Assessment Of Safety-critical Systems Research Articles

A model-based system engineering approach to manage railway safety-related decisions

The safety assessment of Safety Critical Systems (SCSs) is a challenging task since it involves different actors and a combination of several knowledge domains. This increases the complexity of the integration of safety requirements into the design model. Consequently, there is a need for a shared model with an unambiguous terminology aiming to avoid misunderstandings between both safety and design teams. In this paper, we propose a model-based system engineering approach in order to support the goal-oriented safety reasoning and to provide a common model between both safety and requirement engineering driven by goals. Furthermore, the present study considers the safety rules development process based on the Organization-based Access Control (Or-BAC) model, which is normally used to improve the security of the information systems. Then, the common vocabulary proposed for the inter- pretation of the considered notions of domains is defined. Moreover, safety requirements are expressed with a high level of abstraction according to the required railway knowledge and the requirement trace- ability process is considered through an up-bottom reasoning using the Unified Modeling Language (UML) diagrams. The proposed approach aims to provide a methodology able to identify safety conditions in order to anticipate risks and to make better safety-related decisions. Finally, the proposed methodology is evaluated through a real accident scenario analysis in order to validate its adaptability to represent real critical situations.

Availability Assessment of IMA System Based on Model-Based Safety Analysis Using AltaRica 3.0

The integrated modular avionics (IMA) system is widely used in all classes of aircraft as a result of its high functional integration and resource utilization in developing advanced avionics systems. However, a series of challenges related to safety assessment exist in the background of the logical architecture for multi-message interactions of the IMA system. Traditional safety assessment methods are mainly based on engineering experience, and are difficult to reuse, incomplete, and even error-prone. Here we propose a method to assess the availability of the IMA system based on the thinking of model-based safety analysis. To aid the proposed method, we implement a tool to generate a AltaRica 3.0 file used to assess the IMA system model. The simulation results show that the proposed method makes the availability assessment fast, efficient, and effective. Moreover, we apply this method to the modification analysis of the IMA system under the condition of satisfying the safety requirement. Our study can enhance the safety assessment of safety-critical systems effectively, assist the design of IMA systems, and reduce the amount of errors during the programming process of the safety model.

Dynamic availability assessment of safety critical systems using a dynamic Bayesian network

Availability analysis of safety critical systems is an integral part of ensuring safety both in onshore and offshore process operations. However, the availability assessment of these systems is complex due to their multistate failure scenarios (dormant failure and failure on demand) and multistate functionality (operational failure). In the present study, a dynamic Bayesian network (DBN)-based dynamic availability assessment technique is proposed. This approach offers much flexibility in representing different failure scenarios and the interdependence of failure causes. Sensitivity and importance analyses have also been performed to identify the most influential failure causes. This helps to design better management strategies and provides more realistic reliance on safety critical systems. Applications of the proposed methodology are demonstrated on two safety critical systems: a fire alarm system and a hazard scenario in a steam generation system. This methodology will offer a pivotal step forward in dynamic safety analysis.

Dependability Metrics to Assess Safety-Critical Systems

Metrics are commonly used in engineering as measures of the performance of a system for a given attribute. For instance, in the assessment of fault tolerant systems, metrics such as the reliability, R(t) and the Mean Time To Failure (MTTF) are well-accepted as a means to quantify the fault tolerant attributes of a system with an associated failure rate, /spl lambda/. Unfortunately, there does not seem to be a consensus on comparable metrics to use in the assessment of safety-critical systems. The objective of this paper is to develop two metrics that can be used in the assessment of safety-critical systems, the steady-state safety, S/sub ss/, and the Mean Time To Unsafe Failure (MTTUF). S/sub ss/ represents the evaluation of the safety as a function of time, in the limiting case as time approaches infinity. The MTTUF represents the average or mean time that a system will operate safely before a failure that produces an unsafe system state. A 3-state Markov model is used to model a safety-critical system with the transition rates computed as a function of the system coverage C/sub sys/, and the hazard rate /spl lambda/(t). Also, /spl lambda/(t) is defined by the Weibull distribution, primarily because it allows one to easily represent the scenarios where the failure rate is increasing, decreasing, and constant. The results of the paper demonstrate that conservative estimates for lower bounds for both S/sub ss/ & the MTTUF result when C/sub sys/ is assumed to be a constant regardless of the behavior of /spl lambda/(t). The derived results are then used to evaluate three example systems.

Tool Support for Implementation and Analysis of Traceability Structures

AbstractTraceability has become established as a key subject of requirements engineering research. Our research has resulted in the proposal of information structures to record information in support of the early stages of the software development process, and the establishment of a traceability procedure for the development and assessment of safety critical systems. For this procedure to be feasible for large‐scale systems, there is a need to represent, structure and analyse the consistency and completeness of large amounts of disparate information. It is thus essential to provide adequate tool support. In this paper we address automation of the basic activities of the procedure, and investigate some candidate tools which can provide some or all of the features required by automation.

Assessing dependability of safety critical systems using diverse evidence

A primary objective of the DATUM (Dependability Assessment of safety critical systems Through the Unification of Measurable evidence) project was to improve the way dependability of software intensive safety-critical systems was assessed. The authors' hypothesis was that improvements were possible if multiple types of evidence could be incorporated. To achieve the objective, the authors had to investigate how to obtain improved dependability predictions given certain specific information over and above failure data alone. A framework for modelling uncertainty and combining diverse evidence was provided in such a way that it could be used to represent an entire argument about a system's dependability. The various methods and technologies for modelling uncertainty were examined in depth and a Bayesian approach was selected as the most appropriate method. To implement this approach for combining evidence, Bayesian Belief Networks (BBNs) were used. With the help of a BBN tool, a framework for dependability assessment was provided that met the original objective and which was subsequently proved to be practical and highly popular. A major benefit of this approach was that otherwise hidden assumptions used in an assessment become visible and auditable.

Knowledge engineering in the communication of Information for safety critical systems

The design and assessment of safety critical systems often involves broad and distributed teams of designers, suppliers and analysts who represent diverse areas of expertise and motivations. Accurate and effective communication between these groups is therefore an issue of primary importance. The formalisation of specifications and arguments of safety can be of significant benefit in ensuring the consistency of evidence in such cases, when it must be presented across many domains. However, a formal description of a safety critical system may be unconvincing unless it is presented in a form which is (or forms which are) accessible to the broad range of users and assessors of safety cases. This raises issues of human communication which include the tailoring of information to particular communicative tasks; the efficacy of differing media for communication and the cognitive impact that such differing media have. This paper draws together work in fields of knowledge engineering, knowledge based systems and human communication in an effort to address, from a sound theoretical basis, these and other communication issues raised by the use of formal descriptions in safety critical systems. Further, this paper argues that a primary role for knowledge based systems techniques in safety critical systems is in supporting the communication of information.

Technology and assessment of safety‐critical systems. Felix Redmill and Tom Anderson (Eds), Published by Springer‐Verlag, London, U.K., 1994. ISBN 3‐540‐19859‐8, 257 pages. Price: £35.00, soft cover

Software Testing, Verification and ReliabilityVolume 5, Issue 2 p. 133-133 Book and Journal ReviewFree Access Technology and assessment of safety-critical systems. Felix Redmill and Tom Anderson (Eds), Published by Springer-Verlag, London, U.K., 1994. ISBN 3-540-19859-8, 257 pages. Price: £35.00, soft cover First published: 1995 https://doi.org/10.1002/stvr.4370050208AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onEmailFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume5, Issue21995Pages 133-133 RelatedInformation

The role of mathematically formal methods in the development and assessment of safety-critical systems

Programmable systems are being used in an increasing number of applications where their failure may endanger life. Concern over the correctness of the software in these systems is making both suppliers and customers turn towards mathematically formal methods for software production. This paper provides an introduction to formal methods, including an outline of some of the most mature methods, and discusses some pertinent industrial experience.

Progress in the use of automatic flight controls in safety critical applications

High authority automatic flight control systems are now in wide use in both transport and combat aircraft. These have required the development of failure survival system architectures, and techniques in safety assessment to ensure that the risk of fatal accidents attributable to the automatic control aspect is acceptably remote.Most of the current systems are analogue in nature, and employ sufficient redundancy to survive at least one failure during operation. Future systems will employ quadruplex or triplex-monitored architectures, capable of surviving at least two failures, and will be mainly digital in concept. The design and safety assessment techniques developed for analogue systems have been adequate for current systems, but the new digital technology and more extensive use of systems in safety critical applications will demand further development of the various aspects involved.A major contribution to the design and safety assessment of safety critical systems was made during the past two decades in the programmes for the development of automatic landing for civil aircraft, culminating in the system in the Anglo-French Concorde.