Hazard and risk analysis of railway vehicle control systems according to safety integrity levels

This article presents an approach to the verification of the safety integrity level (SIL) of rail vehicle subassemblies in accordance with the applicable railway standards PN-EN ISO 50126-1, PN-EN ISO 50126:2, and PN-EN ISO 50129. Particular attention has been given to the calculation procedure related to the determination of the tolerable hazard rate and tolerable functional failure rate indicators in a situation where various reliability indicators have been declared for components of rail vehicles, such as MTTFD or B10D. In this case, the verification of the safety integrity level using the above mentioned railway standards may be difficult, and it becomes necessary to use additional standards for safety systems based on electronic components. An example is the PN-EN ISO 13849-1:2006-01 standard, which contains a calculation method based on the transformation of the exponential model, which is useful for hazard and risk analyses of electronic systems containing components with different reliability indices. Another supplementary standard is the PN-EN 61025:2007 standard, which concerns fault tree analysis. Based on the above-mentioned standards, an algorithm was developed to verify the safety integrity level of the frequency converter control system. The obtained results allowed us to confirm the fulfillment of the functional safety requirements of the considered system.