DOT/FRA/ORD-24-11 Final Report | February 2024

Fire Performance of a Cryogenic ISO UN-T75 Storage 

Tank Using Analytical Methods and Fire Testing

Phase 2: Testing with LNG in an ISO Tank
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1. AGENCY USE ONLY (Leave blank) 2. REPORT DATE

October 24, 2023 

3. REPORT TYPE AND DATES COVERED

Final Report, 09/2016 to 08/2017 

4. TITLE AND SUBTITLE

Fire Performance of a Cryogenic ISO UN-T75 Storage Tank Using Analytical Methods and 

Fire Testing, Phase 2: Testing with LNG in ISO Tank

5. FUNDING NUMBERS

693JJ622C000003 

6. AUTHOR(S)

Jason Huczek – ORCiD: 0000-0002-2656-853X

Marc Janssens – ORCiD: 0000-0003-0088-4013

Kyle Fernandez – ORCiD: 0000-0003-2740-354X

Keith Friedman – ORCiD: 0000-0002-3133-4113

Garrett Mattos – ORCiD: 0000-0003-4682-7110

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)

Southwest Research Institute (SwRI) Freidman Research Corporation (FRC)

6220 Culebra Road, Bldg. 143 1508-B Ferguson Lane

San Antonio, TX 78238 Austin, TX 78754 

8. PERFORMING ORGANIZATION 

REPORT NUMBER

01.27392 

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES)

U.S. Department of Transportation 

Federal Railroad Administration

Office of Research and Development

Washington, DC 20590

10. SPONSORING/MONITORING

AGENCY REPORT NUMBER

DOT/FRA/ORD-24-11

11. SUPPLEMENTARY NOTES

COR: Francisco González, III

12a. DISTRIBUTION/AVAILABILITY STATEMENT

This document is available to the public through the FRA Web site at http://www.fra.dot.gov. 

12b. DISTRIBUTION CODE

13. ABSTRACT (Maximum 200 words)

FRA sponsored a study by Southwest Research Institute to conduct research and testing of a cryogenic storage tank in Liquefied 

Natural Gas (LNG) service and evaluate its thermal safety performance under fire conditions using analytical methods and fire 

testing. This report documents the second phase of this research. In Phase I, the team filled the test tank with liquid nitrogen (LN2) 

in place of LNG and the pressure relief system was evaluated and determined to work properly in the specified test conditions. 

Based on those results, researchers in Phase II essentially repeated the same test with the tank filled with LNG. The report 

provides additional detail of the test tank, the flatcar supporting the tank, the development of a safety plan, characterization of the 

fire exposure source, description of the instrumentation used in the experiment, test results, and detailed data analysis.

14. SUBJECT TERMS

Liquefied Natural Gas (LNG), Liquid Nitrogen (LN2), ISO UN-T75 Tank, Flatcar, Pressure Relief 

Valve/Device (PRV/PRD), Directional Flame Thermometer (DFT), Incident Heat Flux, Surface 

Temperature 

15. NUMBER OF PAGES

69 

16. PRICE CODE

17. SECURITY CLASSIFICATION

OF REPORT

Unclassified

18. SECURITY CLASSIFICATION

OF THIS PAGE

Unclassified

19. SECURITY CLASSIFICATION

OF ABSTRACT

Unclassified

20. LIMITATION OF ABSTRACT

Standard Form 298 (Rev. 8/98)

Prescribed by ANSI Std. Z39.18
ii

METRIC/ENGLISH CONVERSION FACTORS

ENGLISH TO METRIC METRIC TO ENGLISH

LENGTH (APPROXIMATE) LENGTH (APPROXIMATE) 

1 inch (in) = 2.5 centimeters (cm) 1 millimeter (mm) = 0.04 inch (in)

1 foot (ft) = 30 centimeters (cm) 1 centimeter (cm) = 0.4 inch (in)

1 yard (yd) = 0.9 meter (m) 1 meter (m) = 3.3 feet (ft)

1 mile (mi) = 1.6 kilometers (km) 1 meter (m) = 1.1 yards (yd)

1 kilometer (km) = 0.6 mile (mi)

AREA (APPROXIMATE) AREA (APPROXIMATE) 

1 square inch (sq in, in2) = 6.5 square centimeters (cm2) 1 square centimeter (cm2) = 0.16 square inch (sq in, in2) 

1 square foot (sq ft, ft2) = 0.09 square meter (m2) 1 square meter (m2) = 1.2 square yards (sq yd, yd2) 

1 square yard (sq yd, yd2) = 0.8 square meter (m2) 1 square kilometer (km2) = 0.4 square mile (sq mi, mi2) 

1 square mile (sq mi, mi2) = 2.6 square kilometers (km2) 10,000 square meters (m2) = 1 hectare (ha) = 2.5 acres

1 acre = 0.4 hectare (he) = 4,000 square meters (m2)

MASS - WEIGHT (APPROXIMATE) MASS - WEIGHT (APPROXIMATE) 

1 ounce (oz) = 28 grams (gm) 1 gram (gm) = 0.036 ounce (oz)

1 pound (lb) = 0.45 kilogram (kg) 1 kilogram (kg) = 2.2 pounds (lb)

1 short ton = 2,000 pounds 

(lb)

= 0.9 tonne (t) 1 tonne (t) =

=

1,000 kilograms (kg)

1.1 short tons

VOLUME (APPROXIMATE) VOLUME (APPROXIMATE) 

1 teaspoon (tsp) = 5 milliliters (ml) 1 milliliter (ml) = 0.03 fluid ounce (fl oz)

1 tablespoon (tbsp) = 15 milliliters (ml) 1 liter (l) = 2.1 pints (pt)

1 fluid ounce (fl oz) = 30 milliliters (ml) 1 liter (l) = 1.06 quarts (qt)

1 cup (c) = 0.24 liter (l) 1 liter (l) = 0.26 gallon (gal)

1 pint (pt) = 0.47 liter (l)

1 quart (qt) = 0.96 liter (l)

1 gallon (gal) = 3.8 liters (l)

1 cubic foot (cu ft, ft3) = 0.03 cubic meter (m3) 1 cubic meter (m3) = 36 cubic feet (cu ft, ft3)

1 cubic yard (cu yd, yd3) = 0.76 cubic meter (m3) 1 cubic meter (m3) = 1.3 cubic yards (cu yd, yd3)

TEMPERATURE (EXACT) TEMPERATURE (EXACT) 

[(x-32)(5/9)] °F = y °C [(9/5) y + 32] °C = x °F

QUICK INCH - CENTIMETER LENGTH CONVERSION

0 1 2 3 4 5

Inches

Centimeters 0 1 2 3 4 5 6 987 1110 1312

QUICK FAHRENHEIT - CELSIUS TEMPERATURE CONVERSIO

 -40° -22° -4° 14° 32° 50° 68° 86° 104° 122° 140° 158° 176° 194° 212°

 

°F

 °C -40° -30° -20° -10° 0° 10° 20° 30° 40° 50° 60° 70° 80° 90° 100°

For more exact and or other conversion factors, see NIST Miscellaneous Publication 286, Units of Weights and 

Measures. Price $2.50 SD Catalog No. C13 10286 Updated 6/17/98
iii

Acknowledgements

Southwest Research Institute and Freidman Research Corporation acknowledge Francisco 

González III and Phani Raj at the Federal Railroad Administration for their technical guidance 

throughout this project.
iv

Contents

Executive Summary ................................................................................................................... 1

1. Introduction .......................................................................................................................... 2

1.1 Background ..............................................................................................................2

1.2 Objectives................................................................................................................2

1.3 Overall Approach and Scope ....................................................................................2

1.4 Organization of the Report .......................................................................................2

2. Test Articles......................................................................................................................... 3

2.1 LNG ISO Test Tank .................................................................................................3

2.2 Flatcar for ISO Tank Installation ..............................................................................3

3. Safety Plan Development ..................................................................................................... 5

3.1 LNG vs LN2 in ISO Tank ........................................................................................5

3.2 BLEVE Considerations............................................................................................5

3.2.1 Potential for BLEVE ................................................................................................5

3.2.2 Energy Release Models............................................................................................6

3.2.3 Location of Staff During Phase 2 Test ......................................................................8

4. Characterization of Fire Exposure Source............................................................................. 9

4.1 Accident Scenario ....................................................................................................9

4.2 Burning Duration Calculations.................................................................................9

4.3 Fire Source Modifications........................................................................................9

4.4 Final Fire Source Conditions.................................................................................. 10

5. Test Instrumentation............................................................................................................12

5.1 Internal Instrumentation ......................................................................................... 14

5.2 External Instrumentation ........................................................................................ 16

5.2.1 Directional Flame Thermometer............................................................................. 16

5.2.2 Weld-Pad Surface Temperature Thermocouple Probe............................................. 16

5.2.3 Copper Disc Calorimeter........................................................................................ 17

5.2.4 General Instrumentation Layout Sketch.................................................................. 18

5.2.5 Drone Video Footage of Phase 2 Fire Test.............................................................. 20

6. Test Results.........................................................................................................................21

6.1 Selected Photographs ............................................................................................. 21

6.2 Video Observations................................................................................................ 23

6.3 Data Summary........................................................................................................ 24

7. Data Analysis Results..........................................................................................................30

7.1 Initial Test Conditions............................................................................................ 30

7.2 External Heating..................................................................................................... 33

7.3 Internal Temperature .............................................................................................. 34

7.4 Internal Pressure..................................................................................................... 37
v

7.5 PRV Response........................................................................................................ 40

7.6 Mass Loss and Fluid Heating.................................................................................. 41

7.7 PRV Jet Flame Response........................................................................................ 45

8. Summary and Conclusions..................................................................................................51

9. References...........................................................................................................................52

Appendix A. CVA ISO Storage Tank Drawings........................................................................53

Appendix B. Instrumentation Drawings.....................................................................................55
vi

Illustrations

Figure 1. ISO Tank Photograph Prior to Testing (left: View from West; right: View from 

Northeast)............................................................................................................................3

Figure 2. Flatcar Photographs (top: Flatcar Being Installed; bottom: Flatcar Trucks)...................4

Figure 3. BLEVE Conditions Illustrated on Methane Saturation Curve .......................................6

Figure 4. Sach’s Scaling: Scaled Overpressure vs. Scaled Distance for BLEVE Events...............7

Figure 5. Sach’s Scaling Summary Results..................................................................................8

Figure 6. Location of Staff Bunker (yellow box) During Phase 2 Test (left: 408 m from Bunker 

to Propane Tank; right: 404 m from Bunker to Test Article)................................................8

Figure 7. Structural Steel Pilons Installed to Support the Flatcar During the Test....................... 10

Figure 8. Phase 2 Propane Test Burner Schematic..................................................................... 11

Figure 9. Phase 2 Propane Test Burner Photographs.................................................................. 11

Figure 10. Arrangement of Interior Thermocouples (provided by CVA).................................... 14

Figure 11. Detail of Center Float as well as Shell Radial Floats (provided by CVA).................. 15

Figure 12. Detail of Penetration Location for Exit of Thermocouples (provided by CVA)......... 15

Figure 13. Detail of Additional Internal Thermocouples (provided by CVA)............................. 15

Figure 14. Directional Flame Thermometer............................................................................... 16

Figure 15. Weld-Pad Surface Temperature Thermocouple Probe............................................... 17

Figure 16. Copper Disc Calorimeter.......................................................................................... 17

Figure 17. External Instrumentation Sketch............................................................................... 18

Figure 18. Additional Weld-Pad Surface TCs Nominal Locations (Elevation View).................. 18

Figure 19. External Instrumentation Sketch (Nominal Distances to Cameras and Instrumentation)

.......................................................................................................................................... 19

Figure 20. Centerline Weld-Pad TCs (black squares) and DFT Locations (green squares) – 

Elevation View from the East and West............................................................................. 19

Figure 21. Fire Source DFT Locations (red squares) and Burner Pan Dimensions (Elevation 

View) ................................................................................................................................ 20

Figure 22. Drone Footage Still Shot of Test Tank and DAQ Location ....................................... 20

Figure 23. Selected Setup and Pre-Test Photographs................................................................. 22

Figure 24. Selected Testing Photographs................................................................................... 22

Figure 25. Selected Post-Test Photographs................................................................................ 23

Figure 26. Selected DFT Heat Flux Data................................................................................... 25

Figure 27. Incident Heat Flux to Downfield Targets Data.......................................................... 25

Figure 28. Internal Temperatures in Center of Tank .................................................................. 26
vii

Figure 29. Internal Temperatures at Ends of Tank ..................................................................... 26

Figure 30. Internal Tank Pressure and Level Data ..................................................................... 27

Figure 31. Annular Space Pressure and Pressure Relief Discharge Pressure............................... 27

Figure 32. Post-Test Internal Tank Temperature Data................................................................ 28

Figure 33. Post-Test Internal Tank and Level Pressure Data...................................................... 28

Figure 34. Post-Test Annular Space and Pressure Relief Piping Pressure Data .......................... 29

Figure 35. Pressure Gauge on Tank Indicating ~49 psig (337,843 Pa gage) 1 h Prior to Test ..... 31

Figure 36. Liquid-level Gauge on Tank Indicating ~25.9” H2O 1 H Prior to Test ...................... 31

Figure 37. Steady-state Internal Temperature Prior to Test ........................................................ 32

Figure 38. Vapor-space TCs; Tank-mounted (left), Float-mounted (right) ................................. 32

Figure 39. Incident Heat Flux to External Tank During Fire Test .............................................. 33

Figure 40. Incident Heating to External Tank During Fire Test.................................................. 33

Figure 41. Cumulative Incident Heating to External Tank During Fire Test............................... 34

Figure 42. Center Float Thermocouples: “T” Denotes Gas Phase Region & “B” Denotes Liquid 

Phase Region..................................................................................................................... 34

Figure 43. Radial Float Thermocouples: “SRF” Denotes Shell Radius & “HRF” Denotes Head 

Radius ............................................................................................................................... 35

Figure 44. Thermocouples in the “A” Section............................................................................ 35

Figure 45. Thermocouples in the “B” Section............................................................................ 36

Figure 46. Thermocouples in the “C” Section............................................................................ 36

Figure 47. Rate of LNG Temperature Change ........................................................................... 37

Figure 48. Internal Tank Pressure vs Time for the First 60 Minutes of the Test.......................... 37

Figure 49. Rate of Change of Internal Tank Pressure................................................................. 38

Figure 50. PRV Flame Comparison Prior to (left) and During (right) the Rapid Pressure Drop 

[~00:38:30] ....................................................................................................................... 38

Figure 51. Internal Tank Pressure vs Time [60-120 min]........................................................... 39

Figure 52. Progression of Piping Cabinet Door Failure over ~3 Min 50 s; Note the Increase in 

Fire Size as More of the Door is Melted [1:21:47 – 1:25:37] .............................................. 39

Figure 53. Internal Tank Pressure vs Time [120-360 min]......................................................... 40

Figure 54. Internal Tank Pressure vs Time [360 min- end] ........................................................ 40

Figure 55. Typical Post-Test Piping Cabinet Fire Behavior [04:23:33]...................................... 41

Figure 56. Cumulative Mass Loss vs. Time ............................................................................... 42

Figure 57. Heat Required to Vaporize Fluid to Account for the Vapor Exhausted from the PRV 

System .............................................................................................................................. 42
viii

Figure 58. Percent Liquid (by Volume) vs. Bulk Fluid Temperature at 7 Key Data Points......... 43

Figure 59. Percent Liquid (by Mass) vs. Bulk Fluid Temperature at 7 Key Data Points............. 43

Figure 60. Mixture Quality vs. Temperature at 7 Key Data Points............................................. 44

Figure 61. Pressure vs. Specific Volume for 5 Key Data Points [Methane; NIST] ..................... 44

Figure 62. Temperature vs. Specific Volume for 5 Key Data Points [Methane; NIST]............... 45

Figure 63. Jet Flame Geometry at Internal Tank Pressure of 114 psi (PRD setting) ................... 45

Figure 64. Jet Flame Geometry at Internal Tank Pressure of 125 psig........................................ 46

Figure 65. Jet Flame Geometry at Internal Tank Pressure of 150 psig........................................ 46

Figure 66. Jet Flame Geometry at Maximum Internal Tank Pressure (180 psig); Note how 

Horizontal the Jet is with Most of the Flame Off-Screen to the Left................................... 47

Figure 67. Jet Flame at Internal Tank Pressure of ~129 psig (view from drone) [~00:41:15]...... 47

Figure 68. Jet Flame at Internal Tank Pressure of ~156 psig [00:46:52]..................................... 48

Figure 69. Jet flame at Internal Tank Pressure of ~180 psig [00:56:00]...................................... 48

Figure 70. Frost on Deformed External Tank Jacket [1:07:24]................................................... 48

Figure 71. Trycock Valve Prior to Test...................................................................................... 49

Figure 72. Flames Observed at the Trycock Valve Location [~1:12:19]..................................... 49

Figure 73. View of Piping Cabinet Prior to (left) and Subsequent to (right) the Ignition of Leaked 

Gas [~1:12:20] .................................................................................................................. 50
ix

Tables

Table 1. Summary of Calculated Energy Source Levels for BLEVE............................................6

Table 2. Summary of Calculated Energy Source Levels for BLEVE............................................7

Table 3. DAQ 1 Test Instrumentation List.................................................................................12

Table 4. DAQ 2 Test Instrumentation List.................................................................................13

Table 5. Test Observations........................................................................................................23

Table 6. Initial Conditions.........................................................................................................30

Table 7. Fluid Properties at t=0 (Saturated Properties) [Data from NIST Chemistry WebBook 

Standard Reference Database (SRD) Number 69]..............................................................31

Table 8. General Summary of Installed Valves and their Working Temperature ........................39

Table 9. Estimated Mass Loss...................................................................................................41

Table 10. Summary of Heat Input to Fluid during 56 Min Fire Test...........................................42
1

Executive Summary

To realize potential reductions in Greenhouse Gas (GHG) emissions, fuel costs, and refueling 

times, the railroad industry is considering alternative fuels to diesel, including Liquefied Natural 

Gas (LNG) and Compressed Natural Gas (CNG). However, the safety performance of alternatefuel tank cars under derailment-induced fire conditions has not been verified. To address this, the 

Federal Railroad Administration (FRA) sponsored a study by Southwest Research Institute to 

conduct research and testing of a cryogenic storage tank in LNG service and evaluate its thermal 

safety performance under fire conditions using analytical methods and fire testing. 

This report documents the second phase of this research. In Phase I1

, the team filled the test tank 

with liquid nitrogen (LN2) in place of LNG and the pressure relief system was evaluated and 

determined to work properly in the specified test conditions. Based on those results, researchers 

in Phase II essentially repeated the same test with the tank filled with LNG. 

Two different tender design approaches are under consideration by the Association of American 

Railroads Natural Gas Fuel Technical Advisory Group: 1) a tank car-based design based on the 

DOT 113 specification tank car; and 2) two 40-ft International Organization for Standardization 

(ISO) LNG containers back to back on a flat car. The team conducted fire testing on the second 

of these designs, a portable tank filled with LNG, located on top of a flat rail car, and exposed to 

a propane pool fire. Researchers fire-tested the tank car and demonstrated the performance of the 

pressure relief valve system installed on the tank. The pressure relief valves (PRVs) opened and 

were able to relieve the pressure in the tank fast enough to avoid a Boiling Liquid Expanding 

Vapor Explosion (BLEVE) event. In addition, several types of data were collected during the 

experiment to understand how fire exposure affects the internal and external heating of the tank. 

The report provides additional detail of the test tank, the flatcar supporting the tank, the 

development of a safety plan, characterization of the fire exposure source, description of the 

instrumentation used in the experiment, test results, and detailed data analysis. This information 

may be used in future computer modeling efforts to predict performance with different tanks and 

fire scenarios.

1 FRA Report No. DOT/FRA/ORD-20/02
2

1. Introduction

The Federal Rail Administration (FRA) sponsored Southwest Research Institute (SwRI) to 

conduct research and evaluate the fire performance of a cryogenic storage tank filled with 

Liquefied Natural Gas (LNG) using analytical methods and fire testing. This second phase of 

testing was conducted in June 2022. 

1.1 Background

This report documents Phase 2 of the research study. In Phase I2

, the test tank was filed with 

liquid nitrogen (LN2) and the pressure relief system was evaluated and determined to work 

properly in the specified test conditions. Based on those results, the team essentially repeated the 

same test with the tank filled with LNG.

1.2 Objectives

The objective of this project was to conduct fire testing of an International Organization for 

Standardization (ISO) tank filled with LNG, located on top of a flat rail car, and exposed to a 

propane pool fire, and evaluate the pressure relief valve system.

1.3 Overall Approach and Scope

The team exposed a portable LNG tank for rail shipment to fire conditions and evaluated the 

performance of the pressure relief valve system. In addition, several types of data were collected 

during the experiment to understand how fire exposure affects the internal and external heating 

of the tank. 

1.4 Organization of the Report

The report provides additional detail of the test tank and the flatcar supporting the tank (Section 

2), development of a safety plan (Section 3), characterization of the fire exposure source and 

burning duration (Section 4), description of the instrumentation used in the experiment (Section 

5), test results (Section 6), preliminary modeling calculations (Section 7), and research 

conclusions (Section 8). 

2 FRA Report No. DOT/FRA/ORD-20/02
3

2. Test Articles

The team used two primary test articles for this project, an ISO UN-T75 storage tank and a flat 

car supporting the tank. The following subsections provide additional details about these test 

articles.

2.1 LNG ISO Test Tank

An ISO UN-T75 storage tank, outfitted for LNG service, was procured from Cryogenic Vessel 

Alternatives (CVA)3

. The tank’s model number is CVA-12K-114-ISO and it measures 40 ft 

long, 8.5 ft high, and 8 ft wide. Figure 1 provides selected photographs of the tank used in this 

experiment. Additional figures may be referenced in Appendix A of this report.

Figure 1. ISO Tank Photograph Prior to Testing (left: View from West; right: View from 

Northeast)

Team members positioned a small propane burner and steel mesh wall approximately 15 ft from 

the tank end to ensure ignition of the PRV exhaust, prevent flashback, and improve visibility of 

the flame during testing. 

On June 28, 2022, the test tank was filled with 9500 gallons of LNG by Airgas USA, LLC. This 

resulted in a starting fill level of nominally 78 percent. Additional details on the initial conditions 

of the LNG in the test tank are provided in Section 7 of this report.

2.2 Flatcar for ISO Tank Installation

Florida East Coast Railway (FECR) donated a flatcar for this project. This car consists of two 

connected cars. One of these cars was used for Phase I fire testing, and the second car was used

in this Phase 2 testing. Figure 2 shows a photograph of the flatcar and the trucks at the remote 

test site. 

3 CVA was acquired by Taylor Wharton during the project. 
4

 

Figure 2. Flatcar Photographs (top: Flatcar Being Installed; bottom: Flatcar Trucks)
5

3. Safety Plan Development

The team submitted a test plan that included technical details of the safety plan. The content of 

the plan for Phase 1 and Phase 2 was largely the same and was focused on designing the 

experiments to keep personnel safe. For Phase 1, the plan primarily centered on determining safe 

standoff distances for overpressure and exposure from the propane fires source, based on 

historical event data available at the time. The details of that analysis are not repeated in this 

report. 

For Phase 2, the plan primarily focused on the change from LN2 to LNG and how it could 

impact the safety of personnel at the site. The primary hazard of interest was the possibility of a 

Boiling Liquid Expanding Vapor Explosion (BLEVE) and the plan confirmed the safe standoff 

distance required in the event of a BLEVE during the test. Additional details are provided below. 

3.1 LNG vs LN2 in ISO Tank

Team member SwRI’s Fire Technology Department (FTD) performed a fire test of an LNG 

cryogenic tank filled with LN2 and secured on top of a flat car on May 11, 2017, at SwRI’s 

remote test site in Sabinal, Texas. Based on the successful performance of the pressure relief 

system in the first test, the team conducted testing with LNG at the same remote test site on June 

28, 2022. 

3.2 BLEVE Considerations

The FTD was supported by SwRI’s Mechanical Engineering Division to estimate the likelihood 

and consequences of a BLEVE event given the test parameters. 

The team determined that 1) a BLEVE event was considered unlikely provided the pressure 

relief valves (PRVs) on the portable tank operate as intended, but 2) in case the PRVs did not 

operate as intended, resulting in catastrophic tank failure, the personnel and data recording 

equipment at the test site should be located at a safe standoff distance (~450 m).

3.2.1 Potential for BLEVE

Total potential energy released during BLEVE event defines the degree of hazard. However, 

BLEVE theory states that instantaneous nucleation and volumetric boiling of liquid content 

requires the temperature of the multiphase mixture be at or above the superheat limit temperature 

(Tsl) [1, 2]. For BLEVE events that move from the saturation curve to ambient pressure directly, 

the total mechanical energy release is substantially reduced [3, 4]. Figure 3 shows the saturation 

curve for methane (CH4) as well as the superheat limit temperature as a function of temperature 

and pressure. The pressures noted relate to the nominal operating pressures observed in Phase 1 

testing and are labeled “SwRI Test Conditions.” The region of the graph contained within the 

red, blue, and black dotted lines are the critical conditions for a BLEVE.


8

Figure 5. Sach’s Scaling Summary Results

3.2.3 Location of Staff During Phase 2 Test

Based on the calculations above, the location of the staff bunker during testing was located 

approximately 400 m from the test article and LNG source for the exposure fire. Figure 6 show 

these nominal locations at the remote test site. In each figure, the yellow highlighted box 

represents where the data collection and witnessing observers were located during the test.

Figure 6. Location of Staff Bunker (yellow box) During Phase 2 Test (left: 408 m from 

Bunker to Propane Tank; right: 404 m from Bunker to Test Article)
9

4. Characterization of Fire Exposure Source 

The team considered a real accident scenario to determine the test duration. The following 

sections provide more detail about the assumed scenario, the calculated burning duration of the 

scenario (with safety factor) and the fire source to be used in the experiment for this duration.

4.1 Accident Scenario

The team considered an accident scenario in which a central ISO tank was exposed to an 18.3 × 

6.1-m (60 × 20 ft) LNG spill/fire by two adjacent ISO tanks. Each ISO tank had a capacity of 

approximately 37,854 liters (10,000 gallons) of LNG. Therefore, the time was calculated for 

75,708 liters (20,000 gallons) of LNG to evaporate (over a 20 s spill time) and burn (over the 

remainder of the calculated duration) based on literature values of published regression rates. 

This time was then used to calculate the required amount of liquid propane needed to provide 

exposure in testing. 

4.2 Burning Duration Calculations

FRA provided a summary reference [8] on the topic of LNG regression rates in a series of largescale experiments and recommended the rate to be used in this calculation.

The team sent a burning duration estimate [9] to FRA in December 2016 containing specific

calculations and a summary of the input parameters used along with the relevant references for 

each input parameter. A safety factor of 2 was applied to the estimate based on earlier 

discussions with FRA. The team concluded that the maximum test duration would be 

approximately 73 min. The amount of propane required was calculated based on an exposure 

area of 12.2 × 3.1-m (40 × 10-ft) (i.e., nominal footprint of ISO tank on flatcar) for a test 

duration of 73 min.

Researchers amended the burning duration estimate [9] to include the required amount of 

propane to achieve the 73 min burning duration. The estimates, based on literature burning rates 

for propane [10], showed the required amount of propane for the experiment was approximately 

30,283 liters (8000 gallons). 

4.3 Fire Source Modifications

In Phase 1, the test burner consisted of a steel pan with a network of piping drilled with outlet 

holes for the liquid propane discharge. This piping was submerged at the start of the test under a 

layer of water, which was used to allow the liquid propane to evenly diffuse and form a pool fire 

under the flatcar and test tank. 

Due to the intensity of the fire, it was not possible to maintain this water layer in the burner, and 

after approximately 60 min, the water was fully evaporated from the fire source. The water likely 

affected the heat transfer into the flatcar and test tank; since it was not possible to maintain the 

water layer, it is difficult to account for this in the data analysis. 

For this reason, the team decided not to use water as the diffusion medium for the Phase II test. 

Instead, the liquid propane was allowed to flow into the test pan and gravel/stones were used as 

the diffusion medium.
10

In addition to the change in diffusion medium, the burner area was made 1 m wider. This was 

based on analysis from Phase 1 to maximum the heat input into the test tank. 

Finally, additional structural supports were added under the flat car, within the fire burner. In 

Phase 1, the flatcar was observed to sag during the fire exposure, which can affect the heat 

transfer into the test article in a non-conservative way. For Phase 2, the team decided to provide 

additional support and delay or prevent the sagging of the flatcar during the test to maximize the 

heat input. Figure 7 shows a photograph of these additional supports.

Figure 7. Structural Steel Pilons Installed to Support the Flatcar During the Test

4.4 Final Fire Source Conditions

The fire source consisted of a 40 × 13-ft (i.e., nominal footprint of ISO tank on flatcar) LPG 

burner. A piping array was installed in the steel burner pan. The array comprised 8 branch lines 

and each branch line comprised 24 1/8-in. diameter holes. 

The piping array was installed in the burner pan with the holes pointed downward, which 

allowed the LPG to diffuse evenly through the gravel layer contained in the burner pan. LPG was 

fed to the burner array at the Northwest and Southeast corners from a 2-in. buried pipe. An LPG 

supply system comprising an 8000 gal LPG tank, pump loop, and flow meter was setup 

approximately 300 m away from the test area. 

An emergency stop button was routed to the control room to allow test personnel to safely stop 

the flow of LPG to the burner in case of an emergency. 

Figure 8 shows a schematic of the Phase 2 burner construction and Figure 9 shows two 

photographs of the burner under construction and at final installation.
11

Figure 8. Phase 2 Propane Test Burner Schematic

 

Figure 9. Phase 2 Propane Test Burner Photographs
12

5. Test Instrumentation

Researchers used several types of instrumentation in this experiment. A total of 24 internal 

temperature measurements were taken, in addition to internal tank pressure, annular space 

vacuum pressure (between the inner and outer tanks), and pressure relief device (PRD) line 

pressure. Externally, 18 thermocouples (TCs) were provided around the tank and fire source to 

characterize the convective power of the fire and measure boundary layer temperatures. These 

are referred to as weld pad TCs in the test plan and Table 3. 

An additional 18 TCs, referred to as directional flame thermometers (DFTs), were used to 

characterize the total heat flux from the fire and into the tank at several locations. Incident heat 

flux was measured at two targets (copper discs in Table 3) as well as blast pressure, in the event 

of a catastrophic failure. Finally, the liquid propane flow rate and the wind speed were measured. 

The test was also documented with high definition (HD) cameras from two stationary views and

consumer drone video footage from two alternating drone cameras.

The team used two data acquisition systems (DAQs). DAQ 1 was used to collect the data from 

instruments closer to the test article. DAQ 2 was used to collect the data related to the LPG 

burner supply as well as the ambient temperature. Table 3 and Table 4 provide lists of the 

instrumentation and channel assignments used for each DAQ.

Table 3. DAQ 1 Test Instrumentation List

Channel No. Description* DAQ ID

1 Center Float – Top – Large Probe CF-T-LP

2 Center Float – Top – Medium Probe CF-T-MP

3 Center Float – Top – Small Probe CF-T-SP

4 Center Float – Bottom – Large Probe CF-B-LP

5 Center Float – Bottom – Medium Probe CF-B-MP

6 Center Float – Bottom – Small Probe CF-B-SP

7 Shell Radial Float 1 SRF-1

8 Shell Radial Float 2 SRF-2

9 Head Radial Float 1 HRF-1

10 Head Radial Float 2 HRF-2

11 Zone A – Thermocouple 1 A-TC1

12 Zone A – Thermocouple 2 A-TC2

13 Zone A – Thermocouple 3 A-TC3

14 Zone A – Thermocouple 4 A-TC4

15 Zone B – Thermocouple 1 B-TC1

16 Zone B – Thermocouple 2 B-TC2

17 Zone B – Thermocouple 3 B-TC3

18 Zone B – Thermocouple 4 B-TC4

19 Zone B – Thermocouple 5 B-TC5

20 Zone B – Thermocouple 6 B-TC6

21 Zone C – Thermocouple 1 C-TC1

23 Zone C – Thermocouple 2 C-TC2

24 Zone C – Thermocouple 3 C-TC3

25 Zone C – Thermocouple 4 C-TC4

27 Weld Pad - West side of tank – North end of tank – center temp WP-W-N-C

28 Weld Pad - West side of tank – Center of tank – center temp WP-W-C-C

29 Weld Pad - West side of tank – South end of tank – center temp WP-W-S-C

32 Weld Pad - East side of tank – North end of tank – center temp WP-E-N-C
13

Channel No. Description* DAQ ID

33 Weld Pad - East side of tank – Center of tank – center temp WP-E-C-C

34 Weld Pad - East side of tank – South end of tank – center temp WP-E-S-C

35 West Tank Side – North differential flame thermometer – fire WTS-N-DFT-F

36 West Tank Side – North differential flame thermometer – tank WTS-N-DFT-T

37 West Tank Side – center differential flame thermometer – fire WTS-C-DFT-F

38 West Tank Side – center differential flame thermometer – tank WTS-C-DFT-T

39 West Tank Side – South differential flame thermometer – fire WTS-S-DFT-F

40 West Tank Side – South differential flame thermometer – tank WTS-S-DFT-T

41 East Tank Side – South differential flame thermometer – fire ETS-S-DFT-F

42 East Tank Side – South differential flame thermometer – tank ETS-S-DFT-T

43 East Tank Side – center differential flame thermometer – fire ETS-C-DFT-F

44 East Tank Side – center differential flame thermometer – tank ETS-C-DFT-T

45 East Tank Side – North differential flame thermometer – fire ETS-N-DFT-F

46 East Tank Side – North differential flame thermometer - tank ETS-N-DFT-T

47 North – fire source differential flame thermometer – fire N-FS-DFT-F

48 North – fire source differential flame thermometer – tank N-FS-DFT-T

49 North – fire source gas temperature N-FS-GT

50 Center – fire source differential flame thermometer – fire C-FS-DFT-F

51 Center – fire source differential flame thermometer – tank C-FS-DFT-T

52 Center – fire source gas temperature C-FS-GT

53 South – fire source differential flame thermometer – fire S-FS-DFT-F

54 South – fire source differential flame thermometer – tank S-FS-DFT-T

55 South – fire source gas temperature S-FS-GT

56 Copper disc for incident heat flux – 75 ft. North – Bead CD-N-B

57 Copper disc for incident heat flux – 75 ft. North – Disc CD-N-D

58 Copper disc for incident heat flux – 75 ft. West – Bead CD-W-B

59 Copper disc for incident heat flux –75 ft. West– Disc CD-W-D

60 Weld Pad - West side of tank – North end of tank – top temp WP-W-N-T

61 Weld Pad - West side of tank – North end of tank – bottom temp WP-W-N-B

62 Weld Pad - West side of tank – Center of tank – top temp WP-W-C-T

63 Weld Pad - West side of tank – Center of tank – bottom temp WP-W-C-B

64 Weld Pad - West side of tank – South end of tank – top temp WP-W-S-T

65 Weld Pad - West side of tank – South end of tank – bottom temp WP-W-S-B

66 Weld Pad - East side of tank – North end of tank – top temp WP-E-N-T

67 Weld Pad - East side of tank – North end of tank – bottom temp WP-E-N-B

68 Weld Pad - East side of tank – Center of tank – top temp WP-E-C-T

69 Weld Pad - East side of tank – Center of tank – bottom temp WP-E-C-B

70 Weld Pad - East side of tank – South end of tank – top temp WP-E-S-T

71 Weld Pad - East side of tank – South end of tank – bottom temp WP-E-S-B

72 Pressure relief valve discharge pressure PRV-P

73 Internal Tank Pressure IT-P

*Non-fire source DFTs – Back = Tank Side; Front = Fire Side; Fire Source DFTs – Back = Tank Side; Front = Fire Side; Copper Discs – 

Front = Exposed Copper Disc, Back = Internal TC

Table 4. DAQ 2 Test Instrumentation List

Channel No. Description DAQ ID

1 LPG Flow Rate LPG-F

2 Liquid propane discharge pressure (FT 0-200 PSI) LPG-P

3 LPG Density LPG-D

4 LPG Temperature LPG-T

5 Ambient Air Temperature AMB-T
14

5.1 Internal Instrumentation

The internal instrumentation configuration represented the largest change in the Phase 2 test 

setup. In Phase 1, the internal data was lost after approximately 40 minutes because the internal 

TCs were overheated in a short section of piping that was difficult to adequately protect with 

insulation. 

Several design changes were made for Phase 2 to avoid this problem. First, the TC type was 

changed from Type T to Type K. Type T is more accurate at cryogenic temperatures but is less 

resistant to higher temperatures as the test tank is heated and the system temperatures increase. In 

addition, the TC insulation and sheathing were changed to perform better at elevated 

temperatures.

Internal instrumentation included the gas/liquid/surface temperatures measured inside the test 

tank, as well as the internal tank pressure, annular space tank pressure and LNG liquid level. The 

team worked with CVA and one of their vendors, Conax Technologies, to accommodate internal 

temperature measurements. 

In Phase 1, the pass-through connectors were in the piping cabinet, which was a challenging area 

to protect, leading to TC failure due to fire exposure. For the Phase 2 test, CVA provided access 

for the routing of the interior TCs through the top middle part of the tank, which was a much 

better area to protect those connections from fire exposure.

Figure 10 and Figure 11 show the arrangement of interior instrumentation as discussed above. 

Figure 11 provides a detail for the center and radial floats. Figure 12 provides a detail of the exit 

position for the TCs. Figure 13 provides detail for additional internal TCs. These figures are also 

provided in Appendix B. 

Figure 10. Arrangement of Interior Thermocouples (provided by CVA)
15

Figure 11. Detail of Center Float as well as Shell Radial Floats (provided by CVA)

Figure 12. Detail of Penetration Location for Exit of Thermocouples (provided by CVA)

Figure 13. Detail of Additional Internal Thermocouples (provided by CVA)
16

In addition, researchers worked with CVA to measure the inner tank pressure, annular space (i.e., 

vacuum) pressure, and liquid level (the team ordered a separate meter from CVA to estimate the 

liquid level). Also, a second vacuum pressure port was added to the top of the tank where the 

internal TCs are routed out of the tank because it is an easier section of the tank to protect with 

insulation in a fire test.

5.2 External Instrumentation

The external instrumentation included TCs used to characterize the fire source intensity, the heat 

flux at the exterior of the test tank, and incident heat flux downrange to targets.

In addition to the thermal instrumentation described above, video and photographs were archived 

for review. A selected group of photographs are included in this report. 

5.2.1 Directional Flame Thermometer 

The DFT was originally developed for measuring temperatures and heat fluxes in pool fires [11]. 

The DFT is conceptually like the plate thermometer but consists of two 3-mm thick, 120 × 120-

mm Inconel plates with a 25-mm thick ceramic fiber blanket in between (see Figure 14). The 

blanket is compressed to 19-mm thickness. A 1.6-mm diameter sheathed Type K TC with 

insulated junction is in a groove on the inside of each plate.

An advantage of the DFT over the plate thermometer is that the heat transfer through a DFT can 

be calculated with an inverse heat transfer code such as IHCP1D [12]. The use of these devices 

in fire experiments has been standardized recently in ASTM E3057 [13]. 

Figure 14. Directional Flame Thermometer

5.2.2 Weld-Pad Surface Temperature Thermocouple Probe

The Weld-Pad Surface Temperature Thermocouple Probe is designed for use in industrial 

applications to measure surface temperature by way of weld, braze, or clamp attachment. The 

pad is flexible to form to the contour of a flat or curved surface. The pad material is 304 stainless 

steel and measures 1.0 × 1.0 × 0.01 in. (25-mm × 25-mm × 0.25 mm) and the TC is Type K. 

Figure 15 shows a photograph of one of the weld-pad TCs. 
17

Figure 15. Weld-Pad Surface Temperature Thermocouple Probe

5.2.3 Copper Disc Calorimeter

Incident heat flux downrange was calculated from the response of a custom designed copper disk 

calorimeter. The sensor comprises a thin copper disc, approximately 0.3-mm (12 mil) thick and 

13-mm (1/2-in.) diameter. The chromel and alumel wires of a 24 AWG type K TC are silver 

soldered to the back side of the disc. The TC wires are then pulled through small holes and taped 

to the backside of a 13-mm (1/2-in.) thick, 100 × 100 mm (4 × 4-in.) piece of ceramic fiber board 

(Unifrax Duraboard LD), so that the copper disc is in contact with the exposed surface of the 

ceramic fiberboard (see Figure 16). The exposed side of the copper disc and ceramic fiberboard 

are coated with a thin layer of black, heat-resistant paint with a known emissivity/absorptivity of 

0.9 (Thurmalox® Solar Collector Coating, 250 Selective Black). 

Figure 16. Copper Disc Calorimeter

The ceramic fiber board is backed by a 13-mm (1/2-in.) thick calcium silicate substrate, which is 

backed by a 25-mm (1-in.) thick layer of ceramic fiber blanket. All these materials are housed in 

a small metal enclosure measuring 100 × 100 × 50 mm deep (4 × 4 × 2 in. deep). The housing 

and additional substrates are not pictured.
18

5.2.4 General Instrumentation Layout Sketch

Figure 17 provides a plan view general layout of the external instrumentation at the remote site. 

Figure 18 provides a sketch of the additional weld-pad TCs that were added to obtain additional 

model validation data. Note that the fire source differential flame thermometers depicted in red 

were located between the fire source and underside of the flatcar. The differential flame 

thermometers depicted in green were located approximately 2 in. from the outer tank wall at the 

same nominal location as the weld-pad TCs and internal TCs at the same baffle position. 

Figure 17. External Instrumentation Sketch

Figure 18. Additional Weld-Pad Surface TCs Nominal Locations (Elevation View)

Figure 19 provides a similar plan view with distances to cameras and instrumentation. Figure 20

and Figure 21 provide elevation view details of the location of weld-pad TCs and DFTs. The 

additional Weld-Pad TCs that are shown schematically in Figure 18 were installed approximately 

17 in. below and 24 in. above the centerline positions shown in Figure 20. These dimensions are 

not shown on Figure 20 for clarity of viewing.

ISO Outer Tank Outline

Fire Source Outline
19

Figure 19. External Instrumentation Sketch (Nominal Distances to Cameras and 

Instrumentation)

Figure 20. Centerline Weld-Pad TCs (black squares) and DFT Locations (green squares) – 

Elevation View from the East and West
20

Figure 21. Fire Source DFT Locations (red squares) and Burner Pan Dimensions 

(Elevation View)

5.2.5 Drone Video Footage of Phase 2 Fire Test

The team opted to incorporate drone video footage into Phase 2. The team used multiple drones 

and battery packs so that a second drone could be deployed immediately after the return of the 

first drone to ensure more continuous footage. After the drone returned to base, the battery was 

replaced, memory card checked for available space, and the drone prepared to re-deploy when 

necessary. Figure 22 shows a still shot from one of the drones during checkout tests of the test 

tank installed at the remote test location. 

Figure 22. Drone Footage Still Shot of Test Tank and DAQ Location
21

6. Test Results

The team worked with SwRI’s Fire Technology Department to perform a fire test of an LNG 

cryogenic tank secured on top of a flat car on June 28, 2022, at SwRI’s remote test site in 

Sabinal, Texas. 

The tank was exposed to the external LPG fire source for approximately 56 min. Table 5

summarizes the test observations. Figure 26 – Figure 31 provide the data from the test for the 

first 3.5 h. Selected post-test data is provided in Figure 32 – Figure 34. 

The tank safely vented its contents and did not rupture, so no blast pressure data was collected or 

included in the instrumentation list. 

The following sections provide selected photographs of the setup, testing, and post-test 

conditions, a summary of the video observations, a summary of the test data, and post-test 

observations and recommendations.

6.1 Selected Photographs

Figure 23 – Figure 25 show the test setup and pre- and post-test condition of the tank. 

 

 LPG Supply Tank, Pump and Bypass PG Flow Meter

 

 Container Control Room ISO Tank (east side) 

 

 ISO Tank (west side) ISO Tank (north side) 
22

 

ISO Tank (South Side) Instrumentation Trailer (NW of ISO Tank)

 

 Valve Cabinet Valve Cabinet

Figure 23. Selected Setup and Pre-Test Photographs

 

 Test in Progress (view from east side) Test in Progress (view from west side) 

 

 Test in Progress (PRV operating) Test in Progress (PRV operating) 

Figure 24. Selected Testing Photographs
23

 

Post-Test: ISO Tank (east side) Post-Test: ISO Tank (west side) 

 

Post-Test: ISO Tank (north side) Post-Test: Close-Up of Valve Cabinet

Figure 25. Selected Post-Test Photographs

6.2 Video Observations

Table 5 summarizes the observations recorded during the test. The data acquisition system was 

started approximately 21 min and 50 s prior to burner ignition based on when the PRD actuation 

synchronized with the video.

Table 5. Test Observations

Time

(h:min:s) Observations

-15:00:00 Tank is filled with LNG

00:00:00 Ignition of propane burner under flatcar (7:34 am on June 29, 2022)

00:02:40 Vacuum pressure increased to 200 mTorr (initially at ~35 mTorr)

00:04:00 Vacuum pressure increased to 1100 mTorr (maximum of meter range) and stayed at this value for 

duration of test

00:06:30 Noticeable deformation beginning on east side of tank external jacket

00:23:40 Internal tank pressure increased to 75 psig (initially at ~45 psig)

00:29:12 Internal tank pressure increased to 100 psig

00:32:00 Internal tank pressure increased to 114 psig (PRD setting) 

00:32:22 Activation of PRD and ignition of LNG jet flame ~1 s later

00:32:45 PRD reset (closed); jet flame extinguished
24

Time

(h:min:s) Observations

00:33:19 PRD open; jet flame ignited

00:33:43 PRD reset; jet flame extinguished

00:34:03 PRD open; jet flame ignited

00:48:16 

The liquid propane source was shut off due to the internal tank pressure (160 psig) rising fast to a 

value that was deemed detrimental to the structural integrity of the internal tank. The internal 

pressure peaked at ~180 psig, before starting to decrease after fire exposure terminated.

00:53:30 Burner flames reduced to roughly 50% their nominal size

00:54:30 Burner flames reduced to roughly 10% of their nominal size

00:56:10 Residual propane exposure fire self-extinguished after consuming all the remaining propane in the 

supply line and burner pan

00:56:30 Frost visible on external tank (east side)

01:12:19 First indication of flames within the piping cabinet/tank end

01:25:00 Fire engulfs entire piping cabinet end

01:30:00 – 

03:30:00 

Continued venting of test article, including substantial fire in piping cabinet leading to likely 

failure of mechanical fitting connections and possibly affecting internal tank pressure 

measurement

03:30:00 Data file stopped and new file started within a few seconds to begin logging post-test data of 

internal temperatures and pressure (10:44 am on June 29, 2022)

09:57:00 Internal tank pressure decreased to 6-8 psig, data file stopped, and another file started to collect 

data overnight (3:11 p.m. on June 29, 2022)

26:00:00 Approximately 9:30 am on June 30, 2022 – internal tank pressure decreased to ~3-6 psig and 

cabinet fire size visually decreased compared to previous day

32:30:00 Approximately 4 pm on June 30, 2022 – internal tank pressure decreased to ~1-4 psig, cabinet fire 

still burning, but intensity continuing to decrease

Post-test

Internal tank temperatures and pressure continued to be monitored intermittently until fire burned 

out after approximately 48 h. After cabinet fire was out and tank had cooled to nominal ambient 

conditions, the tank was purged with nitrogen before arrangements were made to transport the 

tank back to SwRI’s main campus and complete the cleanup activities offsite. 

6.3 Data Summary

Figure 26 provides a summary of the temperature and heat flux data from the DFTs centrally 

located on each side of the tank and over the fire source. Figure 27 shows the incident heat flux 

data, as determined from the copper disc calorimeters. Figure 28 and Figure 29 show the internal 

tank temperatures in the center and the ends of the tank for the first few hours of the test. Figure 

30 shows the internal pressure and level data in the tank over the first few hours of the test and 

Figure 31 shows the annular space pressure and pressure relief pipe pressure for the early part of 

the test. Figure 32 - Figure 34 show selected data over the extended post-test duration. 

As seen in Figure 26, the fire exposure to the tank was not uniform likely due to wind conditions. 

This resulted in a more severe exposure on the east side of the tank compared to the west side. 

The peak incident heat flux to the east side of the tank was 225.2 kW/m2 and the peak incident 

heat flux to the west side of the tank was 32.1 kW/m2. The peak incident heat flux from the fire 

source to the bottom of the flatcar was 105.7 kW/m2

. 
25

Temperature Graph Heat Flux Graph

Center – East – DFT

Center – West – DFT

Center – Fire Source – DFT

Figure 26. Selected DFT Heat Flux Data

Temperature Graph Heat Flux Graph

North Copper Disc Calorimeter

West Copper Disc Calorimeter

Figure 27. Incident Heat Flux to Downfield Targets Data
26

Figure 27 shows the incident heat flux to targets 23 m away in the north and west directions. The 

peak incident heat flux to these targets was relatively low; the peak in the north direction was 

2.68 kW/m2 and the peak in the west direction was 1.27 kW/m2

. It was likely higher in the north 

direction for a longer duration due to the continued burning in the valve cabinet area after the fire 

exposure was terminated. Unfortunately, no similar measurement was taken on the east side of 

the tank, which would have likely been the highest radiative heat flux due to the non-uniform 

exposure on the tank from the fire source due to the ambient wind conditions.

Figure 28 and Figure 29 show that the internal temperatures throughout the tank changed 

relatively consistently over the duration of the fire exposure. The internal temperature increased 

from approximately -215 °C to -165 °C. 

Figure 28. Internal Temperatures in Center of Tank

Figure 29. Internal Temperatures at Ends of Tank
27

Figure 30. Internal Tank Pressure and Level Data

Figure 30 shows the internal tank pressure increase from 345 kPa (50 psig) to 1.24 MPa (180 

psig) over the fire exposure duration. The tank liquid level was also measured during the test and 

reflected by the IT-L series in Figure 30. Unfortunately, after approximately 110 min, this signal 

was unreliable, likely due to overheating. 

The pressure relief valves (PRVs) seemed to operate at the correct nominal pressure. As seen in 

Figure 31, the first large increase on the PRV-P channel occurred at an internal tank pressure of 

approximately 807 kPa (117 psig), which coincides with the stated set pressure of 793 kPa (115 

psig). From this point in the test, the PRVs continued to open and close as necessary based on the 

internal pressure. Figure 31 also shows the annular space pressure between the inner and outer 

tank. Based on this data as well as the fast internal tank pressure rise during the fire exposure, it 

is likely the vacuum in the annular space was lost within a few minutes of fire exposure.

Figure 31. Annular Space Pressure and Pressure Relief Discharge Pressure
28

In Figure 32 - Figure 34, selected post-test data are presented to show how the temperatures 

stabilized as the tank burned off its contents. In Figure 34, it can be seen how half of the 

temperatures increase more rapidly since they are located above the liquid level and how the 

other half are only starting to increase after approximately 30 h. 

Figure 32. Post-Test Internal Tank Temperature Data

Figure 33. Post-Test Internal Tank and Level Pressure Data
29

Figure 34. Post-Test Annular Space and Pressure Relief Piping Pressure Data

31

Figure 35. Pressure Gauge on Tank Indicating ~49 psig (337,843 Pa gage) 1 h Prior to Test

Figure 36. Liquid-level Gauge on Tank Indicating ~25.9” H2O 1 H Prior to Test

The fluid properties at t=0 were estimated based on the measured data provided in Table 6 with 

the assumption that the fluid was at steady state and fully saturated. These data are summarized 

in Table 7. 

Table 7. Fluid Properties at t=0 (Saturated Properties) [Data from NIST Chemistry 

WebBook Standard Reference Database (SRD) Number 69] 

Property Liquid Gas/Vapor

Temperature (K) 136.7 145.7

Pressure (MPa) – absolute 0.53835 0.85139

Density (kg/m3) 382.7 13.381

Cp 3.7551 2.7626

Cv 1.9558 1.7470

Sound Speed (m/s) 1074.7 286.3
32

Figure 37 shows that the average start-of-test temperature recorded by the 11 TCs submerged in 

the fluid was 136.7 K (minimum = 135.6 K, maximum = 137.7 K). For the seven TCs exposed to 

the vapor space but attached to a float, the average start-of-test temperature was 136.7 K 

(minimum = 136.0 K, maximum = 137.5 K). For the six TCs exposed to the vapor space but 

attached to the internal tank, the average start-of-test temperature was 145.7 K (minimum = 

144.5 K, maximum = 147.2 K). The difference in the vapor temperatures is most likely due to 

the different mounting surfaces used (i.e., floats vs tab welded to internal tank wall). Figure 38

shows closeup views of each type of TC mounting. 

The float-mounted vapor-space TCs were designed to sit 6.5 to 14 in. above the surface of the 

liquid. At the start of the test the tank-mounted vapor-space thermocouples were located 50-127 

mm (2-5 in.) above the surface of the liquid (at 74-78 percent fill). 

Figure 37. Steady-state Internal Temperature Prior to Test

Figure 38. Vapor-space TCs; Tank-mounted (left), Float-mounted (right)
33

7.2 External Heating

Incident heat flux to the external tank was measured via six DFTs evenly spaced along the 

approximate centerline of the tank (three on each side) and three DFTs under the railcar. 

The data from these DFTs (Figure 39), supplemented by Fire Dynamics Simulator (FDS) 

models, were used to predict the total heat load to the external tank during the fire test and

calibrate an FDS model. The resulting FDS data (i.e., incident heat flux) was used to create a 

higher resolution map of heat flux onto the tank that was summed over the total external area of 

the tank. 

Figure 39. Incident Heat Flux to External Tank During Fire Test

Heating was asymmetrical due to wind activity with the East side of the tank subjected to much 

greater heat flux than the West side of the tank. 

Based on the data and FDS simulations the total incident heat applied to the external tank 

progressively increased throughout the test and was calculated to peak at 3900 kW at 37.2 min 

and at 3885 kW at 44.7 min as shown in Figure 40. 

Figure 40. Incident Heating to External Tank During Fire Test
34

The average incident heat during the last 10 minutes of active propane flow (t=38 min to t=48 

min) was 3497 kW, while the average heating for the proceeding 10 min was 10 percent lower at 

3129 kW. The cumulative heat applied to the tank (Figure 41) was calculated to be 7.35 GJ 

during the 48 min of full propane flow and 8.29 GJ during the 56 min of the fire test.

Figure 41. Cumulative Incident Heating to External Tank During Fire Test

7.3 Internal Temperature

The internal tank temperatures were recorded with numerous TCs located within the nominal 

liquid and vapor space. The data recorded by these sensors are provided in Figure 42 through 

Figure 46. 

Figure 42. Center Float Thermocouples: “T” Denotes Gas Phase Region & “B” Denotes 

Liquid Phase Region
35

Figure 43. Radial Float Thermocouples: “SRF” Denotes Shell Radius & “HRF” Denotes 

Head Radius

Figure 44. Thermocouples in the “A” Section
36

Figure 45. Thermocouples in the “B” Section

Figure 46. Thermocouples in the “C” Section

The total change in temperature over the duration of the fire test was approximately 29 deg K 

with a maximum liquid temperature of 165.7 K. The temperature began to rise roughly 8 min 

into the fire test. The vapor space temperature, as indicated by the center float, increased more 

rapidly than the liquid from t=12 min through to propane shutoff at which point the temperatures 

converged. 
37

Some anomalies in the recordings are apparent in the data, possibly due to exposure of the TC 

wires to the extreme heat. In aggregate, the temperature data demonstrated a consistent 

temperature rise throughout the test. 

The rate of temperature change of the LNG increased throughout the test until it peaked at 1.7 

deg K per minute at t=42.8 min, roughly the same time the tank heat flux peaked (Figure 47). 

After peaking, the rate of temperature change decreased, trending to zero at roughly t=58 min. 

Figure 47. Rate of LNG Temperature Change

7.4 Internal Pressure

The internal tank pressure rose steadily after burner ignition and continued to rise until the 

burner was extinguished (Figure 48). The maximum pressure reached during the test was 1.24 

MPa (180.3 psig) at t=55 min. Three PRD activation events occurred during the fire portion of 

the test at 00:32:20, 00:33:19, and 00:34:03 and can be clearly seen in the time history curve in 

Figure 48. 

Figure 48. Internal Tank Pressure vs Time for the First 60 Minutes of the Test
38

Figure 49 shows the rate of change of the internal tank pressure.The pressure began to increase 

approximately 7 min into the test at an average rate of 2 psi/min. The maximum rate of pressure 

increase (5.6 psi/min) occurred just prior to initial PRD activation (~00:32:20). Rapid decreases 

in pressure (-10 to -25 psi/min) occurred simultaneously with each of the three PRD activations. 

After re-seating, rapid increases in pressure (15 to 20 psi/min) occurred briefly before returning 

to nominal rates (~3.6 psi/min). The rapid but un-sustained rate of pressure loss during the initial 

15-20 s of PRD activation is possibly related to inertial effects of the fluid within the pressure 

sensor tube moving due to the transient opening event. 

Figure 49. Rate of Change of Internal Tank Pressure

During periods of continuous PRD activation with maximum fire engulfment (00:34:03 – 

00:48:16), the rate of pressure change varied from 3.2 psi/min to a maximum of 5.2 psi/min with 

an average rate of 3.6 psi/min. The maximum rate of internal tank pressure changes over this 

period (5.2 psi/min) occurred 3 min prior to propane supply shutoff (00:45:20). Just prior to 

propane shutoff the pressure in the internal tank was increasing at a rate of 4.6 psi/min. 

A rapid decrease in pressure from 00:38:30-00:38:45 (~15 second duration) occurred at the same 

time and for the same duration that the PRD jet flame was observed to significantly increase in 

size (Figure 50). The cause of this response is unknown but may be due to the opening and reclosing of the second PRV.

 

Figure 50. PRV Flame Comparison Prior to (left) and During (right) the Rapid Pressure 

Drop [~00:38:30]
39

A substantial pressure drop was noticeable approximately 87 min into the test (Figure 51). This 

occurred shortly after the piping end cabinet became fully engulfed in flames following the 

failure of the aluminum service panel (Figure 52). 

Figure 51. Internal Tank Pressure vs Time [60-120 min]

Figure 52. Progression of Piping Cabinet Door Failure over ~3 Min 50 s; Note the Increase 

in Fire Size as More of the Door is Melted [1:21:47 – 1:25:37] 

It is likely that the packing material within the globe, ball, and needle valves in that area suffered 

thermal failures and allowed natural gas to leak out and catch fire. These valves and their 

maximum working temperatures are summarized in Table 8 for reference. The drop in pressure 

is most likely due to the increase in gas leakage out of the tank through the failed service valves. 

Table 8. General Summary of Installed Valves and their Working Temperature

Description Maximum working 

temperature (C [F])

Herose, 1⁄2”-2” Globe, SS Body, Bronze Top Work 120 [248]

Fire Block, 1”-2”, Ball, SS 180-200 [356-395]

Generant, 1⁄2”, High Pressure Relief Valve 121-232 [250-450]

Hy-Lok, 1⁄4” Needle, SV-NV, SS 315 [600]
40

For the remainder of the post-test events, the tank pressure continued to decrease without any 

substantial rate change or noticeable events (see Figure 53 and Figure 54). 

Figure 53. Internal Tank Pressure vs Time [120-360 min]

Figure 54. Internal Tank Pressure vs Time [360 min- end]

7.5 PRV Response

PRV actuation was confirmed through video (i.e., static and drone cameras) in combination with 

audio captured in the video recordings and supported by simultaneous transient pressure 

readings. The PRV pressure sensor, which was mounted in the exhaust pipe downstream of the 

PRVs, did not produce any usable data. The response appeared very different from that collected 

in the previous test with LN2. 

The PRV system activated three separate times during the fire portion of the test. The PRV 

exhaust was ignited within approximately 1 s of opening each time. Each opening event can be 
41

seen in the pressure vs time plot in Figure 48. It is unknown whether one or both valves were 

open during these activation events. 

The PRV system actively released fluid into the atmosphere for 1374 s (22 min and 54 s) during 

the fire portion of the test. The PRV system continued releasing fluid from the PRV for the 

duration (6 h) of the video footage.

The size of the PRV exhaust cloud and flame decreased significantly, but did not stop, after 

90 min. This is coincident with the internal tank pressure dropping below the required PRV 

closing pressure (102.6 psig). One or both PRVs were most likely thermally damaged and unable 

to fully seal by this point even though the internal pressure had dropped below their designed 

closing pressure. The PRV exhaust and piping cabinet valve leaks continued to burn for the 

duration of the video (6 h) with behavior like that shown in Figure 55. 

Figure 55. Typical Post-Test Piping Cabinet Fire Behavior [04:23:33]

7.6 Mass Loss and Fluid Heating

The total mass lost during the test was estimated based on calculated nominal PRV pressuredependent flow rates. The flow rates are provided by the manufacturer for air but were calculated 

specifically for methane using the orifice equation method. 

The estimated mass loss for the fire-portion and post-fire periods of the test are summarized in 

Table 9. The cumulative mass loss versus time for the fire-portion of the test is provided in 

Figure 56. 

Table 9. Estimated Mass Loss

Duration Single PRV Both PRVs

22 min 54 s (fire-portion; up to burner extinguish) 684 kg (1508 lb) 1368 kg (3016 lb)

~36-48 h (post-fire; remaining fluid) 13078 kg (28832 lb) 12394 kg (27324 lb)
42

Figure 56. Cumulative Mass Loss vs. Time

The amount of heat absorbed by the fluid during the fire test can be estimated by summing the 

energy required to 1) increase the temperature of the fluid (liquid and vapor) during the test (i.e., 

Sensible heat), and 2) vaporize enough liquid to account for the mass of vapor exhausted from 

the PRV system (i.e., Latent heat). High and low estimates of heating requirements were 

calculated based on whether a single PRV or both PRVs were active. The relief valve calculation 

code (CGA S-1.2-2009, Section 5.3) assumes that PRV performance is additive (i.e., the exhaust 

capacity for 2 PRVs is twice the capacity for 1 PRV). However, the response of multiple PRVs is 

likely to be dependent on their actual installation. 

Table 9 shows a summary of the heat input to fluid during the fire test. The amount of heat 

energy required to raise the temperature of the fluid during the test was calculated using the 

temperature-dependent heat capacities of methane (liquid and vapor) along with the timedependent remaining fluid mass and time-dependent temperature change. The incremental heat 

required was calculated at 1 s intervals. The fluid was assumed to heat evenly due to convective 

mixing. 

Table 10. Summary of Heat Input to Fluid during 56 Min Fire Test

Single PRV Double PRV

Sensible heat (GJ) 0.693 1.386

Latent heat – Exhaust (GJ) 0.261 0.522

Total heat (GJ) 0.954 1.908

Figure 57. Heat Required to Vaporize Fluid to Account for the Vapor Exhausted from the 

PRV System
43

As the bulk fluid was heated throughout the test, the saturated liquid density decreased, causing 

it to take up more volume. The increase in liquid volume during the test can be seen in Figure 58. 

Depending on the amount of mass exhausted from the system (one or two PRV flow), the 

relative mass of liquid may increase or decrease (Figure 59). 

Figure 58. Percent Liquid (by Volume) vs. Bulk Fluid Temperature at 7 Key Data Points

Figure 59. Percent Liquid (by Mass) vs. Bulk Fluid Temperature at 7 Key Data Points

As heat was added to the closed system (up to first PRV activation) the mixture quality increased 

as the vapor density rapidly rose (Figure 60). Assuming single PRV flow, the mixture quality 

changed little during the ~23 min of PRV activation. Assuming double PRV flow, the mixture 

quality increased rapidly, indicating that the mixture was moving away from Saturated Liquid 

conditions. 
44

Figure 60. Mixture Quality vs. Temperature at 7 Key Data Points

Five key data points for the bulk fluid condition are plotted on the Pressure-Volume and 

Temperature-Volume curves for methane in Figure 61 and Figure 62. All points lie within the 

Vapor-Dome which confirms the presence of a two-phase mixture consisting of mostly Saturated 

Liquid. 

The specific volume of the mixture remains constant in a closed volume (prior to PRV 

activation) with heating while pressure and temperature increase. After PRV activation, the 

pressure and temperature continued to increase along with increases in the specific volume of the

mixture. This is consistent with a decrease in the percent liquid (by mass) of the system.

Figure 61. Pressure vs. Specific Volume for 5 Key Data Points [Methane; NIST]
45

Figure 62. Temperature vs. Specific Volume for 5 Key Data Points [Methane; NIST]

7.7 PRV Jet Flame Response

The PRV exhaust ignited within 1 s of the valve opening. A mesh screen was positioned 

approximately 2 meters downstream of the exhaust to mitigate the chance of flashback. The 

screen also improved visualization of the flame and provided some obstruction to its motion. The 

“northwest” views in Figure 63, Figure 64, Figure 65, and Figure 66 show the difference in 

flame size based on the internal tank pressure. Greater tank pressure is clearly associated with 

greater PRV jet flame length in this scenario. Similar behavior can be observed from the dronecaptured images in Figure 67, Figure 68, Figure 69. 

Figure 63. Jet Flame Geometry at Internal Tank Pressure of 114 psi (PRD setting)
46

Figure 64. Jet Flame Geometry at Internal Tank Pressure of 125 psig

Figure 65. Jet Flame Geometry at Internal Tank Pressure of 150 psig
47

Figure 66. Jet Flame Geometry at Maximum Internal Tank Pressure (180 psig); Note how 

Horizontal the Jet is with Most of the Flame Off-Screen to the Left

Figure 67. Jet Flame at Internal Tank Pressure of ~129 psig (view from drone) [~00:41:15]
48

Figure 68. Jet Flame at Internal Tank Pressure of ~156 psig [00:46:52]

Figure 69. Jet flame at Internal Tank Pressure of ~180 psig [00:56:00]

Figure 70. Frost on Deformed External Tank Jacket [1:07:24]
49

 

Figure 71. Trycock Valve Prior to Test

Figure 72. Flames Observed at the Trycock Valve Location [~1:12:19]
50

 

Figure 73. View of Piping Cabinet Prior to (left) and Subsequent to (right) the Ignition of 

Leaked Gas [~1:12:20]
51

8. Summary and Conclusions

In this Phase 2 research conducted in June of 2022, an ISO Tank filled with LNG was exposed to 

an LPG fire for approximately 56 min, after which the LNG continued to burn through the PRV

and leakages in the piping cabinet for an additional 48 h. There was no BLEVE or other 

catastrophic failure observed during the test. 

Based on the internal pressure rise and vacuum pressure measurement, the vacuum likely 

degraded relatively quickly into the fire exposure. The pressure inside the inner tank increased to 

a peak of approximately 180 psig. The PRV system worked properly, and the pressure valves 

began operating at approximately 114 psig. The valves intermittently reseated (at least partially)

and reopened before fully opening for the majority of the test duration.

There was additional venting after the fire exposure stopped; this continued for more than two 

days. The pressure in the tank was at atmospheric level by the morning of July 1, 2022.

While one or more PRVs appeared to open at the specified set pressure and remain open for the 

duration of the test, the internal tank pressure and temperature continued to rise. While under full 

heat exposure from the pool fire the internal tank pressure rose at an average rate of 3.6 psi/min 

and up to 4.6 psi/min just before propane shutoff. If this trend were to continue the internal tank 

would reach 288 psi in another 30 min and 396 psi in another 60 min of fire exposure. 

The pressure rise is, of course, related to the ability of the PRVs to remove mass from the 

internal tank. While the mass flow rates through the PRVs at elevated pressure in the 

configuration installed on the UN-T75 is not known, it is estimated that at the end of the fire test 

(180 psi) the flow through the PRV(s) was effectively choked. Thus, mass flow through the 

PRVs would not increase substantially with increasing tank pressure and the average pressure 

rise assumption is likely appropriate. 

Future work could investigate the performance of the PRVs at elevated pressure and in their 

configurations as installed on the UN-T75. 
52

9. References

1. Casal et al. (2001). Modeling and Understanding BLEVEs. Handbook of Hazardous 

Material Spills Technology, Chapter 22. 

2. Casal, J. & Salla, J. M. (2006). Using liquid superheating energy for a quick estimation of 

overpressure in BLEVEs and similar explosions. Journal of Hazardous Materials. 

3. Ke, W. (2009). CO2 BLEVE (Boiling Liquid Expanding Vapor Explosion). Masters Thesis.

4. Prugh, R. W. (1991). Quantify BLEVE Hazards. Chemical Engineering Progress. 

5. Birk, A.M., Davison, C., & Cunnigham, M. (2007). Blast over-pressure from medium scale 

BLEVE tests. J Loss Prev Process Ind, 20, 194–206. 

6. Genova, B., Silvestrini, M., & Trujillo, F.J. (2008). Evaluation of the blast wave overpressure 

and fragment initial velocity for a BLEVE event via empirical correlations derived by a 

simplified model of released energy. J Loss Prev Process Ind, 21, 110–117. 

7. Baker, et. al. (2005). CPR 14E Yellow Book.

8. Raj, P. (2007). LNG fires: A review of experimental results, models and hazard prediction 

challenges. Journal of Hazardous Materials, 140, 444–464. 

9. Huczek, J. (2016). Burning Duration Estimates.xlsx. Federal Railroad Administration. 

10. Hurley, M., et.al. (2016). SFPE Handbook of Fire Protection Engineering, 5th Edition, 

Chapter 26: Heat Release Rates. Society of Fire Protection Engineers, 863-867. 

11. Keltner, N., Nash, L., Beitel, J., Parker, A., Welsh, S., & Gilda, B. (2001). Fire Safety Test 

Furnace Characterization Unit. Thermal Measurements: The Foundation of Fire Standards, 

ASTM STP 1427. Dallas, TX. 128-146. 

12. Beck, J. (1999). User's Manual for IHCP1D, a Program for Calculating Surface Heat Fluxes 

from Transient Temperatures Inside Solids. Beck Engineering Consultants Co., Okemos, MI.

13. ASTM E3057-16: Measuring Heat Flux Using Directional Flame Thermometers with 

Advanced Data Analysis Techniques. ASTM International, West Conshohocken, PA.
53

Appendix A.

CVA ISO Storage Tank Drawings

Figure A-1. General Arrangement (Left Side) of CVA ISO Storage Tank

Figure A-2. General Arrangement (Right Side) of CVA ISO Storage Tank
54

Figure A-3. General Arrangement (Front and Rear Sides) of CVA ISO Storage Tank

Figure A-4. Piping Arrangement of CVA ISO Storage Tank
55

Appendix B.

Instrumentation Drawings

Figure B-1. Overall Arrangement of Thermocouples in Inner Tank (provided by CVA)

Figure B-2. ISO Tank Showing Details for Central Floats and Top Outlet Connection for 

Wires (provided by CVA)
56

Figure B-3. ISO Tank Showing Additional Details for Radial Floats at the End of the Tank

(provided by CVA)

Figure B-4. ISO Tank Showing Additional Details for Thermocouples Installed on Shell of 

Inner Tank (provided by CVA)
57

Figure B-5. Additional Detailed Drawing of Central Float Design (provided by CVA)

Figure B-6. Additional Detailed Drawing of Radial Float Design (provided by CVA)
58

Abbreviations and Acronyms

AAR Association of American Railroads

BLEVE Boiling Liquid Expanding Vapor Explosion

CFD Computational Fluid Dynamics

CNG Compressed Natural Gas

CVA Cryogenic Vessel Alternatives, Inc.

DAQ Data Acquisition System

DFT Directional flame thermometer

DOT Department of Transportation

FDS Fire Dynamics Simulator

FE Finite Element

FECR Florida East Coast Railway

FRA Federal Railroad Administration

FRC Freidman Research Corporation

FTD Fire Technology Department 

GHG Greenhouse Gas

HRRPUA heat release rate per unit area

ISO International Organization for Standardization

LN2 Liquid Nitrogen

LNG Liquefied Natural gas

LPG Liquefied Petroleum Gas

OSHA Occupational Safety and Health Administration

PRV Pressure Relief Valve

SwRI Southwest Research Institute

TAG Technical advisory group

TC Thermocouple