RISK ACCEPTABILITY CRITERIA FOR RAILWAYS

1. 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 PSAM6, San Juan, Puerto Rico, USA - June 2002

2. RISK ACCEPTABILITY CRITERIA FOR RAILWAYS • Introduction Railways involve risks that have to be reduced to an acceptable level CENELEC Standards propose principles for determining acceptability do not specify acceptance criteria Railway administrations define criteria for risk acceptance Need a comprehensible definition of "risk" Then the criteria can be determined PSAM6, San Juan, Puerto Rico, USA - June 2002

3. 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 PSAM6, San Juan, Puerto Rico, USA - June 2002

4. 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 PSAM6, San Juan, Puerto Rico, USA - June 2002

5. 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 PSAM6, San Juan, Puerto Rico, USA - June 2002

6. 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" PSAM6, San Juan, Puerto Rico, USA - June 2002

7. 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 PSAM6, San Juan, Puerto Rico, USA - June 2002