuels within and surrounding the substation. Although it was well recognized that creating a barrier between substations and the adjacent wildlands would be beneficial, it would be difficult to understand what the appropriate distance or clearance should be to serve as an appropriate fuel break.

Partnering with experts from the California Department of Forestry and Fire Protection (CAL-Fire), PG&E adopted the Utility Defensible Space (UDS) program and applied the program on its entire fleet of electrical substations that reside within the California Public Utilities Commission (CPUC) defined High Fire Threat Districts (HFTD) and High Fire Risk Areas (HFRA). The UDS program is based on the California Public Resources Code section 4291 which describes defensible space as a buffer between structures and the surrounding area.

Adequate defensible space acts as a barrier to slow or halt the progress of fire that would otherwise engulf property. It also helps ensure the safety of firefighters providing defense. PG&E has adopted the practice into internal work procedures and has effectively applied the program to electric substations within HFTD/HFRA.

Applicability

PG&E owns, operates and maintains approximately 975 substations within its service territory across northern and central California. 25% of which are located within HFTD/HFRA boundaries. Although the PRC 4291 program was originally intended for residential properties, it has been successfully adopted into internal work procedures and applied at all 244 substations and switchyards since 2019.

The work procedure provides instructions for the defensible space inspections of permanently installed substations and powerhouse switchyards located within HFTD/HFRA.

The execution of inspections and subsequent mitigations in the procedure are intended to minimize the risk of a fire ignition event within powerhouse switchyards and substations that could propagate outward from electrical equipment and into wildland. The procedure also considers regionally appropriate vegetation management suggestions that preserve and restore native species that are fire resistant or drought tolerant, or both, minimize erosion, minimize water consumption, and permit trees near facilities for shade, aesthetics, and habitat. At least once per annum, PG&E performs defensible space inspections at 100% of the substations located within HFTD/HFRA boundaries and performs mitigations by thinning, pruning or removing trees, brush or other vegetation to create space and reduce the continuity of fuels and other debris or stored materials within the following defensible space zones.

Defensible Space Zones:

Zone 0 – Ember Resistant Zone (0 to 5 feet, SEE details below).
Zone 1 – Clean Zone (0 to 30 feet, SEE details below).
Zone 2 – Reduced Fuel Zone (30 to 100 feet, SEE details below)

Figure 7, Example of Modeled DS Zones

Figure 7, Example of Modeled DS Zones image

Zone 0

Limits plants or planting to low growing, nonwoody, properly maintained plants within a 5 ft. perimeter from buildings, structures, decks, electrified equipment, etc.

Zone 1 – The Clean Zone

Measures 30 feet from all outermost buildings or energized equipment to create a firebreak that removes the following dead or dying vegetation to create a clean Zone:

  • Grass
  • Plants
  • Shrubs
  • Trees
  • Branches
  • Leaves
  • Weeds
  • Pine needles

Zone 2 – Reduce Fuel Zone

Measures from the 30-foot clean zone outward to 100 feet away from outermost buildings or energized equipment for fuel reduction.

  • Ensures minimum vertical clearance between limbs.
  • Increases horizontal spacing distances between trees and shrubs.

The Zone 2 reduced fuel zone also removes the following where possible.

  • Fallen Leaves and Needles
  • Twigs and Bark
  • Small branches and cones

Figure 8, Minimum Vertical Clearance

Figure 8, Minimum Vertical Clearance tree image

Figure 9, Minimum Horizontal Clearance

Figure 9, Minimum Horizontal Clearance tree image

Case Studies

Two events within PG&E’s service territory have demonstrated the effectiveness of the substation defensible space program for protecting against both outbound and inbound fires.

Case Study #1 Electra Fire, (Inbound Fire): July 4th, 2022, the Electra Fire (cause undetermined) burned 4,470 acres across Amador and Calaveras counties. Defensible Space has proven to be highly effective against inbound fire from spreading into the Electra substation and Powerhouse. Several members of the public escorted and “sheltered in place” for safety and protection into Electra Powerhouse. The fire burned up to the defensible space boundaries and provided complete firebreak protection in stopping the fire from advancing into the substation and powerhouse. No injuries and no equipment damage.

Figure 10, Image of Electra Powerhouse and Switchyard Modeled Defensible Space

Figure 10, Image of Electra Powerhouse and Switchyard Modeled Defensible Space arial image

Figure 11, Electra Fire Burn Scar

Figure 11, Electra Fire Burn Scar arial image

Case Study #2 Calaveras Cement Substation Outbound Fire – June 5th, 2020, a 12kV single phase voltage regulator failed within the substation releasing burning oil within and beyond the substation fence line. The fire was contained to an approximate 500 sq. ft. burn area near the fence and was mostly self-extinguished due to lack of fuels that were managed and managed by the defensible space program during the prior year.

Figure 12, Image of Substation in 2018 Before Defensible Space was Completed.

Figure 12, Image of Substation in 2018 Before Defensible Space was Completed arial image

Figure 13, Image of Substation in 2019 After Defensible Space Completed

Figure 13, Image of Substation in 2019 After Defensible Space Completed arial image

Figure 14, Image of Fire on June 5th, 2020.

brush fire along fence near regulator failure

Conclusion

Although PG&E does not have a history with substation induced wildfires and despite having a firm maintenance and inspection program to ensure operational health of substation assets, it continues to believe in the effectiveness of substation defensible space. The United States Department of Energy cites that much of the U.S. electric power grid was bult in the 1960’s and 1970s. Many of PG&E’s assets were installed much earlier with many substation assets approaching end of life. Age could result in an increased likelihood of substation equipment failures thus increasing the risk of igniting a wildfire. This risk can be minimized by developing and implementing a substation defensible space vegetation management program for substations located in areas where wildfire risks are increased.

Although implementing a defensible space program does not reduce the probability of a substation equipment failure, it instead focuses the probabilistic reduction of the failed component’s ability to ignite vegetation or debris within 100’ of the source. Through development, customizations and continual maturation, there is proven value in establishing utility defensible space program that is effective and provides layers of defense to protect the environment and people against the consequences of potential catastrophic wildfires.

  1. 1 Dr. T. Wall, G. McDonald, C. Enquist and S. Leroy, International Association of Wildland Fire “Drivers of California’s Changing Wildfires” “State Has Potential to Be a Model for Change”.
  2. 2 J.E. Keeley, J. Guzman-Morales, A. Gershunov, A.D. Syphard, D. Cayan, D.W. Pierce, M. Flannigan, and T.J. Brown, “Science Advances, Ignitions Explain More Than Temperature or Precipitation in Driving Santa Ana wind Fires” 21 Jul 2021 Vol 7, Issue.

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