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  • RAMS and Fault Tree Analysis

    Nadine Cranenburgh


    RAMS (Reliability, Availability, Maintainability, Safety) is a management process used to avoid failures during the planning stage of projects. RAMS Management ensures that systems are defined, risk analyses are performed, hazards are identified and detailed reviews and safety cases are executed and reported. One specific goal is to provide hard evidence to achieve authorisation for operations.

    These terms can be summarised as follows:

    • Reliability – as ability to perform a specific function and may be assessed as design reliability or operational reliability
    • Availability – as ability to keep a functioning state in the given environment
    • Maintainability – as ability to be timely and easily maintained (including servicing, inspection and check, repair and/or modification)
    • Safety – as ability not to harm people, the environment, or any assets during a whole life cycle.

    Fault Tree Analysis

    The Fault Tree Analysis (FTA) is the core of probabilistic safety value analysis. The FTA depicts the functional system and quantifies all relevant factors to evaluate reliability, availability, maintainability and safety of the complete system. All components of a system will be evaluated systematically and analysed according to their roles and functions within the system.

    Starting at the Top Event (System Failure) all functions, and the assigned failure status of the system’s components are evaluated. This results in a Boolean Model (Fault Tree) which is quantified by the characteristic reliability values. The logical linking of events is based on the following graphical elements as shown in the diagram below.
    Diagram courtesy of Taylor Burns, RiskConsult, GmbH

    Example results

    After completing the analysis, the following example information (see diagram below) can be used to help improve the safety of the system. In the below example it was found that due to an error in a braking system that the reliability was only 78 per cent. By taking a low risk tolerant approach and using the VaR95 value we can determine that the down time within one year will be less than 6.5 hours, and in this case the corrective maintenance costs would be in the order of $6200. For the full example please see the following link

    Diagram courtesy of Taylor Burns, RiskConsult, GmbH

    Analysing the example braking system for safety of a period of one hour, we can see the system has a high level of safety, with the average probability of a dangerous failure per hour being 4.8E-11. 

    Diagram courtesy of Taylor Burns, RiskConsult, GmbH

    The information on this page was primarily sourced from:

    • Text provided by Taylor Burns, Project Engineer, RiskConsult, GmbH
    • Peer review conducted by Pedram DaneshMand, Director, Project Risk Consulting, Audit, Assurance & Risk Consulting, KPMG
    • RiskConsult RIAAT Software RAMS Analysis webpage, 2019.

    Edited by Nadine Cranenburgh

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