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

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 DETERMINATIONM. Vanuzzo, M. Carcassi.

Dipartimento di Ingegneria Meccanica, Dipartimento di Ingegneria Meccanica, Nucleare e della Produzione (DIMNP),Nucleare e della Produzione (DIMNP),

University of PisaUniversity of Pisa

Università di Pisa



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



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)



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



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



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..)



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



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



COMPARISON OF NFPA AND ISO METHODOLOGIES

NFPA ISO

Database Sandia 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

?



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)



COMPARISON OF NFPA AND ISO METHODOLOGIES

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



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

NOTABLYDIFFERENT



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)

Leakag

e Freq

uen

cy (/yr)

3% considered by NFPA

RupturesMajor leaksMedium leaksMinor leaks

{0.10% - 1% Range considers by ISO

GAP?



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 ?


THANK YOU.

Contact Author:

Matteo Vanuzzo (UNIPI-ITALY)

[email protected]

Presented by:

Marco Carcassi (UNIPI-ITALY)

[email protected]



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.

Documents

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