Verification and Validation 

of Selected Fire Models for 

Nuclear Power Plant 

Applications 

Volume 1: 

Main Report 

January 2006 

U.S. Nuclear Regulatory Commission Electric Power Research Institute 

Office of Nuclear Regulatory Research 3412 Hillview Avenue 

Washington, DC 20555-0001 Palo Alto, CA 94303 

 

NUREG-1824 EPRI 1011999 

Draft for Comment Preliminary Report

Verification & Validation of Selected 

Fire Models for Nuclear Power Plant 

Applications 

Volume 1: Main Report 

NUREG-1824 EPRI 1011999 

January 2006 

U.S. Nuclear Regulatory Commission Electric Power Research Institute (EPRI) 

Office of Nuclear Regulatory Research (RES) 3412 Hillview Avenue 

Division of Risk Analysis and Applications Palo Alto, CA 94303 

Two White Flint North, 11545 Rockville Pike 

Rockville, MD 20852-2738 

U.S. NRC-RES Project Manager EPRI Project Manager 

M. H. Salley R. P. Kassawara 
DISCLAIMER OF WARRANTIES AND LIMITATION OF LIABILITIES 

THIS DOCUMENT WAS PREPARED BY THE ORGANIZATION(S) NAMED BELOW AS AN 

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iii 

COMMENTS ON DRAFT NUREG-1824 REPORT 

This report is being published jointly by the U.S. Nuclear Regulatory Commission (NRC) and 

the Electric Power Research Institute (EPRI). Any interested party may submit comments on 

this report for consideration by the NRC and EPRI staffs. Comments may be accompanied by 

additional relevant information or supporting data. Please specify both the report number (Draft 

NUREG-1824) and the volume number in your comments, and send them by March 31, 2006, to 

the following address: 

Chief Rules Review and Directives Branch 

U.S. Nuclear Regulatory Commission 

Mail Stop T-6D59 

Washington, DC 20555-0001 

For any questions about the material in this report, please contact: 

Mark Henry Salley 

Mail Stop T-10E50 

U.S. Nuclear Regulatory Commission 

Washington, DC 20555-0001 

Phone: (301) 415-2840 

Email: MXS3@nrc.gov

If EPRI members also wish to provide comments to EPRI, they may send them to the following 

address: 

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Electric Power Research Institute 

3412 Hillview Avenue 

Palo Alto, CA 94304 

Phone: (650) 855-2775 

Email: RKASSAWA@epri.com

v 

CITATIONS 

This report was prepared by 

U.S. Nuclear Regulatory Commission, 

Office of Nuclear Regulatory Research (RES) 

Two White Flint North, 11545 Rockville Pike 

Rockville, MD 20852-2738 

Principal Investigators: 

K. Hill 

J. Dreisbach 

Electric Power Research Institute (EPRI) 

3412 Hillview Avenue 

Palo Alto, CA 94303 

Science Applications International Corp (SAIC)

4920 El Camino Real 

Los Altos, CA 94022 

Principal Investigators: 

F. Joglar 

B. Najafi 

National Institute of Standards and Technology

Building Fire Research Laboratory (BFRL) 

100 Bureau Drive, Stop 8600 

Gaithersburg, MD 20899-8600 

Principal Investigators: 

K McGrattan 

R. Peacock 

A. Hamins 

Volume 1, Main Report: B. Najafi, M.H. Salley, F. Joglar, J. Dreisbach 

Volume 2, FDTS

: K. Hill, J. Dreisbach 

Volume 3, FIVE-REV. 1: F. Joglar 

Volume 4, CFAST: R. Peacock, J. Dreisbach, P. Reneke (NIST) 

Volume 5, MAGIC: F. Joglar, B. Guatier (EdF), L. Gay (EdF), J. Texeraud (EdF) 

Volume 6, FDS: K. McGrattan, J. Dreisbach 

Volume 7, Experimental Uncertainty: A. Hamins, K. McGrattan 

This report describes research sponsored jointly by U.S. Nuclear Regulatory Commission, Office 

of Nuclear Regulatory Research (RES) and Electric Power Research Institute (EPRI). 

The report is a corporate document that should be cited in the literature in the following manner: 

Verification and Validation of Selected Fire Models for Nuclear Power Plant Applications, 

Volume 1: Main Report, U.S. Nuclear Regulatory Commission, Office of Nuclear Regulatory 

Research (RES), Rockville, MD: 2005 and Electric Power Research Institute (EPRI), Palo Alto, 

CA. NUREG-1824 and EPRI 1011999.

vii 

ABSTRACT 

There is a movement to introduce risk- and performance-based analyses into fire protection 

engineering practice, both domestically and worldwide. This movement exists in the general fire 

protection community, as well as the nuclear power plant (NPP) fire protection community. 

In 2002, the National Fire Protection Association (NFPA) developed NFPA 805, PerformanceBased Standard for Fire Protection for Light-Water Reactor Electric Generating Plants, 2001 

Edition. In July 2004, the U.S. Nuclear Regulatory Commission (NRC) amended its fire 

protection requirements in Title 10, Section 50.48, of the Code of Federal Regulations (10 CFR 

50.48) to permit existing reactor licensees to voluntarily adopt fire protection requirements contained 

in NFPA 805 as an alternative to the existing deterministic fire protection requirements. In 

addition, the nuclear fire protection community wants to use risk-informed, performance-based 

(RI/PB) approaches and insights to support fire protection decision-making in general. 

One key tool needed to support RI/PB fire protection is the availability of verified and validated 

fire models that can reliably predict the consequences of fires. Section 2.4.1.2 of NFPA 805 

requires that only fire models acceptable to the Authority Having Jurisdiction (AHJ) shall be 

used in fire modeling calculations. Further, Sections 2.4.1.2.2 and 2.4.1.2.3 of NFPA 805 state 

that fire models shall only be applied within the limitations of the given model, and shall be 

verified and validated. 

This report is the first effort to document the verification and validation (V&V) of five fire models 

that are commonly used in NPP applications. The project was performed in accordance with the 

guidelines that the American Society for Testing and Materials (ASTM) set forth in Standard 

E1355-04, “Evaluating the Predictive Capability of Deterministic Fire Models.” The results of 

this V&V are reported in the form of ranges of accuracies for the fire model predictions. 

ix 

CONTENTS 

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

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

1.2 Programmatic Overview..................................................................................................1-1

1.2.1 Objectives...........................................................................................................1-2

1.2.2 Approach ............................................................................................................1-3

1.3 Report Structure..............................................................................................................1-4

2 TECHNICAL APPROACH......................................................................................................2-1

2.1 Library of Nuclear Power Plant Fire Scenarios ...............................................................2-4

2.1.1 Switchgear Room ...............................................................................................2-4

2.1.2 Cable Spreading Room ......................................................................................2-5

2.1.3 Main Control Room ............................................................................................2-5

2.1.4 Pump Room .......................................................................................................2-6

2.1.5 Turbine Building .................................................................................................2-6

2.1.6 Multi-Compartment Corridor...............................................................................2-6

2.1.7 Multi-Level Building ............................................................................................2-7

2.1.8 Containment Building (PWR)..............................................................................2-7

2.1.9 Battery Room .....................................................................................................2-8

2.1.10 Diesel Generator Room......................................................................................2-8

2.1.11 Computer Room .................................................................................................2-8

2.1.12 Outdoors.............................................................................................................2-8

2.2 Fire Models......................................................................................................................2-8

2.2.1 Libraries of Engineering Calculations: FDTs and FIVE-Rev1 ............................2-9

2.2.2 Two-Zone Fire Models: CFAST and MAGIC.....................................................2-9

2.2.3 Field Fire Model: FDS .....................................................................................2-10

2.3 Experimental Data.........................................................................................................2-10

2.3.1 Factory Mutual & Sandia National Laboratories (FM/SNL) Test Series ...........2-10

2.3.2 The National Bureau of Standards (NBS) Test Series .....................................2-11
x 

2.3.3 The International Collaborative Fire Model Project (ICFMP) Benchmark 

Exercise Test Series.......................................................................................................2-12

2.4 Selection of Fire Scenario Attributes.............................................................................2-13

2.5 Quantitative Validation ..................................................................................................2-17

2.6 Reporting and Applicability of the Validation Results....................................................2-20

2.6.1 Applicability of the V&V Results .......................................................................2-20

2.6.2 Characterization of Fire Model Predictions Based on Validation Results.........2-24

3 RESULTS AND CONCLUSIONS...........................................................................................3-1

3.1 Results ............................................................................................................................3-1

3.1.1 Validation............................................................................................................3-1

3.1.2 Verification..........................................................................................................3-4

3.2 Summary.........................................................................................................................3-4

3.3 Conclusions.....................................................................................................................3-5

4 REFERENCES .......................................................................................................................4-1
xi 

FIGURES 

Figure 2-1: Overview of the Approach for V&V Study of Selected Fire Models 

for Nuclear Power Plant Application ..........................................................................................2-3 

Figure 2-2: Typical Switchgear Room Fire Scenario ................................................................2-4 

Figure 2-3: Typical Cable Spreading Room Fire Scenario .......................................................2-5 

Figure 2-4: Typical Main Control Room Fire Scenario..............................................................2-5 

Figure 2-5: Typical Pump Room Fire Scenario.........................................................................2-6 

Figure 2-6: Typical Turbine Building Fire Scenario...................................................................2-6 

Figure 2-7: Typical Multi-Compartment Corridor Fire Scenario ................................................2-7 

Figure 2-8: Typical Multi-Level Building Fire Scenario..............................................................2-7 

xiii 

TABLES 

Table 2-1: FDTs and FIVE-Rev1 Models for the Fire Scenario Attributes Selected for this V&V 

Study..........................................................................................................................................2-9 

Table 2-2: Fire Modeling Attributes as Outputs .......................................................................2-16 

Table 2-3: Summary of the Fire Tests Used for Validation against Typical NPP Fire Scenario 

Attributes..................................................................................................................................2-18 

Table 2-4: List of selected normalized parameters for application of the validation results to NPP 

fire scenarios............................................................................................................................2-21 

Table 2-5: Summary of the fire experiments in terms of commonly used metrics ...................2-24 

xv 

REPORT SUMMARY 

This report documents the verification and validation (V&V) of five selected fire models 

commonly used in support of risk-informed and performance-based (RI/PB) fire protection at 

nuclear power plants (NPPs). 

Background 

Over the past decade, there has been a considerable movement in the nuclear power industry to 

transition from prescriptive rules and practices towards the use of risk information to supplement 

decision-making. In the area of fire protection, this movement is evidenced by numerous 

initiatives by the U.S. Nuclear Regulatory Commission (NRC) and the nuclear community 

worldwide. In 2001, the National Fire Protection Association (NFPA) completed the 

development of NFPA Standard 805, “Performance-Based Standard for Fire Protection for Light 

Water Reactor Electric Generating Plants 2001 Edition.” Effective July, 16, 2004, the NRC 

amended its fire protection requirements in 10 CFR 50.48(c) to permit existing reactor licensees 

to voluntarily adopt fire protection requirements contained in NFPA 805 as an alternative to the 

existing deterministic fire protection requirements. RI/PB fire protection relies on fire modeling 

for determining the consequence of fires. NFPA 805 requires that the “fire models shall be 

verified and validated,” and “only fire models that are acceptable to the Authority Having 

Jurisdiction (AHJ) shall be used in fire modeling calculations.” 

Objectives 

The objective of this project is to examine the predictive capabilities of selected fire models. 

These models may be used to demonstrate compliance with the requirements of 10 CFR 50.48(c) 

and the referenced NFPA 805, or support other performance-based evaluations in NPP fire 

protection applications. In addition to NFPA 805 requiring that only verified and validated fire 

models acceptable to the AHJ be used, the standard also requires that fire models only be applied 

within their limitations. The V&V of specific models is important in establishing acceptable 

uses and limitations of fire models. Specific objectives of this project are: 

• Perform V&V study of selected fire models using a consistent methodology (ASTM E1355) 

and issue a report to be prepared by U.S. Nuclear Regulatory Commission Office of Nuclear 

Regulatory Research (RES) and Electric Power Research Institute (EPRI). 

• Investigate the specific fire modeling issues of interest to the NPP fire protection 

applications. 

• Quantify fire model predictive capabilities to the extent that can be supported by comparison 

with selected and available experimental data. 
xvi 

The following fire models were selected for this evaluation: (i) NRC’s NUREG-1805 Fire 

Dynamics Tools (FDTs), (ii) EPRI’s Fire-Induced Vulnerability Evaluation Revision 1 (FIVERev. 1), (iii) National Institute of Standards and Technology’s (NIST) Consolidated Model of 

Fire Growth and Smoke Transport (CFAST), (iv) Electricite de France’s (EdF) MAGIC, and (v) 

NIST’s Fire Dynamics Simulator (FDS). 

Approach 

This program is based on the guidelines of the ASTM E1355, “Evaluating the Predictive 

Capability of Deterministic Fire Models,” for verification and validation of the selected fire 

models. The guide provides four areas of evaluation: 

• Defining the model and scenarios for which the evaluation is to be conducted, 

• Assessing the appropriateness of the theoretical basis and assumptions used in the model, 

• Assessing the mathematical and numerical robustness of the model, and 

• Validating a model by quantifying the accuracy of the model results in predicting the course 

of events for specific fire scenarios. 

Traditionally, a V&V study reports the comparison of model results with experimental data, and 

therefore, the V&V of the fire model is for the specific fire scenarios of the test series. While 

V&V studies for the selected fire models exist, it is necessary to ensure that technical issues 

specific to the use of these fire models in NPP applications are investigated. The approach 

below was followed to fulfill this objective. 

1. A set of fire scenarios were developed. These fire scenarios establish the “ranges of 

conditions” for which fire models will be applied in NPPs. 

2. The next step summarizes the same attributes or “range of conditions” of the “fire 

scenarios” in test series available for fire model benchmarking and validation exercises. 

3. Once the above two pieces of information were available, the validation test series, or 

tests within a series, that represent the “range of conditions” was mapped for the fire 

scenarios developed in Step 1. The range of uncertainties in the output variable of 

interest as predicted by the model for a specific “range of conditions” or “fire scenario” 

are calculated and reported. 

The scope of this V&V study is limited to the capabilities of the selected fire models. There are 

potential fire scenarios in NPP fire modeling applications that do not fall within the capabilities 

of these fire models and therefore are not covered by this V&V study. 

Results 

The results of this study are presented in the form of relative differences between fire model 

predictions and experimental data for fire modeling attributes important to NPP fire modeling 

applications, e.g., plume temperature. The relative differences sometimes show agreement, but 

may also show both under-prediction and over-prediction. These relative differences are 

affected by the capabilities of the models, the availability of accurate applicable experimental 

data, and the experimental uncertainty of this data. The relative differences were used, in 

combination with some engineering judgment as to the appropriateness of the model and the 
xvii 

agreement between model and experiment, to produce a graded characterization of the fire 

model’s capability to predict attributes important to NPP fire modeling applications. 

This report does not provide relative differences for all known fire scenarios in NPP applications. 

This incompleteness is due to a combination of model capability and lack of relevant 

experimental data. The first can be addressed by improving the fire models while the second 

needs more applicable fire experiments. 

EPRI Perspective 

The use of fire models to support fire protection decision-making requires that their limitations 

and confidence in their predictive capability is well understood. While this report makes 

considerable progress towards that goal, it also points to ranges of accuracies in the predictive 

capability of these fire models that could limit their use in fire modeling applications. Use of 

these fire models present challenges that should be addressed if the fire protection community is 

to realize the full benefit of fire modeling and performance-based fire protection. This requires 

both short term and long term solutions. In the short term a methodology will be to educate the 

users on how the results of this work may affect known applications of fire modeling. This may 

be accomplished through pilot application of the findings of this report and documentation of the 

insights as they may influence decision-making. Note that the intent is not to describe how a 

decision is to be made, but rather to offer insights as to where and how these results may, or may 

not be used as the technical basis for a decision. In the long term, additional work on improving 

the models and performing additional experiments should be considered. 

Keywords 

Fire Fire Modeling Verification and Validation (V&V) 

Performance-based Risk-informed regulation Fire Hazard Analysis (FHA) 

Fire safety Fire protection Nuclear Power Plant 

Fire Probabilistic Risk Assessment (PRA) Fire Probabilistic Safety Assessment 

 (PSA) 

xix 

PREFACE 

This report is presented in seven volumes. Volume 1, the Main Report, provides general 

background information, programmatic and technical overviews, and project insights and 

conclusions. Volumes 2 through 6 provide detailed discussions of the verification and validation 

(V&V) of the following five fire models: 

Volume 2 Fire Dynamics Tools (FDTs

) 

Volume 3 Fire-Induced Vulnerability Evaluation, Revision 1 (FIVE-Rev1) 

Volume 4 Consolidated Model of Fire Growth and Smoke Transport (CFAST) 

Volume 5 MAGIC 

Volume 6 Fire Dynamics Simulator (FDS) 

Finally, Volume 7 quantifies the uncertainty of the experiments used in the V&V study of these 

five fire models. 

xxi 

FOREWORD 

Fire modeling and fire dynamics calculations are used in a number of fire hazards analysis (FHA) studies and 

documents, including fire risk analysis (FRA) calculations; compliance with, and exemptions to the regulatory 

requirements for fire protection in 10 CFR Part 50; “Specific Exemptions”; the Significance Determination 

Process (SDP) used in the inspection program conducted by the U.S. Nuclear Regulatory Commission (NRC); 

and, most recently, the risk-informed performance-based (RI/PB) voluntary fire protection licensing basis 

established under 10 CFR 50.48(c). The RI/PB method is based on the National Fire Protection Association 

(NFPA) Standard 805, “Performance-Based Standard for Fire Protection for Light-Water Reactor Generating 

Plants.” 

The seven volumes of this NUREG-series report provide technical documentation concerning the predictive 

capabilities of a specific set of fire dynamics calculation tools and fire models for the analysis of fire hazards in 

nuclear power plant (NPP) scenarios. Under a joint memorandum of understanding (MOU), the NRC Office of 

Nuclear Regulatory Research (RES) and the Electric Power Research Institute (EPRI) agreed to develop this 

technical document for NPP application of these fire modeling tools. The objectives of this agreement include 

creating a library of typical NPP fire scenarios and providing information on the ability of specific fire models to 

predict the consequences of those typical NPP fire scenarios. To meet these objectives, RES and EPRI initiated 

this collaborative project to provide an evaluation, in the form of verification and validation (V&V), for a set of five 

commonly available fire modeling tools. 

The road map for this project was derived from NFPA 805 and the American Society for Testing and Materials 

(ASTM) Standard E1355-04, “Evaluating the Predictive Capability of Deterministic Fire Models.” These 

industry standards form the methodology and process used to perform this study. Technical review of fire 

models is also necessary to ensure that those using the models can accurately assess the adequacy of the scientific and 

technical bases for the models, select models that are appropriate for a desired use, and understand the levels 

of confidence that can be attributed to the results predicted by the models. This work was performed using 

state-of-the-art fire dynamics calculation methods/models and the most applicable fire test data. Future 

improvements in the fire dynamics calculation methods/models and additional fire test data may impact the results 

presented in the seven volumes of this report. 

This document does not constitute regulatory requirements, and RES participation in this study neither 

constitutes nor implies regulatory approval of applications based on the analysis contained in this text. The 

analyses documented in this report represent the combined efforts of individuals from RES and EPRI, both of 

which provided specialists in the use of fire models and other FHA tools. The results from this combined 

effort do not constitute either a regulatory position or regulatory guidance. Rather, these results are intended 

to provide technical analysis, and they may also help to identify areas where further research and analysis are 

needed. 

 _________________________________

 Carl J. Paperiello, Director 

 Office of Nuclear Regulatory Research 

 U.S. Nuclear Regulatory Commission

xxiii 

ACKNOWLEDGMENTS 

The work documented in this report benefited from contributions and considerable technical 

support from several organizations. 

The verification and validation (V&V) studies for FDTs (Volume 2), CFAST (Volume 4), and 

FDS (Volume 6) were conducted in collaboration with the U.S. Department of Commerce, 

National Institute of Standards and Technology (NIST), Building and Fire Research Laboratory 

(BFRL). Since the inception of this project in 1999, the NRC has collaborated with NIST 

through an interagency memorandum of understanding (MOU) and conducted research to provide 

the necessary technical data and tools to support the use of fire models in nuclear power plant 

fire hazard analysis (FHA). 

We appreciate the efforts of Doug Carpenter and Rob Schmidt of Combustion Science 

Engineers, Inc. for their comments and contribution to Volume 2. 

In addition, we acknowledge and appreciate the extensive contributions of Electricité de France 

(EdF) in preparing Volume 5 for MAGIC. 

We also appreciate the efforts of organizations participating in the International Collaborative 

Fire Model Project (ICFMP) to Evaluate Fire Models for Nuclear Power Plant Applications, 

which provided experimental data, problem specifications, and insights and peer comment for 

the international fire model benchmarking and validation exercises, and jointly prepared the 

panel reports used and referred in this study. We specifically appreciate the efforts of the 

Building Research Establishment (BRE) and the Nuclear Installations Inspectorate in the United 

Kingdom, which provided leadership for ICFMP Benchmark Exercise (BE) #2, as well as 

Gesellschaft fuer Anlagen-und Reaktorsicherheit (GRS) and Institut fuer Baustoffe, Massivbau 

und Brandschutz (iBMB) in Germany, which provided leadership and valuable experimental data 

for ICFMP BE #4 and BE #5. In particular, ICFMP BE #2 was led by Stewart Miles at BRE; 

ICFMP BE #4 was led by Walter Klein-Hessling and Marina Rowekamp at GRS, and R. 

Dobbernack and Olaf Riese at iBMB; and ICFMP BE #5 was led by Olaf Riese and D. Hosser at 

iBMB, and Marina Rowekamp at GRS. We acknowledge and sincerely appreciate all of their 

efforts. 

We greatly appreciate Paula Garrity, Technical Editor for the Office of Nuclear Regulatory 

Research, and Linda Stevenson, agency Publication Specialist, for providing editorial and 

publishing support for this report. We also greatly appreciate Dariusz Szwarc, Nuclear Safety 

Professional Development Program participant, for his assistance finalizing this report. 

xxv 

LIST OF ACRONYMS 

AGA American Gas Association 

AHJ Authority Having Jurisdiction 

ASME American Society of Mechanical Engineers 

ASTM American Society for Testing and Materials 

BE Benchmark Exercise 

BFRL Building and Fire Research Laboratory 

BRE Building Research Establishment 

CFAST Consolidated Fire Growth and Smoke Transport Model 

CFR Code of Federal Regulations

EdF Electricité de France 

EPRI Electric Power Research Institute 

FDS Fire Dynamics Simulator 

FDTs

 Fire Dynamics Tools (NUREG-1805) 

FHA Fire Hazard Analysis 

FIVE-Rev1 Fire-Induced Vulnerability Evaluation, Revision 1 

FM-SNL Factory Mutual & Sandia National Laboratories 

FPA Foote, Pagni, and Alvares 

FRA Fire Risk Analysis 

GRS Gesellschaft fuer Anlagen-und Reaktorsicherheit (Germany) 

HRR Heat Release Rate 

IAFSS International Association of Fire Safety Science 

iBMB Institut für Baustoffe, Massivbau und Brandschutz 

ICFMP International Collaborative Fire Model Project 

IEEE Institute of Electrical and Electronics Engineers 

MCC Motor Control Center 
xxvi 

MQH McCaffrey, Quintiere, and Harkleroad 

MOU Memorandum of Understanding 

NBS National Bureau of Standards (now NIST) 

NFPA National Fire Protection Association 

NIST National Institute of Standards and Technology 

NPP Nuclear Power Plant 

NRC U.S. Nuclear Regulatory Commission 

NRR Office of Nuclear Reactor Regulation (NRC) 

RES Office of Nuclear Regulatory Research (NRC) 

RI/PB Risk-Informed, Performance-Based 

SDP Significance Determination Process 

SFPE Society of Fire Protection Engineers 

V&V Verification & Validation 
1-1

1 

INTRODUCTION 

1.1 Background 

Over the past decade, there has been a considerable movement in the nuclear power industry 

to transition from prescriptive rules and practices toward the use of risk information to supplement 

decision-making. In the area of fire protection, this movement is evidenced by numerous initiatives 

by the U.S. Nuclear Regulatory Commission (NRC) and the nuclear community worldwide. 

In 2001, the National Fire Protection Association (NFPA) completed its development of 

NFPA 805, Performance-Based Standard for Fire Protection for Light-Water Reactor 

Electric Generating Plants, 2001 Edition [Ref. 1]. Effective July 16, 2004, the NRC amended 

its fire protection requirements in Title 10, Section 50.48(c), of the Code of Federal Regulations

[10 CFR 50.48(c)] to permit existing reactor licensees to voluntarily adopt fire protection 

requirements contained in NFPA 805 as an alternative to the existing deterministic fire protection 

requirements [Ref. 2]. 

Risk-informed, performance-based (RI/PB) fire protection relies on fire modeling to determine 

the consequences of fires. NFPA 805 states that “fire models shall be verified and validated,” 

and “only fire models that are acceptable to the authority having jurisdiction [AHJ] shall be used 

in fire modeling calculations.” 

1.2 Programmatic Overview 

Under a joint Memorandum of Understanding [Ref. 3], the NRC’s Office of Nuclear Regulatory 

Research (RES) and the Electric Power Research Institute (EPRI) initiated a collaborative project 

for verification and validation (V&V) of five selected fire models to support RI/PB fire protection 

and implementation of the voluntary fire protection rule that adopts NFPA 805 as an RI/PB alternative. 

This V&V effort may also serve to increase the confidence of reviewers who evaluate fire models 

that are used in other programs, such as the Fire Protection Significance Determination Process (SDP). 

This collaboration brings together the combined information and knowledge generated by 

the NRC and EPRI fire research programs in this area. This effort also recognizes the considerable 

knowledge that resides in the fire science community in general, and attempts to use that knowledge, 

particularly within the context of the fire models being evaluated. This report is the direct result 

of this collaboration between RES and EPRI. 
Introduction 

1-2 

1.2.1 Objectives 

The purpose of this report is to describe an evaluation of the predictive capabilities of certain 

fire models for applications specific to nuclear power plants (NPP). These models may be used 

to demonstrate compliance with the requirements of 10 CFR 50.48(c) [Ref. 2] and the referenced 

NFPA standard, NFPA 805 [Ref. 1]. 

Engineering analyses and methods that are applied to demonstrate compliance with the 

performance criteria in NFPA 805 need the requisite degree of defensible technical justification, 

as dictated by the scope and complexity of the specific application. These analyses are performed 

by qualified analysts and should include any necessary V&V of analytical methods relevant to 

the specific application. 

Section 2.4.1.2 of NFPA 805 states that only fire models acceptable to the AHJ shall be used in 

fire modeling calculations. Further, Sections 2.4.1.2.2 and 2.4.1.2.3 of NFPA 805 state that fire 

models shall only be applied within the limitations of the given fire model, and shall be verified 

and validated. Thus, V&V is necessary to establish acceptable uses and limitations of fire 

models. In addition, analysts need to justify the appropriateness of fire model for specific 

applications. 

This project was driven by the following objectives: 

• Conduct a V&V study of the selected fire models using a consistent methodology (ASTM 

E1355) for NPP fire protection applications. 

• Quantify predictive capabilities of fire models to the extent that can be supported by 

comparison with applicable and available fire experiment data. 

This study evaluated the following five fire modeling tools: 

(1) NRC’s Fire Dynamics Tools (FDTS

) (documented in Volume 2 of this report) 

(2) EPRI’s Fire-Induced Vulnerability Evaluation, Revision 1 (FIVE-Rev1) (documented in 

Volume 3 of this report) 

(3) National Institute of Standards and Technology’s (NIST) Consolidated Model of Fire Growth 

and Smoke Transport (CFAST) (documented in Volume 4 of this report) 

(4) Electricité de France’s (EdF) MAGIC code (documented in Volume 5 of this report) 

(5) NIST’s Fire Dynamics Simulator (FDS) (documented in Volume 6 of this report). 
Introduction 

1-3 

1.2.2 Approach 

This program follows the guidelines of ASTM E1355, “Evaluating the Predictive Capability of 

Deterministic Fire Models” (Ref. 4), which the American Society for Testing and Materials 

(ASTM) distributes as a guide to evaluate fire models. That standard identifies four areas of 

evaluation for predictive fire models: 

(1) Define the model and scenarios for which the evaluation is to be conducted. 

(2) Assess the appropriateness of the theoretical basis and assumptions used in the model. 

(3) Assess the mathematical and numerical robustness of the model. 

(4) Validate the model by quantifying the uncertainty and relative difference1 of the model 

results in predicting the course of events for specific NPP fire scenarios. 

Traditionally, a V&V study reports on the comparison of model results with experimental data 

from a test series and, as such, the V&V of the fire model is for the specific fire scenarios of the 

test series. V&V studies for the selected fire models do already exist, but it is necessary to 

investigate the technical issues specific to the use of these models in NPP fire modeling 

applications. 

In order to accomplish the above-mentioned objectives, the following approach was developed 

and implemented in this study. 

(1) Develop a set of fire scenarios that establish the possible fire protection applications for 

which fire models may be applied in NPPs. In so doing, it is important to identify the 

important factors that can affect the fire phenomena. The following are those factors that 

principally influence the fire phenomena and predicted quantities: 

• fire source, peak heat release rate (HRR), and fire duration 

• geometry and construction of the compartment (shape, volume, single- or multicompartment/multi-level) 

• ventilation (natural or mechanical) 

• target (cables with different properties and tenability) 

(2) Summarize the range of values of these factors found in experimental test series available for 

fire model validation evaluation. 

(3) Map the range of values of the factors in the experimental test series with the set of NPP fire 

scenarios developed in Step 1. In so doing, calculate and report the range of relative 

differences between experimental data and model prediction for the range of values. 

The scope of this V&V study is limited to the capabilities of the selected fire models. As such, 

certain potential fire scenarios in NPP fire modeling applications do not fall within the 

capabilities of these fire models and, therefore, are not covered by this study. Examples of such 

fire scenarios include high-energy arcing faults and fire propagation between control panels 

[Ref. 5, Section 7.2.2]. 

 

1 See section 2.5 for the specific definition of relative difference 
Introduction 

1-4 

1.3 Report Structure 

This report is presented in seven volumes: 

• Volume 1, “Main Report,” provides general background information, programmatic and 

technical overviews, project results, insights, and conclusions. The description of the typical 

commercial NPP fire scenarios is contained in section 2 of Volume 1. 

• Volumes 2 through 6 provide detailed discussions of the V&V of the FDTs, FIVE-Rev 1, 

CFAST, MAGIC, and FDS fire models. Each report follows the guidelines provided by 

ASTM E1355 and contains the following chapters: 

3⁄4 Chapter 1, Introduction 

3⁄4 Chapter 2, Model Definition, briefly describes the fire model. 

3⁄4 Chapter 3, Theoretical Bases for the Model, includes theoretical descriptions of the fire 

model. In addition, this chapter provides a literature review and discusses 

the capabilities, limitations, and range of applications of the model. 

3⁄4 Chapter 4, Mathematical and Numerical Robustness, discusses the mathematical and 

numerical robustness of the fire model. 

3⁄4 Chapter 5, Model Sensitivity, presents the results of sensitivity analyses conducted for 

the fire model. In general, the sensitivity analysis evaluates model variations from a base 

case scenario, as they are affected by changes in the input parameters. 

3⁄4 Chapter 6, Model Validation, documents the methodology and results of the V&V study. 

3⁄4 Chapter 7, References

3⁄4 Appendix A, Technical Details for Validation Study

3⁄4 Appendix B, Input Files

• Volume 7 presents a summary description of the fire tests and estimates of experimental 

uncertainty used in this V&V study.
2-1

2 

TECHNICAL APPROACH 

ASTM E1355 establishes a process for conducting a V&V study of a fire model. In general, the 

process can be summarized in the following tasks: 

• Model and scenario definition documents the model and the scenarios or phenomenon of 

interest for the V&V study. 

• Description of the theoretical basis for the model documents a detailed technical 

description of the thermo-physical processes addressed by the fire model. 

• Mathematical and numerical robustness documents an evaluation of the numerical 

implementation of the model. 

• Model sensitivity documents a sensitivity analysis of the model. 

• Model evaluation documents the results of the validation study. 

There is, however, a technical challenge in implementing these tasks. Specifically, the universe 

of fire scenarios in commercial nuclear power plants (NPP) is large and diverse. Also many 

scenarios have characteristics or attributes that either cannot be modeled using state of the art 

computational fire models, and/or no experimental data is available for supporting a quantitative 

V&V study of that particular characteristic or attribute. Improvements in these two specific 

limitations — limited fire modeling capabilities and/or insufficient experimental data — 

are needed. 

In order to address these challenges, and still perform a quantitative V&V study consistent with 

ASTM E1355, the following approach has been selected: 

(1) Define a list of typical NPP fire scenarios. This list of fire scenarios is intended to be a 

reflection of the wide range of fire scenarios found in NPPs. In the context of this V&V 

study, the list of scenarios attempts to capture all the potential fire scenarios and the resulting 

conditions that could be predicted by some fire models. Many of these scenarios do not have 

any available experimental data to support a quantitative model evaluation. 

(2) Select test series from which experimental data will be used to perform the quantitative 

validation. The selected test series reflects some of the characteristics of the fire scenarios 

included in the list described in item 1 above. 

(3) Select and describe the fire models for which an evaluation can be conducted. 

Consistent with ASTM E1355, the description of the selected fire models includes a review 

of the theoretical basis and fundamental assumptions, an assessment of the mathematical and 

numerical robustness, and a sensitivity analysis, as well as validation with experimental data. 
Technical Approach 

2-2 

(4) Define fire scenario parameters. As mentioned earlier, neither state of the art fire model 

capabilities nor the available experimental data can support a quantitative V&V study of 

every relevant attribute in all potential NPP fire scenarios. Therefore, based on the 

capabilities of the selected fire models, and the available experimental data, the project team 

identified 13 fire scenario attributes for which a quantitative validation study can be 

conducted. 

(5) Conduct the quantitative validation study for each fire-modeling tool. The quantitative 

validation studies are conducted by comparing experimental data with fire modeling tool 

predictions. 

(6) Report validation results. Results from the quantitative validation study are reported as 

relative differences for peak experimental measurements and model predictions, as well as 

graphical comparisons between experimental measurements and model predictions. 

Figure 2-1 graphically represents this approach. The following sections describe the steps of this 

approach in greater detail. 
Technical Approach 

2-3 

Figure 2-1: Overview of the Approach for V&V Study of Selected Fire Models 

for Nuclear Power Plant Application 

Quantitative V&V - Vol 1, Section 2.5 

(ASTM E1355, Sections 11.3.7, & 11.3.9)

Performing quantitative V&V by comparing 

model predictions to experimental data. 

Fire Modeling Parameters – Vol. 1, Section 

2.4 

Defining the attributes of fire scenarios for 

which a quantitative V&V can be conducted. 

Fire Modeling Codes – Vol. 1, Section 2.3

(ASTM E1355, Chapters 7, 8, 9 & 10)

Selecting the fire modeling codes and the 

capabilities of the code for which the V&V is 

conducted. 

Assessing theoretical bases, assumptions, 

numerical robustness, and sensitivities. 

Fire Experiments – Vol. 1, Section 2.2 

(ASTM E1355, Sections 11.3.3, & 

11.3.3)

Defining the set of fire experiments that 

will support the quantitative V&V. 

NPP Fire Scenarios – Vol. 1, Section 2.1

(ASTM E1355, Section 7.2) 

Defining the fire scenarios for which the 

V&V is conducted. 

Report V&V Results — Vol. 1, Section 2.6 

(ASTM E1355, Chapter 12)

Reporting V&V results in the form of graphical 

comparisons and relative differences. 
Technical Approach 

2-4 

2.1 Library of Nuclear Power Plant Fire Scenarios 

To conduct the V&V study in accordance with ASTM E1355, it was necessary to define 

the scenarios or phenomena of interest to evaluate each model. For the purpose of the V&V 

study, a fire scenario definition should include a complete description of the phenomena of 

interest in the evaluation to facilitate appropriate application of the model. As mentioned in the 

introduction to this chapter, this list of fire scenarios is intended to reflect the collection of fire 

scenarios found in NPPs. In the context of this V&V study, the list of scenarios captures all the 

phenomena of interest that would be predicted by some fire models, but may or may not have 

experimental data to support a quantitative model evaluation. 

The list of fire scenarios presented in this section expands and modifies the list originally 

compiled and documented by EPRI as part of the development of its “Fire Modeling Guide for 

Nuclear Power Plant Applications” [Ref. 5]. The basis for the selection of these fire scenarios is 

documented in Chapter 3 of this document. Further information on NPP fire scenarios is found 

in NUREG/CR-6850 [Ref. 6]. This document discusses risk methods that may be used to 

evaluate scenarios that can be outside the applicability of the fire modeling tools evaluated in this 

report. Such scenarios include high-energy arcing faults, main control board fires, and hydrogen 

fires.

The generic list of scenarios includes fires in the switchgear room (SWGR), cable spreading room (CSR), 

main control room (MCR), pump room, turbine building, multiple compartment (corridor) scenarios, 

multi-level building, containment (PWR), battery room, diesel generator room, computer room, 

and outdoors. The descriptions below of the fire scenario are examples of how and where a fire 

could start. The sources of fires described are representative of the typical configurations in 

most NPPs, and therefore are the most probable. 

2.1.1 Switchgear Room 

The SWGR is often an important area in a commercial NPP. A fire in a SWGR can have 

significant fire risk repercussions and, hence, the SWGR is one of the two plant locations that are 

most often identified as the top fire risk contributors in fire risk assessments performed under the 

IPEEE program. The reason the SWGR can be essential to plant operation is that it typically 

contains equipment and circuits that provide the electrical power needed to operate and control 

the plant. This area also contains potential sources of high-energy arcing faults that may be 

located close to other safety-related equipment and/or circuits. Figure 2-2 graphically represents 

the SWGR fire room scenario. The source of a fire in this scenario may be an electrical cabinet. 

The size of the fire will depend on the type and amount of cables present in the cabinet and the 

ventilation conditions within the cabinet itself. The ventilation conditions in the room may be 

natural ventilation with one or two open doors, or mechanical ventilation. Important targets may 

be cables in a cable tray located above the switchgear cabinet that are exposed to plume 

conditions or radiant heat flux from the fire. 

[Figure TBD] 

Figure 2-2: Typical Switchgear Room Fire Scenario 
Technical Approach 

2-5 

2.1.2 Cable Spreading Room 

The CSR is another critical location in a commercial NPP because it often contains redundant 

instrumentation and control circuits needed for plant operation. The CSR generally contains a 

high cable concentration (in cable trays and/or conduits), and fire propagation in open cable trays 

can be an important aspect of fire modeling. Some NPPs have areas called cable tunnels or cable 

lofts, which present similar challenges. These areas may also contain significant amounts of 

cables in trays or conduits and may contain redundant circuits. Figure 2-3 graphically represents 

the scenario. The source of a fire in this scenario may be transient combustibles, or electrical 

cable failure. The size of the fire will depend on the type and amount of trash in the area. The 

ventilation conditions in the room may be mechanical ventilation, or possibly some level of 

natural ventilation via leakage around closed doors. Important targets may be cables in a cable 

tray located above the fire cabinet that are exposed to plume conditions or an electrical cabinet 

exposed to radiant heat flux from the fire. 

[Figure TBD] 

Figure 2-3: Typical Cable Spreading Room Fire Scenario

2.1.3 Main Control Room 

Like the SWGR, the MCR is typically one of the two plant locations that are most often 

identified as the top fire risk contributors in fire risk assessments performed under the IPEEE 

program. The MCR contains redundant instrumentation and control circuits that are critical to 

plant control and safe shutdown. Analyses of fires in the MCR pose unique challenges, including 

timing of fire detection, smoke generation, migration, and habitability; fire propagation within 

very large panels; and fire propagation between panels. It should also be noted that some NPPs 

have areas (i.e., a relay room, auxiliary equipment room, or remote shutdown panel) that are 

similar to MCRs in that they contain redundant instrumentation and control circuits that are critical 

to plant control and safe-shutdown. However, such areas are not constantly manned like MCRs 

and may instead be equipped with automatic suppression systems. Figure 2-4 graphically represents 

a MCR scenario. This scenario can apply to one or more unit NPP control rooms. The source of 

a fire in this scenario may be a control cabinet. The size of the fire will depend on the type and 

amount of cables within the cabinet, as well as cabinet ventilation and detection and suppression 

activities in the constantly-manned control room. The ventilation conditions in the room will be 

mechanical ventilation. Important targets are adjacent control cabinets exposed to radiant heat 

flux from the fire. 

[Figure TBD] 

Figure 2-4: Typical Main Control Room Fire Scenario 
Technical Approach 

2-6 

2.1.4 Pump Room 

This location represents areas in a plant where a relatively large fire is possible in a small 

enclosure. Figure 2-5 graphically represents the scenario. The source of a fire in this scenario 

may be ignition of an oil pool spilled from a pump. The size of the fire will depend on the type 

and amount of oil spilled, as well as the area and depth of the pool itself. The growth of this fire 

typically will be fast, and depending on the size of the room, the fire could possibly generate 

flashover conditions that may challenge the walls and ceiling. The ventilation conditions in the 

room will be mechanical ventilation with leakage around closed doors. Targets of interest in 

these scenarios may be the walls and ceiling of the enclosure, which are fire barriers, as well as 

any other safety-related equipment and cables located in the room or area.

[Figure TBD]

Figure 2-5: Typical Pump Room Fire Scenario 

2.1.5 Turbine Building 

A turbine building is usually a multi-level enclosure2

, in which the top level is commonly referred 

to as the turbine operating deck. A fire scenario on the turbine deck was selected to examine large 

(e.g., turbine lube oil) or small (e.g., transient or panel) fires in large enclosures with high 

ceilings. A multi-level turbine building fire is described in Section 2.1.7. The scenario can apply 

to buildings with one or more turbines. Figure 2-6 graphically represents the scenario. The 

source of a fire in this scenario may be ignition of an oil pool spilled from one of the turbines. 

The size of the fire will depend on the type and amount of oil spilled, as well as the area and 

depth of the pool itself. The growth of this fire will be fast. Other sources of fire in the turbine 

building could be electrical fires, transformer or switchgear fires, and hydrogen fires. The 

ventilation conditions will be natural ventilation, with many open doors and windows. There 

may also be mechanical ventilation using roof-mounted exhaust fans and/or mechanical supply. 

Targets of interest in these scenarios may be structural steel members and fire barriers, as well as 

any other safety-related equipment and cables located in the area and exposed to the fire. 

[Figure TBD] 

Figure 2-6: Typical Turbine Building Fire Scenario 

2.1.6 Multi-Compartment Corridor 

Many commercial NPPs have enclosures with multiple compartments that open into a common 

space or corridor. The significance of these enclosures in terms of fire safety varies from plant-toplant because they house various mechanical, electrical, waste treatment, or other equipment and/or 

circuits. Figure 2-7 graphically represents this scenario, which consists of a fire in one 

compartment affecting targets in an adjacent compartment. The multi-compartment corridor 

considered in this scenario consists of interconnected rooms and corridors in the same level. 

These geometries may have soffits between the connecting rooms. The source of a fire in this 

 

2 Some NPPs (typically in warmer climates) do not have a turbine building, and the main turbine is open 

to the elements. 
Technical Approach 

2-7 

scenario may be ignition of an oil pool spilled from a pump in one of the adjacent rooms. The 

size of the fire will depend on the type and amount of oil spilled, as well as the area and depth of 

the pool itself. The growth of this fire typically will be fast, and depending on the size of the 

room, the fire could potentially generate flashover conditions in the room of origin, and fire 

effluent may spill out and effect targets in adjacent rooms. The ventilation conditions will be 

natural ventilation, with leakage paths between compartments around normally closed doors. 

There may also be mechanical ventilation using both injection and extraction systems. Targets 

of interest in these scenarios are often safety-related equipment and cables located in the corridor 

outside the room of fire origin, or an adjacent room. 

[Figure TBD]

Figure 2-7: Typical Multi-Compartment Corridor Fire Scenario 

2.1.7 Multi-Level Building 

A typical NPP has locations where multiple elevations in the same building are separated by 

partial floors/ceilings, open hatches, or staircases. Typical examples include turbine buildings, 

pressurized-water reactor (PWR) auxiliary buildings, and boiling-water reactor (BWR) 

buildings. The multi-level turbine building in this scenario is a three-level space that includes 

the turbine deck. (Section 2.1.5 describes a turbine deck fire scenario.) This scenario consists of 

an oil spill fire affecting targets located on a different level. Figure 2-8 graphically represents 

the scenario, which can apply to turbine buildings with one or more units. The source of a fire in 

this scenario may be ignition of an oil pool spilled from an oil tank located under one of the 

turbine generators. The size of the fire will depend on the type and amount of oil spilled, as well 

as the area and depth of the pool itself. The energy and smoke created will flow through 

mezzanine opening between levels. The growth of this fire will be fast. The ventilation 

conditions will be natural ventilation via opening on the upper level. There may also be 

mechanical ventilation using roof-mounted exhaust fans and/or mechanical supply. Targets of 

interest in these scenarios may be cables in cable tray located on the upper levels. 

[Figure TBD] 

Figure 2-8: Typical Multi-Level Building Fire Scenario 

2.1.8 Containment Building (PWR) 

The containment building in a PWR plant was selected because of its geometrical characteristics, 

which include cylindrical boundaries, high domed ceiling, and a large volume. This scenario 

involves an oil spill fire from the reactor coolant pump (RCP). The size of the fire will depend 

on the type and amount of oil spilled, as well as the area and depth of the pool itself. The 

containment in a PWR has internal air recirculation systems with cooling units. There is no fresh 

air added into the containment atmosphere during normal operation. The target of interest in this 

scenario is an elevated cable tray located outside the fire plume. 
Technical Approach 

2-8 

2.1.9 Battery Room 

Battery rooms are usually relatively small concrete rooms with two or more large banks of batteries. 

These rooms are kept closed and are typically free of transient combustibles and fixed ignition 

sources other than the batteries. The scenario consists of a battery fire attributable to a hydrogen 

leak. The size of the fire depends on the amount of hydrogen released and the environmental 

conditions in the room at the time of the leak. The ventilation conditions will be mechanical 

ventilation. The targets of interest in this scenario are cables and batteries. 

2.1.10 Diesel Generator Room 

Diesel generator rooms are relatively medium-sized rooms, which house the standby diesel generator 

(SBDG) and associated electrical cabinets. This scenario consists of a fuel oil fire near the diesel 

generator. The size of the fire will depend on the type and amount of fuel oil spilled, as well as 

the area and depth of the pool itself. The growth of this fire will be fast. The ventilation 

conditions in the room will be mechanical ventilation with leakage around closed doors. Targets 

of interest in these scenarios may be cables located in the room exposed to HGL temperatures. 

2.1.11 Computer Room 

Computer rooms are typically located in close proximity to the main control rooms in NPPs. 

In addition to computers and other office equipment, some computer rooms may house control 

cabinets. The ignition source for this scenario is a transient combustible fire, namely a computer 

workstation. The size of the fire will depend on the amount and type of materials involved. The 

ventilation conditions will be mechanical ventilation. The targets of interest may be a control 

cabinet or cables above the fire. 

2.1.12 Outdoors 

Outdoor fire scenarios can involve large oil-filled transformers or hydrogen tanks and can affect 

or propagate to nearby equipment. The fire ignition source in this scenario is oil dripping from a 

transformer in the switchyard. The size of the fire will depend on the type and amount of oil 

spilled, as well as the area, depth of the pool itself, as well as the substrate onto which the oil was 

spill. The growth of this fire will be fast. The target of interest is an adjacent transformer. 

2.2 Fire Models 

There are numerous fire models that have been developed and maintained by various 

organizations to predict fire-generated conditions. This study selects five of these fire models 

that represent a wide range of capabilities and mathematical and computational sophistication. 

These fire models are: 

• Two libraries of engineering calculations: FDTs

 and FIVE-Rev1 

• Two two-zone models: CFAST and MAGIC 

• One field model: FDS 

These particular models were chosen based on the fact that most of them have been used fairly 

extensively to calculate fire conditions in NPP fire protection applications, or were developed by 
Technical Approach 

2-9 

stakeholders within the nuclear industry for NPP fire protection applications. FDS was chosen to 

represent the most complex types of models available for fire protection applications. 

2.2.1 Libraries of Engineering Calculations: FDTs

 and FIVE-Rev1 

FDTs

 is a library of engineering calculations (also referred to as hand calculations) in the form of 

Microsoft® Excel® spreadsheets. For the most part, the models in the FDTs

 library are closed form 

algebraic expressions programmed in spreadsheets to provide a user-friendly interface 

that reduces input and computational errors. Technical details concerning the engineering 

calculations and use of the spreadsheets are available in NUREG-1805 [Ref. 6]. 

FIVE-Rev1 is another library of engineering calculations in the form of Microsoft® Excel®

spreadsheets. Specifically, FIVE-Rev1 library consists of functions programmed in Visual Basic 

for Applications, which is the programming language within Excel. Having the models 

programmed as Microsoft Excel functions allows the use of Excel spreadsheets as the interface. 

Technical details concerning the engineering calculations and their use in the Excel environment 

are available in EPRI TR-1002981 [Ref. 5]. 

The FDTs

 and FIVE-Rev1 libraries include different models, and some of those models were not 

evaluated for this V&V study, due to applicability and a lack of experimental data. The fire 

scenario attributes that were selected for this study (see section 2.4 for the description of these 

attributes) are those that are used in NPP fire modeling applications. For the most part, these 

selected models are included in both libraries. 

Table 2-1: FDTs and FIVE-Rev1 Models for the Fire Scenario Attributes Selected for this V&V 

Study 

Attribute (See Section 2.4) FDTs FIVE-Rev1 

1. Hot gas layer temperature MQH, FPA, Beyler, Beyler & 

Deal MQH, FPA 

2. Hot gas layer height Yamana & Tanaka No model 

3. Ceiling jet temperature No model Alpert’s ceiling jet 

temperature correlation 

4. Plume temperature Heskestad’s plume 

temperature correlation 

Heskestad’s plume 

temperature correlation 

5. Flame height Heskestad’s flame height 

correlation 

Heskestad’s flame height 

correlation 

6. Radiated heat flux to targets Point source flame radiation 

model 

Point source flame radiation 

model 

2.2.2 Two-Zone Fire Models: CFAST and MAGIC 

Fire modeling programs that were developed under the assumption that a fire will generate two 

distinct zones with uniform thermal properties are referred to as two-zone models. This V&V 

study evaluated two two-zone models, CFAST and MAGIC. 
Technical Approach 

2-10 

CFAST [Ref. 8] is a two-zone fire model that predicts the environment that arises within 

compartments as a result of a fire prescribed by the user. CFAST was developed and is 

maintained primarily by the Fire Research Division of the National Institute of Standards and 

Technology (NIST). In terms of modeling capabilities, CFAST provides the average 

temperatures of the upper and lower gas layers within each compartment; flame height; ceiling, 

wall, and floor temperatures within each compartment; flow through vents and openings; visible 

smoke and gas species concentrations within each layer; target temperatures; heat transfer to 

targets; sprinkler activation time; and the impact of sprinklers on the fire HRR. 

MAGIC [Ref. 9] is a two-zone fire model developed and maintained by Electricité de France 

(EdF). It is available through EPRI to its members. In terms of modeling capabilities, MAGIC 

predicts (1) environmental conditions in the room (such as hot gas layer temperature, and 

oxygen/smoke concentrations), (2) heat transfer-related outputs to walls and targets (such as 

incident convective, radiated, and total heat fluxes), (3) fire intensity and flame height, and 

(4) flow velocities through vents and openings. 

2.2.3 Field Fire Model: FDS 

FDS [Ref. 10] is a computational fluid dynamics (CFD) model of fire-driven fluid flow. 

The model numerically solves a form of the Navier-Stokes equations appropriate for low-speed, 

thermally-driven flow, with an emphasis on smoke and heat transport from fires. The partial 

derivatives of the equations for conservation of mass, momentum, and energy are approximated 

as finite differences, and the solution is updated in time on a three-dimensional, rectilinear grid. 

Thermal radiation is computed using a finite volume technique on the same grid as the flow solver. 

Lagrangian particles are used to simulate smoke movement and sprinkler discharge. 

FDS computes the temperature, density, pressure, velocity, and chemical composition within 

each numerical grid cell at each discrete time step. There are typically hundreds of thousands 

to several million-grid cells, and thousands to hundreds of thousands of time steps. In addition, 

FDS computes the temperature, heat flux, mass loss rate, and various other quantities at solid 

surfaces. 

2.3 Experimental Data 

This section provides a general overview of the tests series and experiments selected for this study. 

Volume 7 augments this overview by providing detailed descriptions of these experiments. 

Some test series included many experiments, from which only a few were chosen for this V&V 

study. One overriding reason for this is the sheer amount of data that is generated and must be 

processed can be overwhelming, so limiting the number of experiments to consider was 

necessary. The experiments within the test series that were chosen are representative of the 

overall series of tests, as well as representative of the fire scenarios in NPPs listed above. 

Volume 7, Section 1.2 has a more complete explanation for the selection of the experiments. 

2.3.1 Factory Mutual & Sandia National Laboratories (FM/SNL) Test Series 

A series of fire tests was conducted at Sandia National Laboratories under the sponsorship of the 

NRC in the mid-1980s. Specifically tests were conducted using simple gas-fired burner, heptane 

pool, methanol pool, and solid polymethyl-methacrylate (PMMA) fires. Four (4) of these tests 

were conducted with a full-scale control room mockup in place. Parameters varied during 
Technical Approach 

2-11 

testing were fire intensity, enclosure ventilation rate, and fire location. The primary purpose at 

the time of these tests was to provide data for use in validating computer fire environment 

simulation models that would subsequently be used in analyzing NPP enclosure fire scenarios, 

specifically MCR scenarios. 

These tests were conducted in an enclosure measuring 18.3 m x 12.2 m x 6.1 m (60 ft x 40 ft x 

20 ft), which was constructed at the Factory Mutual Research Corporation fire test facility in 

Rhode Island. All of the tests utilized forced ventilation conditions. The ventilation system was 

designed to simulate typical NPP installation practices and ventilation rates. 

NUREG/CR-4681 [Ref. 11] provides a detailed description of the FM/SNL test series, including 

the types and location of measurement devices as well as some results. Additional results 

are reported in NUREG/CR-5384 [Ref. 12]. 

This study used data from only the three tests with data reported in NUREG/CR-4681 (namely 

FM/SNL Tests 4, 5, and 21). For all three tests, the fire source was a propylene gas-fired burner 

with a diameter of approximately 0.9 m (2.95 ft), with its rim located approximately 0.1 m (0.33 

ft) above the floor. For FM/SNL Tests 4 and 5, the burner was centered along the longitudinal 

axis centerline, 6.1 m (20 ft) laterally from the nearest wall. For FM/SNL Test 21, the burner 

was placed within simulated benchboard electrical cabinets. 

2.3.2 The National Bureau of Standards (NBS) Test Series 

A total of 45 tests representing 9 different sets of experiments, with multiple replicates of each set, 

were conducted in a three-room suite that is described in detail in NBSIR 88-3752 [Ref. 13]. 

The suite consisted of two relatively small rooms, designated here as Rooms 1 and 3, which were 

connected via doorways and short connecting passageways to a relatively long corridor, 

designated as Room 2. Rooms 1 and 3 opened only onto the corridor (Room 2) via doorways; 

they did not open to the external environment other than through normal construction leakage paths. 

The corridor had a doorway to the external environment, as well as doorways to Rooms 1 and 3. 

The fire source, a gas-fired burner, was located against the rear wall of Room 1. The following 

parameters were varied in the 9 different sets of experiments: 

• fire size, including nominal 100, 300, and 500 kW fires 

• door positions, including open and closed doors between the corridor and Room 3, as well as 

between the corridor and the external environment 

In this study, the tests designated as Sets 1, 2, and 4 in NBSIR 88-3752 are used for comparison. 

All three of these sets had a fire source intensity of 100 kW, but the sets differed based on door 

position. Specifically, the door between Rooms 1 and 2 was open for all three sets. However, 

for Set 1, the door between Room 2 and the external environment was open (providing a source 

of fresh air to the suite), while the door between Rooms 2 and 3 was closed (effectively isolating 

Room 3 from this test). By contrast, for Set 2, the door between Room 2 and the external 

environment was closed, as was the door between Rooms 2 and 3 (again isolating Room 3). 

For Set 4, the door between Room 2 and the external environment was open (again providing 

a source of fresh air to the suite), as was the door between Rooms 2 and 3. 

Experimental data used for these comparisons was obtained in electronic format from NIST. 

These data were converted to spreadsheet format for tests designated as MV100A through 
Technical Approach 

2-12 

MV100AB. Average values for the nine data sets were also converted to spreadsheet format, 

but were not used for these comparisons. Rather, an exemplar test was selected from each data set 

for comparison purposes. Specifically, Test MV100A was used for Set 1, Test MV100O 

was used for Set 2, and Test MV100Z was used for Set 4. The selected data are also available 

in EPRI’s Fire Modeling Code Comparison TR-108875 [Ref. 14]. 

2.3.3 The International Collaborative Fire Model Project (ICFMP) Benchmark 

Exercise Test Series 

To date, four full-scale fire test series have been completed as part of the ICFMP. The ICFMP is 

a separate, but related, project designed to perform some validation of fire models from around 

the world. ICFMP participants conduct a series of experiments and provide the data to other 

participants in order to compare fire model outputs to experimental data. These test series are 

referred to as benchmark exercises (BE). This V&V study includes experimental data from BEs 

#2, 3, 4, and 5. A brief description of each follows: 

• BE #2 [Ref. 15]: The ICFMP objective of BE #2 was to examine scenarios that are more 

challenging for zone models. In particular, these scenarios included fires in larger room 

volumes that are representative of turbine halls in nuclear power plants. The tests were 

conducted inside the VTT Fire Test Hall, which has dimensions of 19 m high by 27 m long 

by 14 m wide. Each case involved a single heptane pool fire, ranging from 2 MW to 4 MW. 

• BE #3 [Ref. 16]: This ICFMP exercise comprised a series of 15 large-scale fire tests, 

sponsored in part by the NRC, that were performed at NIST between June 5 and 20, 2003. 

These tests consisted of 350 kW, 1.0 MW, and 2 MW fires in a marinite room with 

dimensions of 21.7 m x 7.15 m x 3.7 m (71.2 ft x 23.5 ft x 12.1 ft). The room had one door 

with dimensions of 2 m x 2 m (6.6 ft x 6.6 ft), and a mechanical air injection and extraction 

system. Ventilation conditions and fire size were varied among the 15 tests. The numerous 

experimental measurements included temperatures in gas layers and surfaces, heat fluxes, 

and gas velocities, among others. 

• BE #4 [Ref. 17]: This test series was conducted at the Institut Für Baustoffe, Massivbau Und 

Brandschutz (iBMB), in Germany. Each of these tests simulated a relatively large fire in a 

relatively small concrete room. Only one test from this series was selected for this study. 

• BE #5 [Ref. 18]: This exercise, which was conducted at the iBMB in Germany, consisted of 

four large-scale tests inside the same concrete enclosure as BE #4 with realistically routed 

cable trays. Only one test was selected for this study. 
Technical Approach 

2-13 

2.4 Selection of Fire Scenario Attributes 

A complete V&V of a particular model for a given NPP fire scenario may not be possible 

because (1) the availability of experimental data is limited, and/or (2) a selected tool has limited 

modeling capabilities. Therefore, this implementation of ASTM E1355 is intended to benefit 

as much as possible from the available data to establish the modeling capabilities and limitations 

of the selected fire models in typical NPP fire scenarios. 

An important consideration in evaluating the capabilities of fire models in NPPs is the range of 

fire scenarios for which the models may be used. From a fire modeling perspective, most NPPs 

have similar configurations and fire hazards. That is, fire scenarios are characterized by similar 

attributes. Consequently, the V&V project team developed the following list of typical NPP fire 

modeling attributes, which provided the basic framework for conducting the V&V study and 

classifying the quantitative results: 

(1) Hot gas layer temperature: The hot gas layer temperature is particularly important in 

NPP fire scenarios because it can provide an indication of target damage away from 

the ignition source. Models predict the increase in environmental temperature attributable 

to the energy released by a fire in a volume. However, different models define this volume 

in different ways. In the FDTs

 and FIVE-Rev1 models available for predicting hot gas 

layer temperature, the assumed volume is the volume of the room and the output is a 

uniform room temperature. In the CFAST and MAGIC two-zone models, the room is 

divided into upper and lower control volumes. Thus, the hot gas layer temperature output 

from these two-zone models is a uniform temperature in the upper control volume (which 

is referred to as the hot gas layer because it accumulates hot gases that are transported to 

the upper part of the room by the fire plume). Finally, in the FDS field model, the room is 

divided into numerous control volumes. Thus, FDS can provide outputs for the average 

temperature of the control volumes in the upper layer of the computational domain, as 

determined by a reduction of temperature profile data. 

(2) Hot gas layer height: The height of the hot gas layer is also important in NPP fire scenarios 

because it indicates whether a given target is immersed in and affected by hot gas layer 

temperatures. The concept of hot gas layer height is most relevant in two-zone models 

(CFAST and MAGIC), in which this attribute defines the interface between the upper and 

lower control volumes. The FDS field model also provides the hot gas layer height output, 

which is calculated from the temperature profile within the height of the room. In addition, 

the FDTs

 library includes one model that predicts hot gas layer height before the layer 

reaches a vent, assuming steady-state fire conditions in the room. The FIVE-Rev 1 library 

does not have a model for predicting hot gas layer height in the scenarios evaluated in this 

V&V study. 

(3) Ceiling jet temperature: The ceiling jet is the shallow layer of hot gases that spreads 

radially below the ceiling as the fire plume flow impinges on it. This layer of hot gases has 

a distinct temperature that is higher than the temperature associated with the hot gas layer. 

This attribute is important in NPP fire scenarios that subject targets to unobstructed ceiling jet 

gases. The FIVE-Rev1 and MAGIC models calculate ceiling jet temperature using a semiempirical correlation, and the ceiling jet temperature can be obtained from the FDS model 

by inspecting the temperature profile in the pre-defined grid. The FDTs

 library does not 
Technical Approach 

2-14 

include a model for calculating ceiling jet temperature, and the CFAST model does not 

provide ceiling jet temperature as a direct output. 

(4) Plume temperature: The fire plume is the buoyant flow rising above the ignition source, 

which carries the hot gases that ultimately accumulate in the upper part of a room to form 

the hot gas layer. The plume is characterized by a distinct temperature profile, which is 

expected to be higher than the ceiling jet and hot gas layer. This attribute is particularly 

important in NPP fires because of the numerous postulated scenarios that involve targets 

directly above a potential fire source. Models in the FDTs

 and FIVE-Rev1 libraries predict 

fire plume temperatures using closed form semi-empirical correlations, and the MAGIC 

model predicts plume temperatures in a similar manner. The plume temperature can also 

be obtained from the FDS model by inspecting the temperature profile in the pre-defined 

grid. The CFAST model does not provide plume temperatures as an output. 

(5) Flame height: The height of the flame is important in those NPP fire scenarios where 

targets are located close to the ignition source. Some of these scenarios subject the target 

to flame temperatures because the distance between the target and the ignition source is 

less than the predicted flame height. A typical example would be cable trays above an 

electrical cabinet. Models in the FDTs and FIVE-Rev 1 libraries predict flame height using 

a close form semi-empirical correlation. MAGIC and CFAST models also predict flame 

height in a similar manner. The FDS combustion model has the capability to calculate 

flame height. 

(6) Radiated heat flux to targets: Radiation is an important mode of heat transfer in fire 

events. The modeling tools within the scope of this study address fire-induced thermal 

radiation (or radiated heat flux) with various levels of sophistication, from simply estimating 

flame radiation, to calculating radiation from different surfaces and gas layers in the 

computational domain. The FDTs and FIVE-Rev1 libraries include models for calculating 

flame radiation at a specified distance from the flames. By contrast, CFAST, MAGIC, 

and FDS have sophisticated heat transfer models that account for radiation exchanges 

between room surfaces and the upper and lower gas layers. Therefore, the incident thermal 

radiation to which a given target is exposed is a result of the heat balance at the surface of 

the target (which includes all of the exchanges), as well as the thermal radiation received 

from the flames. 

(7) Total heat flux to targets: In contrast to thermal radiation (or radiated heat flux), the total 

heat flux a target is subjected includes convective heat transfer. Convective heat transfer is a 

significant contributor to target heat-up in scenarios that involve targets in the hot gas layer, 

ceiling jet, or fire plume. The CFAST and MAGIC two-zone models and the FDS field 

model account for convection, although CFAST (in particular) does not model target 

heating in the plume and ceiling jet sub-layers. The heat transfer models in the FDTs

 and 

FIVE-Rev1 libraries do not account for convective heat transfer. 

(8) Total heat flux to walls: This attribute is generally identical to “total heat flux to targets” 

(above). Nonetheless, it was included as a separate attribute in this V&V study in order to 

evaluate model capabilities to determine the incident heat flux to walls, floors, and ceilings, 

which includes the contributions of radiation and convection. Because the heat conducted 

through the walls, floors, and ceilings does not contribute to room heat-up, it can be 

an important factor in the heat balance in control volume(s) in contact with the surfaces. 
Technical Approach 

2-15 

Of the models within the scope of this study, only the CFAST and MAGIC two-zone models 

and the FDS field model calculate total heat flux to walls, floors, and ceilings. 

(9) Wall temperature: This attribute was included as a separate attribute in this V&V study 

to evaluate model capabilities to determine the temperature of walls, floors, and ceilings. 

Of the models within the scope of this study, only the CFAST and MAGIC two-zone models 

and the FDS field model provide the temperatures of these surfaces as outputs, since such 

outputs are part of the calculations required to determine the heat losses through 

boundaries. 

(10) Target temperature: The calculation of target temperature is perhaps the most common 

objective of fire modeling analyses. The calculation of target temperature involves an 

analysis of localized heat transfer at the surface of the target after determining the fireinduced conditions in the room. The CFAST and MAGIC two-zone models and the FDS 

field model calculate the surface temperature of the target as a function of time, and 

consider the heat conducted into the target material. By contrast, the available model in the 

FIVE-Rev1 library assumes a constant incident heat flux and a semi-infinite solid. The 

FDTs

 library does not include a model for estimating target temperature. 

(11) Smoke concentration: The smoke concentration can be an important attribute in NPP fire 

scenarios that involve rooms where operators may need to perform actions during a fire. 

This attribute specifically refers to soot concentration, which affects how far a person can 

see through the smoke (visibility). The CFAST and MAGIC two-zone models and the FDS 

field model calculate smoke concentration as a function of time. These models determine smoke 

concentration as the fire plume carries combustion products into the hot gas layer. FDTs

and FIVE-Rev1 libraries do not contain direct outputs of smoke concentration. 

(12) Oxygen concentration: Oxygen concentration is an important attribute potentially 

influencing the outcome of fires in NPPs due to compartmentalized nature of nuclear power 

plants. Oxygen concentration has a direct influence on the burning behavior of a fire, 

especially if the concentration is relatively low. The CFAST and MAGIC two-zone 

models calculate the oxygen concentration in the upper and lower layers, and the FDS 

model calculates the oxygen concentration in each control volume defined in the 

computational domain. The FDTs and FIVE-Rev1 libraries do not include models for 

calculating oxygen concentration. 

(13) Room pressure: Room pressure is a rarely used attribute in nuclear power plant fire 

modeling. It may be important when it contributes to smoke migration to adjacent 

compartments. CFAST, MAGIC and FDS calculate room pressure as they solve energy 

and mass balance equations in the control volume. FDTs

 library has a model for a sealed 

compartment that is not validated in this study. FIVE-Rev1 library does not have 

correlation to calculate room pressure. 
Technical Approach 

2-16 

Table 2-2: Fire Modeling Attributes as Outputs 

Fire Models 

Fire Modeling Attributes 

FDTs

 FIVE CFAST MAGIC FDS 

Hot Gas Layer Temperature Yes Yes Yes Yes Yes 

Hot Gas Layer Height Yes No Yes Yes Yes 

Ceiling Jet Temperature No Yes No Yes Yes 

Plume Temperature Yes Yes No Yes Yes 

Flame Height Yes Yes Yes Yes Yes 

Radiated Heat Flux to Targets Yes Yes Yes Yes Yes 

Total Heat Flux to Targets No No Yes Yes Yes 

Total Heat Flux to Walls No No Yes Yes Yes 

Wall Temperature No No Yes Yes Yes 

Target Temperature No No Yes Yes Yes 

Smoke Concentration No No Yes Yes Yes 

Oxygen Concentration No No Yes Yes Yes 

Room Pressure No No Yes Yes Yes 
Technical Approach 

2-17 

2.5 Quantitative Validation 

In keeping with the guidance in the ASTM E1355 and the objectives of this study, the following 

approach was used for quantification of the results of the validation of the selected fire models. 

The numerical comparison between an experimental observation and a corresponding model 

prediction is referred to as “relative difference” throughout this report. Relative differences have 

been calculated for each of the attributes listed in Section 2.4 using point estimate peak values 

from fire experiments and model predictions. The following equation has been selected for 

relative difference calculations: 

( ) ( )

( ) p o

p o p o

E E

M M E E

E

M E

−

− − − = ∆

∆ − ∆

ε =

where ∆M is the difference between the peak value (Mp) of the model prediction and the ambient 

value (Mo), and ∆E is the difference between the experimental observation (Ep) and the ambient 

value (Eo). 

Table 2-3 summarizes the fire experiments and instruments used for quantitative validation of 

the different fire modeling parameters. The graphical comparisons of measured and predicted 

fire generated condition profiles and calculated relative differences for each of the five fire 

models are detailed in Appendix A to Volumes 2 through 6. This information is the basis for the 

conclusions summarized in this volume. 
Technical Approach 

2-18 

Table 2-3: Summary of the Fire Tests Used for Validation against Typical NPP Fire Scenario Attrib

Selected Test Series/Experiments/Sensors 

ICFMP BE #3 ICFMP BE #5 FM/SNL ICFMP BE #4 ICFMP 

Fire Modeling Parameters 

Tests 1-5, 7-10, 13-18 Test 4 Tests 4,5, & 21 Test 1 Part I, C

1, 2

1. HGL temperature Vertical thermocouple arrays Vertical thermocouple arrays Vertical thermocouple arrays Vertical thermocouple arrays Vertical thermoc

arrays 

2. HGL height Vertical thermocouple arrays Vertical thermocouple arrays Vertical thermocouple arrays Vertical thermocouple arrays Vertical thermoc

arrays 

3. Ceiling jet temperature Thermocouple NA Thermocouple NA NA 4. Plume temperature NA NA Thermocouple NA Thermoc5. Flame height Pictures No Data No Data No Data Pictures 6. Radiant heat flux to target 

(cables) Radiometers No Data No Data No Data No Data 

7. Total heat flux to targets Heat Flux Gauges Heat Flux Gauges No Data Heat Flux Gauges No Data 8. Total heat flux to walls Heat Flux Gauges No Data No Data No Data No Data 9. Wall surface temperature Thermocouples Thermocouples No Data Thermocouples No Data 10. Target (cable) surface 

temperature Thermocouples Thermocouples No Data Thermocouples No Data 
Selected Test Series/Experiments/Sensors 

ICFMP BE #3 ICFMP BE #5 FM/SNL ICFMP BE #4 ICFMP 

Fire Modeling Parameters 

Tests 1-5, 7-10, 13-18 Test 4 Tests 4,5, & 21 Test 1 Part I, C

1, 2

11. Smoke concentration Smoke Obs./Conc. No Data No Data No Data No Data 12. Oxygen concentration Oxygen meter Oxygen meter No Data Flawed Data No Data 13. Room pressure Pressure transducer No Data No Data No Data No Data 
Technical Approach 

2-20 

2.6 Reporting and Applicability of the Validation Results 

Section 2.1 of this Volume listed typical nuclear power plant fire scenarios. The validation 

results of this study are limited by the general characteristics of the fire experiments selected. 

Consequently, the validation results need to be identified as corresponding to specific NPP fire 

scenarios to determine its applicability. 

In general, the use of the quantitative results of this validation in support of fire modeling 

requires the following two steps: 

1. Applicability of V&V Results - First, the user needs to assess the applicability of the 

validation results for the scenario under consideration, and 

2. Characterization of fire model predictions based on the V&V results – Once the user 

determines the applicability of the validation, the user must determine the level of confidence 

in the model prediction based on the quantitative results of this validation. 

2.6.1 Applicability of the V&V Results 

The following is one method that may be used to determine applicability of these validation 

results to other scenarios of interest. The description of this method is reported here to 

demonstrate the rigor users should use in determining applicability of these validation results. 

Other methods may be appropriate. 

The applicability of the validation results can be determined using normalized parameters 

traditionally used in fire modeling applications. Normalized parameters allow users to compare 

results from scenarios of different scales by normalizing physical characteristics of the scenario. 

Table 2-4 lists selected normalized parameters that may be used to compare encountered 

scenarios with the experiments used in this validation study. It is intended to provide guidance 

on which groups to consider when evaluating a certain attribute based on the validation results. 

Table 2-5 lists the ranges of values for different physical characteristics and normalized 

parameters based on the experiments considered in this validation study. 

The user could calculate the normalized parameters that are relevant to the fire scenario being 

evaluated. If the parameters fall within the ranges evaluated in this validation, then the results of 

this study offer appropriate validation for the scenario. If they fall outside the range, then a 

validation determination cannot be made based on the results in this study. For any given fire 

scenario, more than one normalized parameter may be necessary for determining applicability of 

the validation results.
Technical Approach 

2-21 

Table 2-4: List of selected normalized parameters for application of the validation results 

to NPP fire scenarios 

Parameter Normalized Parameter 

HGL Temp 

HGL Height 

Ceiling Jet Temp 

Plume Temp 

Flame Height 

O2 Conc. 

Room Press 

Heat release 

rate 2

*

c T gDD

Q Q

∞ p ∞

= ρ

& , X 

Fire 

diameter 

2/5

*

⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛

=

∞c T∞ g

Q D

ρ p

& X X X X 

Room/Target 

height * D

H X X 

Ceiling jet 

radial 

distance H

r X 

Natural 

Ventilation 

r

Q H A h

r

m m c 2

1 0.23

F O2

∆ ×

= =

& & & φ ,

AND 

A H c T g

Q Q

o o ∞ p ∞

= ρ

& *

X X (1) (1) X X 

Mechanical 

Ventilation 

r

Q H V

r

m m c & & & & 2

1 0.23

F O2

∆ ×

φ = =

X X (1) (1) X X 

Notes: 

(1) These parameters should be checked for ceiling-jet and plume temperature calculations when 

assuming well-ventilated compartment. 
Technical Approach 

2-22 

Following paragraphs describe each of the normalized parameters. 

Heat Release Rate (HRR orQ& ): The most important parameter of any fire experiment is the 

heat release rate. In some cases, the fire model is used to predict the HRR. Here, however, the 

HRR is given, and the model is used to predict how the fire’s energy is transported throughout 

the space of interest. A normalized quantity relating the HRR to the diameter of the fire, D, is 

commonly known asQ * : 

2

*

c T gDD

Q Q

∞ p ∞

= ρ

&

Where: Q& is the heat release rate (kW), 

ρ ∞ is the ambient density (kg/m3), 

T∞ is the ambient temperature (K), 

p c is the specific heat (kJ/kg-K), 

g is the acceleration of gravity (m/s2), and 

D is the diameter of the fire (m). 

A large value of Q* describes a fire whose energy output is relatively large compared to its 

physical diameter, like an oil well blowout fire. A low value describes a fire whose energy 

output is relatively small compared to its diameter, like a brush fire. Most conventional 

accidental fire scenarios have Q* values on the order of 1. Its relevance to the current validation 

study is mainly in the assessment of flame height. 

Fire Diameter: The physical diameter of the fire is not always a well-defined property. A 

typical compartment fire may not have a well-defined diameter, whereas a circular pan filled 

with a burning liquid fuel has an obvious diameter. Fortunately, it is not the physical diameter of 

the fire that matters when assessing the “size” of the fire, but rather a characteristic diameter, D*: 

2/5

*

⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛

=

∞c T∞ g

Q D

ρ p

&

In many instances, D* is comparable to the physical diameter of the fire (in which case Q* is on 

the order of 1). This group should be used when the fire scenario consists of a fire with a given 

diameter. A good example application is the evaluation of validation results for unconfined oil 

spill fire scenarios. 

Room Height: The quantities Q* and D* relate the fire’s HRR to its physical dimensions. The 

height of the compartment relative to D* indicates the relative importance of the fire plume to 

the overall transport of the hot gases. Much of the mixing of fresh air and combustion products 

takes place within the plume, and this dilution of the smoke and the decrease in the gas 

temperature ultimately determines the hot gas layer temperature. Thus, the parameter H/D* can 

be used to assess the importance of the plume relative to other features of the fire-driven flow, 
Technical Approach 

2-23 

like the ceiling jet or doorway flow. This group is appropriate for evaluating applicability of 

validation results for scenarios involving targets inside the fire plume. 

Ventilation: It is important to know whether a given compartment fire is limited by its fuel 

supply or by its oxygen supply. In all six test series, the fuel supply was specified as a test 

parameter. The oxygen supply was controlled either by the size of the compartment opening or 

by the flow rate of the ventilation system. Although less precise, it is possible to estimate the 

mass flow of oxygen for each test configuration. Where there is a door to the compartment, an 

estimate of the maximum achievable oxygen supply is given by: 

m A h

2

1 0.23 O2

& = ×

Where: A is the area of the opening (m2

) 

h is its height (m), and 

0.23 is the mass fraction of oxygen in air. 

Note that in many of the test series under consideration, this theoretical mass flow of oxygen was 

not achieved because the fires were of short duration. However, the estimate is useful for this 

exercise. 

For an active ventilation system, the mass flow rate of oxygen is approximately 

m V& & O air 0.23 2 = × ρ

Where: ρair is the density of the air (kg/m3

), and 

 V& is the ventilation rate (m3

/sec) 

Of course, not all of the air supplied by the ventilation system would reach the fire, especially for 

ceiling-mounted supply ducts. 

The global equivalence ratio,φ , is the ratio of the mass flow of fuel to the mass flow of oxygen, 

normalized by the stoichiometric ratio, r. The estimated values of φ in the table below are based 

on the maximum fuel and oxygen flow rates for the given test series. The values are all 

considerably less than one, meaning that these fires would be characterized as well- or overventilated. The test with the highest value of φ is ICFMP BE #4, Test 1, which has an 

equivalence ratio of about 0.6. It is also notable in that its HRR to volume ratio is about an order 

of magnitude larger than all the other test series. Although still over-ventilated, the fire is 

relatively large with respect to its compartment volume. All of the other fires could be 

characterized as relatively small with respect to the compartment. 
Technical Approach 

2-24 

Table 2-5: Summary of the fire experiments in terms of commonly used metrics 

Test Series Q&

(kW) 

Q* 

D 

(m) 

D* 

(m) 

H 

(m) H/D* 

V

(m3) O2

m&

(kg/s) 

φ

ICFMP BE #2 1800--3600 1.0 1.2, 1.6 1.2-3.6 19 12-16 5900 3.0 0.1 

ICFMP BE #3 400--2300 0.4-1.9 1.0 0.7-1.3 3.8 3-5 580 0.6 0.3 

ICFMP BE #4 3500 2.6 1.1 1.6 5.7 3.6 74 0.4 0.6 

ICFMP BE #5 400 0.7 0.8 0.7 5.6 8 73 0.3 0.1 

FM/SNL 500 0.5 0.9 0.7 6.1 9 1400 1.3 0.03 

NBS MultiRoom 

100 1.5 0.34 0.4 2.4 6 15 0.2 0.05 

2.6.2 Characterization of Fire Model Predictions Based on Validation Results 

Once the user determines the validation results reported here are applicable (see section 2.6.1), 

the user must determine the predictive capability of the fire models. The capability is 

characterized based on the quantitative results of the validation study and judgment of the V&V 

project team using criteria described below. 

The process of deducing the predictive capability of the model from the quantitative results is 

documented in volumes 2 through 6 of this report. Appendix A to each volume contains detailed 

comparisons of model prediction and experimental measurements. Chapter 6 of these volumes 

describes how these quantitative results were used to arrive at the characterization of predictive 

capability of the model using the approach described below. 

The following two criteria are used to characterize the predictive capability of the model: 

Criterion 1 - Are the physics of the model appropriate for the calculation being made? This 

criterion reflects an evaluation of the underlying physics described by the model and the physics 

of the fire scenario. Generally the scope of this study is limited to the fire scenarios that are 

within the stated capability of the selected fire models, e.g., this study does not address the fire 

scenarios that involve flame spread within single and multiple cable trays. 

Criterion 2 - Are there calculated relative differences outside the experimental uncertainty? This 

criterion is used as an indication of the accuracy of the model prediction. Since fire experiments 

are used as a way of establishing confidence in model prediction, the confidence can only be as 

good as our experiments. Therefore, if model predictions fall within the ranges of experimental 

uncertainties, the predictions are determined to be accurate. However, one should recognize that 

the experimental uncertainties vary with the experiment and the attribute being measured (see 

volume 7 of this report). These ranges could be as much as +50% for the experiments and 

attributes we used in this validation study. This leads to some judgment about the relative 

difference proximity relative to the range of uncertainty, as the uncertainty ranges are not 

necessarily all-inclusive or definitive. 

The predictive capability of the model is characterized as follows based on the above criteria. 
Technical Approach 

2-25 

GREEN: If both criteria are satisfied, i.e., the model physics are appropriate for the calculation 

being made and the calculated relative differences are within or very near experimental 

uncertainty, then the V&V team concluded that the fire model prediction is accurate for the 

ranges of experiments in this study, and as described in tables 2-4 and 2-5. A grade of GREEN 

indicates the model can be used with confidence to calculate the specific attribute. The user 

should recognize, however, that the accuracy of the model prediction is still somewhat uncertain 

and for some attributes, such as smoke concentration and room pressure, these uncertainties may 

be rather large. 

YELLOW±: If the first criterion is satisfied and the calculated relative differences are outside 

the experimental uncertainty but indicate a consistent pattern of model over-prediction or underprediction, then the model predictive capability is characterized as YELLOW+ for overprediction, and YELLOW– for under-prediction. The model prediction for the specific attribute 

may be useful within the ranges of experiments in this study, and as described in tables 2-4 and 

2-5, but the users should take care and use caution when interpreting the results of the model. A 

complete understanding of model assumptions and scenario applicability to these V&V results is 

necessary. Generally, the model may be used if the grade is YELLOW+ when the user ensures 

that model over-prediction reflects conservatism. The user must exercise caution when using 

models with capabilities described as YELLOW±. 

YELLOW: If the first criterion is satisfied and the calculated relative differences are outside 

experimental uncertainty with no clear pattern of over- or under-prediction, then the model 

predictive capability is characterized as YELLOW. Caution should be exercised when using a 

fire model for predicting these attributes. In this case, the user is referred to the details related to 

the experimental conditions and validation results documented in volumes 2 through 6. The user 

is advised to review and understand the model assumptions and inputs, as well as the conditions 

and results to determine and justify the appropriateness of the model prediction to the fire 

scenario for which it is being used. 

RED: If the first criterion is not met, then the particular fire model capability should not be used. 

No color: This V&V study did not investigate this capability. This may be due to one or more 

reasons that include unavailability of appropriate data or lack of model, sub-model, or output. 

As suggested in the criteria above, there is a level of engineering judgment in the classification 

of fire model predictive capabilities. Specifically, engineering judgment is exercised in the 

following two areas: 

1. Evaluation of the modeling capabilities of the particular tool if the model physics are 

appropriate. 

2. Evaluation of the magnitude of relative differences when compared to the experimental 

uncertainty. Judgment in this area impacts the determination of Green versus Yellow colors. 

In general, a Green or Yellow classification suggests that the V&V team determined that the 

model physics are appropriate for the calculation been made, within assumptions. The difference 

between the colors is due to the magnitude of the calculated relative differences. Judgment 

considerations include general experimental conditions, experimental data quality, and the 

characterization of the experimental uncertainty. 

3-1

3 

RESULTS AND CONCLUSIONS 

This chapter summarizes the results and findings of this V&V study. Section 3.1 presents the 

results using the approach discussed in section 2.6.2 of this Volume. Readers should also review 

Chapter 6 of Volumes 2 through 6 for more detailed discussions of the quantitative results. In 

addition, Appendix A to each volume presents a graphical representation of the experimental 

observations and outputs from the models. 

Section 3.2 discusses observations concerning the results. These observations highlight patterns 

and relationships between the results presented and experiments. Section 3.3 contains our 

conclusion of our findings. 

3.1 Results 

3.1.1 Validation 

Table 3-1 summarizes the results of this validation study. As discussed in section 2.6.2, the 

predictive capabilities of the models are graded based on the quantitative values of relative 

difference between model prediction and experimental measurements. 

The validation results show that none of the models have attributes that are RED. This is 

because all the models appropriately represent the physics of the scenarios, within the 

simplifying assumptions of the calculation method. Most of the correlations employed within 

the models were empirically confirmed theoretical derivations of general physical phenomena, as 

summarized in Chapter 3 of the volumes. All of the relative differences that fell significantly 

outside of the combined uncertainty could be explained in terms of the simplifying assumptions 

within the models and the comparison of these assumptions with the experimental 

configurations. 
Results and Conclusions 

3-2 

Table 3-1: Results of the Validation & Verification of the Selected Fire Models for Nuclear Power Plant Fire Mod

Parameter Fire Model 

FDTS FIVE-Rev 1 CFAST MA

Room of Origin YELLOW+ YELLOW+ GREEN GR

Hot gas layer temperature (“Upper Layer Temperature”) Adjacent Room YELLOW YELHot gas layer height (“Layer interface height”) GREEN GRCeiling jet temperature (“Target/Gas temperature”) YELLOW+2 YELPlume temperature YELLOW YELLOW+2 GRFlame height GREEN GREEN GREEN GROxygen concentration GREEN GRSmoke concentration YELLOW YELRoom pressure GREEN GRTarget temperature YELLOW YELRadiant heat flux YELLOW YELLOW YELLOW YELTotal heat flux YELLOW YELWall temperature YELLOW YELTotal heat flux to walls YELLOW YEL
Notes: 

1. FDS does not use an empirical correlation to predict the flame height. Rather, it solves a set of equations appropria

and predicts the flame height as the uppermost extent of the combustion zone. This is a challenging calculation an

emphasizes that caution should be exercised by users. 

2. FIVE approximates the plume and ceiling jet temperature as the sum of hot gas layer temperature and plume and c

obtained from the correlations. 
Results and Conclusions 

3-4 

3.1.2 Verification 

All five models have been verified by this study as appropriate for fire protection applications, 

within the assumptions for each individual model or sub model. 

During the process of this study, a number of modifications and corrections to the five selected 

fire models were identified and implemented. These modification and corrections were 

identified during the validation as a result of trying to interpret the results. The nature of these 

modifications and corrections cover a wide range from inconsequential to those that could lead to 

incorrect result. 

3.2 Summary 

This section presents a summary of observations from the results of this study. These 

observations are based on review of these results and generally apply to the five fire models 

considered in this study. While there may be valid technical reasons for some of these 

observations, it is not our intent to discuss the possible reasons and/or perspectives behind these 

observations. 

• A clear general pattern of more accurate predictions by any one model is not apparent. 

While some of the models are more accurate in predicting certain attributes they may be less 

accurate in predicting other attributes in the same scenario. 

• For the fire scenarios considered in the current validation study, and for the output quantities 

of interest, the libraries of engineering calculations (FDTs

, FIVE-Rev1) have limited 

capabilities. These libraries do not have appropriate methods for estimating many of the fire 

scenario attributes evaluated in this study. The correlations the libraries do have are 

empirically derived and contain many inherently limiting assumptions. The user must be 

cautious when using these tools. 

• The two-zone models performed well when compared with the experiments considered. 

These models have a much wider capability of predicting the fire scenario attributes 

important in NPPs. As indicated by the validation results, these models accurately predicted 

the attributes evaluated in this study. The reason for this may be the relatively simple 

experimental configurations conform well to the simple two-layer assumption that is the 

basis of these models. However, users must remain cautious when applying these models to 

more complex scenarios, or when predicting complicated phenomena, like heat fluxes. 

• For the experiments considered, the results of the field model, FDS, are not significantly 

better than those of the two-zone models that are also evaluated in this study (CFAST, 

Volume 4 and MAGIC, Volume 5). FDS solves the basic transport equations instead of 

empirical correlations, making it a more predictive model. However, the computational cost 

of solving the basic equations is substantial. The two-zone models produce answers in 

seconds to minutes, while FDS produces comparable answers in hours to days. FDS is better 

suited to predict fire environments within more complex configurations because it predicts 

the local effects of a fire. 

• The decision to use any of these models can depend on many considerations. Rarely do real 

fire scenarios conform neatly to some of the simplifying assumptions inherent in the models. 
Results and Conclusions 

3-5 

Fire plumes are rarely free and clear of obstacles -- fires often occur in cabinets or near walls. 

Ceilings are rarely flat and unobstructed – duct work and cable trays often block the clear 

paths. Although engineering calculations and two-zone models can be applied in some of 

these instances, their accuracy cannot be assured. Field model predictions can be more 

accurate in more complex scenarios. However, the time it takes to get and understand a 

prediction may also be an important consideration in the decision to use a particular model 

for a specific scenario. 

• Like all predictive models, the best predictions come with a clear understanding of the 

limitations of the model and of the inputs provided to do the calculations. 

3.3 Conclusions 

This study provides justification for verification and provides validation via comparisons 

between experimental data collected in large-scale fire tests and predictions from five fire 

modeling tools. The validation results of this study are presented in the form of color-coded 

characterization of the predictive capability of fire models for important parameters for NPP fire 

modeling applications. These characterizations are developed based on the quantitative relative 

differences that are calculated using model prediction and applicable experimental 

measurements. The judgment of predictive capability considers the uncertainty in the 

experimental measurements. 

The results of this study are limited somewhat by a lack of relevant data from fire experiments 

that represent NPP fire scenarios. The study is also limited by the capability of the models to 

simulate all potential NPP fire scenarios, such high-energy arching faults and ensuing fires and 

fire propagation between control panels. These much more complicated fire scenarios can be 

analyzed using the methods described in NUREG/CR-6850 [Ref. 6]. 

The use of fire models to support fire protection decision-making requires understanding of their 

limitations and confidence in their predictive capabilities. While this report tends to improve the 

confidence level in some cases, it also shows that some models are limited in their applications 

based on relative differences between experimental data and model calculations. Fully 

understanding the predictive capabilities of fire models is a challenge that should be addressed if 

the fire protection community is to realize the full benefit of fire modeling. 

The results of this project clearly suggest that any fire modeling analysis should consider the 

predictive capabilities associated with the analytical tool when interpreting its results. 

4-1

4 

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Commission, Washington, DC, June 16, 2004. 

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14. EPRI 108875, “Fire Modeling Code Comparison,” September 1998. 
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4-2 

15. Hostikka, S., Kokkala, M., Vaari, J., “Experimental Study of the Localized Room Fires,” 

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