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2. PSAM6, San Juan, Puerto Rico, USA - June 2002. RISK ACCEPTABILITY CRITERIA FOR RAILWAYS. IntroductionRailways involve risks that have to be reduced to an acceptable levelCENELEC Standardspropose principles for determining acceptabilitydo not specify acceptance criteriaRailway administrations define criteria for risk acceptanceNeed a comprehensible definition of "risk"Then the criteria can be determined.
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1. 1 PSAM6, San Juan, Puerto Rico, USA - June 2002 RISK ACCEPTABILITY CRITERIA FOR RAILWAYS
Odd Nordland
SINTEF, Trondheim, Norway
odd.nordland@sintef.no
Frank Renpenning
SIEMENS Transportation Systems, Brunswick, Germany
frank.renpenning@siemens.com
2. 2 PSAM6, San Juan, Puerto Rico, USA - June 2002
3. 3 PSAM6, San Juan, Puerto Rico, USA - June 2002 RISK ACCEPTABILITY CRITERIA FOR RAILWAYS Risk measurement
Risk is defined differently in different standards
risk = probability x consequences
Which consequences?
For railways: harm to passengers
Collective risk vs. individual risk
Collective risk: number of victims per year
absolute values
will increase with traffic increase
Individual risk: accident probability per person and year
relative values
more practical to use
4. 4 PSAM6, San Juan, Puerto Rico, USA - June 2002 RISK ACCEPTABILITY CRITERIA FOR RAILWAYS Risk acceptance principles
ALARP (UK)
As Low As Reasonably Practicable
reduce unacceptable risks to acceptable level
effort ("price") must be reasonable and practicable
GAMAB (FR)
Globalement Au Moins Aussi Bon (globally at least as good)
allows for trade-offs
similar to ALARP
MEM (DE)
Minimum Endogenous Mortality
objective principle, but risk is subjective
controversial, difficult to apply
5. 5 PSAM6, San Juan, Puerto Rico, USA - June 2002 RISK ACCEPTABILITY CRITERIA FOR RAILWAYS Risk Acceptance Criteria (1)
Norway:
start with tolerable hazard rates (THR) for SIL4 according to standards
total hazard depends on equipment types and quantities, deployment profiles, traffic density etc.
apply ALARP with THR as boundary between unacceptable and acceptable
Sweden:
not more than 1 hazardous event per 100 years in the railway network
must new equipment compensate for old equipment?
for calculations, assume identical equipment everywhere
effectively an application of GAMAB
6. 6 PSAM6, San Juan, Puerto Rico, USA - June 2002 RISK ACCEPTABILITY CRITERIA FOR RAILWAYS Risk Acceptance Criteria (2)
Germany
Apply "accepted rules of engineering practice" or
if not, show that the same safety level has been achieved
Effectively an application of GAMAB
"German" MEM is controversial
UK
ALARP is used
relates acceptability to necessary effort
effort is expressed with "Value of Preventing a Fatality"
"ALARP is a philosophy for continuous improvement"
Must be supplemented with "good practice"
7. 7 PSAM6, San Juan, Puerto Rico, USA - June 2002 RISK ACCEPTABILITY CRITERIA FOR RAILWAYS Conclusions
There is no set of generally accepted risk acceptance principles
Harmonisation is necessary for interoperability
difficult, because risk acceptance is a political question
Standards propose principles
leave the details to the legislative bodies
MEM is not generally accepted
GAMAB appears to be most widespread
results are not uniform
ALARP has greatest potential to bring improvements