An Exact Formula for the Hazardous Event Frequency

The remaining risk of safety-instrumented systems is an important non-functional requirement that is regulated by international standards. Several ways towards computing the safety as a function of its relevant design parameters have been studied in the literature. However, the standard approach onl...

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Bibliographic Details
Published in2024 Annual Reliability and Maintainability Symposium (RAMS) pp. 1 - 6
Main Authors Zimmermann, Armin, Hildebrandt, Andreas
Format Conference Proceeding
LanguageEnglish
Published IEEE 22.01.2024
Subjects
Fault Tolerance
Hazardous Event Frequency
Maintenance engineering
Phase frequency detectors
Probability of Failure on Demand
Random access memory
Reliability
Safety
Safety-Critical Systems
Safety-Instrumented System
Stochastic processes
Taylor series
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Summary:The remaining risk of safety-instrumented systems is an important non-functional requirement that is regulated by international standards. Several ways towards computing the safety as a function of its relevant design parameters have been studied in the literature. However, the standard approach only covers two special cases of high or low demand, which simplify the treatment by either ignoring the effects of demand rate or test interval on the safety. More detailed treatments in the literature derive Markov models, which can be numerically analyzed, or approximate solutions using Taylor series expansions etc. This paper introduces closed-form exact formulas for the average probability of failure on demand (PFD) and the resulting hazardous event frequency (HEF, or accident rate), taking into account demand rate and test interval. It integrates all cases of low, high and medium demand in one formula. The derivation is based on an analysis of the cyclostationary semi-Markov stochastic process of the safety-integrated system and its symbolic transient analysis over the test interval.
ISSN:2577-0993
DOI:10.1109/RAMS51492.2024.10457804