Risk informed separation distances for hydrogen refuelling stations

1. Frederic Barth Air Liquide Hydrogen Energy Risk informed separation distances for hydrogen refuelling stations

2. Background and general motivation • Approach developed for ISO/DIS 20100 Gaseous Hydrogen – Fuelling stations within TC197/WG 11 Fueling stations by TG1 Separation distances • To substantiate lay-out requirements for HRS sub-systems • Applied to gaseous hydrogen systems • Hydrogen supply system (e.g. tube trailer) • Hydrogen compression skid • Hydrogen buffer storage • Hydrogen dispensers • Hydrogen is being developed for generalized use as an energy carrier: • Higher operating pressures than previously considered • Installation and use in public settings • Variety of applications (e.g. RV fuelling stations, back-up power, materials handling…) • Inherently safe designs and built-in safety measures  Need of a robust rationale and approach for addressing these new applications consistently

3. Separation distances in codes & standards Rationale • Purpose : a generic means for mitigating the effect of a foreseeable incident and preventing a minor incident escalating into a larger incident (EIGA IGC 75/05) • Apply separation as appropriate, along with other means, to achieve freedom from unacceptable risk • Separation is not always necessary, nor most appropriate means • Where applied, appropriate separation can be defined by application of a risk criterion • Protection against catastrophic events is essentially achieved by other means than separation, such as prevention, specific means of mitigation, or emergency response, which are also addressed.

4. Separation distances in codes & standards Form of specification • Continue to express requirements by means of a good table that is suitable for the covered application • Most practical • Tabled distances have been checked • Same distance for similar systems supports standardization • Relying on a formulas raises the risk that design parameters will be chosen to minimise safety distance requirements although this choice does not reduce the actual risk level to exposures • Practical value added of specifying distance by means of formulas is not clear • Different applications may require different tables • e.g. Fuelling stations, bulk hydrogen storage systems, hydrogen installations in non industrial environment

5. Table based separation distances specification – Basic steps Table Lines : Exposures or sources of hazard ; Columns: system category • Select system characteristics that fundamentally determine actual risk impact • Define system categories associated to a graduation of risk impact • Taking into account different types of equipment actually used • Limit the number of categories to justified need • Use a risk model to determine the separation distances for each category, by application of a criterion on estimated residual risk, • Based on max values for the category • Higher risk  Greater separation • Populate the distance table and evaluate the result.

6. Selection of system characteristics that fundamentally determine actual risk impact • Separation distances should not be determined only by Pressure and Internal Diameter. Need to integrate fundamental factors determining actual risk impact, such as inventory, system complexity, and exposure criticality • Over sensitivity to a detail design parameter such as internal diameter needs to be avoided

7. Selection of system characteristics that fundamentally determine actual risk impact • Storage system size • Small • Large • Complexity level as reflected by number of components • Very simple (for Small systems only) • Simple • Complex • For Small systems only : pressure • Regular • High

8. Categorization of compressed hydrogen storage systems • Boundaries defined according to equipment types in use

9. Resulting categorization for gaseous hydrogen storage systems • 8 categories

10. Separation distance To be applied Separation distance (m) 10 30 1 3 Leaks Cumulated frequencyof feared effects from leaks greater than X g/s - - 2 1 10 10 - 3 10 FearedEffect - 4 10 Target - 5 10 - 6 10 Reference leak size Risk model for determination of a separation distance requirement from a system occ./yr 10 10 Frequency - 3 10 - 4 10 - 5 10 - 6 10 Leak Leak rate rate 10 10 100 100 0,01 0,01 0,1 0,1 1 1 (g/s) (g/s)

11. Key parameters of risk model • Cumulative leak frequency vs leak size See next slides • Probability of having the feared event (injury) when a leak occurs Pignition x Geometric factor = 0,04 x 0,125 = 0,005 • Consequence model providing distance up to which leaks can produce the feared event, in function of leak size and type of feared effect (e.g thermal effects or 4% H2 concentration) Sandia National Laboratories jet release and fire models • Target value for the feared event frequency, Non-critical exposure: 10-5 /yr Critical exposure: 4 10-6/yr • Risk model does not provide an accurate evaluation of risk, but allows to take into consideration the main risk factors consistently  Separation distances are risk informed

12. Determination of system leak frequency distributionin function of component leak frequency distribution • Consider main contributors to leaks • Joints, Valves, Hoses, Compressors • Estimate cumulated leak frequency in function leak size (% of flow section) for each type of component, from available statistical data • Estimate cumulated leak frequency in function of leak size for the whole system, by summation of contributing component leak frequency data

13. Component leak frequency – Source of input to risk model • Risk model requires leak frequency input for following leak size ranges : [0.01% ; 0,1%], [0.1% ; 1%][1% ; 10%][10% ; 100%] • Use of published leak frequencies compiled by SNL (J. LaChance) Extract for valves, where information on leak size is provided (34% of records): • Data input to risk model:Leak size range [0.01% ; 0,1%] [0.1% ; 1%] [1% ; 10%] [10% ; 100%]Log. average freq. of extrapolated “Small leaks” “Large leaks” “Ruptures”

14. Risk model leak frequency input for valves (1) • Frequency and size of “small leaks”

15. Risk model leak frequency input for valves (2) • Frequency and size of “small leaks”

16. Risk model leak frequency input for valves (3) • Note : adequacy of using log-average of “Small leak”, “Large leak”, and “Rupture” frequencies as risk model input for [0.1% ; 1%], [1% ; 10%],[10% ; 100%] ranges was verified for all types of components

17. Risk model component leak frequency functions

18. Consequence Model • Interpolation of flame length and flammable cloud length formulas developed by SNL (Bill Houf) :

19. Risk informed leak diameters& separation distances for storage/transfer systems

20. Separation distance requirements for compressedfor gaseous hydrogen storage/transfer systems

21. Thank youfrederic.barth@airliquide.com