Risk informed separation distances for hydrogen refuelling stations

Risk informed separation distances for hydrogen refuelling stations ¢ ¢ Frederic Barth Air Liquide Hydrogen Energy International Conference on Hydrogen Safety 2011 – San Francisco, 12 Sept 2011

Background and general motivation ¢ Approach developed for ISO/DIS 20100 Gaseous Hydrogen – Fuelling stations within TC 197/WG 11 Fueling stations by TG 1 Separation distances ¢ To substantiate lay-out requirements for HRS sub-systems ¢ Applied to gaseous hydrogen systems a a ¢ 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: a Higher operating pressures than previously considered a Installation and use in public settings a 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 ICHS 2011 – San Francisco, 12 Sept 2011 2

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. ICHS 2011 – San Francisco, 12 Sept 2011 3

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 a Most practical a Tabled distances have been checked a Same distance for similar systems supports standardization a 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 a Practical value added of specifying distance by means of formulas is not clear ¢ Different applications may require different tables a e. g. Fuelling stations, bulk hydrogen storage systems, hydrogen installations in non industrial environment ICHS 2011 – San Francisco, 12 Sept 2011 4

Table based separation distances specification – Basic steps Table Lines : Exposures or sources of hazard ; Columns: system category 1. Select system characteristics that fundamentally determine actual risk impact 2. Define system categories associated to a graduation of risk impact a Taking into account different types of equipment actually used a Limit the number of categories to justified need 3. Use a risk model to determine the separation distances for each category, by application of a criterion on estimated residual risk, a Based on max values for the category a Higher risk Greater separation 4. Populate the distance table and evaluate the result. ICHS 2011 – San Francisco, 12 Sept 2011 5

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 ICHS 2011 – San Francisco, 12 Sept 2011 6

Selection of system characteristics that fundamentally determine actual risk impact 1. Storage system size a Small a Large 2. Complexity level as reflected by number of components a Very simple (for Small systems only) a Simple a Complex 3. For Small systems only : pressure a Regular a High ICHS 2011 – San Francisco, 12 Sept 2011 7

Categorization of compressed hydrogen storage systems ¢ Boundaries defined according to equipment types in use ICHS 2011 – San Francisco, 12 Sept 2011 8

Resulting categorization for gaseous hydrogen storage systems ¢ 8 categories ICHS 2011 – San Francisco, 12 Sept 2011 9

Risk model for determination of a separation distance requirement from a system occ. /yr Separation distance To be applied Frequency 10 -1 1 10 3 30 Separation distance (m) Leaks Cumulated frequency of feared effects from leaks greater than X g/s 10 -2 10 -3 10 -4 Feared Effect Target 10 -5 10 -6 0, 01 0, 1 1 10 100 Leak rate (g/s) Reference leak size ICHS 2011 – San Francisco, 12 Sept 2011 10

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% H 2 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 ICHS 2011 – San Francisco, 12 Sept 2011 11

Determination of system leak frequency distribution in function of component leak frequency distribution ¢ Consider main contributors to leaks a 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 ICHS 2011 – San Francisco, 12 Sept 2011 12

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. La. Chance) 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” ICHS 2011 – San Francisco, 12 Sept 2011 13

Risk model leak frequency input for valves (1) ¢ Frequency and size of “small leaks” ICHS 2011 – San Francisco, 12 Sept 2011 14

Risk model leak frequency input for valves (2) ¢ Frequency and size of “small leaks” ICHS 2011 – San Francisco, 12 Sept 2011 15

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 ICHS 2011 – San Francisco, 12 Sept 2011 16

Risk model component leak frequency functions ICHS 2011 – San Francisco, 12 Sept 2011 17

Consequence Model ¢ Interpolation of flame length and flammable cloud length formulas developed by SNL (Bill Houf) : ICHS 2011 – San Francisco, 12 Sept 2011 18

Risk informed leak diameters & separation distances for storage/transfer systems ICHS 2011 – San Francisco, 12 Sept 2011 19

Separation distance requirements for compressed for gaseous hydrogen storage/transfer systems ICHS 2011 – San Francisco, 12 Sept 2011 20

Thank you frederic. barth@airliquide. com ICHS 2011 – San Francisco, 12 Sept 2011 21