EN 50126-2 EUROPEANSTANDARD NORME EUROPEENNE EUROPAISCHE NORM October2017 ICS 45.020 Supersedes CLC/TR 50126-2:2007 English Version Railway Applications - The Specification and Demonstration of Reliability, Availability, Maintainability and Safety (RAMS) - Part 2: Systems Approach to Safety Applicationsferroviaires-Spéecificationetdémonstrationde Bahnanwendungen - Spezifikation und Nachweis von la fiabilite, de la disponibilite, de la maintenabilite et de la Zuverlassigkeit, Verfugbarkeit, Instandhaltbarkeit und sécurite (FDMS) - Partie 2: Approche systematique pour la Sicherheit (RAMS) - Teil 2: Systembezogene sécurite Sicherheitsmethodik This European Standard was approved by CENELEC on 2017-07-03. CENELEC members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CENELEC member. This European Standard exists in three official versions (English, French, German). A version in any other language made by translation under the responsibility of a CENELEC member into its own language and notified to the CEN-CENELEC Management Centre has the samestatus as the official versions. CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Croatia, Cyprus, the Czech Republic, Denmark, Estonia, Finland,Former Yugoslav Republic of Macedonia, France, Germany,Greece, Hungary,Iceland, Ireland, Italy, Latvia, Switzerland, Turkey and the United Kingdom. CENELEC European Committee for Electrotechnical Standardization Comite Europeen de Normalisation Electrotechnique Europaisches Komitee fuir Elektrotechnische Normung CEN-CENELEC Management Centre: Avenue Marnix 17, B-1000 Brussels 2017 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members. Ref.No.EN50126-2:2017E EN50126-2:2017 (E) Contents Page European foreword 5 Introductior 6 Scope 2 Normative references. 3 Terms and definitions 4 Abbreviations. 5 Safety process.. 5.1 Risk assessment and hazard control... 5.2 A. Risk assessment. 10 5.2.1 General 5.2.2 Conducting risk assessment 11 5.3 B. Outcome of the risk assessment. 5.4 C. Hazard control 5.5 D. Revision of risk assessment 12 5.6 Responsibilities ....... 13 6 Safety demonstration and acceptance . 13 6.1 Introduction.. 13 6.2 Safety demonstration and safety acceptance process.. 13 6.3 Responsibility in managing the Safety Case 17 6.4 Modifications after safety acceptance . 17 6.5 Dependencies between Safety Cases .. 17 6.6 Relationship between safety cases and system architecture . 7 Organisation and Independence of Roles.. 19 7.1 General .. 7.2 Early phases of the lifecycle (phases 1 to 4). 19 7.3 Later phases of the lifecycle (starting from phase 5).. .20 7.4 Personnel Competence.. 21 8 Risk assessment. 22 8.1 Introduction 22 8.2 Risk Analysis . 22 8.2.1 General .22 8.2.2 The risk model. 8.2.3 Techniques for the consequence analysis. 8.2.4 Expert Judgement.... .25 8.3 Risk acceptance principles and risk evaluation .25 8.3.1 Use of Code of Practice ... .25 8.3.2 Use of a reference system .. .26 8.3.3 Use of Explicit Risk Estimation... .27 8.4 Application of explicit risk estimation 28 8.4.1 Quantitative approach...... .28 8.4.2 Variability using quantitative risk estimates.. 30 8.4.3 Qualitative and semi-quantitative approaches 31 2 EN 50126-2:2017 (E) 9 Specification of System Safety Requirements . .32 9.1 General ... .32 9.2 Safety requirements . .32 9.3 Categorization of Safety Requirements.... .32 9.3.1 General .... .32 9.3.2 Functional safety requirements .33 9.3.3 Technical safety requirements ... 9.3.4 Contextual safety requirements..... 10 Apportionment of functional Safety Integrity requirements... .35 10.1 Deriving and apportioning system safety requireme