Abstract
Objective safety assessments by ISA (Independent Safety Assessor) in agreement with international standards including concepts of SIL, RAMS, etc., are required for guided transportation systems (e.g., railways) intended for overseas expansion from Japan. In this paper, a study on standard safety assessment methods which are internationally acceptable is reported. IEC 62425 (Safety Case) and IEC 62278 (RAMS) were selected as preferred international standards with which the standard assessment methods of this study were required to be in conformity. As an ISA, NTSEL has been carrying out many safety assessments and confirming that the probability of seriously dangerous events is sufficiently low. The assessment criteria used to be the equivalent of the excellent safety achievements of Japanese railways or higher, but recently, numerical criteria, such as SIL4, are employed. Application of FMEA and FTA is recommended by IEC 62425, and procedures of FMEA and FTA are described in IEC 60812 and IEC 61025 respectively. Such descriptions about FMEA and FTA in these international standards match with NTSEL's traditional safety assessment methods, and, therefore, these NTSEL's methods will continue to be adopted. As stated above, a basic structure of standard ISA's safety assessment reports has been presented.
