Cable Heat Release,

Ignition, and Spread in

Tray Installations During 

Fire (CHRISTIFIRE) 

Phase 1: Horizontal Trays

Office of Nuclear Regulatory Research

NUREG/CR-7010, Vol. 1
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Cable Heat Release, 

Ignition, and Spread in 

Tray Installations During 

Fire (CHRISTIFIRE) 

Phase 1: Horizontal Trays

Manuscript Completed: May 2011

Date Published: July 2012

Prepared by: 

Kevin McGrattan

Andrew Lock

Nathan Marsh

Marc Nyden

Scott Bareham

Michael Price (Summer Undergraduate Research Fellow)

National Institute of Standards and Technology

Building and Fire Research Laboratory

Gaithersburg, Maryland 20899-8663

Alexander B. Morgan

Mary Galaska

Kathy Schenck

University of Dayton Research Institute

Multi-Scale Composite and Polymers Division

Dayton, Ohio 45469-0160

David Stroup, NRC Project Manager

NRC Job Code N6549

Office of Nuclear Regulatory Research

NUREG/CR-7010, Vol. 1

iii 

ABSTRACT

This report documents the first phase of a multi-year NRC research initiative entitled 

CHRISTIFIRE (Cable Heat Release, Ignition, and Spread in Tray Installations during FIRE). 

The overall goal of the program is to better understand and quantify the burning characteristics 

of grouped electrical cables commonly found in nuclear power plants. The first phase of the 

program focuses on horizontal tray configurations. The experiments conducted range from 

micro-scale, in which very small (5 mg) samples of cable materials were burned in a calorimeter 

to determine their heat of combustion and other properties; to full-scale, in which horizontal 

arrays of ladder-back trays loaded with varying amounts of cable were burned under a large 

oxygen-depletion calorimeter. Additional experiments include cone calorimetry, smoke and 

effluent characterization in a small test furnace, and intermediate-scale calorimetry involving a 

single tray of heated cables exposed to a bank of radiant panels. The results of the small-scale 

experiments will serve as input data for fire models; while the results of the full-scale 

experiments will serve as validation data for the models. 

v 

CONTENTS 

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

LIST OF FIGURES ..................................................................................................................... ix

LIST OF TABLES ..................................................................................................................... xiii

EXECUTIVE SUMMARY ........................................................................................................ xv

ACKNOWLEDGEMENTS ...................................................................................................... xix

ABBREVIATIONS .................................................................................................................... xxi

1 BACKGROUND ................................................................................................................... 1

1.1 Introduction ...................................................................................................................... 1

1.2 Standard Cable Testing Configurations ........................................................................... 2

1.3 Past Cable Fire Experiments ............................................................................................ 2

1.4 Past Cable Fire Modeling Efforts ..................................................................................... 4

1.5 Current Research Needs ................................................................................................... 5

2 TECHNICAL APPROACH ................................................................................................. 7

2.1 Objective of CHRISTIFIRE ............................................................................................. 7

2.2 Overview of CHRISTIFIRE Phase 1 Experiments .......................................................... 7

2.3 Chemical Composition of Cables and Combustion Products .......................................... 8

2.4 Heat Release and Spread Rates of Cable Fires ................................................................ 9

3 CABLE PROPERTIES ...................................................................................................... 11

3.1 Properties of Cables Used in CHRISTIFIRE ................................................................. 11

3.2 Classification of Plastic Materials .................................................................................. 16

3.2.1 Thermoplastics ........................................................................................................ 16

3.2.2 Thermosets .............................................................................................................. 16

4 MICRO-CALORIMETRY MEASUREMENTS ............................................................. 17

4.1 Description ..................................................................................................................... 17

4.2 Results ............................................................................................................................ 17

5 TUBE FURNACE MEASUREMENTS ............................................................................ 25

5.1 Description ..................................................................................................................... 25

5.1.1 Test Procedure ........................................................................................................ 25

5.1.2 Quantification of CO and CO2 ................................................................................ 26

5.1.3 Quantification of HCN, HCl and HBr .................................................................... 26

5.1.4 Quantification of soot ............................................................................................. 28

5.2 Results ............................................................................................................................ 28

6 CONE CALORIMETER MEASUREMENTS ................................................................ 33

6.1 Description ..................................................................................................................... 33

6.1.1 Procedure for preparing cable samples for Cone Calorimeter testing .................... 33

6.2 Results for Individual Cable Types ................................................................................ 37

6.2.1 Cable #11 ................................................................................................................ 38

6.2.2 Cable #16 ................................................................................................................ 40

6.2.3 Cable #23 ................................................................................................................ 42

6.2.4 Cable #43 ................................................................................................................ 44

6.2.5 Cable #46 ................................................................................................................ 46

6.2.6 Cable #219 .............................................................................................................. 48

6.2.7 Cable #220 .............................................................................................................. 50

6.2.8 Cable #270 .............................................................................................................. 52
vi

6.2.9 Cable #271 .............................................................................................................. 54

6.2.10 Cable #367 .............................................................................................................. 56

6.2.11 Cable #700 .............................................................................................................. 58

6.2.12 Cable #701 .............................................................................................................. 60

6.3 Summary of Results ....................................................................................................... 62

7 RADIANT PANEL EXPERIMENTS ............................................................................... 63

7.1 Overview ........................................................................................................................ 63

7.2 Experimental Measurements .......................................................................................... 65

7.3 Results ............................................................................................................................ 65

7.3.1 Cable #11 ................................................................................................................ 66

7.3.2 Cable #16 ................................................................................................................ 68

7.3.3 Cable #23 ................................................................................................................ 70

7.3.4 Cable #43 ................................................................................................................ 72

7.3.5 Cable #46 ................................................................................................................ 74

7.3.6 Cable #219 .............................................................................................................. 76

7.3.7 Cable #220 .............................................................................................................. 78

7.3.8 Cable #271 .............................................................................................................. 80

7.3.9 Cable #367 .............................................................................................................. 82

7.3.10 Cable #700 .............................................................................................................. 84

7.3.11 Cable #701 .............................................................................................................. 86

7.4 Discussion ...................................................................................................................... 90

8 MULTIPLE TRAY EXPERIMENTS ............................................................................... 93

8.1 General Description ........................................................................................................ 93

8.2 Results, Multiple Tray Experiments, Series 1 ................................................................ 94

8.2.1 Multiple Tray Test 1 (MT-1) .................................................................................. 96

8.2.2 Multiple Tray Test 2 (MT-2) .................................................................................. 98

8.2.3 Multiple Tray Test 3 (MT-3) ................................................................................ 100

8.2.4 Multiple Tray Test 4 (MT-4) ................................................................................ 102

8.2.5 Multiple Tray Test 5 (MT-5) ................................................................................ 104

8.2.6 Multiple Tray Test 6 (MT-6) ................................................................................ 106

8.2.7 Multiple Tray Test 7 (MT-7) ................................................................................ 108

8.2.8 Multiple Tray Test 8 (MT-8) ................................................................................ 110

8.2.9 Multiple Tray Test 9 (MT-9) ................................................................................ 112

8.2.10 Multiple Tray Test 10 (MT-10) ............................................................................ 114

8.2.11 Multiple Tray Test 11 (MT-11) ............................................................................ 116

8.2.12 Multiple Tray Test 12 (MT-12) ............................................................................ 118

8.2.13 Multiple Tray Test 13 (MT-13) ............................................................................ 120

8.2.14 Multiple Tray Test 14 (MT-14) ............................................................................ 122

8.2.15 Multiple Tray Test 15 (MT-15) ............................................................................ 124

8.2.16 Multiple Tray Test 16 (MT-16) ............................................................................ 126

8.3 Results, Multiple Tray Experiments, Series 2 .............................................................. 130

8.3.1 Multiple Tray Test MT-17 and MT-18 ................................................................. 132

8.3.2 Multiple Tray Test MT-19 and MT-20 ................................................................. 134

8.3.3 Multiple Tray Test MT-21 and MT-22 ................................................................. 136

8.3.4 Multiple Tray Tests MT-23 and MT-24 ............................................................... 138
vii

8.3.5 Multiple Tray Tests MT-25 and MT-26 ............................................................... 140

8.4 Burn Patterns ................................................................................................................ 142

9 MODELING ...................................................................................................................... 145

9.1 Summary of Data Collection for Modeling .................................................................. 145

9.2 The FLASH-CAT Model ............................................................................................. 147

9.2.1 Model Overview ................................................................................................... 147

9.2.2 FLASH-CAT Model Input Parameters ................................................................. 151

9.2.3 Model Validation .................................................................................................. 155

9.2.4 Discussion of Model Results ................................................................................ 166

10 CONCLUSIONS AND FUTURE WORK ...................................................................... 169

10.1 Heat Release Rate ..................................................................................................... 169

10.2 Ignition...................................................................................................................... 169

10.3 Spread ....................................................................................................................... 170

10.4 General Observations ............................................................................................... 170

10.5 Future Work .............................................................................................................. 171

11 REFERENCES .................................................................................................................. 173

APPENDIX A TESTING STANDARDS FOR CABLES ................................................. 177

Discussion ........................................................................................................................... 179

Low Intensity Test Methods ............................................................................................... 180

 

ix 

LIST OF FIGURES 

Figure 3-1. Photograph of some of the cables used in CHRISTIFIRE. ..................................... 13

Figure 4-1. Pyrolysis Combustion Flow Calorimeter (PCFC). ................................................. 17

Figure 4-2. Micro-Calorimetry results for Cables 11, 16 and 23. .............................................. 19

Figure 4-3. Micro-Calorimetry results for Cables 43, 46 and 219. ............................................ 20

Figure 4-4. Micro-Calorimetry results for Cables 220, 269 and 271......................................... 21

Figure 4-5. Micro-Calorimetry results for Cables 367, 700 and 701......................................... 22

Figure 5-1. ISO/TS 19700 Tube Furnace. ................................................................................. 25

Figure 5-2. FTIR spectrum of the products of burning electrical cable. .................................... 27

Figure 5-3. Yields of various product gases. ............................................................................. 29

Figure 5-4. Cross-correlations of gas pairs ................................................................................ 30

Figure 5-5. Residue/char yield of various cables ....................................................................... 31

Figure 6-1. Typical cable sample for Cone Calorimeter. ........................................................... 33

Figure 6-2. Sample holder for Cone Calorimeter. ..................................................................... 34

Figure 6-3. Tray for holding cables in Cone Calorimeter. ......................................................... 35

Figure 6-4. Sample holder assembly for Cone Calorimeter. ..................................................... 35

Figure 6-5. The completed holder assembly for the Cone Calorimeter. .................................... 36

Figure 6-6. Modified sample holder for Cone Calorimeter. ...................................................... 36

Figure 6-7. Sample output from Cone Calorimeter. .................................................................. 37

Figure 6-8. Photograph of Cable #11 after Cone Calorimeter test at 25 kW/m2. ...................... 38

Figure 6-9. Photograph of Cable #11 after Cone Calorimeter test at 50 kW/m2. ...................... 39

Figure 6-10. Heat Release Rates for Cable #11 in the Cone Calorimeter. .................................. 39

Figure 6-11. Photograph of Cable #16 after Cone Calorimeter test at 25 kW/m2. ...................... 40

Figure 6-12. Photograph of Cable #16 after Cone Calorimeter test at 50 kW/m2. ...................... 41

Figure 6-13. Heat Release Rates for Cable #16 in the Cone Calorimeter. .................................. 41

Figure 6-14. Photograph of Cable #23 after Cone Calorimeter test at 25 kW/m2. ...................... 42

Figure 6-15. Photograph of Cable #23 after Cone Calorimeter test at 50 kW/m2. ...................... 43

Figure 6-16. Heat Release Rates for Cable #23 in the Cone Calorimeter. .................................. 43

Figure 6-17. Photograph of Cable #43 after Cone Calorimeter test at 25 kW/m2. ...................... 44

Figure 6-18. Photograph of Cable #43 after Cone Calorimeter test at 50 kW/m2. ...................... 45

Figure 6-19. Heat Release Rates for Cable #43 in the Cone Calorimeter. .................................. 45

Figure 6-20. Photograph of Cable #46 after Cone Calorimeter test at 25 kW/m2. ...................... 46

Figure 6-21. Photograph of Cable #46 after Cone Calorimeter test at 50 kW/m2. ...................... 46

Figure 6-22. Heat Release Rates for Cable #46 in the Cone Calorimeter. .................................. 47

Figure 6-23. Photograph of Cable #219 after Cone Calorimeter test at 25 kW/m2. .................... 48

Figure 6-24. Photograph of Cable #219 after Cone Calorimeter test at 50 kW/m2. .................... 48

Figure 6-25. Heat Release Rates for Cable #219 in the Cone Calorimeter. ................................ 49

Figure 6-26. Photograph of Cable #220 after Cone Calorimeter test at 25 kW/m2. .................... 50

Figure 6-27. Photograph of Cable #220 after Cone Calorimeter test at 50 kW/m2. .................... 51

Figure 6-28. Heat Release Rates for Cable #220 in the Cone Calorimeter. ................................ 51

Figure 6-29. Photograph of Cable #270 after Cone Calorimeter test at 25 kW/m2. .................... 52

Figure 6-30. Photograph of Cable #270 after Cone Calorimeter test at 50 kW/m2. .................... 53

Figure 6-31. Heat Release Rates for Cable #270 in the Cone Calorimeter. ................................ 53

Figure 6-32. Photograph of Cable #271 after Cone Calorimeter test at 25 kW/m2. .................... 54

Figure 6-33. Photograph of Cable #271 after Cone Calorimeter test at 50 kW/m2. .................... 55
x

Figure 6-34. Heat Release Rates for Cable #271 in the Cone Calorimeter. ................................ 55

Figure 6-35. Photograph of Cable #367 after Cone Calorimeter test at 25 kW/m2. .................... 56

Figure 6-36. Photograph of Cable #367 after Cone Calorimeter test at 50 kW/m2. .................... 57

Figure 6-37. Heat Release Rates for Cable #367 in the Cone Calorimeter. ................................ 57

Figure 6-38. Photograph of Cable #700 after Cone Calorimeter test at 25 kW/m2. .................... 58

Figure 6-39. Photograph of Cable #700 after Cone Calorimeter test at 50 kW/m2. .................... 59

Figure 6-40. Heat Release Rates for Cable #700 in the Cone Calorimeter. ................................ 59

Figure 6-41. Photograph of Cable #701 after Cone Calorimeter test at 25 kW/m2. .................... 60

Figure 6-42. Photograph of Cable #701 after Cone Calorimeter test at 50 kW/m2. .................... 61

Figure 6-43. Heat Release Rates for Cable #701 in the Cone Calorimeter. ................................ 61

Figure 7-1. Side view of Radiant Panel Apparatus .................................................................... 64

Figure 7-2. End view of Radiant Panel Apparatus. ................................................................... 64

Figure 7-3. Photographs and HRR of RP Tests 21 and 22, Cable #11. ..................................... 67

Figure 7-4. Photographs of RP Test 6. ....................................................................................... 68

Figure 7-5. HRR of RP Tests 6-10, Cable #16. ......................................................................... 69

Figure 7-6. Photographs of RP Test 28 (left) and 29 (right). ..................................................... 70

Figure 7-7. Photographs of RP Test 28 and HRR of Tests 27-29, Cable #23. .......................... 71

Figure 7-8. Photographs of RP Test 14 and HRR of Tests 14 and 15, Cable #43. .................... 73

Figure 7-9. Photographs of RP Test 16 and HRR of Tests 16 and 17, Cable #46. .................... 75

Figure 7-10. Photograph of the remains of the cables in RP-24. ................................................. 76

Figure 7-11. Photographs of RP Test 23 and HRR of Tests 23 and 24, Cable #219. .................. 77

Figure 7-12. Fairly vigorous burning in RP-25. .......................................................................... 78

Figure 7-13. Photographs of RP Test 25 and HRR of Tests 25 and 26, Cable #220. .................. 79

Figure 7-14. Photograph of RP Test 18 showing dripping and burning in the catch pan. ........... 80

Figure 7-15. Photographs of RP Test 18 and HRR of Tests 18-20, Cable #271. ........................ 81

Figure 7-16. Photograph of RP Test 11 showing burning to the end of the tray. ........................ 82

Figure 7-17. Photographs of RP Test 11 and HRR of Tests 11-13, Cable #367. ........................ 83

Figure 7-18. Photograph of RP Test 1, showing a relatively heavy load of cable. ...................... 84

Figure 7-19. Photographs of RP Test 0 and HRR of Tests 0, 1 and 2, Cable #700. .................... 85

Figure 7-20. Photographs of RP Test 3. ....................................................................................... 86

Figure 7-21. HRR of RP Tests 3-5 and 30-31, Cable #701. ........................................................ 87

Figure 7-22. Summary of the radiant panel heat release rates. .................................................... 90

Figure 8-1. Multiple Tray (MT) cable test apparatus. ............................................................... 94

Figure 8-2. Multiple Tray Experiment 1 .................................................................................... 97

Figure 8-3. Multiple Tray Experiment 2. ................................................................................... 99

Figure 8-4. Multiple Tray Experiment 3 .................................................................................. 101

Figure 8-5. Multiple Tray Experiment 4 .................................................................................. 103

Figure 8-6. Multiple Tray Experiment 5 .................................................................................. 105

Figure 8-7. Multiple Tray Experiment 6 .................................................................................. 107

Figure 8-8. Multiple Tray Experiment 7 .................................................................................. 109

Figure 8-9. Multiple Tray Experiment 8 .................................................................................. 111

Figure 8-10. Multiple Tray Experiment 9 .................................................................................. 113

Figure 8-11. Multiple Tray Experiment 10 ................................................................................ 115

Figure 8-12. Multiple Tray Experiment 11 ................................................................................ 117

Figure 8-13. Multiple Tray Experiment 12 ................................................................................ 119
xi

Figure 8-14. Multiple Tray Experiment 13 ................................................................................ 121

Figure 8-15. Damage to cables following Multiple Tray Test 14. ............................................. 122

Figure 8-16. Multiple Tray Experiment 14 ................................................................................ 123

Figure 8-17. Fire spread to the ends of Tray 3, Multiple Tray Test 15. .................................... 124

Figure 8-18. Multiple Tray Experiment 15 ................................................................................ 125

Figure 8-19. Damage to cables, Multiple Tray Test 16. ............................................................ 126

Figure 8-20. Multiple Tray Experiment 16 ................................................................................ 127

Figure 8-21. Heat Release Rates for MT-17 and MT-18. .......................................................... 132

Figure 8-22. Multiple Tray Test 17 after 25 min. ...................................................................... 133

Figure 8-23. Multiple Tray Test 18 after approximately 20 min. .............................................. 133

Figure 8-24. Heat Release Rates for Tests MT-19 and MT-20. ................................................ 134

Figure 8-25. Photograph of Multiple Tray Test MT-19. ........................................................... 135

Figure 8-26. Photograph of Multiple Tray Test MT-20. ........................................................... 135

Figure 8-27. Heat Release Rates for Multiple Tray Tests MT-21 and MT-22. ......................... 136

Figure 8-28. Photograph of Multiple Tray Test MT-21. ........................................................... 137

Figure 8-29. Photograph of Multiple Tray Test MT-22. ........................................................... 137

Figure 8-30. Heat Release Rates for Multiple Tray Tests MT-23 and MT-24. ......................... 138

Figure 8-31. Photograph of Multiple Tray Test MT-23. ........................................................... 139

Figure 8-32. Photograph of Multiple Tray Test MT-24. ........................................................... 139

Figure 8-33. Heat Release Rates for Multiple Tray Tests MT-25 and MT-26. ......................... 140

Figure 8-34. Photograph of Multiple Tray Test MT-25. ........................................................... 141

Figure 8-35. Photograph of Multiple Tray Test MT-26. ........................................................... 141

Figure 8-36. Explanation of spread rate and angle. ................................................................... 143

Figure 9-1. Idealized time history of the local heat release rate per unit area. ........................ 149

Figure 9-2. FLASH-CAT model results for Multiple Tray Test 17. ....................................... 150

Figure 9-3. Comparison of predicted and measured HRR for Multiple Tray Tests 1-3. ......... 156

Figure 9-4. Comparison of predicted and measured HRR for Multiple Tray Tests 4-6. ......... 157

Figure 9-5. Comparison of predicted and measured HRR for Multiple Tray Tests 7-9. ......... 158

Figure 9-6. Comparison of predicted and measured HRR for Multiple Tray Tests 10-12. ..... 159

Figure 9-7. Comparison of predicted and measured HRR for Multiple Tray Tests 13-15. ..... 160

Figure 9-8. Comparison of predicted and measured HRR for Multiple Tray Tests 16-18. ..... 161

Figure 9-9. Comparison of predicted and measured HRR for Multiple Tray Tests 19-20. ..... 162

Figure 9-10. Comparison of predicted and measured HRR for Multiple Tray Tests 21-22. ..... 163

Figure 9-11. Comparison of predicted and measured HRR for Multiple Tray Tests 23-24. ..... 164

Figure 9-12. Comparison of predicted and measured HRR for Multiple Tray Tests 25-26. ..... 165

Figure 9-13. Comparison of peak HRR and total energy release for FLASH-CAT. ................. 166

Figure 9-14. Photograph of MT-19 compared to the FLASH-CAT model prediction. ............. 167

 

xiii 

LIST OF TABLES 

Table 2-1. Outline of CHRISTIFIRE Experimental Program ..................................................... 8

Table 3-1. Cables used in CHRISTIFIRE ................................................................................. 12

Table 3-2. Properties of the cables used in CHRISTIFIRE ...................................................... 14

Table 4-1. Summary of the Micro-Calorimetry Experiments. The bold font indicates the 

primary reaction. ...................................................................................................... 23

Table 5-1. Species and Frequency Windows for FTIR Analysis. ............................................. 28

Table 6-1. Measured heat release rates from Cone Calorimeter experiments ........................... 62

Table 7-1. Summary of the Radiant Panel Experiments ........................................................... 88

Table 8-1. Summary of Multiple Tray Experiments, Series 1. ............................................... 128

Table 8-2. Parameters of Multiple Tray Experiments, Series 2 .............................................. 131

Table 8-3. Spread rate and spread angle for Multiple Tray Tests. .......................................... 144

Table 9-1. Summary of measured properties of the cables used in CHRISTIFIRE. .............. 146

Table 9-2. Input parameters for the FLASH-CAT Model. ...................................................... 154

Table A-1. Standard Fire Tests for Electrical Cables ............................................................... 177 

 

xv 

EXECUTIVE SUMMARY 

Fires in grouped electrical cable trays pose a distinct fire hazard in nuclear power plants (NPPs). 

In the past, cable tray installations have fueled fires that resulted in serious damage to NPPs. 

The 1975 fire at the Browns Ferry NPP demonstrated the vulnerability of electrical cables when 

exposed to elevated temperatures as a result of a fire. The behavior of cables in a fire depends on 

a number of factors, including their constituent material and construction, as well as their 

location and installation geometry. 

While there has been a considerable amount of work done over the past 40 years to measure 

cable properties and model their behavior, it is still a considerable challenge to predict the actual 

heat release rate of an array of cable trays. Guidance documents like NUREG/CR-6850, 

NUREG-1805, and the SFPE Handbook of Fire Protection Engineering contain lengthy tables of 

material properties, burning rates, flame spread equations, and other information gleaned from 

past experimental and modeling efforts. Still, there is no consensus on how to calculate the heat 

release rate (HRR) of a stack of cable trays using either a simple or a detailed fire model. 

The CAROLFIRE (CAble Response tO Live FIRE, NUREG/CR-6931) project provided 

information on the electrical failure mechanisms of cables in fire, including a relatively simple 

model to predict a cable’s thermally-induced electrical failure (THIEF). However, the 

measurements and modeling of CAROLFIRE did not provide information about the HRR and 

flame spread rates of burning cables. This report describes Phase 1 of the CHRISTIFIRE (Cable 

Heat Release, Ignition and Spread in Tray Installations during FIRE) testing program conducted 

by the National Institute of Standards and Technology (NIST). The overall goal of this multiyear program is to quantify the burning characteristics of grouped electrical cables installed in 

cable trays. This first phase of the program focuses on horizontal tray configurations. 

CHRISTIFIRE addresses the burning behavior of a cable in a fire beyond the point of electrical 

failure. The data obtained from this project can be used for the development of fire models to 

calculate the HRR and flame spread of a cable fire. The experiments conducted range from 

bench-scale measurements of the effluent from small samples of burning cables to full-scale 

measurements of the HRR and spread rate of cables burning within typical ladder-back, open 

cable trays. The results provide the most extensive set of cable thermal response and failure data 

to date. The results of the small-scale experiments can serve as input data for fire models; while 

the results of the full-scale experiments are valuable as validation data for the models. Follow on 

phases of the CHRISTIFIRE program will address additional variables such as vertical tray 

configurations, cable fire retardant coatings, and other variables. 

A summary of the CHRISTIFIRE Phase 1 experiments and modeling effort is listed below: 

Micro-Scale Calorimetry: Following the procedure set forth in ASTM D 7309, small (5 mg) 

samples of cable jackets and insulation were burned within a small calorimeter to measure the 

heat of combustion, pyrolysis temperature, heat release capacity, and residue yield. The results 

of these experiments provide direct input for a variety of fire models. Simple models can use the 

heat of combustion, pyrolysis temperature, and residue yield to estimate how much of a given 

cable can be burned, and at what temperature, and with what amount of heat being released. 

More detailed models can use the kinetic parameters (pre-exponential factor and activation 
xvi

energy) that can be extracted from the measurement. These parameters describe the multiple 

reaction decomposition of the material into fuel gas and residue/char. In light of the results of 

the larger-scale experiments, it was found that the pyrolysis temperature is the most important 

result of the MCC experiments. The cable with lowest measured pyrolysis temperature was 

found to burn most readily at all the scales tested. 

Bench-Scale Effluent Characterization: Following the procedure set forth in ISO/TS 19700, 

meter-long cable segments were slowly fed through a small furnace, referred to as the Tube 

Furnace, and the effluent was captured and measured via a variety of spectrometric techniques. 

The gases analyzed included CO2, CO, HCl, H2O, and soot particulate. The purpose of these 

experiments was to provide models with the production rates of various exhaust gases that are of 

interest in hazard analyses of fire. Several cables were found to contain significant amounts of 

chlorine that formed HCl upon burning, a leading cause of corrosion in industrial settings. 

Bench-Scale Calorimetry: Following the procedure set forth in ASTM D 6113, the standard 

Cone Calorimeter test was modified to accommodate electrical cables. In the experiment, 10 cm 

(4 in) by 10 cm (4 in) arrays of cables were exposed to heat fluxes of 25 kW/m2

, 50 kW/m2, and 

75 kW/m2, and the heat release rate per unit area (HRRPUA) was measured. The objective of 

these experiments was to determine if the measured HRRPUA was comparable to what was 

measured at intermediate and full-scale. It was found that thermoset cables typically burn in the 

range 100 kW/m2 to 200 kW/m2, and thermoplastic cables typically burn in the range 200 kW/m2

to 300 kW/m2

. These measurements are consistent with similar measurements made at 

intermediate and full scale. 

Intermediate-Scale Calorimetry: The Radiant Panel (RP) Apparatus is a specially-designed 

device for measuring the burning rate of cables at a larger scale than the Cone Calorimeter. It 

consists of a single horizontal 1.2 m (4 ft) long, 0.45 m (18 in) wide ladder-back cable tray 

containing varying numbers of cables that are exposed to an array of radiant panels that are 

positioned overhead. The objective of these experiments was to compile a table of heat release 

rates per unit area (HRRPUA) for a variety of heat flux levels and tray fill levels. It was found 

that the values of HRRPUA measured in the Radiant Panel Apparatus were consistent with the 

burning rates at bench-scale (Cone Calorimeter) and full-scale (Multiple Tray Experiments). 

Full-Scale Calorimetry: The Multiple Tray (MT) Experiments were composed of vertical stacks 

of three to seven cable trays. There were 26 experiments conducted in total. These 26 

experiments were divided into two series. 

Series 1 addresses a fairly common tray configuration where 0.45 m (18 in) horizontal, ladderbacked trays are stacked over top of each other with 0.3 m (1 ft) spacing. The type and amount 

of cables in each tray was varied. The cables in a given tray (or often for a given experiment) 

were typically of a single type. The aim was to test at full-scale those cables that were tested in 

the Radiant Panel Apparatus and in the Cone Calorimeter to determine if the burning rate data 

collected at bench and intermediate-scales could be applied to the full-scale experiments. 

Series 2 involved mixtures of cables that were not tested under the Radiant Panel Apparatus or 

the Cone Calorimeter. This series was designed to assess the effect of changing the vertical tray 
xvii

spacing, tray width, and tray fill. As with Series 1, these tests also provided experimental data 

for model validation. 

Modeling: Following the current guidance set forth in NUREG/CR-6850, Appendix R, a simple 

model of upward fire spread in horizontal tray configurations was developed. The model, 

referred to as FLASH-CAT (Flame Spread over Horizontal Cable Trays), makes use of semiempirical estimates of lateral and vertical flame spread, and measured values of combustible 

mass, heat of combustion, heat release rate per unit area, and char yield. Because the measured 

values of these parameters was found to be scale and configuration-dependent, the model makes 

use of effective values that are selected only on the basis of whether the cable is judged to be of 

the thermoset or thermoplastic type. The only information that is specific to an individual cable 

is its mass per unit length, combustible mass fraction, and whether it is considered a thermoset or 

thermoplastic cable. The model was compared to the 26 Multiple Tray Experiments, and it was 

observed that the predicted HRR was between a factor of one to two times greater than the 

measured values. These experiments thus provide confirmatory experimental validation of the 

calculation methods set forth in NUREG/CR-6850. 

This report also contains a DVD containing videos of the intermediate and full-scale experiments 

along with the measured heat release rates. 

 

xix 

ACKNOWLEDGEMENTS 

The work described in this report was supported by the Office of Nuclear Regulatory Research 

(RES) of the US Nuclear Regulatory Commission (USNRC). The CHRISTIFIRE program was 

directed by David Stroup. Jason Dreisbach and Mark Salley contributed valuable advice on the 

design and objectives of the experiments. Gabriel Taylor and Felix Gonzalez provided valuable 

information on the cable composition and typical installation practice. 

The experiments described in this report were conducted primarily in the Large Fire Laboratory 

of the National Institute of Standards and Technology (NIST). Matthew Bundy is the laboratory 

supervisor and helped plan the testing schedule. He also managed the sizeable clean-up 

operation that was needed because of the highly corrosive nature of the cable combustion 

effluent. Laurean DeLauter, Anthony Chakalis, and Marco Fernandez built the various 

experimental apparatus. Doris Rinehart and Artur Chernovsky managed the data acquisition 

equipment and software. 

The majority of the cables were purchased by US NRC for previous experimental programs 

conducted at Brookhaven National Laboratory (BNL) and Sandia National Laboratory (SNL). 

Anthony Hamins and Jay McElroy of NIST arranged for the transfer of the cables to the NIST 

campus in Gaithersburg, Maryland and assembled an inventory list of the cables. 

This report was issued for public comment on September 28, 2010 (75 FR 61521). Useful 

comments and suggestions were provided by the following individuals: 

Sean Hunt, Hughes Associates, Inc. 

Robert Webster, AREVA 

Vijay D’Souza, Progress Energy 

Richard Wachowiak, EPRI 

Moon-Ha Jee, Korea Electric Company Research Institute 

 

xxi

ABBREVIATIONS 

ASTM American Society for Testing and Materials 

AWG American Wire Gauge 

BNL Brookhaven National Laboratory 

CAROLFIRE Cable Response to Live Fire 

CHRISTIFIRE Cable Heat Release, Ignition, and Spread in Tray Installations 

CPE Chlorinated Polyethylene 

CSPE Chloro-Sulfanated Polyethylene 

EN European standard test designation 

EPR Ethylene-Propylene Rubber 

EPRI Electric Power Research Institute 

FAA Federal Aviation Administration 

FLASH-CAT Flame Spread over Horizontal Cable Trays 

FMRC Factory Mutual Research Corporation 

FTIR Fourier Transform Infrared Spectroscopy 

HRR Heat Release Rate 

HRRPUA Heat Release Rate Per Unit Area 

IEC International Electrotechnical Commision 

IEEE Institute of Electrical and Electronics Engineers 

ISO International Organization for Standardization 

MCC Micro-Combustion Calorimetry 

MT Multiple Tray 

NDIR Non-Dispersive Infrared 

NEC National Electric Code 

NFPA National Fire Protection Association 

NIST National Institute of Standards and Technology 

NPP Nuclear Power Plant 

NRC Nuclear Regulatory Commission 

NRR NRC Office of Nuclear Reactor Regulation 

OD Outer Diameter 

PCFC Pyrolysis Combustion Flow Calorimeter 

PE Polyethylene 

PRA Probabilistic Risk Assessment 

PVC Poly-vinyl Chloride 

RES NRC Office of Nuclear Regulatory Research 

RP Radiant Panel 

SNL Sandia National Laboratories 

SP Swedish National Testing and Research Institute 

SR Silicone Rubber 

TC Thermocouple 

THIEF Thermally-Induced Electrical Failure 

TP Thermoplastic 

TS Thermoset 

UL Underwriters Laboratories 
xxii

VTT Valtion Teknillinen Tutkimuskeskus (Technical Research Centre, Finland) 

XLPE or XPE Cross-Linked Polyethylene 

XLPO Cross-Linked Polyolefin 
1

1 BACKGROUND 

1.1 Introduction 

Electrical cables perform numerous functions in nuclear power plants (NPP). Power cables 

supply electricity to motors, transformers, heaters, and light fixtures; control cables connect plant 

equipment such as motor-operated valves (MOVs) and motor starters to remote initiating devices 

(e.g., switches, relays, and contacts); instrumentation cables transmit low-voltage signals 

between input devices and readout display panels. NPPs typically contain hundreds of miles of 

electrical cables. A typical boiling-water reactor (BWR) requires approximately 97 km 

(60 miles) of power cable, 80 km (50 miles) of control cable and 400 km (250 miles) of 

instrument cable. A pressurized-water reactor (PWR) may require even more cables. The 

containment building of Waterford Steam Electric Generating Station, Unit 3 requires nearly 

1,600 km (1,000 miles) of cable (US NRC, NUREG/CR-6384). 

The in situ fire fuel load is clearly dominated by electrical cable insulating materials in most 

areas of an NPP. These electrical cables will be found in both the cable routing raceways 

throughout the plant and in the electrical cabinets. In a postulated NPP fire scenario, they can be 

an ignition source, an intervening combustible, and/or a device that can potentially lose 

functionality. These cables are made up of a variety of thermoplastic and thermoset materials. 

The primary characteristics that distinguish one cable type from another with respect to fire 

behavior include cable jacket formulation, conductor insulator formulation, multiple versus 

single-conductor, conductor size, and flammable to non-flammable material mass ratios. 

Electrical cables have been responsible for a number of fires in NPP’s over the years. In 1975, a 

serious fire involving electrical cables occurred at the Browns Ferry NPP operated by the 

Tennessee Valley Authority (NUREG-0050). The fire caused damage to more than 1,600 cables 

resulting in loss of all Unit 1 emergency core cooling system equipment. The damage was 

extensive because of the flammability of the cables, including ease of ignition, and flame 

spreading. 

The amount of experimental evidence and analytical tools available to calculate the development 

and effects of cable tray fires is relatively small when compared to the vast number of possible 

fire scenarios that can be postulated for NPPs in the U.S. Many of the large-scale fire tests 

conducted on cables are qualification tests in which the materials are tested in a relatively largescale configuration and qualitatively ranked on a comparative basis. Appendix A provides a 

summary of these tests. While providing a relative ranking of cables, this type of test typically 

does not address the details of fire growth and spread, and does not provide any useful data for 

model calculations. 

There have also been a variety of studies focused on small scale material characterization tests. 

Many investigators have questioned the degree to which small-scale test results reflect true fire 

behavior, especially plastic materials. Until these small-scale test results have been more fully 
2

validated through larger-scale test data, caution must be exercised in the use of small-scale test 

results in the prediction of full-scale fire behavior. 

The need for data about the fire hazards of cables also relates to the methods contained in 

NUREG/CR-6850 “Fire PRA Methodology for Nuclear Power Facilities.” The fire PRA method 

requires data on cable flame spread and heat release rates and fire spread from cable tray to cable 

tray. As mentioned above, the currently available data is limited. As such, there is a need for 

more data to reduce the uncertainty associated with the PRA methods as they are applied to 

NFPA 805 applications. 

1.2 Standard Cable Testing Configurations 

Gonzalez and Dreisbach (2007) identified roughly 40 flame propagation tests for cables from the 

NFPA, UL, FM, IEEE, IEC and other standards writing organizations. Appendix A of this report 

includes excerpts from that study. All but six of the tests reviewed address vertical 

configurations; and of the six, none address the single and multiple tray configurations that are 

typically found throughout U.S. NPPs. Within the U.S. nuclear community, a cable is classified 

as “qualified” if it passes the standard test, IEEE-383. The test uses a 0.3 m (1 ft) wide, 2.4 m 

(8 ft) high vertical rack to support the cables. The cables are positioned in the center of the rack, 

15 cm (6 in) off the rack and spaced one-half a cable diameter apart. A 21 kW air-propane premixed burner is used to ignite the cables with a 20 min exposure. Cables that propagate the 

flames above the top of the rack fail to qualify. Most of the other standard tests cited by 

Gonzalez and Dreisbach are similar in scope. Almost none of the tests is of any value for fire 

modeling because they only determine whether a particular cable passes or fails; they do not 

quantify in a useful way the burning behavior of the cables. 

A similar survey to that of Gonzalez and Dreisbach was performed by the National Institute of 

Standards and Technology (NIST) in 1991 (Babrauskas et al. 1991). The study noted that test 

standards up to that point in time focused primarily on ignitability, flame spread rate, or distance 

of flame propagation. The concept of heat release rate (HRR) as a determiner of fire hazard was 

a relatively new idea at that time, as were devices like the Cone Calorimeter (ASTM E 1354) and 

measurement techniques like oxygen consumption calorimetry. The authors concluded that most 

of the standard test methods and cable fire experiments performed up to the point in time were 

not useful sources of input data for fire models. In 1991, two-zone fire models were fairly 

common, and these models required a fire’s HRR as input. Even the recently developed benchscale apparatus for measuring HRR were not particularly useful without a robust methodology 

for extrapolating the results to full-scale. 

1.3 Past Cable Fire Experiments 

This section presents a time-line of past cable fire experiments performed in the U.S. and abroad. 

The focus is on experimental studies of cable fires, not electrical failure due to fires. There has 

been a considerable amount of work performed at various testing laboratories on thermally 

induced electrical failure, most recently the US NRC-sponsored CAROLFIRE program (Nowlen 

et al. 2008). However, the focus of this report is on electrical cable fires, not functionality. 
3

 1976-1981, Sandia National Laboratories, Cable Tray Fire Testing: A useful survey of fire 

experiments involving electrical cables is entitled, “A Summary of Nuclear Power Plant 

Safety Research at Sandia National Laboratories, 1975-1987” (Nowlen 1989). The 

experiments involving cables are listed as follows: 

1976 Electrically Initiated Cable Fire Tests 

1977 Exposure Fire Cable Fire Tests 

1978 Fire Retardant Cable Coating Tests 

1978 Cable Tray Fire Barrier Tests 

1979 Cable Tray Fire Corner Effects Tests 

1981 Burn Mode Analysis of Cable Fires 

A highlight of this test program occurred in July, 1977, when a single experiment was 

conducted involving 14 horizontal cable trays arranged in two stacks of 7 and ignited at the 

base of one stack with a propane burner (Klamerus 1977). The fire propagated upwards 

within the stack of origin and then spread to the adjacent stack. The objective of the 

experiment was to determine if the fire would propagate between safety divisions mandated 

at the time. The cable was IEEE-383 qualified. This test followed on a series of other fire 

experiments involving various configurations of trays. The data collected consisted of visual 

observations and thermocouple (temperature) measurements to assess when the fire had 

reached a particular point. No large-scale calorimetry was performed either via mass loss or 

oxygen depletion methods; thus, no heat release rate data is available. However, an 

important observation was that the fire spread upwards forming a V-shaped burn pattern, the 

angle of which was estimated to be 35° from the vertical. This information, along with the 

time intervals for tray to tray spread, has been incorporated into Appendix R of the guidance 

document, NUREG/CR-6850. 

 1975-2000, Factory Mutual Research Corporation (FMRC): A number of bench-scale and 

full-scale experiments were conducted to quantify the burning behavior of electrical cables. 

A summary of this work is contained in Tewarson’s chapter of the SFPE Handbook, 4th

Edition (2008). Highlights include the development of the Fire Propagation Apparatus 

(ASTM E 2058). Lee (1985), working at the National Bureau of Standards, estimated that 

the measured burning rates for various cables in the FMRC flammability apparatus correlated 

with full-scale, multiple tray cable fire experiments when a scaling factor was applied. 

Specifically, it was estimated by Lee that the heat release rate per unit area of cables within 

stacked horizontal trays was approximately 0.45 times that measured in the FMRC apparatus. 

This correlation is included in NUREG/CR-6850. 

 2000, Europe, FIPEC (Fire Performance of Electrical Cables) research program: A 

consortium of test laboratories from the UK, Italy, Sweden and Belgium conducted an 

extensive multi-year investigation of cable fires (Grayson et al. 2000). It involved both 

experiments and numerical modeling. The experiments were organized in the following 

way: 
4

“Real-scale” experiments intended to reproduce actual cable installations 

“Full-scale” standard tests in cable trays 

Cone Calorimeter testing of cable segments arranged side by side in a single layer 

Cone Calorimeter testing of cable materials (jackets, insulators, fillers) 

The “real-scale” experiments were done either with three horizontal trays within a relatively 

narrow corridor or one vertical tray in a corner. The “full-scale” standard tests were 

conducted using a modified form of the IEC 60332-3 test standard, a vertical flame spread 

test similar to IEEE-383. The term “real-scale” implies that the configuration is based on 

actual installation practice rather than a testing standard configuration. One of the objectives 

of the program was to correlate the Cone Calorimeter results with both the real and full-scale 

results. The testing suggests that it is possible, to a certain extent, to predict the flammability 

of a particular cable type within a fully-loaded tray based on its heat and smoke production 

from a 10 cm by 10 cm array of cable segments subjected to a constant external heat flux. 

 1996, SP, Sweden: Bench-scale measurements of cables were performed at SP in Sweden, in 

addition to numerical modeling of flame spread (Van Hees and Thureson 1996). 

 1997, VTT, Finland: There has also been some experimental work on cable fires conducted 

at VTT Technical Research Centre of Finland (Mangs and Keski-Rahkonen 1997). Most of 

the experiments, however, involved very specific configurations that make it difficult to 

utilize the test results for other configurations or modeling. 

1.4 Past Cable Fire Modeling Efforts 

There have been a number of attempts to model cable fires over the past 30 years. Some of the 

early models were similar in concept to heat transfer models designed to study arrays of 

cylindrical pipes or heating elements (Hunter 1979). Models developed in the 1980s and 1990s 

made use of empirical correlations and concepts that were developed specifically for fire 

applications, like flame heights and ignition times (Van Hees and Thureson 1996; 

Grayson et al. 2000). These models also began to make use of bench-scale data from newly 

invented devices like the Cone Calorimeter (ASTM E 1354). In the late 1990s and continuing to 

the present, CFD (computational fluid dynamics) models have been modified to account for 

burning cables (Grayson et al. 2000; Hietaniemi et al. 2004) 

In the U.S., simple calculation methods for cable fires evolved from the experimental work done 

at Sandia National Laboratories, Factory Mutual, and various other testing labs. NUREG/CR6850 (2004) and NUREG-1805 (Iqbal and Salley 2004) contain surveys of experimental results 

that are pertinent to modeling. The information is derived from bench-scale and full-scale cable 

fire experiments conducted between approximately 1975 and 2000. Based on these experiments, 

both documents recommend a set of relatively simple calculation methods to assess various 

phenomena related to cable fires. For example, the recommended method of estimating the heat 

release rate of a specified area of a burning cable tray is to assume that it is a fraction (0.45) of 

the heat release rate per unit area of a small sample of cable in a particular flammability 

apparatus under a constant external heat flux (60 kW/m2

). The correlation was proposed by 
5

B.T. Lee (1985) of the National Bureau of Standards (now NIST) using experimental 

measurements made by Tewarson et al. (1979) and Sumitra (1982) at Factory Mutual Research 

Corporation. The estimate of the rate of flame spread within a single tray is not based on any 

experiments involving cable, but rather is a general purpose formula involving parameters such 

as the incident heat flux, thermal inertia of the cables, ignition temperature, and so forth. A 

model of upward fire spread through a stack of horizontal cable trays is based on a single 

experiment conducted at Sandia National Laboratories (Nowlen, 1989). 

1.5 Current Research Needs 

While there has been a considerable amount of work done over the past 40 years to measure 

cable properties and model their fire behavior, it is still a considerable challenge to predict the 

heat release rate of a stack of cable trays. Guidance documents, like the SFPE Handbook (2008), 

NUREG-1805, Fire Dynamics Tools (Iqbal and Salley 2004), and NUREG/CR-6850, contain 

lengthy tables of material properties, burning rates, flame spread equations, and other 

information gleaned from past experimental and modeling efforts. Still, there is no consensus on 

how to predict the heat release rate of a stack of cable trays using a simple or a detailed fire 

model. The main reasons for the current state of affairs are: 

 While there are numerous standard tests used to “qualify” cables, most tests address vertical 

configurations of very specific cable arrangements, and almost all produce only a “Pass” or 

“Fail” rating. This information is very important for selecting appropriate types of cable, but 

it is not useful for modeling purposes. 

 Past cable fire experiments, for the most part, have been conducted to assess very specific 

scenarios and configurations. It is difficult to extract from such experiments information, 

like burning rates, that can be applied to a wider variety of scenarios. Few of the 

experiments were designed to provide input data for current generation fire models, Indeed, 

during the 1970s and 1980s, fire models were little more than empirical correlations, and 

there was no need at the time for detailed material properties, like kinetic constants. 

 Efforts by Tewarson (SFPE 2008) and others to compile a database of cable material 

properties has yielded lengthy lists of properties for different cable materials, but these data 

are difficult to apply in modeling because the properties are dependent on the configuration 

of the measurement apparatus. Also, cables are made up of multiple materials, including a 

substantial amount of copper, and thermo-physical properties of the individual materials 

cannot be easily combined into “effective” properties for the entire cable. 

 Past modeling efforts have produced a number of useful concepts for both simplified and 

detailed models, but these models often rely on empirical data that is tied to a particular 

configuration (vertical or horizontal, for example), or data that is difficult to obtain (like 

spreading rates), or data that varies from test apparatus to test apparatus (heat of combustion, 

for example). 
6

 Those models that have been developed for cable fires require experimental data for 

validation: Many of the large-scale experiments performed over the past 40 years have been 

used to develop empirical models of cable fire growth and spread. As such, these 

experiments cannot be used to validate fire models because they have already been used to 

calibrate the models. For example, much of the guidance in NUREG/CR-6850 for 

calculating the heat release and spread rates of cables fires is derived directly from the 

experiments performed by Sandia National Laboratories and Factory Mutual Research 

Corporation. 

 Past experiments that could potentially be used for model validation often have little 

information about the properties of the cables. In such cases, only the simplest of fire models 

that do not require detailed property information can make use of these experiments. 

 Experiments performed prior to the 1980s often do not include a heat release rate 

measurement based on oxygen-consumption calorimetry or mass loss. In such cases, there is 

very little information that can be used to validate a fire model because the primary quantity 

that the typical model needs to predict the effects of a fire is its heat release rate. 

The CHRISTIFIRE program seeks to fill some of the gaps that currently exist for modeling cable 

fires. The most important aspect of the program is the conduct of realistic, full-scale fires of 

typical cable installations, along with the necessary information about the cables to perform 

simple and detailed model calculations. The degree to which the various models can or cannot 

predict the heat release rate of these fires will indicate the usefulness of certain kinds of data or 

certain numerical techniques. 
7

2 TECHNICAL APPROACH 

2.1 Objective of CHRISTIFIRE 

The CHRISTIFIRE (Cable Heat Release, Ignition, and Spread in Tray Installations during FIRE) 

experimental program is a U.S. Nuclear Regulatory Commission (US NRC) Office of Nuclear 

Regulatory Research (RES) initiated effort to quantify the mass and energy release rates from 

burning electrical cables. The project is a collaborative effort that includes the NRC Office of 

Nuclear Reactor Regulation (NRR) as peer reviewers and the National Institute of Standards and 

Technology (NIST) as the primary experimental laboratory. 

The related project CAROLFIRE (Cable Response to Live Fire, NUREG/CR-6931) has provided 

much needed information on the electrical failure mechanisms of cables in fire, including a 

relatively simple model to predict a cable’s thermally-induced electrical failure (THIEF). 

However, the measurements and modeling of CAROLFIRE did not provide information about 

the heat release and spread rates of burning cables. CAROLFIRE demonstrated that ignition and 

electrical failure often occur within seconds of each other, but measurements were not made to 

quantify the burning behavior beyond the point of electrical failure. 

CHRISTIFIRE addresses the burning behavior of a cable in a fire beyond the point of electrical 

failure. Its primary aim is to provide data for the development of fire models that can predict the 

heat release rate (HRR) of a cable fire. To predict the HRR, the model must account for the 

ignition and spread of a fire both vertically and laterally within stacks of cable trays. Phase 1 of 

CHRISTIFIRE focuses on stacks of horizontal trays. 

The CHRISTIFIRE Phase 1 experimental program has two main thrusts – bench-scale 

measurements of the effluent from small samples of burning cables and full-scale measurements 

of the heat release and fire spread rate of cables burning within typical ladder-type trays. Both 

sets of measurements are designed to provide the necessary input data for numerical fire models 

that are typically used to assess the consequences of accidental fires within various 

compartments in an NPP. Unlike most standard fire tests involving cables, these experiments are 

not intended as qualification or classification tests. In fact, typical qualification tests focus on 

vertical cable trays, but CHRISTIFIRE Phase 1 involves only horizontal trays because these are 

found in virtually every compartment of a plant. 

2.2 Overview of CHRISTIFIRE Phase 1 Experiments 

The CHRISTIFIRE test program shares a number of aspects with those described in the previous 

chapter. Given that there are innumerable permutations of cable types, trays, barriers, 

orientations and so forth, it is impractical to develop a comprehensive testing program to 

evaluate all possible arrangements. However, if it can be shown that relatively inexpensive 

bench-scale experiments can be used to predict the outcome of large-scale experiments, and if 

the same bench-scale data can be used as input for fire models, the need for expensive largescale testing decreases significantly. The simplest example of such an approach is the current 
8

estimation technique for heat release rate recommended in NUREG/CR-6850 (2004) and 

NUREG-1805 (Iqbal and Salley, 2004), in which bench-scale heat release rate measurements 

using a device similar in design to the Cone Calorimeter are used for large-scale calculations. 

The existing approach, however, is based on only a handful of experiments performed under a 

single set of conditions. One objective of the current program is to make measurements of heat 

release rates under a variety of conditions and at a number of different scales. 

The CHRISTIFIRE research program consists of experiments performed on a variety of length 

scales, from micro-scale chemical analyses to full-scale, realistic cable tray configurations. 

Table 2-1 summarizes the experiments. The experiments can be roughly divided into two types: 

(1) measurements of heat release and spread rates, and (2) measurements of the composition of 

the cable materials and combustion products. From the perspective of fire modeling, these 

experiments quantify the production rates of mass and energy from a tray of burning cables. 

Table 2-1. Outline of CHRISTIFIRE Experimental Program 

Scale Description Number of Tests Related 

Standard 

Small Tube Furnace 9 cables ISO/TS 19700 

Micro Micro-Combustion Calorimeter 12 insulators; 12 jackets ASTM D 7309 

Small Cone Calorimeter 12 cables at 3 heat fluxes ASTM D 6113 

Intermediate Radiant Panel Apparatus 33 None 

Full Stacked Horizontal Trays 26 None 

2.3 Chemical Composition of Cables and Combustion Products 

The Tube Furnace (ISO/TS 19700) is a bench-scale device specifically designed to measure the 

composition of the effluent of a burning item. The objective of these measurements is to 

quantify the yields of the major combustion products from burning cables. This information is 

needed in fire modeling to quantify the production rates of various gases. 

Whereas the Tube Furnace measurements provide a detailed breakdown of the combustion 

products, it is not possible within the scope of the project to obtain a more detailed description of 

the cable materials other than the basic polymers used in the insulation and jacket. Fire models 

typically do not use this information. Instead, they require information about the thermal 

decomposition of the materials. For this reason, a device known as a Micro-Combustion 

Calorimeter or MCC (ASTM D 7309) was used to measure the mass loss rate of a slowly heated, 

small sample of material, from which various reaction parameters can be derived. There are two 

reasons for performing this measurement. First, it identifies the temperatures at which the main 

decomposition reactions occur, providing explanations for, and a ranking of, experimental results 

at larger scale. Second, these data can be used in the more detailed numerical models of fire as 

an alternative to specifying explicitly the heat release and spread rates. Such data are necessary 

for predicting, as opposed to specifying, the burning rate of the cables. 
9

2.4 Heat Release and Spread Rates of Cable Fires 

In CHRISTIFIRE Phase 1, cables were burned at three scales: full, intermediate, and benchscale. The bench-scale apparatus was the Cone Calorimeter (ASTM E 1354; ASTM D 6113; 

ISO 5660-1), which measures the heat release rate per unit area (HRRPUA) of a 10 cm by 10 cm 

(4 in by 4 in) single layer of cable segments. 

The intermediate-scale experiments involve a specially-designed device referred to as the 

Radiant Panel Apparatus. This device uses radiant panels to expose a roughly 1 m (3 ft) long 

section of cable within a 0.45 m (18 in) wide tray to a constant heat flux. Much like the Cone 

Calorimeter in design, the Radiant Panel Apparatus provides a heat release rate per unit area of a 

more realistic arrangement of cables within a commonly used ladder-back tray. One of the 

objectives of the radiant panel experiments is to compare the measured HRRPUA with that of 

the Cone Calorimeter. The Radiant Panel Apparatus is not a standard device, nor is it intended 

to be. It is expensive and requires a considerable amount of electrical power. It is not practical 

to burn samples of every cable type used in nuclear plants throughout the United States, past, 

present and future, in such a device. If it can be shown that the burning rate measured in the 

Cone Calorimeter, set to a particular exposing heat flux, is similar to the Radiant Panel 

Apparatus, then the Cone Calorimeter measurement can be used for fire model analysis. Past 

experimental programs to assess cable burning behavior have almost all used more or less this 

same strategy. 

The full-scale experiments consist of vertical stacks of horizontal trays that are up to 3.6 m 

(12 ft) in length. Unlike the Cone Calorimeter and Radiant Panel Apparatus, the full-scale 

experiments involve no external radiant heat source. Instead, a 40 kW natural gas burner is used 

to ignite the cables within the lowest tray, and the fire spreads upwards. The heat feedback 

within the stack of trays is provided naturally by the burning cables above and below. These 

tests are to be used to validate the models that make use of the micro, bench and intermediatescale measurements. 

 

11

3 CABLE PROPERTIES 

In the summer of 2006, two shipping containers filled with new, used, and aged electrical cables 

were shipped from Brookhaven National Laboratories to the Large Fire Laboratory at NIST. 

Most of the cables were manufactured in the late 1970s and early 1980s. The cables had been 

used for environmental qualification studies (10 CFR 50.49) in the 1980’s and 1990’s. These 

cables were surplus from that program with substantial amount that had never even been unrolled 

from the spool. The cables that were studied in the CHRISTIFIRE project were selected from 

this collection, plus a few newer samples were surplus from circuit testing at Sandia National 

Laboratories in Albuquerque, New Mexico. Twelve different cables were selected for testing at 

all scales, plus about 20 other cable types were chosen for the second multiple tray test series. 

The basis of selection was mainly variety and quantity. For many of the cable samples, there 

was not sufficient quantity to test at all scales. These cables were mixed together with others in a 

specified ratio and used in the full-scale experiments. 

3.1 Properties of Cables Used in CHRISTIFIRE 

Table 3-1 and Table 3-2 on the following pages contain a general description of the cables used 

in Phase 1 of the project. Note that the “Item No.” or “Cable #” is merely an identifier and has 

no relevance beyond this project. Note also that the cables shown in the photograph (Figure 3-1) 

are those for which tests at all scales were conducted. The property data was obtained by 

dissecting 20 cm (8 in) segments into their constituent parts – jacket, filler, insulation, 

conductors. 
Table 3-1. Cables used in CHRISTIFIRE 

Item No. Source Date Cable Markings 2 Rockbestos No Markings 3 Rockbestos ROCKBESTOS® 600V FIREWALL® III XHHW NEC TYPE TC (UL) 7 Rockbestos ROCKBESTOS® 600V FIREWALL® III XHHW NEC TYPE TC (UL) 11 Rockbestos 1980 ROCKBESTOS® 600V FIREWALL® III XHHW NEC TYPE TC (UL) 13 Rockbestos ROCKBESTOS® 600V FIREWALL® III XHHW NEC TYPE TC (UL) 15 Rockbestos ROCKBESTOS® FIREWALL® III XHHW NEC TYPE TC (UL) 16 Rockbestos 1981 ROCKBESTOS® 600V FIREWALL® III XHHW NEC TYPE TC (UL) 17 Rockbestos ROCKBESTOS® 600V FIREWALL® III XHHW NEC TYPE TC (UL) 20 Rockbestos ROCKBESTOS® FIREWALL® III 1978-8A469 21 Rockbestos ROCKBESTOS® FIREWALL® III XHHW NEC TYPE TC (UL) 22 Rockbestos ROCKBESTOS® 600V FIREWALL® III XHHW NEC TYPE TC (UL) 23 Rockbestos 1981 ROCKBESTOS® FIREWALL® III 600V 6/C 16 AWG 25 Rockbestos ROCKBESTOS® 90 °C DRY 75 °C WET Firewall III NEC Type TC 34 Rockbestos ROCKBESTOS® 600V FIREWALL® III 12/C 16 AWG 43 Rockbestos 1975 ROCKBESTOS® FIREWALL® III 600V 12/C 16 AWG 45 Rockbestos ROCKBESTOS® FIREWALL® III XHHW NEC TYPE TC (UL) 46 Rockbestos 1981 ROCKBESTOS® 600V FIREWALL® III XHHW NEC TYPE TC (UL) 47 Rockbestos ROCKBESTOS® FIREWALL® III Thermocouple extension cable ASA/ISA Type KX 212 Anaconda ANACONDA FLAME-GUARD 219 Anaconda ANACONDA FLAME-GUARD 1KV 220 Anaconda ANACONDA FLAME-GUARD 1KV 261 Suprenant ITT SUPRENANT Div. L/U 9941 COMPOSITE CABLE 269 Brand-Rex BRAND-REX TS75285 TRIAX RG-11A/U TYPE 270 Brand-Rex BRAND-REX TRIAXIAL CABLE RG11 A/U TYPE 271 Brand-Rex BRAND-REX XLP/CU POWER & CONTROL CABLE 2/C #14 600V SUN RES XHHW TYPE TC (UL) 272 Brand-Rex BRAND-REX SHIELDED COMPOSITE CABLE RG 62B/U+1/C 20KV +6/C 300V 273 Brand-Rex BRAND-REX INSTRUMENT CABLE 90C MJ6T 

12
Item 

No. Source Date Cable Markings 312 Okonite OKONITE CO. PLT#7 Cu Class 1E 1C12 327 General Cable GENERAL CABLE XLP 337 No Markings 367 Kerite 1989 KERITE 1989 #6 AWG CU 5KV HTK NON SHIELDED CABLE TEST # M0325 503 Rockbestos ROCKBESTOS® FIREWALL® III XHHW NEC TYPE TC (UL) 505 Rockbestos ROCKBESTOS® FIREWALL® III XHHW NEC TYPE TC (UL) 612 Rockbestos ROCKBESTOS® FIREWALL® III XHHW NEC TYPE TC (UL) 700 Rockbestos- Surprenant 2005 7/C 12 AWG ROCKBESTOS-SURPRENANT(G) X-LINK(R) TC 600V 90 DEG C WET OR DRY SUN RES DIR BUR NEC TYPE TC (UL) FMRC GP-1 K2 COLOR CODE FRXLPE LSZH-XLPO C12-0070 701 General Cable BICC 2006 GENERAL CABLE® BICC® BRAND SUBSTATION CONTROL CABLE 7/C #12AWG 600V 30 MAY 2006 

 11 13 15 16 20 21 23 43 46 219 220 269 270 271 367 700 701 

Figure 3-1. Photograph of some of the cables used in CHRISTIFIRE. 

13
Table 3-2. Properties of the cables used in CHRISTIFIRE 

Cable 

No. 

Insulation 

Material 

Jacket 

Material 

Classification 

Conductors 

Diameter 

(mm) 

Jacket 

Thickness (mm) 

Insulator 

Thickness (mm) 

Mass per unit 

Length (kg/m) 

Copper Mass 

Fraction 

Jacket Mass 

Fraction 

Insulation Mass 

Fraction 

Filler Material 

Mass Fraction 

2 XLPE Neoprene TS 4 19 2 1.5 0.568 0.46 0.33 0.17 0.04 3 XLPE Neoprene TS 19 24 2.5 1 1.104 0.53 0.26 0.21 0.00 7 XLPE Neoprene TS 12 21 2.5 1 0.752 0.48 0.32 0.19 0.00 

11 XLPE CSPE TS 37 32 3.1 1.1 1.985 0.55 0.23 0.22 0.00 16 XLPE Neoprene TS 4 19 2.2 1.8 0.671 0.52 0.27 0.18 0.03 17 TS 5 14 1.8 1 0.345 0.44 0.35 0.18 0.03 22 TS 9 18.5 2.1 1 0.606 0.45 0.34 0.19 0.02 23 XLPE CSPE TS 6 14 2.7 0.9 0.253 0.31 0.48 0.16 0.05 25 XLPE Neoprene TS 3 10 1.6 1 0.146 0.32 0.47 0.19 0.02 34 TS 12 19 2.2 0.7 0.499 0.38 0.40 0.17 0.05 43 XLPE Neoprene TS 12 15 2.3 0.8 0.357 0.38 0.38 0.21 0.03 45 TS 7 17 2 0.9 0.456 0.47 0.36 0.15 0.01 46 XLPE Neoprene TS 7 15 1.9 1.2 0.437 0.48 0.32 0.20 0.00 47 TS 2 9 1.6 0.9 0.114 0.30 0.54 0.12 0.03 

212 EPR CSPE TS 3 13 2 1.5 0.247 0.23 0.45 0.22 0.10 219 EPR CSPE TS 3 14 2.4 1.5 0.296 0.39 0.39 0.22 0.00 220 EPR CSPE TS 7 18 2.6 1.2 0.560 0.38 0.32 0.30 0.00 261 XLPE XLPE TS 10 18 2.5 0.9 0.397 0.27 0.42 0.29 0.02 269 XLPE CSPE TS 1 12 1.0 0.6/3.6 0.240 0.47 0.30 0.23 0.00 270 XLPE CSPE TS 1 12 0.6 0.8/3.5 0.235 0.49 0.27 0.24 0.00 271 XLPE XLPE TS 2 10 1.6 0.9 0.123 0.30 0.48 0.15 0.07 272 TS 8 14 1.5 0.7 0.252 0.40 0.31 0.26 0.04 273 XLPE XLPE TS 18 20 1.9 0.7 0.532 0.57 0.29 0.12 0.02 312 EPR Neoprene TS 3 12 1.6 1 0.239 0.38 0.45 0.16 0.00 327 TS 5 17.5 2.5 1.5 0.454 0.33 0.46 0.19 0.02 337 TS 1 24 6 N/A 1.381 0.72 0.28 0.00 0.00 367 EPR TS 1 16 2.3 3.5 0.441 0.27 0.45 0.28 0.00 503 TS 7 15.5 2.2 1 0.457 0.48 0.33 0.19 0.00 

14
Cable 

No. 

Insulation 

Material 

Jacket 

Material 

Classification 

Conductors 

Diameter 

(mm) 

Jacket 

Thickness (mm) 

Insulator 

Thickness (mm) 

Mass per unit 

Length (kg/m) 

Copper Mass 

Fraction 

Jacket Mass 

Fraction 

Insulation Mass 

Fraction 

Filler Material 

Mass Fraction 

505 TS 2 10 1.2 1 0.120 0.31 0.44 0.14 0.11 612 TS 3 12 1.7 1 0.237 0.39 0.41 0.16 0.04 700 XLPE TS 7 12 1.0 0.7 0.322 0.67 0.17 0.16 0.00 701 PE PVC TP 7 14 1.5 0.8 0.366 0.58 0.24 0.18 0.00 

Notes: 1. The accuracy of each table entry is implied by the number of significant digits. 2. The Classification of thermoset (TS) or thermoplastic (TP) is applied to the entire cable based on the composition of its materials 

and its electrical performance at high temperature. 

3. Filler Material is considered to be anything that is non-metallic and does not serve as an outer jacket or insulator. 4. The Jacket and Insulation Thicknesses were measured with calipers accurate to a hundredth of a mm but rounded to the nearest 

tenth because of local variations in material thickness. 

5. Cable #269 and #270 are triaxial cables with an outer jacket, two layers of metal shielding, and an inner and outer insulation 

material. The thicker of the two insulation layers surrounds the single conductor. 

6. The size of the conductors, as indicated by the AWG (American Wire Gauge) value, is not a useful parameter for this project. Of 

more value is the Copper Mass Fraction, which indicates the overall mass of copper in the cable. 

7. The Insulation Material and Jacket Material are based on the cable inventory list provided by Brookhaven National Laboratory. 

8. When there is no entry in the “Insulation Material” and/or “Jacket Material” column, the material could not be determined. 

15
16

3.2 Classification of Plastic Materials 

The information in this section has been taken from Appendix F of NUREG/CR-6931, Volume 1 

(Nowlen and Wyant 2007). It is important because throughout this report, cables are referred to 

as either thermoset or thermoplastic. The distinction is of importance when developing 

simplified models of burning behavior. Thermoplastics can be heated, melted, and then cooled 

to solid form. Thermosets, if heated, will reach their decomposition temperature before their 

melting temperature, and will degrade irreversibly if exposed to sufficiently high temperatures. 

Of relevance to fire performance is the fact that thermoset cables tend to withstand higher 

temperatures and burn at lower rates than thermoplastics. 

3.2.1 Thermoplastics 

Thermoplastics can be deformed and/or liquefied by heat addition and can be cooled to solid 

form. At the molecular level, the long polymer molecules attract each other by Van der Waals 

forces, dipole-dipole interactions, and hydrogen bonding and/or aromatic ring stacking, but there 

is no direct bonding or linking between molecular chains. These forces and interactions are 

inversely proportional to the temperature and the distance between the molecules. In the solid 

form the long polymer molecules are close together and the force between them keeps the 

material solid. If the thermal energy of the molecules is increased the molecules will separate 

and expand. If the heat addition is continued, the plastic will become more malleable but will 

not flow until it reaches its melting point. Once melted, the plastic will flow as a viscous fluid 

depending on the polymer characteristics and degree of polymerization. If heat continues to be 

added, the plastic will reach its degradation temperature. Once the degradation temperature is 

reached, the energy added to the molecules is large enough to break the covalent bonds of the 

molecules causing irreversible change in the properties of the plastic. 

3.2.2 Thermosets 

Unlike thermoplastics, thermoset molecules, once cured, are covalently bonded to each other. 

They cannot be liquefied by heat addition and cooled to solid form. If heat is added, the kinetic 

energy of the molecules will increase and the molecules will increase their vibration, but they 

will not be able to separate excessively. When temperature increases, the plastic might get softer 

but the degradation temperature will be reached before its glass transition temperature. Once the 

degradation temperature is reached, the plastic molecules will begin to lose molecular integrity 

and the covalent bonds will start to break. Once this happens, the process is irreversible and the 

polymer will have lost its original chemical and physical properties. In general, thermoset 

polymers have better mechanical properties, are stiffer, and can withstand higher temperatures 

during longer periods of time than thermoplastic polymers. 
17

4 MICRO-CALORIMETRY MEASUREMENTS 

4.1 Description 

Micro-combustion calorimetric (MCC) measurements were made using the pyrolysis combustion 

flow calorimeter (PCFC) developed by Lyon and co-workers at the U.S. Federal Aviation 

Administration (FAA) William J. Hughes Technical Center (Lyon et al. 2004). This device, 

shown in Figure 4-1, is used to measure the heat generated from the combustion of small (4 mg 

to 6 mg) material samples by oxygen depletion calorimetry. Samples are pyrolyzed at a 

specified heating rate in an anerobic atmosphere (typically N2) and the resulting gases are mixed 

with excess oxygen and combusted in a separate chamber. The heat release rate (HRR) from the 

specimen is obtained from measurements of the concentration of oxygen in the effluent exiting 

the combustor as a function of time. The methodology is the basis for the standard test 

ASTM D 7309. 

Figure 4-1. Pyrolysis Combustion Flow Calorimeter (PCFC). 

4.2 Results 

The results of the PCFC measurements for 12 cables are shown in Figure 4-2 through Figure 4-5 

and summarized in Table 4-1. For each cable, the insulation and jacket material were tested 

separately, and at least three replicates were performed for each (only one replicate is shown for 

each sample). The samples, weighing between 4 mg and 6 mg, were cut from the cable jackets 

and conductor insulation material of each of the 12 cables. These samples were pyrolyzed in the 

PCFC at a rate of 1.0 °C/s from 100 °C to 600 °C in a nitrogen atmosphere and the effluent 

Combustor

Mixing 

Section

Pyrolyzer

Sample Cup

Scrubber

Flow Meter

O2 Sensor

Exhaust

Purge Gas Inlet

Oxygen Inlet
18

combusted at 900 °C in a separate chamber with a mixture consisting of 20 % O2 and 80 % N2. 

The heating rate of 1 °C/s was chosen to be roughly comparable to a real fire. 

The resulting curve shows the heat release rate of the sample as it was heated, normalized by the 

mass of the original sample. There are usually one, two or three noticeable peaks in the curve, 

corresponding to temperatures where an important decomposition is occurring. Each peak can 

be characterized by the maximum value of the heat release rate (ݍ(௣, the temperature (ܶ௣ሻ, and 

the fraction of the original sample mass that is pyrolyzed in the reaction (ܻ଴). This last value is 

estimated from the relative area underneath that particular peak. The heat of combustion ሺ߅߂ሻ is 

the area under the entire curve divided by the factor, ሺ1 െ ߥ௥ሻ, where ߥ ௥is the fraction of the 

original mass that remains as residue. Sometimes this is referred to as the “char yield.” 

The temperatures and heat release rates corresponding to the peaks in the curve are important in 

that they convey when, and at what rate, these various materials burn. A further benefit of these 

results is that it is possible to derive the kinetic parameters, ܣ) ௜1/s) and ܧ) ௜kcal/mol), that define 

the decomposition reactions: 

ܻ݀௜

݀ݐ ൌ െܣ	௜ܻ ௜݁ିா೔/ோ் ; ܻ௜ሺ0ሻ ൌ ܻ௜,଴ (4-1) 

Here, ܻ௜ is the mass fraction of the i-th component of the solid, ܴ is the universal gas constant 

(kcal/mol/K), and ܶ is the temperature (K). Whenever there is a peak in the heat release rate 

curve, the second derivative of ܻ௜ is zero, and it is possible to obtain values of the kinetic 

parameters simply by estimating values of ݍ௣, ܶ௣, and ܻ଴ from the plots. In fact, each plot on the 

following pages shows a dashed line and a solid line. The dashed line is the original 

measurement, and the solid line is the solution of the decomposition equation above using kinetic 

parameters obtained from the values of ݍ௣, ܶ௣, and ܻ଴. 

Although the value of the maximum HRR is sensitive to heating rate, this dependency can be 

effectively removed by dividing it by the heating rate. The resulting quantity, which has the 

same units as heat capacity, is called heat release capacity. According to Lyon (2004), these 

variables (Tp, THR, HRC) along with char yield (ratio of the mass of the residual char to the 

original mass of the sample), are reliable indicators of materials flammability. Their physical 

significance is as follows. The char yield is the fraction of material that does not volatilize under 

the prescribed conditions and is clearly related to the total heat release, which is the effective fuel 

load per gram of material. The pyrolysis temperature, Tp, is comparable to the ignition 

temperature of the material, and the heat release capacity represents the maximum amount of 

heat a gram of sample can release (per unit temperature increase) in a fire. 

The test specification (ASTM D 7309-07) states that the estimated standard relative uncertainty 

based on the reproducibility of the heat release rate measurement is ±6 %, with the majority of 

the error arising from the uncertainty in the assumed heat released by complete combustion per 

unit mass of oxygen consumed (13.1 MJ/kg). 
19

Figure 4-2. Micro-Calorimetry results for Cables 11, 16 and 23. 

 
20

Figure 4-3. Micro-Calorimetry results for Cables 43, 46 and 219. 

 
21

Figure 4-4. Micro-Calorimetry results for Cables 220, 269 and 271. 

 
22

Figure 4-5. Micro-Calorimetry results for Cables 367, 700 and 701. 

 
23

Table 4-1. Summary of the Micro-Calorimetry Experiments. The bold font indicates the 

primary reaction. 

No. Cable 

Comp. ܻ଴,ଵ ܻ଴,ଶ ܻ଴,ଷ

ܶଵ

(°C) 

ܶଶ

(°C) 

ܶଷ

(°C) 

ଵ,௣ݍ

(W/g)

ଶ,௣ݍ

(W/g)

ଷ,௣ݍ

(W/g) ߥ௥

ܪ∆

(kJ/g) 

11 Insulator 0.06 0.91 0.03 360 485 425 35 564 30 0.06 26.7 

16 Insulator 0.06 0.91 0.03 355 485 440 47 475 50 0.08 26.1 

23 Insulator 0.08 0.92 --- 355 485 --- 47 498 --- 0.06 25.0 

43 Insulator 0.10 0.90 --- 320 485 --- 20 558 --- 0.07 30.8 

46 Insulator 0.05 0.92 0.03 370 485 430 25 510 60 0.15 29.7 

219 Insulator 0.25 0.75 --- 340 480 --- 20 306 --- 0.49 32.6 

220 Insulator 0.22 0.78 --- 340 480 --- 21 312 --- 0.48 33.7 

269 Insulator 0.06 0.90 0.04 375 490 435 20 546 60 0.16 33.8 

271 Insulator 0.07 0.88 0.05 375 490 440 40 410 70 0.09 26.6 

367 Insulator 0.30 0.65 0.05 320 480 395 30 366 50 0.39 38.4 

700 Insulator 0.05 0.92 0.03 375 485 435 17 481 50 0.17 28.7 

701 Insulator 0.63 0.37 --- 300 460 --- 216 58 --- 0.28 17.5 

11 Jacket 0.26 0.33 0.41 300 345 450 13 408 41 0.49 15.5 

16 Jacket 0.26 0.33 0.41 300 345 450 13 408 41 0.48 16.4 

23 Jacket 0.26 0.33 0.41 300 345 450 13 408 41 0.55 14.0 

43 Jacket 0.26 0.33 0.41 300 345 450 13 408 41 0.51 17.2 

46 Jacket 0.26 0.33 0.41 300 345 450 13 408 41 0.53 14.8 

219 Jacket 0.35 0.65 --- 350 470 --- 32 162 --- 0.46 25.0 

220 Jacket 0.35 0.65 --- 350 470 --- 32 162 --- 0.44 24.6 

269 Jacket 0.27 0.70 0.03 300 470 280 20 190 30 0.30 22.6 

271 Jacket 0.27 0.70 0.03 300 470 280 20 190 30 0.32 22.1 

367 Jacket 0.31 0.69 --- 325 470 --- 37 175 --- 0.47 25.0 

700 Jacket 0.10 0.90 --- 375 470 --- 11 280 --- 0.44 27.6 

701 Jacket 0.66 0.34 --- 310 460 --- 156 47 --- 0.22 18.0 

25

5 TUBE FURNACE MEASUREMENTS 

5.1 Description 

Bench-scale experiments to determine cable fire effluent composition were conducted in a Tube 

Furnace as specified by ISO/TS 19700, “Controlled equivalence ratio method for the 

determination of hazardous components of fire effluents,” depicted in Figure 5-1. It consists of 

three main parts: (1) a quartz tube running through an electrically heated furnace; (2) a 30 L 

(8 gal) dilution and sampling chamber; and (3) a specimen boat and drive mechanism, which can 

advance the specimen into the furnace at a controlled rate. Air is supplied at both the upstream 

end of the quartz tube and in the dilution and sampling chamber. By controlling the upstream air 

flow rate and the specimen feed rate, the equivalence ratio in the Tube Furnace can be adjusted 

to model several fire stages. All experiments were conducted under well-ventilated conditions, 

with the temperature and equivalence ratio (normalized fuel to air ratio) set as specified in 

ISO 19706 (650 °C (1200 °F) and 0.5, respectively). However, in some cases, to promote 

flaming combustion of the cables it was necessary to increase the temperature to as high as 

825 °C (1517 °F), and even then, not all cables would sustain continuous flaming combustion. 

Figure 5-1. ISO/TS 19700 Tube Furnace. 

5.1.1 Test Procedure 

Test specimens were placed in the sample boat, which was then placed in the (cool) upstream 

end of the quartz tube. Once the appropriate temperature and air flow rates were established, the 

drive mechanism was activated to advance the specimen into the furnace. At the same time, a 

portion of the exhaust from the dilution chamber was diverted to gas analysis instruments. 

Ideally, the combustion of the specimen reaches a steady-state, at which point gas concentrations 

can be recorded and yields derived. However, complex items like multi-conductor cables burn in 

a less uniform manner than, for example, common plastics. However, it is still possible to 

identify ignition and extinction events, and to determine average yields from the period in 

between. 

In many cases, the cables were too large to be fed through the furnace intact. In these cases, the 

cables were disassembled into the component insulated conductor, filler, and jacket material and 
26

the same relative fraction of each was used. For example, one out of four insulated conductors, a 

fourth of the filler, and a fourth of the jacket, sliced longitudinally. It has been found by way of 

simple experiments that it makes essentially no difference whether a specimen is intact. 

However, it is important that the linear density of each component remain constant along the 

boat. 

For each cable and set of conditions, three separate experiments were conducted; for each 

experiment the yield of each gas and soot was measured. The average of the three yields is 

reported, and the uncertainty is their standard deviation, representing the run-to-run variation of 

the measurement. 

5.1.2Quantification of CO and CO2

CO and CO2 were quantified using a non-dispersive infrared (NDIR) gas analyzer; oxygen was 

quantified by a paramagnetic analyzer in the same instrument. Gas was continuously drawn 

from the exposure chamber by a small pump and passed through a series of traps and filters, first 

a coiled tube immersed in a water ice bath, then an impinger bottle immersed in dry ice, with its 

upper half filled with glass wool, and finally a glass fiber disk filter. The intent was to remove 

particulates and condensable species, including water, that would otherwise interfere with and 

possibly harm the analyzer. While sampling, the flow was maintained at 1 L/min for the CO and 

CO2 detectors and 0.2 L/min for the O2 detector. The analyzer itself was calibrated daily with 

zero and span gases (a mixture of 5000 μL/L CO and 0.08 L/L of CO2 in nitrogen, and ambient 

air 0.207 L/L oxygen). 

5.1.3Quantification of HCN, HCl and HBr 

HCN, HCl, and HBr were quantified using a Fourier Transform Infrared (FTIR) Spectrometer, 

equipped with a stainless steel flow cell with 2 mm KBr windows and a 0.1 m path length, 

maintained at 170 °C (338 °F). Gas samples were drawn through a heated 0.635 cm (0.25 in) 

stainless steel tube from the sampling and dilution chamber, at approximately the same location 

as the sampling line for the NDIR. The sample was pulled through the sampling line and flow 

cell by a small pump located downstream from the flow cell, and then exhausted into the lab 

exhaust duct. The pump flow was measured at 10 L/min maximum, but was at times lower due 

to fouling of the sampling lines with smoke deposits. The signal to noise ratio was also 

improved by averaging up to several hundred spectra prior to quantification. An example of a 

spectrum resulting from this procedure is shown in Figure 5-2. Using these spectra, HCN, HCl, 

and HBr were quantified using the Autoquant, a software package for performing real time and 

off-line quantitative analyses of target compound based on the Classical Least Squares (CLS) 

algorithm as described by Haaland et. al (1985). In this method, the measured spectra are fit to 

linear combinations of reference spectra corresponding to the target compounds. 

Calibration spectra were obtained from a quantitative spectral library assembled by the Midac 

Corporation (1999) and from a collection of spectra provided by the Federal Aviation 

Administration who performed bench-scale fire tests on similar materials (Speitel 2001). In this 

analysis, the least squares fits were restricted to characteristic frequency regions or windows for 
27

each compound that were selected in such a way as to maximize the discrimination of the 

compounds of interest from other components present in fire gases. Table 5-1 lists the species 

included in this analysis and the frequency windows used for their quantification. Other species 

including acetylene and acrolein were initially included in the analysis, but after a careful 

examination of the spectra recorded in the experiments, it was determined that they are not 

present in measurable quantities. Although CO and CO2 are not quantified by this method, they 

are included in the analysis so that their presence does not produce “false positives” in other 

species that absorb in the same frequency regions. All reference spectra were recorded at 170 °C 

(338 °F) and ambient pressure. 

Figure 5-2. FTIR spectrum of the products of burning electrical cable. 

5000 4500 4000 3500 3000 2500 2000 1500 1000 500

Wavenumber (cm-1)

H2O

H2O

CO2

CO2

CO2

HCl

Absorbance
28

Table 5-1. Species and Frequency Windows for FTIR Analysis. 

Compound Reference 

Volume Fraction 

(μL/L) 

Frequency Window (cm-1) 

Minimum 

Detection Limit 

(μL/L) 

C3H4O 2250 850 to 1200, 2600 to 2900 20 

C2H2 387 3190 to 3420 NAa

CH4 483 2800 to 3215 NAa

CO 2410 2050 to 2225 20 

H2O 100 000 1225 to 2150, 3400 to 4000 NAa

HBr 2260 2400 to 2800 20 

HCl 9870 2600 to 3100 20 

HCN 507 710 to 722, 3200 to 3310 30 

CO2 47 850 2230 to 2300 50 a

Because these compounds do not contribute to toxicity, their minimum detection limits were not 

quantified. 

5.1.4Quantification of soot 

Soot was quantified gravimetrically by drawing gas from the sampling and dilution chamber at a 

fixed rate of 1 L/min through a 47 mm (1.9 in) diameter Teflon membrane filter. The filter was 

weighed before and after sampling, resulting in an average soot yield for the entire experiment. 

5.2 Results 

Nine of the cables tested at other scales were selected for testing in the Tube Furnace. An 

additional six cables that appeared visually different from these were also tested, but did not 

yield appreciably different results. In general, there are no clear trends linking cable appearance, 

burning behavior, and yields of gases of interest. Nor are there any correlations between 

measured product gases. 

Cables were burned in over-ventilated conditions with an average equivalence ratio of 0.53 with 

a run-to-run variation of ±0.18. 

Figure 5-3 shows the yields of gases produced from burning cables. Yields, in units of g/g, range 

as follows: 0.59 to 1.72 for CO2; 0.19 to 0.50 (although one of the other cables had a CO yield of 

essentially zero); 0.01 to 0.28 for HCl1

; and 0.008 to 0.064 for soot. HCN was not detected in 

any experiment. Error bars depicted in the plot are the standard deviations of that specific gas 

yield across three separate experiments. For cables 23 and 271, an instrumentation failure 

prevented the measurement of HCL, and the uncertainties for those two cables are the maximum 

yield measured from any other cable. 

 

1

 Note that during the first series of full-scale, Multiple Tray Experiments in May, 2009, a considerable amount of 

acidic liquid accumulated in the ducts that carried the exhaust gases from the fire. It is believed that the high levels 

of HCl in the smoke reacted with the galvanized portion of the duct work to form the corrosive liquid. A 

professional cleaning crew was hired to clean the ducts. 
29

Figure 5-4 shows the cross-correlations of yields of pairs of measured gases as well as soot. 

Each point represents a specific number cable. Based on the extremely low R2 values and the 

scatter about the least-squares fit, there appears to be no mathematical correlation between the 

yields of any of these gases or the soot. This is unfortunate in that it will not be possible to 

extrapolate the yield of any one gas from any other, and emphasizes that in equipment testing, all 

must be measured independently. 

Figure 5-3. Yields of various product gases. 

The residue fraction (Figure 5-5), defined as the mass of plastics remaining in the sample boat 

after an experiment divided by the initial mass of plastics, ranged from 0.04 to 0.29. It did not 

have any noticeable correlation with the gas or soot yields. These numbers are substantially 

lower than those measured in the micro-calorimeter, a difference attributable to the fact that in 

the micro-calorimeter, the specimens are exposed to an oxygen-free environment, while in the 

well-ventilated Tube Furnace they are exposed to fresh air, even when flaming has subsided. 

0.00

0.50

1.00

1.50

2.00

2.50

16 23 46 219 220 271 367 700 701

Cable Number

Yield (g/g)

CO2

CO

HCl

Soot
30

Figure 5-4. Cross-correlations of gas pairs 

R2 = 0.0063

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.00 0.50 1.00 1.50 2.00 2.50

Yield CO2

Yield CO

R2 = 0.0028

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.00 0.20 0.40 0.60 0.80

Yield CO

Yield HCl

R2 = 0.1714

0.000

0.005

0.010

0.015

0.020

0.025

0.030

0.035

0.040

0.045

0.050

0.00 0.10 0.20 0.30 0.40

Yield HCl

Yield Soot

R2 = 0.0811

0.00

0.50

1.00

1.50

2.00

2.50

0.000 0.020 0.040 0.060 0.080 0.100

Yield Soot

Yield CO2

R2 = 0.0312

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.00 0.50 1.00 1.50 2.00 2.50

Yield CO2

Yield HCl

R2 = 9E-05

0.000

0.010

0.020

0.030

0.040

0.050

0.060

0.070

0.080

0.090

0.00 0.20 0.40 0.60

Yield CO

Yield Soot
31

Figure 5-5. Residue/char yield of various cables 

 

Cable Number

16 23 46 219 220 271 367 700 701

Residue Fraction

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

33

6 CONE CALORIMETER MEASUREMENTS 

6.1 Description 

The Cone Calorimeter is a widely-used device in fire protection engineering for measuring the 

heat release rate of a material sample under a constant imposed heat flux. In the CHRISTIFIRE 

program, 12 cable samples were tested at 3 different heat fluxes (25 kW/m2

, 50 kW/m2, and 

75 kW/m2) to determine at which flux the burning rate of cables best matched that measured in 

the Radiant Panel Apparatus and in the Multiple Tray Experiments. 

The Cone Calorimeter measurements were performed at the University of Dayton Research 

Institute in October, 2009. The experiments were conducted on a FTT Dual Cone Calorimeter at 

three imposed heat fluxes (25, 50, and 75 kW/m2) with an exhaust flow of 24 L/s using the 

standardized Cone Calorimeter procedure for cable burns, ASTM D 6113-03, “Standard Test 

Method for Using a Cone Calorimeter to Determine Fire-Test-Response Characteristics of 

Insulating Materials Contained in Electrical or Optical Fiber Cables.” Sample preparation for all 

cable samples used the procedure outlined in Sections 8.1.2 and 8.1.4 of the standard, with some 

modifications as described in the procedure below. The heat release rate measurements have a 

standard relative uncertainty of ±10 %, based on an assumed specimen surface area of 88.4 cm2

(13.7 in2). All samples were tested in triplicate at each heat flux, except for the cases at 

75 kW/m2. 

6.1.1 Procedure for preparing cable samples for Cone Calorimeter testing 

Step 1. Cable samples were cut into 10 cm (4 in) segments and wrapped in aluminum foil with 

shiny side up (Figure 6-1). 

Figure 6-1. Typical cable sample for Cone Calorimeter. 

Step 2. Supplies included the frame bottom, tray, ceramic insert, mineral wool, sample, grid, and 

frame top (Figure 6-2). 
34

Figure 6-2. Sample holder for Cone Calorimeter. 

Step 3. Depending on the make-up of the cables, specimens were sometimes prepared using 

trays. The tray was placed on top of the frame base, and the ceramic insert and mineral wool 

were placed into the tray (Figure 6-3). 

Mineral 

Wool Frame 

Bottom Tray 

Ceramic 

Insert 

Sample 

Grid

Frame 

Top 
35

Figure 6-3. Tray for holding cables in Cone Calorimeter. 

Step 4. The sample and grid were then placed on top of the mineral wool (Figure 6-4). 

Figure 6-4. Sample holder assembly for Cone Calorimeter. 

Step 5. Finally, the entire specimen and tray assembly were covered with the top of the frame 

(Figure 6-5). 
36

Figure 6-5. The completed holder assembly for the Cone Calorimeter. 

Note 1. If no tray was necessary, Steps 1 through 5 were followed but the ceramic insert, 

mineral wool, sample and grid were placed directly into the frame base (Figure 6-6). 

Figure 6-6. Modified sample holder for Cone Calorimeter. 

Note 2. In order to make certain that the entire sample assembly fit into the sample frame, 

several combinations of ceramic tile and thicknesses of mineral wool were used. 
37

6.2 Results for Individual Cable Types 

The following pages contain a brief description2

 of the Cone Calorimeter measurements, along 

with the measured heat release rates for the cable samples at the different heat flux exposures. 

As part of the analysis, an effective heat release rate per unit area (HRRPUA) is calculated. 

Figure 6-7 displays the heat release rate per unit area as a function of time for three replicate 

experiments. The solid curves indicate the actual test data. The dashed lines display a simplified 

time history of the data that is useful for modeling. The flat part of the simplified function is 

taken as the average HRR. To compute it, first define the total heat released per unit area, ܳᇱᇱ, 

by integrating the heat release rate per unit area, ݍሶᇱᇱ, over the duration of the experiment: 

ܳᇱᇱ ൌන ݍሶ

ᇱᇱ

ஶ

଴

(6-1) ݐ݀ ሻݐሺ

Next, define the points in time, ݐଵ and ݐଶ,	before which 10 % of the total energy has been 

released and after which 90 % of the energy has been released, respectively: 

0.1	ܳᇱᇱ ൌන ݍሶ

ᇱᇱ

௧భ

଴

ሺݐሻ ݀ݐ ; 0.1 ܳᇱᇱ ൌන ݍሶ

ᇱᇱ

ஶ

௧మ

(6-2) ݐ݀ ሻݐሺ

The average heat release rate per unit area is now defined during the time period over which 

80 % of the total energy has been released: 

ݍሶ തതതᇱᇱത ൌ ׬ ݍሶ

ᇱᇱ݀ݐ ௧మ

௧భ

ݐଶ െ ݐଵ

(6-3)

Figure 6-7. Sample output from Cone Calorimeter. 

 

2

 Note that there is no narrative for the measurements performed with an imposed heat flux of 75 kW/m2. 

0 600 1200 1800 2400 3000

0

50

100

150

200

250

300

350

400

Time (s)

HRR (kW/m2)

Cable 701, Heat Flux 25 kW/m2

Rep. 1, HRRavg=121 kW/m2

Cable 701, Heat Flux 25 kW/m2

Rep. 2, HRRavg=105 kW/m2

Cable 701, Heat Flux 25 kW/m2

Rep. 3, HRRavg=103 kW/m2
38

6.2.1 Cable #11 

Imposed Heat Flux: 25 kW/m2

At the beginning of the test, occasional loud pops and crackling were heard, followed by a 

prolonged period of flashing, and then the flames went out. The spark igniter was left in for 

another 300 s, but the smoke production eventually stopped, the mass loss decreased to zero, and 

the sample did not reignite. The samples appeared to be mostly intact at the end of the test with 

only some surface damage (Figure 6-8). The underlying jacket and internal insulation appeared 

to be completely undamaged. No aluminum trays were used with these samples. 

Figure 6-8. Photograph of Cable #11 after Cone Calorimeter test at 25 kW/m2

. 

Imposed Heat Flux: 50 kW/m2 

Sample #1 in this set smoked, then loud popping was heard after exposure to the heater. This 

was followed by flashing and then unsteady ignition and then the flame went out. The spark was 

re-inserted and sporadic flashing continued, but eventually this stopped as well. The spark was 

left in for 400 s with no re-ignition and mass loss decreased significantly. The sample after this 

test showed mostly surface damage and some discoloration of the insulation material. Sample #2 

showed the same behavior as Sample #1, but the spark was left in for 600 s after the first 

flameout. The sample did not ignite after 600 s, but more smoke was noted even though the 

mass loss rate was fairly low. More discoloration of the insulation was noted in the sample after 

the test. Sample #3 showed the same behavior as the first two samples, but the spark was left in 

for 900 s. The sample exhibited sporadic flashing. The spark was left in for another 300 s and 

finally the sample reignited, but the flames were still unsteady. Some dripping was noted out the 

bottom of the holder which eventually became a steady stream of molten/decomposing polymer 

and insulation that leaked out the bottom of the holder. The final sample residue was greatly 

damaged and most of the interior insulation had been burned away leaving just metal wires that 

had collapsed down and some soot/char residues. (Figure 6-9) No aluminum trays were used 

with this sample. The HRRs for Cable #11 obtained from the Cone Calorimeter for three 

imposed heat fluxes (25 kW/m2

, 50 kW/m2, and 75 kW/m2) are shown in Figure 6-10. 
39

Figure 6-9. Photograph of Cable #11 after Cone Calorimeter test at 50 kW/m2

. 

Figure 6-10. Heat Release Rates for Cable #11 in the Cone Calorimeter. 

0 600 1200 1800 2400 3000 3600 4200

0

50

100

150

200

250

300

Time (s)

HRR (kW/m2)

Cable 11, Heat Flux 25 kW/m2

Rep. 1, HRRavg=6 kW/m2

Cable 11, Heat Flux 25 kW/m2

Rep. 2, HRRavg=10 kW/m2

Cable 11, Heat Flux 25 kW/m2

Rep. 3, HRRavg=3 kW/m2

0 600 1200 1800 2400 3000 3600 4200

0

50

100

150

200

250

300

Time (s)

HRR (kW/m2)

Cable 11, Heat Flux 50 kW/m2

Rep. 1, HRRavg=27 kW/m2

Cable 11, Heat Flux 50 kW/m2

Rep. 2, HRRavg=27 kW/m2

Cable 11, Heat Flux 50 kW/m2

Rep. 3, HRRavg=90 kW/m2

0 600 1200 1800 2400 3000 3600 4200

0

50

100

150

200

250

300

Time (s)

HRR (kW/m2)

Cable 11, Heat Flux 75 kW/m2

Rep. 1, HRRavg=127 kW/m2
40

6.2.2 Cable #16 

Imposed Heat Flux: 25 kW/m2

The cables smoked for a long time under this heat flux before igniting, with some flashing 

(unsteady ignition) noted directly under the spark igniter noted. Later, the sample generated 

popping noises along with a prolonged flashing period before the sample finally ignited. The 

sample then burned for a short time. The spark was reinserted with more flashing noted, but 

eventually this stopped and the sample would not re-ignite – even smoking of the sample slowed 

down and the mass loss rate greatly decreased. During this flashing period there was substantial 

soot buildup on the spark igniter, making it difficult to keep the sample ignited. Sample 3 in this 

set was tested without a metal tray since dripping from the insulation appeared to be minimal. 

While the sample took even longer to ignite without the tray, the fire behavior was the same. 

From the sample picture below (Figure 6-11), it appears that the outer jacket chars and protects 

the underlying insulation from further thermal damage other than some dripping/flowing of the 

insulation out the ends of the cable. 

Figure 6-11. Photograph of Cable #16 after Cone Calorimeter test at 25 kW/m2

. 

Imposed Heat Flux: 50 kW/m2 

Samples 1 and 3 ignited quickly and burned for a few minutes, then extinguished. Sample 2, 

however, burned much longer to leave a white ash all over the sample surface. The underlying 

insulation was melted for Samples 1 and 3, but it did not ignite (Figure 6-12). No aluminum 

trays were used. The HRRs for Cable #16 obtained from the Cone Calorimeter for three 

imposed heat fluxes (25 kW/m2

, 50 kW/m2, and 75 kW/m2) are shown in Figure 6-13. 
41

Figure 6-12. Photograph of Cable #16 after Cone Calorimeter test at 50 kW/m2. 

Figure 6-13. Heat Release Rates for Cable #16 in the Cone Calorimeter. 

0 600 1200 1800 2400 3000 3600 4200

0

50

100

150

200

250

300

Time (s)

HRR (kW/m2)

Cable 16, Heat Flux 25 kW/m2

Rep. 1, HRRavg=60 kW/m2

Cable 16, Heat Flux 25 kW/m2

Rep. 2, HRRavg=14 kW/m2

Cable 16, Heat Flux 25 kW/m2

Rep. 3, HRRavg=41 kW/m2

0 600 1200 1800 2400 3000 3600 4200

0

50

100

150

200

250

300

Time (s)

HRR (kW/m2)

Cable 16, Heat Flux 50 kW/m2

Rep. 1, HRRavg=71 kW/m2

Cable 16, Heat Flux 50 kW/m2

Rep. 2, HRRavg=130 kW/m2

Cable 16, Heat Flux 50 kW/m2

Rep. 3, HRRavg=54 kW/m2

0 600 1200 1800 2400 3000 3600 4200

0

50

100

150

200

250

300

Time (s)

HRR (kW/m2)

Cable 16, Heat Flux 75 kW/m2

Rep. 1, HRRavg=173 kW/m2
42

6.2.3 Cable #23 

Imposed Heat Flux: 25 kW/m2

Sample 1 smoked, flashed, and then ignited with a crackling noise heard during burning. The 

sample went out and the spark was reinserted but the sample would only flash and not re-ignite. 

The spark was left in for 600 s with flashing only occurring at the spark and not at the sample 

surface. At 800 s the sample finally reignited, but only at the edges of the sample holder. Some 

dripping was noted out the bottom of the sample holder at the end of the test – no aluminum tray 

was used for the first sample. For the second and third samples, the aluminum tray was used and 

dripping no longer occurred and fire behavior was otherwise the same. However, Sample 2 

and 3 were even harder to keep lit with the reinserted spark and Sample 3 would not re-ignite at 

all, even after 800 s of additional exposure. Sample 3 does not exhibit burning damage except 

for the melting of the blue filler material that leaked out at the ends. The other samples show 

significant damage to the cable surface and the underlying insulation (Figure 6-14). 

Figure 6-14. Photograph of Cable #23 after Cone Calorimeter test at 25 kW/m2. 

Imposed Heat Flux: 50 kW/m2 

Upon exposure to the cone heater, Sample 1 smoked, flashed quickly, and then ignited. 

However, the flames quickly went out and the spark was reinserted. The sample did nothing at 

first and then began to flash again, eventually reigniting but the flames always appeared unsteady 

through the entire test. Smoke was observed followed by lots of non-flaming drips out the 

bottom of the sample holder. This sample used no aluminum tray. Aluminum trays were used 

for Samples 2 and 3, which did not change fire behavior any and only partially mitigated the 

dripping behavior. Figure 6-15 is a photograph of Cable #23 test samples after Cone Calorimeter 

tests. The HRRs for Cable #23 obtained from the Cone Calorimeter for three imposed heat 

fluxes (25 kW/m2

, 50 kW/m2, and 75 kW/m2) are shown in Figure 6-16. 
43

Figure 6-15. Photograph of Cable #23 after Cone Calorimeter test at 50 kW/m2. 

Figure 6-16. Heat Release Rates for Cable #23 in the Cone Calorimeter. 

0 600 1200 1800 2400 3000

0

50

100

150

200

250

300

Time (s)

HRR (kW/m2)

Cable 23, Heat Flux 25 kW/m2

Rep. 1, HRRavg=47 kW/m2

Cable 23, Heat Flux 25 kW/m2

Rep. 2, HRRavg=41 kW/m2

Cable 23, Heat Flux 25 kW/m2

Rep. 3, HRRavg=4 kW/m2

0 600 1200 1800 2400 3000

0

50

100

150

200

250

300

Time (s)

HRR (kW/m2)

Cable 23, Heat Flux 50 kW/m2

Rep. 1, HRRavg=99 kW/m2

Cable 23, Heat Flux 50 kW/m2

Rep. 2, HRRavg=89 kW/m2

Cable 23, Heat Flux 50 kW/m2

Rep. 3, HRRavg=89 kW/m2

0 600 1200 1800 2400 3000

0

50

100

150

200

250

300

Time (s)

HRR (kW/m2)

Cable 23, Heat Flux 75 kW/m2

Rep. 1, HRRavg=135 kW/m2
44

6.2.4 Cable #43 

Imposed Heat Flux: 25 kW/m2

The samples smoked, popped a bit (some blistering was noted) with some flashing, but there was 

no sustained ignition. The test was stopped at 500 s due to no significant mass loss and decrease 

in smoke release. The inner insulation for this sample set appears to be mostly undamaged after 

the test (Figure 6-17). No aluminum trays were used with this sample set. 

Figure 6-17. Photograph of Cable #43 after Cone Calorimeter test at 25 kW/m2

. 

Imposed Heat Flux: 50 kW/m2 

The samples smoked, followed by some crackling, some flashing, and then the sample ignited. 

They burned for a while and then went out and could not be reignited with the spark. The 

samples appear to be mostly undamaged (Figure 6-18), much like the 25 kW/m2

 sample data. 

No aluminum trays were used with this sample set. The HRRs for Cable #43 obtained from the 

Cone Calorimeter for three imposed heat fluxes (25 kW/m2

, 50 kW/m2, and 75 kW/m2) are 

shown in Figure 6-19. 
45

Figure 6-18. Photograph of Cable #43 after Cone Calorimeter test at 50 kW/m2. 

Figure 6-19. Heat Release Rates for Cable #43 in the Cone Calorimeter. 

0 600 1200 1800 2400 3000

0

50

100

150

200

250

300

Time (s)

HRR (kW/m2)

Cable 43, Heat Flux 25 kW/m2

Rep. 1, HRRavg=8 kW/m2

Cable 43, Heat Flux 25 kW/m2

Rep. 2, HRRavg=4 kW/m2

Cable 43, Heat Flux 25 kW/m2

Rep. 3, HRRavg=6 kW/m2

0 600 1200 1800 2400 3000

0

50

100

150

200

250

300

Time (s)

HRR (kW/m2)

Cable 43, Heat Flux 50 kW/m2

Rep. 1, HRRavg=60 kW/m2

Cable 43, Heat Flux 50 kW/m2

Rep. 2, HRRavg=78 kW/m2

Cable 43, Heat Flux 50 kW/m2

Rep. 3, HRRavg=71 kW/m2

0 600 1200 1800 2400 3000

0

50

100

150

200

250

300

Time (s)

HRR (kW/m2)

Cable 43, Heat Flux 75 kW/m2

Rep. 1, HRRavg=169 kW/m2
46

6.2.5 Cable #46 

Imposed Heat Flux: 25 kW/m2

Fire behavior was the same as that noted for Cable #43, but no crackling or popping noises were 

heard and the surface of the samples did not blister. Some damage to the inner insulation was 

noted (Figure 6-20). No aluminum trays were used with this sample set. 

Figure 6-20. Photograph of Cable #46 after Cone Calorimeter test at 25 kW/m2

. 

Imposed Heat Flux: 50 kW/m2 

Fire behavior for this sample set was the same as that noted for Cable #43, but no crackling or 

popping heard. No damage to underlying insulation was noted (Figure 6-21). No aluminum 

trays were used with this sample set. The HRRs for Cable #46 obtained from the Cone 

Calorimeter for three imposed heat fluxes (25 kW/m2

, 50 kW/m2, and 75 kW/m2) are shown in 

Figure 6-22. 

Figure 6-21. Photograph of Cable #46 after Cone Calorimeter test at 50 kW/m2

. 
47

Figure 6-22. Heat Release Rates for Cable #46 in the Cone Calorimeter. 

0 600 1200 1800 2400

0

50

100

150

200

250

300

Time (s)

HRR (kW/m2)

Cable 46, Heat Flux 25 kW/m2

Rep. 1, HRRavg=17 kW/m2

Cable 46, Heat Flux 25 kW/m2

Rep. 2, HRRavg=3 kW/m2

Cable 46, Heat Flux 25 kW/m2

Rep. 3, HRRavg=14 kW/m2

0 600 1200 1800 2400

0

50

100

150

200

250

300

Time (s)

HRR (kW/m2)

Cable 46, Heat Flux 50 kW/m2

Rep. 1, HRRavg=61 kW/m2

Cable 46, Heat Flux 50 kW/m2

Rep. 2, HRRavg=59 kW/m2

Cable 46, Heat Flux 50 kW/m2

Rep. 3, HRRavg=62 kW/m2

0 600 1200 1800 2400

0

50

100

150

200

250

300

Time (s)

HRR (kW/m2)

Cable 46, Heat Flux 75 kW/m2

Rep. 1, HRRavg=172 kW/m2
48

6.2.6 Cable #219 

Imposed Heat Flux: 25 kW/m2

When the cables ignited, the flame spread all over the sample surface with a steady flame. Some 

blue colored flames were noted near the bottom edges of the sample during burning. No 

aluminum trays were used with this sample set. The samples by the end of the burn were 

completely consumed with only a fragile white ash on the surface (Figure 6-23). 

Figure 6-23. Photograph of Cable #219 after Cone Calorimeter test at 25 kW/m2

. 

Imposed Heat Flux: 50 kW/m2 

The samples ignited quickly with lots of popping heard followed by pieces of the sample surface 

flying out of the top of the sample holder. This behavior died down as the flames died down in 

intensity. No aluminum trays were used with this sample set. Figure 6-24 is a photograph of 

Cable #219 test samples after Cone Calorimeter tests. The HRRs for Cable #219 obtained from 

the Cone Calorimeter for three imposed heat fluxes (25 kW/m2, 50 kW/m2, and 75 kW/m2) are 

shown in Figure 6-25. 

Figure 6-24. Photograph of Cable #219 after Cone Calorimeter test at 50 kW/m2. 
49

Figure 6-25. Heat Release Rates for Cable #219 in the Cone Calorimeter. 

0 600 1200 1800 2400

0

50

100

150

200

250

300

Time (s)

HRR (kW/m2)

Cable 219, Heat Flux 25 kW/m2

Rep. 1, HRRavg=141 kW/m2

Cable 219, Heat Flux 25 kW/m2

Rep. 2, HRRavg=132 kW/m2

Cable 219, Heat Flux 25 kW/m2

Rep. 3, HRRavg=127 kW/m2

0 600 1200 1800 2400

0

50

100

150

200

250

300

Time (s)

HRR (kW/m2)

Cable 219, Heat Flux 50 kW/m2

Rep. 1, HRRavg=134 kW/m2

Cable 219, Heat Flux 50 kW/m2

Rep. 2, HRRavg=148 kW/m2

Cable 219, Heat Flux 50 kW/m2

Rep. 3, HRRavg=140 kW/m2

0 600 1200 1800 2400

0

50

100

150

200

250

300

Time (s)

HRR (kW/m2)

Cable 219, Heat Flux 75 kW/m2

Rep. 1, HRRavg=187 kW/m2
50

6.2.7 Cable #220 

Imposed Heat Flux: 25 kW/m2

The first sample took a very long time to ignite with fire behavior similar to that of Cable #219. 

Later in the test, there were flaming drips out the bottom of the holder noted, and an aluminum 

tray was used for Sample 2. This sample however did not ignite even by 1000 s (see charred 

cable in the middle of the photograph below). So for Sample 3 the aluminum tray was removed 

and the sample ignited at 980 s with flaming drips noted again out the bottom of the sample 

holder later in the test. Figure 6-26 is a photograph of Cable #220 test samples after Cone 

Calorimeter tests. 

Figure 6-26. Photograph of Cable #220 after Cone Calorimeter test at 25 kW/m2

. 

Imposed Heat Flux: 50 kW/m2 

Upon exposure to the heater, the samples smoked, with some flashing and popping heard before 

ignition occurred. Some pieces popped and flew out of sample holder, but not as extensive as 

that noted with Cable 219. Sample 2 extinguished after burning for a little bit but reignited after 

60 s of spark re-exposure. No aluminum trays were used with these samples. Figure 6-27 is a 

photograph of Cable #220 test samples after Cone Calorimeter tests. 

The HRRs for Cable #220 obtained from the Cone Calorimeter for two imposed heat fluxes 

(25 kW/m2

 and 50 kW/m2) are shown in Figure 6-28. Note that no test was done at 75 kW/m2. 
51

Figure 6-27. Photograph of Cable #220 after Cone Calorimeter test at 50 kW/m2. 

Figure 6-28. Heat Release Rates for Cable #220 in the Cone Calorimeter. 

0 600 1200 1800 2400 3000 3600

0

50

100

150

200

250

Time (s)

HRR (kW/m2)

Cable 220, Heat Flux 25 kW/m2

Rep. 1, HRRavg=117 kW/m2

Cable 220, Heat Flux 25 kW/m2

Rep. 2, HRRavg=3 kW/m2

Cable 220, Heat Flux 25 kW/m2

Rep. 3, HRRavg=107 kW/m2

0 600 1200 1800 2400 3000 3600

0

50

100

150

200

250

Time (s)

HRR (kW/m2)

Cable 220, Heat Flux 50 kW/m2

Rep. 1, HRRavg=11 kW/m2

Cable 220, Heat Flux 50 kW/m2

Rep. 2, HRRavg=148 kW/m2

Cable 220, Heat Flux 50 kW/m2

Rep. 3, HRRavg=137 kW/m2
52

6.2.8 Cable #270 

Imposed Heat Flux: 25 kW/m2

Following ignition, some bubbling was noted beneath the surface of the jacket material. 

Eventually the bubbling subsided as the flame grew bigger. Some smoke was observed coming 

out the bottom of the sample holder later in the test. By the end of the test the sample surface 

was badly damaged and the sample frame and grid showed significant corrosion/discoloration 

from the samples combustion gases (Figure 6-29). Prying apart the frame and grid at the end of 

the experiment showed that some dripping had occurred so an aluminum tray was used for the 

second sample. Fire behavior for the second sample was the same as the first, but the ignition 

was delayed a bit. Smoke was still observed to come out the bottom of the sample holder 

though, and so for the third sample, the aluminum tray was not used. Fire behavior of the third 

sample was identical to that of the first. 

Figure 6-29. Photograph of Cable #270 after Cone Calorimeter test at 25 kW/m2

. 

Imposed Heat Flux: 50 kW/m2 

Following ignition, the sample suddenly extinguished. Upon reinserting the spark, the sample 

quickly reignited and began to burn vigorously. Some pieces of char would deform and flow 

over the top edge of the holder with flaming drips noted. During the growth of the peak flame 

height, a high pitched whining sound could be heard. Occasional smoke and drips out the 

bottom of the holder were noted. The final sample residues were notable in that the copper braid 

was intact and quite rigid, forming hollow tubes where the center copper wire had fallen to the 

bottom of the tube. No insulation or jacket material beyond char was left behind for these badly 

damaged samples (Figure 6-30). No aluminum trays were used with this sample set. The HRRs 

for Cable #270 obtained from the Cone Calorimeter for three imposed heat fluxes (25 kW/m2

, 

50 kW/m2, and 75 kW/m2) are shown in Figure 6-31. 
53

Figure 6-30. Photograph of Cable #270 after Cone Calorimeter test at 50 kW/m2. 

Figure 6-31. Heat Release Rates for Cable #270 in the Cone Calorimeter. 

0 600 1200 1800 2400 3000 3600

0

100

200

300

400

500

600

700

800

Time (s)

HRR (kW/m2)

Cable 270, Heat Flux 25 kW/m2

Rep. 1, HRRavg=169 kW/m2

Cable 270, Heat Flux 25 kW/m2

Rep. 2, HRRavg=191 kW/m2

Cable 270, Heat Flux 25 kW/m2

Rep. 3, HRRavg=213 kW/m2

0 600 1200 1800 2400 3000 3600

0

100

200

300

400

500

600

700

800

Time (s)

HRR (kW/m2)

Cable 270, Heat Flux 50 kW/m2

Rep. 1, HRRavg=293 kW/m2

Cable 270, Heat Flux 50 kW/m2

Rep. 2, HRRavg=300 kW/m2

Cable 270, Heat Flux 50 kW/m2

Rep. 3, HRRavg=302 kW/m2

0 600 1200 1800 2400 3000 3600

0

100

200

300

400

500

600

700

800

Time (s)

HRR (kW/m2)

Cable 270, Heat Flux 75 kW/m2

Rep. 1, HRRavg=510 kW/m2
54

6.2.9 Cable #271 

Imposed Heat Flux: 25 kW/m2

During the early stages of burning, some popping of pieces off the sample surface occurred, but 

the sample did not burn long. The spark igniter was reinserted with some minor flashing 

observed but no sustained ignition was observed. Interior insulation appears to be mostly 

undamaged, again indicating that the jacket was providing significant thermal protection for the 

underlying material (Figure 6-32). No aluminum trays were used with this sample set. 

Figure 6-32. Photograph of Cable #271 after Cone Calorimeter test at 25 kW/m2

. 

Imposed Heat Flux: 50 kW/m2 

Then the sample smoked and ignited with more little glowing sparks/coals coming off the sample 

surface during testing. Eventually this stopped and the sample continued burning for awhile and 

then extinguished. While the surface of the sample was badly damaged, the underlying material 

was still mostly untouched (Figure 6-33). No aluminum trays were used with this sample set. 

The HRRs for Cable #271 obtained from the Cone Calorimeter for three imposed heat fluxes 

(25 kW/m2

, 50 kW/m2, and 75 kW/m2) are shown in Figure 6-34. 
55

Figure 6-33. Photograph of Cable #271 after Cone Calorimeter test at 50 kW/m2. 

Figure 6-34. Heat Release Rates for Cable #271 in the Cone Calorimeter. 

0 600 1200 1800 2400 3000 3600

0

50

100

150

200

250

300

Time (s)

HRR (kW/m2)

Cable 271, Heat Flux 25 kW/m2

Rep. 1, HRRavg=15 kW/m2

Cable 271, Heat Flux 25 kW/m2

Rep. 2, HRRavg=10 kW/m2

Cable 271, Heat Flux 25 kW/m2

Rep. 3, HRRavg=13 kW/m2

0 600 1200 1800 2400 3000 3600

0

50

100

150

200

250

300

Time (s)

HRR (kW/m2)

Cable 271, Heat Flux 50 kW/m2

Rep. 1, HRRavg=83 kW/m2

Cable 271, Heat Flux 50 kW/m2

Rep. 2, HRRavg=113 kW/m2

Cable 271, Heat Flux 50 kW/m2

Rep. 3, HRRavg=113 kW/m2

0 600 1200 1800 2400 3000 3600

0

50

100

150

200

250

300

Time (s)

HRR (kW/m2)

Cable 271, Heat Flux 75 kW/m2

Rep. 1, HRRavg=199 kW/m2
56

6.2.10 Cable #367 

Imposed Heat Flux: 25 kW/m2

The samples ignited with some spitting of surface pieces out of the sample holder and crackling 

sounds were noted. The pieces that landed outside the holder left white marks on the metal and 

corroded parts of the aluminum foil used to protect the load cell under the sample. The sample 

only burned for a little while and then would not reignite. The underlying insulation appeared 

undamaged although the surface of the sample appeared heavily damaged from the short 130 s to 

140 s burn time (Figure 6-35). No aluminum trays were used. 

Figure 6-35. Photograph of Cable #367 after Cone Calorimeter test at 25 kW/m2

. 

Imposed Heat Flux: 50 kW/m2 

Numerous flaming particles were observed “spitting” out of the sample surface initially in the 

fire. The fire growth then began to die down and eventually picked back up, growing steadily 

and then burning for a very long time (50 min). Some dripping out of the sample holder was 

noted. The final samples were badly damaged, composed of fragile white ash on the surface and 

partially collapsed char tubes and damaged copper wire deeper into the sample (Figure 6-36). 

No aluminum trays were used. The HRRs for Cable #367 obtained from the Cone Calorimeter 

for three imposed heat fluxes (25 kW/m2

, 50 kW/m2, and 75 kW/m2) are shown in Figure 6-37. 
57

Figure 6-36. Photograph of Cable #367 after Cone Calorimeter test at 50 kW/m2. 

Figure 6-37. Heat Release Rates for Cable #367 in the Cone Calorimeter. 

0 600 1200 1800 2400 3000 3600

0

50

100

150

200

250

300

Time (s)

HRR (kW/m2)

Cable 367, Heat Flux 25 kW/m2

Rep. 1, HRRavg=80 kW/m2

Cable 367, Heat Flux 25 kW/m2

Rep. 2, HRRavg=60 kW/m2

Cable 367, Heat Flux 25 kW/m2

Rep. 3, HRRavg=71 kW/m2

0 600 1200 1800 2400 3000 3600

0

50

100

150

200

250

300

Time (s)

HRR (kW/m2)

Cable 367, Heat Flux 50 kW/m2

Rep. 1, HRRavg=110 kW/m2

Cable 367, Heat Flux 50 kW/m2

Rep. 2, HRRavg=100 kW/m2

Cable 367, Heat Flux 50 kW/m2

Rep. 3, HRRavg=110 kW/m2

0 600 1200 1800 2400 3000 3600

0

50

100

150

200

250

300

Time (s)

HRR (kW/m2)

Cable 367, Heat Flux 75 kW/m2

Rep. 1, HRRavg=169 kW/m2
58

6.2.11 Cable #700 

Imposed Heat Flux: 25 kW/m2

There was very little smoke or mass loss even up to 600 s and no ignition noted. The third 

sample was exposed for 800 s, after which it finally ignited but then extinguished again after a 

short burning period. The spark igniter was reinserted for another 200 s with prolonged flashing 

noted, but the sample would not stay lit. Excessive soot buildup on the spark igniter caused the 

spark to go out more than once and resulted in stopping the test for Sample 3. Due to its 

prolonged heat exposure, Sample 3 exhibited more thermal damage to the surface and insulation 

than the other two samples (sample at far right in Figure 6-38). No aluminum trays were used. 

Figure 6-38. Photograph of Cable #700 after Cone Calorimeter test at 25 kW/m2

. 

Imposed Heat Flux: 50 kW/m2 

The samples smoked and then ignited with no flashing noted. As the flame intensity grew, the 

flame turned green in color, followed by a blue color and then eventually turned yellow with 

some dark blue noted at the edges of the sample holder. Later in the burn smoke was observed to 

come out of the sample followed by occasional flames. Sample 1 used no aluminum tray, but 

Samples 2 and 3 did. However, there was no significant difference in the fire behavior. The 

final sample residues were badly damaged with bare copper wires noted sticking out the ends of 

the samples (Figure 6-39). 

The HRRs for Cable #700 obtained from the Cone Calorimeter for two imposed heat fluxes 

(25 kW/m2

 and 50 kW/m2) are shown in Figure 6-40. Note that no sample was tested at 

75 kW/m2. 
59

Figure 6-39. Photograph of Cable #700 after Cone Calorimeter test at 50 kW/m2. 

Figure 6-40. Heat Release Rates for Cable #700 in the Cone Calorimeter. 

0 600 1200 1800 2400 3000

0

50

100

150

200

250

300

350

400

Time (s)

HRR (kW/m2)

Cable 700, Heat Flux 25 kW/m2

Rep. 1, HRRavg=3 kW/m2

Cable 700, Heat Flux 25 kW/m2

Rep. 2, HRRavg=5 kW/m2

Cable 700, Heat Flux 25 kW/m2

Rep. 3, HRRavg=63 kW/m2

0 600 1200 1800 2400 3000

0

50

100

150

200

250

300

350

400

Time (s)

HRR (kW/m2)

Cable 700, Heat Flux 50 kW/m2

Rep. 1, HRRavg=161 kW/m2

Cable 700, Heat Flux 50 kW/m2

Rep. 2, HRRavg=125 kW/m2

Cable 700, Heat Flux 50 kW/m2

Rep. 3, HRRavg=123 kW/m2
60

6.2.12 Cable #701 

Imposed Heat Flux: 25 kW/m2

The samples smoked, flashed several times, ignited briefly, and extinguished. The spark was 

reinserted. Eventually the samples began to flash again and then finally re-ignited with a much 

larger peak of heat release noted. Much later into the test a dark blue flame could be seen at the 

edges of the sample holder and some occasional drips out the bottom of the sample holder noted 

shortly before the sample extinguished. Blue-green flames were noted at the ends of the cables 

deep in the char right before the sample extinguished. No aluminum trays were used. 

Significant damage to the sample surface was noted as can be seen in the picture below (Figure 

6-41), including exposure of the bare copper wire. 

Figure 6-41. Photograph of Cable #701 after Cone Calorimeter test at 25 kW/m2

. 

Imposed Heat Flux: 50 kW/m2 

The samples smoked, flashed, and ignited fairly quickly. The samples deformed greatly while 

burning, with the char surface forming blisters that would crack open and eventually burn back. 

Blue colors noted later into the burning of the sample with some blue and green colors noted 

right before extinguishment. No aluminum trays were used. Significant damage to the sample 

surface was noted as can be seen in Figure 6-42, including exposure of the bare copper wire. 

The HRRs for Cable #701 obtained from the Cone Calorimeter for three imposed heat fluxes 

(25 kW/m2

, 50 kW/m2, and 75 kW/m2) are shown in Figure 6-43. 
61

Figure 6-42. Photograph of Cable #701 after Cone Calorimeter test at 50 kW/m2

. 

Figure 6-43. Heat Release Rates for Cable #701 in the Cone Calorimeter. 

0 600 1200 1800 2400 3000

0

50

100

150

200

250

300

350

400

Time (s)

HRR (kW/m2)

Cable 701, Heat Flux 25 kW/m2

Rep. 1, HRRavg=121 kW/m2

Cable 701, Heat Flux 25 kW/m2

Rep. 2, HRRavg=105 kW/m2

Cable 701, Heat Flux 25 kW/m2

Rep. 3, HRRavg=103 kW/m2

0 600 1200 1800 2400 3000

0

50

100

150

200

250

300

350

400

Time (s)

HRR (kW/m2)

Cable 701, Heat Flux 50 kW/m2

Rep. 1, HRRavg=176 kW/m2

Cable 701, Heat Flux 50 kW/m2

Rep. 2, HRRavg=200 kW/m2

Cable 701, Heat Flux 50 kW/m2

Rep. 3, HRRavg=177 kW/m2

0 600 1200 1800 2400 3000

0

50

100

150

200

250

300

350

400

Time (s)

HRR (kW/m2)

Cable 701, Heat Flux 75 kW/m2

Rep. 1, HRRavg=266 kW/m2
62

6.3 Summary of Results 

The results of the Cone Calorimeter measurements are summarized in Table 6-1. For each cable 

and each imposed heat flux level, the average heat release rate per unit area is listed. In some 

cases, the average value was calculated after rejecting one or two of the replicate trials where the 

cable did not ignite or burn sufficiently long to derive appropriate values. 

Table 6-1. Measured heat release rates from Cone Calorimeter experiments 

Cable 

Number 

HRRPUA (kW/m2

) 

Imposed Heat Flux (kW/m2) 

25 50 75 

11 6 90 127 

16 50 130 173 

23 44 92 135 

43 6 70 169 

46 15 61 172 

219 133 140 187 

220 112 143 No Test 

270 191 298 510 

271 13 113 199 

367 70 107 169 

700 63 136 No Test 

701 110 184 266 

Cable #270 had a significantly higher heat release rate than the other cables tested. It is a triaxial 

cable with XLPE insulation and a CSPE jacket. Cable #271 is a power and control cable from 

the same manufacturer. Although both are technically classified as thermoset cables, they both 

burned with a relatively high HRR. 

Cable #701 is a thermoplastic cable and burned with a relatively high HRR. 

As will be discussed in the next chapter, Cables #219, #220, #270, and #701 also burned with a 

relatively high HRR in the Radiant Panel Apparatus. 
63

7 RADIANT PANEL EXPERIMENTS 

7.1 Overview 

The Radiant Panel (RP) Apparatus consists of a single horizontal ladder-back cable tray 

containing varying numbers of cables that are exposed to an array of radiant panels that are 

positioned overhead. The radiant panels serve as a surrogate for the hot gas layer (HGL) in a 

cable fire. The tray is 1.2 m (4 ft) long and 0.45 m (18 in) wide. There are six radiant panels3

positioned in two symmetric banks. See Figure 7-1 and Figure 7-2 for photographs of the 

apparatus. Measurements with a heat flux gauge demonstrated that this configuration could 

produce a heat flux of approximately 30 kW/m2

 over a length of 0.6 m (2 ft) of the cable tray. 

The heat flux varied from the end of the tray to the middle by approximately 10 %. 

The objective of these experiments was to compile a table of heat release rates per unit area 

(HRRPUA) for a variety of heat flux levels and tray fill levels. The cables were arranged in a 

way that is typical of “random fill” installations, although each experiment made use of only one 

type of cable. The number of cables was varied between approximately 25 % and 75 % of the 

amount allowed by the National Electric Code (NEC), 2008 Edition (NFPA 70). The NEC limits 

the total cross-sectional area of the cables within a 0.45 m (18 in) tray to 135 cm2

 (21 in2). 

It should be noted that the Radiant Panel Apparatus was designed and built specifically for the 

CHRISTIFIRE project, and it is not intended to be used as a standard testing apparatus. Its 

purpose is to determine if the HRRPUA measured in the Cone Calorimeter (a standard 

apparatus) is consistent with the burning rate at a larger scale. 

 

3

 The radiant panels are manufactured by Chromalox, model CPHI-1224T quartz faced panels. They are 25 cm by 

30 cm (10 in by 12 in), run on 480 V AC, and produce a maximum radiant output of 4.8 kW each, or a maximum 

heat flux of 62 kW/m2

. The uncertainty of the radiative output was not determined for an individual panel. The heat 

flux from the group of six was determined by a radiometer positioned approximately at the center of the tray prior to 

the experiment. 
64

Figure 7-1. Side view of Radiant Panel Apparatus 

Figure 7-2. End view of Radiant Panel Apparatus. 
65

7.2 Experimental Measurements 

The measurements in the Radiant Panel Apparatus consisted of the following: 

 Heat Release Rate: The Radiant Panel Apparatus was positioned beneath the 1 MW hood in 

the NIST Large Fire Laboratory. Using the measured HRR4, the heat release rate per unit 

area (HRRPUA) was calculated by assuming that the area of burning cables was the product 

of the width of the tray (0.45 m or 18 in) and the length of cables exposed to the radiant 

panels (approximately 1 m or 3 ft). 

 Mass Loss Rate: The cable tray and its supporting rig was placed on a single scale5. By 

calculating the first derivative of its output, a mass loss rate could be calculated. The 

effective heat of combustion was calculated by determining (via linear regression) the ratio 

of the HRR determined from oxygen consumption calorimetry and the mass loss rate. 

 Combustible Mass: Not all of the combustible (non-metallic) mass was consumed by the 

fire. For many of the cables, char and ash remained in the tray after the experiment. For 

each test, the fraction of the combustible mass that was actually consumed by the fire was 

calculated based on the mass loss rate of the entire apparatus. 

 Adiabatic Surface Temperature: Three plate thermometers (EN 1363-1 2000) were 

positioned approximately 30 cm (1 ft) apart along the centerline of the tray. They were used 

to monitor the “exposing” temperature of the radiant panels. 

7.3 Results 

Twelve different cables were tested in the Radiant Panel series. Altogether there were 33 tests 

conducted (numbered 0 through 32), usually with each cable tested at two different exposing 

heat fluxes. For some cables, there were other parameter variations, like the amount of cables in 

the tray. Table 7-1 summarizes the results of the Radiant Panel Series. Note that an important 

parameter in the experiments was the extent to which the cables were packed densely or loosely 

in the tray. Most of the experiments involved a single row of cables. “Dense” packing implies 

that the cables were packed tightly in a single row with gaps between cables of approximately 

1 mm, while “Loose” implies random loading typical of control and instrument cable 

installations. 

 

4

 The procedure and accuracy of the oxygen consumption calorimetry used in the NIST Large Fire Laboratory is 

documented by Bryant (2004). In brief, the expanded uncertainty (95 % confidence interval) is 9 % of the measured 

value of the HRR for fires under the 1 MW hood. A significant portion of the uncertainty is due to the fact that the 

chemical composition of the fuel is not completely known. 

5

 The scale used in the experiment was manufactured by Mettler Toledo, under the model name Jaguar KC300. For 

an applied load of 50 kg (110 lb), the manufacturer reports the accuracy (95 % confidence interval) to be 0.02 %. 

This means that the reported mass is accurate to within approximately ±10 g (0.4 oz). 
66

7.3.1 Cable #11 

Test 

No. 

Nominal 

Heat Flux 

(kW/m2

) 

No. of 

Cables Packing 

Max 

HRR 

(kW) 

RP-21 32 14 Dense 135 

RP-22 32 7 Loose 140 

Cable #11 was notably larger than all of the other cables used in the program. Its size was a 

consideration when testing it in the Radiant Panel Apparatus. In Test 21, 14 cables were laid 

tightly in a single row with little gaps in between, whereas in Test 22, only 7 cables were laid in 

a row, with roughly one cable diameter spacing. Both tests showed peak HRRPUA values 

(Figure 7-3) of about 300 kW/m2

, although not surprisingly the loosely packed configuration 

allowed the fire to grow faster. 

 
67

 

Figure 7-3. Photographs and HRR of RP Tests 21 and 22, Cable #11. 

Radiant Panel Test 21

Time (s)

0 900 1800 2700 3600 4500 5400

Heat Release Rate (kW)

0

50

100

150

200

HRR (O2 cal.)

HRR (mass loss)

Radiant Panel Test 22

Time (s)

0 900 1800 2700 3600 4500 5400

Heat Release Rate (kW)

0

50

100

150

200

HRR (O2 cal.)

HRR (mass loss)
68

7.3.2 Cable #16 

Test 

No. 

Nominal 

Heat Flux 

(kW/m2

) 

No. of 

Cables Packing 

Max 

HRR 

(kW) 

RP-6 32 24 Loose 55 

RP-7 16 24 Loose 55 

RP-8 5 24 Loose 45 

RP-9 22 24 Loose 51 

RP-10 32 24 Loose 76 

Cable #16 was used to assess the effect of the radiant panel heat flux on the burning rate. Tests 6 

(Figure 7-4) and 7 demonstrate that a lower heat flux delays ignition, but does not significantly 

change the peak HRR. With a very low heat flux, as in Test 8, it is difficult to maintain steady 

burning over the full extent of the exposed tray. Test 9 was similar to Tests 6 and 7, with a heat 

flux falling between the two. Test 10 was meant to replicate Test 6, and it demonstrates that 

slight differences in the way the cables are laid into the tray can lead to noticeable changes in the 

HRR (Figure 7-5). 

Figure 7-4. Photographs of RP Test 6. 
69

Figure 7-5. HRR of RP Tests 6-10, Cable #16. 

Radiant Panel Test 6

Time (s)

0 600 1200 1800 2400 3000 3600

Heat Release Rate (kW)

0

50

100

150

200

HRR (O2 cal.)

HRR (mass loss)

Radiant Panel Test 7

Time (s)

0 600 1200 1800 2400 3000 3600

Heat Release Rate (kW)

0

50

100

150

200

HRR (O2 cal.)

HRR (mass loss)

Radiant Panel Test 8

Time (s)

0 600 1200 1800 2400 3000 3600

Heat Release Rate (kW)

0

50

100

150

200

HRR (O2 cal.)

HRR (mass loss)

Radiant Panel Test 9

Time (s)

0 600 1200 1800 2400 3000 3600

Heat Release Rate (kW)

0

50

100

150

200

HRR (O2 cal.)

HRR (mass loss)

Radiant Panel Test 10

Time (s)

0 600 1200 1800 2400 3000 3600

Heat Release Rate (kW)

0

50

100

150

200

HRR (O2 cal.)

HRR (mass loss)
70

7.3.3 Cable #23 

Test 

No. 

Nominal 

Heat Flux 

(kW/m2

) 

No. of 

Cables Packing 

Max 

HRR 

(kW) 

RP-27 28 34 Dense 78 

RP-28 14 34 Dense 95 

RP-29 15 66 Dense 111 

This series of experiments demonstrates that doubling the number of cables in a tray does not 

significantly increase the HRR, but it does increase the duration of the fire. Figure 7-6 shows a 

single and double layer of cables in the tray. Photographs and HRR from radiant panel tests of 

Cable #23 are shown in Figure 7-7. 

Figure 7-6. Photographs of RP Test 28 (left) and 29 (right). 
71

 

 

Figure 7-7. Photographs of RP Test 28 and HRR of Tests 27-29, Cable #23. 

Radiant Panel Test 27

Time (s)

0 600 1200 1800 2400 3000 3600

Heat Release Rate (kW)

0

50

100

150

200

HRR (O2 cal.)

HRR (mass loss)

Radiant Panel Test 28

Time (s)

0 600 1200 1800 2400 3000 3600

Heat Release Rate (kW)

0

50

100

150

200

HRR (O2 cal.)

HRR (mass loss)

Radiant Panel Test 29

Time (s)

0 600 1200 1800 2400 3000 3600

Heat Release Rate (kW)

0

50

100

150

200

HRR (O2 cal.)

HRR (mass loss)
72

7.3.4 Cable #43 

Test 

No. 

Nominal 

Heat Flux 

(kW/m2

) 

No. of 

Cables Packing 

Max 

HRR 

(kW) 

RP-14 32 30 Dense 93 

RP-15 17 30 Dense 63 

These two radiant panel tests show that a higher exposing heat flux (typically) brings on ignition 

more quickly and a higher peak heat release rate. Note that the mass loss data for these 

experiments could not be used for a second estimate of the HRR because the tray made contact 

with the radiant panels several times during the tests. Photographs from radiant panel Test 14 

and HRR from Tests 14 and 15 are shown in Figure 7-8. 

 
73

 

 

Figure 7-8. Photographs of RP Test 14 and HRR of Tests 14 and 15, Cable #43. 

Radiant Panel Test 14

Time (s)

0 600 1200 1800 2400 3000 3600

Heat Release Rate (kW)

0

50

100

150

200

HRR (O2 cal.)

Radiant Panel Test 15

Time (s)

0 600 1200 1800 2400 3000 3600

Heat Release Rate (kW)

0

50

100

150

200

HRR (O2 cal.)
74

7.3.5 Cable #46 

Test 

No. 

Nominal 

Heat Flux 

(kW/m2

) 

No. of 

Cables Packing 

Max 

HRR 

(kW) 

RP-16 26 28 Dense 55 

RP-17 15 28 Dense 47 

The results of these two tests were as expected in that the higher exposing heat flux ignited the 

cables more quickly, but the peak heat release rate was not significantly higher. 

There was no spread of the fire beyond the end of the radiant panels. Photographs from radiant 

panel Test 16 and HRR from Tests 16 and 17 are shown in Figure 7-9. 

 
75

 

 

Figure 7-9. Photographs of RP Test 16 and HRR of Tests 16 and 17, Cable #46. 

Radiant Panel Test 16

Time (s)

0 600 1200 1800 2400 3000 3600

Heat Release Rate (kW)

0

50

100

150

200

HRR (O2 cal.)

Radiant Panel Test 17

Time (s)

0 600 1200 1800 2400 3000 3600

Heat Release Rate (kW)

0

50

100

150

200

HRR (O2 cal.)

HRR (mass loss)
76

7.3.6 Cable #219 

Test 

No. 

Nominal 

Heat Flux 

(kW/m2

) 

No. of 

Cables Packing 

Max 

HRR 

(kW) 

RP-23 32 32 Dense 118 

RP-24 13 32 Dense 192 

The results of these two tests are not typical because the one with the lower exposing heat flux 

had the higher peak heat release rate. The remains of the cable from radiant panel test 24 are 

shown in Figure 7-10. Photographs from radiant panel Test 23 and HRR from Tests 23 and 24 

are shown in Figure 7-11. 

Figure 7-10. Photograph of the remains of the cables in RP-24. 
77

 

 

Figure 7-11. Photographs of RP Test 23 and HRR of Tests 23 and 24, Cable #219. 

Radiant Panel Test 23

Time (s)

0 600 1200 1800 2400 3000 3600

Heat Release Rate (kW)

0

50

100

150

200

HRR (O2 cal.)

HRR (mass loss)

Radiant Panel Test 24

Time (s)

0 600 1200 1800 2400 3000 3600

Heat Release Rate (kW)

0

50

100

150

200

HRR (O2 cal.)

HRR (mass loss)
78

7.3.7 Cable #220 

Test 

No. 

Nominal 

Heat Flux 

(kW/m2

) 

No. of 

Cables Packing 

Max 

HRR 

(kW) 

RP-25 27 24 Dense 221 

RP-26 17 24 Dense 213 

This cable is similar in construction and materials to #219, but the results of these two tests do 

not show the anomalous behavior that was seen in Figure 7-11. Note in Figure 7-12 that there 

was a considerable amount of dripping material burning in the catch pan during the test. 

Photographs from radiant panel Test 25 and HRR from Tests 25 and 26 are shown in 

Figure 7-13. 

Figure 7-12. Fairly vigorous burning in RP-25. 
79

 

 

Figure 7-13. Photographs of RP Test 25 and HRR of Tests 25 and 26, Cable #220. 

Radiant Panel Test 25

Time (s)

0 600 1200 1800 2400 3000 3600

Heat Release Rate (kW)

0

50

100

150

200

HRR (O2 cal.)

HRR (mass loss)

Radiant Panel Test 26

Time (s)

0 600 1200 1800 2400 3000 3600

Heat Release Rate (kW)

0

50

100

150

200

HRR (O2 cal.)

HRR (mass loss)
80

7.3.8 Cable #271 

Test 

No. 

Nominal 

Heat Flux 

(kW/m2

) 

No. of 

Cables Packing 

Max 

HRR 

(kW) 

RP-18 26 44 Dense 224 

RP-19 13 44 Dense 149 

RP-20 14 44 Dense 143 

This was a relatively small cable, but it burned fairly vigorously with a fair amount of 

dripping/burning in the catch pan. Figure 7-14 is a photograph of radiant panel test 18 showing 

the dripping and burning in the catch pan. Photographs from radiant panel Test 18 and HRR 

from Tests 18 to 20 are shown in Figure 7-15. 

Figure 7-14. Photograph of RP Test 18 showing dripping and burning in the catch pan. 
81

 

 

Figure 7-15. Photographs of RP Test 18 and HRR of Tests 18-20, Cable #271. 

Radiant Panel Test 18

Time (s)

0 600 1200 1800 2400 3000 3600

Heat Release Rate (kW)

0

50

100

150

200

HRR (O2 cal.)

HRR (mass loss)

Radiant Panel Test 19

Time (s)

0 600 1200 1800 2400 3000 3600

Heat Release Rate (kW)

0

50

100

150

200

HRR (O2 cal.)

HRR (mass loss)

Radiant Panel Test 20

Time (s)

0 600 1200 1800 2400 3000 3600

Heat Release Rate (kW)

0

50

100

150

200

HRR (O2 cal.)

HRR (mass loss)
82

7.3.9 Cable #367 

Test 

No. 

Nominal 

Heat Flux 

(kW/m2

) 

No. of 

Cables Packing 

Max 

HRR 

(kW) 

RP-11 32 25 Dense 181 

RP-12 17 25 Dense 124 

RP-13 15 25 Dense 143 

This cable burned fairly vigorously and the measured heat release rates followed typical trends 

based on the exposing heat flux. Note that the fire spread to the very end of the tray, as shown in 

Figure 7-16. Photographs from radiant panel Test 11 and HRR from Tests 11 to 13 are shown in 

Figure 7-17. 

Figure 7-16. Photograph of RP Test 11 showing burning to the end of the tray. 
83

 

 

Figure 7-17. Photographs of RP Test 11 and HRR of Tests 11-13, Cable #367. 

Radiant Panel Test 11

Time (s)

0 600 1200 1800 2400 3000 3600

Heat Release Rate (kW)

0

50

100

150

200

HRR (O2 cal.)

HRR (mass loss)

Radiant Panel Test 12

Time (s)

0 600 1200 1800 2400 3000 3600

Heat Release Rate (kW)

0

50

100

150

200

HRR (O2 cal.)

HRR (mass loss)

Radiant Panel Test 13

Time (s)

0 600 1200 1800 2400 3000 3600

Heat Release Rate (kW)

0

50

100

150

200

HRR (O2 cal.)

HRR (mass loss)
84

7.3.10 Cable #700 

Test 

No. 

Nominal 

Heat Flux 

(kW/m2

) 

No. of 

Cables Packing 

Max 

HRR 

(kW) 

RP-0 27 40 Loose 79 

RP-1 24 80 Loose 60 

RP-2 32 40 Loose 104 

These three tests demonstrate how doubling the load of cable does not necessarily yield a larger 

fire, but rather a longer one. Notice from the HRR plot for RP-1 that each row of cables appears 

to burn independently. Figure 7-18 is a photograph of radiant panel Test 1 showing a relatively 

heavy load of cable. Photographs from radiant panel Test 0 and HRR from Tests 0, 1, and 2 are 

shown in Figure 7-19. 

Figure 7-18. Photograph of RP Test 1, showing a relatively heavy load of cable. 
85

 

 

Figure 7-19. Photographs of RP Test 0 and HRR of Tests 0, 1 and 2, Cable #700. 

Radiant Panel Test 0

Time (s)

0 600 1200 1800 2400 3000 3600

Heat Release Rate (kW)

0

50

100

150

200

HRR (O2 cal.)

HRR (mass loss)

Radiant Panel Test 1

Time (s)

0 600 1200 1800 2400 3000 3600

Heat Release Rate (kW)

0

50

100

150

200

HRR (O2 cal.)

HRR (mass loss)

Radiant Panel Test 2

Time (s)

0 600 1200 1800 2400 3000 3600

Heat Release Rate (kW)

0

50

100

150

200

HRR (O2 cal.)
86

7.3.11 Cable #701 

Test 

No. 

Nominal 

Heat Flux 

(kW/m2

) 

No. of 

Cables Packing 

Max 

HRR 

(kW) 

RP-3 32 44 Loose 163 

RP-4 16 22 Loose 172 

RP-5 17 22 Loose 160 

RP-30 14 44 Dense 244 

RP-31 28 44 Dense 258 

This cable demonstrates burning behavior of a typical thermoplastic cable. It melts and drips, 

and it burns almost all of the plastic cable content away. In other words, there is very little 

residue left after the burn. Photographs from radiant panel Test 3 are shown in Figure 7-20, and 

HRR from Tests 3 to 5 and Tests 30 to 31 are shown in Figure 7-21. 

Figure 7-20. Photographs of RP Test 3. 

 
87

Figure 7-21. HRR of RP Tests 3-5 and 30-31, Cable #701. 

Radiant Panel Test 3

Time (s)

0 600 1200 1800 2400 3000 3600

Heat Release Rate (kW)

0

50

100

150

200

HRR (O2 cal.)

HRR (mass loss)

Radiant Panel Test 4

Time (s)

0 600 1200 1800 2400 3000 3600

Heat Release Rate (kW)

0

50

100

150

200

HRR (O2 cal.)

HRR (mass loss)

Radiant Panel Test 5

Time (s)

0 600 1200 1800 2400 3000 3600

Heat Release Rate (kW)

0

50

100

150

200

HRR (O2 cal.)

HRR (mass loss)

Radiant Panel Test 30

Time (s)

0 600 1200 1800 2400 3000 3600

Heat Release Rate (kW)

0

50

100

150

200

HRR (O2 cal.)

HRR (mass loss)

Radiant Panel Test 31

Time (s)

0 600 1200 1800 2400 3000 3600

Heat Release Rate (kW)

0

50

100

150

200

HRR (O2 cal.)

HRR (mass loss)
Table 7-1. Summary of the Radiant Panel Experiments 

Test 

No. 

Cable 

No. 

Nominal 

Heat Flux 

(kW/m2) 

No. of 

Cables 

Percent of

NEC Fill 

Limit 

Packing 

Max 

HRR (kW) 

Avg 

HRRPUA

(kW/m2) 

Heat of 

Comb. 

(MJ/kg)

Mass 

Consumed

(kg) 

Residue 

(% of total 

plastic) 

RP-0 700 27 40 33 Loose 79 138 19.4 2.4 44 RP-1 700 24 80 67 Loose 60 55 18.9 4.5 48 RP-2 700 32 40 33 Loose 104 153 -- 4.0 5 RP-3 701 32 44 50 Loose 163 264 16.1 8.1 0 RP-4 701 16 22 25 Loose 172 252 16.6 4.5 0 RP-5 701 17 22 25 Loose 160 184 15.6 3.3 18 RP-6 16 32 24 50 Loose 55 82 14.4 3.9 49 RP-7 16 16 24 50 Loose 55 64 19.8 4.2 46 RP-8 16 5 24 50 Loose 45 30 9.4 2.2 72 RP-9 16 22 24 50 Loose 51 88 15.6 4.3 44 

RP-10 16 32 24 50 Loose 76 119 14.8 5.8 25 RP-11 367 32 25 37 Dense 181 234 18.1 6.9 15 RP-12 367 17 25 37 Dense 124 199 17.6 6.2 23 RP-13 367 15 25 37 Dense 143 205 17.6 6.1 25 RP-14 43 32 30 39 Dense 93 116 -- 4.3 35 RP-15 43 17 30 39 Dense 63 100 -- 4.7 30 RP-16 46 26 28 37 Dense 55 85 -- 4.2 34 RP-17 46 15 28 37 Dense 47 60 15.9 2.9 54 RP-18 271 26 44 26 Dense 224 210 16.5 3.5 8 RP-19 271 13 44 26 Dense 149 160 16.1 3.5 7 RP-20 271 14 44 26 Dense 143 167 14.6 3.7 2 RP-21 11 32 14 84 Dense 135 142 16.3 9.0 28 RP-22 11 32 7 42 Loose 140 184 17.1 5.9 6 RP-23 219 32 32 36 Dense 118 135 15.7 4.6 20 RP-24 219 13 32 36 Dense 192 214 19.3 4.1 30 RP-25 220 27 24 45 Dense 221 180 17.1 5.0 40 RP-26 220 17 24 45 Dense 213 236 17.6 4.6 45 RP-27 23 28 34 39 Dense 78 104 12.3 3.9 35 RP-28 23 14 34 39 Dense 95 107 16.0 3.3 45 RP-29 23 15 66 75 Dense 111 66 12.2 10.6 8 RP-30 701 14 44 50 Dense 244 266 18.3 7.1 12 

88
Test 

No. 

Cable 

No. 

Nominal 

Heat Flux 

(kW/m2) 

No. of 

Cables 

Percent of

NEC Fill 

Limit 

Packing 

Max 

HRR (kW) 

Avg 

HRRPUA

(kW/m2) 

Heat of 

Comb. 

(MJ/kg)

Mass 

Consumed

(kg) 

Residue 

(% of total 

plastic) 

RP-31 701 28 44 50 Dense 258 231 15.2 7.4 9 RP-32 270 24 80 67 Loose 167 270 13.9 11.4 1 

89
90

7.4 Discussion 

The purpose of the Radiant Panel Apparatus is to measure the heat release rate per unit area 

(HRRPUA) of a tray filled with cable at a larger scale than the Cone Calorimeter. The area in 

this case refers to the tray, not the cable itself. In other words, it is the heat release rate divided 

by the length times the width of the tray over which the fire is burning. The HRRPUA takes on a 

range of values depending on the test configuration, exposing heat flux, and overall scale. For 

example, the HRRPUA determined in the Cone Calorimeter is expected to differ from the 

Radiant Panel Apparatus because of the difference in the size of the fire and the corresponding 

difference in the heat fed back to the cable surface. Figure 7-22 displays the range of values for 

the CHRISTIFIRE cables that were tested in the Radiant Panel Apparatus. Note that in most 

cases, the measured HRRPUA increases with increasing exposing heat flux. For cases like 

Cables #219 that show the opposite trend, the cables heated up at the lower heat flux but did not 

ignite for a considerable amount of time. When the cables did ignite, they burned with a 

relatively high HRRPUA because they had already reached high enough internal temperature to 

support the higher pyrolysis rate. 

Figure 7-22. Summary of the radiant panel heat release rates. 

Typical thermoset cables burn at a rate of approximately 150 kW/m2

 and typical thermoplastics 

burn at a rate of approximately 250 kW/m2. These values are similar to those put forth in 

NUREG/CR-6850, Appendix R, which are based on measurements by Tewarson that are 

reported in the SFPE Handbook. 

Cable trays in NPPs typically contain a mixture of cable types. Most installations segregate the 

cables by electrical function (power, instrument and control), but not cable construction. For 

External Heat Flux (kW/m2)

0 10 20 30 40

Heat Release Rate Per Unit Area (kW/m2

)

0

100

200

300

400

Cable #701

Cable #700

Cable #16

Cable #367

Cable #43

Cable #46

Cable #271

Cable #11

Cable #219

Cable #220

Cable #23

Cable #270

}

}

Thermoplastics

Thermosets
91

example, if an NPP was constructed and licensed before 10 CFR 50 Appendix R was issued in 

1980, the majority of the original cables would be made of thermoplastic materials, but later 

modifications would introduce in the same trays cables made of thermoset materials. In addition, 

many older NPPs installed some form of fire retardant cable coating over their thermoplastic 

cables in response to the 1975 Browns Ferry fire. Newer thermoset cables installed in the same 

tray (over the entombed coated cables) may, or may not, also have fire retardant coatings 

installed on them depending on the plant’s licensing basis. Also, it is not unusual to find cables 

that were abandoned in place rather than removed as a part of a plant modification. Though they 

no longer are energized, these cables add to the fuel load. At this time, a reasonable modeling 

approach would be to characterize the cable materials as a mass-weighted average of 

thermoplastics and thermosets. This is discussed in Section 9.2.2, “FLASH-CAT Model Input 

Parameters.” Further discussion about future research on this topic is discussed in Section 10.5, 

“Future Work.” 

 

93

8 MULTIPLE TRAY EXPERIMENTS 

8.1 General Description 

The multiple tray (MT) experiments were composed of vertical stacks of three to seven cable 

trays (one test involved only one tray). There were 26 experiments conducted in total, labeled 

MT-1 through MT-26. These 26 experiments were divided into two series. Series 1 consists of 

Tests MT-1 through MT-16, conducted in May, 2009. Series 2 consists of Tests MT-17 through 

MT-26, conducted in January and February, 2010. 

Series 1 addresses a fairly common tray configuration where 0.45 m (18 in) horizontal, ladderbacked trays are stacked over top of each other with 0.3 m (1 ft) spacing. The type and amount 

of cables in each tray was varied. The cables in a given tray (or often for a given experiment) 

were typically of a single type. The aim was to test at full-scale those cables that were tested in 

the Radiant Panel Apparatus and in the Cone Calorimeter. Because of the limited amount of 

cable of any one type, it was not possible to vary the tray width or vertical spacing in the Series 1 

experiments. The purpose of Series 1 was to determine if the burning rate data collected at 

bench and intermediate-scales could be applied to the full-scale experiments. A summary of the 

test parameters for Series 1 is given in Table 8-1. 

Series 2 involved mixtures of cables that were not tested under the Radiant Panel Apparatus or 

the Cone Calorimeter. This series was designed to assess the effect of changing the vertical tray 

spacing, tray width, and tray fill. As with Series 1, they also provide experimental data for 

model validation. A summary of the test parameters for Series 2 is given in Table 8-2. 

Figure 8-1 shows a typical experiment (MT Test 1) from Series 1. A small 0.3 m by 0.3 m (1 ft 

by 1ft) square, gravel-packed natural gas burner was placed approximately 20 cm (8 in) below 

the lowest tray. The natural gas flow rate to this burner was calibrated to provide 40 kW ± 5 kW. 

The support rig and cable trays were placed upon four scales6

. The heat release rate of the fire 

was measured in two ways. First, the amount of oxygen consumed by the fire was measured via 

oxygen consumption calorimetry instrumentation in the hood7

. Second, the measured mass loss 

rate was multiplied by the heat of combustion that was estimated using data from the small scale 

experiments. 

 

6

 The scales used in the experiment were manufactured by Mettler Toledo, under the model name Jaguar KC300. 

For an applied load of 100 kg (220 lb), the manufacturer reports the accuracy (95 % confidence interval) to be 

0.01 %. This means that the mass reported by each scale is accurate within approximately ±10 g (0.4 oz). 7

 The procedure and accuracy of the oxygen consumption calorimetry is documented by Bryant (2004). In brief, the 

expanded relative uncertainty (95 % confidence interval) is 11 % of the measured value of the HRR for fires larger 

than 400 kW. 
94

Figure 8-1. Multiple Tray (MT) cable test apparatus. 

8.2 Results, Multiple Tray Experiments, Series 1 

Sixteen Multiple Tray Experiments were conducted with the number of trays ranging from 1 to 7 

in May, 2009. Two lengths of tray were used – 2.4 m (8 ft) and 3.6 m (12 ft). The smaller trays 

were supported by a steel rack whose vertical supports were 1.2 m (4 ft) apart, and the larger 

trays were supported by a rack with supports 1.8 m (6 ft) apart. Each rack spaced the trays 

30 cm (1 ft) apart vertically. The measurements consisted of the following: 

 Heat Release Rate. The heat release rate was measured using oxygen consumption 

calorimetry under one of two large hoods. Using the HRR and estimates of the area of 

burning tray, the heat release rate per unit area (HRRPUA) could be estimated. 

 Mass Loss Rate. The trays and support rig were placed on four scales. The mass loss rate 

was calculated by taking the first derivative of the measured mass loss curve. The ratio of 

the HRR to the mass loss rate is the effective heat of combustion. This value changes over 

the course of the experiment. Towards the end of the experiment, when there is little flaming 

combustion but the cables continue to smolder in the trays, there is still an appreciable HRR 

measured via oxygen consumption calorimetry but a relatively low mass loss rate. For this 
95

reason, oxygen consumption calorimetry was used as the primary HRR measurement because 

it is a better indicator of the energy release rate from the fire. 

Note that for the multiple tray experiments, there was no calculation performed to determine 

how much of the non-metallic components of the cable were consumed because it was 

difficult to assess how much of the cable in each tray had actually burned following the 

experiment. 

 Adiabatic Surface Temperature. Plate thermometers (EN 1363-1) were positioned on the 

underside of each tray along the centerline. They were used to monitor the “exposing” 

temperature of the fire below the tray. 

 Videotape. Each experiment was videotaped from a single location that viewed the stack of 

cables broadside. Every five minutes during the experiment an estimate was made of the 

area of burning cables. The heat release rate measurement divided by the estimated area 

produced a time-history of the average heat release rate per unit area of burning cable tray. 

These results are plotted on the following pages. The videos are available on the DVD 

accompanying the report. 
96

8.2.1 Multiple Tray Test 1 (MT-1) 

This experiment consisted of 3 trays, one above the other with a spacing of 30 cm (1 ft). Each 

tray was 2.4 m (8 ft) long, and each was filled with 32 cables (#23) neatly arranged in a single 

row. The burner under the bottom tray was maintained at about 40 kW for most of the 

experiment. 

The heat release rate as a function of time is shown in Figure 8-2. The black curve is the HRR 

obtained via oxygen consumption calorimetry; the red was inferred from the measured mass loss 

rate and the estimated effective heat of combustion. The times when each tray became involved 

in the fire were estimated from visual observations during the experiment. 

The damage to the cables was largely confined within the volume spanned by the 4 vertical 

support columns. The columns were 1.2 m (4 ft) apart. 

 
97

Figure 8-2. Multiple Tray Experiment 1 

Multiple Tray Test 1

Time (s)

0 900 1800 2700 3600 4500

Heat Release Rate (kW)

0

50

100

150

200

250

300

Tray 1 Tray 2

Tray 3

Burner Off

HRR (O2 cal.)

HRR (mass loss)
98

8.2.2 Multiple Tray Test 2 (MT-2) 

This experiment consisted of 3 trays, one above the other with a spacing of 30 cm (1 ft). Each 

tray was 2.4 m (8 ft) long, and each was filled with 44 cables (#701) neatly arranged in a single 

row. The burner under the bottom tray was maintained at about 40 kW for the entire experiment. 

The heat release rate as a function of time is shown in Figure 8-3. The black curve is the HRR 

obtained via oxygen consumption calorimetry; the red was inferred from the measured mass loss 

rate and the estimated effective heat of combustion. The times when each tray became involved 

in the fire were estimated (to the nearest minute) from the video tape. 

The fire spread to the ends of each tray, following a V-pattern by which the cables in front of the 

flames were pre-heated by the fire in the tray above. 

There was virtually no solid residue left after the experiment, only the copper conductors 

remained. 

 
99

Figure 8-3. Multiple Tray Experiment 2. 

Multiple Tray Test 2

Time (s)

0 900 1800 2700 3600 4500

Heat Release Rate (kW)

0

200

400

600

800

1000

Tray 1

Tray 2

Tray 3

HRR (O2 cal.)

HRR (mass loss)

Multiple Tray Test 2

Time (s)

0 900 1800 2700 3600 4500

HRR Per Unit Area (kW/m2

)

0

100

200

300

400

500

600

HRRPUA (O2 cal.)

HRRPUA (mass loss)
100

8.2.3 Multiple Tray Test 3 (MT-3) 

This experiment consisted of 3 trays, one above the other with a spacing of 30 cm (1 ft). Each 

tray was 2.4 m (8 ft) long, and each was filled with 32 cables (#219) neatly arranged in a single 

row. The burner under the bottom tray was maintained at about 40 kW for 10 min. 

The heat release rate as a function of time is shown in Figure 8-4. The black curve is the HRR 

obtained via oxygen consumption calorimetry; the red was inferred from the measured mass loss 

rate and the estimated effective heat of combustion. The times when each tray became involved 

in the fire were estimated (to the nearest minute) from the video tape. 

The damage to the cables was largely confined within the volume spanned by the 4 vertical 

support columns. The columns were 1.2 m (4 ft) apart. 

 
101

Figure 8-4. Multiple Tray Experiment 3 

Multiple Tray Test 3

Time (s)

0 900 1800 2700

Heat Release Rate (kW)

0

50

100

150

200

250

300

Tray 1

Tray 2

Tray 3 Burner

Off HRR (O2 cal.)

HRR (mass loss)

Multiple Tray Test 3

Time (s)

0 900 1800 2700

HRR Per Unit Area (kW/m2

)

0

50

100

150

200

250

300

HRRPUA (O2 cal.)

HRRPUA (mass loss)
102

8.2.4 Multiple Tray Test 4 (MT-4) 

This experiment consisted of 4 trays, one above the other with a spacing of 30 cm (1 ft). Each 

tray was 2.4 m (8 ft) long. Tray 1 (bottom tray) was filled with 28 cables (#43). Tray 2 was 

filled with 18 #43 cables and 10 #21 cables. Tray 3 was filled with 28 #21 cables. Tray 4 was 

filled with 23 #21 cables and 5 #20 cables. All of the cables were from the same manufacturer 

with very similar properties. All of the cables were densely packed neatly in a single row. 

The burner under the bottom tray was maintained at about 40 kW for nearly 48 min. The reason 

the burner was left on for such a long time was that the fire did not spread readily from tray to 

tray. In fact, Tray 1 did not begin burning on its top side until after a gap was opened up in the 

cables to allow flame to break through. The neatly packed cables afforded no means for a 

piloting flame to ignite flammable vapors that had been accumulating on the top side of the tray 

due to the heating from below. Tray to tray upward spread was achieved for all trays by 

“picking” a gap in the cables with a fireman’s pick ax. The time of this action is noted on the 

plot in Figure 8-5. 

The heat release rate as a function of time is shown in Figure 8-5. Note that because the cable 

trays were touched during the experiment by the pick ax, the mass loss data could not be used to 

estimate the heat release rate. The times when each tray became involved in the fire were 

estimated (to the nearest minute) from the video tape. Tray 4 never became fully involved, and 

Trays 1, 2 and 3 required “picking” to achieve ignition on the top sides. 

The damage to the cables was largely confined to a relatively short length of Trays 1, 2 and 3, 

roughly 1 m (3 ft). 

Following the conclusion of Test 4, it was decided to no longer tightly pack the cables into the 

trays because it was clear that such an arrangement might lead to spurious test results. Had no 

manual intervention taken place in Test 4, the result might have been no cable damage except for 

the area just above the burner on the underside of the tray. In an actual cable installation, it 

cannot be assumed whether or not the cables are laid in the tray in such a way as to prevent even 

a small flame from piloting a fire in the tray. 

 
103

Figure 8-5. Multiple Tray Experiment 4 

Multiple Tray Test 4

Time (s)

0 900 1800 2700 3600 4500 5400

Heat Release Rate (kW)

0

20

40

60

80

100

120

140

Tray 1

Tray 2

Tray 3

Burner

Off

Pick Ax Tray 1

HRR (O2 cal.)

Multiple Tray Test 4

Time (s)

0 900 1800 2700 3600 4500 5400

HRR Per Unit Area (kW/m2

)

0

100

200

300

400

HRRPUA (O2 cal.)
104

8.2.5 Multiple Tray Test 5 (MT-5) 

This experiment consisted of 3 trays, one above the other with a spacing of 30 cm (1 ft). Each 

tray was 2.4 m (8 ft) long. Tray 1 (bottom tray) was filled with 26 of cable #21 and 2 of cable 

#23. Tray 2 was filled with 14 of cable #23 and 16 of cable #15. Tray 3 was filled with 25 of 

cable #13. The cables were packed loosely. 

The burner under the bottom tray was maintained at about 40 kW and turned off following the 

observation of sustained burning in Tray 1. 

The heat release rate as a function of time is shown in Figure 8-6. The black curve is the HRR 

obtained via oxygen consumption calorimetry; the red was inferred from the measured mass loss 

rate and the estimated effective heat of combustion. The times when each tray became involved 

in the fire were estimated (to the nearest minute) from the video tape. 

The damage to the cables was relatively minor. The cables in each tray burned over roughly 1 m 

(3 ft) in length. 

 
105

Figure 8-6. Multiple Tray Experiment 5 

Multiple Tray Test 5

Time (s)

0 900 1800 2700

Heat Release Rate (kW)

0

50

100

150

200

Tray 1 Tray 2 Tray 3

Burner

Off

HRR (O2 cal.)

HRR (mass loss)

Multiple Tray Test 5

Time (s)

0 900 1800 2700

HRR Per Unit Area (kW/m2

)

0

50

100

150

200

250

300

HRRPUA (O2 cal.)

HRRPUA (mass loss)
106

8.2.6 Multiple Tray Test 6 (MT-6) 

This experiment consisted of 4 trays, one above the other with a spacing of 30 cm (1 ft). Each 

tray was 2.4 m (8 ft) long. Each tray contained 24 cables, all #13. The cables were packed 

loosely. 

The burner under the bottom tray was maintained at about 40 kW and turned off following the 

observation of sustained burning in Tray 1. However, shortly thereafter, the fire’s HRR dropped 

fairly quickly and it appeared that the fire would shortly go out. It was decided at this point to 

re-light the burner, and the fire grew once again. 

The heat release rate as a function of time is shown in Figure 8-7. The black curve is the HRR 

obtained via oxygen consumption calorimetry; the red was inferred from the measured mass loss 

rate and the estimated effective heat of combustion. The times when each tray became involved 

in the fire were estimated (to the nearest minute) from the video tape. 

The damage to the cables was relatively minor. The cables in each tray burned over roughly 1 m 

(3 ft) in length. 

 
107

Figure 8-7. Multiple Tray Experiment 6 

Multiple Tray Test 6

Time (s)

0 900 1800 2700 3600 4500

Heat Release Rate (kW)

0

50

100

150

200

Tray 4

Burner Off

Burner Re-lit

Burner Off

Tray 2 Tray 3

HRR (O2 cal.)

HRR (mass loss)

Multiple Tray Test 6

Time (s)

0 900 1800 2700 3600 4500

HRR Per Unit Area (kW/m2

)

0

100

200

300

400

HRRPUA (O2 cal.)

HRRPUA (mass loss)
108

8.2.7 Multiple Tray Test 7 (MT-7) 

This experiment consisted of 7 trays, one above the other with a spacing of 30 cm (1 ft). The 

bottom 4 trays were each 2.4 m (8 ft) long, while the top 3 trays were each 3.6 m (12 ft) long. 

Each tray contained 36 cables, all #13. This represented a 50 % increase in loading over Test 6. 

The cables were packed loosely. 

The burner under the bottom tray was maintained at about 40 kW, but it was not turned off 

following the observation of sustained burning in Tray 1 to prevent the decrease in HRR that was 

observed after the burner was turned off in previous experiments. 

The heat release rate as a function of time is shown in Figure 8-8. The black curve is the HRR 

obtained via oxygen consumption calorimetry; the red was inferred from the measured mass loss 

rate and the estimated effective heat of combustion. The times when each tray became involved 

in the fire were estimated (to the nearest minute) from the video tape. 

There was a dramatically different outcome in Test 7 compared to Test 6. The fire grew to over 

1 MW and spread to the end of nearly every tray. 

 
109

Figure 8-8. Multiple Tray Experiment 7 

Multiple Tray Test 7

Time (s)

0 900 1800 2700 3600 4500 5400 6300

Heat Release Rate (kW)

0

200

400

600

800

1000

1200

Tray 5

Tray 6

Tray 7

Burner

Off

Tray 1 Tray 2 Tray 3

Tray 4

HRR (O2 cal.)

HRR (mass loss)

Multiple Tray Test 7

Time (s)

0 900 1800 2700 3600 4500 5400 6300

HRR Per Unit Area (kW/m2

)

0

100

200

300

400

500

600

HRRPUA (O2 cal.)

HRRPUA (mass loss)
110

8.2.8 Multiple Tray Test 8 (MT-8) 

This experiment consisted of 4 trays, one above the other with a spacing of 30 cm (1 ft). Each 

tray was 3.6 m (12 ft) long. Each tray contained 44 cables, all #701. The cables were packed 

loosely. 

The burner under the bottom tray was maintained at about 40 kW, and it was turned off just after 

the fire was observed to have spread to the bottom tray. 

The heat release rate as a function of time is shown in Figure 8-9. The black curve is the HRR 

obtained via oxygen consumption calorimetry; the red was inferred from the measured mass loss 

rate and the estimated effective heat of combustion. The times when each tray became involved 

in the fire were estimated (to the nearest minute) from the video tape. 

The fire spread to the ends of each tray, following a V-pattern by which the cables in front of the 

flames were pre-heated by the fire in the tray above. 

There was virtually no solid residue left after the experiment, only the copper conductors 

remained. 

 
111

Figure 8-9. Multiple Tray Experiment 8 

Multiple Tray Test 8

Time (s)

0 900 1800 2700 3600 4500

Heat Release Rate (kW)

0

200

400

600

800

1000 Burner Off

Tray 2

Tray 3

Tray 4

HRR (O2 cal.)

HRR (mass loss)

Multiple Tray Test 8

Time (s)

0 900 1800 2700 3600 4500

HRR Per Unit Area (kW/m2

)

0

100

200

300

400

HRRPUA (O2 cal.)

HRRPUA (mass loss)
112

8.2.9 Multiple Tray Test 9 (MT-9) 

This experiment had the exact same set-up as Test 8, only with half as many cables in each tray. 

This experiment consisted of 4 trays, one above the other with a spacing of 30 cm (1 ft). Each 

tray was 3.6 m (12 ft) long. Each tray contained 22 cables, all #701. The cables were packed 

loosely. 

The burner under the bottom tray was maintained at about 40 kW, and it was turned off just after 

the fire was observed to have spread to the second tray from the bottom. 

The heat release rate as a function of time is shown in Figure 8-10. The black curve is the HRR 

obtained via oxygen consumption calorimetry; the red was inferred from the measured mass loss 

rate and the estimated effective heat of combustion. The times when each tray became involved 

in the fire were estimated (to the nearest minute) from the video tape. 

Unlike Test 8, the fire did not spread to the ends of each tray. In fact, there was relatively light 

damage to the cables, all confined within about a meter from the burner. 

 
113

Figure 8-10. Multiple Tray Experiment 9 

Multiple Tray Test 9

Time (s)

0 300 600 900 1200

Heat Release Rate (kW)

0

100

200

300

400 Burner

Off

Tray 1 2

Tray 3 Tray 4

HRR (O2 cal.)

HRR (mass loss)

Multiple Tray Test 9

Time (s)

0 300 600 900 1200

HRR Per Unit Area (kW/m2

)

0

50

100

150

200

250

300

HRRPUA (O2 cal.)

HRRPUA (mass loss)
114

8.2.10 Multiple Tray Test 10 (MT-10) 

This experiment consisted of 3 trays, one above the other with a spacing of 30 cm (1 ft). Each 

tray was 2.4 m (8 ft) long, and each was filled with 14 cables (#11). This was a large diameter, 

37 conductor cable. In the Radiant Panel Apparatus the cables were packed fairly tightly in a 

single row. However, in the multiple tray experiment, the cables were arranged loosely, forming 

approximately two rows within each tray. 

The burner under the bottom tray was maintained at about 40 kW until the bottom tray was 

ignited. 

The heat release rate as a function of time is shown in Figure 8-11. The black curve is the HRR 

obtained via oxygen consumption calorimetry; the red was inferred from the measured mass loss 

rate and the estimated effective heat of combustion. The times when each tray became involved 

in the fire were estimated from visual observations during the experiment. 

The damage to the cables was largely confined within the volume spanned by the 4 vertical 

support columns. The columns were 1.2 m (4 ft) apart. 

 
115

Figure 8-11. Multiple Tray Experiment 10 

Multiple Tray Test 10

Time (s)

0 900 1800 2700 3600 4500 5400

Heat Release Rate (kW)

0

50

100

150

200

Burner

Off

Tray 1 Tray 2

Tray 3

HRR (O2 cal.)

HRR (mass loss)

Multiple Tray Test 10

Time (s)

0 900 1800 2700 3600 4500 5400

HRR Per Unit Area (kW/m2

)

0

50

100

150

200

HRRPUA (O2 cal.)

HRRPUA (mass loss)
116

8.2.11 Multiple Tray Test 11 (MT-11) 

This experiment was a replicate of Test 8. The results are similar, but there are noticeable 

differences in the HRR. 

This experiment consisted of 4 trays, one above the other with a spacing of 30 cm (1 ft). Each 

tray was 3.6 m (12 ft) long. Each tray contained 44 cables, all #701. The cables were packed 

loosely. 

The burner under the bottom tray was maintained at about 40 kW, and it was turned off just after 

the fire was observed to have spread to the bottom tray. 

The heat release rate as a function of time is shown in Figure 8-12. The black curve is the HRR 

obtained via oxygen consumption calorimetry; the red was inferred from the measured mass loss 

rate and the estimated effective heat of combustion. The times when each tray became involved 

in the fire were estimated (to the nearest minute) from the video tape. 

The fire spread to the ends of each tray, following a V-pattern by which the cables in front of the 

flames were pre-heated by the fire in the tray above. 

There was virtually no solid residue left after the experiment, only the copper conductors 

remained. 

 
117

Figure 8-12. Multiple Tray Experiment 11 

Multiple Tray Test 11

Time (s)

0 900 1800 2700 3600 4500

Heat Release Rate (kW)

0

200

400

600

800

1000

HRR (O2 cal.)

HRR (mass loss)

Trays 1, 2, 3 and 4

Multiple Tray Test 11

Time (s)

0 900 1800 2700 3600 4500

HRR Per Unit Area (kW/m2

)

0

100

200

300

400

HRRPUA (O2 cal.)

HRRPUA (mass loss)
118

8.2.12 Multiple Tray Test 12 (MT-12) 

This experiment consisted of 3 trays, one above the other with a spacing of 30 cm (1 ft). Each 

tray was 2.4 m (8 ft) long. Each tray contained 40 cables, all #700. The cables were packed 

loosely. 

The burner under the bottom tray was maintained at about 40 kW and turned off following the 

observation of sustained burning in Tray 2. 

The heat release rate as a function of time is shown in Figure 8-13. The black curve is the HRR 

obtained via oxygen consumption calorimetry; the red was inferred from the measured mass loss 

rate and the estimated effective heat of combustion. The times when each tray became involved 

in the fire were estimated (to the nearest minute) from the video tape. 

The damage to the cables was relatively minor. The cables in each tray burned over roughly 1 m 

(3 ft) in length. 

 
119

Figure 8-13. Multiple Tray Experiment 12 

Multiple Tray Test 12

Time (s)

0 300 600 900 1200 1500 1800

Heat Release Rate (kW)

0

50

100

150

200

Burner Tray 1 Off

Tray 2 Tray 3

HRR (O2 cal.)

HRR (mass loss)

Multiple Tray Test 12

Time (s)

0 300 600 900 1200 1500 1800

HRR Per Unit Area (kW/m2

)

0

100

200

300

400

HRRPUA (O2 cal.)

HRRPUA (mass loss)
120

8.2.13 Multiple Tray Test 13 (MT-13) 

This experiment did not actually involve multiple trays. Rather, a single 2.4 m (8 ft) tray was 

positioned the same way as the bottom tray in all the other experiments of this series. The tray 

was loaded the same way as in Test 11 – 44 cables (#701), loosely packed. 

The heat release rate as a function of time is shown in Figure 8-14. The black curve is the HRR 

obtained via oxygen consumption calorimetry; the red was inferred from the measured mass loss 

rate and the estimated effective heat of combustion. Following the ignition of the fire in the tray, 

the burner was turned off. However, the heat release rate dropped down towards zero and by 

15 min the fire was almost out and had not spread beyond the vicinity of the burner. It was 

decided that the burner should be re-lit at 20 min and left on to see if the burner could support the 

fire long enough to allow it to spread to the ends of the tray as it had with this same loading in 

Tests 2, 8 and 11. It did not spread after about an hour beyond columns of the support rig. 

 
121

Figure 8-14. Multiple Tray Experiment 13 

Multiple Tray Test 13

Time (s)

0 900 1800 2700 3600

Heat Release Rate (kW)

0

50

100

150

200

Tray 1

Burner

Off

Burner 

Re-lit

Burner

Off

HRR (O2 cal.)

HRR (mass loss)

Multiple Tray Test 13

Time (s)

0 900 1800 2700 3600

HRR Per Unit Area (kW/m2

)

0

50

100

150

200

HRRPUA (O2 cal.)

HRRPUA (mass loss)
122

8.2.14 Multiple Tray Test 14 (MT-14) 

This experiment consisted of 4 trays, one above the other with a spacing of 30 cm (1 ft). Each 

tray was 2.4 m (8 ft) long. Tray 1 (bottom tray) contained 24 #220 cables. Tray 2 contained 36 

#220 cables. Tray 3 contained 32 #219 cables. Tray 4 contained 42 #219 cables. All trays were 

loosely packed. 

The burner under the bottom tray was maintained at about 40 kW until the bottom tray was 

ignited. After it was turned off, the fire slowly spread to Tray 2 and then Tray 3, but the fires 

within each tray were fairly weak and it appeared that the fire would have died out unless 

something were done. Thus, it was decided to re-light the burner at 30 min, after which the fire 

grew considerably. 

The heat release rate as a function of time is shown in Figure 8-16. The black curve is the HRR 

obtained via oxygen consumption calorimetry; the red was inferred from the measured mass loss 

rate and the estimated effective heat of combustion. The times when each tray became involved 

in the fire were estimated from visual observations during the experiment. 

The damaged cables formed a V-pattern as seen in Figure 8-15. 

Figure 8-15. Damage to cables following Multiple Tray Test 14. 
123

Figure 8-16. Multiple Tray Experiment 14 

Multiple Tray Test 14

Time (s)

0 900 1800 2700 3600 4500 5400

Heat Release Rate (kW)

0

200

400

600

800

Tray 3

Tray 4

Burner

Off

Burner

Re-lit

Burner

Off

Tray 1 Tray 2

HRR (O2 cal.)

HRR (mass loss)

Multiple Tray Test 14

Time (s)

0 900 1800 2700 3600 4500 5400

HRR Per Unit Area (kW/m2

)

0

100

200

300

400

HRRPUA (O2 cal.)

HRRPUA (mass loss)
124

8.2.15 Multiple Tray Test 15 (MT-15) 

This experiment consisted of 3 trays, one above the other with a spacing of 30 cm (1 ft). Each 

tray was 2.4 m (8 ft) long. Tray 1 (bottom tray) contained 25 #16 cables. Tray 2 contained 14 

#12 cables. Tray 3 contained 36 #367 cables. All trays were packed loosely. The objective of 

this experiment was to observe the behavior of cable #367. The first two trays were loaded only 

to produce a fire under Tray 3. 

The burner under the bottom tray was maintained at about 40 kW until all the trays were ignited. 

The reason for this is that the growth of the fire in Trays 1 and 2 was fairly sluggish, and as the 

intent of the experiment was to evaluate the cables in Tray 3, the burner was left on until those 

cables were involved. 

The heat release rate as a function of time is shown in Figure 8-18. The black curve is the HRR 

obtained via oxygen consumption calorimetry; the red was inferred from the measured mass loss 

rate and the estimated effective heat of combustion. The times when each tray became involved 

in the fire were estimated from visual observations during the experiment. 

The fire spread to the ends of Tray 3, but the fire in Trays 1 and 2 stopped just beyond the 

columns of the support rig, as seen in Figure 8-17. 

Figure 8-17. Fire spread to the ends of Tray 3, Multiple Tray Test 15. 
125

Figure 8-18. Multiple Tray Experiment 15 

Multiple Tray Test 15

Time (s)

0 900 1800 2700 3600 4500 5400

Heat Release Rate (kW)

0

100

200

300

400

Burner

Off

Tray 1 Tray 2

Tray 3

HRR (O2 cal.)

HRR (mass loss)

Multiple Tray Test 15

Time (s)

0 900 1800 2700 3600 4500 5400

HRR Per Unit Area (kW/m2

)

0

100

200

300

400

HRRPUA (O2 cal.)

HRRPUA (mass loss)
126

8.2.16 Multiple Tray Test 16 (MT-16) 

This experiment consisted of 3 trays, one above the other with a spacing of 30 cm (1 ft). Each 

tray was 2.4 m (8 ft) long. Tray 1 (bottom tray) contained 80 #270 cables. Tray 2 contained 30 

#270 cables and 50 #269 cables. Tray 3 contained 80 #269 cables. All trays were packed 

loosely. Both cable #269 and #270 were very similar in construction. Both were double 

shielded co-axial cable. 

The burner under the bottom tray was maintained at about 40 kW until the fire had spread to 

Tray 2. 

The heat release rate as a function of time is shown in Figure 8-20. The black curve is the HRR 

obtained via oxygen consumption calorimetry; the red was inferred from the measured mass loss 

rate and the estimated effective heat of combustion. The times when each tray became involved 

in the fire were estimated from visual observations during the experiment. 

The damage to the cables extended about to the columns of the support rig, as shown in Figure 

8-19. 

Figure 8-19. Damage to cables, Multiple Tray Test 16. 
127

Figure 8-20. Multiple Tray Experiment 16 

Multiple Tray Test 16

Time (s)

0 900 1800 2700 3600 4500

Heat Release Rate (kW)

0

200

400

600

800

1000

Tray 1 Tray 2

Tray 3

Burner 

Off

HRR (O2 cal.)

HRR (mass loss)

Multiple Tray Test 16

Time (s)

0 900 1800 2700 3600 4500

HRR Per Unit Area (kW/m2

)

0

200

400

600

800

HRRPUA (O2 cal.)

HRRPUA (mass loss)
Table 8-1. Summary of Multiple Tray Experiments, Series 1. 

Test 

No. Cable # Trays Cables per Tray Loading Fill (Note 1) (% of NEC max) Comments/Damage 

MT-1 23 3 x 8 ft 32 Tight 36 Damage confined to 4 ft inner bay (Note 2) MT-2 701 3 x 8 ft 44 Tight 50 Fire spread to ends, all trays MT-3 219 3 x 8 ft 32 Tight 36 Damage confined to 4 ft inner bay (Note 2) MT-4 43, 21, 20 4 x 8 ft 28 Tight 37 Pick ax required to aid upward spread Damage confined to 2 ft MT-5 21, 23, 15, 13 3 x 8 ft 28 Loose 32, 34, 29 Damage confined to 2 ft MT-6 13 4 x 8 ft 24 Loose 27 Damage confined to 2 ft MT-7 13 4 x 8 ft 3 x 12 ft 36 Loose 41 50 % more cable than MT-6 Fire spread to ends, all trays MT-8 701 4 x 12 ft 44 Loose 41 Fire spread to ends except lowest tray MT-9 701 4 x 12 ft 22 Loose 25 50 % less cable than MT-8 Damage confined to 6 ft inner bay (Note 2) 

MT-10 11 4 x 8 ft 14 Loose 83 Damage confined to 4 ft inner bay (Note 2) MT-11 701 4 x 12 ft 44 Loose 50 Replicate of MT-8 Fire spread to ends, all trays MT-12 700 3 x 8 ft 40 Loose 34 Light Damage above burner MT-13 701 1 x 8 ft 44 Loose 50 Test to see if spread can occur for only one tray. Damage only in vicinity of burner 

128
Test 

No. Cable # Trays Cables per Tray Loading Fill (Note 1) (% of NEC max) Comments/Damage 

MT-14 219, 220 4 x 8 ft 

Tray 1: 24 #220Tray 2: 36 #220Tray 3: 32 #219Tray 4: 42 #219

Loose 45, 68, 36, 48 

Slow vertical spread to 3rd tray; substantial 

spread after relight of burner. 

Spread nearly to end of trays 

MT-15 12, 16, 367 3 x 8 ft 

Tray 1: 25 #16 Tray 2: 14 #12 Tray 3: 36 #367

Loose 53, 83, 54 Test of Kerite cable in the 3rd tray Tray 3 burns to the end 

MT-16 269, 270 3 x 8 ft 80 Loose 67 Shielded, triaxial cable Fire spread nearly to end of Tray 3 

Notes: 

1 The column entitled “% of NEC max” indicates the volume of the tray occupied by cables as a fraction of the limit imposed by 

the National Electric Code (NFPA 70 2008). 

2 The “inner bay” of the rack is the area between the support columns. 

129
130

8.3 Results, Multiple Tray Experiments, Series 2 

A second series of Multiple Tray Experiments was conducted in January and February, 2010. 

Unlike the first series, conducted in May, 2009, these experiments consisted of mixtures of 

cables. It is common to find different cable manufacturers and sizes installed in NPP cable trays. 

This is especially true when the NPP has performed plant modifications and upgrades over its 

life. Series 2 experiments with mixed cable construction provides insight on how these 

configurations will perform. Table 8-2 lists the number and type of cable used in each tray for 

each experiment. 

Also, these experiments were intended to assess the effect of tray width, tray spacing, and tray 

fill. The first series of Multiple Tray Experiments involved only one tray width (0.45 m, 18 in) 

and one tray spacing (0.30 m, 12 in). 

Note that although it was observed that melted plastic dripped from the upper trays, there did not 

appear to be any downward spread of fire. 
Table 8-2. Parameters of Multiple Tray Experiments, Series 2 

Test

No.

Tray

Spacing

(in)

Tray

Width

(in)

Tray

Loading

(%)

2 Cable 3 Cable 7 Cable

17 Cable

22 Cable

25 Cable

34 Cable

45 Cable

47 Cable

212 Cable

261 Cable

272 Cable

273 Cable

312 Cable

327 Cable

337 Cable

503 Cable

505 Cable

612 Cable

700 Cable

701 Cable

MT‐17 12 18 50 2 3 4 2 4 2 3 2 3 3MT‐18 12 36 50 4 6 8 4 8 4 6 4 6 6MT‐19 12 18 50 2 3 4 2 4 2 3 2 3 3MT‐20 12 36 25 2 3 4 2 4 2 3 2 3 3MT‐21 18 18 50 2 3 4 2 4 2 3 2 3 3MT‐22 15 36 50 4 6 8 4 8 4 6 4 6 6MT‐23 9 18 50 2 3 4 2 4 2 3 2 3 3MT‐24 9 36 25 2 3 4 2 4 2 3 2 3 3MT‐25 12 18 50 3 2 6 2 1 3 5 3 5 4 4MT‐26 12 12 75 3 2 6 2 1 3 5 3 5 4 4

Notes: 1. The numbers in the columns labeled “Cable n” indicate the number of that particular cable used in the test. 

2. MT-22 was the last test conducted, and because of the lack of cables it was necessary to make a few substitutions to maintain the 

same approximate composition of cable as the other experiments. 

131
132

8.3.1 Multiple Tray Test MT-17 and MT-18 

Tests 17 and 18 were designed to assess the effect of doubling the width of the tray from 0.45 m 

(18 in) to 0.90 m (36 in). In both experiments, the trays were loaded to 50 % of the NEC limit, 

which means that the wider tray contained twice as much cable as the narrower. Each test used 

seven trays stacked 0.3 m (12 in) apart. The trays were 12 ft (3.6 m) long, but to save cable for 

the rest of the series, only 3 ft of cable was used in the lowest tray, followed by 4 ft, 5 ft, 7 ft, 

8 ft, 9 ft, and 12 ft at the top. The intent of this loading arrangement was to capture the so-called 

V-pattern of upward spread without wasting an excessive amount of cable in the lower trays. 

However, because the fire spread to the ends of the loaded portion of each tray, it was decided in 

subsequent experiments to include greater lengths of cable in the lower trays. 

Figure 8-21 displays the HRR of both experiments. The doubling of the cable mass (by way of 

doubling the horizontal surface area) more than doubles the HRR. The total burning time of the 

two tests is comparable. 

Figure 8-22 and Figure 8-23 are photographs of Tests MT-17 and MT-18, respectively. Figure 

8-23 demonstrates the increased burning area of the wider trays. 

Figure 8-21. Heat Release Rates for MT-17 and MT-18. 

 

Multiple Tray Test 17 and 18

Time (s)

0 900 1800 2700 3600 4500 5400

Heat Release Rate (kW)

0

500

1000

1500

2000

Test MT-17

Test MT-18
133

Figure 8-22. Multiple Tray Test 17 after 25 min. 

Figure 8-23. Multiple Tray Test 18 after approximately 20 min. 
134

8.3.2 Multiple Tray Test MT-19 and MT-20 

Tests MT-19 and MT-20 were designed to assess the effect of doubling the size of the tray while 

maintaining the same cable mass. Test MT-19 involved a stack of 7 trays, 0.45 m (18 in) in 

width and loaded to 50 % of the NEC limit. Test MT-20 involved the same amount of cable, 

only now spread out in a 0.90 m (36 in) wide tray. The trays were spaced 0.3 m (12 in) apart in 

both tests. The lowest tray contained 5 ft (out of 12) of cable, the next tray contained 7 ft, and 

the five trays above contained the full length of 12 ft of cable. 

Figure 8-24 shows the HRR of both experiments. The total amount of cable burned in each test 

is comparable, as evidenced by the comparable areas under both curves, but the burn time for the 

MT-19 is roughly twice as great as MT-20. This clearly demonstrates that the upward spread 

and burning rate of the cables are influenced by the higher relative loading of the trays in MT-19. 

In MT-20, the fire spread rapidly upward because the cables were spaced far enough apart in the 

tray that the flames were able to pass through, rather than around, the cables. 

The photographs shown in Figure 8-25 and Figure 8-26 demonstrate that the wider trays enable 

the fire to reach its peak in roughly half the time, and because more trays are burning 

simultaneously, the peak HRR is more than double. 

Figure 8-24. Heat Release Rates for Tests MT-19 and MT-20. 

 

Multiple Tray Tests 19 and 20

Time (s)

0 900 1800 2700 3600 4500 5400

Heat Release Rate (kW)

0

500

1000

1500

2000

Test MT-19

Test MT-20
135

Figure 8-25. Photograph of Multiple Tray Test MT-19. 

Figure 8-26. Photograph of Multiple Tray Test MT-20. 
136

8.3.3 Multiple Tray Test MT-21 and MT-22 

Tests MT-21 and MT-22 were originally intended to assess the impact of increasing the vertical 

cable spacing from 0.3 m (12 in) to 0.45 m (18 in). However, during Test MT-21, the fire did 

not spread beyond the second tray. The tray width in this test was 0.3 m (12 in). The 40 kW 

burner was left on for 45 min (instead of the usual 15), and still the fire burned only weakly in 

the second tray and more or less burned out within the area just above the burner in the lowest 

tray. Because of this, it was decided not to use the 18 in spacing in Test MT-22, but rather 15 in 

(0.38 m) spacing with 0.90 m (36 in) wide trays, loaded to 50 % of the NEC limit. 

The HRR of MT-21 and MT-22 are shown together in Figure 8-27 even though the two 

experiments are not easily compared. The photographs (Figure 8-28 and Figure 8-29) on the 

following page show the dramatically different outcomes of the two experiments. 

Figure 8-27. Heat Release Rates for Multiple Tray Tests MT-21 and MT-22. 

 

Multiple Tray Tests 21 and 22

Time (s)

0 900 1800 2700 3600 4500 5400 6300 7200

Heat Release Rate (kW)

0

500

1000

1500

2000

2500

3000

Test MT-21

Test MT-22
137

Figure 8-28. Photograph of Multiple Tray Test MT-21. 

Figure 8-29. Photograph of Multiple Tray Test MT-22. 
138

8.3.4 Multiple Tray Tests MT-23 and MT-24 

Tests MT-23 and MT-24 were designed to assess the effect of decreasing the vertical tray 

spacing from 0.3 m (12 in) to 0.23 m (9 in). At the same time, these experiments demonstrated 

that spreading out cables over a wider tray (36 in in Test 24) leads to more rapid growth and a 

higher peak HRR. The same type and number of cables were used in both tests. 

Figure 8-30 displays the HRR for MT-23 and MT-24. Photographs of the experiments are 

shown in Figure 8-31 and Figure 8-32, respectively. It is important to note that the fire in the 

36 in wide trays (MT-24) spread to both ends of all of the trays, while the fire in the 18 in wide 

trays (MT-23) only spread to one end due to a slight breeze in the test building caused by an 

asymmetric arrangement of air intake ducts. 

Figure 8-30. Heat Release Rates for Multiple Tray Tests MT-23 and MT-24. 

 

Multiple Tray Tests 23 and 24

Time (s)

0 900 1800 2700 3600 4500 5400

Heat Release Rate (kW)

0

500

1000

1500

2000

Test MT-23

Test MT-24
139

Figure 8-31. Photograph of Multiple Tray Test MT-23. 

Figure 8-32. Photograph of Multiple Tray Test MT-24. 
140

8.3.5 Multiple Tray Tests MT-25 and MT-26 

Tests MT-25 and MT-26 were conducted with a different mixture of cables than Tests MT-17 

through MT-24. Table 8-2 provides the make-up of each tray. Also, MT-25 and MT-26 used 

only five trays each, spaced 0.3 m (12 in) apart. The lowest tray contained 5 ft of cable (out of 

12), the next tray contained 7 ft, and the next three trays contained 12 ft each. Both tests used 

the same amount of cable, but in Test MT-25 the cables were spread in a 0.45 m (18 in) tray 

while in MT-26, the cables were spread in a 0.3 m (12 in) wide tray. The objective of the test 

was to see if the change in tray width would lead to a similar result as for the wider trays. 

Figure 8-33 shows the HRR for MT-25 and MT-26. The results demonstrate that spreading the 

same mass of cable within a tray that is 1.5 times as wide leads to more rapid upward spread and 

a higher peak HRR. The photograph of MT-25 shown in Figure 8-34 shows that burning is 

nearly complete in the wider tray test at 48 min whereas the fire in the narrower tray is still 

burning near its peak after 1 h (Figure 8-35). A slight breeze in the test lab caused the fire to 

spread to the left. 

Figure 8-33. Heat Release Rates for Multiple Tray Tests MT-25 and MT-26. 

 

Multiple Tray Tests 25 and 26

Time (s)

0 900 1800 2700 3600 4500 5400

Heat Release Rate (kW)

0

200

400

600

800

1000

Test MT-25

Test MT-26
141

Figure 8-34. Photograph of Multiple Tray Test MT-25. 

Figure 8-35. Photograph of Multiple Tray Test MT-26. 

 
142

8.4 Burn Patterns 

In all of the Multiple Tray Experiments, the fires spread upward to form a V-shaped burning 

pattern initially, followed by either continuous lateral spread to the left and/or right, or limited 

spread that did not progress to the end of the tray. Similar observations of the V-shaped pattern 

were made by Nowlen and included in NUREG/CR-6850, Appendix R. Nowlen estimated the 

spread angle from a seven tray experiment to be 35°. The authors of NUREG/CR-6850 also 

recommend spread rates of 3.2 m/h (0.2 ft/min) for typical TP cables and 1.1 m/h (0.05 ft/min) 

for TS. These spread rate estimates were made based on theoretical spread models rather than 

actual observation. 

The results of the 26 Multiple Tray Experiments were analyzed in light of the observations and 

guidance given in NUREG/CR-6850. Figure 8-36 is a photograph of a 7 tray experiment (MT23) showing the initial V-pattern and lateral spread path. Table 8-3 summarizes the 

measurements. The dashed lines indicate the initial upward spread pattern, and the arrows 

indicate the movement of the fire following its ascent to the top tray. The spread angles were 

determined by overlaying on the photograph two straight lines emanating from the burner that 

were judged to best encompass the initial V-pattern. The uncertainty of this procedure is 

approximately ±5°. While the average spread angle (20°-25°) is less than that recommended by 

NUREG/CR-6850 (35°), there is considerable scatter and no discernible pattern in the results. In 

other words, it would be difficult to predict the spread angle based on the cable composition or 

configuration. For this reason, the simple model to be developed in the next chapter will retain 

the use of the 35° spread angle because there is not enough data to allow for a refined estimate. 

As for the spread rates, it was difficult to determine if the fire spread could be considered “selfsustaining,” that is, if the fire could have continued to spread beyond the limits of the 8 ft or 12 ft 

trays used in the experiments. A self-sustaining cable fire was defined, for these tests, as a fire 

that enveloped all of the tiers of trays and spread, with the ignition source removed, to both ends 

of the cable trays. Under this definition, Multiple Tray Tests 2, 11, 20, 22, 23, 24, and 25 were 

judged to be self-sustaining. For these fires, the horizontal spread rate was calculated by 

dividing the distance the fire spread by the time required to travel that distance. The time was 

begun after the V-shaped fire had separated into two separate fires spreading in opposite 

directions. This was done to eliminate the influence of each fire on the spread rate of the other. 

The average of the two spread rates was taken because there was a slight breeze in the laboratory 

that tended to increase the spread rate in one direction and decrease it in the other. The 

uncertainty in the spread rate was approximately ±0.5 m/h, based on repeated estimates by 

several different analysts. 
143

Figure 8-36. Explanation of spread rate and angle. 

Spread Angles 

Spread Distance Spread Distance 
144

Table 8-3. Spread rate and spread angle for Multiple Tray Tests. 

Test Number Cable 

Type 

Left Side 

Angle 

(deg) 

Right 

Side 

Angle 

(deg) 

Average Spread 

Distance for Left and 

Right Sides 

(m) 

Spread Rate for 

Self-Sustaining 

Fires 

(m/hr) 

1 TS 8 9 0.3 - 

2 TP 28 40 0.7 2.7 

3 TS 36 2 - - 

4 TS - - - - 

5 TS 17 0 0.0 - 

6 TS 10 12 0.1 - 

7 TS 34 28 0.6 - 

8 TP 36 19 1.0 - 

9 TP 9 4 0.2 - 

10 TS 26 3 0.2 - 

11 TP 31 23 0.7 2.6 

12 TS 17 17 0.1 - 

13 TP - - - - 

14 TS 34 34 0.4 - 

15 TS 29 32 0.5 - 

16 TS 28 20 0.3 - 

17 Mix 22 25 0.4 - 

18 Mix 27 21 0.5 - 

19 Mix 23 25 0.6 - 

20 Mix 26 19 0.3 3.7 

21 Mix - - - - 

22 Mix 24 32 1.2 - 

23 Mix 32 42 0.5 - 

24 Mix 16 16 1.1 3.2 

25 TS 28 25 0.3 2.6 

26 TS 29 19 0.3 1.8 

Average 25 20 0.5 2.8 
145

9 MODELING 

One of the major goals of the CHRISTIFIRE program is to gather data to support the 

development of improved methods to model cable fires. This chapter describes a relatively 

simple model that can be used to predict the heat release rate from a vertical stack of horizontal 

cable trays. The relative simplicity of the model is a direct result of the fact that the data 

collected during this and other cable fire projects is subject to considerable uncertainty based on 

the test method, scale, and cable type. Before introducing the model, a summary of the data 

collected during this phase of the project is warranted. 

9.1 Summary of Data Collection for Modeling 

The preceding chapters present a considerable amount of information about the burning of 

electrical cables, but it is difficult to use the data directly in a fire model because the most 

important properties that have been measured, such as the heat release rate per unit area 

(HRRPUA), the heat of combustion, and the char/residue yield, are effective properties that 

depend significantly on the particular test configuration. For example, the HRRPUA that is 

determined from the Radiant Panel Apparatus and the Cone Calorimeter is dependent on the size 

of the sample, the imposed heat flux, and the heat fed back from the fire itself. As another 

example, the heat of combustion that is extracted from the Micro-Calorimeter (MCC) data is 

different from that which is extracted from the Radiant Panel Apparatus or Cone Calorimeter 

because the MCC makes use of an oxygen-depleted environment. 

Table 9-1 lists some important parameters for modeling cable fires. Of these, only the bulk 

physical properties like Outer Diameter (OD), Mass/Length, and Plastic Mass Fraction can be 

measured with a degree of accuracy that would warrant a detailed description within a model. 

The other properties are significantly affected by the specific test configuration, and, thus, 

models employing these parameters cannot include a detailed treatment of the physical 

phenomena. 

Another problem with the measurements of thermo-physical properties of the cables is that there 

are literally hundreds of different types of cables currently installed in NPPs, manufactured over 

a span of approximately 40 years of evolving polymer technology. Compiling a comprehensive 

database of material properties for the purpose of fire modeling would be an enormous 

undertaking. Given the uncertainty associated with the various bench-scale measurements, it 

would be of questionable value as well. Archibald Tewarson of FM Global (Factory Mutual) has 

compiled an extensive list of heats and products of combustion for a wide variety of materials, 

including those used in cables (SFPE, 2008). However, the list includes mostly effective 

properties of materials that are in general dependent on the details of the measurement apparatus. 

In addition, it is difficult to combine the properties of the individual materials that make up a 

cable because these materials burn in stages; first the jacket, followed by the insulation material 

and filler. 
Table 9-1. Summary of measured properties of the cables used in CHRISTIFIRE. 

Cable 

No. 

OD 

(mm) 

Mass/ 

Length 

(kg/m) 

Plastic 

Mass 

Fraction 

Residue Yield Heat of Combustion (MJ/kg) HRRPUA (kW/m2) 

Tube 

Furnace MCC Radiant Panel Cone Radiant Panel Cone Radiant Panel 

11 32 1.985 0.45 -- 0.28 0.2 16.4 16.7 127 160 16 19 0.671 0.48 0.09 0.32 0.5 23.8 15.0 173 100 23 14 0.253 0.69 0.33 0.43 0.4 13.2 12.2 135 100 43 15 0.357 0.62 -- 0.35 0.3 17.0 -- 169 110 46 15 0.437 0.52 0.20 0.38 0.5 16.2 15.9 172 80 

219 14 0.296 0.61 0.27 0.47 0.3 20.5 19.3 187 200 220 18 0.560 0.62 0.33 0.46 0.4 22.5 17.3 -- 200 269 12 0.240 0.53 -- 0.24 0.0 18.1 13.9 510 270 271 10 0.123 0.70 0.18 0.27 0.1 28.1 16.0 199 180 367 16 0.441 0.73 0.40 0.44 0.3 23.3 18.0 169 210 700 12 0.322 0.33 0.30 0.31 0.5 22.5 19.2 -- 150 701 14 0.366 0.42 0.15 0.25 0.0 18.0 16.1 266 250 

Note: The precision of the measurement is indicated by the number of significant figures. 

146
147

9.2 The FLASH-CAT Model 

This section describes a relatively simple model for predicting the growth and spread of a fire 

within a vertical stack of horizontal cable trays. The model is referred to as FLASH-CAT, short 

for Flame Spread over Horizontal Cable Trays. The basic assumptions are taken from 

Appendix R of NUREG/CR-6850, with some additional information provided by the small and 

intermediate-scale experiments described in this report. Following the description of the model, 

the results of the 26 Multiple Tray Experiments are compared with the predictions of the model. 

9.2.1 Model Overview 

The FLASH-CAT model makes use of the following assumptions: 

 The cable trays are horizontal and stacked vertically with a spacing of less than 0.45 m 

(18 in). 

 The cables burn in the open; that is, they are away from walls and well below the ceiling. 

 The cables are not exposed to elevated temperature sources except for the ignition source 

below. 

 There are no barriers separating the trays, and the tray tops and bottoms are open. 

 The cables are not protected with coatings, armor shielding, or thermal blankets of any kind. 

 There is a fire beneath the lowest tray. 

 The initial extent of the fire in the lowest tray is equal to the width of the source fire. 

 Each tray has at least a single row of cables, or roughly 25 % of the NEC limit. 

Under these assumptions, the fire is assumed to propagate upwards through the array of cable 

trays according to an empirically determined timing sequence. In other words, the time for the 

fire to spread from one tray to the tray above is a function only of its order in the stack, not the 

thermal properties of the cables. The length of cables within a given tray that ignite initially 

increases as the fire spreads upwards. Lateral spread of the fire begins as soon as the cables 

within the tray ignite. This produces a solid V-shaped burning pattern that expands laterally with 

time. As the mass of combustible material within the center of the V is consumed, the V-shape 

becomes an expanding, open wedge of burning cable. The fires in each tray continue to spread 

until the end of the tray is reached. 

Burning Rate: Once a given tray has ignited, the model assumes that the cables burn over a 

length that is greater than that of the tray below. The length increases according to the formula: 

ܮ௜ାଵ ൌ ܮ൅ ௜2݄ ௜tanሺ35°ሻ (9-1)

Here, ݄௜ is the vertical distance between the two trays. The value of 35° is based on observations 

of cable fire experiments performed at Sandia National Laboratories and documented in 

NUREG/CR-6850. The spread angles measured as part of the CHRISTIFIRE test program do 

not conclusively provide evidence that would suggest a different value than that which is 

currently recommended. See Section 8.4 for details. 
148

The fire is assumed to span the width, ܹ, of the tray. The heat release rate of the fire within the 

tray is initially equal to the length times the width times the specified heat release rate per unit 

area (HRRPUA). This last parameter is described below. 

Vertical Spread Rate: NUREG/CR-6850 suggests that a fire propagates upward through the 

stack of trays as follows. The lowest (first) tray ignites after 5 min of exposure to the ignition 

source. The second tray ignites 4 min following the ignition of the first tray. The third tray 

ignites 3 min after the second. The fourth tray ignites 2 min after the third. The fifth tray ignites 

1 min after the fourth. It is assumed that each subsequent ignition occurs 1 min apart. 

Horizontal Spread Rate (S): NUREG/CR-6850 provides estimates of horizontal spread rates 

for a typical thermoset (XPL) and thermoplastic (PVC) cable. The values are 1.1 m/h (3.5 ft/h) 

and 3.2 m/h (10.6 ft/h), respectively. It is assumed that the fire in a given tray spreads laterally at 

this rate until the end of the tray is reached. 

Fire Duration: NUREG/CR-6850 does not discuss fire duration. However, given a known 

combustible mass and a specified heat release rate (Figure 9-1), the duration of the fire, ∆ݐ, at a 

given location is calculated: 

ൌ ݐ∆

݉௖

ܪ∆ᇱᇱ

ሶݍ 5

avg

ᇱᇱ /6 (9-2)

where ݉௖

ᇱᇱ is the combustible mass per unit area, ∆ܪ is the heat of combustion, and ݍሶavgᇱᇱ is the 

heat release rate per unit area (HRRPUA)8.. The combustible mass per unit area can be found by 

calculating: 

݉௖

ᇱᇱ ൌ ܻ݊௣ሺ1 െ ߭ሻ݉′

ܹ (9-3)

where n is the number of cables per tray, ܻ௣ is the mass fraction of non-metallic material, ߭ is the 

char yield, ݉′ is the mass per unit length of cable, and ܹ is the width of the tray. Note that not 

all of the non-metallic materials in a cable will burn. There is almost always some solid residue 

or char left behind. The mass of this residue divided by the mass of the original combustible 

material is designated by ߭. 

 

8 Note that the fraction 5/6 is a result of the fact that the average heat release rate per unit area is based on 80 % of 

the total energy release. 
149

Figure 9-1. Idealized time history of the local heat release rate per unit area. 

Heat Release Rate: The total heat release rate of the fire, ܳሶ

ሺݐሻ, is calculated by summing the 

local heat release rate per unit area, ݍሶᇱᇱ, over all of the burning trays: 

ܳሶ

ሺݐሻ ൌ ܳሶ

burner ൅ܹ෍ ቈන ݍሶ

ᇱᇱ ቀݐ െ ݐign,iሺݔሻቁ ݀ݔ

௅/ଶ

ି௅/ଶ ቉

ேtrays

௜ୀଵ

(9-4)

The time of ignition for the point, x, of the i-th tray is: 

ݐign,௜ሺݔሻ ൌ ݐign,௜,଴ ൅ max ቆ0 , |ݔ |െ ܮ௜/2

ܵ ቇ (9-5)

The time, ݐign,௜,଴, is the time when the tray first ignites, whereas ݐign,௜ሺݔሻ, is the time when the 

cables located at the point x first ignite. If this point is within the original section of cable that 

first ignites, the two ignition times are the same. 

Model Output: The primary output of the FLASH-CAT model is the time history of the heat 

release rate, ܳሶ

ሺݐሻ. In addition, it is possible to create a simple animation showing the 

progression of the fire upwards and outwards as a function of time. Figure 9-2 shows the 

evolution of Multiple Tray Test 17 as predicted by FLASH-CAT. The color red indicates 

burning cables, black indicates burned out cables, and white indicates unburned cables. 

 
150

Figure 9-2. FLASH-CAT model results for Multiple Tray Test 17. 
151

9.2.2 FLASH-CAT Model Input Parameters 

This section describes the information needed by the FLASH-CAT model to predict the heat 

release rate from a vertical stack of open horizontal cable trays that are not directly below a 

ceiling or against a wall. The parameters for all 26 full-scale experiments are listed in Table 9-2. 

Test #: There were 26 experiments involving multiple horizontal ladder-back trays, denoted by 

the abbreviation MT for Multiple Tray. Tests 1-16 were conducted in May, 2009, and Tests 17-

26 were conducted in January and February, 2010. 

Cable ID: Each spool of cable used in CHRISTIFIRE was assigned a number for tracking 

purposes. It has no other meaning other than to identify it. Note that each of Tests 1-16 made 

use of only a few different cables. These cables had been tested in the Radiant Panel Apparatus, 

the Cone Calorimeter, the Tube Furnace, and the Micro-Calorimeter, as well. Tests 17-26 used 

fixed combinations of cables. Tests 17-24 all used the same cables mixed together in the same 

ratio. Tests 25 and 26 used a different mixture. 

No. Cables (n): This parameter indicates the number of cables in each tray. 

No. Trays (ܰtraysሻ: The number of horizontal trays used in the test. 

Tray Spacing (݄௜ሻ: The vertical distance from the bottom of tray i to the bottom of tray (i+1). 

The various racks used to support the trays used 3 inch spacing increments. The vertical spacing 

ranged from 0.23 m to 0.46 m (9 in to 18 in). In Test 13, only one tray was used in order to 

determine if the fire would spread over a single tray. 

Tray Length: Only two tray lengths were used in the series, 8 ft (2.4 m) and 12 ft (3.6 m). Note 

that in Tests 1-16, each tray was filled with cables along its entire length. In Tests 17-26, some 

of the trays contained shortened cables near the bottom of the stack to save on supply. 

Tray Width (W): Three tray widths were used in the series, 12 in (0.3 m), 18 in (0.45 m), and 

36 in (0.90 m). Most tests involved 18 in wide ladder-back trays, a common size in U.S. plants. 

Mass/Length (݉ᇱ

ሻ: The mass per unit length of a single cable, accurate to roughly 1 g/m. 

Plastic Mass Fraction (ܻ௣ሻ: The fraction of the cable’s mass that is not metal. The Plastic 

Mass Fraction can be measured easily by disassembling a 10 to 20 cm length of cable into its 

constituent parts and weighing each with a scale that has an accuracy of plus or minus 1 mg, in 

which case the value can be reliably determined with an accuracy of ±1 %. In cases where there 

is a mixture of cables, the plastic mass fraction for each type can be determined and an average 

value can be computed using the formula: 

ܻ௣

ഥ ൌ ∑ ܻ௣,௜ ݉௜ ௡ ᇱ ௜ୀଵ

∑ ݉௜ ௡ ᇱ ௜ୀଵ

(9-6)
152

Char Yield (߭ሻ: The (mass) fraction of the non-metallic (plastic) part of the cable that is left 

behind after the fire. This quantity can be determined from any of the bench-scale tests, but its 

value is dependent on the test configuration and procedure. For this reason, a value of 0.25 has 

been chosen for all thermoset cables, and a value of 0 for thermoplastics. In the former case, the 

cables have been observed to form a char, and the char yield ranges from about 0.1 to 0.5. In the 

latter case, almost all of the combustible material melts and then burns away. 

HRRPUA ሺݍሶavg

ᇱᇱ ሻ: Heat Release Rate Per Unit Area (of tray). Correlated values of HRRPUA 

are listed in NUREG/CR-6850, Appendix R.3, “Heat Release Rate from Cable Tray Fires.” The 

lowest value listed is 0.45×178=80 kW/m2 for an XPE/XPE (thermoset) cable. The highest 

value is 0.45×589=265 kW/m2

 for a PE/PVC (thermoplastic) cable. The measured values from 

the Cone Calorimeter (Table 6-1) and the Radiant Panel Apparatus (Figure 7-22) for a variety of 

cables used in CHRISTIFIRE fall within this range. 

For FLASH-CAT, the recommended value of HRRPUA is 150 kW/m2

 for thermoset cables and 

250 kW/m2

 for thermoplastics. If there is a mixture of thermoset and thermoplastic materials 

within the cables and/or within the tray, the HRRPUA can be expressed as a mass-weighted 

average of the two recommended values. For example, if 30 % of the combustible mass is 

composed of thermoset materials and 70 % of thermoplastic, the HRRPUA can be taken as 

HRRPUA	ൌ	ሺ0.3	ൈ	150ሻ	൅	ሺ0.7	ൈ	250ሻ		ൌ	220	kW/mଶ (9-7) 

Currently, the weighted average appears based on HRR from small scale testing to be the most 

reasonable way to model mixed cable tray loading. Section 10.5, “Future Work,” discusses 

future research planned in this area. 

Heat of Combustion ሺΔܪሻ: The energy released per unit mass of fuel consumed. This is the 

value used to convert the mass loss rate to the heat release rate. It is only an effective value, 

found by averaging over (usually) the steady burning phase of the fire. Its value is subject to 

considerable uncertainty because each of the cable components has a different heat of 

combustion, and the value is not necessarily a constant over the entire burning period. This is 

especially true of charring materials. For this reason, a single value of 16 MJ/kg has been 

selected for all cable types in the FLASH-CAT model. Measured values from the Radiant Panel 

Apparatus, Cone Calorimeter, and Micro-Combustion Calorimeter are inconsistent. The values 

change from test to test, and device to device. If more reliable data can be found in the future, it 

can easily be used in the model. 

Burner Length, Width, HRR, Duration, and Offset: These parameters merely establish the 

fire of origin. In CHRISTIFIRE, a 40 kW±5 kW natural gas burner was positioned 

approximately 20 cm (8 in) below the bottom tray. It was typically not extinguished until the fire 

had established itself in the first two trays. 

Spread Rate (S): Several of the multiple tray experiments exhibited spread rates comparable to 

those recommended by NUREG/CR-6850, Appendix R. However, there is not enough new data 

to suggest that the currently recommended values are inappropriate. Thus, the suggested rates 

for horizontal spread of thermoplastic cables is 3.2 m/h and for thermoset 1.1 m/h. For a mixture 
153

of materials within the cable and/or tray, it is recommended that the spread rate corresponding to 

the predominant material should be applied. 
Table 9-2. Input parameters for the FLASH-CAT Model. 

# Test

ID Cable

cables No.

trays No.

Spacing Tray

Length Tray

Width Tray

Mass/Length

Mass Plastic

Fraction

Yield Char

HRRPUA

of Heat

Combustion

Length Burner

Width Burner

HRR Burner

Burner

Duration

Offset Burner

Rate Spread

m m m kg/m kg/kg kg/kg kW/m2 kJ/kg m m kW s m m/h

1 23 32 3 0.3 2.4 0.45 0.253 0.69 0.25 150 16000 0.3 0.3 40 2400 0.2 1.12 701 44 3 0.3 2.4 0.45 0.366 0.42 0 250 16000 0.3 0.3 40 3600 0.2 3.23 219 32 3 0.3 2.4 0.45 0.296 0.61 0.25 150 16000 0.3 0.3 40 650 0.2 1.14 43 28 4 0.3 3.6 0.45 0.357 0.62 0.25 150 16000 0.3 0.3 40 2800 0.2 1.15 16 28 3 0.3 2.4 0.45 0.671 0.48 0.25 150 16000 0.3 0.3 40 400 0.2 1.16 16 24 4 0.3 3.6 0.45 0.671 0.48 0.25 150 16000 0.3 0.3 40 900 0.2 1.17 16 36 7 0.3 3.6 0.45 0.671 0.48 0.25 150 16000 0.3 0.3 40 1100 0.2 1.18 701 44 4 0.3 3.6 0.45 0.366 0.42 0 250 16000 0.3 0.3 40 250 0.2 3.29 701 22 4 0.3 3.6 0.45 0.366 0.42 0 250 16000 0.3 0.3 40 260 0.2 3.2

10 11 14 3 0.3 2.4 0.45 1.985 0.45 0.25 150 16000 0.3 0.3 40 1200 0.2 1.111 701 44 4 0.3 3.6 0.45 0.366 0.42 0 250 16000 0.3 0.3 40 100 0.2 3.212 700 40 3 0.3 2.4 0.45 0.322 0.33 0.25 150 16000 0.3 0.3 40 550 0.2 1.113 701 44 1 None 2.4 0.45 0.366 0.42 0 250 16000 0.3 0.3 40 3300 0.2 3.214 219 35 4 0.3 2.4 0.45 0.296 0.61 0.25 150 16000 0.3 0.3 40 3600 0.2 1.115 367 36 3 0.3 2.4 0.45 0.441 0.73 0.25 150 16000 0.3 0.3 40 2700 0.2 1.116 269 80 3 0.3 2.4 0.45 0.24 0.53 0 250 16000 0.3 0.3 40 1000 0.2 1.117 Mix 28 7 0.3 3.6 0.45 0.52 0.53 0.25 150 16000 0.3 0.3 40 900 0.2 1.118 Mix 56 7 0.3 3.6 0.90 0.52 0.53 0.25 150 16000 0.3 0.3 40 900 0.2 1.119 Mix 28 7 0.3 3.6 0.45 0.52 0.53 0.25 150 16000 0.3 0.3 40 900 0.2 1.120 Mix 28 7 0.3 3.6 0.90 0.52 0.53 0.25 150 16000 0.3 0.3 40 900 0.2 1.121 Mix 28 7 0.45 3.6 0.45 0.52 0.53 0.25 150 16000 0.3 0.3 40 900 0.2 1.122 Mix 56 7 0.38 3.6 0.90 0.52 0.53 0.25 150 16000 0.3 0.3 40 900 0.2 1.123 Mix 28 7 0.23 3.6 0.45 0.52 0.53 0.25 150 16000 0.3 0.3 40 900 0.2 1.124 Mix 28 7 0.23 3.6 0.90 0.52 0.53 0.25 150 16000 0.3 0.3 40 900 0.2 1.125 Mix 38 5 0.3 3.6 0.45 0.39 0.49 0.25 150 16000 0.3 0.3 40 900 0.2 1.126 Mix 38 5 0.3 3.6 0.30 0.39 0.49 0.25 150 16000 0.3 0.3 40 900 0.2 1.1

154
155

9.2.3 Model Validation 

Figures 9-3 through 9-12 on the following pages present results comparing the measured HRR 

from the 26 Multiple Tray Experiments with predictions of the FLASH-CAT model. The 

predictions have been made using only information obtained by dissecting a few tens of 

centimeters worth of cable. The information that could not be obtained directly from inspection 

of the cable has been taken from NUREG/CR-6850 or from effective averages of the bench-scale 

experiments in CHRISTIFIRE, as explained in the previous section. 

It is important to note that these 26 experiments were not used in any way to calibrate the model. 

The basic model formulation is based on the guidance set forth in NUREG/CR-6850, and the 

input parameters were obtained either by direct measurement of the cables or from 6850. As 

such, this exercise constitutes model validation, not calibration. 
156

Figure 9-3. Comparison of predicted and measured HRR for Multiple Tray Tests 1-3. 

 

0 10 20 30 40 50 60 70 80 90 0

500

1000

1500

2000

2500

3000

Time (min)

Heat Release Rate (kW)

Multiple Tray Test 1 Exp

Model

0 10 20 30 40 50 60 70 80 90 0

500

1000

1500

2000

2500

3000

Time (min)

Heat Release Rate (kW)

Multiple Tray Test 2 Exp

Model

0 10 20 30 40 50 60 70 80 90 0

500

1000

1500

2000

2500

3000

Time (min)

Heat Release Rate (kW)

Multiple Tray Test 3 Exp

Model
157

Figure 9-4. Comparison of predicted and measured HRR for Multiple Tray Tests 4-6. 

 

0 10 20 30 40 50 60 70 80 90 0

500

1000

1500

2000

2500

3000

Time (min)

Heat Release Rate (kW)

Multiple Tray Test 4 Exp

Model

0 10 20 30 40 50 60 70 80 90 0

500

1000

1500

2000

2500

3000

Time (min)

Heat Release Rate (kW)

Multiple Tray Test 5 Exp

Model

0 10 20 30 40 50 60 70 80 90 0

500

1000

1500

2000

2500

3000

Time (min)

Heat Release Rate (kW)

Multiple Tray Test 6 Exp

Model
158

Figure 9-5. Comparison of predicted and measured HRR for Multiple Tray Tests 7-9. 

 

0 10 20 30 40 50 60 70 80 90 0

500

1000

1500

2000

2500

3000

Time (min)

Heat Release Rate (kW)

Multiple Tray Test 7 Exp

Model

0 10 20 30 40 50 60 70 80 90 0

500

1000

1500

2000

2500

3000

Time (min)

Heat Release Rate (kW)

Multiple Tray Test 8 Exp

Model

0 10 20 30 40 50 60 70 80 90 0

500

1000

1500

2000

2500

3000

Time (min)

Heat Release Rate (kW)

Multiple Tray Test 9 Exp

Model
159

Figure 9-6. Comparison of predicted and measured HRR for Multiple Tray Tests 10-12. 

 

0 10 20 30 40 50 60 70 80 90 0

500

1000

1500

2000

2500

3000

Time (min)

Heat Release Rate (kW)

Multiple Tray Test 10 Exp

Model

0 10 20 30 40 50 60 70 80 90 0

500

1000

1500

2000

2500

3000

Time (min)

Heat Release Rate (kW)

Multiple Tray Test 11 Exp

Model

0 10 20 30 40 50 60 70 80 90 0

500

1000

1500

2000

2500

3000

Time (min)

Heat Release Rate (kW)

Multiple Tray Test 12 Exp

Model
160

Figure 9-7. Comparison of predicted and measured HRR for Multiple Tray Tests 13-15. 

 

0 10 20 30 40 50 60 70 80 90 0

500

1000

1500

2000

2500

3000

Time (min)

Heat Release Rate (kW)

Multiple Tray Test 13 Exp

Model

0 10 20 30 40 50 60 70 80 90 0

500

1000

1500

2000

2500

3000

Time (min)

Heat Release Rate (kW)

Multiple Tray Test 14 Exp

Model

0 10 20 30 40 50 60 70 80 90 0

500

1000

1500

2000

2500

3000

Time (min)

Heat Release Rate (kW)

Multiple Tray Test 15 Exp

Model
161

Figure 9-8. Comparison of predicted and measured HRR for Multiple Tray Tests 16-18. 

 

0 10 20 30 40 50 60 70 80 90 0

500

1000

1500

2000

2500

3000

Time (min)

Heat Release Rate (kW)

Multiple Tray Test 16 Exp

Model

0 10 20 30 40 50 60 70 80 90 0

500

1000

1500

2000

2500

3000

Time (min)

Heat Release Rate (kW)

Multiple Tray Test 17 Exp

Model

0 10 20 30 40 50 60 70 80 90 0

500

1000

1500

2000

2500

3000

Time (min)

Heat Release Rate (kW)

Multiple Tray Test 18 Exp

Model
162

Figure 9-9. Comparison of predicted and measured HRR for Multiple Tray Tests 19-20. 

 

0 10 20 30 40 50 60 70 80 90 0

500

1000

1500

2000

2500

3000

Time (min)

Heat Release Rate (kW)

Multiple Tray Test 19 Exp

Model

0 10 20 30 40 50 60 70 80 90 0

500

1000

1500

2000

2500

3000

Time (min)

Heat Release Rate (kW)

Multiple Tray Test 20 Exp

Model
163

Figure 9-10. Comparison of predicted and measured HRR for Multiple Tray Tests 21-22. 

 

0 10 20 30 40 50 60 70 80 90 0

500

1000

1500

2000

2500

3000

Time (min)

Heat Release Rate (kW)

Multiple Tray Test 21 Exp

Model

0 10 20 30 40 50 60 70 80 90 0

500

1000

1500

2000

2500

3000

Time (min)

Heat Release Rate (kW)

Multiple Tray Test 22 Exp

Model
164

Figure 9-11. Comparison of predicted and measured HRR for Multiple Tray Tests 23-24. 

 

0 10 20 30 40 50 60 70 80 90 0

500

1000

1500

2000

2500

3000

Time (min)

Heat Release Rate (kW)

Multiple Tray Test 23 Exp

Model

0 10 20 30 40 50 60 70 80 90 0

500

1000

1500

2000

2500

3000

Time (min)

Heat Release Rate (kW)

Multiple Tray Test 24 Exp

Model
165

Figure 9-12. Comparison of predicted and measured HRR for Multiple Tray Tests 25-26. 

 

0 10 20 30 40 50 60 70 80 90 0

500

1000

1500

2000

2500

3000

Time (min)

Heat Release Rate (kW)

Multiple Tray Test 25 Exp

Model

0 10 20 30 40 50 60 70 80 90 0

500

1000

1500

2000

2500

3000

Time (min)

Heat Release Rate (kW)

Multiple Tray Test 26 Exp

Model
166

9.2.4 Discussion of Model Results 

The FLASH-CAT model captures general features of the experiments, including variations in 

tray width, loading and cable type. The model has no mechanism for distinguishing the vertical 

spacing. With a few exceptions, the model tends to over-predict the peak HRR and the total 

energy release (see Figure 9-13). This is a desirable feature in light of the fact that no 

information about a particular cable is required of the model user other than its bulk properties 

which can be measured easily with nothing more than a ruler and a scale. The other inputs to the 

model are characteristic values taken from sources like NUREG/CR-6850. 

Figure 9-13. Comparison of peak HRR and total energy release for FLASH-CAT. 

A key assumption in the FLASH-CAT model is that the fire will spread laterally until all of the 

cable is consumed. In many of the multiple tray experiments, this did not happen, and damage 

was confined to the initial V-shaped region above the ignition point. For this reason, the 

FLASH-CAT model in many cases over-predicts the HRR and the total consumption of cable. 

The lateral spread rates for thermoplastic and thermoset cables that are listed in NUREG/CR6850 are based on estimates of the thermo-physical properties of “typical” TP and TS cables. As 

can be seen in Figure 9-14, it is very difficult to predict from first principles if the fire is going to 

spread laterally at all, and if it does, at what rate. For example, during Multiple Tray Test 19, 

there was a slight breeze (on the order of 0.1 m/s) in the laboratory that caused the fire to spread 

to the left. The fire did not spread to the right beyond its initial V-pattern. The breeze was 

created by an asymmetric layout of air intake ducts, but nevertheless was strong enough to affect 

the progression of the fire. Rather than try to fine-tune the model, it has been decided to use the 

spread rates suggested in NUREG/CR-6850 because there is no evidence that these rates led to 

an under-prediction of the fire spread in any experiment. In addition, the breeze in the test lab is 

typical of air movement in any industrial facility, including NPPs. As with any model, such 

physical phenomena can be added, but this level of detail is unwarranted at this time given the 

Measured Peak HRR (kW)

0 1000 2000 3000

Predicted Peak HRR (kW)

0

1000

2000

3000

Measured Energy Release (GJ)

012345

Predicted Energy Release (GJ)

0

1

2

3

4

5
167

other uncertainties of the model. Future work will examine the effects of wind aided flame 

spread, and model refinements will then be considered. 

Figure 9-14. Photograph of MT-19 compared to the FLASH-CAT model prediction. 

The following notes apply to specific experiments: 

Test 4: In the experiment, the cables were packed tightly together within the trays. As a result, 

the fire did not spread upward as expected because the flames were not able to penetrate the 

densely packed cables. In fact, the technicians had to open up gaps in the cable through which 

the fire could spread upwards. An assumption of the model is that the fire will propagate 

upwards according to an empirical timing sequence (5-4-3-2-1 minutes). This implies that no 

barrier, including densely packed cables, inhibits the upward spread. 

Test 7 and 8: In these experiments, there was a similar loading of cables. However, in Test 7, 

the cables were thermoset and required more time to reach ignition temperature than the 

thermoplastic cables in Test 8. For this reason, the time to peak HRR is under-predicted for 

Test 7 and over-predicted for Test 8. 

Test 9: This experiment used a relatively light load of thermoplastic cable. The model assumes 

a relatively high HRRPUA and spread rate for this type of cable, but in the experiment the fire 

did not spread laterally. 

Test 14: In the experiment, the burner below the lowest tray was extinguished before the fire in 

the lowest tray had established itself. The burner was turned back on 30 min after the start of the 

test in order to give the fire a chance to spread to the top of the stack. There is no mechanism in 

the simple timing sequence of the model to account for the on-off-on operation of the burner. 

Test 21: In the experiment, the trays were separated by 18 in (0.45 m), and as a result, the fire 

did not spread beyond the second tray. The model always assumes that the fire will spread 

upwards, and as a result over-predicts the HRR of this test. 

 

169

10 CONCLUSIONS AND FUTURE WORK 

This report documents Phase 1 of the CHRISTIFIRE Project (Cable Heat Release, Ignition, and 

Spread in Tray Installations during FIRE). The goal of the project is to collect data to support 

the development of predictive fire models for nuclear power plant applications. The experiments 

performed during the first phase of the project have addressed horizontal, ladder-back trays filled 

with unshielded cables in open configurations. The results of the 26 full-scale experiments have 

been used to validate a simple model called FLASH-CAT (Flame Spread over Horizontal Cable 

Trays). FLASH-CAT is essentially a compendium of the guidance contained within Appendix R 

of NUREG/CR-6850, “Cable Fires.” The following sections summarize important findings of 

Phase 1. 

10.1 Heat Release Rate 

Measurements in both the Radiant Panel Apparatus and the Cone Calorimeter indicate that the 

heat release rate per unit area (HRRPUA) of a burning cable tray falls in a range from 

100 kW/m2 to 200 kW/m2 for thermoset cables, and from 200 kW/m2 to 300 kW/m2 for 

thermoplastics. These values are consistent with the recommended full-scale9 values in 

NUREG/CR-6850. For a given cable type, the HRRPUA varied due to the arrangement of the 

cables in the tray and due to the geometric configuration of the test apparatus. For this reason, it 

is recommended that for the purpose of simplified modeling, only two approximate values of the 

HRRPUA be applied – 150 kW/m2 for thermoset cables, 250 kW/m2 for thermoplastic cables, 

and a mass-weighted average for mixtures. This last assumption requires confirmation in future 

testing. These effective values of the HRRPUA in the FLASH-CAT model yielded predictions 

of the total HRR that were comparable or greater than the experimentally measured values. 

The duration of a cable fire depends on the amount of combustible material contained within 

each cable. NUREG/CR-6850, Appendix R, contains no guidance on the combustible mass or 

the duration of the fire. For all practical purposes, the combustible mass of a cable is the mass of 

all non-metallic components that are consumed by fire. For thermoplastic cables, it was 

observed that virtually all of the non-metallic components (jacket, insulators, filling) were 

consumed by fire. For thermosets, approximately 75 % of the non-metallic mass was consumed 

by fire, with char remaining as a residue. Thus, the char yield for thermoplastic cables is 0, and 

for thermosets it is 0.25. The duration of the fire is a function of the HRRPUA, mass per unit 

area, and the heat of combustion. A single effective heat of combustion of 16 MJ/kg provided 

reasonable results for all cable types in the FLASH-CAT model. Effective values of the char 

yield of 0.25 for thermosets and 0 for thermoplastics were used in the FLASH-CAT model. 

10.2 Ignition 

Cone calorimeter experiments were conducted with 12 different cables at specified heat fluxes of 

25 kW/m2, 50 kW/m2, and 75 kW/m2. In the 25 kW/m2 experiments, ignition was achieved but 

in many cases without sustained burning. Currently, Appendix H of NUREG/CR-6850 

 

9 NUREG/CR-6850, Appendix R, suggests that full-scale burning rates for cables be extrapolated from bench-scale 

measurements by multiplying the bench-scale values by a factor of 0.45. 
170

recommends that it is to be assumed that a sustained heat flux of 11 kW/m2 causes ignition (and 

electrical failure) of a thermoset cable and a heat flux of 6 kW/m2 causes ignition (and failure) of 

a thermoplastic cable. The cone calorimeter results suggest that the recommended ignition heat 

fluxes might be too low to cause ignition and sustained burning of a group of electrical cables. 

However, further testing is needed to determine a more appropriate critical heat flux for ignition 

and sustained burning. 

10.3 Spread 

Currently, NUREG/CR-6850, Appendix R, recommends horizontal flame spread rates of 

0.3 mm/s (1.1 m/h) for thermoset cables and 0.9 mm/s (3.2 m/h) for thermoplastic cables. 

However, in many of the multiple tray experiments the fire did not spread beyond the V-shaped 

region formed by the initial upward spread of the fire. For those experiments where the fire was 

observed to spread to the ends of the trays, video analysis yielded spread rates that were 

comparable to those currently recommended in NUREG/CR-6850. It is not possible to predict 

definitively from the results of the various bench-scale measurements whether or not a given 

cable configuration would be conducive to flame spread. For this reason, the recommended 

spread rates from NUREG/CR-6850 have been implemented in the FLASH-CAT model. Also, 

it was observed in a number of full-scale experiments that a slight breeze in the test lab (caused 

by asymmetric supply air ducts) resulted in asymmetric spread patterns. In short, a fairly light 

breeze was sufficient to support wind-aided flame spread. This suggests that it would be very 

difficult to predict a priori whether a given cable would support flame spread because of the 

sensitivity of the spread rate to external conditions. Future phases of this program will explore 

the effects of wind-aided flame spread. 

NUREG/CR-6850, Appendix R, recommends a timing sequence for the upward spread of the 

fire in a vertical array of horizontal cables. This sequence was implemented in the FLASH-CAT 

model. Comparisons with the full-scale experiments indicate that this timing sequence predicts 

reasonably well the vertical spread of the fire. However, in one experiment, the trays were 

separated10 by 0.45 m (18 in), in which case the fire did not spread beyond the lowest tray in the 

array. With a spacing of 0.38 m (15 in) the fire did spread beyond the first tray. These results 

suggest that the simple timing sequence for upward spread in NUREG/CR-6850 is limited to 

cases where the tray separation is less than approximately 0.45 m (18 in). However, more 

experiments are needed to support this conclusion. 

10.4 General Observations 

Reference documents like the SFPE Handbook of Fire Protection Engineering contain extensive 

lists of thermo-physical properties for a wide variety of commercially-available materials that 

can burn. NUREG/CR-6850, Appendix R, lists some of these properties for cables, usually in 

terms of the insulation and jacket materials. However, it was found in the present study that it is 

difficult to characterize properties solely in terms of the material type. For example, cables with 

XLPE insulation and neoprene jackets do not necessarily all burn with the same heat release rate 

 

10 Vertical tray separation is expressed in terms of the distance from the top of a given tray to the top of the tray 

above. 
171

per unit area. The cable diameter, copper content, type of additives, and number of conductors 

can be as important as the base polymers. In addition, the different measurement techniques 

produce significantly different results for cables, often as a result of the geometric configuration 

of the apparatus. Given the variability in cable construction and measurement technique, it does 

not benefit the overall modeling effort to compile an exhaustive “database” of properties for the 

hundreds of different cable types currently installed in NPPs. Simple models like FLASH-CAT 

do not warrant detailed estimates of cable properties because it uses empirically determined input 

parameters. Detailed models would typically require a given cable of interest to be specially 

tested and would not be able to make use of a generic list of material properties. For the purpose 

of estimating the burning rates of unshielded cables in horizontal tray configurations, it is 

sufficient to know the mass per unit length and combustible mass fraction. These parameters can 

all be easily obtained with common measuring devices, and a few tens of centimeters of cable 

sample. Parameters like the heat release rate per unit area (HRRPUA), char yield, and heat of 

combustion can be assumed based on representative values for thermoset and thermoplastic 

cables. 

10.5 Future Work 

Phase II of the CHRISTIFIRE program will investigate the burning behavior of cables within 

horizontal and vertical enclosures. The experiments conducted during Phase I only considered 

relatively open configurations of horizontal trays. Phase II will involve trays that are installed 

below a ceiling or within a vertical duct, in which case the heat from the burning cables can get 

trapped within the enclosure leading to an increased level of radiative heating that can potentially 

spread the fire more quickly. Beyond Phase II, the effect of barriers such as cable tray covers 

and fire retardant coatings will be considered. Future work is also planned to explore the 

treatment of mixtures of thermoset and thermoplastic cables within the same tray. 

 

173

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Chourio, G. (2007) Probabilistic Models to Estimate Fire-Induced Cable Damage in Nuclear 

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Anleitner (2006) Report of Experimental Results for the International Fire Model Benchmarking 

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model results with experimental data, VTT Working Papers 4, VTT Technical Research Centre 

of Finland, Espoo, Finland. 

Hunter, L.W. (1979) “Models of Horizontal Electric Cables and Cable Trays Exposed to a Fire 

Plume,” Combustion and Flame, 35:311-322. 

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ISO/TS 19700 (2007) Controlled equivalence ratio method for the determination of hazardous 

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Klamerus, L.J. (1977) A Preliminary Report on Fire Protection Research Program (July 6, 1977 

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Lyon, R. (2007) “Flammability Screening of Plastics Containing Flame Retardant Additives,” 

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176

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177 

APPENDIX A TESTING STANDARDS FOR CABLES 

This Appendix has been extracted from the letter report entitled, “Response to NRR FAQ 06-

0022, Guidance on Standards and Flame Propagation Tests,” June 21, 2007, prepared by Felix E. 

Gonzalez and Jason Dreisbach, US NRC RES Fire Research Branch (ADAMS Accession 

Number ML072050222). Its purpose was to provide a response to an FAQ (Frequently Asked 

Question) concerning flame propagation (spread) tests for electrical cables. The response 

evaluates current flame propagation tests compared to the IEEE 383-1974 standard. This 

standard had been previously referenced as the US NRC minimum test standard and acceptance 

criteria for cable flame propagation tests. 

Table A-1 provides a summary of various test methods designed to assess the fire performance 

of electrical cables. The follow-on discussion compares these methods with IEEE 383-1974. 

Tests with lower burner heat outputs than the IEEE 383-1974 standard are difficult to compare 

due to the difference in test sample size. These low heat exposure tests are discussed but are not 

directly compared to IEEE 383-1974. 

Note that a flame propagation test procedure in one standard could be included or referenced in 

another. This does not mean that the two standards are the same. Rather, it means that the 

standard uses the same testing procedure for flame propagation testing. A standard might have 

other sections that have nothing to do with flame propagation, like smoke and aging test 

procedures, materials of construction, or markings. For this reason, the data was organized in 

terms of flame tests instead of individual standards. 

Table A-1. Standard Fire Tests for Electrical Cables 

Title Number Standard Title 

FT-6 / Flame Travel Test (horizontal) 

NFPA 262 Standard Method of Test for Flame Travel and Smoke of Wires and 

Cables for Use in Air-Handling Spaces (2007 Ed) 

CSA 22.2 

No. 0.3 Test Methods for Electrical Wires and Cables (Jan 2005) 

Fire Test (Riser/vertical) UL 1666 

Test for Flame Propagation Height of electrical and Optical-Fiber 

Cables Installed Vertically in Shafts (4th Ed Nov 2000 Revisions thru Jul 

2002 ) 

FT-4 / Vertical Flame Test (vertical) 

UL 1581 Reference Standard for Electrical Wires, Cables, and Flexible Cords (4th

Ed Oct 2001 Revisions thru Aug 2006) 

UL 1685 Vertical-Tray Fire-Propagation and Smoke-Release Test for Electrical 

and Optical-Fiber Cables (2nd Ed Feb1997 Revisions thru Nov 2000) 

UL 83 Thermoplastic-Insulated Wires and Cables (13th Ed Nov 2003 Revisions 

thru Apr 2006) 

UL 44 Thermoset-Insulated Wires and Cables (16th Ed July2005 Revisions thru 

Nov 2005) 

CSA 22.2 

No. 0.3 Test Methods for Electrical Wires and Cables (Jan 2005) 

IEEE 1202-1991 IEEE Standard for Flame Testing of Cables for Use in Cable Tray in 

Industrial and Commercial Occupancies (1991) 

Flame test qualification (vertical) IEEE 383-2003 

IEEE Standard for Qualifying Class 1E Electric Cables and Field 

Splices for Nuclear Power Generating Stations 

(2003; Revision of IEEE 383-1974) 
178 

Title Number Standard Title 

Vertical Cable Tray Flame Test 

(vertical) ICEA T-29-520 Conducting Vertical Cable Tray Flame Tests with Theoretical Heat 

Input Rate of 210000 Btu/hr (Sep 1986) 

Vertical Flame Spread (vertical) 

IEC 60332-3-21 

Tests on Electric Cables Under Fire Conditions Parts 3-21 to 23: Test 

for Vertical Flame Spread of Vertically-Mounted Bunched Wires or 

Cables: Category A (F/R), A & B (Oct 2000) 

IEC 60332-3-22 

IEC 60332-3-23 

Vertical Tray Flame Test (vertical) 

UL 1581 Reference Standard for Electrical Wires, Cables, and Flexible Cords (4th

Ed Oct 2001 Revisions thru Aug 2006) 

UL 83 Thermoplastic-Insulated Wires and Cables (13th Ed Nov2003 Revisions 

thru Apr 2006) 

UL 44 Thermoset-Insulated Wires and Cables (16th Ed July2005 Revisions thru 

Nov2005) 

UL 1685 Vertical-Tray Fire-Propagation and Smoke-Release Test for Electrical 

and Optical-Fiber Cables (2nd Ed Feb 1997 Revisions thru Nov 2000) 

Vertical Cable Tray Flame Test 

(vertical) ICEA T-30-520 Guide for Conducting Vertical Cable Tray Flame Tests with Theoretical 

Heat Input of 70000 Btu/hr (Sep 1986) 

Flame test (vertical) IEEE 383-1974 IEEE Standard for Type Test of Class 1E Electric Cables, Field Splices, 

and Connections for Nuclear Power Generating Stations (1974) 

Flame test (vertical) IEEE 817-1993 IEEE Standard Test Procedure for Flame-Retardant Coatings Applied to 

Insulated Cables in Cable Trays (1993) 

Vertical Flame Spread (vertical) IEC 60332-3-24 

Tests on Electric Cables Under Fire Conditions Parts 3-21 to 23: Test 

for Vertical Flame Spread of Vertically-Mounted Bunched Wires or 

Cables: Category C (Oct 2000) 

Vertical Flame Propagation (vertical) IEC 60332-1-2 Test for vertical flame propagation for a single insulated wire or cable - 

Procedure for 1 kW pre-mixed flame (2004-07) 

Vertical Flame Propagation (vertical) IEC 60332-1-3 Test for vertical flame propagation for a single insulated wire or cable - 

Procedure for determination of flaming droplets/particles (2004-07) 

VW-1 Vertical Wire Flame Test 

(vertical) 

UL 1581 Reference Standard for Electrical Wires, Cables, and Flexible Cords (4th

Ed Oct 2001 Revisions thru Aug 2006) 

UL 83 Thermoplastic-Insulated Wires and Cables (13th Ed Nov 2003 Revisions 

thru Apr 2006) 

UL 44 Thermoset-Insulated Wires and Cables (16th Ed July 2005 Revisions 

thru Nov 2005) 

CSA 22.2 

No. 0.3 Test Methods for Electrical Wires and Cables (Jan 2005) 

FT-1 Vertical Flame Test (vertical) 

UL 1581 Reference Standard for Electrical Wires, Cables, and Flexible Cords (4th

Ed Oct 2001 Revisions thru Aug 2006) 

UL 83 Thermoplastic-Insulated Wires and Cables (13th Ed Nov 2003 Revisions 

thru Apr 2006) 

UL 44 Thermoset-Insulated Wires and Cables (16th Ed July 2005 Revisions 

thru Nov 2005) 

CSA 22.2 

No. 0.3 Test Methods for Electrical Wires and Cables (Jan 2005) 

Flame test (vertical) IPCEA S-61-402 Thermoplastic-Insulated Wire and Cable for the Transmission and 

Distribution of Electrical Energy (Oct 1994) 

FT-2 Horizontal Flame Test 

(horizontal) 

UL 1581 Reference Standard for Electrical Wires, Cables, and Flexible Cords (4th

Ed Oct 2001 Revisions thru Aug 2006) 

UL 83 Thermoplastic-Insulated Wires and Cables (13th Ed Nov 2003 Revisions 

thru Apr 2006) 

UL 44 Thermoset-Insulated Wires and Cables (16th Ed July2005 Revisions thru 

Nov 2005) 

CSA 22.2 

No. 0.3 Test Methods for Electrical Wires and Cables (Jan 2005) 
179 

Title Number Standard Title 

Standard Test Method for Flame 

Spread (vertical) ASTM D5537-03 

Standard Test Method for Heat Release, Flame Spread, Smoke 

Obscuration, and Mass Loss testing of Insulating Materials Contained in 

electrical or Optical Fiber Cables When Burning in a Vertical Cable 

Tray Configuration (Dec 2003) 

Fire Propagation Test FM 3972 Test Standard for Cable Fire Propagation (Mar 1994) 

Discussion 

IEEE 383-1974 is the baseline test with which the other tests will be compared. It is a 20 kW 

(70000 BTU/h) heat exposure, vertical test. As in all the 20 kW tests discussed below, it has a 

20 minute exposure time. This test requires cables to self-extinguish before reaching the top of 

the tray (8 ft or 2.4 m) to pass the test. 

One of the most severe flame tests is the FT-6 Horizontal Flame Test included in the NFPA 262 

and CSA C22.2 No. 0.3 standards. It is a horizontal flame test used for cables in plenum 

applications. This test uses a burner heat output of 86 kW (294000 BTU/h). This test has one of 

the lowest acceptable damage lengths, the second highest heat output, and uses a high air flow in 

its chamber during testing to increase flame spread. 

The UL 1666 Fire Riser Test is another of the more severe flame tests. It is a vertical test used 

for cables in riser shaft applications. It has the highest heat output of all the tests (154.5 kW), 

second highest exposure time (30 min) and high air flow in its chamber during testing. This test 

has an acceptable cable damage length of 12 ft (3.66 m). Even though the damage criteria is less 

severe than the IEEE 383-1974 (12 ft vs 10 ft), the higher exposed heat and time makes this test 

more severe. 

The FT-4/Vertical Flame Test, included in standards IEEE 1202-1991, CSA C22.2 No. 0.3, 

UL 1685, and referenced in UL 1581, UL 44, and UL 83, is the most rigorous of the 20 kW tests. 

The testing conditions and equipment in all of the 20 kW tests are essentially the same. What 

makes this test the most difficult to pass of the 20 kW tests is its low acceptable damage length 

of 4.9 ft (1.5 m). 

The ICEA T-29-520 standard is essentially the same as the 20 kW IEEE 383-1974 tests except 

with a burner heat output of 62 kW. The distance acceptance criterion is the same as IEEE 383-

1974. Cables passing this test meet or exceed the performance of IEEE 383-1974 tested cables, 

and could have similar cable performance to tests like the FT-4/Vertical Flame Test. 

The Vertical Flame Spread test (IEC 60332-3-21, IEC 60332-3-22 and IEC 60332-3-23) uses a 

20 kW burner. In these tests, the recommended acceptance length of damage is 10.2 ft (3.1 m) 

which is less rigorous than the 8 ft (2.44 m) of acceptable damage of the IEEE 383-1974 

standard, but the heat exposure time is 40 min, twice the time exposed in IEEE 383-1974. 

The Vertical Tray Flame Test (UL 1581, 1685, 83, and 44) and Vertical Cable Tray Flame Test 

(ICEA T-30-520) both use a 20 kW burner. These two tests are very similar to the IEEE 383-

1974. The three have the same acceptable damage length of 8 ft (2.44 m) and require cables to 
180 

self-extinguish before reaching the top of the tray. Also, the heat exposure time is 20 min. 

These tests have minor variations in procedure and equipment used. 

IEEE 817-1993 Flame Test is mainly used to determine whether cables need to be coated or not. 

It does not have pass/fail criteria. If cable damage reaches the top of the tray, the cable is 

recommended to be coated. 

The IEC 60332-3-24 standard is very similar to IEEE 383-1974 but has less strict acceptance 

criteria. This test has the same burner heat output and exposure time as IEEE 383-1974 but has 

an acceptable damage length of 10.2 ft (3.1 m) making the test less severe. 

Note that the IEC 60332-3-10 standard is the description of the apparatus used in the IEC 60332-

3-21, IEC 60332-3-22, IEC 60332-3-23, and IEC 60332-3-24 standards discussed above and not 

an actual test. 

Low Intensity Test Methods 

The tests discussed below have burner heat outputs equal or lower than 1 kW. It is not 

appropriate to compare these methods to IEEE 383-1974 due to the vast difference in test 

samples and burner heat outputs. These low heat exposure tests will be discussed for 

completeness, but will not be directly compared to the IEEE 383-1974 baseline standard. 

Vertical Flame Propagation Tests (IEC 60332-1-2 and IEC 60332-1-3) are both 1 kW burner 

tests. Both exposure times vary from 1 to 8 minutes, depending on the sample diameter. IEC 

60332-1-2 requires more than 50 mm (1.97 in) of distance between the lower edge of the top 

support and the onset of charring and less than 540 mm (21.26 in) from the lower edge to the top 

support. IEC 60332-1-3 requires that the filter paper used as indicator does not ignite during the 

test. 

The four 500 W tests are very similar in terms of heat exposure time and passing criteria. These 

tests are: the VW-1 Vertical Wire Flame Test (UL 1581 and CSA C22.2 No.0.3, and referenced 

in UL 83 and UL 44), the FT-1 Vertical Flame Test (UL 1581 and CSA 22.2 No.0.3 and 

referenced in UL83 and UL44), Flame Test (ICEA S-61-402), and the FT-2 Horizontal Flame 

Test (UL 1581 and CSA 22.2 No.0.3, and referenced in UL 83, and UL 44). The first three are 

vertical flame tests and have exposure times of 75 seconds total with different time intervals 

between heat applications. The three are very similar and require that samples do not burn more 

than 60 seconds or burn less than 25 % of the indicator and/or cotton batting. The FT-2 test is a 

horizontal test with a heat exposure time of 30 seconds and requires that the cable self-extinguish 

and that no flaming particles ignite cotton under specimen. 

The ASTM D5537-03 Standard Test Method for Flame Spread is used to determine the heat 

release rate by measuring gas concentrations and flow. It also measures Flame Propagation by 

blistering and char length. This test does not have any acceptance criteria. 
181 

The FM 3972 Test Standard for Cable Fire Propagation is used to calculate a Fire Propagation 

Index to classify cable fire propagation characteristics. In the test procedure, a pilot flame is 

used to ignite the cables. After that, the flame is extinguished and heaters are used until the cable 

self-extinguishes. Measurements of the combustion gas concentrations and flow, time, and heat 

release rate are used to calculate the Fire Propagation Index. This test does not have any 

acceptance criteria. 

NRC FORM 335

(12-2010)

NRCMD 3.7

U.S. NUCLEAR REGULATORY COMMISSION 1. REPORT NUMBER

(Assigned by NRC, Add Vol., Supp., Rev.,

and Addendum Numbers, If any.)

BIBLIOGRAPHIC DATA SHEET

(See instructions on the reverse) NUREG/CR-7010

Volume 1

2. TITLE AND SUBTITLE 3. DATE REPORT PUBLISHED

Cable Heat Release, Ignition, and Spread in Tray Installations during Fire (CHRISTIFIRE)

Phase 1: Horizontal Trays

5. AUTHOR(S)

Kevin McGrattan, Andrew Lock, Nathan Marsh, Marc Nyden, Scott Bareham, Michael Price,

Alexander Morgan, Mary Galaska, Kathy Schenck

MONTH

July

4. FIN OR GRANT NUMBER

N6549

6. TYPE OF REPORT

Technical

YEAR

2012

7. PERIOD COVERED (Inclusive Dates)

October 2008 - June 2010

8. PERFORMING ORGANIZATION • NAME AND ADDRESS (If NRC, provide Division, Office or Region,U. S. Nuclear Regulatory Commission, and mailing address; if

contractor, provide name and mailing address.)

National Institute of Standards and Technology

Engineering Laboratory

Fire Research Division

Gaithersburg, MD 20899

9. SPONSORING ORGANIZATION. NAME AND ADDRESS (If NRC, type "Same as above", if contractor, provide NRC Division, Office or Region, U. S. Nuclear Regulatory

Commission, and mailing address.)

Division of Risk Analysis

Office of Nuclear Regulatory Research

US Nuclear Regulatory Commission

Washington, DC 20555-0001

10. SUPPLEMENTARY NOTES

D. Stroup, NRC Project Manager

11. ABSTRACT (200 words or less)

This report documents the first phase of a multi-year NRC research initiative entitled CHRISTIFIRE (Cable Heat Release, Ignition,

and Spread in Tray Installations during FIRE). The overall goal of the program is to better understand and quantify the burning

characteristics of grouped electrical cables commonly found in nuclear power plants. The first phase of the program focuses on

horizontal tray configurations. The experiments conducted range from micro-scale, in which very small (5 mg) samples of cable

materials were burned in a calorimeter to determine their heat of combustion and other properties; to full-scale, in which horizontal

arrays of ladder-back trays loaded with varying amounts of cable were burned under a large oxygen-depletion calorimeter. Additional

experiments include cone calorimetry, smoke and effluent characterization in a small test furnace, and intermediate-scale calorimetry

involving a single tray of heated cables exposed to a bank of radiant panels. The results of the small-scale experiments will serve as

input data for fire models; while the results of the full-scale experiments will serve as validation data for the models.

12. KEY WORDS/DESCRIPTORS (List words or phrases that will assist researchers in locating the report.)

Fire Experiments

Cable Fires

NRC FORM 335 (12-2010)

13. AVAILABILITY STATEMENT

unlimited

14. SECURITY CLASSIFICATION

(This Page)

unclassified

(This Report)

unclassified

15. NUMBER OF PAGES

16. PRICE


UNITED STATES 

NUCLEAR REGULATORY COMMISSION

WASHINGTON, DC 20555-0001

--------------------

OFFICIAL BUSINESS
NUREG/CR-7010, Vol. 1 Cable Heat Release, Ignition, and Spread in Tray Installations During Fire 

(CHRISTIFIRE) Phase 1: Horizontal Trays