(123a) Decoding SIS: Are You Doing What’s Necessary to Prevent Disasters?

When your facility is tasked with becoming compliant with industry safety standards, where do you start? If you are assigned to support a process that involves a safety instrumented system (SIS) or installing an SIS for the first time, what does that entail? How are you supposed to know what all those SIS acronyms mean? For professionals working under OSHA 29 CFR 1910.119 PSM-covered facilities, there is a whole safety lifecycle to learn about and adhere to.

What could be hiding under the radar of a plant SIS? Risk assessments define hazard scenarios with known initiating event frequencies. How do we prevent these hazard consequences? By verifying the reliability and availability assumptions of our SIL Verification design parameters. Without proper understanding of what assumptions your SIS risk mitigation is based upon, or without proper maintenance of your SIS equipment, your hazard and risk assessment gap closure may be invalidated.

Do you know what factors into the assumptions of an SIS design?

• Are your safety devices being replaced at their specified asset life?
• Are your safety devices being tested at the interval specified in your calculations?
• Are your safety devices being tested with the necessary rigor to uncover dangerous failures as specified in your calculations?

Do you know what following the Functional Safety Lifecycle entails?

• Does your facility have a Functional Safety Management Plan?
• Do you perform Functional Safety Assessments on your SIS Design?
• Does your facility keep records of all device failures to evaluate performance of the safety devices against the assumed reliability?

This paper will illustrate the very real consequences which can result from failing to uphold SIS design assumptions or follow the Functional Safety Lifecycle.