اختلاط ارزیابی ایمنی رسمی و شبکه های بیزی در برآورد ریسک ناوبری رودخانه یانگ تسه

Formal safety assessment (FSA), as a structured and systematic risk evaluation methodology, has been increasingly and broadly used in the shipping industry around the world. Concerns have been raised as to navigational safety of the Yangtze River, China's largest and the world's busiest inland waterway. Over the last few decades, the throughput of ships in the Yangtze River has increased rapidly due to the national development of the Middle and Western parts of China. Accidents such as collisions, groundings, contacts, oil-spills and fires occur repeatedly, often causing serious consequences. In order to improve the navigational safety in the Yangtze River, this paper estimates the navigational risk of the Yangtze River using the FSA concept and a Bayesian network (BN) technique. The navigational risk model is established by considering both probability and consequences of accidents with respect to a risk matrix method, followed by a scenario analysis to demonstrate the application of the proposed model.

The Yangtze River has become the world's busiest navigable inland waterway, according to People's Daily of August 30, 2010 [1]. The number of the foreign ships sailing through the Yangtze River has increased sharply from an average of hundreds per year in the 1970s to an average of hundreds per day in the 2010s, mainly due to China's opening up policy. The increase of the traffic in the river has also seen an growth in accidents such as collisions, groundings, contacts, oil-spills and fires, causing serious consequences to the sustainable development of the Yangtze River. Greater attention has therefore been paid to the safety assessment of the Yangtze River from government, industry and academics. 1.1. Maritime risk assessment of the Yangtze River A management mechanism of emergency response has been established by Chang Jiang Maritime Safety Administration (MSA) in order to minimise the consequences of maritime accidents [2], while various methods such as Analytic Hierarchy Process (AHP), grey synthetic evaluation, fuzzy mathematics and Formal Safety Assessment (FSA) have been introduced to investigate the occurrences of accidents. Previous studies include the following: Zhang et al. [3] established a model for navigational risk assessment using the AHP approach. Yang [4] evaluated the risk level in a typical confined channel of the Yangtze River based on the grey synthetic evaluation. A FSA method was applied by Gao [5] to estimate the risk in a multi-bridge waterway. Several approaches including AHP, fuzzy mathematics and FSA, were demonstrated by Qin [6], dealing with various maritime safety issues. The above studies have identified the main hazards and several measures to control the navigational risk of the Yangtze River. However, these risk analysis studies are mainly based on subjective data with expert judgements or questionnaires used. Furthermore, while quantitative methods have become more and more popular in maritime risk assessment and the FSA approach is highly appreciated worldwide, few researchers have made use of the strengths of both approaches together. Lastly, none of the above publications consider risk probability and consequences simultaneously. Therefore, this study estimates the navigational risk of the Yangtze River using a quantitative method, Bayesian network (BN) incorporating both objective and subjective data, in line with the FSA concept. 1.2. FSA framework In 2002, a FSA framework, proposed by the UK Maritime and Coastguard Agency (MCA) was approved by the International Maritime Organization (IMO, 2002) as a formal policy making tool, consisting of the following five steps: 1) The identification of hazards. 2) The assessment of risks associated with those hazards. 3) Ways of managing the risks estimated. 4) Cost benefit assessment of the risk control options (RCOs). 5) Decisions on which options to be selected. The logical structure of FSA is shown in Fig. 1[7]. Full-size image (19 K) Fig. 1. FSA framework. Figure options FSA is a proven approach to marine safety which involves using the techniques of risk and cost–benefit assessment to assist in making decisions. It has been applied to many aspects of worldwide maritime systems [8], [9], [10], [11], [12], [13] and [14], however few of its applications are in the Yangtze River and most of them use qualitative judgement only. For example, the work in Gao [5] briefly discusses the risks in a multi-bridge waterway using the FSA method and provides a few risk control suggestions for safety management. 1.3. Paper origins The Inland Waterway Transportation System (IWTS), is a low energy consuming and low air pollution transportation method, but the increasing national concern as to the safety and efficiency of the 2838 km navigable waterway of Yangtze have to be addressed. Though FSA has been acknowledged as one of the proven methods in maritime risk analysis, a literature search shows that few of its applications are in the IWTS and even fewer have been combined with quantitative risk analysis methods. In view of such findings, this paper incorporates the FSA method and BN technique in an estimation of navigational risk in order to create a basis for the stakeholders to make rational risk-based decisions and thus enhance the navigational safety of the Yangtze River. This paper will focus on the application of the first route of the FSA framework (including Steps 1, 2 and 5) to the Yangtze River. The risk influencing factors which could cause or substantially contribute to a major accident are defined as Safety Critical Factors (SCFs). They will be identified with reference to historical data statistics, followed by accident consequences modelling based on a data-based BN process. Finally, the navigational risk of the Yangtze River will be modelled in a BN in accordance with a typical risk matrix, considering both consequences and probability of the navigational risk. The following section will start the procedure with hazard identification.

In this paper, the FSA principles are applied to evaluate the navigational risk in the Yangtze River. Hazard identification has been made using historical data to analyse the characteristics of navigational risk in the Yangtze River. This is followed by accident consequences modelling using a data-based BN process. Finally, the risk BN has been established using the risk matrix method and applied in a scenario analysis for demonstration purposes. In this research, by examining the effect of different parameters (e.g. ship type and gross tonnage) and their various conditions, the consequence assessment by using the BN enables identification of the parameters and conditions that have the greatest impact on accident consequences. The case study shows that the type of ships largely affect CoA. Specially barges and tugs, passenger ships and tankers cause more consequences than other types do. Also there is a significant difference between various sizes of ships, with more consequences for those vessels greater than 2000 GT. The consequences of accidents vary with the type of accident, with groundings tending to be the most troublesome. The results of this model also suggest that dry season is closely associated with a significant increase in CoA, thus particular attention should be taken during the winter in the Yangtze River. Analysis of two individual scenarios in a PSA study has demonstrated the application of the proposed risk BN model. The results prove that navigational risk is significantly increased. by severe weather and confined channel conditions, and that show large privately owned vessels would benefit from further RCOs so as to keep their risk level as low as reasonably practicable. BN is often used to model PoA in previous studies. Here it is employed to model both consequences and PoA. The paper also introduces a risk matrix method to BN. The critical risk factors associated with inland waterways in general and the Yangtze River in specific are investigated to measure their importance quantitatively. Historical accident data was derived from data banks to highlight the possible consequences of accidents in the Yangtze River, which could be used as a reference to facilitate risk analysis of other IWTSs. Future work of this study is intended to include RCOs investigation, cost benefit analysis and decision making in accordance with the guidelines of FSA.