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

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

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

On the basis of the previous considerations 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

COMPARISON OF NFPA AND ISO METHODOLOGIES Database Sandia database Components release frequencies Bayesian analysis Linear versions (on a log-log plot) of the values generated by Sandia National Laboratories ? (www.hydrogensafety.info/2010/aug/separationDistances.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/year 10-5/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 area always smaller, it varies according to the type of system that is considered ? 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) ICHS 2011 - San Francisco, USA - September 12 -14

COMPARISON OF NFPA AND ISO METHODOLOGIES DIFFERENT CONSIDERATIONS REQUIREMENTS NFPA3 ISO2 RISK INFORMED RISK BASED Statistical Analysis Accident Scenarios Risk Criterion Uncertainties Parametric Assumption SAME METHODOLOGY BUT DIFFERENT LEAK SIZES CONSIDERED DIFFERENT CONSIDERATIONS ICHS 2011 - San Francisco, USA - September 12 -14

CHOISE OF LEAK DIAMETER NFPA ISO UNIVERSITY 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 ICHS 2011 - San Francisco, USA - September 12 -14

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 Medium leaks Major leaks Ruptures 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

to prevent escalation and protect targets from great releases (NFPA) 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 targets from more probable small releases (ISO) to prevent escalation and protect targets from great releases (NFPA) or ICHS 2011 - San Francisco, USA - September 12 -14

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

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