A Novel Method for Safety Analysis of Cyber-Physical Systems—Application to a Ship Exhaust Gas Scrubber System

Victor Bolbot,George Psarros,Rainer Hamann,Gerasimos Theotokatos,Evangelos Boulougouris

doi:10.3390/safety6020026

Victor Bolbot, George Psarros + Show 3 more

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https://doi.org/10.3390/safety6020026

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Abstract

Cyber-Physical Systems (CPSs) represent a systems category developed and promoted in the maritime industry to automate functions and system operations. In this study, a novel Combinatorial Approach for Safety Analysis is presented, which addresses the traditional safety methods’ limitations by integrating System Theoretic Process Analysis (STPA), Events Sequence Identification (ETI) and Fault Tree Analysis (FTA). The developed method results in the development of a detailed Fault Tree that captures the effects of both the physical components/subsystems and the software functions’ failures. The quantitative step of the method employs the components’ failure rates to calculate the top event failure rate along with importance metrics for identifying the most critical components/functions. This method is implemented for an exhaust gas open loop scrubber system safety analysis to estimate its failure rate and identify critical failures considering the baseline system configuration as well as various alternatives with advanced functions for monitoring and diagnostics. The results demonstrate that configurations with SOx sensor continuous monitoring or scrubber unit failure diagnosis/prognosis lead to significantly lower failure rate. Based on the analysis results, the advantages/disadvantages of the novel method are also discussed. This study also provides insights for better safety analysis of the CPSs.

Highlights

Cyber-Physical Systems (CPSs) represent a class of systems advancing in a number of application areas including the maritime industry [1]
The present study aims at developing a new, more effective and inclusive safety analysis method for the CPSs, with focus on Industrial and automation Control Systems (ICS), which supports the implementation of quantitative safety analysis
The analysis in the CASA method subsequent steps will focus on the environmental pollution [A-3] and on [H-5] (Exhaust gas not complying with regulatory requirements.), as this study scope is to demonstrate the functionality of the CASA method

Summary

Introduction

Cyber-Physical Systems (CPSs) represent a class of systems advancing in a number of application areas including the maritime industry [1]. Typical examples of the CPSs include the Industrial and automation Control Systems (ICS), robots, and Cyber-Physical Systems of Systems [4]. Whilst CPSs are expected to bring significant benefits, they are considered to be complex, which implies that they may behave unpredictably [4,5,6]. Their complexity can be attributed to a number of Safety 2020, 6, 26; doi:10.3390/safety6020026 www.mdpi.com/journal/safety

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