Integration of safety studies into a detailed design phase for a navy ship

Transcription

1 Integration of safety studies into a detailed design phase for a navy ship A. Fulfaro & F. Testa Fincantieri-Direzione Navi Militari, Genova, Italy Abstract The latest generation of Italian Navy ships has moved a giant step forward in the approach to the main relevant transwarship activities which have an impact on all the design phases and at the whole warship level. Among all the activities developed, the safety topics have been implemented more and more, shifting from prescriptions essentially based on past experience to goals based on risk considerations, that were included in the scope of the contractual specifications. In its supplier role, Fincantieri for the first time has been challenged with the requirement of demonstrating the vessel safety by means of risk assessment studies during the developed design phases. The studies followed a twofold stream of activities, that is, analysis of the ship s systems (including Platform and Combat System) and analysis of the health and safety of the persons onboard. The safety analysis was essentially based on the study of some contractual hazards already selected by the Client. By means of the typical risk assessment tools (such as Fault Tree Analysis), properly injected as far as possible with Navy operating experience, a level of probability and severity was associated to each hazard, a risk matrix was constructed and the results checked against the Navy acceptance criteria. The process has been completed with the integration of the main safety requirements into the design. The aim of the present paper is to give an overview of the process. Keywords: transwarship, safety cases, design measures, requirements, hazard, risk analysis, fire propagation, preliminary, final, navy, military ship.

2 800 Risk Analysis IV 1 Introduction This section provides an overview of the general methodology used for implementing a safety approach into the design of the latest generation of multinational Navy ships (frigates), according to consolidated standards. The major item is to point out the increased impact of the safety studies in the different ship design phases as well as on the whole ship considering it in a more global vision of the new transwarship activities 2 Background The modern military transwarship activities have been raised out in the last ten years with the principal scope to increase the level of survivability of a ship. Different fields of application have reached a stronger relevance mainly to provide a better evaluation of the susceptibility, vulnerability and recoverability of a ship (see also fig. 1: Survivability approach for advanced ship design) Survivability approach for advanced ship design SURVIVABILITY Susceptibility (Inability to avoid weapon effect) Vulnerability (Inability to withstand weapon effect) Recoverability (Capacity to re-operate after sustained damage ) Safety and Damage Control Figure 1: Survivability approach for advanced ship design. One of the major developed characteristic in the survivability studies is the new increased attention to all the critical aspects for the safety of a ship and of the persons on board during a normal mission. The principal scope is to reach an adequate availability for the main systems\equipment on board optimizing the time stressed procedures, the level of training and the criteria to reduce and control a risk also with design modifications. The safety activity is generally subdivided into the following two tasks: Selection analysis and of the Laws and Regulations relevant for the safety of the ship and of the persons

3 Risk Analysis IV 801 Safety studies related to the main hazardous event on board (risk analysis to evaluate the probability and severity of an hazardous event and to define the risk classification. The above last point is the matter of the present paper showing how a consolidated and usual methodology is going to be integrated in the different design phases. The five steps of the applied methodology are: hazard identification, risk assessment, risk control options, cost benefit assessment and decision making recommendations. A short overview for each step is also provided. SAFETY PROCESS DEFINITION Hazard Identification PRELIMINARY SAFETY STUDIES LAWS AND RULES APPLICABLE LIST OF MAJOR RISKS COVERED BY L & R NO DEVELOPMENT AND PRODUCTION RESIDUAL RISKS ANALYSIS SAFETY REQUIREMENTS YES DEFINITION OF SAFETY REQUIREMENTS AND Q&A PARAMETERS RESIDUAL RISK REPORT INDUSTRY SAFETY REVIEWS NO YES COMPLIANCE? DETAILED HAZARD OR ZONAL ANALYSIS MITIGATION MEASURES Check if thereis a gap between safety requirementsand design WARSHIP SAFETY CERTIFICATION FINAL SAFETY REPORT CUSTOMER ACCEPTANCE SAFETY REVIEW Figure 2: Safety process. 3 General methodology for Warship risk analysis The primary effort is to identify the potential univocal causes of accidents for the ship or the systems on board that are not otherwise addressed in the safety standards. As a consequence of this process, additional risk control options or

4 802 Risk Analysis IV safety requirements are determined and evaluated to minimise the risks of damage and injury. If the risk cannot be fully eliminated due to design constraints a sort of risk register is proposed to the customer for acceptance. Hereafter is provided a short overview of the general process. 3.1 Hazard identification (HI) The first step of work is an Hazard identification adapted on the type of ship considered and on its own operative profile. A list of hazards only indicative is here proposed: Loss of a propulsion line during Replenishment at Sea (RAS) operations in rough sea Fire out of control due to: -Human factor (negligence or maintenance activity) - Electrical hazard (short circuit) - Fire fighting failure (mechanical or human non action) Smoke propagation due to: - Fire not immediately under control. - Bad disposition of ventilation (operating configuration) with a fire hazard in other adjacent rooms. Loss of integrity of pressure pipes or carrying hazardous substances due to: -Leak on a coupling or on a clamp. -Vaporisation in case of pressured circuit - Leak of gas on bringing to air piping or during black water tank opening - Closing of air intakes or of ventilation holes - Maintenance without individual protection (breathable air) Risk of Intoxication due to: -Polluted water supplied in a harbour. -Maintenance defect (failure in periodic quality controls) -Polluted water produced by ship osmoses -Lack of hygiene in food catering or during preparing phases (bacteriological contamination) Collision due to Total loss of Propulsion or Fire in propulsion room. 3.2 Preliminary hazard analysis The Preliminary hazard analysis (PHA) is a task of the Safety Studies started during the Preliminary Phase of the design. The objective of this task is to define a first assessment for the safety requirements with a preliminary evaluation of the main hazards selected from the Hazard Identification for both Platform and Combat Systemand a first evaluation of the consequences. The first step of this analysis is a preliminary hazard identification with no assessment of the perceived risk, which would determine the acceptability of a hazard as a product of the severity and probability of occurrence. This full analysis will be assessed only in the design phase due to insufficient information available to provide acceptable levels of safety in the feasibility

5 Risk Analysis IV 803 phase therefore, until an analysis of the hazard is undertaken, the judgement of the significant safety issues that can have an impact on the outline design remains, to some degree, subjective. The main stone for the PHA will be: Previous incident where known Perceived hazards, event sequence and potential consequences Engineered safeguards and operational procedures During the course of the safety assessment, generic hazard will be identified (Hazard Identification) in relation to the whole warship and its operational profile, together with more specific hazards for each of the key areas here summarised: KEY AREAS General Arrangement and Overall Ship aspects Magazine and Weapons ditching Lifesaving, Escape route, Seamanship and Replenishment at Sea operation Firefighting Platform Management System Electrical generation and distribution Helo and Combat System interface The Preliminary hazard identification report provides an initial baseline document for each nation to develop the safety substantiation and justification during the next design phase as the detailed design develops. Dedicated recommendations will be foreseen for the overall ship issues and more specific systems or operational areas. Guidelines on way ahead will complete the work by using dedicated tables as follow to summarize the results: Table 1: Preliminary hazards analysis. Hazard type Key area Description Zone\system\ equipment Prel. Recommendation\ Mitigation Number of event sequence In the first table after having assessed the hazard type linked with a preselected key area more detailed information are expected regarding the relevant design area and the systems\equipment which will be subjected to complete full analysis in the design phases.

6 804 Risk Analysis IV Table 2: Consequence. Number of event sequence Consequences description Safeguard The preliminary recommendations and mitigation measures give a guideline for the technical experts recollecting all the safety issues. All the event sequences identified will be completed with a severity\probability risk analysis when the data are available in the following phases of the project and collected in the full risk analysis. 3.3 Full risk analysis The study was conducted through typical risk assessment techniques, that had to be adjusted to the frigate context, For all the hazards, the applied policy required the analysis to cover the operational scenarios corresponding to peacetime operation and combat situation with no damage, and the risks to be compliant with the Safety Principles and the Risk Classification Scheme, described below. The Safety Principles to be met were generally: the compliance with the relevant safety legislation of the Nations involved; the application of the As Low As Reasonably Practicable principle, if necessary; the use of international safety standards; the implementation of a Safety Management System. The result was in form of tables including a description of the hazard, the conditions that may cause it to generate a mishap, and the consequences that result when a mishap occurs. For the classification of the accidents in severity categories and in probability categories, the following methods should be used, as far as possible: - use of Navies statistics / lessons learnt - agreed qualitative assessments by experts (from the Nations and from industry), - results of dedicated studies, if necessary (e.g. in relation to specific requirements from other industrial entities which products are to be integrated on board) and/or as far as major risks are concerned. However, on Navy ships the probabilistic quantification was found not to be always viable, due the novelty of the approach and the lack of publicly available information on equipment failures, incidents, casualties etc. Therefore, priority to the possible consequences was given in order to classify the risks. 3.4 Main process and results After the assessment, each hazard was verified against its acceptability criteria.

7 Risk Analysis IV 805 The ALARP approach implies that, if the resulting occurrence probability of the hazard under investigation (calculated in the analysis) does not meet the defined requirements, an action to reduce the risk is needed. This will be evaluated by applying the As Low As Reasonably Practicable (ALARP) principle. This calls for weighing the efficacy that any particular measure will have in reducing the calculated risk against the costs in money, time and resources required to avert it and other consequences of introducing the measure. The aim is to reduce every possible risk so that it is falls in the acceptable region. The risk can be considered tolerable only if the reduction is impracticable, or if its cost is disproportionate to the gained improvement The output study was generally organized in tables (see table 3 for example), drafted for each of the selected hazards. Table 3: Example of output risk analysis. Subsystem concerned Initiating event Immediate consequence Aggravating factors Worst final consequence Crew Risk Level Ship Risk Design measures/ remarks Upon approval of the Risk classification, the Safety Experts produced all the final Safety recommendations in order to give to technical experts a list of risk control measures to be integrated into the design or the operating practice. 3.5 Risk control measures After implementing the risk control measures, the risks associated to each hazard are expected to fall within the acceptability area. If this is not possible to proof (as often is the case, because of the paucity of data for the analyses and the difficulty of constructing a proper risk model), or if no further risk control measure is feasible, the Client may consent to a derogation, according to its judgement. In particular, for risk for which no viable reducing measure could be proposed, the industries were asked to produce a risk register which will be analysed by the Client for a final decision. In any case and when necessary, reduction measures are identified during the process. However, it could be necessary to achieve a trade-off between solutions to analyse the expected effectiveness of each alternatives. Mishap risk mitigation is an iterative process that culminates when a residual risk has been reduced to a level acceptable to the appropriate authority. Two major reduction axes are available: Reduction (elimination) of the hazardous condition occurrence (i.e. improvement of the failure tolerance whenever possible), Implementation of protective devices to reduce (eliminate) associated consequences

8 806 Risk Analysis IV Among the Safety solutions usually proposed as mitigation measures one or more of the following could be selected: design hazards out, incorporate safety devices, provide warning devices, develop procedures and training. In order to complete the process, in some cases a verification of the mitigation measure through appropriate analysis, testing or inspection may be required to confirm the acceptability of the residual risk (see also Fig. 3). Figure 3: Check list-example to assess the safety requirements into the Design from Horizon Project. 3.6 Detailed relevant impact on design: safety cases The safety cases will be dealt with starting from the safety-critical areas of equipment/systems, identified by the safety management process that includes the Laws and regulation activity and the Safety studies. Once identified the risk mitigation measures, they will be included in the system specification, or in the purchase specification if they are related to isolated pieces of equipment. Risk mitigation measures may also consist of mere additional procedures to be implemented by the crew. In the following table the Safety integration process into design is summarised.

9 Risk Analysis IV 807 Safety Integration Process Compliance with National Health and Safety Laws & Regulations Identification and treatment of potential risks Study of different hazards Safety implementation actions at equipment/system/ww level Safety Case A Safety Case B Safety Case C Safety Case X Safety Case Y Safety Case Z Safety Cases (for each equipment, system and at WW level) = Acceptance evidence (demonstration that the Frigate and its equipment/systems are acceptably safe) + Tools for the mngmt of Safety through its in-service life (in particular how to manage the residual risks) Legislation report Safety studies report Safety Report (Preliminary & First issue) Figure 4: Safety cases. 4 Conclusions The proposed paper is a short overview of the safety methodological approach developed for the different design phases of a military ship. The new generation frigates are going to integrate the results of all the transwarship activities but however many fields of application should be detected in more detail and related to the level of safety on board as for example the fire propagation or the magazine detonation risk due to the non-secondary effects of these basic events for the global survivability of the ship References [1] IMO MSC/Circ and MEPC/Circ. 392, Guidelines for FSA for the Use in the IMO Rule-Making Process (2002). [2] Horizon International Project-Safety Acceptance process and Safety plan (2001)