Safety rules evolution, introducing UNI EN 13849-1(PL) and CEI EN 62061(SIL) machines norm, has fixed a new approach to the fail-safe functionality design both in the building of new plants and in the update of existing plants. TECHCAB S.R.L. practices with particular interest that evolution, along with the implications that followed. The design method proposed by the new norms unfolds through an iterative process shared between the parts (been them machines manufacturers or plants final users).

Identification of the dangers: in this first step has to be identified the characteristics for any safety function.

Fix the performance level requested (PLr): PLr parameter represents the performance level requested for a specific safety function, higher is the risk, larger has to be the control system safety requirement.

Fix the single safety function: after valued the PLr, it takes to design the control system by following the right standard, then calculate the resultant PL which has to be greater or equal to PLr.