EN 50126-2:2017+A1 EUROPEANSTANDARD NORMEEUROPEENNE EUROPAISCHE NORM November 2024 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 Applications ferroviaires - Specification et demonstration de Bahnanwendungen - Spezifikation und Nachweis von ia fiabilite, de la disponibilité, de la maintenabilite et de la Zuverlassigkeit, Verfugbarkeit, Instandhaltbarkeit und sécurite (FDMS) -Partie 2: Approche systematique pour la Sicherheit (RAMS) - Teil 2: Systembezogene sécurité 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 ManagementCentreortoanyCENELEC member. This European Standard exists in three official versions (English, French, German). A version in any other language made by translation same status 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, Itaiy, Latvia, Lithuania,Luxembourg,Malta, the Netherlands,Norway,Poland, Portugal,Romania, Serbia, Slovakia, Slovenia,Spain,Sweden, Switzerland, Turkey and the United Kingdom. CENELEC European Committee for Electrotechnical Standardization Comité Europeen de Normalisation Electrotechnique Europaisches Komitee fir 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. EN 50126-2:2017 E EN 50126-2:2017+A1:2024 (E) Contents Page European foreword 5 European foreword to Amendment 1 .5 Introduction. 6 Scope. 2 Normative references. 8 3 Terms and definitions 4 Abbreviations.. 8 5 Safety process.. 9 5.1 Risk assessment and hazard control. 9 5.2 A. Risk assessment. 10 5.2.1 General 10 5.2.2 Conducting risk assessment 11 5.3 B. Outcome of the risk assessment. 11 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 . Organisation and Independence of Roles. 19 7 7.1 General.. 19 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 Risk assessment. .22 8.1 Introduction 8.2 Risk Analysis. .22 8.2.1 General .22 8.2.2 The risk model. . 22 8.2.3 Techniques for the consequence analysis .24 8.2.4 Expert Judgement.. .25 8.3 Risk acceptance principles and risk evaluation, .25 8.3.1 Use of Code of Practice ... 8.3.2 Use of a reference system . 8.3.3 Use of Explicit Risk Estimation.. 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+A1:2024 (E) 9 Specification of System Safety Requirements 9.1 General ... .32 9.2 Safety requirements ... .32 9.3 Categorization of Safety Requirements. .32 9.3.1 General ...... 9.3.2 Functional safety requirements . ..33 9.3.3 Technical safety requirements .. ..34 9.3.4 Contextual safety requirements... .34 10 Apportionment of functional Safety Integrity requir