Total Safety Assessment: An Efficient Tool For Ships

Saturday, March 03, 2001
During the last two decades the shipbuilding and marine industry has taken huge steps in rule development and general safety awareness. This development has been driven through accidents for damage safety and for fire safety and retroactive rules have been applied for the first time. In spite of the increased rule framework incidents and accidents do happen. Human nature is, of course, one of the main reasons but not the only one. The developed safety rules and design methods have been lacking the practical part.

Formal safety assessment is acknowledged as an overall future approach for design of safe ships but the methodology has not yet been available for designers and operators to run the safety assessment easily with practical results for existing ships and for newbuildings.

Failure Mode and Effect Analysis (FMEA), Reliability Block Diagrams, operability and availability analysis and fault trees are leading to a lot of theoretical paperwork without practical results, measures or recommendations. For a modern passenger cruise ship some 10.000-15.000 block diagrams might be produced but methodology has not been available to take these into a practical level. Another missing part is failure statistics for modern passenger ships and ferries.

A new approach has been developed by Deltamarin called Total Safety Assessment (TSA) fulfilling the principles of the formal safety assessment. The developed method systematically covers the ship geographically and all the installed systems including propulsion and electric power production, energy production, emergency power, bridge systems, safety systems as well as passenger comfort related systems.

Total Safety Assessment has been developed together with two major shipowners, Royal Caribbean International and Color Line, giving the emphasis on passenger cruise ships and ferries. The objectives of the work have been to develop a generic ship model in order to find and present all the safety related issues, to develop a systematic approach to avoid any grey areas, to keep the amount of required work on reasonable level and to have the crew/operational people involved in all phases to improve the understanding, acceptance and overall safety culture. A global method is developed with which all the ship operations and structures (functions and areas) are assessed and located in four different sectors related to time of occurrence and type of function: normal operation of the vessel, operation in case of failure incident, systems and structures (areas and spaces) in normal operation and failure impact on systems and structures. The first two topics are related to human behavior and to the present operation related aspects whereas the last two topics are related to hardware.

The work proceeds in four steps. The Generic Ship Model is first developed for the specific ship or newbuilding, this model describes the breakdown of all functions aboard down to system, subsystem and even component level when needed. This model ensures that the assessment/design will be comprehensive, nothing is missing and impact of each subsystem is clearly presented towards the overall availability and safety. This model is further utilized for the ship audit, surveyors know in beforehand what to look for and where.

Reliability Block Diagrams are developed for each system not in a typical way but in topographical way including fire subdivision and watertight compartmentation in the diagram. Specific evaluation criteria are developed together with the crew/operational people to enable efficient ship checks and to win the crew commitment. An onboard data collecting and reporting system is developed based on the generic model for collecting reliable and specific failure and operational data.

Generic model and data collecting system together form the novel reporting system. First report is always given to the crew immediately after the survey. A priority factor was needed to give an order for the improvements, this includes probabilities for any incident, consequences (local or global), off-hire time and costs. The first test cases have proven the developed system to give practical and valuable results. Weak points, risky areas, spaces and systems have been detected. System and function availability have been improved. Fire, flooding and incident risks have been described and crew awareness has increased, e.g. impact of modifications is easy to check with the developed system. Some of the improvement proposals have been carried out by the crew immediately. The index system give a practical tool for the owner to evaluate the required improvements in different categories, e.g. absolute musts, high fire risk, local system improvement with global or local impacts, high flooding risks, impact and recovery after failure, system availability, e.g. to keep schedule, etc. Proposed improvements and required investments are also considered within the index system. The method is now further developed for newbuilding projects starting from analysis of the total arrangement of the vessel, location of high risk spaces and areas, system location and routing down to system configuration. The system will be called Risk Based Design.

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