Quantitative Risk Assessment Safety Studies and Risk Mitigation

  • Slides: 49
Download presentation
Quantitative Risk Assessment, Safety Studies and Risk Mitigation Jeffrey La. Chance Sandia National Laboratories

Quantitative Risk Assessment, Safety Studies and Risk Mitigation Jeffrey La. Chance Sandia National Laboratories Presented at the 2 nd International Conference on Hydrogen Safety San Sebastian, Spain 12 September 2007 3/11/2021 Preliminary Data

Outline • • 3/11/2021 Role of QRA in Hydrogen Safety Applications of QRA Risk-Informed

Outline • • 3/11/2021 Role of QRA in Hydrogen Safety Applications of QRA Risk-Informed Codes and Standards Separation Distances Application to an Example Facility Input Data and Assumptions for QRA Models Results Summary Preliminary Data

Project Background • Work performed under U. S. DOE Hydrogen, Fuel Cells & Infrastructure

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 3/11/2021 Preliminary Data

Hydrogen Safety • Public perception of hydrogen safety has been skewed by major incidents

Hydrogen Safety • Public perception of hydrogen safety has been skewed by major incidents such as the Hindenburg accident • In reality, the use of hydrogen has an excellent safety record • The expanded use of hydrogen will include new challenges (e. g. , very high pressures) that will require design features and operational requirements to manage the risk to acceptable levels Risk assessment (both qualitative and quantitative) provides a means to demonstrate hydrogen safety ! 3/11/2021 Preliminary Data

The Role of Risk Assessment • Various levels of risk assessment can be utilized

The Role of Risk Assessment • Various levels of risk assessment can be utilized to assess the risk associated with a hydrogen facility: – Qualitative methods such as Failure Modes Effects Analysis are typically used to identify hazards and specify accident prevention and mitigation features – Semi-Quantitative methods such as risk matrices can identify risk-significant accidents Quantitative Risk Assessment (QRA) evaluates the facility risk and provides much more! 3/11/2021 Preliminary Data

Quantitative Risk Assessment • QRA is a systematic process for evaluating the risk associated

Quantitative Risk Assessment • QRA is a systematic process for evaluating the risk associated with a facility for: – Verification that it meets an accepted risk criteria – Identification of important accidents, components, operations contributing to risk – Identification and evaluation of risk reduction and control measures – Identification of risk management requirements (e. g. , maintenance intervals) 3/11/2021 Preliminary Data

Applications of QRA • Primary application is to determine that a facility is safe!

Applications of QRA • Primary application is to determine that a facility is safe! – Can be performed for evaluating early prototype facilities and for evaluating standard designs – Can be used as part of facility permitting process • Can be used to generate risk-informed code and standard requirements – National Fire Protection Association has generated guidance for this application 3/11/2021 Preliminary Data

Risk-Informed Codes and Standards • Use of a risk-informed process is one way to

Risk-Informed Codes and Standards • Use of a risk-informed process is one way to establish the requirements necessary to ensure public safety – Comprehensive QRA used to identify and quantify scenarios leading to hydrogen release and ignition – Accident prevention and mitigation requirements identified based on QRA – Results combined with other considerations to establish minimum code and standard requirements needed for an established risk level • Required prevention and mitigation features can be specified as a function of important facility parameters: – Hydrogen generation method – Volume and pressure of hydrogen – Location of components (e. g. , inside versus outside) 3/11/2021 Preliminary Data

Separation Distances • Specified distances in codes separating H 2 components from the public,

Separation Distances • Specified distances in codes separating H 2 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) • Options for evaluating: – Consequence-based (deterministic) • Worst case leak size (e. g. , equivalent to flow area) • More probable break size (e. g. , 20% flow area) – Risk-informed (based on acceptable risk level) Separation distances based solely on the consequences of hydrogen leaks can be long for high pressure systems! 3/11/2021 Preliminary Data

Sandia Hydrogen Leak Model • Used to evaluate separation distances for jet releases •

Sandia Hydrogen Leak Model • Used to evaluate separation distances for jet releases • Model predicts (as function of system volume, pressure, and leak size): – Radiant heat flux from hydrogen jet flames • Radial and axial positions downstream of the jet as a function of time – Visible flame length for ignited jets – Hydrogen concentrations in jets – Separation distances based on free jets • Model validated against Sandia/SRI experiments • Reference: Houf and Schefer, “Predicting Radiative Heat Fluxes and Flammability Envelopes from Unintended Releases of Hydrogen, ” IJHE Paper GI-353 3/11/2021 Preliminary Data

Example of Consequence-Based Separation Distances for a Jet Fire Leak Diameter (mm) 3/11/2021 Preliminary

Example of Consequence-Based Separation Distances for a Jet Fire Leak Diameter (mm) 3/11/2021 Preliminary Data

Separation Distances for Different Consequence Measures – Jet Fires Consequence Parameter 3/11/2021 Preliminary Data

Separation Distances for Different Consequence Measures – Jet Fires Consequence Parameter 3/11/2021 Preliminary Data

Separation Distances for Different Consequence Measures – Jet Fires 3/11/2021 Preliminary Data

Separation Distances for Different Consequence Measures – Jet Fires 3/11/2021 Preliminary Data

Risk-Informed Approach • Uses risk insights from QRA plus other considerations to help define

Risk-Informed Approach • Uses risk insights from QRA plus other considerations to help define code requirements Risk = Frequency X Consequence from all accidents • Requires definition of important consequences • Requires definition of acceptable risk levels • Requires comprehensive evaluation of all possible accidents • Accounts for parameter and modeling uncertainty present in analysis 3/11/2021 Preliminary Data

Risk Approach for Establishing Separation Distances Cumulative frequency of accidents resulting in consequences that

Risk Approach for Establishing Separation Distances Cumulative frequency of accidents resulting in consequences that requires this separation distance 3/11/2021 Preliminary Data

Application to Example Facility • Evaluated risk-based separation distances for a representative fueling facility

Application to Example Facility • Evaluated risk-based 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 3/11/2021 Preliminary Data

Example Facility Description • Facility can refuel 100 cars/day • All components located outside

Example Facility Description • Facility can refuel 100 cars/day • All components located outside • Gas storage was sized for 500 kg of hydrogen(12. 63 m 3 for 70 MPa facility) • Analyzed gas storage area and distribution piping 3/11/2021 Preliminary Data

Analysis Assumptions • No protective barriers are installed around the outside gas storage area

Analysis Assumptions • No protective barriers are installed around the outside gas storage area • No isolation of a gas storage leak from upstream of isolation valve is possible • Pipe leaks downstream of isolation valve can be isolated • State-of-the art hydrogen leak or flame detector sends signal to isolation valve resulting in closure within 10 s • Immediate ignition results in injury or damage 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 – Injury or damage assumed out to a distance corresponding to ignitable concentration levels (used to determine separation distance) • Pipe leak orientation was assumed directed at lot line or structures/equipment resulting in maximum separation distances • Impact of surfaces on jet flames not included 3/11/2021 Preliminary Data

Failure Data Used in Analysis Hydrogen component leakage frequencies. Component Mean Component Leakage Frequency

Failure Data Used in Analysis Hydrogen component leakage frequencies. Component Mean Component Leakage Frequency Small Leak Large Leak Rupture 1 E-4/yr 1 E-5/yr 1 E-6/yr 3 E-6/m-yr 3 E-7/m-yr 3 E-8/m-yr 0. 1/yr 1 E-2/yr 1 E-3/yr Pump 3 E-3/yr 3 E-4/yr 3 E-5/yr Compressor 3 E-2/yr 3 E-3/yr 3 E-4/yr Electrolyser 1 E-4/yr 1 E-5/yr 1 E-6/yr Vaporizer 1 E-3/yr 3 E-4/yr 5 E-5/yr Valve 1 E-3/yr 1 E-4/yr 1 E-5/yr Pipe Joints and Unions 3 E-2/yr 4 E-3/yr 5 E-4/yr Flange 3 E-4/yr 3 E-5/yr NA Filter 3 E-3/yr 3 E-4/yr 3 E-5/yr Instrument Line 1 E-3/yr 3 E-4/yr 5 E-5/yr Vessel Pipe Refueling Hose 3/11/2021 Preliminary Data

Leakage Frequency Distributions Large leak assumed = 1 mm diameter; leak diameter distributed as

Leakage Frequency Distributions Large leak assumed = 1 mm diameter; leak diameter distributed as inverse function of diameter 3/11/2021 Preliminary Data

Gas Pipe Leak Event Tree 3/11/2021 Pipe Leak or Rupture Downstream of Immediate Ignition

Gas Pipe Leak Event Tree 3/11/2021 Pipe Leak or Rupture Downstream of Immediate Ignition of Hydrogen Jet Detection of Hydrogen or Flame Automatic Isolation of Pipe within 10 s Delayed Ignition of Hydrogen PIPE_LEAK I-IGNITION DETECTION ISOLATION D-IGNITION pipe leak - (New Event Tree) Preliminary Data # END-STATE-NAMES 1 JET-FIRE-(10 -S) 2 JET-FIRE 3 JET-FIRE 4 GAS-RELEASE-(10 -S) 5 FLASH-FIRE 6 GAS-RELEASE 7 FLASH-FIRE 8 GAS-RELEASE 2007/01/27 Page 0

Gas Pipe Results: Un-isolated Jet Fires Mean frequency of any size un-isolated pipe leak

Gas Pipe Results: Un-isolated Jet Fires Mean frequency of any size un-isolated pipe leak < 1 E-6/yr Decreasing leak frequency is countered by increasing ignition probability 3/11/2021 Preliminary Data

Gas Pipe Results: Isolated Jet fire Frequency of isolated jet fires are higher but

Gas Pipe Results: Isolated Jet fire Frequency of isolated jet fires are higher but the exposure time is short (10 s) which reduces potential for structural or equipment damage and personnel injury. 3/11/2021 Preliminary Data

Gas Pipe Results: Isolated Jet fire 3/11/2021 Preliminary Data

Gas Pipe Results: Isolated Jet fire 3/11/2021 Preliminary Data

Gas Pipe Results: Flash Fires Delayed ignition assumed to result in flash fire and

Gas Pipe Results: Flash Fires Delayed ignition assumed to result in flash fire and injury/damage out to various hydrogen concentration levels. 3/11/2021 Preliminary Data

Gas Storage Leak Event Tree 3/11/2021 Preliminary Data

Gas Storage Leak Event Tree 3/11/2021 Preliminary Data

Gas Storage Results: Un-isolated Jet Fires Accident frequencies are affected by leakage contribution from

Gas Storage Results: Un-isolated Jet Fires Accident frequencies are affected by leakage contribution from different components. Heat Flux 3/11/2021 Preliminary Data

Gas Storage Results: Flash Fires Flash fires require longer separation distances than jet fires.

Gas Storage Results: Flash Fires Flash fires require longer separation distances than jet fires. Hydrogen Concentration 3/11/2021 Preliminary Data

Gas Storage Sensitivity Study – Volume of Stored Gas Limiting gas storage volume can

Gas Storage Sensitivity Study – Volume of Stored Gas Limiting gas storage volume can lead to reduced separation distances. Mass of Gaseous Hydrogen 3/11/2021 Preliminary Data

Gas Storage Sensitivity Study – Storage Pressure 3/11/2021 Preliminary Data

Gas Storage Sensitivity Study – Storage Pressure 3/11/2021 Preliminary Data

Leak Orientation Sensitivity Leak orientation is important in determining separation distances for jet fires.

Leak Orientation Sensitivity Leak orientation is important in determining separation distances for jet fires. Leak Orientation to Target 3/11/2021 Preliminary Data

Transient Effects Integrated dose for 60 s = 1070 (kw/m 2)1. 333 s. Probability

Transient Effects Integrated dose for 60 s = 1070 (kw/m 2)1. 333 s. Probability of second degree burns = 0. 7, fatality = 0. 5. 3/11/2021 Preliminary Data

Example Parameter Uncertainties 3/11/2021 Preliminary Data

Example Parameter Uncertainties 3/11/2021 Preliminary Data

Use of Low Consequence Measures Can Lead To Wrong Separation Distances 3/11/2021 Preliminary Data

Use of Low Consequence Measures Can Lead To Wrong Separation Distances 3/11/2021 Preliminary Data

Separation Distance Results • Separation distances are significantly affected by facility operating parameters (H

Separation Distance Results • Separation distances are significantly affected by facility operating parameters (H 2 pressure and volume) • Consequence-based separation distances can be prohibitively long for large leak diameters • If small leak diameters can be justified, short separation distances even for high pressures can be justified • Risk methods can be used as a basis to help justify selection of leak diameter and separation distances • Risk-informed separation distances are significantly affected by component leakage frequency data and selected consequence parameters and risk criteria • Installation of mitigation features can reduce the frequency and consequences from leakage events • Selection of low consequence parameters to set separation distance can result in unacceptable risk 3/11/2021 Preliminary Data

Backup Slides 3/11/2021 Preliminary Data

Backup Slides 3/11/2021 Preliminary Data

Current Separation Distances in ICC International Fire Code for H 2 Gas Outdoor Equipment

Current Separation Distances in ICC International Fire Code for H 2 Gas Outdoor Equipment or Feature Distance (ft) Lot line 10 Outdoor public assembly 25 Offsite sidewalks and onsite/offsite parked vehicles 15 Ignition sources 10 Noncombustible building walls (2 hour fire barrier) Combustible building walls 5 25 Above ground flammable liquid storage 50 Below ground flammable liquid storage 20 Above ground flammable gas storage 3/11/2021 Preliminary Data 25 or 50

Failure Data Used in Analysis 3/11/2021 Preliminary Data

Failure Data Used in Analysis 3/11/2021 Preliminary Data

Failure Data Used in Analysis 3/11/2021 Preliminary Data

Failure Data Used in Analysis 3/11/2021 Preliminary Data

Potential of Injury from Jet Fires Reduced time of exposure to heat flux reduces

Potential of Injury from Jet Fires Reduced time of exposure to heat flux reduces the radiation dose and the magnitude of injury. Average Thresholds: Third Degree Burn Second Degree Burn 25 k. W/m 2 First Degree Burn 4. 7 k. W/m 2 1. 6 k. W/m 2 3/11/2021 Preliminary Data

How Do You Select Leak Diameter? • Ideally, examine appropriate leak data to determine

How Do You Select Leak Diameter? • Ideally, examine appropriate leak data to determine leak distribution – Select leak size that encompasses a designated percentage of leaks (e. g. , 50% or 95%) • Use precedents (e. g. , 20% flow area cited in several documents) • Base selection on available analyses (e. g. , offshore process leakage data) 3/11/2021 Preliminary Data

Leak Distribution Sensitivity 3/11/2021 Preliminary Data

Leak Distribution Sensitivity 3/11/2021 Preliminary Data

Offshore Leakage Data 3/11/2021 Preliminary Data

Offshore Leakage Data 3/11/2021 Preliminary Data

Use of Risk Can Eliminate Large Leaks from Consideration Risk Criteria Increasing Leak Diameter

Use of Risk Can Eliminate Large Leaks from Consideration Risk Criteria Increasing Leak Diameter 3/11/2021 Preliminary Data

Example Facility 3/11/2021 Preliminary Data

Example Facility 3/11/2021 Preliminary Data

Consequence Parameters and Risk Criteria Used in Current Analysis Consequence Parameters – Radiant Heat

Consequence Parameters and Risk Criteria Used in Current Analysis Consequence Parameters – Radiant Heat Flux from Jet Fires: • 1. 6 k. W/m 2 – no harm to individuals for long exposures • 4. 7 k. W/m 2 – injury (second degree burns) within 20 seconds • 25 k. W/m 2 – 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 • <2 E-4/yr – fatality risk from all other high-risk hazards in society 3/11/2021 Preliminary Data

Example Separation Distances Due to Flash Fires Gas Storage Leaks- Flash Fires 1 Consequence-Based

Example Separation Distances Due to Flash Fires Gas Storage Leaks- Flash Fires 1 Consequence-Based Separation Distance (m)2 Risk Criteria 35 MPa 70 MPa 105 MPa 2 E-4/yr 22. 7, 72. 3 30. 0, 96. 6 35. 0, 112. 7 26 32 36 5 E-5/yr - - - 30 44 49 1 E-5/yr - - - 59 76 87 5 E-6/yr - - - 72 82 92 1. 2. 3/11/2021 Maximum Risk-Informed Separation Distances (m) Separation distances for - 4% H 2 concentrations. Values are for 4. 2 mm and 13. 5 mm leaks, respectively. Preliminary Data

Summary • QRA can help ensure hydrogen facility safety directly – Identifies important accidents

Summary • QRA can help ensure hydrogen facility safety directly – Identifies important accidents – Evaluates effectiveness of preventive and mitigation features – Used to establish risk management strategies • QRA can help establish hydrogen code and standard requirements – Compliance with minimum requirements ensures an accepted level of risk is achieved 3/11/2021 Preliminary Data

Future Efforts • Continue evaluating safety distances for example facility to further demonstrate methodology

Future Efforts • Continue evaluating safety distances for example facility to further demonstrate methodology – Examine other gas-related accidents (e. g. , vapor cloud explosions) – Examine liquid hydrogen storage leaks/ruptures • Evaluate facilities using different methods for onsite hydrogen production (gas reforming and electrolysis) • Improve risk 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); Bayesian approaches to data analysis • Identify methods for determining 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 3/11/2021 Preliminary Data