SAFETY DISTANCES: COMPARISON OF THE METODOLOGIES FOR THEIR DETERMINATION M. Vanuzzo , M. Carcassi.

1. SAFETY DISTANCES: COMPARISON OF THE METODOLOGIESFOR THEIR DETERMINATION M. Vanuzzo,M. Carcassi. Università di Pisa Dipartimento di Ingegneria Meccanica, Nucleare e della Produzione (DIMNP), Universityof Pisa ICHS 2011 - San Francisco, USA - September 12 -14

2. CONTENTS • Definition of Safety and Separation distances • Standard and Regulation inherent to hydrogen safety distances • Risk- Informed approach • Comparison of NFPA and ISO methodologies for the determination of safety distances • Consideration about the choice of the leak diameter • Conclusion ICHS 2011 - San Francisco, USA - September 12 -14

3. CONSIDERED STANDARD AND REGULATIONS • Regulation NFPA 2 “Hydrogen technical code” (United States) - • EIGA IGC Doc 75/07/E “Determination of Safety Distances” (EU) • Standard ISO 20100 “ Gaseous hydrogen Fuelling stations “ • Regulation-Draft of “Technical rules for distribution and the transport of hydrogen in pipelines” (Italy) • Regulation "Approval of the technical rule of fire prevention, construction and exercise of hydrogen fueling station“(Italy) ICHS 2011 - San Francisco, USA - September 12 -14

4. DEFINITION OF SAFETY AND SEPARATION DISTANCES • EIGA: “the safety distance is the minimum separation between a hazard source and an object (human, equipment or environment) which will mitigate the effect of a likely foreseeable incident and prevent a minor incident escalating into a larger incident”. • SANDIA: “Separation or safety distances are used to protect the public and other facilities from the consequences of potential accidents related to the operation of a facility. Separation distances are also used to reduce the potential that a minor accident at one portion of a facility propagates to another part of the facility thus increasing the resulting consequences.” (SAND 2009-0874) • ISO (ISO/DIS 20100): the same definition of EIGA • NFPA 2 NO DEFINITION but refers to SANDIA report ICHS 2011 - San Francisco, USA - September 12 -14

5. RISK RELATED (INFORMED/BASED) NFPA2 introduces a new methodology for the determination of hydrogen safety distances, the risk informed process. The definition of “risk-informed” is presented in the Sandia’s report : “Risk-informed is a methodology that utilizes risk insights obtained from quantitative risk assessments (QRAs) combined with other considerations to establish code requirements. “ “Risk-basedis a methodology that utilizes risk obtained from quantitative risk assessments (QRAs) compared with a specific acceptance risk criteria. “ RISK INFORMED = RISK BASED + OTHER CONSIDERATIONS ICHS 2011 - San Francisco, USA - September 12 -14

6. RISK INFORMED SPECIFICATION { Statistical Analysis (leak frequencies) Quantitative Risk Assessment Accident Scenarios (jet / flash fire) Risk Criterion (risk guideline) What are the “other consideration”? Uncertainties (statistical analysis, ignition probabilities, harm criteria etc..) Parametric Assumption (pressure, system size, system category etc..) ICHS 2011 - San Francisco, USA - September 12 -14

7. NFPA METHODOLOGY • Hydrogen-specific component leak frequencies • Harm criteria • Cumulative probability to determine which range of leaks represents the most likely leak size • The risk resulting from different leaks sizes was also evaluated for four standard gas storage configurations • The choice of the leak dimensions is based on risk reasonably close to 2x10-5. On the basis of the previous considerations Leak area = 3% of the flow area ICHS 2011 - San Francisco, USA - September 12 -14

8. ISO METHODOLOGY • Hydrogen-specific component leak frequencies • Harm criteria • The safety distances are defined for different types of hydrogen systems forming a well identifiable physical module • Introduction of a definition of leak likelihood for every physical module. This level of leak likelihood is assumed to be reflected by the value of the Leak Probability Indicator (LPI) for that system. • Choice of the leak dimension’s risk lower than 10-5/year for the public, 10-4/year for customers. On the basis of the previous considerations The leak diameter varies according to the type of system that is considered ICHS 2011 - San Francisco, USA - September 12 -14

9. COMPARISON OF NFPA AND ISO METHODOLOGIES ? ICHS 2011 - San Francisco, USA - September 12 -14

10. UNCLARITY IN THE ISO METHODOLOGY Statistical analysis for determination of component release frequencies The reason for shifting the frequencies of one order of magnitude ? (www.hydrogensafety.info/2010/aug/separationDistances.pdf) ICHS 2011 - San Francisco, USA - September 12 -14

11. COMPARISON OF NFPA AND ISO METHODOLOGIES SAME METHODOLOGY BUT DIFFERENT LEAK SIZES CONSIDERED DIFFERENT CONSIDERATIONS ICHS 2011 - San Francisco, USA - September 12 -14

12. CHOISE OF LEAK DIAMETER NOTABLY DIFFERENT ICHS 2011 - San Francisco, USA - September 12 -14

13. LEAK DIMENSION EVALUATION 0.10% - 1% Range considers by ISO { 1.0E+01 ? 1.0E+00 Leakage Frequency (/yr) 1.0E-01 GAP 1.0E-02 1.0E-03 1.0E-04 1.0E-05 Minor leaks Ruptures Medium leaks Major leaks 1.0E-06 3% considered by NFPA 1.0E-07 0.01% 0.10% 1.00% 10.00% 100.00% Leakage Area (% Flow Area) ICHS 2011 - San Francisco, USA - September 12 -14

14. CONCLUSIONS { METHODOLOGY SAFETY DISTANCE DETERMINATION PROCESS CONSIDERATIONS LEAK DIMENSION SAFETY DISTANCE VALUE For this reason is important to clearly define for which purpose the safety distances should be used ? to prevent escalation and protect targetsfrom more probable small releases (ISO) to prevent escalation and protect targets from great releases (NFPA) or ICHS 2011 - San Francisco, USA - September 12 -14

15. THANK YOU. Contact Author: Matteo Vanuzzo (UNIPI-ITALY) matteo7785@libero.it Presented by: Marco Carcassi (UNIPI-ITALY) carcassi@ing.unipi.it

16. DEFINITION OF SAFETY AND SEPARATION DISTANCES • ITALIAN REGULATION FOR HYDROGEN FILLING STATION defines three kind of safety distances: • Protection safety distance: “the least value of horizontally distances among the plant’s perimeter and every dangerous element of the activity; • Internal safety distance: “the least value of horizontally distances among the various dangerous elements of an activity; • External safety distance: “the least value of horizontally distances among every dangerous element of an activity and the perimeter of the nearest external building. ICHS 2011 - San Francisco, USA - September 12 -14