Safety Instrumented Function (SIF) design is based on performance requirements. During design, assumptions concerning SIF equipment failure rates, SIF demand rates, proof test frequencies, mission time are made. These form the basis for the expected performance.
Are those assumptions realistic? Is the SIF really operating as assumed?
IEC 61511 expects users to periodically compare actual performance with assumed performance. How do we do that? What is needed to get statistically viable results from the collected data? How does the data apply? How do we make sure we avoid drawing unrealistic conclusions?
This presentation will look at answers to these questions.
Presented at the Hazards35 Process Safety Conference in Birmingham, UK (Nov 2025).
Iwan van Beurden, CFSE is the Chief Technology Officer, Director of Product Development at exida. He supports exida’s end-user services, exida’s manufacturer services, and exida certification activities. He has over 20 years of professional experience in the Functional Safety field. Mr. van Beurden is responsible for the development, maintenance, and certification of the exSILentia® integrated Safety Lifecycle tool and associated products. Mr. van Beurden also performs IEC 61508 development support, Functional Safety Assessments, and a variety of reliability analyses. He supports all safety lifecycle tasks, ranging from the Process Hazard Analysis, Layer of Protection Analysis, SIL Selections, and SIL Verifications, to proof test specification and operational event recording. Mr. van Beurden also performs process gap analyses to determine the level of effort companies need to undertake for compliance with IEC 61508 or IEC 61511. He gives training for exida and is also an ISA fellow and instructor.
Mr. van Beurden previously worked for Yokogawa Industrial Safety Systems in Apeldoorn, the Netherlands. He worked both in the R&D and in the Operations department as a Safety Assessment specialist. He was involved with the implementation of IEC 61508 within Yokogawa Industrial Safety Systems dealing with SIS reliability calculations and the safety education of engineers. Mr. van Beurden is a Certified Functional Safety Expert (CFSE) and a member of ISA. He has published various papers and magazine articles. He holds a Master of Science degree from Eindhoven University of Technology in Eindhoven, the Netherlands, where he majored in reliability engineering and graduated cum laude.