Fail-Safe Design

Software Design
3 February 2017
3 February 2017

The evolution of safety standards, with the introduction of UNI EN 13849-1 (PL) and CEI EN 62061 (SIL) in the machinery regulations, has introduced a new approach to the design of fail-safe functions, both during the construction of new plants and the updating of existing ones. TECHCAB S.R.L. has followed these developments with keen interest, together with the resulting implications. The design method proposed by the new standards unfolds through an iterative process shared with the stakeholders, whether they are machine manufacturers or plant end users.


Identify the hazards on the machine: during this phase, the characteristics for each safety function are established.


Establish the required Performance Level (PLr): the PLr parameter represents the required performance level for a given safety function. The greater the risk, the higher the safety requirement of the control system needs to be.


Define the methods for implementing the individual safety functions: once the PLr has been estimated, the control system must be designed following criteria that require compliance with this evaluation. The resulting PL is calculated, checking that it is greater than or equal to the PLr.