NR NR/L2/SIG/11201/MODA09 ISSUE 4 PDF

Introduction

Some type of risk assessment to demonstrate functional safety should be used whenever departure from a Network Rail company standard is proposed. The degree of detail in the analysis should reflect the degree of departure from the standard and the level of risk involved.

It should be demonstrated that any hazards identified present an acceptable risk to passengers, public or employees. Mitigation measures shall be implemented for those hazards which present an unacceptable risk.

Similar risk assessments may also be performed where it is desired to improve the reliability, availability, maintainability or safety of an existing system or element.

It is generally simpler to analyse the system at signalling function level (i.e. signals, points, level crossings, etc.), but, where justified by the risk, a safety analysis at component level (such as relays and contacts) may be appropriate.