1. safety distances: comparison of the metodologies for their determination – M. Vanuzzo, M. Carcassi ICHS 2011 - San Francisco, USA - September 12 -14 SAFETY DISTANCES: COMPARISON OF THE METODOLOGIES FOR THEIR DETERMINATION M. Vanuzzo, M. Carcassi. Dipartimento di Ingegneria Meccanica, Nucleare e della Produzione (DIMNP), University of Pisa Università di Pisa

2. safety distances: comparison of the metodologies for their determination – M. Vanuzzo, M. Carcassi ICHS 2011 - San Francisco, USA - September 12 -14 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

3. safety distances: comparison of the metodologies for their determination – M. Vanuzzo, M. Carcassi ICHS 2011 - San Francisco, USA - September 12 -14 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)

4. safety distances: comparison of the metodologies for their determination – M. Vanuzzo, M. Carcassi ICHS 2011 - San Francisco, USA - September 12 -14 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

5. safety distances: comparison of the metodologies for their determination – M. Vanuzzo, M. Carcassi ICHS 2011 - San Francisco, USA - September 12 -14 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-based is a methodology that utilizes risk obtained from quantitative risk assessments (QRAs) compared with a specific acceptance risk criteria. “ RISK INFORMED = RISK BASED + OTHER CONSIDERATIONS

6. safety distances: comparison of the metodologies for their determination – M. Vanuzzo, M. Carcassi ICHS 2011 - San Francisco, USA - September 12 -14 RISK INFORMED SPECIFICATION Quantitative Risk Assessment { Statistical Analysis (leak frequencies) 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..)

7. safety distances: comparison of the metodologies for their determination – M. Vanuzzo, M. Carcassi ICHS 2011 - San Francisco, USA - September 12 -14 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

8. safety distances: comparison of the metodologies for their determination – M. Vanuzzo, M. Carcassi ICHS 2011 - San Francisco, USA - September 12 -14 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

9. safety distances: comparison of the metodologies for their determination – M. Vanuzzo, M. Carcassi ICHS 2011 - San Francisco, USA - September 12 -14 COMPARISON OF NFPA AND ISO METHODOLOGIES NFPAISO Database Sandia database Components release frequencies Bayesian analysisLinear versions (on a log-log plot) of the values generated by Sandia National Laboratories ? (www.hydrogensafety.info/2010/aug/s eparationDistances.pdf) Probability of ignition Jet fire (with probability of 0.008) and flash fire (with probability 0.004) Jet fire (with probability of ignition equal to 0.04) Different adaptability of application Determination of the unique leak diameter Takes into account systems constituted by different numbers and different kinds of components. Acceptance criterion of the select risk 2 10-5/year10-5/year for the public, 10-4/year for customers refueling their vehicle and it’s under development the risk for critical exposures Leak sizes considered 3% of the flow areaalways smaller, it varies according to the type of system that is considered ?

10. safety distances: comparison of the metodologies for their determination – M. Vanuzzo, M. Carcassi ICHS 2011 - San Francisco, USA - September 12 -14 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)www.hydrogensafety.info/2010/ aug/separationDistances.pdf

11. safety distances: comparison of the metodologies for their determination – M. Vanuzzo, M. Carcassi ICHS 2011 - San Francisco, USA - September 12 -14 COMPARISON OF NFPA AND ISO METHODOLOGIES REQUIREMENTSNFPA 3 ISO 2 RISK INFORMED RISK BASED Statistical Analysis Accident Scenarios Risk Criterion Uncertainties Parametric Assumption SAME METHODOLOGY BUT DIFFERENT LEAK SIZES CONSIDERED DIFFERENT CONSIDERATIONS

12. safety distances: comparison of the metodologies for their determination – M. Vanuzzo, M. Carcassi ICHS 2011 - San Francisco, USA - September 12 -14 CHOISE OF LEAK DIAMETER NFPAISOUNIVERSITY OF PISA CHINA (study) Leak diameter dimension for a pipeline 17-20% of pipe diameter Around 3 % of pipe diameter for very simple system 2.5% of pipe diameter (PIPELINE) Full bore rupture NOTABLY DIFFERENT

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

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

15. safety distances: comparison of the metodologies for their determination – M. Vanuzzo, M. Carcassi THANK YOU. Contact Author: Matteo Vanuzzo (UNIPI-ITALY) matteo7785@libero.it Presented by: Marco Carcassi (UNIPI-ITALY) carcassi@ing.unipi.it

16. safety distances: comparison of the metodologies for their determination – M. Vanuzzo, M. Carcassi ICHS 2011 - San Francisco, USA - September 12 -14 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.