BV looks to FSA

Bureau Veritas is involved in a number of Formal Safety Assessment (FSA) studies that include the EC projects Nereus and Safety First for stability safety and fire safety of passenger roros respectively, a Safety at Speed project for design safety of high speed craft and an IACS PT/SSI assessment of risk control options for side shell integrity of bulk carriers. This is in addition to a study to develop a risk model of bulk carrier casualties, according to the IMO FSA Guidelines, that has been completed by the classification society.

The study was part of an international cooperative project led by the UK?s Maritime and Coast Guard Agency (MCA) on the FSA of Bulk Carriers, with the results presented at MSC75 during May. The study highlights the high criticality of hatch covers and side shell integrity. The society claims that it provides a powerful tool in the form of quantified fault trees and event trees for the development of new risk control options and to measure the impact of future FSA-based rules.

One of the more interesting results of the study was that hatch cover incidents result in one and a half times more fatalities than side shell incidents with four times less occurrences.

The work programme was aimed at creating a description of relevant accident categories for cause-consequence analysis. Hazards to bulkers identified in previous studies were ranked and grouped in accident categories, which constitute the top events of the fault trees and/or the initiating events of the event trees.

Fault tree structures were devised and quantified based on historical data. The work scheme made allowance for the use of expert interpretation or evaluation if there was insufficient statistical data. However, BV says that this was not necessary as it was able to show that a meaningful result could be based on actual data, which it felt would generate greater confidence in the system.

Event tree structures were developed for the relevant accident categories. And a sensitivity analysis was conducted to assess the influence of the relative branches and events of the trees. Risk profiles were produced for individual or crew risk, estimated on the basis of the event trees? output and with the support of historical data and expert judgement.

An extensive study was done in order to develop accident scenarios using risk contribution trees through co-operation with Lloyd?s Register of Shipping and the MCA to match the scenarios with the accidental data existing so far.

Risk contribution trees have been built for all accident categories mentioned in the Lloyd?s Casualty Database. Then, as the project focused on accidents where the bulk carriers had a specific behaviour difference (more frequent accidents than other ship types or with higher consequences for the crew), the loss of hull integrity (LOHI) category has been quantified and an analysis has been performed in order to highlight the contribution of the factors leading to LOHI.

From the statistical base provided by previous studies which analysed more than 500 cases of accidents of bulk carriers resulting in the LOHI, over the period of 1978 to 2000, the fault trees and the event trees were developed, to provide an adequate representation of the events contributing potentially to the loss of integrity of the hull, and their frequency of occurrence.

It provided the advantage of delivering the project with a factual data set on which the risk assessment could be based, resulting in derived Potential Loss of Life (PLL) values that represent actual loss of life attached to each cause. BV says that it was possible to establish for each category of incidents and each class of bulk carriers the frequencies of incidents and loss of life per ship year, or PLL.

The project team was formed by a core of FSA specialists, supported by a group of technical experts and was co-ordinated by a BV project manager, with the participation of four safety and risk analysis engineers.

The analysis highlighted four critical events among the several items considered: A1 Hatch cover, B4 Side shell failure, B12 Other and C3 Stability compromised.

The fault trees suggest the most significant high level event is that of side shell failure (B4) due to fatigue/wastage with 146 identified cases, across all sizes of bulk carrier, resulting in 113 lives lost. The classification society says that the location of this varies across each bulk carrier type, although it is clear it is not always been initiated in nos. 1 and 2 hold.

Side shell failure due to collision, escalating to loss of structural integrity and sinking, accounts for 26 cases, but has caused 130 fatalities. BV says that this statistic is dominated by the handysize category in combination with dense cargo.

Hatch cover failures account for a total of 40 incidents, which have resulted in 565 fatalities. Hatch cover failures appear to be the result of covers being dislodged (possibly due to failing securing devices or unsecured hatches). However structural failure of hatch covers is also apparent and cannot be ruled out. Hatch cover failures are dominated by Handysize bulk carriers in terms of incidents (25 incidents and 387 fatalities. However when the number of vessels in operation are taken into account (ship-years), the problem exists statistically in all bulk carrier sizes and the size of vessel is not significant.

One of these items stands for a category of unspecified events generically named Other (B12); the results of the analysis are affected by the uncertainty connected to these unknown scenarios. BV says that further analysis focussed on these events could improve the risk evaluation.

The developed fault and event trees provide a suitable basis from which risk control options can be derived.

As the application of FSA within the maritime industry is relatively new, future FSA studies would benefit from similar work to enhance casualty records.

The availability of improved data would enable lower levels in fault trees to be populated without judgement. To achieve this it is suggested consideration be given to examining the degree of availability of information contained in the database of casualties used by the Flag State Implementation Committee for the purposes of interrogation in connection with FSA studies.

It could be noted that the frequencies of different categories of incidents are quite equally distributed among the BC classes with an exception for the side shell incident which is significantly more frequent for Panamax and Capesize than for the other classes and for the Mini class which seems less subject to LOHI incidents.

Regarding PLL the predominance of hatch cover and side shell incidents is marked with a greater dependence of consequences for side shell incidents than for hatch cover incidents with the BC Class involved. Hatch cover incidents result in 1.5 time more fatalities than side shell incidents with four time less occurrences.