In the context of hardware safety integrity, the highest safety integrity level that can be
claimed for a safety function is limited by the hardware safety integrity constraints which shall
be achieved by implementing one of two possible routes (to be implemented at system or subsystem level):
– Route 1H based on hardware fault tolerance and safe failure fraction concepts; or,
– Route 2H based on component reliability data from feedback from end users, increased
confidence levels and hardware fault tolerance for specified safety integrity levels.
Application standards based on the IEC 61508 series may indicate the preferred Route (i.e.
Route 1H or Route 2H).
The “H” subscript in the above routes designates hardware safety integrity to distinguish it from Route 1S, Route 2S and Route 3S for systematic safety integrity.