It is estimated that about 66% of the Programmable Electronic Systems (PES) running in the process
industry were installed before the publication of today’s commonly used safety standards (IEC 61508
and IEC 61511/ISA 84)
Some of those safety systems, particularly the ones installed between the late 1980’s and early 2000,
1. General‐purpose PLCs,
2. Not designed or certified according to the IEC 61508,
3. Might not satisfy current requirements on IEC 61508
In some cases they were not implemented according to ISA84 or IEC 61511.
This whitepaper covers the changes in the safety standards affecting those systems, a follow up
whitepaper will address the safety life cycle activities involved in modifying or decommissioning an
existing system to install certified Safety Systems according to today’s standards.