A Structured Approach to Justify SIS Project Investments
CCPS Latin American Conference on Process Safety
2009
2nd Latin American Process Safety Conference and Expo
2nd Latin American Process Safety Conference and Expo
Safety Instrumented Systems
In spite of all requirements stated in the international standards concerning Safety in the
Process industry, it is still a challenge for engineers to justify investments in Safety Instrumented
Systems, mainly during the enterprise initial phases.
Some operator companies prefer for new facilities a fixed price supply contract. So, in the
bidding process and for budget matters, a pre-defined SIS solution must be defined sometimes
even before the process conceptual design is well defined: failure rates and probabilities (i.e.
PFDs) are released but P&IDs are not. This pre-defined SIS design provides an equal basis for all
the contractors participating in the bidding process, all of them looking for the contract.
Questions are:
1. What if pre-defined SIS design is below real safety requirements?
2. What if pre-defined SIS design is above real safety requirements?
This paper will provide an overview of the factors impacting costs during the different
phases of a Safety Project and the opportunities experienced by some of our customers. Some
basic numbers will be presented for projects where the basic engineering, mainly for bidding
purposes, has pre-designed the SIS with some redundancy level, like dual valves (1oo2) and triple
(2oo3) sensors. After the PHA / SIL Selection / Conceptual SIS design (SIL verification), client
sometimes takes the decision of simplify design and/or reduce redundancy in safety
instrumentation. In other cases, these SIS design simplifications have been done sometimes by the
contractor (less equipment to supply in a fixed price project), and sometimes by the final user
(larger proof test intervals, less equipment to maintain and/or less spurious trips).
By means of actual examples, where the customers name will be suppressed for
confidentiality matters, it will be presented the pros and cons of some applications, using an
innovative and integrated method of analysis that shows in numbers the benefits of SIS
management systems.