NUREG-2218

An International Phenomena

Identification and Ranking

Table (PIRT) Expert Elicitation

Exercise for High Energy 

Arcing Faults (HEAFs) 

Office of Nuclear Regulatory Research
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NUREG-2218

An International Phenomena 

Identification and Ranking 

Table (PIRT) Expert Elicitation 

Exercise for High Energy 

Arcing Faults (HEAFs)

Manuscript Completed: May 2017

Date Published: January 2018 

Prepared by: 

K. Hamburger

Kenneth Hamburger, NRC Project Manager 

Office of Nuclear Regulatory Research 

iii

ABSTRACT

This report documents the results of a phenomena identification and ranking table (PIRT) exercise 

performed for nuclear power plant (NPP) high energy arc fault (HEAF) analysis applications 

conducted on behalf of the U.S. Nuclear Regulatory Commission’s (NRC’s) Office of Nuclear 

Regulatory Research. 

The PIRT exercise was performed via a facilitated expert elicitation process. In this case, the 

expert panel comprised six international HEAF experts. The panel was facilitated by NRC staff. 

The objective of a PIRT exercise is to identify key phenomena associated with the intended 

application and to then rank the current state of knowledge relative to each identified 

phenomenon. The expert panel was presented with a series of specific HEAF scenarios, each of 

which is based on the types of scenarios typically considered in NPP applications. Each scenario 

includes a figure of merit (i.e., a specific goal to be achieved in analyzing the scenario using HEAF

analysis or modeling tools). Given each scenario, the panel identified phenomena that are of 

potential interest to an assessment based on the figure of merit. The identified phenomena are 

then ranked relative to their importance in predicting the figure of merit. Each phenomenon is 

then further ranked for the existing state of knowledge and the adequacy of existing modeling 

tools to predict that phenomenon. 

The PIRT panel covered three HEAF scenarios and identified a number of areas potentially in 

need of further analysis and model development. This report discusses the results in detail.

v 

FOREWORD

Analysis of the most recent international nuclear power plant (NPP) fire event data identifies an 

increase in the number of high energy arc fault (HEAF) events. The international HEAF 

operational experience illustrates that significant damage can occur during a HEAF event. In the 

interest of safe nuclear operations, it is imperative that engineers, operators, and probabilistic risk 

assessment (PRA) practitioners understand the risk potential of a HEAF and protect safety 

systems from its effects.

This report documents the work of an international group of nuclear fire safety experts from five 

countries participating in a structured, facilitated expert elicitation. The experts evaluated three 

different HEAF scenarios encountered in NPPs. By following the NRC’s well-established 

phenomena identification and ranking table (PIRT) process, expert insights are gained into 

important areas of HEAF phenomena. These include answers to questions such as: 

• How well do we think we understand the phenomena?

• What are their importance and potential for NPP damage?

• Where are the gaps in our state of knowledge?

The results of the PIRT identify and rank important:

• Level 1 phenomena such as target characterization, arc characterization, and arc mitigation.

• Level 2 phenomena such as internal and external ensuing fires, pressure effects, and

electrical configuration effects.

• Level 3 phenomena including internal and external cabinet enclosure effects, effects of fire

detection and suppression, and room configuration.

These rankings can then be used as a technical compass to help guide and inform future testing 

and research endeavors.

This report builds upon previous Organization for Economic Cooperation and Development/ 

Nuclear Energy Agency and NRC HEAF work. This research continues to advance our 

understanding of this complex phenomenon and its impact on safety. I hope this work will 

ultimately be used to make a positive contribution to NPP fire safety.

Mark Henry Salley, P.E.

Chief, Fire and External Hazards Analysis Branch

Office of Nuclear Regulatory Research

United States Nuclear Regulatory Commission

June 2, 2017

Rockville, Maryland

vii

TABLE OF CONTENTS

ABSTRACT................................................................................................................................iii

FOREWORD...............................................................................................................................v

LIST OF TABLES........................................................................................................................ix

EXECUTIVE SUMMARY............................................................................................................xi

ACKNOWLEDGMENTS ..........................................................................................................xiii

ABBREVIATIONS AND ACRONYMS.......................................................................................xv

1 INTRODUCTION...................................................................................................................1-1

1.1 Background..........................................................................................................................1-1

1.2 Objectives............................................................................................................................1-3

1.3 Scope...................................................................................................................................1-3

1.4 Report Organization.............................................................................................................1-4

2 OVERVIEW OF THE PIRT PROCESS APPLIED.................................................................2-1

2.1 Background..........................................................................................................................2-1

2.2 Selection of Panelists ..........................................................................................................2-1

2.3 Panelist Preparation ............................................................................................................2-1

2.3.1 Knowledge Base.........................................................................................................2-2

2.3.2 Orientation Materials...................................................................................................2-2

2.4 The PIRT Process Applied ..................................................................................................2-2

2.4.1 Scenario Development...............................................................................................2-2

2.4.2 Steps in the PIRT Process........................................................................................ 2-2

2.4.3 Phenomena Ranking Definitions............................................................................... 2-4

2.4.4 Parameter Ranking Definitions ................................................................................. 2-6

2.4.5 Country-Specific Concerns and Input ....................................................................... 2-6

2.4.6 Panelist Feedback .................................................................................................... 2-7

2.5 Summary Scenario Descriptions .........................................................................................2-8

2.5.1 HEAF Scenario 1 ...................................................................................................... 2-8

2.5.2 HEAF Scenario 2 ...................................................................................................... 2-9

2.5.3 HEAF Scenario 3 .................................................................................................... 2-10

3 SUMMARY OF LEVEL 1 PHENOMENA ..............................................................................3-1

3.1 Ranking Methodology..........................................................................................................3-1

3.2 Discussion of Level 1 Phenomena ......................................................................................3-3

3.2.1 Target Characterization ..............................................................................................3-3

3.2.2 Arc Characterization ...................................................................................................3-4
viii

3.2.3 Arc Mitigation ..............................................................................................................3-5

3.2.4 Cabinet Lineup Effects................................................................................................3-5

3.3 Additional Discussions.........................................................................................................3-5

3.3.1 External Duct Housing Configuration..........................................................................3-6

3.3.2 Internal Ensuing Fire...................................................................................................3-6

3.3.3 Pressure Effects..........................................................................................................3-6

4 CONCLUSIONS AND RECOMMENDATIONS.......................................................................4-1

4.1 Practical Considerations for PRA Practitioners ....................................................................4-1

4.2 Characterizing Target Damage.............................................................................................4-1

4.3 Arc Mitigation........................................................................................................................4-1

4.4 Internal Ensuing Fire.............................................................................................................4-2

4.5 Arc Characterization .............................................................................................................4-3

4.6 Pressure Effects ...................................................................................................................4-3

5 REFERENCES.......................................................................................................................5-1

5.1 References Found in this Report..........................................................................................5-1

5.2 Additional Documents Included in the Knowledge Base ......................................................5-3

APPENDIX A PIRT HEAF SCENARIO 1.................................................................................A-1

APPENDIX B PIRT HEAF SCENARIO 2.................................................................................B-1

APPENDIX C PIRT HEAF SCENARIO 3....................................................................................C-1

APPENDIX D PANIELIST RÉSUMÉS.........................................................................................D-1

APPENDIX E TECHNICAL EXPERT AND ADVISOR RÉSUMÉS............................................E-1

APPENDIX F INTRODUCTORY MATERIALS PRESENTED AT THE FIRST PANEL

 MEETING...............................................................................................................F-1
ix

LIST OF TABLES

Table 2-1 Phenomena Importance Ranking Definitions...................................................................2-4

Table 2-2 Phenomena State of Knowledge Model Adequacy Ranking Definitions.........................2-5

Table 2-3 Phenomena State of Knowledge Data Adequacy Ranking Definitions...........................2-5

Table 2-4 Phenomena State of Knowledge Availability of New Data Ranking Definitions..............2-6

Table 2-5 Parameter Importance Ranking Definitions......................................................................2-6

Table 2-6 Parameter State of Knowledge Ranking Definitions........................................................2-6

Table 3-1 Numerical Equivalents for Ranking Values......................................................................3-1

Table 3-2 Importance Rankings for Pressure Effects, Scenario 1...................................................3-1

Table 3-3 Numerical Equivalent of Table 3-2...................................................................................3-1

Table 3-4 State of Knowledge for Pressure Effects, Scenario 1......................................................3-2

Table 3-5 Numerical Equivalent of Table 3-4...................................................................................3-2

Table 3-6 Summary of Phenomena Rankings for All Scenarios......................................................3-3 

xi 

EXECUTIVE SUMMARY

Background

This report documents the results of an international phenomena identification and ranking table 

(PIRT) expert elicitation exercise performed for high energy arcing fault (HEAF) hazards. This 

PIRT exercise was conducted on behalf of the U.S. Nuclear Regulatory Commission’s (NRC’s) 

Office of Nuclear Regulatory Research (RES) and facilitated by RES staff.

Objectives

The objective of this PIRT exercise is to develop an ordered list of phenomena involved in a HEAF 

event. This list will be ordered by priority; the more important a phenomena is judged to be and 

the poorer its state of knowledge is judged to be, the higher its priority. This information can be 

used in the development of a “roadmap” for future research and allows for an informed focusing of 

resources for research and regulatory entities.

Approach

The expert panel was presented with a series of specific HEAF scenarios, each based on the 

types of scenarios typically encountered in nuclear power plant (NPP) applications. For each 

scenario, a specific figure of merit was defined; that is, a specific goal to be achieved in analyzing 

the scenario. The panel identifies all those related phenomena that are of potential interest to an 

assessment of the scenario via probabilistic risk assessment (PRA) tools and methods. The 

phenomena are then ranked relative to their importance in predicting the figure of merit. Each 

phenomenon is then further ranked for the existing state of knowledge with respect to the ability of 

existing tools and methods to predict that phenomena, the underlying base of knowledge

associated with the phenomena, and the potential for developing new data to support 

improvements to the existing tools. 

The PIRT panel covered three distinct HEAF scenarios. The first was a HEAF occurring in an 

electrical enclosure with a cable tray passing over the enclosure. The second was a HEAF 

occurring in a bus duct passing over an electrical enclosure. The third was a HEAF occurring in 

an electrical enclosure situated in a bank of similar enclosures.

Results

As a result of the process, “level one” phenomena were identified. The level one phenomena are 

those that were ranked with high importance and low state of knowledge. These would nominally 

represent potential research priorities. The level one phenomena identified by the panel included 

the following:

• Electrical arc characterization: thermal and magnetic effects of the arc, arc ejecta (smoke,

ionized gas, conductive particulate), arc location, and migration.

• Pressure effects: mechanical shock, projectile impact, and degradation of the compartment

pressure boundary.

• Arc mitigation: the use of HEAF-resistant equipment, thermal insulation, or “HEAF shields” to

minimize damage incurred as a result of a HEAF.
xii

• Target characterization: establishing the sensitivity of target equipment to various failure

mechanisms, and associated damage criteria.

• Internal ensuing fire: the likelihood, impact, and phenomenology of an enclosure fire ignited by

a HEAF event.
xiii

ACKNOWLEDGMENTS 

The author wishes to thank the members of the expert panel─Dr. Hajime Kabashima (S/NRA/R), 

Mr. Sangkyu Lee (KINS), Mr. Nicholas Melly (U.S. NRC), Dr. Marina Röwekamp (GRS), 

Dr. Koji Shirai (CRIEPI), and Dr. Sylvain Suard (IRSN)─for their dedication to the process and for 

their perseverance. The panelists’ technical advisors─Dr. Mikimasa Iwata, Mr. Hee Jin Ko, 

Mr. Cheoung Joon Lee, and Mr. Seonghyeon Yi─provided invaluable insight, and their 

contributions are greatly appreciated. 

The author also wishes to thank the technical area experts who supported the panelists─Mr. Scott 

Bareham, Dr. Anthony Putorti, Mr. Tomasz Stefanski, and Mr. Stephen Turner. 

Lastly, the author wishes to thank the NRC staff members who supported the development and 

execution of the PIRT exercise─Mr. Theron Brown, Ms. Tammie Rivera, Mr. Mark Henry Salley, 

Mr. David Stroup, Mr. Gabriel Taylor, and Mr. Joseph Zabel. 

xv 

ABBREVIATIONS AND ACRONYMS

CNSC Canadian Nuclear Safety Commission (Canada).

CRIEPI Central Research Institute of Electric Power Industry (Japan).

CSN Consejo de Seguridad Nuclear (Spain).

DID Defense in Depth. 

ERFBS Electrical Raceway Fire Barrier System(s). 

EMI Electromagnetic Interference.

EPRI Electric Power Research Institute.

FAQ Frequently Asked Questions (Reactor Oversight Program).

GDC General Design Criteria (10 CFR Part 50 Appendix A).

GRS Gesellschaft für Anlagen- und Reaktorsicherheit (Germany).

HEAF High Energy Arcing Fault. 

HRR Heat Release Rate.

IAGE Integrity and Aging (Task Group).

IRSN Institut de Radioprotection et de Sûreté Nucléaire (France). 

KINS Korea Institute of Nuclear Safety (S Korea).

LER Licensee Event Report.

NEA Nuclear Energy Agency.

NPP Nuclear Power Plant.

OECD Organisation for Economic Co-operation and Development.

PIRT Phenomena Identification and Ranking Table. 

PRA Probabilistic Risk Analysis.

RES Office of Nuclear Regulatory Research.

S/NRA/R Regulatory Standard and Research Development, Secretariat of Nuclear 

Regulation Authority (Japan).

SSC(s) Systems, Structures, and Components.

STUK Säteilyturvakeskus (Finland). 

ZOI Zone of Influence

1-1

1 INTRODUCTION

1.1 Background

Switchgear, load centers, and bus bars/ducts (440 V and above) are subject to a unique failure 

mode and, as a result, unique fire characteristics. In particular, these types of high-energy 

electrical devices are subject to high-energy arcing faults (HEAFs). This fault mode leads to the 

rapid release of electrical energy in the form of heat, vaporized copper, and mechanical force. 

Faults of this type are also commonly referred to as high energy, energetic, or explosive electrical 

equipment faults or fires. Similar failure modes can occur in large oil-filled transformers. [1] 

The arcing or energetic fault scenario in these electrical devices consists of two distinct phases, 

each with its own damage characteristics and detection/suppression response and effectiveness. 

The first phase is a rapid release of energy in the form of heat, light, and pressure. This energetic 

first phase is due to the high current arcs between electrical conductors. The second phase 

consists of ensuing fire(s) that may involve the electrical device itself as well as any external 

exposed combustibles such as overhead exposed cable trays or nearby panels that may be 

ignited during the energetic phase. This second phase is treated similar to other postulated fires 

within the zone of influence. [1] 

International operating experience documents a significant number of HEAFs that have occurred 

worldwide in operating nuclear power plant (NPP) facilities. An Organisation for Economic Cooperation and Development/Nuclear Energy Agency (OECD/NEA) report from June 2013 

documents 48 such instances in 10 member countries [2]. This number represents about 10

percent of the fire events reported through the OECD/NEA Fire Incidents Records Exchange 

(FIRE) program. 

Appendix A to 10 CFR Part 50 [3] lists the General Design Criteria (GDC) or minimum 

requirements for the principal design of a water-cooled NPP. Two criteria are particularly 

applicable to HEAFs: criterion 3 and criterion 17. Criterion 3 requires that structures, systems, 

and components (SSCs) important to safety be designed to minimize the probability and effect of 

fires and explosions. Criterion 17 requires that the onsite electric power supplies have sufficient 

independence, redundancy, and testability to perform their safety functions assuming a single 

failure. The “defense in depth” (DID) approach to NPP design and operation requires multiple 

independent and redundant layers of defense so that no single layer, no matter how robust, is 

exclusively relied upon. The DID strategy, as it applies to HEAFs, consists of:

1. Prevention – Maintenance practices designed to eliminate the underlying causes of faults

(loose connections, degraded insulation, foreign materials, etc.).[4]

2. Mitigation – Selective coordination to limit the duration and magnitude of the fault as well as

design and location of plant SSCs such that a HEAF, should it occur, does as little damage as

possible to nearby equipment and does not endanger the functionality of redundant

equipment.

3. Safe shutdown – Ensuring the ability of the plant to safely shut down and maintain the reactor

in a safe state in the event of a HEAF.

HEAF events have, in many cases, presented extra challenges to the safe shutdown of a reactor. 

The electrical disturbance responsible for the HEAF can cause loss of essential electrical power, 

and the physical damage and products of combustion can present significant challenges to the 
1-2

operators and fire brigade members responding to the emergency.[5][6][7] HEAFs can present 

one of the more risk-significant and challenging fire scenarios that an NPP will face.

In 2008, the U.S. Nuclear Regulatory Commission (NRC) contracted with Sandia National 

Laboratories to perform a literature review on HEAFs. The review [8] concluded that the focus of 

research had primarily been limited to the behaviors of the initiating equipment and the initial arc 

flash in the context of personnel safety. More research was necessary to evaluate the HEAF 

phenomenon in the context of damage to adjacent equipment.

Two methods are available to model the effects of a HEAF [9]. The first is described in 

NUREG/CR-6850, “EPRI/NRC-RES Fire PRA Methodology for Nuclear Power Facilities, Volume 

2: Detailed Methodology, Appendix M for Chapter 11, High Energy Arcing Faults” [1]. This 

method stipulates the following assumptions:

1. The faulting device is destroyed.

2. Adjacent cubicles in the same cabinet bank will trip open.

3. Unprotected cables that enter the panel in an air-drop configuration are destroyed.

4. The first unprotected cable tray within 1.5 m of the top of the cabinet will ignite.

5. Vulnerable equipment within 0.9 m horizontally of the front or rear doors will be destroyed.

This method is subject to an unknown degree of uncertainty because it was derived from one 

single well-documented HEAF event that occurred at the San Onofre Nuclear Generating Station, 

Unit 3, on February 3, 2001 [10]. The second method can be found in “Fire Probabilistic Risk 

Assessment Methods Enhancements Supplement 1 to NUREG/CR-6850 and EPRI 1011989” 

section 7 bus duct (counting) guidance for high energy arcing faults (FAQ 07-0035) [11]. This 

method stipulates the following assumptions for HEAFs occurring in bus ducts:

1. Molten material will be ejected from the bottom of the bus duct and spread downwards in the

shape of a right circular cone whose sides are at an angle of 15 degrees from the vertical axis.

2. The cone will expand to a maximum diameter of 20 feet (37 feet below the point of origin)

beyond which point molten material will fall straight down in a cylindrical shape of 20-foot

diameter.

3. Molten material will be ejected outwards from the fault point in the shape of a sphere with a

1.5-foot radius.

4. Exposed combustible material within these zones will ignite.

In an effort to confirm these modeling methods described in NUREG/CR-6850 and to better 

characterize HEAFs, an OECD/NEA working group conducted an experimental program between

2014 and 2016, hereafter referred to as “phase one.” Led by the NRC, this phase consisted of 26 

full-scale HEAF experiments conducted at KEMA Powertest LLC’s Chalfont facility. This test 

program was largely exploratory; the test equipment was whatever participant countries could 

donate, and various measurement techniques were evaluated. The results of the phase one 

testing suggest that the current modeling methodology may, in some cases, be nonconservative, 

especially where aluminum components are involved. The full results of this experimental 

campaign are documented in an NEA/CSNI report issued in 2017 [12].

In August 2016, the Regulatory Standard and Development Department Secretariat on Nuclear 

Regulation Authority (S/NRA/R) and the NRC jointly published an International Report titled 
1-3

NUREG/IA-0470 Volume 1, “Nuclear Regulatory Authority Experimental Program to Characterize 

and Understand High Energy Arcing Fault (HEAF) Phenomena” [13]. The focus of this report was 

to better understand the seismic-induced HEAF that occurred in 6.9 kV switchgear at the 

Onagawa NPP during the March 11, 2011, Great Eastern Earthquake in Japan. The research 

focused on simulating the HEAF that occurred and recording data such as temperature, heat flux, 

and heat-release rates (HRR) from ensuing fires. The report was also one of the first to identify 

high thermal energy released when aluminum electrical components are involved.

The phase one testing and joint S/NRA/R NRC report demonstrated the need for additional, more 

focused testing to further refine HEAF modeling methodology. Given the complexity of a HEAF 

event and related phenomena, the Office of Nuclear Regulatory Research held a Phenomena

Identification Ranking Table (PIRT) exercise in February 2017 to aid in the process of planning 

future testing.

1.2 Objectives

The objective of this PIRT exercise is to develop an ordered list of phenomena involved in a HEAF 

event. This list will be ordered by priority; the more important a phenomena is judged to be, and 

the poorer its state of knowledge is judged to be, the higher its priority. This information can be 

used in the development of a “roadmap” for future research and will allow for an informed focusing 

of resources for research and regulatory entities.

1.3 Scope

The scope of the PIRT exercise defines the bounds of:

1. The scenarios to be analyzed.

2. The figures of merit to be achieved.

3. The phenomena’s state of knowledge.

A well-defined scope will ensure that the scenarios are relevant to the intended application and 

that the group’s analysis does not stray into tangents and hypotheticals.

The scope of this PIRT exercise is:

1. A high-energy electric arc fault event.

2. Occurring in a nuclear power generating station.

3. In low voltage (less than 600V) or medium voltage (between 600V and 15 kV) equipment or

circuits.

4. NOT in the switchyard or electrical transmission/distribution network and equipment

Although an arc fault in the switchyard may result in a loss of offsite power, it is 

phenomenologically separate from other HEAF scenarios because:

1. It is not confined in a compartment.

2. It is not located near safety-related equipment.

3. High voltages (greater than 15kV) are common.
1-4 

For these reasons, arc faults occurring on the switchyard side of the main generator and beyond 

are outside of the project scope.

1.4 Report Organization

Section 2 of this report discusses the PIRT process used, the preparation of the PIRT panelists, 

the instructions and ranking definitions given to the panelists, and a description of three HEAF 

scenarios.

Section 3 is a summary of the “level 1” phenomena in each of the three scenarios—those 

phenomena that rank highly for importance and poorly for state of knowledge. These are, in 

essence, the primary candidates for future research activity.

Section 4 synthesizes the panelists’ rankings, comments, and discussions into a series of 

recommendations for future research.

Appendices A-C contain the formatted output of the PIRT, with each panelist’s anonymized 

rankings.
2-1

2 OVERVIEW OF THE PIRT PROCESS APPLIED

2.1 Background

A phenomena identification and ranking table (PIRT) is a structured expert elicitation process. It is 

a methodical, tested process for compiling expert opinions, assessing the state of knowledge, and 

identifying research priorities on a particular topic. The U.S. Nuclear Regulatory Commission 

(NRC) has sponsored or performed a number of PIRT exercises. Two recent PIRTs that were 

performed by the NRC’s Fire Research Branch were NUREG/CR-6978, “A Phenomena 

Identification and Ranking Table (PIRT) Exercise for Nuclear Power Plant Fire Modeling 

Applications,” [14] and NUREG/CR-7150 Volume 1, “Phenomena Identification and Ranking 

Table (PIRT) Exercise for Nuclear Power Plant Fire-Induced Electrical Circuit Failure.” [15] 

2.2 Selection of Panelists

This PIRT exercise was a follow-up to phase one testing and a prerequisite to future phase two 

testing. For this reason, each country/agency that participated in the phase one testing was 

invited to send one representative to sit on the panel. At their discretion, each country/agency 

was also invited to send technical experts—non-voting representatives who could advise the 

panelist, but whose input would not be recorded.

An invitation was extended to the following countries/organizations: 

• CNSC (Canada)

• KINS (S Korea)

• GRS (Germany)

• IRSN (France)

• STUK (Finland)

• CRIEPI (Japan)

• NRA (Japan)

• CSN (Spain)

• NRC (United States)

• EPRI (United States)

Of these 10 agencies, the following sent representatives:

• KINS (S Korea) – Mr. Sangkyu Lee

• GRS (Germany) – Dr. Marina Röwekamp

• IRSN (France) – Dr. Sylvain Suard

• CRIEPI (Japan) – Dr. Koji Shirai

• NRA (Japan) – Dr. Hajime Kabashima

• NRC (United States) – Mr. Nicholas Melly

2.3 Panelist Preparation

None of the PIRT panelists had participated in a PIRT before. To maximize what could be 

accomplished during the week of the PIRT, the panelists were provided with a variety of 

preparation and orientation materials.
2-2

2.3.1 Knowledge Base

Several months in advance of the PIRT, panelists were given access to an online file store 

containing relevant literature on high energy arcing faults. In addition to those materials provided, 

panelists were asked to contribute any other material of which they were aware. This knowledge 

store is essentially the equivalent of a literature review for this exercise. These materials include 

both nuclear and non-nuclear studies, and a list of these materials are given in the references 

section of this report (section 5.2). 

The objective of providing these materials was to calibrate the panelists for their evaluation of 

phenomena state of knowledge. To draw a conclusion about whether a phenomenon has been 

adequately characterized, some knowledge of the current literature is required.

2.3.2 Orientation Materials

In addition to access to the online knowledge base, panelists were provided with periodic 

orientation materials. These materials largely dealt with the PIRT process itself to familiarize 

panelists with the steps involved. These orientation materials also included worked example 

scenarios and logistical information.

2.4 The PIRT Process Applied

2.4.1 Scenario Development

The scenarios to be analyzed were developed so that they span the plausible range of HEAF 

events while still staying within the scope of the PIRT. The development of these scenarios was 

guided by documented operating experience and common NPP configurations. The scenarios 

are mainly focused on the HEAF source equipment. The panelists were instructed to consider the 

targets only in a generic manner. In reality, each target is unique and will respond differently to 

the environmental conditions caused by a HEAF; however, the behavior of specific targets is a 

voluminous subject and outside the scope of the PIRT. Therefore, when considering the damage 

states of a target in the scenarios, panelists listed phenomena that are applicable to any generic 

target of a similar equipment class.

Each scenario is accompanied by a “figure of merit” (i.e., a goal to be achieved through analysis 

of the scenario). In other PIRTs, the figure of merit is often the prediction of a specific quantity, 

such as ceiling jet temperature or pressure rise. In the case of this PIRT, where all possible 

mechanisms of failure are being considered, the figure of merit for each scenario is simply the 

determination of the extent of damage to the targets. This broad figure of merit allowed panelists 

to consider any and all phenomena.

2.4.2 Steps in the PIRT Process

The PIRT process follows a series of formal steps, each of which is outlined here.

2.4.2.1 Presentation of the HEAF Scenario

The first step is the presentation of a HEAF scenario, which includes a description of the predefined elements and characteristics of the scenario as well as the specific objectives and goals 

of our analysis. Section 2.5 details the three scenarios used in this PIRT.
2-3

2.4.2.2 Phenomena Identification

The next step is for the panel to identify all phenomena relevant to the scenario and the analysis 

goals. A phenomenon is loosely defined as “something that is observed to happen.” In the 

context of this PIRT, a phenomenon is something that has, or might have, a model associated 

with it. A phenomenon may include one or more sub-phenomena, which are grouped accordingly.

As an example, an external ensuing fire that occurs as a result of a HEAF is a phenomenon. It is a 

physical occurrence that PRA practitioners need to model. This phenomena can be broken down 

into sub-phenomena, each with its own sub-model. Examples of sub-phenomena for an external 

ensuing fire are ignition, fire development, and smoke generation.

2.4.2.3 Parameter Identification

In concert with the identification of phenomena, panelists were also asked to identify key 

parameters associated with the phenomenon. If phenomena can be thought of as events to be 

modeled, parameters are the inputs to those models. These are quantities that can be measured 

and reported with standard units. Each phenomenon or sub-phenomenon may encompass 

multiple key parameters.

Continuing the example above, some relevant parameters for the sub-phenomena of an external 

ensuing fire are heat release rate, fire growth rate, and time to peak heat release rate.

The process components outlined here and in in section 2.4.2.2 are almost like a “brainstorming 

session” in that the group will need to think of all phenomena and parameters that might have an 

impact on the scenario objective. Even phenomena or parameters that are likely to have a minor 

impact on the objective should be identified; their relative importance will be decided by the group 

in the next stage.

2.4.2.4 Phenomena Importance Ranking

In the next step, the panel ranks each identified phenomenon for its importance to the figure of 

merit. If the group can achieve consensus in their ranking through discussion, it lends extra 

credibility to the ranking, but consensus is not required. Each panel member is entitled to their 

opinion, and it is recorded as it is received. This stage of the PIRT requires that the panel 

members be familiar with the available experimental evidence to provide well-informed opinions 

about what factors influence the characteristics of HEAF events and their relative importance.

Section 2.4.3 describes the possible rankings for phenomena importance and their definitions.

2.4.2.5 State of Knowledge Ranking

In the next step, the panel assessed the state of knowledge for each phenomenon. This includes 

the current body of knowledge regarding a particular phenomenon as well as the ability to acquire 

information regarding that phenomenon. If new measurement techniques or equipment are 

required to increase the state of knowledge regarding a particular phenomenon, this should be 

reflected in the output of the PIRT.

Section 2.4.3 describes the possible rankings for phenomena state of knowledge and their 

definitions.
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2.4.2.6 Parameter Importance and State of Knowledge Ranking

In addition to ranking the identified phenomena, panelists were asked to identify and rank key

parameters for each of the phenomena where applicable. The ranking of a parameter is relative 

to its parent phenomenon. A phenomenon may be ranked as unimportant, but its child 

parameters may be highly important to characterizing that phenomenon. This process was

applied even to the lowly ranked phenomena for reasons of extensibility—while this panel may

deem a phenomenon unimportant to the overall analysis, future research may contradict such a 

judgment.

Section 2.4.4 describes the possible rankings for parameter importance and state of knowledge 

and their definitions.

2.4.3 Phenomena Ranking Definitions

It is important that PIRT participants have consistent and well-defined criteria to rank the 

phenomena and their states of knowledge. For simplicity and consistency, a low, medium, high 

scale was used. One category ranked the importance of the phenomenon, and three categories

ranked the current state of knowledge regarding that phenomenon.

It is also important to remember that these rankings are expert opinions. Empirical evidence may 

or may not be available to support these rankings, but the expert should try to justify the ranking

as much as possible. A ranking of “high” indicates that the given phenomenon is very important to 

predicting the figure of merit. Without knowledge of the phenomenon, an accurate prediction 

would not be possible. A ranking of “medium” indicates a phenomenon that has some 

appreciable impact on predicting the figure of merit but is not particularly important. Without

knowledge of this phenomenon, a rough estimate would still be possible. A ranking of “low”

indicates that the expert does not believe the phenomenon is important to predicting the figure of

merit and that modeling this phenomenon is not necessary. An additional category of “uncertain”

is available that indicates the expert believes a phenomenon has an impact on predicting the 

figure of merit but is unable to assess the magnitude of that impact.

The following phenomena importance ranking definitions were used throughout the PIRT: 

Table 2-1 Phenomena Importance Ranking Definitions 

Descriptor Definition

High (H) First order of importance to the figure of merit of interest.

Medium (M) Secondary order of importance to the figure of merit of interest.

Low (L) Negligible importance to figure of merit of interest. Not necessary to 

model this phenomenon for this application.

Uncertain (U) Potentially important. Importance should be explored through sensitivity 

study and/or discovery experiments and the PIRT revised accordingly.

Model adequacy rankings answer the question “How well does the current HEAF modeling 

methodology estimate the phenomenon?”
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The following model adequacy ranking definitions were used throughout the PIRT: 

Table 2-2 Phenomena State of Knowledge Model Adequacy Ranking Definitions 

Descriptor Definition

High (H) At least one mature physics-based or correlation-based model is available 

that is believed to adequately represent the phenomenon over the full 

parameter space of the applications.

Medium (M) Significant discovery activities have been completed. At least one 

candidate model form or correlation form has emerged that is believed to 

nominally capture the phenomenon over some portion of the application 

parameter space.

Low (L) No significant discovery activities have occurred and model form is still 

unknown or speculative.

Data adequacy descriptors answer the question “How good is the data that would be used as

model input, or to validate a potential model?” For example, the distance between a target and

the source equipment is data that is readily available, very precise, and easy to vary for

experimentation. Data regarding electromagnetic interference caused by a HEAF might be less

available or of lower fidelity. It is important to differentiate between the adequacy of data and the 

adequacy of the model. There is no “uncertain” category; if a panelist is not aware of pertinent

data, the adequacy of the data was considered to be “low.”

The following data adequacy descriptors were used throughout the PIRT: 

Table 2-3 Phenomena State of Knowledge Data Adequacy Ranking Definitions 

Descriptor Definition

High (H) A highly reliable assessment can be made based on existing knowledge. 

Data needed are readily available.

Medium (M) Data are available but are not ideal due to questions of fidelity. 

Moderately reliable assessments of models can be made based on 

existing knowledge. 

Low (L) Assessments cannot be made with even moderate reliability based on 

existing knowledge.

The last ranking category is the ability to gather new data for a particular phenomenon. These 

descriptors answer the question “How easy would it be to get the data we need if we don’t already 

have it?” This category can help prioritize the collection of data in future experiments if some data 

are known to be easier to collect than others. 
2-6

The following data adequacy descriptors for the potential to develop new data were used 

throughout the PIRT: 

Table 2-4 Phenomena State of Knowledge Availability of New Data Ranking Definitions 

Descriptor Definition

High (H) Data needed are readily obtainable based on existing experimental 

capabilities.

Medium (M) Data would be obtainable but would require moderate, readily attainable 

extensions to existing capabilities.

Low (L) Data are not readily obtainable and/or would require significant 

development of new capabilities.

Panelists were not required to rank a phenomenon if they choose not to. If a panelist decided that

he/she did not want to rank a phenomenon either for importance or state of knowledge, a ranking 

of “X” was entered.

2.4.4 Parameter Ranking Definitions

The following parameter importance and ranking definitions were used throughout the PIRT: 

Table 2-5 Parameter Importance Ranking Definitions 

Descriptor Definition

High (H) First order of importance in characterizing the parent phenomenon.

Medium (M) Secondary order of importance in characterizing the parent phenomenon.

Low (L) Negligible importance in characterizing the parent phenomenon.

Uncertain (U) Potentially important. Importance should be explored through sensitivity 

study and/or discovery experiments and the PIRT revised accordingly.

Unlike phenomena, a single category was used to rank the state of knowledge for the identified 

parameters. The following parameter state of knowledge ranking definitions were used 

throughout the PIRT: 

Table 2-6 Parameter State of Knowledge Ranking Definitions 

Descriptor Definition

High (H) The parameter’s influence on its parent phenomenon is well 

characterized, and the parameter is easily measured.

Medium (M) The parameter’s influence on its parent phenomenon is known but not 

well characterized, and measurement of the parameter is possible.

Low (L) The parameter’s influence on its parent phenomenon is unknown, and 

measurement of the parameter is difficult or impossible.

2.4.5 Country-Specific Concerns and Input

Although the PIRT focused on the physical phenomenology of HEAF events and the general

scientific state of knowledge, concerns specific to the panelists’ represented country or 

organization inevitably arose. Some panelists stated that several phenomena were not relevant 

for their applications and chose a ranking of “Unknown” or no ranking at all. Other panelists noted 
2-7

that even the HEAF scenarios, as general as they were, would be an improbable or impossible 

configuration in their countries’ facilities; therefore, their consideration of such scenarios was

based less on experience and more on expert judgment, and this is reflected in their rankings.

The associated cost was another concern, especially when considering the ability to obtain new

data. For many phenomena, the only way to obtain the necessary data would be to run full-scale 

experiments that are costly and time consuming. Although the state-of-knowledge rankings are 

supposed to reflect the scientific community’s technical abilities, practical considerations like time 

and money are inevitably factored in.

2.4.6 Panelist Feedback

During the PIRT, panelists raised three procedural issues that are worth documenting here with 

the intent that future PIRTs can improve upon the process and that readers understand what was

done and why.

The first issue discussed was whether it was a judicious use of time to rank key parameters for

phenomena that had already been ranked of “low” importance. Establishing the key parameters

for a phenomenon that will likely not be investigated seems, on the surface, to be impractical. The 

reason for doing so is that the panelists were working from the base of knowledge that existed at

the time when the PIRT was held. As the state of knowledge improves, phenomena previously

thought to be insignificant may be reconsidered, and having their key parameters ranked puts

future readers at an advantage.

The second issue was the difficulty in assessing the ability to obtain new data for the state-ofknowledge rankings. Where the state of a model was judged to be poor or nonexistent, panelists

were unable to reliably assess what data would need to be obtained or the ease of obtaining it. In 

cases like this, panelists were asked to rely on their judgment in assessing this state-ofknowledge category. 

Lastly, it was noted during the PIRT exercise that a very large number of phenomena were being 

ranked “highly important” compared to those phenomena being ranked of “medium” or “low” 

importance. This is the result of an inevitable selection bias; when the panelists were asked to list

all phenomena that could be of importance in predicting the figure of merit, the only phenomena 

they listed were those that could conceivably have an appreciable impact. In other words, the list

of phenomena that the panelists needed to rank had already been preselected for some level of

importance. This results in the median importance value being relatively high, with discrepancies

between panelists being the largest source of variation.
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2.5 Summary Scenario Descriptions

2.5.1 HEAF Scenario 1

2.5.1.1 Scenario Description

Figure 2-1 Scenario 1 – HEAF in a “Train A” Switchgear with “Train B” Cables Overhead 

A high energy arcing fault occurs in a low/medium voltage switchgear that supplies power to 

“Train A” systems. The cables from an overhead cable tray enter the cabinet from the top (airdrop configuration). A cable tray carrying cables that supply power to redundant “Train B”

systems is located near the “Train A” switchgear and cable tray.

2.5.1.2 Figure of Merit

Determining the extent of damage to the cables in the “Train B” cable tray. 
2-9

2.5.2 HEAF Scenario 2

2.5.2.1 Scenario Description

Figure 2-2 Scenario 2 – HEAF in a “Train B” Bus Duct above a “Train A” Switchgear 

A high energy arcing fault occurs in a non-segregated bus duct supplying power to “Train B” 

systems. A switchgear supplying power to redundant “Train A” systems is located nearby. 

2.5.2.2 Figure of Merit 

Determining the extent of damage to the switchgear. 
2-10

2.5.3 HEAF Scenario 3

2.5.3.1 Scenario Description

Figure 2-3 Scenario 3 – HEAF in a “Train A” Switchgear in a Bank with “Train B” Cables 

 Overhead 

A high energy arcing fault occurs in a low/medium voltage switchgear supplying power to “Train A” 

systems in a bank of similar switchgears. The cables from an overhead cable tray enter the 

cabinets from the top (air-drop configuration). A cable tray carrying cables that supply power to 

“Train B” systems is located nearby. 

2.5.3.2 Figure of Merit 

Determining the extent of damage to the adjacent switchgears and the cables in “Train B” cable 

tray. 
3-1

3 SUMMARY OF LEVEL 1 PHENOMENA

3.1 Ranking Methodology

The method used to convert the panelists’ rankings into an ordered, prioritized list is as follows: 

First, each ranking was given a corresponding numerical score as shown in Table 3-1. 

Table 3-1 Numerical Equivalents for Ranking Values 

Ranking Value

Low (L) 1

Low-Medium (L-M) 2

Medium (M) 3

Medium-High (M-H) 4

High (H) 5

Unknown (U) No value

Not Applicable (N/A) No value

Decline to Answer (X) No value

Second, the average of all the values in a phenomenon (including its sub-phenomena) was taken 

for both importance and state of knowledge. An example using tables A7 and A19 (pressure 

effects for scenario 1) is illustrated below tables 3-2 – 3-5. 

Table 3-2 Importance Rankings for Pressure Effects, Scenario 1 

Phenomenon Description Importance Ranking

P1 P2 P3 P4 P5 P6

7. Pressure Effects

A. Projectile/missile damage L H M H H L

B. Pressure wave L H M H H M

The corresponding numerical values are assigned, and an arithmetic average is calculated. 

Table 3-3 Numerical Equivalent of Table 3-2 

Phenomenon Description Importance Ranking Table Average P1 P2 P3 P4 P5 P6

7. Pressure Effects

A. Projectile/missile

damage

1 5 3 5 5 1

3.5

B. Pressure wave 1 5 3 5 5 3
3-2

Table 3-4 State of Knowledge for Pressure Effects, Scenario 1 

Phenomenon Description

State of Knowledge Ranking

Model 

Adequacy

Data 

Availability

Ability to Collect 

New Data

7. Pressure Effects

A. Projectile/missile damage M L-M L

B. Pressure wave H H N/A

The corresponding numerical values are assigned, and an arithmetic average is calculated. 

Table 3-5 Numerical Equivalent of Table 3-4 

Phenomenon 

Description

State of Knowledge Ranking

Table Average Model 

Adequacy

Data 

Availability

Ability to 

Collect New 

Data

7. Pressure Effects

A. Projectile/missile

damage

3 2 1

3.2

B. Pressure wave 5 5 N/A

Lastly, a rank was assigned using the following simple relationship:

RRRRRRRR = IIIIIIIIIIII IIIIaaaaaa

SS oo KK KKKK KKKK aaaaaa

In the case of the example above, this would be:

RRRRRRRR = 3.5

3.2 = 1.09

This process was applied to each phenomenon, and a summary of their rankings across all three 

scenarios sorted by average rank in descending order is shown in Table 3-6. 
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Table 3-6 Summary of Phenomena Rankings for All Scenarios 

Phenomenon Scenario 1 

Rank

Scenario 2 

Rank

Scenario 3 

Rank

Average 

Rank

Level 1 Phenomena

Target Characterization 1.53 1.61 1.53/1.56 1.56

Arc Characterization 1.33 1.27 2.00 1.53

Arc Mitigation 1.75 1.19 1.23 1.39

Cabinet Lineup Effects 1.29 1.29

Level 2 Phenomena

Internal Ensuing Fire 1.63 0.31 1.54 1.16

External Ensuing Fire 1.27 0.82 1.32 1.14

Pressure Effects 1.09 0.40 1.67 1.05

Electrical Configuration Effects 1.00 1.00 1.00 1.00

Level 3 Phenomena

External Cabinet Enclosure Effects 0.80 1.04 0.76 0.87

Internal Cabinet (Bus Duct) Configuration 

Effects

0.91 0.72 0.93 0.85

Suppression Effects 0.80 0.40 0.67 0.62

Room Configuration 0.79 0.43 0.65 0.62

Fire Detection 0.50 0.40 0.26 0.39

As is evident from Table 3-6, the list of phenomena was split into three equal-sized groups: level 

1, level 2, and level 3. It is important to note that this grouping conveys no information about the 

absolute priority of any phenomenon, only its priority relative to the others. Level 1 phenomena 

are those that present the highest research priority, whereas level 3 phenomena are those that

present the lowest research priority.

3.2 Discussion of Level 1 Phenomena

For the level 1 phenomena listed in Table 3-6, the highlights of the panelists’ discussions are 

included in this section.

3.2.1 Target Characterization

During the PIRT, panelists considered the targets in a generic sense; that is, they ranked 

phenomena associated with any generic piece of equipment of a similar class. The panel’s

opinion is that, unsurprisingly, the properties of the target will have a first order impact on the 

damage that it sustains.

This phenomenon was broken down into three main sub-phenomena:

A) Characterization of target damage criteria

B) Target arrangement effects

C) Target sensitivity to damage

Sub-phenomena (A) refers to the ability to assign some type of damage threshold to the target at 

hand such as maximum temperature, maximum heat flux, maximum pressure, etc. The panelists 

noted that threshold damage criteria exist for fire scenarios, where the fire is expected to follow 
3-4

some assigned growth pattern. No such criteria exists for a HEAF exposure, and any ability to 

predict whether a target is damaged is moot without them. 

Sub-phenomena (B) refers to the target’s position and orientation relative to the HEAF source. 

This item was not so easy to consider as it represents a departure from the currently employed 

“zone of influence” (ZOI) method and the standard method of analysis; here, the distance from the 

source equipment is being considered as a variable in calculating target damage rather than a 

binary in/out of ZOI. 

Sub-phenomenon (C) refers to a target’s susceptibility to damage from a number of items: heat, 

pressure, smoke, conductive particulate, and others. Different classes of equipment are likely to 

respond differently to each of these hazards although it may be impractical to characterize the 

sensitivity and damage criteria of each potential target that would represent the most realistic 

treatment of the scenario. Sub-phenomena (A) and (C) are linked but not identical. Susceptibility 

to various modes of damage is an important factor in establishing meaningful damage threshold 

criteria, but the knowledge of a target’s physical response is different from the knowledge of its 

functional response.

Characterization of the target in scenario 2 is similar to that of scenario 1. The higher ranking of 

this phenomenon in scenario 2 is partially due to simpler source equipment. With a bus duct that 

is unlikely to experience an ensuing fire, the properties of the target receive more weight.

Scenario 3 featured two targets for panelists to consider: the enclosures adjacent to the source 

enclosure and an overhead cable tray. Each target was considered separately, but they are 

combined here for the purposes of discussion. As with scenarios 1 and 2, the panelists ranked 

the phenomenology of each target in a generic sense; that is, their rankings apply to any piece of 

equipment of a similar class. The panelists’ ranking of the phenomena, sub-phenomena, and 

parameters for both targets are similar. “Orientation effects” was not considered for the enclosure 

targets because the position and orientation are fixed by the scenario definition. There was 

slightly more uncertainty about the response of an electrical enclosure to a HEAF than a cable 

tray due to their relative complexity. Panelists noted that enclosure sensitivity to certain failure 

mechanisms would be a function of enclosure type and contents; considering this type of target in 

a generic sense is a rough approximation.

3.2.2 Arc Characterization

Characterization of the arc is essentially the characterization of the source term. Within this 

phenomenon, the highly ranked items were characterizing the arc’s electrical properties (voltage, 

current, duration, etc.); arc breeching of the enclosure; arc ejecta; and the thermal effects of the 

arc.

The state of knowledge regarding the characteristics of the arc is mixed. Models and data exist 

for the electrical properties of the arc, although some important properties such as duration have 

external dependencies that cannot be accounted for. The panel is not aware of any models for 

the breeching of the enclosure or arc ejecta. These two areas are critically important: a breeched 

enclosure presents a far greater hazard to adjacent equipment, and arc ejecta (smoke, conductive 

particulate, ionized gas) may be a significant failure mechanism for target equipment.

In scenario 2 as in scenario 1, characterization of the arc is highly ranked. One topic of discussion 

among the panelists was whether, and in what ways, an arc occurring in a bus duct differs from an 

arc occurring in an electrical enclosure. The current guidance in NUREG/CR-6850 [1][11] lays out 
3-5

separate methods for evaluation of the ZOI in bus ducts and electrical enclosures due largely to 

what has been observed in operating experience and the expected arrangement of the bus duct 

relative to potential targets. This approach, while practical, says little about the underlying 

phenomena involved, and the panel wondered whether a single model could accurately describe 

an arc in both types of equipment. Also, as in scenario 1, the highly ranked sub-phenomena were 

the electrical characterization of the arc (voltage, current, duration); the thermal effects of the arc; 

arc breeching of the enclosure; and arc ejecta.

3.2.3 Arc Mitigation

Arc mitigation refers to the intentional shielding of targets from potential arc source equipment. 

Within this phenomenon, discussions were focused around “HEAF shields,” which have no formal 

definition; electrical raceway fire barrier systems (ERFBS); and fire-retardant cable coatings. The 

presence of a barrier between the HEAF source and target equipment should moderate the 

incident thermal energy, pressure front, and arc ejecta effects.

The reasons for low state of knowledge rankings are myriad. Because no formal or industrystandard definition exists for a “HEAF shield,” no performance criteria or qualifications exist. The 

panel is not aware that any test campaign has evaluated the impact of such a shield, and no 

operating experience is available to quantify its performance. The panel is unanimous in their

opinion that the performance of ERFBS and fire-retardant cable coatings is reasonably 

understood under fire conditions but not under HEAF conditions. Panelists raised the possibility 

that the pressure wave from the HEAF could damage an ERFBS and render it ineffective. In 

addition, the effects of a high heat, short-duration exposure of a HEAF event on these shields is 

not well understood. The typical assumptions that apply to fire exposures do not apply here; there 

is no growth phase, the velocity of hot gases is much higher, and the constituents of the hot gases 

are different. Any analytical model to predict the effects of a HEAF on a shield would require 

analyses of heat and mass transfer as well as solid mechanics, and no such tool has been applied 

to the evaluation of HEAF shields.

3.2.4 Cabinet Lineup Effects

Only scenario 3 featured a cabinet lineup, so only one data point was available for the calculation 

of this phenomenon’s average rank.

The discussions on cabinet lineup effects were focused on what properties were unique to banks 

of enclosures and how they might affect the results of a HEAF event. These include how the 

cabinets are situated next to one another; what separations are between them (none, single wall, 

double wall, air gap); the presence of penetrations or false floor between cabinets; and the 

position of the HEAF source within the bank. Some of these properties, such as cabinet 

separation, are closely linked to target phenomena like shielding and orientation. However, the 

panel’s consensus was that cabinet lineup effects should be treated as its own category because 

banks of cabinets do not respond as if they are several closely spaced but discrete targets. 

Mechanical coupling of the enclosures and shared penetrations often occurs. 

3.3 Additional Discussions

This section captures some of the important points of the panelists’ discussion that do not directly 

pertain to level 1 phenomena but are worth noting nonetheless.
3-6

3.3.1 External Duct Housing Configuration

The importance of the external duct housing configuration is attributed to its structural design 

including the thickness, material, and penetrations/access points. Test data from the OECD/NEA 

program provides direct evidence for the significant impact of the duct housing material; in test 26, 

several inches of aluminum housing were oxidized creating a fireball that melted equipment over 

20 feet away. Although the configuration of the external duct housing encompasses a number of 

things, the driver behind its ranking is the possible presence of aluminum in the housing.

3.3.2 Internal Ensuing Fire

The source equipment identified in scenario 1 was a generic electrical enclosure, and the 

associated target was a redundant cable tray passing over the enclosure. The panelists identified 

the occurrence of an ensuing fire in the source enclosure as being of first-order importance in 

predicting the damage to the cable tray. Although a HEAF would likely produce temperature far in 

excess of any ensuing fire, the extended duration of an ensuing fire poses a secondary threat to 

adjacent equipment.

The highly ranked sub-phenomena discussed included ignition, characterization of the fire source, 

and development of the fire. These are all critical phenomena in predicting the behavior and 

effects of a standard cabinet fire.

The state of knowledge regarding internal fires reflects this missing link. The lowest ranked 

phenomenon was fire ignition, and the panelists are unsure how to predict or model ignition in a 

HEAF scenario.

3.3.3 Pressure Effects

Panel discussions on pressure effects were centered on two failure mechanisms: a pressure

wave and a projectile. In the former, a wave of pressure disturbance propagates through the 

medium (air) imparting mechanical energy to targets; in the latter, the pressure wave accelerates 

a solid object, which subsequently imparts mechanical energy to a target upon impact. The term 

“shock wave,” which implies supersonic propagation, is not used here. Pressure measurements 

during phase one experiments were unreliable and noisy, and propagation speed was not 

measured.

Cabinets in a lineup may be particularly sensitive to a pressure wave depending on their 

configuration. Where sensitive electronic equipment is present, being in the same bank as a 

HEAF may be sufficient to cause damage even where no thermal insult is incurred. For the 

enclosures immediately adjacent to the source cabinet, the construction of the separating walls 

becomes important. Operating experience and test results clearly document the ability of a HEAF 

to open or dislodge enclosure doors and bow or deform enclosure walls. The panel theorized that 

this type of mechanical shock could raise the possibility of a secondary HEAF in an adjacent 

cabinet.
4-1

4 CONCLUSIONS AND RECOMMENDATIONS

4.1 Practical Considerations for PRA Practitioners

The phenomena identification and ranking table (PIRT) was useful in identifying the phenomena 

that are most influential in predicting the impact of a high energy arcing fault (HEAF); however,

certain practical considerations must be taken into account when analyzing the data for the 

formulation of a test plan.

Ultimately, the goal of the HEAF research program is to refine and improve the methodology by 

which probabilistic risk assessment (PRA) practitioners estimate the risk of a postulated HEAF 

event. The input to any such model or methodology must be available to the practitioner. It would 

be unproductive to study the impact of microscale or stochastic phenomena knowing that it 

cannot be incorporated into the applicable guidance.

4.2 Characterizing Target Damage

One of the consistently highly ranked phenomena was the characterization of the target 

equipment and its susceptibility to various types of damage. This phenomenon fundamentally 

differs from the others in that it is not a property of the HEAF or source equipment. Even if a 

HEAF can be modeled with perfect accuracy, the ability to convert that data into a damage state 

for a given target is critical in assessing risk.

Although thermal damage appears to be the greatest threat both in experimental observations 

and PIRT responses, HEAF events fall outside the range of applicability for classical fire models. 

The temperature of the arc column can be in excess of 15,000 °C, which is unmatched even by 

rocket fuel or thermite. HEAF events also do not have growth or decay phases; the energy is 

released suddenly and intensely before the event terminates just as suddenly. With this type of 

energy release, the thermal inertia of targets must be taken into account—a simple temperature 

threshold for damage does not adequately describe the target vulnerability.

Any future research program should focus on modeling the HEAF and on modeling the damage to 

targets as a function of the environmental conditions created by the HEAF. In scenario 3, the 

difference in response of the two targets (cable tray and enclosure) was discussed, which raised 

the possibility that a one-size-fits-all zone of influence approach may not be sufficient. Different 

classes of target equipment may need to be considered separately.

Though thermal conditions were a focal point during phase one testing, the PIRT suggests that 

pressure effects and the effects of conductive particulate on electronic equipment should be 

considered as well.

4.3 Arc Mitigation

The multi-tiered approach to safety advocated by “defense in depth” (DID) strategies applies to 

HEAF as well as any phenomenon. Operating plants have placed a heavy emphasis on the 

“prevention” aspect of DID with selective coordination designed to limit the duration of an arc fault 

to a few cycles—not enough to cause significant external damage. These protective schemes are 

often effective in limiting the damage from arc faults, but a non-trivial number of these arc faults 

are accompanied by the failure of an upstream breaker resulting in event durations that have 

exceeded 10 seconds. The frequency of these events, coupled with the catastrophic damage 

they can cause, demand more than a single element of DID.
4-2

If a HEAF cannot be prevented, the next logical step is to mitigate the damage it can cause. This 

can be done in a number of ways, but the panel discussions were focused around enclosing the 

source equipment (e.g., “arc resistant” cabinets1

); protecting the target equipment (ERFBS, cable 

coatings); or placing barriers between the two. The pros and cons of each option were discussed.

Enclosures designed to contain the blast of a HEAF represent a costly solution to this problem. 

The panel deemed the replacement of electrical enclosures susceptible to HEAF with such 

enclosures beyond the realm of feasibility; however, their use in new construction was seen as 

slightly more reasonable.

Target protection is used extensively in fire protection but, where HEAFs are concerned, 

questions abound. Little data is available regarding the ability of classical fire protection methods 

(ERFBS, cable coatings) to withstand the impact of a HEAF. Target protection may be an 

effective method of HEAF mitigation, but further study is needed.

The last method―a physical barrier separating the source and target equipment (or “HEAF 

shield”)―strikes a good balance between cost and efficacy in theory. Some operating facilities 

have already installed some form of HEAF shield. Because no formal or industry-standard 

definition for such a barrier is available, no performance criteria or qualifications exist. The panel 

is not aware of any test campaign that has evaluated the impact of such a shield, and no 

operating experience is available to quantify its performance. This is an area that requires further 

study and should be considered in future research test plans.

4.4 Internal Ensuing Fire

Internal ensuing fires show up as high-priority items in both scenarios where the source 

equipment is an electrical enclosure (as opposed to a bus duct, which was assumed not to be 

able to support a significant sustained internal fire.) Based on operating experience and test 

evidence, internal ensuing fires are the most likely secondary hazard in a HEAF scenario.

The U.S. Nuclear Regulatory Commission and others have performed a significant amount of 

work in an attempt to quantify the behavior of a fire in an electrical enclosure [16][17]. What has 

not been quantified is the link between a HEAF and the advent of a fire. Specifically, the following 

two questions arose during the PIRT:

a) What is the likelihood of an internal fire pursuant to a HEAF?

b) Can the HEAF simply be modeled as a very energetic ignition event or does it impact the

development of the fire through pre-heating and other phenomena?

Item (a) is not just a question of frequency—it should be the goal of future research to determine 

what conditions must be present for a sustained internal ensuing fire. From phase one testing, a 

rough pattern has emerged: arcs with durations of less than two seconds did not cause internal 

ensuing fires likely due to the linear relationship between arc duration and total energy. More 

tests are needed to establish whether arc energy (and by extension, arc duration) is the primary 

criteria for predicting ensuing fires and other conditions that are necessary or favorable for an 

ensuing fire.

1 The term “arc-resistant” is a misnomer and generally refers to a cabinet designed to route hot gases and flames 

away from service personnel in the event of an arc. It is not designed to prevent or extinguish arcs.
4-3

Item (b) is critical for a PRA analysis of the ensuing fire and could implicate the need for a 

fundamentally different method of analysis. The typical fire models used for electrical enclosure 

fires assume a growth phase that lasts for several minutes, steady burning at peak heat release 

rate for several more minutes, and then a decay phase. If a HEAF is sufficiently energetic, it may 

heat and simultaneously ignite all cabinet internals, skipping the growth phase entirely. This type 

of behavior was observed several times during phase one testing. In addition to skipping a growth 

phase, the instantaneous ignition of cabinet internals may lead to shorter duration, higher intensity 

fires than would typically be expected. A sensitivity study on plant response to this alternate fire 

growth curve is in order. Future research should focus on the impact of a HEAF on the growth 

and development of an ensuing fire as compared to a standard electrical enclosure fire.

4.5 Arc Characterization

Characterization of the arc is essentially characterization of the “source term”—the driver behind 

any resultant damage, analogous to the heat release rate term in a fire model. The electrical 

properties of the arc including voltage, current, and duration determine the amount of energy 

released into the environment of interest. It is important to distinguish between the electrical 

properties of the equipment in which the arc occurs and the electrical properties of the arc itself. 

Although the former is known to a high degree of accuracy, the latter is subject to some 

uncertainty.

One area that was discussed at length was the location of the arc and whether it was predictable. 

The arc location is an important parameter for predicting the flow path of the plasma and ionized 

gas, if and where the arc will migrate, and whether the arc is likely to breech the enclosure. 

Unfortunately, past test data is not helpful in this regard as the arc was initiated in a 

predetermined location with the use of shorting wire as described in the IEEE standard for testing 

switchgear internal arcing faults.[18] Determining whether the location of an arc is predictable, 

random, or stochastic should be a focus of future experimental work.

Arc ejecta, which includes the smoke, ionized gas, and conductive particulate expelled by the arc, 

were also discussed. Ionized gas and conductive particulate may present a failure mechanism for 

nearby equipment that has previously not been considered. During phase one testing, conductive 

particulate from the arc caused shorting in laboratory equipment several meters away from the 

test enclosure. Panelists noted the importance of quantifying this ejecta but also that it would be 

difficult or impossible to separate the ejecta into its constituents. Future research should focus on 

establishing the properties of the ejecta (thermal conductivity, electrical conductivity, mean particle 

size) and its potential impact on target equipment.

4.6 Pressure Effects

After thermal effects, the panel ranked pressure effects as the greatest hazard to surrounding 

systems, structures, and components. The mechanical energy imparted by a pressure wave or 

projectile has the potential to disable equipment, trip breakers, cause secondary arcs, damage 

pressure boundaries (fire doors and dampers), and change the ventilation properties of the source 

enclosure.

Pressure measurements during phase one testing are difficult to analyze, and the impact of 

pressure effects is mostly anecdotal. From the test report:

“Due to the EMI generated by the large currents, voltages, and arc activity, the pressure 

signals are noisy. The EMI tends to be most severe during large changes in current, 
4-4

voltage, and arc activity, and these are the same periods where large changes are 

expected in enclosure pressure. For this reason, it is difficult to determine whether the 

transducer signal peaks are actually pressure peaks.[12] 

Despite the difficulty in obtaining reliable pressure measurements, some qualitative data are 

available. In numerous tests, cabinet access doors were blown open, cabinet internals were 

violently dislodged, and enclosure walls were deformed. An LER [19] and inspection report [20] 

from a 2017 HEAF event at Turkey Point document the deformation of a fire door due to pressure 

increase, which raises the concern of an ensuing fire unbounded by the normal compartmentation 

scheme.

The lack of high-quality pressure measurements factored into the low state of knowledge rankings 

for pressure-related phenomena. Future test programs would benefit from a better method of 

pressure measurement free from EMI, both inside and outside the enclosure.
5-1

5 REFERENCES

5.1 References Found in this Report

Fire PRA Methodology for Nuclear Power Facilities, Volume 2: Detailed Methodology, 

NUREG/CR-6850/EPRI 1010989, U.S. NRC, September 2005. 

OECD FIRE Project – Topical Report No. 1, Analysis of High Energy Arcing Fault (HEAF) Fire 

Events, NEA/CSNI/R(2013)6, Organisation for Economic Co-operation and Development 

(OECD) Nuclear Energy Agency (NEA), Committee on the Safety of Nuclear Installations 

(CSNI), 2013. 

http://www.oecd-nea.org/nsd/docs/2013/csni-r2013-6.pdf 

Code of Federal Regulations (CFR), Title 10, Part 50, Appendix A, “General Design Criteria 

for Nuclear Power Plants.” 

NRC Information Notice (IN) 2016-08, “Inadequate Work Practices Resulting in Faulted Circuit 

Breaker Connections.” June 2016. 

Diablo Canyon Unit 1, LER 2000-004-00, “Unit 1 Unusual Event Due to a 12 kV Bus Fault,” 

Jun 13, 2000. 

H. B; Robinson Steam Electric Plant, Unit No. 2, LER 2010-002-00, “Plant Trip due to

Electrical Fault,” May 27, 2010.

Raughley & Lanik. Operating Experience Assessment Energetic Faults in 4.16 kV to 13.8 kV 

Switchgear Bus Ducts that Caused Fires in Nuclear Plants 1986-2001. NRC, February 2002. 

SANDIA REPORT SAND2008-4820 “High Energy Arcing Fault Fires in Switchgear 

Equipment, A Literature Review 

A Review of Current Calculation Methods Used to Predict Damage from High Energy Arcing 

Fault (HEAF) Events, NEA/CSNI/R(2015)10, Organisation for Economic Co-operation and 

Development (OECD) Nuclear Energy Agency (NEA), Committee on the Safety of Nuclear 

Installations (CSNI), June 2015. 

https://www.oecd-nea.org/nsd/docs/2015/csni-r2015-10.pdf 

San Onofre Nuclear Generating Station, LER 362/2001-001, “Fire and RPS/ESF Actuations 

Caused By The Failure of a Non-Safety Related 4.16 kV Circuit Breaker,” February 2, 2001. 

 Fire Probabilistic Risk Assessment Methods Enhancements Supplement 1 to NUREG/ 

 CR-6850 and EPRI 1011989” section 7 bus duct (counting) guidance for high-energy arcing 

 faults (FAQ 07-0035) 

 Report on the Testing Phase (2014-2016) of the High Energy Arcing Fault Events (HEAF) 

Project: Experimental Results from the International Energy Arcing Fault Research 

Programme. NEA/CSNI/R(2017)7, Organisation for Economic Co-operation and Development

(OECD) Nuclear Energy Agency (NEA), Committee on the Safety of Nuclear Installations 

(CSNI), 2017. 

https://www.oecd-nea.org/nsd/docs/2017/csni-r2017-7.pdf 

 NUREG/IA-0470 Volume 1 “Nuclear Regulatory Authority Experimental Program to 

Characterize and Understand High Energy Arcing Fault (HEAF) Phenomena” 

 A Phenomena Identification and Ranking Table (PIRT) Exercise for Nuclear Power Plant 

 Fire Modeling Applications, NUREG/CR-6978/SAND2008-3997P, U.S. NRC, November 2008. 
5-2

Joint Assesment of Cable Damage and Quantification of Effects from Fire (JACQUE-FIRE), 

Volume 2: Expert Elicitation Exercise for Nuclear Power Plant Fire-Induced Electrical Circuit 

Failure, NUREG/CR-7150/BNL-NUREG-98204-2012/EPRI 3002001989, U.S. NRC, May 

2014. 

Heat Release Rates of Electrical Enclosure Fires (HELEN-FIRE), NUREG/CR-7197, U.S. 

NRC, April, 2016. 

Refining and Characterizing Heat Release Rates from Electrical Enclosure During Fire 

(RACHELLE-FIRE), Volume 1: Peak Heat Release Rates and Effect of Obstructed Plume, 

NUREG-2178/EPRI 3002005578, U.S. NRC, April 2016. 

IEEE C37.20.7-2007 Corrigendum 1 “IEEE Guide for Testing Metal-Enclosed Switchgear 

Rated up to 38 kV for Internal Arcing Faults.” 

Turkey Point Unit 3, LER 2017-001-00, “Loss of 3A 4kV Vital Bus Results in Reactor Trip, 

Safety System Actuaions and Loss of Safety Injection Function,” May 16, 2017. 

Turkey Point Nuclear Generating Station – NRC Reactive Inspection Report 

05000250/2017008 and 05000251/2017008. May 12, 2017. 
5-3

5.2 Additional Documents Included in the Knowledge Base

• Shirai, Goda, Iwata et al. Fundamental Investigation on Successive Fire due to the High

Energy Arcing Faults Event for the High-Voltage Switchgear. April 2014.

• Iwata, Tanaka, Miyagiet al. CFD Calculation of Pressure Rise and Energy Flow of Hot

Gases Due to Short-Circuit Fault Arc in Switchgears. IEEE, 2015.

• Iwata, Tanaka, Ohtaka, et al. CFD Calculation of Pressure Rise Due to Internal AC and

DC Arcing in a Closed Container. IEEE, July 2011.

• Iwata, Anantavanich, & Pietsch. Influence of Current and Electrode Material on Fraction

Kp of Electric Arc Energy Leading to Pressure Rise in a Closed Container During Internal

Arcing. IEEE, July 2010.

• Beckstead, M. W. A Summary of Aluminum Combustion, Brigham Young University,

January 2004.

• Land III, H. Bruce. The Behavior of Arcing Faults in Low-Voltage Switchboards. IEEE,

April 2008.

• Land III, H. Bruce. Determination of the Cause of Arcing Faults in Low-Voltage

Switchboards. IEEE, April 2008.

• Davis, St. Pierre, Castor, et al. Practical Solution Guide to Arc Flash Hazards. ESA Inc,

2003.

• Arc-Fault Primer: Numerical, Analytical, and Experimental Characteristics of Initiation and

Sustainment of Arc Plasmas (DRAFT), SAND2017-XXXX.

• Lee, Gammon, Johnson, et al. IEEE/NFPA Arc Flash Phenomena Collaborative

Research Project (Presentation). January 2011.

• Zhou, Nie, Zeng, et al. Effects of Aluminum Content on TNT Detonation and Aluminum

Combustion using Electrical Conductivity Measurements, PREP 2015.

• McBride & Weaver. Review of Arcing Phenomena in Low Voltage Current Limiting Circuit

Breakers. IEEE, January 2001.

• Kwon, Gromov, Ilyin, et al. The Mechanism of Combustion of Superfine Aluminum

Powders. Combustion and Flame 133, 2003.

• Babrauskas, V. Electric Arc Explosions. Interflam, 2010.

• IEEE Std C37.20.7 IEEE Guide for Testing Medium-Voltage Metal-Enclosed Switchgear

for Internal Arcing Faults. IEEE, 2001.

• Lee, R. The Other Electrical Hazard: Electric Arc Blast Burns. IEEE, 1982.

• Land III, Gammon. Addressing Arc Flash Problems in Low Voltage Switchboards: A Case

Study in Arc Fault Protection. IEEE, 2013.

• Frieberg & Pietsch. Calculation of Pressure Rise Due to Arcing Faults. IEEE, April 1999.

• Jones, Liggett, Capelli-Schellpfeffer, et al. Staged Tests Increase Awareness of Arc-Flash

Hazards in Electrical Equipment. IEEE, April 2000.

A-1

APPENDIX A PIRT HEAF SCENARIO 1

A.1 HEAF Scenario 1

A.1.1 Scenario Description

A high energy arcing fault occurs in a low/medium voltage switchgear that supplies power to 

“Train A” systems. The cables from an overhead cable tray enter the cabinet from the top (airdrop configuration). A cable tray carrying cables that supply power to redundant “Train B” 

systems is located near the “Train A” switchgear and cable tray.

A.1.2 Figure of Merit

Determining the extent of damage to the cables in the “Train B” cable tray. 

A.2 List of Identified Phenomena

Phenomenon 1: Electrical Configuration Effects

A. Power supply characterization

B. Electrical protection coordination2

2 Electrical protection coordination refers to the coordination and configuration of upstream breakers with the 

objective of minimizing the duration of an electrical fault
A-2

Phenomenon 2: Internal Cabinet Configuration Effects

A. Cabinet compartmentation

B. Breaker configuration

C. Cabinet combustible loading

D. Cabinet bus bar configuration

Phenomenon 3: External Cabinet Enclosure Configuration Effects

A. Cabinet ventilation

B. Cabinet structural design

C. Cabinet penetrations

Phenomenon 4: Arc Characterization

A. Arc electrical characterization

B. Arc migration

C. Arc breeching of enclosure

D. Thermal effects of the arc

E. Magnetic effects of the arc3

F. Electromagnetic interference

G. Arc ejecta

Phenomenon 5: Fire Detection4

A. Presence of fire detection

B. Characterizing the detection system

Phenomenon 6: Fire Suppression

A. Presence of fire suppression

B. Characterizing the suppression system

Phenomenon 7: Pressure Effects

A. Projectile/missile damage

B. Pressure wave

3 Magnetic effects refers to the applied forces on ferrous materials by a magnetic field that can induce bending and 

deformation, as opposed to the interference that it may cause. Interference is addressed separately. 4 Fire detection was assumed not to automatically trigger fire suppression. Fire suppression is considered as a 

separate phenomenon.
A-3

Phenomenon 8: Internal Ensuring Fire5

A. Fire ignition

B. Characterization of the fire source

C. Fire development

D. Smoke generation

E. Altered ventilation effects6

Phenomenon 9: External Ensuing Fire

A. Fire ignition

B. Characterization of the fire source

C. Fire development

D. Smoke generation

Phenomenon 10: Room Configuration Effects

A. Room integrity7

B. Room arrangement

C. Room ventilation

Phenomenon 11: Arc Mitigation

A. Intentional shielding

B. Electrical raceway fire barrier system effects8

C. Fire-retardant coating effects9

Phenomenon 12: Generic Cable Tray (Target) Characterization

A. Characterizing target damage criteria

B. Target arrangement effects

C. Target sensitivity to damage

5 Internal ensuing fire refers to a sustained fire that occurs inside the source cabinet. 6 Altered ventilation effects refers to the manner in which changes to the cabinet’s structure and integrity as a 

result of the HEAF impact the ventilation paths for an internal ensuing fire.

7

 Room integrity refers to the pressure boundary of the room in which the HEAF occurs, and how its response to 

the increased pressure will impact target damage. For example, consider whether blowing open a fire door or 

damper will affect target damage.

8 Electrical raceway fire barrier systems refers to a wrap or enclosure that is installed around electrical cable trays 

with the intent of mitigating fire damage.

9 Fire-retardant coating refers to a permanently installed coating or spray that is applied directly to the cables in a 

cable tray.
A-4

A.3 Phenomena Importance Rankings

Table A-1 Importance Ranking for Scenario 1, Electrical Configuration Effects 

Phenomenon Description Importance Ranking Additional Not

P1 P2 P3 P4 P5 P6

1. Electrical Configuration Effects

A. Power supply characterization H H H H H H 

B. Electrical protection coordination H H H H H H 

Table A-2 Importance Ranking for Scenario 1, Internal Cabinet Configuration Effects 

Phenomenon Description Importance Ranking Additional Not

P1 P2 P3 P4 P5 P6

2. Internal Cabinet Configuration

Effects

A. Cabinet compartmentation M M H M M L 

B. Breaker configuration L/M H M M M H P1 notes that whether 

primary or secondary s

affects the importance

C. Cabinet combustible loading H H M H H H 

D. Cabinet bus bar configuration M H M H M H 

Table A-3 Importance Ranking for Scenario 1, External Cabinet Enclosure Configuration Effects 

Phenomenon Description Importance Ranking Additional Not

P1 P2 P3 P4 P5 P6

3. External Cabinet Enclosure

Configuration Effects

A. Cabinet ventilation M H H M H H 

B. Cabinet structural design L H H M M M 

C. Cabinet penetrations M H H H M H 
A-5

Table A-4 Importance Ranking for Scenario 1, Arc Characterization 

Phenomenon Description Importance Ranking Additional N

P1 P2 P3 P4 P5 P6

4. Arc Characterization

A. Arc electrical characterization H H H H H H 

B. Arc migration M M H M M M 

C. Arc breeching of enclosure H H H H M H 

D. Thermal effects of the arc H H H H H H 

E. Magnetic effects of the arc L L L M U L 

F. Electromagnetic interference L L L M U L 

G. Arc ejecta H M H H H L 

Table A-5 Importance Ranking for Scenario 1, Fire Detection 

Phenomenon Description Importance Ranking Additional N

P1 P2 P3 P4 P5 P6

5. Fire Detection

A. Presence of fire detection H L H L H L 

B. Characterizing fire detection system M L M L M L 

Table A-6 Importance Ranking for Scenario 1, Fire Suppression 

Phenomenon Description Importance Ranking Additional N

P1 P2 P3 P4 P5 P6

6. Fire Suppression

A. Presence of fire suppression H L H M H L 

B. Fire suppression effects H H H M H H 
A-6

Table A-7 Importance Ranking for Scenario 1, Pressure Effects 

Phenomenon Description Importance Ranking Additional N

P1 P2 P3 P4 P5 P6

7. Pressure Effects

C. Projectile/missile damage L H M H H L 

D. Pressure wave L H M H H M 

Table A-8 Importance Ranking for Scenario 1, Internal Ensuing Fire 

Phenomenon Description Importance Ranking Additional N

P1 P2 P3 P4 P5 P6

8. Internal Ensuing Fire

A. Fire ignition H H H H H H 

B. Characterization of the fire source H H H H H H 

C. Fire development H H H H H H 

D. Smoke generation L M M M M M 

E. Altered ventilation effects M H H M H H 

Table A-9 Importance Ranking for Scenario 1, External Ensuing Fire 

Phenomenon Description Importance Ranking Additional N

P1 P2 P3 P4 P5 P6

9. External Ensuing Fire

A. Fire ignition H H H H H H 

B. Characterization of the fire source H H H H H H 

C. Fire development H H H H H H 

D. Smoke generation L L M H M L 
A-7

Table A-10 Importance Ranking for Scenario 1, Room Configuration Effects 

Phenomenon Description Importance Ranking Additional No

P1 P2 P3 P4 P5 P6

10. Room Configuration Effects

A. Room integrity L H M L M X 

B. Room arrangement M H M M M H 

C. Room ventilation M H M M M H 

Table A-11 Importance Ranking for Scenario 1, Arc Mitigation 

Phenomenon Description Importance Ranking Additional No

P1 P2 P3 P4 P5 P6

11. Arc Mitigation

A. Intentional shielding M M H H H H 

B. Electrical raceway fire barrier system H L H H H H 

C. Fire-retardant coating M M H M H H 

Table A-12 Importance Ranking for Scenario 1, Generic Cable Tray (Target) Characterization 

Phenomenon Description Importance Ranking Additional No

P1 P2 P3 P4 P5 P6

12. Generic Cable Tray (Target)

Characterization

A. Characterizing target damage criteria H H H H H H 

B. Target arrangement effects H H H M H H 

C. Target sensitivity to damage H H H H H H 
A-8

A.4 Phenomena State of Knowledge Rankings

Table A-13 State of Knowledge Ranking for Scenario 1, Electrical Configuration Effects 

Phenomenon Description

State of Knowledge Ranking

Additional 

Model 

Adequacy

Data 

Availability

Ability to 

Collect 

New Data

7. Electrical Configuration Effects

A. Power supply characterization H H N/A

B. Electrical protection coordination H H N/A

Table A-14 State of Knowledge Ranking for Scenario 1, Internal Cabinet Configuration Effects 

Phenomenon Description

State of Knowledge Ranking

Additional 

Model 

Adequacy

Data 

Availability

Ability to 

Collect 

New Data

8. Internal Cabinet Configuration

Effects

A. Cabinet compartmentation H H N/A

B. Breaker configuration M-H M H 

C. Cabinet combustible loading M-H M M P1 notes that this p

known for older fac

D. Cabinet bus bar configuration H H N/A
A-9

Table A-15 State of Knowledge Ranking for Scenario 1, External Cabinet Enclosure Configuration Effec

Phenomenon Description

State of Knowledge Ranking

Additional 

Model 

Adequacy

Data 

Availability

Ability to 

Collect 

New Data

9. External Cabinet Enclosure

Configuration Effects

A. Cabinet ventilation H H N/A

B. Cabinet structural design H H N/A

C. Cabinet penetrations H H N/A

Table A-16 State of Knowledge Ranking for Scenario 1, Arc Characterization 

Phenomenon Description

State of Knowledge Ranking

Additional 

Model 

Adequacy

Data 

Availability

Ability to 

Collect 

New Data

10. Arc Characterization

A. Arc electrical characterization L-M L/H L-M Panelists note tha

arc are easy to pre

and duration, are 

B. Arc migration M L-M U 

C. Arc breeching of enclosure L L L 

D. Thermal effects of the arc M-H M H 

E. Magnetic effects of the arc L-M L-M M-H

F. Electromagnetic interference L-M L-M M-H

G. Arc ejecta L L L 
A-1

0

Table A-17 State of Knowledge Ranking for Scenario 1, Fire Detection 

Phenomenon Description

State of Knowledge Ranking

Additional 

Model 

Adequacy

Data 

Availability

Ability to 

Collect 

New Data

11. Fire Detection

A. Presence of fire detection H H N/A

B. Characterizing fire detection system H H N/A

Table A-18 State of Knowledge Ranking for Scenario 1, Fire Suppression 

Phenomenon Description

State of Knowledge Ranking

Additional 

Model 

Adequacy

Data 

Availability

Ability to 

Collect 

New Data

12. Fire Suppression

A. Presence of fire suppression H H N/A

B. Fire suppression effects H H N/A

Table A-19 State of Knowledge Ranking for Scenario 1, Pressure Effects 

Phenomenon Description

State of Knowledge Ranking

Additional 

Model 

Adequacy

Data 

Availability

Ability to 

Collect 

New Data

13. Pressure Effects

A. Projectile/missile damage M L-M L 

B. Pressure wave H H N/A
A-11

Table A-20 State of Knowledge Ranking for Scenario 1, Internal Ensuing Fire 

Phenomenon Description

State of Knowledge Ranking

Additional 

Model 

Adequacy

Data 

Availability

Ability to 

Collect 

New Data

14. Internal Ensuing Fire

A. Fire ignition L L L 

B. Characterization of the fire source H M M-H

C. Fire development M M M 

D. Smoke generation M L-M M-H

E. Altered ventilation effects M M L-M

Table A-21 State of Knowledge Ranking for Scenario 1, External Ensuing Fire 

Phenomenon Description

State of Knowledge Ranking

Additional 

Model 

Adequacy

Data 

Availability

Ability to 

Collect 

New Data

15. External Ensuing Fire

A. Fire ignition L/H L/H M Panelists note that 

spreading to an ex

are poor for HEAF-

B. Characterization of the fire source H H N/A

C. Fire development M M H 

D. Smoke generation M M H 
A-1

2

Table A-22 State of Knowledge Ranking for Scenario 1, Room Configuration Effects 

Phenomenon Description

State of Knowledge Ranking

Additiona

Model 

Adequacy

Data 

Availability

Ability to 

Collect 

New Data

16. Room Configuration Effects

A. Room integrity M M M-H

B. Room arrangement H H N/A

C. Room ventilation H H N/A

Table A-23 State of Knowledge Ranking for Scenario 1, Arc Mitigation 

Phenomenon Description

State of Knowledge Ranking

Additiona

Model 

Adequacy

Data 

Availability

Ability to 

Collect 

New Data

17. Arc Mitigation

A. Intentional shielding L L-M H 

B. Electrical raceway fire barrier system L/H L/H H Panelists note tha

known for fire sce

scenarios.

C. Fire-retardant coating L/H L/H H Panelists note tha

retardant coatings 

but not for HEAF.
A-1

3

Table A-24 State of Knowledge Ranking for Scenario 1, Generic Cable Tray (Target) Characterization 

Phenomenon Description

State of Knowledge Ranking

Additional 

Model 

Adequacy

Data 

Availability

Ability to 

Collect 

New Data

18. Generic Cable Tray (Target)

Characterization

A. Characterizing target damage criteria M M H 

B. Target arrangement effects M M H 

C. Target sensitivity to damage L-M L-M M 
A-1

4

A.5 Phenomena Key Parameters Ranking

Table A-25 Key Parameters Ranking for Scenario 1, Electrical Configuration Effects 

Parameters Importance Ranking State of 

Knowledge Addition

P1 P2 P3 P4 P5 P6

1A. Power Supply Characterization

1. Line Voltage H H H H H H H 

2. Rated Current H H M H M M H 

3. Short Circuit Current H H H H H M H 

4. Frequency L H L L L L H 

5. Grounded/Ungrounded M H M L L L H 

6. Number of Phases U U L L L U H 

7. MVA Available H H H H H H H 
A-1

5

Table A-26 Key Parameters Ranking for Scenario 1, Internal Cabinet Configuration Effects 

Parameters Importance Ranking State of 

Knowledge

P1 P2 P3 P4 P5 P6

2A. Cabinet Compartmentation

1. Volume M H H M H L H 

2. Internal Barriers M M M M M M M-H

2B. Breaker Configuration

3. Arc Extinguishing Mechanism L/M L L L L L H 

4. Total Breaker Combustible Load L/M H M H H H H 

5. Extinguishing Medium L/M L M L M L H 

6. Breaker Connection Material L/M M M H H H H 

2C. Cabinet Combustible Loading

7. Mass H H M H H M M 

8. Bundle Tightness M U L M M H M 

9. Thermoset/Thermoplastic H H M H M H H 

10. Cables Jacketed/Unjacketed M H H H M H H 

11. Combustion Properties H H M H H H M 

2D. Cabinet Bus Bar Configuration

12. Bus Bar Spacing L H M H H H H 

13. Bus Bar Material H H H H H H H 

14. Number of Bus Bars per Phase M M L M M M H 

15. Bus Bar Insulation L H L M M M H 

16. Bus Bar Orientation L M M M M L H 

17. Bus Bar Cross-Sectional Area L M L M L L H 

18. Bus Bar Mounting/Supports L L M L L M H 
A-1

6

Table A-27 Key Parameters Ranking for Scenario 1, External Cabinet Enclosure Configuration Effects 

Parameters Importance Ranking State of 

Knowledge Addition

P1 P2 P3 P4 P5 P6

3A. Cabinet Ventilation

1. Active/Passive Ventilation L U M H H L H 

2. Ventilation Opening Area H H H H H M H 

3. Ventilation Deflection L U M M M L M-H

4. Ventilation Opening Location L H H M H M H 

5. Presence of Active Louvres L U L U U L H 

3B. Cabinet Structural Design

6. Wall Material M M M H L L H 

7. Wall Thickness M M L H M M H 

8. Door Latch Type X M M M M M H 

9. Door Gasketing X M L M M L H 

10. Wall Fastening (Welded, bolted,

riveted)

M M L M M M H 

11. Single/Double Wall X U L M M L H 

3C. Cabinet Penetrations

12. Location of Penetrations L H H H M M H 

13. Penetration Sealing H M H H M H H 

14. Penetration Type (Compression,

conduit, raceway)

L M M M M M H 

15. Viewing Ports/Mechanical Openings U U M H M M H 
A-1

7

Table A-28 Key Parameters Ranking for Scenario 1, Arc Characterization 

Parameters Importance Ranking State of 

Knowledge Additi

P1 P2 P3 P4 P5 P6

4A. Arc Electrical Characterization

1. Arc Voltage H H H H H H L-M

2. Arc Current (Asymmetric) L M H H L H H 

3. Arc Current (RMS) H U H H H M H 

4. Arc Energy H H H H H H M 

5. Arc Duration H H H H H H M 

6. Arc Location H H H M H H L 

4B. Arc Migration

7. Arc Migration Speed H M H H H L H 

8. Type (Ionized Gas/Magnetic Field) U H M H H L L 

4D. Thermal Effects of the Arc

9. Arc Heat Flux H H H H M H M 

10. Bus Bar Melting H M M H M M M(H) P5 note

validate

melting

ranked 

high pe

model.

11. Oxidation of Adjacent Materials H H H H M H L 

4G. Arc Ejecta

12. Ionized Gas L H H H H H L 

13. Smoke L L L L M L L 

14. Conductive Particulate H U M H M H L 
A-1

8

Table A-29 Key Parameters Ranking for Scenario 1, Fire Detection 

Parameters Importance Ranking State of 

Knowledge Addition

P1 P2 P3 P4 P5 P6

5A. Presence of Fire Detection

1. Detector Location H H H M H H H 

5B. Detection Characteristics

2. Detector Type (Heat/smoke/optical) H L M M M L H 

Table A-30 Key Parameters Ranking for Scenario 1, Fire Suppression 

Parameters Importance Ranking State of 

Knowledge Addition

P1 P2 P3 P4 P5 P6

6A. Presence of Fire Suppression

1. Internal/External to Cabinet H H H M M H H 

2. Proximity H H H M M L H 

6B. Characterizing the Suppression 

System

3. Actuation (Manual/Automatic) M U H M M M H 

4. Survivability H H H M X X L 

5. Suppression Type M L H L M M H 

Table A-31 Key Parameters Ranking for Scenario 1, Pressure Effects 

Parameters Importance Ranking State of 

Knowledge Addition

P1 P2 P3 P4 P5 P6

7B. Pressure Wave

1. Magnitude H H M H H H M-H

2. Propagation H M M H H H M 
A-1

9

Table A-32 Key Parameters Ranking for Scenario 1, Internal Ensuing Fire 

Parameters Importance Ranking State of 

Knowledge Addition

P1 P2 P3 P4 P5 P6

8A. Fire Ignition

1. Internal Cabinet Temperature M H H H H H L 

8B. Characterization of Fire Source

2. Heat Release Rate H H H H H H M-H

3. Heat Release Rate per unit Area M L H M H L M 

8C. Fire Development

4. Time to Peak M U H M H M M-H

5. Fire Growth Rate M H H H H H M-H

8E. Altered Ventilation Effects

6. Altered Internal Vent Properties M H H H H M M 

7. Altered Enclosure Vent Properties M H H H H H M 

Table A-33 Key Parameters Ranking for Scenario 1, External Ensuing Fire 

Parameters Importance Ranking State of 

Knowledge Addition

P1 P2 P3 P4 P5 P6

9B. Characterization of Fire Source

1. Heat Release Rate H H H H H H H 

2. Heat Release Rate per unit Area M L H M H L H 

3. Fire Geometry L M M H H H H 

9C. Fire Development

4. Time to Peak H L H M H M H 

5. Fire Growth Rate H H H H H H H 
A-2

0

Table A-34 Key Parameters Ranking for Scenario 1, Room Configuration Effects 

Parameters Importance Ranking State of 

Knowledge Addition

P1 P2 P3 P4 P5 P6

10A. Room Integrity

1. Fire Dampers M U M H H X L 

2. Penetrations M U M H H X L 

10B. Room Arrangement

3. Dimensions M U M H H H H 

4. Contents M U L H H L H 

5. Construction Material M U L M M L H 

6. Location of Source within Room L L H M M H H 

10C. Room Ventilation

7. Type (Active/Passive) H M L H H M H 

Table A-35 Key Parameters Ranking for Scenario 1, Arc Mitigation 

Parameters Importance Ranking State of 

Knowledge Addition

P1 P2 P3 P4 P5 P6

11A. Intentional Shielding

1. Thickness H M M H H H H 

2. Material H H H H H H H 

11B. Electrical Raceway Fire Barrier 

System

3. Rating M H M U H M H 

11C. Fire-Retardant Coating Effects

4. Thickness H U H H H H M 

5. Material M M H H H H H 

6. Age L U M U H H H 
A-21

Table A-36 Key Parameters Ranking for Scenario 1, Generic Cable Tray (Target) Characterization 

Parameters Importance Ranking State of 

Knowledge Additio

P1 P2 P3 P4 P5 P6

12A. Target Damage

1. Damage Criteria L H H H H H L/H Panelists 

criteria, c

critical te

fire scena

scenarios

2. Critical Heat Flux H H H H H H L/H

3. Critical Temperature H H H H H H L/H

4. Exposure Time H H H H H H M 

12B. Target Arrangement Effects

5. Distance to HEAF Source H H H H H H H 

6. Orientation Relative to HEAF

Source

H H H H H H H 

12C. Target Sensitivity

7. Sensitivity to Shock L U M M M L M 

8. Sensitivity to Heat H M H H H H H 

9. Sensitivity to EMI/RFI L L M L U L M 

10. Sensitivity to Light L L L L L L M 

11. Sensitivity to Ionized Gas L M M L H M M 

12. Sensitivity to Conductive Particulate L L M L L L M 

13. Sensitivity to Smoke L L L L L L M 
A-2

2

A.6 Scenario 1 Phenomena Calculated Rank Values and Grouping

Phenomenon Importance State of Knowledge Rank 

Arc Mitigation (11) 4.2 2.4 1.75 

Internal Ensuing Fire (8) 4.4 2.7 1.63 

Target Characterization (12) 4.9 3.2 1.53 

Arc Characterization (4) 3.6 2.7 1.33 

External Ensuing Fire (9) 4.3 3.4 1.27 

Pressure Effects (7) 3.5 3.2 1.09 

Electrical Configuration Effects (1) 5 5 1.00 

Internal Cabinet Configuration Effects (2) 3.8 4.2 0.91 

External Cabinet Enclosure Effects (3) 4 5 0.80 

Suppression Effects (6) 4 5 0.80 

Room Configuration (10) 3.4 4.3 0.79 

Fire Detection (5) 2.5 5 0.50 

33rd percentile for Rank: 0.87

66th percentile for Rank: 1.28
B-1

APPENDIX B PIRT HEAF SCENARIO 2

B.1 HEAF Scenario 2

B.1.1 Scenario Description

A high energy arcing fault occurs in a non-segregated bus duct supplying power to “Train B” 

systems. A switchgear supplying power to redundant “Train A” systems is located nearby.

B.1.2 Figure of Merit

Determining the extent of damage to the switchgear.

B.2 List of Identified Phenomena

Phenomenon 1: Electrical Configuration Effects

A. Power supply characterization

B. Electrical protection coordination10

Phenomenon 2: Internal Bus Duct Configuration Effects

A. Duct compartmentation

B. Duct combustible loading

10 Electrical protection coordination refers to the coordination and configuration of upstream breakers with the 

objective of minimizing the duration of an electrical fault
B-2

C. Duct bus bar configuration

Phenomenon 3: External Bus Duct Housing Configuration Effects

A. Duct ventilation

B. Duct structural design

C. Duct mounting

Phenomenon 4: Arc Characterization

A. Arc electrical characterization

B. Arc migration

C. Arc breeching of enclosure

D. Thermal effects of the arc

E. Magnetic effects of the arc11

F. Electromagnetic Interference

G. Arc ejecta

Phenomenon 5: Fire Detection12

A. Presence of fire detection

B. Characterizing the detection system

Phenomenon 6: Fire Suppression

A. Presence of fire suppression

B. Characterizing the suppression system

Phenomenon 7: Pressure Effects

A. Projectile/missile damage

B. Pressure wave

Phenomenon 8: Internal Ensuring Fire13

A. Fire ignition

B. Characterization of the fire source

C. Fire development

11 Magnetic effects refers to the applied forces on ferrous materials by a magnetic field that can induce bending 

and deformation, as opposed to the interference that it may cause. Interference is addressed separately.

12 Fire detection was assumed not to automatically trigger fire suppression. Fire suppression is considered as a 

separate phenomenon.

13 Internal ensuing fire refers to a sustained fire that occurs inside the source cabinet.
B-3

D. Smoke generation

E. Altered ventilation effects14

Phenomenon 9: External Ensuing Fire

A. Fire ignition from molten metal

B. Fire ignition from arc heat

C. Characterization of the fire source

D. Fire development

E. Smoke generation

Phenomenon 10: Room Configuration Effects

A. Room integrity15

B. Room arrangement

C. Room ventilation

Phenomenon 11: Arc Mitigation

A. Intentional shielding

B. Electrical raceway fire barrier system effects16

C. Fire-retardant coating effects17

D. Cable tray design

Phenomenon 12: Generic Enclosure (Target) Characterization

A. Characterizing target damage criteria

B. Target arrangement effects

C. Target sensitivity to damage

14 Altered ventilation effects refers to the manner in which changes to the cabinet’s structure and integrity as a 

result of the HEAF impact the ventilation paths for an internal ensuing fire. 15 Room integrity refers to the pressure boundary of the room in which the HEAF occurs, and how its response to 

the increased pressure will impact target damage. For example, consider whether blowing open a fire door or 

damper will affect target damage.

16 Electrical raceway fire barrier systems refers to a wrap or enclosure that is installed around electrical cable trays 

with the intent of mitigating fire damage.

17 Fire-retardant coating refers to a permanently installed coating or spray that is applied directly to the cables in a 

cable tray.
B-4

Table B-1 Importance Ranking for Scenario 2, Electrical Configuration Effects 

Phenomenon Description Importance Ranking Additional No

P1 P2 P3 P4 P5 P6

1. Electrical Configuration Effects

A. Power supply characterization H H H H H H 

B. Electrical protection coordination H H H H H H 

Table B-2 Importance Ranking for Scenario 2, Internal Bus Duct Configuration Effects 

Phenomenon Description Importance Ranking Additional No

P1 P2 P3 P4 P5 P6

2. Internal Bus Duct Configuration

Effects

A. Duct compartmentation M M M H M M 

B. Duct combustible loading L L L L H L 

C. Duct bus bar configuration M M M M M L 

Table B-3 Importance Ranking for Scenario 2, External Bus Duct Housing Configuration Effects 

Phenomenon Description Importance Ranking Additional No

P1 P2 P3 P4 P5 P6

3. External Bus Duct Housing

Configuration Effects

A. Duct ventilation L L L L L L 

B. Duct structural design H H H H H H 

C. Duct mounting H L L L L L 

B.3 Phenomena Importance Rankings
B-5

Table B-4 Importance Ranking for Scenario 2, Arc Characterization 

Phenomenon Description Importance Ranking Additional No

P1 P2 P3 P4 P5 P6

4. Arc Characterization

A. Arc electrical characterization H H H H H H P5 notes that arc vol

that of the switchgea

move along the duct

B. Arc migration H L L M M L 

C. Arc breeching of enclosure H H H H H H Panelists note that H

always breech the ho

important phenomen

that a HEAF may no

such if breeching did 

D. Thermal effects of the arc H H H H H H 

E. Magnetic effects of the arc L L L L L L 

F. Electromagnetic interference L L L L L L 

G. Arc ejecta M-H M-H M-H M-H M-H M-H

Table B-5 Importance Ranking for Scenario 2, Fire Detection 

Phenomenon Description Importance Ranking Additional No

P1 P2 P3 P4 P5 P6

5. Fire Detection

A. Presence of fire detection H M M L L M 

B. Characterizing fire detection system M L L L L L 
B-6

Table B-6 Importance Ranking for Scenario 2, Fire Suppression 

Phenomenon Description Importance Ranking Additional No

P1 P2 P3 P4 P5 P6

6. Fire Suppression

A. Presence of fire suppression H L L L L L 

B. Fire suppression effects H L L L L L 

Table B-7 Importance Ranking for Scenario 2, Pressure Effects 

Phenomenon Description Importance Ranking Additional No

P1 P2 P3 P4 P5 P6

7. Pressure Effects

A. Projectile/missile damage H L L L L L 

B. Pressure wave L L L M M M 
B-7

Table B-8 Importance Ranking for Scenario 2, Internal Ensuing Fire 

Phenomenon Description Importance Ranking Additional No

P1 P2 P3 P4 P5 P6

8. Internal Ensuing Fire

F. Fire ignition L L L L L L 

G. Characterization of the fire source L-H L L L L L P1 notes that the imp

the fire source depen

aluminum present.

H. Fire development L L L L L L 

I. Smoke generation L L L L L L P5 raised the possibi

like a chimney and ex

different location.

P6 states that in all kn

breeches, exhausted 

the arc origin.

J. Altered ventilation effects L L L L L L 

Table B-9 Importance Ranking for Scenario 2, External Ensuing Fire 

Phenomenon Description Importance Ranking Additional No

P1 P2 P3 P4 P5 P6

9. External Ensuing Fire

A. Fire ignition from molten metal M-H L L L L L Panelists note that se

molten metal has not 

testing. Transient com

likely to ignite than fix

considered on a situa

B. Fire ignition from arc heat H M M M M H 

C. Characterization of the fire source H H H H H H 

D. Fire development H H H H H H 

E. Smoke generation L L L L L L 
B-8

Table B-10 Importance Ranking for Scenario 2, Room Configuration Effects 

Phenomenon Description Importance Ranking Additional N

P1 P2 P3 P4 P5 P6

10. Room Configuration Effects

A. Room integrity L L L L L M P5 notes that a HEA

the point where it pe

bypass room integri

B. Room arrangement M M M L L M 

C. Room ventilation L H L L L M 

Table B-11 Importance Ranking for Scenario 2, Arc Mitigation 

Phenomenon Description Importance Ranking Additional N

P1 P2 P3 P4 P5 P6

11. Arc Mitigation

A. Intentional shielding H H H H H H 

B. Electrical raceway fire barrier system H H H H H H 

C. Fire-retardant coating M M H H H H 

D. Cable tray design M M M M M M 

Table B-12 Importance Ranking for Scenario 2, Generic Enclosure (Target) Characterization 

Phenomenon Description Importance Ranking Additional N

P1 P2 P3 P4 P5 P6

12. Generic Enclosure (Target)

Characterization

A. Characterizing target damage criteria H H H H H H 

B. Target arrangement effects H H H H H H 

C. Target sensitivity to damage H H H H H H 
B-9

B.4 Phenomena State of Knowledge Rankings

Table B-13 State of Knowledge Ranking for Scenario 2, Electrical Configuration Effects 

Phenomenon Description

State of Knowledge Ranking

Additional 

Model 

Adequacy

Data 

Availability

Ability to 

Collect 

New Data

1. Electrical Configuration Effects

A. Power supply characterization H H N/A

B. Electrical protection coordination H H N/A

Table B-14 State of Knowledge Ranking for Scenario 2, Internal Bus Duct Configuration Effects 

Phenomenon Description

State of Knowledge Ranking

Additional 

Model 

Adequacy

Data 

Availability

Ability to 

Collect 

New Data

2. Internal Bus Duct Configuration

Effects

A. Duct compartmentation M M M-H

B. Duct combustible loading H H N/A

C. Duct bus bar configuration M M M 
B-1

0

Table B-15 State of Knowledge Ranking for Scenario 2, External Bus Duct Housing Configuration Effects 

Phenomenon Description

State of Knowledge Ranking

Additional N

Model 

Adequacy

Data 

Availability

Ability to 

Collect 

New Data

3. External Bus Duct Housing

Configuration Effects

A. Duct ventilation L H N/A P6 notes that any m

likely useless, as the 

by the arc in all know

B. Duct structural design M M H 

C. Duct mounting L L L 

Table B-16 State of Knowledge Ranking for Scenario 2, Arc Characterization 

Phenomenon Description

State of Knowledge Ranking

Additional N

Model 

Adequacy

Data 

Availability

Ability to 

Collect 

New Data

4. Arc Characterization

A. Arc electrical characterization M-H H N/A

B. Arc migration M-H M-H N/A

C. Arc breeching of enclosure L L-M L-M Panelists note that t

observational. No qu

D. Thermal effects of the arc M M M 

E. Magnetic effects of the arc M-H M-H N/A

F. Electromagnetic interference L L M-H

G. Arc ejecta L L L Panelists note again 

observational data is 

extremely difficult to 

its constituents.
B-11

Table B-17 State of Knowledge Ranking for Scenario 2, Fire Detection 

Phenomenon Description

State of Knowledge Ranking

Additional 

Model 

Adequacy

Data 

Availability

Ability to 

Collect 

New Data

5. Fire Detection

A. Presence of fire detection H H N/A P2 notes that mod

but there is no spe

conditions—the de

B. Characterizing fire detection system H H N/A

Table B-18 State of Knowledge Ranking for Scenario 2, Fire Suppression 

Phenomenon Description

State of Knowledge Ranking

Additional 

Model 

Adequacy

Data 

Availability

Ability to 

Collect 

New Data

6. Fire Suppression

A. Presence of fire suppression H H N/A

B. Fire suppression effects M M H 

Table B-19 State of Knowledge Ranking for Scenario 2, Pressure Effects 

Phenomenon Description

State of Knowledge Ranking

Additional 

Model 

Adequacy

Data 

Availability

Ability to 

Collect 

New Data

7. Pressure Effects

A. Projectile/missile damage M-H M-H N/A P5 notes that pred

very difficult if the i

known. Identifying 

B. Pressure wave H H N/A
B-1

2

Table B-20 State of Knowledge Ranking for Scenario 2, Internal Ensuing Fire 

Phenomenon Description

State of Knowledge Ranking

Additional 

Model 

Adequacy

Data 

Availability

Ability to 

Collect 

New Data

8. Internal Ensuing Fire

A. Fire ignition M L M 

B. Characterization of the fire source H M-H N/A

C. Fire development M-H M M-H P6 notes that obse

fire development in 

D. Smoke generation M-H M-H N/A

E. Altered ventilation effects M-H M-H N/A

Table B-21 State of Knowledge Ranking for Scenario 2, External Ensuing Fire 

Phenomenon Description

State of Knowledge Ranking

Additional 

Model 

Adequacy

Data 

Availability

Ability to 

Collect 

New Data

9. External Ensuing Fire

A. Fire ignition from molten metal M M H 

B. Fire ignition from arc heat M L-M H P1 notes that expo

modeling less than 

C. Characterization of the fire source M M-H H P1 notes that cabin

sources—characte

D. Fire development M M-H H 

E. Smoke generation H H N/A
B-1

3

Table B-22 State of Knowledge Ranking for Scenario 2, Room Configuration Effects 

Phenomenon Description

State of Knowledge Ranking

Additional 

Model 

Adequacy

Data 

Availability

Ability to 

Collect 

New Data

10. Room Configuration Effects

A. Room integrity M M H P1 and P6 note tha

for room integrity, b

applicable to HEAF

B. Room arrangement H H N/A

C. Room ventilation H H N/A

Table B-23 State of Knowledge Ranking for Scenario 2, Arc Mitigation 

Phenomenon Description

State of Knowledge Ranking

Additional 

Model 

Adequacy

Data 

Availability

Ability to 

Collect 

New Data

11. Arc Mitigation

A. Intentional shielding M M M-H Panelists note that 

experiments exist, 

can possible be ap

applicable model cu

B. Electrical raceway fire barrier system M M H 

C. Fire-retardant coating M M H P4 notes that the o

should be consider

applied as a remed

important.

D. Cable tray design M M H 
B-1

4

Table B-24 State of Knowledge Ranking for Scenario 2, Generic Enclosure (Target) Characterization 

Phenomenon Description

State of Knowledge Ranking

Additional N

Model 

Adequacy

Data 

Availability

Ability to 

Collect 

New Data

12. Generic Cable Tray (Target)

Characterization

A. Characterizing target damage criteria M M H 

B. Target arrangement effects M M H 

C. Target sensitivity to damage L-M L-M M Panelists noted mo

the effects of target 

but others are negle
B-1

5

B.5 Phenomena Key Parameters Ranking

Table B-25 Key Parameters Ranking for Scenario 2, Electrical Configuration Effects 

Parameters Importance Ranking State of 

Knowledge Additiona

P1 P2 P3 P4 P5 P6

1A. Power Supply Characterization

1. Line Voltage H H H H H H H 

2. Rated Current H H H H M H H 

3. Short Circuit Current H H H H H H H 

4. Frequency L L L L L L H 

5. Grounded/Ungrounded M L L L L L H 

6. MVA Available H H H H H H H 
B-1

6

Table B-26 Key Parameters Ranking for Scenario 2, Internal Bus Duct Configuration Effects 

Parameters Importance Ranking State of 

Knowledge

A

P1 P2 P3 P4 P5 P6

2A. Duct Compartmentation

1. Dimensions M M M M M M H P6 not

of the d

importa

be bre

2. Internal Partitions H H H H H H H 

2B. Duct Combustible Loading

3. Combustible Mass H H H H H M H 

4. Combustion Properties H H H H H M H 

2C. Duct Bus Bar Configuration

5. Bus Bar Spacing H H H H H H H 

6. Bus Bar Material H H H H H H H 

7. Bus Bar Insulation M M M M M M L 

8. Bus Bar Orientation M M M M M M H 

9. Bus Bar Cross-Sectional Area M LM M M M M H P2 not

area is 

supply

importa

bus ba

10. Bus Bar Joints H H H H H H H Panelis

becaus

arc loc

11. Bus Bar Mounting/Supports L L L L L L H 
B-1

7

Table B-27 Key Parameters Ranking for Scenario 2, External Bus Duct Housing Configuration Effects 

Parameters Importance Ranking State of 

Knowledge Addition

P1 P2 P3 P4 P5 P6

3A. Duct Ventilation

1. Ventilation Opening Area H H H H H H H 

2. Ventilation Opening Location M M M M M M H 

3B. Duct Structural Design

3. Wall Material H H H H H H H 

4. Wall Thickness H H H H H H H 

5. Access Ports M M M M M M H 

3C. Duct Mounting

6. Robustness H L L M L L L 

7. Orientation H H H M H H H 
B-1

8

Table B-28 Key Parameters Ranking for Scenario 2, Arc Characterization 

Parameters Importance Ranking State of 

Knowledge Additio

P1 P2 P3 P4 P5 P6

4A. Arc Electrical Characterization

1. Arc Voltage H H H H H H M 

2. Arc Current (Asymmetric) L H H H L H H 

3. Arc Current (RMS) H H H H H H H 

4. Arc Energy H H H H H H M-H

5. Arc Duration H H H H H H M 

6. Arc Location M L L L L L L 

4B. Arc Migration

7. Arc Migration Speed H H H H H H M-H

8. Type (Ionized Gas/Magnetic Field) U H H H H H L-M

4D. Thermal Effects of the Arc

9. Arc Heat Flux H H H H H H M 

10. Bus Bar Melting H H H H H H M 

11. Oxidation of Adjacent Materials H H H H H H L 

4G. Arc Ejecta

12. Ionized Gas L H H H H H L 

13. Smoke L L L L L L L 

14. Conductive Particulate H H H H H H L 
B-1

9

Table B-29 Key Parameters Ranking for Scenario 2, Fire Detection 

Parameters Importance Ranking State of 

Knowledge Additio

P1 P2 P3 P4 P5 P6

5B. Detection Characteristics

1. Detector Type (Heat/smoke/optical) H H H H H H H

Table B-30 Key Parameters Ranking for Scenario 2, Fire Suppression 

Parameters Importance Ranking State of 

Knowledge Additio

P1 P2 P3 P4 P5 P6

6A. Presence of Fire Suppression

1. Proximity H H H H H H H 

6B. Characterizing the Suppression 

System

2. Actuation (Manual/Automatic) H M M M M M H 

3. Survivability M H H H H H L 

4. Suppression Type M H H H H H M-H

Table B-31 Key Parameters Ranking for Scenario 2, Pressure Effects 

Parameters Importance Ranking State of 

Knowledge Additio

P1 P2 P3 P4 P5 P6

7B. Pressure Wave

1. Magnitude H H H H H H M-H

2. Propagation H H H H H H M 
B-2

0

Table B-32 Key Parameters Ranking for Scenario 2, Internal Ensuing Fire 

Parameters Importance Ranking State of 

Knowledge Addition

P1 P2 P3 P4 P5 P6

8A. Fire Ignition

1. Internal Duct Temperature H H H H H H L-M

8B. Characterization of Fire Source

2. Heat Release Rate H H H H H H M-H

3. Heat Release Rate per unit Area M M M M M L M 

8C. Fire Development

4. Time to Peak H H H H H H M-H

5. Fire Growth Rate H H H H H H M-H

8E. Altered Ventilation Effects

6. Altered Duct Vent Properties M H M M M M M 

Table B-33 Key Parameters Ranking for Scenario 2, External Ensuing Fire 

Parameters Importance Ranking State of 

Knowledge Addition

P1 P2 P3 P4 P5 P6

9B. Characterization of Fire Source

1. Heat Release Rate H H H H H H H 

2. Heat Release Rate per unit Area M M M M M M M-H

3. Fire Geometry L M M L H M M-H

9C. Fire Development

4. Time to Peak H H H H H H M-H

5. Fire Growth Rate H H H H H H M-H
B-21

Table B-34 Key Parameters Ranking for Scenario 2, Room Configuration Effects 

Parameters Importance Ranking State of 

Knowledge Addition

P1 P2 P3 P4 P5 P6

10A. Room Integrity

1. Fire Dampers M L L L L L L-M

2. Penetrations M L L L L L L-M

10B. Room Arrangement

3. Dimensions M M M M M M H 

4. Contents H M L M L L H 

5. Construction Material L M M M M M H 

6. Location of Source within Room L M L L L L M-H

10C. Room Ventilation

7. Type (Active/Passive) H H H H H H M-H

Table B-35 Key Parameters Ranking for Scenario 2, Arc Mitigation 

Parameters Importance Ranking State of 

Knowledge Addition

P1 P2 P3 P4 P5 P6

11A. Intentional Shielding

1. Thickness H H H H H H H 

2. Material H H H H H H H 

11B. Electrical Raceway Fire Barrier 

System

3. Rating U U U U U U H 

11C. Fire-Retardant Coating Effects

4. Thickness H H H H H H M 

5. Material H H H H H H H 

6. Age L U U U U L M-H
B-2

2

Table B-36 Key Parameters Ranking for Scenario 2, Generic Enclosure (Target) Characterization 

Parameters Importance Ranking State of 

Knowledge

P1 P2 P3 P4 P5 P6

12A. Target Damage

1. Damage Criteria H H H H H H M 

2. Critical Heat Flux H H H H H H M 

3. Critical Temperature H H H H H H M 

4. Exposure Time H H H H H H M 

12B. Target Arrangement Effects

5. Distance to HEAF Source H H H H H H M-H

6. Orientation Relative to HEAF

Source

H H H M H M M-H

12C. Target Sensitivity

7. Sensitivity to Shock M M/H M H M-H M M 

8. Sensitivity to Heat H H H H H H M-H

9. Sensitivity to EMI/RFI M M M M U M L-M

10. Sensitivity to Light L L L L L L L-M

11. Sensitivity to Ionized Gas L L/H L/H L L/H L/M M Th

ind

de

tar

ca

its

12. Sensitivity to Conductive Particulate L/M L/H L/H L L/H L/M M Th

ind

de

tar

ca

its

13. Sensitivity to Smoke H L L L L L L-M
B-2

3

B.6 Scenario 2 Phenomena Calculated Rank Values and Grouping

Table B-37 Summary of Scenario 2 Average Rankings and Grouping 

Phenomenon Importance State of Knowledge Rank 

Target Characterization (12) 5 3.1 1.61 

Arc Characterization (4) 3.3 2.6 1.27 

Arc Mitigation (11) 4.3 3.6 1.19 

External Duct Housing Configuration Effects (3) 2.6 2.5 1.04 

Electrical Configuration Effects (1) 5 5 1.00 

External Ensuing Fire (9) 3.2 3.9 0.82 

Internal Bus Duct Configuration Effects (2) 2.6 3.6 0.72 

Room Configuration (10) 1.9 4.4 0.43 

Suppression Effects (6) 1.7 4.2 0.40 

Fire Detection (5) 2 5 0.40 

Pressure Effects (7) 1.8 4.5 0.40 

Internal Ensuing Fire (8) 1.1 3.6 0.31 

33rd percentile for Rank: 0.42

66th percentile for Rank: 1.01

C-1

APPENDIX C PIRT HEAF SCENARIO 3

C.1 HEAF Scenario 3

C.1.1 Scenario Description

A high energy arcing fault occurs in a low/medium voltage switchgear supplying power to “Train A” 

systems in a bank of similar switchgears. The cables from an overhead cable tray enter the 

cabinets from the top (air-drop configuration). A cable tray carrying cables that supply power to 

“Train B” systems is located nearby.

C.1.2 Figure of Merit

Determining the extent of damage to the adjacent switchgears and the cables in “Train B” cable 

tray.

C.2 List of Identified Phenomena

Phenomenon 1: Electrical Configuration Effects

A. Power supply characterization

B. Electrical protection coordination18

Phenomenon 2: Internal Cabinet Configuration Effects

A. Cabinet compartmentation

B. Breaker configuration

18 Electrical protection coordination refers to the coordination and configuration of upstream breakers with the 

objective of minimizing the duration of an electrical fault
C-2

D. Cabinet bus bar configuration

Phenomenon 3: External Cabinet Enclosure Configuration Effects

A. Cabinet ventilation

B. Cabinet structural design

C. Cabinet penetrations

Phenomenon 4: Cabinet Lineup Effects

A. Cabinet-cabinet barrier effects

B. Cabinet position within bank effects19

C. Cabinet-cabinet penetration effects

Phenomenon 5: Arc Characterization

A. Arc electrical characterization

B. Arc migration

C. Arc breeching of enclosure

D. Thermal effects of the arc

E. Magnetic effects of the arc20

F. Electromagnetic interference

G. Arc ejecta

H. Plasma characterization

Phenomenon 6: Fire Detection21

A. Presence of fire detection

B. Characterizing the detection system

Phenomenon 7: Fire Suppression

A. Presence of fire suppression

B. Characterizing the suppression system

19 The effects of the cabinet position within the bank does not refer to the location of targets around the source 

cabinet. This refers to the manner in which the position (middle of the bank, end of the bank) affects the extent of 

damage to whatever targets are present.

20 Magnetic effects refers to the applied forces on ferrous materials by a magnetic field that can induce bending 

and deformation, as opposed to the interference that it may cause. Interference is addressed separately. 21 Fire detection was assumed not to automatically trigger fire suppression. Fire suppression is considered as a 

separate phenomenon.

C. Cabinet combustible loading
C-3

Phenomenon 8: Pressure Effects

A. Projectile/missile damage

B. Pressure wave

Phenomenon 9: Internal Ensuring Fire22

A. Fire ignition

B. Characterization of the fire source

C. Fire development

D. Smoke generation

E. Altered ventilation effects23

Phenomenon 10: External Ensuing Fire

A. Fire ignition

B. Characterization of the fire source

C. Fire development

D. Cabinet-to-cabinet propagation

E. Smoke generation

Phenomenon 11: Room Configuration Effects

A. Room integrity24

B. Room arrangement

C. Room ventilation

Phenomenon 12: Arc Mitigation

A. Intentional shielding

B. Electrical raceway fire barrier system effects25

C. Fire-retardant coating effects26

22 Internal ensuing fire refers to a sustained fire that occurs inside the source cabinet. 23 Altered ventilation effects refers to the manner in which changes to the cabinet’s structure and integrity as a 

result of the HEAF impact the ventilation paths for an internal ensuing fire.

24 Room integrity refers to the pressure boundary of the room in which the HEAF occurs, and how its response to 

the increased pressure will impact target damage. For example, consider whether blowing open a fire door or 

damper will affect target damage.

25 Electrical raceway fire barrier systems refers to a wrap or enclosure that is installed around electrical cable trays 

with the intent of mitigating fire damage.

26 Fire-retardant coating refers to a permanently installed coating or spray that is applied directly to the cables in a 

cable tray.
C-4

Phenomenon 13: Generic Enclosure (Target) Characterization

A. Characterizing target damage criteria

B. Target sensitivity to damage

Phenomenon 14: Generic Cable Tray (Target) Characterization

A. Characterizing target damage criteria

B. Target arrangement effects

C. Target sensitivity to damage
C-5

C.3 Phenomena Importance Rankings

Table C-1 Importance Ranking for Scenario 3, Electrical Configuration Effects 

Phenomenon Description Importance Ranking Additional Not

P1 P2 P3 P4 P5 P6

1. Electrical Configuration Effects

A. Power supply characterization H H H H H H 

B. Electrical protection coordination H H H H H H 

Table C-2 Importance Ranking for Scenario 3, Internal Cabinet Configuration Effects 

Phenomenon Description Importance Ranking Additional Not

P1 P2 P3 P4 P5 P6

2. Internal Cabinet Configuration

Effects

A. Cabinet compartmentation H M M M M M 

B. Breaker configuration M M M M M M 

C. Cabinet combustible loading H H H H H H 

D. Cabinet bus bar configuration M M M H M M 

Table C-3 Importance Ranking for Scenario 3, External Cabinet Enclosure Configuration Effects 

Phenomenon Description Importance Ranking Additional Not

P1 P2 P3 P4 P5 P6

3. External Cabinet Enclosure

Configuration Effects

A. Cabinet ventilation M M M M H M 

B. Cabinet structural design H M M M M L 

C. Cabinet penetrations H M M M M M 
C-6

Table C-4 Importance Ranking for Scenario 3, Cabinet Lineup Effects 

Phenomenon Description Importance Ranking Additional Note

P1 P2 P3 P4 P5 P6

4. Cabinet Lineup Effects

A. Cabinet-cabinet barrier effects H H H H H H 

B. Cabinet-position within bank effects H M M M M M 

C. Cabinet-cabinet penetration effects H H H H H H 

Table C-5 Importance Ranking for Scenario 3, Arc Characterization 

Phenomenon Description Importance Ranking Additional Note

P1 P2 P3 P4 P5 P6

5. Arc Characterization

A. Arc electrical characterization H H H H H H 

B. Arc migration H M M M M M P6 notes that the migra

scenario is more import

2.

C. Arc breeching of enclosure H H H H H H P5 notes that arc breec

lineup increases the pro

secondary arc in an adj

D. Thermal effects of the arc H H H H H H 

E. Magnetic effects of the arc L M M H U M 

F. Electromagnetic interference H L L H L L P4 notes that digital upg

equipment susceptibility 

G. Arc ejecta H H H H H H 

H. Plasma characterization M M M M M M P6 notes that the prope

is inherently tied to the c

arc, and as such, may n

considered separately.
C-7

Table C-6 Importance Ranking for Scenario 3, Fire Detection 

Phenomenon Description Importance Ranking Additional Note

P1 P2 P3 P4 P5 P6

6. Fire Detection

A. Presence of fire detection H L L L L L 

B. Characterizing fire detection system L L L L L L 

Table C-7 Importance Ranking for Scenario 3, Fire Suppression 

Phenomenon Description Importance Ranking Additional Note

P1 P2 P3 P4 P5 P6

7. Fire Suppression

A. Presence of fire suppression M M M M M M P6 notes that there is in 

spreading in a cabinet 

B. Fire suppression effects M M M M M M 

Table C-8 Importance Ranking for Scenario 3, Pressure Effects 

Phenomenon Description Importance Ranking Additional Note

P1 P2 P3 P4 P5 P6

8. Pressure Effects

A. Projectile/missile damage H H H H H H 

B. Pressure wave H H H H H H 
C-8

Table C-9 Importance Ranking for Scenario 3, Internal Ensuing Fire 

Phenomenon Description Importance Ranking Additional Not

P1 P2 P3 P4 P5 P6

9. Internal Ensuing Fire

A. Fire ignition H H H H H H 

B. Characterization of the fire source H H H H H H 

C. Fire development H H H H H H 

D. Smoke generation H L L L L L 

E. Altered ventilation effects H H H H H H 

Table C-10 Importance Ranking for Scenario 3, External Ensuing Fire 

Phenomenon Description Importance Ranking Additional Not

P1 P2 P3 P4 P5 P6

10. External Ensuing Fire

A. Fire ignition L-H H H H H H P1 notes that this depe

of target cabinets in the 

B. Characterization of the fire source H H H H H H 

C. Fire development H H H H H H 

D. Cabinet-cabinet propagation H H H H H H Panelists note that this 

outstanding risk in this 

phenomenon of the hig

E. Smoke generation L L L L L L 
C-9

Table C-11 Importance Ranking for Scenario 3, Room Configuration Effects 

Phenomenon Description Importance Ranking Additional Not

P1 P2 P3 P4 P5 P6

11. Room Configuration Effects

A. Room integrity M M L L M M P2 notes that this is mo

cable tray target.

B. Room arrangement M M M M M M 

C. Room ventilation L H M M M M 

Table C-12 Importance Ranking for Scenario 3, Arc Mitigation 

Phenomenon Description Importance Ranking Additional Not

P1 P2 P3 P4 P5 P6

12. Arc Mitigation

A. Intentional shielding H M H H H H 

B. Electrical raceway fire barrier system M M H H H M 

C. Fire-retardant coating L M M M M L 

Table C-13 Importance Ranking for Scenario 3, Generic Enclosure (Target) Characterization 

Phenomenon Description Importance Ranking Additional Not

P1 P2 P3 P4 P5 P6

13. Generic Enclosure (Target)

Characterization

A. Characterizing target damage criteria H H H H H H 

B. Target sensitivity to damage H H H H H H 
C-1

0

Table C-14 Importance Ranking for Scenario 3, Generic Cable Tray (Target) Characterization 

Phenomenon Description Importance Ranking Additional Not

P1 P2 P3 P4 P5 P6

14. Generic Cable Tray (Target)

Characterization

A. Characterizing target damage criteria H H H H H H 

B. Target arrangement effects M H H H H H 

C. Target sensitivity to damage H H H H H H 
C-11

C.4 Phenomena State of Knowledge Rankings

Table C-15: State of Knowledge Ranking for Scenario 3, Electrical Configuration 

Effects 

Phenomenon Description

State of Knowledge Ranking

Additional 

Model 

Adequacy

Data 

Availability

Ability to 

Collect 

New Data

1. Electrical Configuration Effects

A. Power supply characterization H H N/A

B. Electrical protection coordination H H N/A

Table C-16 State of Knowledge Ranking for Scenario 3, Internal Cabinet Configuration Effects 

Phenomenon Description

State of Knowledge Ranking

Additional 

Model 

Adequacy

Data 

Availability

Ability to 

Collect 

New Data

2. Internal Cabinet Configuration

Effects

A. Cabinet compartmentation H H N/A

B. Breaker configuration M-H M H 

C. Cabinet combustible loading M-H M M 

D. Cabinet bus bar configuration M-H M-H N/A
C-1

2

Table C-17 State of Knowledge Ranking for Scenario 3, External Cabinet Enclosure Configuration Effects 

Phenomenon Description

State of Knowledge Ranking

Additional N

Model 

Adequacy

Data 

Availability

Ability to 

Collect 

New Data

3. External Cabinet Enclosure

Configuration Effects

A. Cabinet ventilation M-H M-H N/A

B. Cabinet structural design M-H M-H N/A

C. Cabinet penetrations M-H H N/A

Table C-18 State of Knowledge Ranking for Scenario 3, Cabinet Lineup Effects 

Phenomenon Description

State of Knowledge Ranking

Additional N

Model 

Adequacy

Data 

Availability

Ability to 

Collect 

New Data

4. Cabinet Lineup Effects

A. Cabinet-cabinet barrier effects M M M-H

B. Cabinet-cabinet penetration effects M M M-H

C. Cabinet position within bank effects M M-H N/A
C-1

3

Table C-19 State of Knowledge Ranking for Scenario 3, Arc Characterization 

Phenomenon Description

State of Knowledge Ranking

Additional N

Model 

Adequacy

Data 

Availability

Ability to 

Collect 

New Data

5. Arc Characterization

A. Arc electrical characterization L-M M M 

B. Arc migration M L-M L-M

C. Arc breeching of enclosure L L L 

D. Thermal effects of the arc M M M-H

E. Magnetic effects of the arc L-M L-M M 

F. Electromagnetic interference L L L-M

G. Arc ejecta L L L 

H. Plasma characterization L-M L-M M 

Table C-20 State of Knowledge Ranking for Scenario 3, Fire Detection 

Phenomenon Description

State of Knowledge Ranking

Additional N

Model 

Adequacy

Data 

Availability

Ability to 

Collect 

New Data

6. Fire Detection

A. Presence of fire detection H H N/A

B. Characterizing fire detection system H H N/A
C-1

4

Table C-21 State of Knowledge Ranking for Scenario 3, Fire Suppression 

Phenomenon Description

State of Knowledge Ranking

Additional 

Model 

Adequacy

Data 

Availability

Ability to 

Collect 

New Data

7. Fire Suppression

A. Presence of fire suppression H H N/A

B. Fire suppression effects M-H M-H N/A

Table C-22 State of Knowledge Ranking for Scenario 3, Pressure Effects 

Phenomenon Description

State of Knowledge Ranking

Additional 

Model 

Adequacy

Data 

Availability

Ability to 

Collect 

New Data

8. Pressure Effects

A. Projectile/missile damage M L-M L-M

B. Pressure wave M-H M-H N/A
C-1

5

Table C-23 State of Knowledge Ranking for Scenario 3, Internal Ensuing Fire 

Phenomenon Description

State of Knowledge Ranking

Additional N

Model 

Adequacy

Data 

Availability

Ability to 

Collect 

New Data

9. Internal Ensuing Fire

A. Fire ignition L L L-M

B. Characterization of the fire source H M M 

C. Fire development M M M 

D. Smoke generation M L-M M-H

E. Altered ventilation effects M M M 

Table C-24 State of Knowledge Ranking for Scenario 3, External Ensuing Fire 

Phenomenon Description

State of Knowledge Ranking

Additional N

Model 

Adequacy

Data 

Availability

Ability to 

Collect 

New Data

10. External Ensuing Fire

A. Fire ignition L-M L-M M 

B. Characterization of the fire source M-H M-H H 

C. Fire development M M H 

D. Cabinet-to-cabinet propagation L-M L-M M 

E. Smoke generation M L-M M 
C-1

6

Table C-25 State of Knowledge Ranking for Scenario 3, Room Configuration Effects 

Phenomenon Description

State of Knowledge Ranking

Additional N

Model 

Adequacy

Data 

Availability

Ability to 

Collect 

New Data

11. Room Configuration Effects

A. Room integrity M M M-H

B. Room arrangement H H N/A

C. Room ventilation H H N/A

Table C-26 State of Knowledge Ranking for Scenario 3, Arc Mitigation 

Phenomenon Description

State of Knowledge Ranking

Additional N

Model 

Adequacy

Data 

Availability

Ability to 

Collect 

New Data

12. Arc Mitigation

A. Intentional shielding L L-M M-H

B. Electrical raceway fire barrier system L-M M H 

C. Fire-retardant coating L-M M H 
C-1

7

Table C-27 State of Knowledge Ranking for Scenario 3, Generic Enclosure (Target) Characterization 

Phenomenon Description

State of Knowledge Ranking

Additional N

Model 

Adequacy

Data 

Availability

Ability to 

Collect 

New Data

13. Generic Enclosure (Target)

Characterization

A. Characterizing target damage criteria M M H

B. Target arrangement effects M M H

C. Target sensitivity to damage L-M L-M M

Table C-28 State of Knowledge Ranking for Scenario 3, Generic Cable Tray (Target) Characterization 

Phenomenon Description

State of Knowledge Ranking

Additional N

Model 

Adequacy

Data 

Availability

Ability to 

Collect 

New Data

14. Generic Cable Tray (Target)

Characterization

A. Characterizing target damage criteria M M H 

B. Target arrangement effects M M H 

C. Target sensitivity to damage L-M L-M M 
C-1

8

C.5 Key Parameter Rankings

Table C-29 Key Parameters Ranking for Scenario 3, Electrical Configuration Effects 

Parameters Importance Ranking State of 

Knowledge Additiona

P1 P2 P3 P4 P5 P6

1A. Power Supply Characterization

1. Line Voltage H H H H H H H 

2. Rated Current H H H H M H H 

3. Short Circuit Current H H H H H H H 

4. Frequency L L L L L L H 

5. Grounded/Ungrounded U H M L L L H 

6. Number of Phases L L L L L L H 

7. MVA Available H H H H H L H 
C-1

9

Table C-30 Key Parameters Ranking for Scenario 3, Internal Cabinet Configuration Effects 

Parameters Importance Ranking State of 

Knowledge

A

P1 P2 P3 P4 P5 P6

2A. Cabinet Compartmentation

1. Dimensions H H H M H H H 

2. Internal Partitions H M M M M M M-H

2B. Breaker Configuration

3. Arc Extinguishing Mechanism L L L L L L H 

4. Breaker Combustible Load H H M H H H H 

5. Extinguishing Medium L L M L M L H 

6. Breaker Connection Material M M M H H H H 

2C. Cabinet Combustible Loading

7. Combustible Mass H H M H H H M 

8. Bundle Tightness H M M M M H M 

9. Thermoset/Thermoplastic H H M H M H M-H

10. Jacketed/Unjacketed H H H H M H M-H

11. Combustion Properties H H H H H H M 

2D. Cabinet Bus Bar Configuration

12. Bus Bar Spacing H H H H H H H 

13. Bus Bar Material H H H H H M H 

14. Number of Bus Bars per Phase M M L M M L M-H

15. Bus Bar Insulation M M M M M M M-H

16. Bus Bar Orientation L M M M M U H 

17. Bus Bar Cross-Sectional Area M M L M L L H 

18. Bus Bar Mounting/Supports L L M L L H H 
C-2

0

Table C-31 Key Parameters Ranking for Scenario 3, External Cabinet Enclosure Configuration Effects 

Parameters Importance Ranking State of 

Knowledge Additiona

P1 P2 P3 P4 P5 P6

3A. Cabinet Ventilation

1. Active/Passive Ventilation H H H H H H H 

2. Ventilation Opening Area H H H H H H H 

3. Ventilation Deflection L L M M M L M-H

4. Ventilation Opening Location L M H M H H M-H

5. Presence of Active Louvres U U U U U L H 

3B. Cabinet Structural Design

6. Wall Material M H H H L H H 

7. Wall Thickness H M M H M M H 

8. Door Latch Type M M M M M M H 

9. Door Gasketing M M M M M M H 

10. Wall Fastening (welded, bolted,

riveted)

L M L M M L H 

11. Single/Double Wall H M M M M M H 

3C. Cabinet Penetrations

12. Location of Penetrations H H M H M H H 

13. Penetration Sealing H M M H M M H 

14. Penetration Type (Compression,

conduit, raceway)

L L M M M L H 

15. Viewing Ports/Mechanical Openings H U M H M M H 
C-21

Table C-32 Key Parameters Ranking for Scenario 3, Cabinet Lineup Effects 

Parameters Importance Ranking State of 

Knowledge Addition

P1 P2 P3 P4 P5 P6

4A. Cabinet-Cabinet Barrier Effects

1. Walls (None/Single/Double) H H H H H H M-H

2. Air Gap MH MH MH U M-H M L-M

4B. Cabinet Position Within Bank Effects

3. Middle/End H H H H H H M-H

4C. Cabinet-Cabinet Penetration Effects

4. Bus Bar Penetrations H H H H H H M-H

5. Cable Penetrations H H H H H H M-H

6. False Floor H H H L H H M 
C-2

2

Table C-33 Key Parameters Ranking for Scenario 3, Arc Characterization 

Parameters Importance Ranking State of 

Knowledge Additiona

P1 P2 P3 P4 P5 P6

5A. Arc Electrical Characterization

1. Arc Voltage H H H H H H M 

2. Arc Current (Asymmetric) H H H H L H H 

3. Arc Current (RMS) H H H H H H H 

4. Arc Energy H H H H H H M 

5. Arc Duration H H H H H H M 

6. Arc Location H M M M H M L 

5B. Arc Migration

7. Arc Migration Speed U M M H M L M-H

8. Type (Ionized Gas/Magnetic Field) U H M H M M L 

5D. Thermal Effects of the Arc

9. Arc Heat Flux H H H H H H M 

10. Bus Bar Melting H H H H H H M-H

11. Oxidation of Adjacent Materials H H H H H H L 

5G. Arc Ejecta

12. Ionized Gas M H H H H H L 

13. Smoke M L M L M L L 

14. Conductive Particulate H H H H M H L 
C-2

3

Table C-34 Key Parameters Ranking for Scenario 3, Fire Detection 

Parameters Importance Ranking State of 

Knowledge Additiona

P1 P2 P3 P4 P5 P6

6A. Presence of Fire Detection

1. Detector Location H H H M H M H 

6B. Detection Characteristics

2. Detector Type (Heat/smoke/optical) M M M M M M H

Table C-35 Key Parameters Ranking for Scenario 3, Fire Suppression 

Parameters Importance Ranking State of 

Knowledge Additiona

P1 P2 P3 P4 P5 P6

7A. Presence of Fire Suppression

1. Internal/External M M M M M M M-H

2. Proximity H H H H H H M-H

7B. Characterizing the Suppression 

System

3. Actuation (Manual/Automatic) M M M M M M H 

4. Survivability X H M M X M L 

5. Suppression Type M H H H H H M-H
C-2

4

Table C-36 Key Parameters Ranking for Scenario 3, Pressure Effects 

Parameters Importance Ranking State of 

Knowledge Additiona

P1 P2 P3 P4 P5 P6

8B. Pressure Wave

1. Magnitude H H H H H H M-H

2. Propagation H H H H H M M 

Table C-37 Key Parameters Ranking for Scenario 3, Internal Ensuing Fire 

Parameters Importance Ranking State of 

Knowledge Additiona

P1 P2 P3 P4 P5 P6

9A. Fire Ignition

1. Internal Cabinet Temperature H H H H H H L 

9B. Characterization of Fire Source

2. Heat Release Rate H H H H H H M-H

3. Heat Release Rate per unit Area M L M M M M M 

9C. Fire Development

4. Time to Peak M M M M M M M-H

5. Fire Growth Rate H H H H H H M-H

9E. Altered Ventilation Effects

6. Altered Internal Vent Properties H H H H H H M 

7. Altered Enclosure Vent Properties H H H H H H M 
C-2

5

Table C-38 Key Parameters Ranking for Scenario 3, External Ensuing Fire 

Parameters Importance Ranking State of 

Knowledge Addition

P1 P2 P3 P4 P5 P6

10B. Characterization of Fire Source

1. Heat Release Rate H H H H H H M-H

2. Heat Release Rate per unit Area M L M M M M M-H

3. Fire Geometry H H H H H H H 

10C. Fire Development

4. Time to Peak M M M M M M H 

5. Fire Growth Rate H H H H H H H 

Table C-39 Key Parameters Ranking for Scenario 3, Room Configuration Effects 

Parameters Importance Ranking State of 

Knowledge Addition

P1 P2 P3 P4 P5 P6

11A. Room Integrity

1. Fire Dampers H H H H H H L-M

2. Penetrations H H H H H H L-M

11B. Room Arrangement

3. Dimensions H H H H H H H 

4. Contents M H H H H H H 

5. Construction Material M M M M M M H 

11C. Room Ventilation

6. Type (Active/Passive) H H H H H H H 
C-2

6

Table C-40 Key Parameters Ranking for Scenario 3, Arc Mitigation 

Parameters Importance Ranking State of 

Knowledge Additional 

P1 P2 P3 P4 P5 P6

12A. Intentional Shielding

1. Thickness H M H H H H H 

2. Material H H H H H H H 

12B. Electrical Raceway Fire Barrier 

System

3. Rating U U U U U U H 

12C. Fire-Retardant Coating Effects

4. Thickness U U U H H U M 

5. Material L U U H H H H 

6. Age L U U U H U H 
C-2

7

Table C-41 Key Parameters Ranking for Scenario 3, Generic Enclosure (Target) Characterization 

Parameters Importance Ranking State of 

Knowledge

Ad

P1 P2 P3 P4 P5 P6

13A. Target Damage

1. Damage Criteria H H H H H H M 

2. Critical Heat Flux H H H H H H M 

3. Critical Temperature H H H H H H M 

4. Exposure Time H H H H H H M 

13C. Target Sensitivity

5. Sensitivity to Shock L H H H H H M 

6. Sensitivity to Heat H H H H H H M-H

7. Sensitivity to EMI/RFI H H H H U H L-M

8. Sensitivity to Light L L L L L L L-M

9. Sensitivity to Ionized Gas L H H H H H M 

10. Sensitivity to Conductive Particulate H H H H H H L-M

11. Sensitivity to Smoke L-H L L L L L M 
C-2

8

Table C-42 Key Parameters Ranking for Scenario 3, Generic Cable Tray (Target) Characterization 

Parameters Importance Ranking State of 

Knowledge

Ad

P1 P2 P3 P4 P5 P6

14A. Target Damage

1. Damage Criteria H H H H H H M 

2. Critical Heat Flux H H H H H H M 

3. Critical Temperature H H H H H H M 

4. Exposure Time H H H H H H M 

14B. Target Arrangement Effects

5. Distance to HEAF Source H H H H H H H 

6. Orientation Relative to HEAF

Source

H H H H H H H 

14C. Target Sensitivity

7. Sensitivity to Shock M M H M M M M 

8. Sensitivity to Heat H H H H H H M-H

9. Sensitivity to EMI/RFI H U U L U L M 

10. Sensitivity to Light L L L L L L M 

11. Sensitivity to Ionized Gas L M M L M M M 

12. Sensitivity to Conductive Particulate H L L L L L M 

13. Sensitivity to Smoke H L L L L L M 
C-2

9

C.6 Scenario 3 Phenomena Calculated Rank Values and Grouping 

Table C-43 Summary of Scenario 3 Average Rankings and Grouping 

Phenomenon Importance State of Knowledge Rank 

Arc Characterization (5) 4 2 2.00 

Pressure Effects (8) 5 3 1.67 

Enclosure (Target) Characterization (13) 5 3.2 1.56 

Internal Ensuing Fire (9) 4.3 2.8 1.54 

Cable Tray (Target) Characterization (14) 4.9 3.2 1.53 

External Ensuing Fire (10) 4.1 3.1 1.32 

Cabinet Lineup Effects (3) 4.4 3.4 1.29 

Arc Mitigation (12) 3.7 3 1.23 

Electrical Configuration (1) 5 5 1.00 

Internal Cabinet Configuration (2) 3.7 4 0.93 

External Enclosure Configuration (3) 3.2 4.2 0.76 

Suppression Effects (7) 3 4.5 0.67 

Room Configuration (10) 2.8 4.3 0.65 

Fire Detection (6) 1.3 5 0.26 

33rd percentile for Rank: 0.95

66th percentile for Rank: 1.44

D-1

APPENDIX D PANELIST RÉSUMÉS
D-2
D-3
D-4 
D-5 
D-6 
D-7 
D-8
E-1

APPENDIX E TECHNICAL EXPERT AND ADVISOR RÉSUMÉS
E-2
E-3
E-4
E-5
E-6
E-7

Stephen L. Turner

Leidos, Inc. 

301 Laboratory Road

Oak Ridge, Tennessee 37830

Education B.S., M.S. Mechanical Engineering, University of Virginia 

Since 1979, Mr. Turner has held various positions at Leidos (formerly Science Applications 

International Corporation) including Assistant Vice President and Chief Scientist in the area of 

nuclear safety. He is currently a consultant at Leidos. 

Mr. Turner has 38 years of experience in nuclear facility safety and probabilistic analysis and 

supported the plans and basis for the implementation of risk-informed regulations based on 

Probabilistic Risk Assessments (PRA) for the Japanese utilities and the nuclear regulator in Japan 

since 2001. Mr. Turner was project manager 18 projects for fire safety including the methods for 

analyses and walk downs to support fire safety assessments to NUREG/CR-6850. This included 

various component fire tests since 2008 at Clemson University for HEPA filter soot loading and at 

Southwest Research Institute (SwRI) for cable fire and oil fire tests similar to the tests that support 

NUREG-6850. Since 2012, he was the project manager for four test projects for High Energy 

Arcing Faults (HEAF) at KEMA Laboratories completing a total of 24 HEAF tests on switchgear, 

distribution panels, and motor control centers. Three of these tests duplicated the conditions of 

the HEAF at the Onagawa power plant that occurred in the 2011 Tohoku Earthquake. He also 

was the project manager at SwRI for six tests using rocket fuel to create HEAF-like conditions in a 

5-cabinet switchgear lineup. He was a principal contributor to NUREG/IA-0470 that documents

these HEAF tests. For the last two years he was the project manager research for modeling and

analysis methods for HEAF phenomenon compiling results for published methods and developing

models in ANSYS-Fluent.
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APPENDIX F INTRODUCTORY MATERIALS PRESENTED AT THE FIRST 

PANEL MEETING

F.1 PIRT Process Refresher

Phenomena Identification and Ranking Table

 Description of scenario

 Scenarios are purposefully vague – this gives the

panel more latitude to choose the important

parameters

 Figure of merit

 The figure of merit is the specific goal to be

achieved through analysis. The phenomena

identified by the panel should be in the context of

achieving this goal.
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Description: A high energy arc fault occurs in a low/medium voltage switchgear that supplies 

power to “Train A” systems. The cables from an overhead cable tray enter the cabinet from the 

top (air-drop configuration). A similarly-configured switchgear supplying power to redundant 

“Train B” systems is located close by.

Figure of Merit: Determining the extent of damage to the “Train B” switchgear.

 The group will identify all phenomena that 

could be important in achieving the figure of 

merit.

 At this stage, no judgement regarding the

importance of the phenomena is necessary.

 The phenomena will be recorded and 

organized into categories as needed.
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 If it has units, or can be measured directly, it 

is probably a parameter. For example, cabinet 

voltage is a parameter. The underlying 

phenomenon would be the cabinet’s 

electrical configuration.

 I will record key parameters as well, but they 

will be ranked separately.

 Once the phenomena are identified, the 

individuals on the panel will rank each as 

being of high (H) medium (M) or low (L) 

importance.

 This will be done individually first, and then 

the rankings will be discussed as a group.
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 For each phenomenon, the panel will rank the 

state of knowledge in 3 categories:

 Model adequacy

 Data adequacy

 Obtainability of new data

 Again, we will use a high (H) medium (M) or 

low (L) scale.

 Finally, the panel will rank the key parameters 

identified earlier for both importance and 

state of knowledge.
F-5

F.2 Recent Experimental Work Performed by NRA

Hajime KABASHIMA and Susumu Tsuchino

Regulatory Standard and Research Department, 

Secretariat of Nuclear Regulation Authority 

(S/NRA/R), Tokyo, Japan

Experimental Studies of High Energy 

Arcing Fault (HEAF) by S/NRA/R

TH32 - Improving Realism in Fire Probabilistic Risk Assessments

Outline

U.S.NRC’s 28th Regulatory Information Conference (RIC 2016)

1. Background

2. Objectives of HEAF tests

3. S/NRA/R HEAF tests

4. S/NRA/R HEAF test results

5. Discussion topics

6. Summary

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F-6

1. Background

U.S.NRC’s 28th Regulatory Information Conference (RIC 2016)

A High Energy Arcing Fault (HEAF)

occurred in the high-voltage (6,900V)

metalclad switchgear (M/C) at Unit 1 of

Onagawa Nuclear Power Station (NPS) of

the Tohoku Electric Power Company Co., Inc.

on March 11, 2011 due to the 2011 off the

Pacific coast of Tohoku Earthquake.

HEAF events, although their impacts

differ each other, have occurred in the

electrical equipment and components in

the NPSs worldwide. Efforts are being

taken to understand the phenomena and

to develop evaluation methods.

March 11, 2011

Onagawa NPS Unit 1

(http://warp.da.ndl.go.jp/info:ndljp/pid/9483636/w

ww.nsr.go.jp/archive/nisa/earthquake/files/houkok

u230530-2.pdf)

2 / 12

2. Objectives of HEAF tests

U.S.NRC’s 28th Regulatory Information Conference (RIC 2016)

To understand the basic characteristics and behavior of

HEAF

To understand what occurred in the Onagawa NPS Unit 1

due to HEAF event during the 2011 off the Pacific coast of

Tohoku Earthquake

- - - - - - - - - - - - - - (In the future) - - - - - - - - - - - - - -

Develop regulatory guidance for Fire Hazards Analysis

Methods for HEAF

・ Models for damage predictions and setting Zone of Influence (ZOI)

・ Methods for the Protection against HEAF

3 / 12
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3. S/NRA/R HEAF tests

U.S.NRC’s 28th Regulatory Information Conference (RIC 2016)

Collaboration with

NRC

NIST 

KEMA

S/NRA/R HEAF Tests

Distribution 

Panel (DP)

Motor Control 

Center (MCC)

Low Voltage HEAF Tests

Metalclad Switchgear 

(M/C) 

5-cabinet lineup

Onagawa Configuration Tests

5-cabinet lineup

Heat source:Rocket fuel

Burned test

Voltage : 480V (Set point)

Current : 52.3kA (Target value)

Arc discharge 

Duration: 2s

HEAF tests: 3 times

Voltage : 480V (Set point)

Current : 63.5kA (Target value)

Arc discharge 

Duration: 2s 

HEAF tests: 4 times

Voltage : 7000V or 7100V (Set point)

Current : 22.6kA - 25.0kA (Target value)

Arc discharge

Duration: 1s, 2s, 3s 

HEAF tests 6 times

4 / 12

(1) Before test (2) Arc discharge occurrence 

(about 0.1 sec after start of test)

(3) Generation of metallic fume

(about 1 second after start of test)

(4) Ensuing Fire

(about 10 minutes after start of test)

4.1 S/NRA/R HEAF test results <Distribution Panel>

U.S.NRC’s 28th Regulatory Information Conference (RIC 2016)

In the DP HEAF tests, ensuing fire occurred in two out of three tests. 

Arc power was approximately 20MW for all the tests. 

Arc power

20MW

0 s 0 .1s

1s 10min

5 / 12
F-8

(1) Before test (2) Arc discharge occurrence

(about 0.2 sec. after start of test)

(3) Blowout of arc discharge metallic fume 

(about 0.5 second after start of test)

(4) Generation of metallic dust

(about 2 second after start of test)

4.2 S/NRA/R HEAF test results <Motor Control Center>

U.S.NRC’s 28th Regulatory Information Conference (RIC 2016)

Test cell

In MCC HEAF test, the ensuing fire did not occur for all four tests. 

Arc power was approximately 20MW for all tests. 

0 s 0 .2s

0.5s 2s

Arc power

20MW

6 / 12

(1) Before test (2) Arc discharge occurrence 

(about 0.2 sec after start of test)

(3) Generation of metallic fume

(about 2 second after start of test)

(4) Ensuing Fire

(about 10 minutes after start of test)

4.3 S/NRA/R HEAF test results <Metalclad Switchgear>

U.S.NRC’s 28th Regulatory Information Conference (RIC 2016)

In the M/C HEAF tests, ensuing fire occurred in four out of six tests. 

Arc power was approximately 20MW for four tests and larger than 20MW for two tests.

Arc power

20MW

0 s 0 .2s

2s 10min

7 / 12
F-9

5.1 Discussion topics <Arc power> 

U.S.NRC’s 28th Regulatory Information Conference (RIC 2016)

Fig. Energy model for arc discharge

 Proportional relationship is confirmed

between the arc energy and the arc

duration for each electric cabinet, and the

arc power is almost constant.

 The arc power is a value multiplied by

an energy density, a flow velocity

and a cross-sectional area of arc jet.

 Two key factors;

・ Saturation phenomena of energy

density

・ Inverse relationship between flow

velocity and cross-sectional area.

 Two data with slightly higher arc power

were obtained. It needs further

consideration. Fig. Relationship between arc discharge duration and arc energy

Electromagnetic 

pinch force

8 / 12

5.2 Discussion topics <Ensuing fire> 

U.S.NRC’s 28th Regulatory Information Conference (RIC 2016)

 S/NRA/R HEAF tests showed that the arc energy required for initiating ensuing fire

differed between distribution panels and metalclad switchgears.

 The values of arc energy which can cause ensuing fire were between 26.3 and

28.6 MJ for the distribution panels and between 42.6 and 57.2 MJ for the

metalclad switchgears.

 Values of arc energy required for causing ensuing fire were obtained. This

triggering energy is considered to be dependent on the characteristics of

individual electric cabinets such as interior volume and ventilation opening area.

Fig. Arc energy required for causing ensuing fire

Metalclad Switchgears

Cubicle size: Large

Ventilation opening area: Large

Length: 2.1 m

Depth: 0.9 m

Height: 2.3 m

Distribution Panel

Cubicle size: Middle

Ventilation opening area: Middle

Length: 0.9 m

Depth: 1.2 m

Height: 2.3 m

If arc discharge duration could be reduced, arc 

energy would be decreased and consequently 

ensuing fire could be prevented. 

9 / 12
F-10

5.3 Discussion topics <Onagawa HEAF event> 

U.S.NRC’s 28th Regulatory Information Conference (RIC 2016)

March 11, 2011

Onagawa NPS Unit 1

(http://warp.da.ndl.go.jp/info:ndljp/pid/9483636/www.nsr.

go.jp/archive/nisa/earthquake/files/houkoku230530-2.pdf)

HEAF event at Onagawa NPS Unit 1, it is supposed from observation of the damage condition 

that the arc discharge was occurred two times in the different Metalclad switchgears. 

One time HEAF test

Two times HEAF test Bus bar: Al 

Bus bar: Al 

Bus bar: Al 

 The damage of metalclad switchgears at Onagawa NPS Unit 1 was more severe

than that after HEAF tests.

 Aluminum bus bars of the metalclad switchgears at Onagawa NPS Unit 1 were

severely damaged compared with those of HEAF tests.

 Burning (oxidation) of the bus bar made of aluminum can cause huge heat

energy release by oxidation of aluminum. Therefore, in addition to the arc energy

due to HEAF, the high energy of aluminum bus bar oxidation should be

considered in the consequence evaluation for HEAF events in electric cabinets.

10 / 12

6. Summary

U.S.NRC’s 28th Regulatory Information Conference (RIC 2016)

 HEAF tests were conducted to obtain the insights about progress of

HEAF events, energy level of arcs and condition for ensuing fire.

Based on the test results, an energy model of arc discharge has

been studied.

 For various electric cabinets, insights of event progress were

obtained pertaining to generation and leakage of arcs, generation

of metal fume and ensuing fire.

 Proportional relationship was observed between arc energy and

arc duration irrespective of types of electric cabinets for all cases.

 Values of arc energy required to cause ensuing fire were obtained.

This triggering energy is considered to be dependent on the

characteristics of individual electric cabinets such as interior

volume and ventilation opening area.

11 / 12
F-11

F.3 Recent Experimental Work Performed by CRIEPI
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NUREG-2218

Kenneth Hamburger

Division of Risk Assessment

Office of Nuclear Regulatory Research

U.S. Nuclear Regulatory Commission

Washington, DC 20555

High Energy Arcing Faults

HEAF

Phenomena Identification and Ranking Table

PIRT

Expert Elicitation

January 2018

Technical

An International Phenomena Identification and Ranking Table (PIRT) 

Expert Elicitation Exercise for High Energy Arcing Faults (HEAFs)

Same as above

K. Hamburger, NRC Project Manager

This report documents the results of a phenomena identification and ranking table (PIRT) exercise 

performed for nuclear power plant (NPP) high energy arc fault (HEAF) analysis applications conducted on 

behalf of the U.S. Nuclear Regulatory Commission’s (NRC’s) Office of Nuclear Regulatory Research. 

The PIRT exercise was performed via a facilitated expert elicitation process. In this case, the expert panel 

comprised six international HEAF experts. The panel was facilitated by NRC staff. The objective of a PIRT 

exercise is to identify key phenomena associated with the intended application and to then rank the current 

state of knowledge relative to each identified phenomenon. The expert panel was presented with a series of 

specific HEAF scenarios, each of which is based on the types of scenarios typically considered in NPP 

applications. Each scenario includes a figure of merit (i.e., a specific goal to be achieved in analyzing the 

scenario using HEAF analysis or modeling tools). Given each scenario, the panel identified phenomena that 

are of potential interest to an assessment based on the figure of merit. The identified phenomena are then 

ranked relative to their importance in predicting the figure of merit. Each phenomenon is then further ranked for 

the existing state of knowledge and the adequacy of existing modeling tools to predict that phenomenon. 

The PIRT panel covered three HEAF scenarios and identified a number of areas potentially in need of 

further analysis and model development. This report discusses the results in detail.



NUREG-2218 An International Phenomena Identification and Ranking Table (PIRT) Expert Elicitation Exercise 

for High Energy Arcing Faults (HEAFs)

January 2018