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Evaluation of uncertainty in safety integrity level calculations
- Source :
- Process Safety Progress. 35:341-348
- Publication Year :
- 2016
- Publisher :
- Wiley, 2016.
-
Abstract
- The evaluation of the safety integrity level (SIL) of a new or existing safety instrumented system (SIS) requires detailed calculations based on the failure rates of the device and the planned maintenance-testing cycle for the system. The failure rates of the devices are taken from standard failure rate tabulations of equipment. The maintenance and testing plans are developed based on plant experience. The quantitative evaluation determines the probability of failure on demand (PFD) for a demand mode SIS and yields the SIL of the SIS. All of the data used in the SIL calculations are uncertain. This article explores the impact of uncertainty on the PFD calculation for a SIS. The “70%” rule of thumb from IEC 61508 is compared to results obtained using probability theory such as variance contribution analysis (VCA). A proposed methodology for handling the uncertainty in the PFD calculations is presented based on the application of the VCA method. An example is worked to demonstrate the methodology. © 2016 American Institute of Chemical Engineers Process Saf Prog 35: 341–348, 2016
- Subjects :
- 021110 strategic, defence & security studies
Engineering
Process (engineering)
business.industry
General Chemical Engineering
0211 other engineering and technologies
Mode (statistics)
Failure rate
IEC 61508
02 engineering and technology
Variance (accounting)
Rule of thumb
Reliability engineering
020401 chemical engineering
Probability theory
Safety instrumented system
0204 chemical engineering
Safety, Risk, Reliability and Quality
business
Subjects
Details
- ISSN :
- 10668527
- Volume :
- 35
- Database :
- OpenAIRE
- Journal :
- Process Safety Progress
- Accession number :
- edsair.doi...........8b078d3d39eb82d504d6001eb5d426e9