Abstract :
SIL is a concept - it is not a tangible property that can be measured scientifically - on its own, it proves nothing. Simply fulfilling a certain set of SIL requirements does not mean that the related function is safe. Is it an assessment or just reverse engineering? Most railway signalling equipment either reuses existing principles, or code, or both. Most “Statements of Compliance” to EN50128 are retrospective. The code exists, we did it that way. “What is a function?” - or “When is a function not a function?”.
