1. Sandia National Laboratories
Risk-Informed Separation
Distances for Hydrogen Fueling Stations
Jeffrey LaChance
Sandia National Laboratories
11/19/2018
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2. Outline Project Background Separation Distances
Risk-Informed Approach Description
Application to an Example Facility
Input Data and Assumptions for QRA Models
Preliminary Results
Conclusions
Future Work
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3. Project Background
Work performed under U.S. DOE Hydrogen, Fuel Cells & Infrastructure Technologies Program, Multi-Year Research, Development and Demonstration Plan
Hydrogen Safety, Codes & Standard R&D
Sandia National Laboratories is developing the scientific basis for assessing credible safety scenarios and providing the technical data for use in the development of codes and standards
Includes experimentation and modeling to understand behavior of hydrogen for different release scenarios
Use of Quantitative Risk Assessment (QRA) methods to help establish separation (setback, safety) distances at hydrogen facilities and to identify accident prevention and mitigation strategies for key risk drivers
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4. Separation Distances
Specified distances in codes separating H2 components from the public, structures, flammable material, and ignition sources
Distance vary with possible consequences from hydrogen releases (e.g., radiation heat fluxes or overpressures)
Distances influenced by facility design parameters (e.g., hydrogen pressure and volume), available safety features (e.g., isolation valves), and release parameters (e.g., leak size and location)
Separation distances based solely on the consequences of hydrogen leaks can be large!
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5. Example of Consequence-Based Separation Distances for a Jet Fire
Leak Diameter(mm)
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6. Separation Distances for Different Consequence Measures
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7. Risk-Informed Approach
Uses risk insights plus other considerations to help define code requirements
Risk = Frequency X
Consequence from all accidents
Requires hydrogen component leak frequencies
Requires definition of important consequences
Uses QRA and consequence models to evaluate risk
Requires definition of acceptable risk levels
Accounts for parameter and modeling uncertainty present in analysis
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8. Risk Approach for Establishing Separation Distances
Cumulative frequency of accidents requiring this separation distance
Cumulative frequency of accidents requiring this separation distance
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9. Use of Risk Eliminates Large Leaks from Consideration
Pipe Leak Frequency
Increasing Leak Diameter
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10. Application to Example Facility
Currently evaluating risk-informed separation distances for a representative fueling facility
To demonstrate risk methodology
To evaluate important facility features (e.g., gas volume and leak isolation features)
To determine importance of modeling parameters (e.g., data, geometry, temporal effects)
To identify key risk scenarios and identify possible ways to reduce the risk to acceptable levels
Work presented is focused on hydrogen jet releases from gas pipes and gas storage cylinders
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11. Example Facility Description
Facility can refuel 100 cars/day
All components located outside
Liquid hydrogen facility with no-onsite production
Liquid storage volume of Mpa
Cryo pump (11 L/min) used to provide pressurized liquid to vaporizer when pressure in gas storage decreases
Natural draft vaporizer
Gas storage was sized for 500 kg of hydrogen(12.63 m3 for psig facility)
Three separate cascades
Two refueling dispensers
Facility meets codes and standards
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12. Leakage Frequency Distributions
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13. Consequence Parameters and Risk Criteria Used in Current Analysis
Radiant Heat Flux from Jet Fires:
1.6 kW/m2 – no harm to individuals for long exposures
4.7 kW/m2 – injury (second degree burns) within 20 seconds
25 kW/m2 – 100% lethality within 1 minute; equipment and structural damage
Hydrogen Concentration from Un-ignited Releases:
4%, 6%, and 8% concentrations – lower flammability limit
Risk Criteria
Frequency of Fatality to Individual at Separation Distance Used as Upper Bound Accident Frequency Criteria
<2E-4/yr – fatality risk from all other high-risk hazards in society
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14. Gas Pipe Analysis Assumptions
Leakage can occur in 50 m of 13.5 mm diameter pipe, 4 valves, 2 instrument lines (4.23 mm D), and 3 flanges
Hydrogen leak or flame detector sends signal to isolation valve resulting in closure within 10s
Immediate ignition results in fatality at separation distance if not automatically detected and isolated (no credit for manual detection and isolation)
Delayed ignition of un-isolated gas jet results in flash fire
Fatality assumed out to distance corresponding to LFL (used to determine separation distance)
Pipe leak orientation was assumed directed at lot line resulting in maximum separation distances
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15. Gas Pipe Leak Event Tree
D-IGNITION
Delayed Ignition of
Hydrogen
ISOLATION
Automatic Isolation
of Pipe within 10s
DETECTION
Detection of
Hydrogen or Flame
I-IGNITION
Immediate Ignition
of Hydrogen Jet
PIPE_LEAK
Pipe Leak or
Rupture
Downstream of #
END-STATE-NAMES 1
JET-FIRE-(10-S) 2
JET-FIRE 3 4
GAS-RELEASE-(10-S) 5
FLASH-FIRE 6
GAS-RELEASE 7 8
pipe leak - (New Event Tree)
2007/01/27
Page 0
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16. Gas Pipe Results: Un-isolated Jet Fires
Mean frequency of any size un-isolated pipe leak < 1E-6/yr
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17. Gas Pipe Results: Isolated Jet fire
Exposure time to isolated jet fires is short which reduces potential for structural or equipment damage and personnel injury.
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18. Frequency of Fatality from Isolated Jet Fire (10 s exposure)
10 s exposure to 25 kw/m2 heat flux results in 20% probability of a fatality (reducing the exposure time to 5 s would further reduce the probability to 5%).
Operating Pressure
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19. Gas Pipe Results: Flash Fires
Delayed ignition assumed to result in flash fire and fatality out to LFL.
Hydrogen
Concentration
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20. Gas Storage Analysis Assumptions
For each storage cylinder, leakage can occur in 1 m of 4.23 mm diameter pipe and 1 valve attached to the cylinder, and from the cylinder itself. Leakage can also occur in manifold and 4 attached valves.
No protective barriers are installed around the gas storage area
No isolation of a gas storage leak from these components is possible
Gas storage is outdoors and thus there is little potential for a hydrogen detonation
Immediate ignition results in fatality at separation distance if not automatically detected and isolated (no credit for manual detection and isolation)
Delayed ignition of un-isolated gas jet results in flash fire
Fatality assumed out to distance corresponding to LFL (used to determine separation distance)
Leak orientation was assumed to result in worst consequences (sensitivity study performed)
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21. Gas Storage Leak Event Tree
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22. Gas Storage Results: Un-isolated Jet Fires
Risk-informed separation distances are affected by leakage contribution from different components.
Leakage from all components
Manifold and cylinder leaks
Heat Flux
Cylinder leaks
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23. Gas Storage Results: Flash Fires
Flash fires, not jet fires, require the longest separation distances (36 m for an LFL of 4% vs.18 m for 25 kw/m2 heat flux - 2E-4/yr fatality criteria).
Hydrogen
Concentration
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24. Gas Storage Sensitivity Study – Volume of Stored Gas
Limiting gas storage volume can lead to reduced risk-informed separation distances.
Mass of Gaseous Hydrogen
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25. Gas Storage Sensitivity Study – Size of Gas Cylinders
Increasing the gas cylinder size reduces the leakage frequency.
Cylinder Size
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26. Example Separation Distances: Lot Lines
Maximum Risk-Informed Separation Distances (m)
Pipe Leaks1
Gas Storage Leaks2
Criteria
5000 psig
10000 psig
15000 psig
2E-4/yr
13-26
16-32
19-36
5E-5/yr
17-30
22-44
24-49
1E-5/yr 9 13 15
29-59
38-76
44-87
5E-6/yr 12 17 20
40-72
40-82
46-92
Pipe separation distances are limited by isolated jet fires (25 Kw/m2).
Gas storage separation distances are limited by flash fires (8% - 4% H2 concentration).
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27. Conclusions from Example Pipe Analysis
Properly designed and installed hydrogen and flame detection and automatic isolation capability can reduce the risk from piping leaks
Frequency of un-isolated jet fire and flash fire scenarios can be small enough to justify short risk-informed separation distances.
Separation distances are limited by isolated jet fire scenarios.
Isolation capability at dispensers, vaporizers, and a facility with a compressor will likely result in similar results as above.
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28. Conclusions from Example Gas Storage Analysis
Gas storage leakage events are likely the dominant risk contributors for the example facility (accidents involving liquid hydrogen have not yet been evaluated)
Relatively short risk-informed separation distances (<20 m) could be justified for jet fires for a fatality risk criteria >1E-5/yr.
However, risk-informed separation distances are limited by flash fire scenarios (separation distances for high pressure facilities >40 m for a fatality risk criteria <1E-5/yr).
Reducing the gas storage volume or using larger volume cylinders can reduce the frequency of gas leaks and resulting risk-informed separation distances.
Risk-informed separation distances may still be too long for gas storage releases. Barriers surrounding the storage area may be required to reduce the risk to acceptable levels.
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29. Future Efforts
Continue evaluating safety distances for example facility
Liquid hydrogen storage leaks/ruptures
Evaluate alternate methods for pressurizing gas (cryo pump vs. compressor)
Dispensers
Evaluate facilities using different methods for onsite hydrogen production (gas reforming and electrolysis)
Improve methodology including consideration of time-dependent impacts, geometry factors, and incorporation of uncertainty
Get consensus on failure data for use in QRA (e.g., leak frequencies and component failure rates)
Identify range of models or data for accident phenomenology probabilities (e.g., ignition and detection probabilities)
Identify key risk drivers for hydrogen facilities and identify what can be done to reduce the risk and separation distances to acceptable levels
Extend evaluation to other types of hydrogen facilities
11/19/2018
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