1. 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 San Francisco, USA - September

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 San Francisco, USA - September

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 “ 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 San Francisco, USA - September

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 )
ISO (ISO/DIS 20100): the same definition of EIGA
NFPA 2 NO DEFINITION but refers to SANDIA report
ICHS San Francisco, USA - September

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-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 San Francisco, USA - September

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 San Francisco, USA - September

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 San Francisco, USA - September

8. 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 San Francisco, USA - September

9. 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 ? (
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 San Francisco, USA - September

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 ? (
ICHS San Francisco, USA - September

11. 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 San Francisco, USA - September

12. 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 San Francisco, USA - September

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
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 San Francisco, USA - September

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 San Francisco, USA - September

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

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 San Francisco, USA - September