nd European Summer School on Hydrogen 2 nd European Summer School on - - PowerPoint PPT Presentation

Risk Management and Hydrogen Safety Risk Management and Hydrogen Safety

Andrei V. Tchouvelev Andrei V. Tchouvelev

2 2nd

nd European Summer School on Hydrogen

European Summer School on Hydrogen Safety Safety Belfast, 30 July Belfast, 30 July – – August 8, 2007 August 8, 2007

Financial Support

Presented research was supported in part by Natural Resources Canada through the activities of the Codes and Standards Working Group of the Canadian Transportation Fuel Cell Alliance, by the research performers, A.V.Tchouvelev & Associates Inc., TISEC Inc., and the Hydrogen Research and by the collaborating industrial partners

2 2

Acknowledgement Acknowledgement

3 3

Concept of Risk Management Concept of Risk Management

Risk management – coordinated activities to direct and control

an organization with regard to risk. Risk management generally includes risk assessment, risk treatment, risk acceptance and risk

• communication. ISO / IEC Guide 73: 2002

4 4

Scope Scope

Quantitative risk comparison of hydrogen and natural gas refuelling options

Project Scope Sourcing Options Hydrogen Natural Gas Delivery Compressed Gas Compressed Gas Pipeline On-Site Generation Reforming

fuel comparison scenario

Electrolysis

5 5

Generic Station Configuration for QRA Generic Station Configuration for QRA

The generic station consists (regardless of technology) of the following major components or “boxes”: 1. fuel delivery / on-site production (will also include purification for reformer technology); 2. compression; 3. storage; 4. dispensing / vehicle interface (vehicles themselves are excluded).

6 6

Qualitative RA Qualitative RA – – TIAX FMEA Study TIAX FMEA Study

FMEA for Hydrogen Fueling Options, CEC-600-2005-001 Design Baseline Considerations:

7 7

Hazard Identification Hazard Identification

Example of HazID analysis (via FMEA) for a electrolyser

Failure Scenarios Selection Failure Scenarios Selection

Tube Trailer:

• S1: Small horizontal leak during unloading
• S2: Catastrophic horizontal leak during unloading

Electrolyser:

• S3: Catastrophic internal leak at hydrogen rinser
• S4: Venting of catastrophic internal leak
• S5: H2 Leak outdoors between compressor and storage

Reformer:

• S6 (and S9): NG supply line leak outdoors
• S7: NG line leak between NG compressor and reformer
• S8: Catastrophic internal leak at PSA unit

CNG Station:

• S10: CNG leak outdoors between compressor and storage

Gas Storage:

• S11: Horizontal jet release (H2 and CH4) at equal pressure and orifice
• S12: Venting of H2 and CH4 at equal flow rate

8 8

9 9

Tube Trailer Failure Scenarios Tube Trailer Failure Scenarios

Small leak via 1 mm orifice, 2640 psig: LFL horizontal extent 4.26 m Catastrophic leak via ½” OD orifice, 2640 psig: LFL horizontal extent 40.5 m

Electrolyser Failure Scenarios Electrolyser Failure Scenarios

Hydrogen release and dispersion from a hydrogen rinser fitting through a ¾” opening at 10 bar

10 10

Electrolyser Failure Scenarios Electrolyser Failure Scenarios

Hydrogen release and dispersion from a hydrogen rinser through a ¾” opening at 10 bar

• Hydrogen release and dispersion:
• Duration of sonic release – 0.7 sec
• Total release duration – 1.0 sec
• Quantity of released hydrogen – 0.5 Nm3

0.02 sec 1.0 sec

11 11

Outdoor Release Comparison Outdoor Release Comparison

Release of H2 and CH4 outdoors between compressor and storage towards storage via 1 mm

• rifice, 4’ from storage

H2 line flow 1.25 kg/h at 6000 psig CH4 line flow 18 kg/h at 4000 psig

Flame length 0.4 m Flame length 3.4 m

12 12

Horizontal Jets Comparison Horizontal Jets Comparison

Storage: hydrogen and CNG release and dispersion from a shut-off valve fitting through a ½” OD at 4125 psi

• Leak orifice ½” OD, 8.48 mm ID
• Leak direction/location: horizontal leak 1 m above the ground
• Domain size: symmetric, 100m by 8 m by 25 m.
• Water volume of cylinders: 2.811 m3
• Initial stagnation pressure: 284.4 bars
• Choked leak duration: H2: 80 sec, CH4: 240 sec
• Simulation time: 0-90 sec for CH4, 0-60 sec for H2

13 13

Steady state CFD results: H Steady state CFD results: H2

2 vs. CH

• vs. CH4

4

Steady CFD results by PHOENICS 3.6.1

Horizontal leak 1m above the ground, OD ½” (ID 8.48 mm) orifice High pressure 284 bars

• H2: 43 m, CH4: 68 m

14 14

Transient CFD results: H Transient CFD results: H2

2 vs. CH

• vs. CH4

4

15 15

Natural Gas (CH4) Storage Venting Natural Gas (CH4) Storage Venting

Venting (sonic and subsonic) of CH4 outdoors: 2,000 scfm, 9 m/s wind, LFL (5% vol.) profile – Fluent, RNG k-e

Sonic, 1” orifice, LFL 1.8 m extent Subsonic, 3” orifice, LFL 4.8 m extent

16 16

Hydrogen Storage Venting Hydrogen Storage Venting

Venting (sonic) of H2 outdoors: 2000 scfm, 9 m/s wind, LFL (4% vol.) profile – Fluent, RNG k-e

Sonic, 1” orifice, LFL 5.5 m extent

17 17

Natural Gas (CH4) Storage Venting Natural Gas (CH4) Storage Venting

Blow-off Velocities for H2 and CH4 (slide by C. Moen, SNL)

18 18

Jet Fire Thermal Radiative Flux Jet Fire Thermal Radiative Flux

Model References

• Y. R. Sivathanu and J. P. Gore, 1993.
• W. Houf and R. Schefer (SNL), 2004-6.

Has been recently validated by SNL for free H2 jet flames

• T. Mogi et al (AIST), 2005.

Used for verification purposes TNO “Yellow Book”, Part 2, p.6.48, 1997. Used for vertical flares Still needs to be validated for hydrogen

19 19

Scenario 1:

Small leak via 1 mm orifice, 2640 psig LFL horizontal extent 4.26 m

Tube Trailer Thermal Effects Tube Trailer Thermal Effects

20 20

Scenario 2:

Catastrophic leak via ½” OD

• rifice, 2640 psig

LFL horizontal extent 40.5 m

Tube Trailer Thermal Effects Tube Trailer Thermal Effects

21 21

Scenario 11:

Catastrophic leak via 8.48 mm orifice at 282 bars from CNG storage system

Storage Horizontal Jet Thermal Effects Storage Horizontal Jet Thermal Effects – – Methane Methane

22 22

Scenario 11:

Catastrophic leak via 8.48 mm orifice at 282 bars from H2 storage system

Storage Horizontal Jet Thermal Effects Storage Horizontal Jet Thermal Effects – – Hydrogen Hydrogen

23 23

Thermal Flux from CNG and H2 Storage Venting

Storage Venting Thermal Effects Storage Venting Thermal Effects

24 24

Ignition Probabilities Approach Ignition Probabilities Approach

Developed by DNV with input from AVT Starting point – historical data review

RELEASE RATE CATEGORY RELEASE RATE (kg/s) GAS LEAK CRUDE CLASS I CLASS II CLASS III

Small < 1 0.010 0.010 0.006 0.004 0.002 Large 1 – 50 0.070 0.030 0.018 0.012 0.007 Massive > 50 0.300 0.080 0.049 0.031 0.018

Historical Ignition Probability Data for Hydrocarbons (Cox, Lees & Ang)

25 25

Ignition Probabilities Considerations Ignition Probabilities Considerations

All considered H2 leaks are less than 1 kg/s Historically reported ratio of immediate to delayed ignition probability is 2 to 1 What is realistic probability for H2 – 1% seems low Key considerations in comparison with methane:

• For a given mass leak, H2 would produce appr. 8 times

bigger flammable cloud than methane (their LFL’s are close)

• Delayed ignition probability is proportional to the flammable

cloud size. Hence, 1 kg/s leak for methane is “equivalent” in volume to 0.125 kg/s for H2

• Though the flammable range of H2 (4 to 75% vol.) is 7.3

times greater than that of methane (5 to 15% vol.), for both gases the size of a cloud above 15 % vol. is about 16% of the total size of cloud above LFL

26 26

Minimum ignition energy vs H2 concentration in air As presented by M.Swain on May 24, 2004

Hydrogen Concentration Minimum Ignition Energy Required (mJ) 29% (stoicheometric) 0.02 10% 0.15 9% 0.21 8% 0.33 7% 0.56 6% 1.0 5% 3.0 4% 10.0

27 27

Ignition Probabilities Considerations Ignition Probabilities Considerations

As proposed by DNV

RELEASE RATE CATEGORY HYDROGEN RELEASE RATE (kg/s) HYDROGEN TOTAL IGNITION PROBABILITY HYDROGEN IMMEDIATE IGNITION PROBABILITY HYDROGEN DELAYED IGNITION PROBABILITY Small Leak

< 0.125 0.012 0.008 0.004

Large Leak

0.125 – 6.25 0.08 0.053 0.027

Massive Leak

> 6.25 0.35 0.23 0.12

Flammable H2 gas mixture within closed systems

Not Applicable 1

• 1

28 28

Adopted Ignition Probabilities Adopted Ignition Probabilities

Example: Scenario 1 Tube Trailer Small Leak

29 29

Frequencies & Probabilities Analysis Frequencies & Probabilities Analysis – – Fault and Event Trees Fault and Event Trees

30

Risk Estimation Risk Estimation

Risk Metrics

• Location Specific Individual Risk (LSIR)

where the summation is extended for all scenarios and: Fs is the frequency of the scenario S PF is the probability of death in the scenario for an individual at the location The frequency of the scenario is taken as: where FO is the end outcome frequency calculated from the post-incident event trees with the formula: where Fi, is the failure frequency of the initiating event for the scenario calculated using a fault tree analysis Pb is the probability of an individual segment of the event tree such as probability of immediate ignition or probability of delayed ignition

30 30

Risk Metrics

• Potential Loss of Life (PLL)

where npresent is the number of persons present and exposed to the event

where A = -36.38; B = 2.56; I = heat radiation load any value greater than 1.6 Kw/m2; t = 20 or 60 seconds (except for electrolyser and reformer cases where leak durations were very short)

• Specific locations with coordinates x=1, R=1 and x=5, R=1

were selected for comparison for all scenarios

• Probit equations (TNO “Purple Book”) were used to estimate

consequence of each fire scenario:

31 31

Risk Estimation Risk Estimation

Tube Trailer Risk Estimation Tube Trailer Risk Estimation

32 32

Summary of Risk Comparison Study Summary of Risk Comparison Study

• Qualitative Assessment:
• Good tool for rough / preliminary risk ranking
• Maybe be misleading regarding real consequences / risks
• Comparison Among Hydrogen Options:
• Sourcing hydrogen on-site and off-site present almost the same risk
• From the individual risk, the electrolysis process presents the lowest risk
• CNG and Hydrogen Storage Comparison:
• Hydrogen storage facility presents a marginally lower (within 20%) risk

compared to an identical CNG storage

• In terms of storage venting, a CNG storage facility may require either a

larger clearance than an identical hydrogen storage facility or a higher vent stack to achieve the same level of thermal radiation from a vertical flare

• Risk Comparison: In summary, an electrolysis refuelling option that

includes compressed hydrogen storage presents the lowest risk among the refuelling options that were considered including a CNG station of equal refuelling capacity to provide equivalent travel mileage

33 33

Risk Evaluation and Risk Criteria Risk Evaluation and Risk Criteria

• Definitions:
• Risk evaluation – the process comparing the estimated risk against risk

criteria to determine the significance of the risk

• Risk criteria – terms of reference by which the significance of risk is

assessed

• Establishment of risk criteria is a key element in risk management

decision making:

• Individual risk reflects the frequency that an average person located

permanently at a certain location is harmed

• Societal risk reflects the relationship between the frequency and the

number of people harmed

• Options for selection of risk criteria:
• Specify that the risk from hydrogen accidents be some fraction of the total

risk to individuals from all unintentional injuries, or

• Utilize just the individual fatality and injury risk associated with only fires

and explosions

• Specify that the risk associated with hydrogen refuelling stations be at par

with the risk associated with gasoline or CNG stations

34 34

Risk Perception Risk Perception

“…This discovery begins a new era in the history of

• civilization. Never in history has society been

confronted with power so full of potential danger and at the same so full of promise for the future of man and for peace of the world…” “…The dangers are obvious. Stores of [this fuel] would constitute a fire and explosive hazard of the first rank…” “…the discovery with which we are dealing involves forces

• f nature too dangerous to fit into our usual

concepts…” From the summary of the Report of the Congressional Horseless Carriage Committee “What’s Gasoline”, 1875.

35 35

Canadian National Standard Q-850 Risk Management: Guidelines for Decision-Makers “Risk involves three key issues:

• The frequency of the loss, that is, how often the loss may
• ccur;
• The consequences of the loss, that is, how large might the

loss be; and

• The perception of the loss, that is, how a potential risk is

viewed by affected stakeholders in terms of its effect on their needs, issues, and concerns. Because there is a need to understand how a potential loss might affect and be perceived by the various stakeholders, it is insufficient, and indeed can be quite misleading, for the decision-maker to consider risk solely in terms of probability and consequence.”

36 36

Risk Perception Risk Perception

Example of “Hindenburg”:

“My only answer to him is

Hindenburg” – Robin

Williams’s comment on Arnold Schwarzenegger’s hydrogen initiative in California (Jay Leno show, June 2006)

• 70 years after, “Hindenburg” still remains a key driver of public

risk perception of hydrogen despite explicit proof by Dr. Addison Bain that hydrogen is not “responsible” for this disaster

37 37

Is This True Representation of Risk? Is This True Representation of Risk? Does this mean that if people THINK hydrogen is risky, it IS risky?

Perception of Safety or Risk? Perception of Safety or Risk?

Safety is a Moving Target because:

• Safety is a societal category while risk is technical
• Safety cannot be calculated while risk can
• Perception is an important component of safety as it affects risk

acceptance criteria

• Hence:
• It is incorrect to state that perception is a component of risk

38 38

Safety and Risk Safety and Risk

• Definition:
• Safety is freedom from unacceptable risk (ISO/IEC Guide 51: 1999)
• This effectively means that:
• Risk is the measure of safety
• Society accepts the fact that there is neither absolute (i.e., 100%) safety

nor zero risk

• Society, de facto, establishes acceptable levels of risk or risk acceptance

criteria

• The need to comply with risk acceptance criteria suggests that:
• Any product must have a basic design that satisfies risk acceptance

criteria and thus ensures minimum acceptable level of safety under intended operating conditions

• Methods and tools are required to measure and verify product compliance

with acceptable levels of risk

• Codes and standards that identify minimum design, performance and

installation requirements as well as regulations that guide permitting and approval processes have to reflect those risk acceptance criteria in order to become risk-informed

39 39

Risk Management and Hydrogen Safety Risk Management and Hydrogen Safety

Andrei V. Tchouvelev Andrei V. Tchouvelev

2 2nd

nd European Summer School on Hydrogen

European Summer School on Hydrogen Safety Safety Belfast, 30 July Belfast, 30 July – – August 8, 2007 August 8, 2007

THE END THE END