Relative Risk Assessment Methodology in Vessel Traffic at Sea

Relative Risk Assessment Methodology in Vessel Traffic at Sea HU Shenping¹, FANG Quangen², Zhang Jinpeng¹, Xi Yongtao¹ ¹Merchant Marine College, ²Shanghai Maritime University, Shanghai, China Abstract The Ship Formal Safety Assessment (FSA) is the premier scientific method that is currently being used for the analysis of maritime safety and the recommendations of concerned regulatory policy. This paper conducts an overview of the FSA methodology and proposes ways to improve it. The applications of both quantitative risk analysis (QRA) and risk-based decision making techniques were discussed, and possible pitfalls or other deficiencies are identified. Then proposals of relative risk assessment methodology are made to alleviate such deficiencies, with a view to achieve a more transparent and objective approach. The results of this paper may be useful if a revision of the FSA tools is contemplated along these discussions. Keywords - Ship, risk assessment, relative risk I. INTRODUCTION One of the main concerns of ship stakeholder including shipbuilders, ship owners, ship operators and maritime administrations is the safety of ships at sea. There are enormous penalties for the lack of safety, in terms of life loses, damage to environment and cargo, which all involved shipping industries want to avoid. This has been reflected in the attention given to both the building activities, the operation of ships, education and training of ship operators [1]. However, the use of formalized approaches to quantification of risks in maritime field has lagged somewhat behind other fields, such as the nuclear and the aerospace, in which often the very high severities of causalities(or casualties?) have promoted the adoption of these methods. The safety culture of anticipating hazards rather than waiting for accidents to reveal them has been widely used in other industries such as the nuclear industries and the aerospace industries. The international shipping industry has begun to move from a reactive approach to a proactive approach to safety through what is known as Formal Safety Assessment (FSA) [2]. After the investigation of the capsizes of the Herald of Free Enterprise, the UK Maritime and Coastguard Agency (previously named as Marine Safety Agency (MSA)) quickly responded and in 1993 proposed to the IMO that formal safety assessment should be applied to ships to ensure a strategic oversight of safety and pollution prevention. The IMO reacted favorably to the UK s formal safety assessment submission. Since then, substantial works including demonstrating its practicability by a trial application to the safety of high speed catamaran ferries and a trial application to the safety of bulk carriers, have been done by the UK MCA[3]. Since the first trial application in FSA, the member states in maritime community realized that FSA is a prerequisite to any significant change to maritime safety regulations. Furthermore, FSA adopts the latest techniques of risk assessment. As a result, FSA is currently the state-of-the-art method to assess maritime risk and formulate safety policy [2]. It is also deeply impressed that the risk management is rapidly developing. There are a number of national standards for risk management. The first was developed by Standards Australia/New Zealand in 1995 (AS/NZS 4360), followed by Canada (CAN/CSA-Q850) in 1997 and United Kingdom (BS-6079-3) in 2000[4, 5]. In maritime field, the recent Goal-Based Standards (GBS) approach aims to be another proactive instruments, and there has been recent discussion at the IMO on the possible links between FSA and GBS [2]. Much of the theory underlying the process of risk management is based on the work of Herbert A. Simon, Nobel Prize winner who identified three basic phases of decision-making under risk and uncertainty : intelligence, or risk identification; design, or risk analysis/ assessment; and choice/implementation, or risk mitigation/treatment. Most formalized approaches to risk management or assessment are based on these three key activities. The purpose of this paper is to conduct an overview of the FSA methodology and propose ways to improve it and achieve the framework of copying the risk of vessel traffic at sea. All concerned information of the FSA approach is looked at and possible pitfalls or other deficiencies are identified. Then some proposals are made to alleviate such deficiencies, with a view to achieve a more transparent and objective approach in copying the risk of vessel traffic at sea. II. REVIEW OF FORMAL SAFETY ASSESSMENT Formal safety assessment is a structured and systematic methodology, aims at enhancing maritime safety, including protection of life, health, the marine environment and property, by using risk analysis and cost benefit assessment. FSA is a new approach to maritime safety which is involved in using the techniques of risk and cost-benefit assessment to assist the decision making process. IMO s guidelines on the application of FSA recommend a five-step approach, consist of (1) Hazard Identification, (2) Risk Analysis, (3) Risk Control Options (RCO), (4) Cost-Benefit Assessment (CBA), (5) Recommendations for Decision Making. An illustrative approach of this framework was given and presented by IACS in MSC s 75th session (IACS 2002). 978-1-4244-8503-1/10/$26.00 2010 IEEE 1493

FSA was introduced by the IMO as a rational and systematic process for assessing the risk related to maritime safety and the protection of the marine environment and for evaluating the costs and benefits of IMO s options for reducing these risks [7]. In MSC s 81st session (May 2006), an FSA Drafting group proposed some amendments to these guidelines (MSC 81/WP.8). These amendments have been approved by the MSC and were subsequently sent to the MEPC for approval, something that happened at its 55th session (October 2006). As a result, there is now an amended set of consolidated FSA guidelines incorporating all recent revisions [8]. Obviously, Formal Safety Assessment was conceived as a successful tool, to provide a transparent decisionmaking process, and to clearly justify proposed measures as generic application, and to allow comparison of different options using cost benefit assessment. Firstly, compared with the safety case approach, it should be noted that there is a significant difference for the formal safety assessment [4]. The philosophy of formal safety assessment is essentially same as the one of the safety case approach. However, a safety case approach is applied to a particular ship, whereas formal safety assessment is designed to be applied to safety issues common to a ship type or to a particular hazard. The major difference between such ship specific applications of the approach and its generic application by regulators is that whilst features specific to a particular ship cannot be taken into account in a generic application, the commonalities and common factors which influence risk and its reduction can be identified and reflected in the regulator s approach for all ships of that type. Secondly, there are four challenges to any approach to modern maritime safety regulations must respond. It has to be proactive, systematic, economic and transparent. FSA focuses on the hazard and frequency of accidents or incidents, not only the consequences or casualties in any case coming as a result of a cost in human life or property, i.e., the ship itself. So it is proactive and rather than waiting for accidents to reveal them [9]. FSA also provides a structured and systematic framework which includes five steps. Thus it is using a formal and structured process. During FSA studies, the decisionmaker will find the balance between safety (in terms of risk reduction) and the cost to the stakeholders of the proposed risk control options. The management style is scientific and effective. Based on the report of FSA project, the user can be clear and justified of the safety level that is achieved. These will result in a more rational and transparent regulatory regime. The use of formal safety assessment by an individual owner for an individual ship on the one hand and by the regulator for deriving the appropriate regulatory requirements on the other hand, is entirely consistent [8]. Thirdly it is the key factor, FSA adopts the latest techniques of risk assessment. At the end, FSA is currently the state-of-the-art method to assess maritime risk and formulate safety policy. With the modern navigation technology rapidly development and the management extents expansion, the sea practices take on the lower frequency and less severity. The researchers in maritime safety have to find the concept of risk to solve the problem in event study, not accident analysis [8, 9]. Thus, we are trying to bend ourselves to quantified risk assessment (QRA) and risk-based decision-making (RDM). These are the fresh domains to the traditional safety analytics. In our opinions, the study on QRA or RMD in maritime industry is one of the future topics together with human reliability and safety culture either theoretical or practical field. III. DILEMMA OF FORMAL SAFETY ASSESSMENT As a serious concern is raised over the safety of ship all over the world, the International Maritime Organization (IMO) has continuously dealt with safety problems in the context of operation, management, survey, ship registration and the role of the administration. The improvement of safety at sea has been highly stressed. The international safety-related marine regulations have been governed by serious marine accidents that have happened as before. The lessons were first learnt from the accidents and then the regulations and rules were produced to prevent similar accidents from occurring. Since 1997, this situation has changed. The maritime community became aware of the enormous power of Formal Safety Assessment (FSA) in 1997[1,7], when the IMO reversed its prior position to require Helicopter Landing Areas (HLAs) on all passenger ships even before the relevant regulation had come into effect. However, a trial application prepared by Norwegian classification society Det Norske Veritas (DNV) for Norway and the International Council of Cruise Lines (ICCL) showed that this could not be justified in terms of cost effectiveness [16]. Specifically, it was shown that the costs of applying this measure were in great disproportion to its benefits for non-ro/ro passenger ships. A decision was therefore made to repeal the requirement. IMO is not known for reversing its positions, and this was one of the rare times. Actually, this was the first time FSA was involved. But later, many people felt that FSA fell into discredit and raised questions on its effectiveness. A high-profile issue aroused if it was not for the mandatory construction of Double Side Skin (DSS) for the bulk carrier in 2004. The International Collaborative (IC) FSA Study, managed by the UK, Japan and the International Association of Classification Societies (IACS) also undertook FSA studies that were reported and arrived at the same recommendation for DSS. However, at the same time Greece submitted documents to present the findings of a comparative study of the three abovementioned FSA applications, which, using the same method, resulted in completely different recommendations, namely that DSS did not necessarily increase safety. To some, the story could be seen as a dispute of interests among countries, or among the various industry stakeholders (ship owners, 1494

shipyards, and class, among others). Whatever the outcome, this case also produced serious collateral damage. Many analysts considered this case to be a failure of the FSA. There was criticism on the action to reverse the earlier thrust by the IMO, and a review of the FSA process was proposed [2] Other than the revision of FSA guidelines, recent FSA related activity within the IMO has moved on two parallel fronts. First, the topic of environmental risk evaluation criteria (with a focus on oil pollution) has caught serious attention, and second there have been submissions of several FSA studies for specific 4 ship types. That is to say, according to this classification, the way of evaluating FSA tools usually has two aims [9]: theoretical recognition of FSA components, their characteristics and spatial or temporal changeability, practical research, what kind of results we are able to achieve from theoretical recognition, and what we can say about maritime impact and technological influence on ships. Here just makes a discussion about the theoretical fronts. A. Risk in maritime transportation As it is well known, the concept of risk stands central in any discussion of safety. With reference to a given system or activity, the phrase safety is normally used to describe the degree of freedom from danger, and the risk concept is a way of evaluating this result. However, the phrase risk can be viewed differently depending on the definite problem. According to the IMO FSA Guidelines, the risk concept was defined as the combination of the frequency and the severity of the consequence. An important paper [10] was published that defined the risk as the triplet of scenario, likelihood, and consequence. It has been put forward another triplet of scenario, time, and consequence to evaluate risk using the likelihood and consequence factors [11]. As a result, the term risk concerned has been reflected the three or more phrases, such as scenario, likelihood (or frequency), and consequence. Also in the FSA Guidelines, the term frequency was defined as the number of occurrences per unit time (e.g. per year); the term consequence was defined as the outcome of an accident(an unintended event involving fatality, injury, ship loss or damage, other property loss or damage, or environmental damage). But an accident scenario was defined as a sequence of events from the initiatal event to one of the final stages. Obviously, the risk concept in FSA Guidelines is different from the traditional concept. It is evidently shown that the risk in FSA most discuses on lifecycle of ship s structure and equipment and frequency in terms of accidents (rather than casualties). In fact, likelihood is one of factors in risk, which is always calculated via probability of events or scenarios. According to FSA guideline, FSA was studied the individual risk and societal risk. Furthermore, environmental risk will be involved in the near term future [2]. The phrase Individual Risk (IR) was in term of that the risk of death, injury and ill health as experienced by an individual at a given location, e.g. a crew member or passenger on board the ship, or belonging to third parties that could be affected by a ship accident. The phrase Societal Risk was in term of that Average risk, in terms of fatalities, experienced by a whole group of people (e.g. crew, port employees, or society at large) exposed to an accident scenario. It has been noticed that most FSA studies have extensively used historical data found in various casualty databases. It is understandable that if historical data are available, risk profiles can be drawn without the need to model scenarios. However, the most important is that the whole philosophy of using historical data is not proactive and therefore it cannot be used for new designs and cannot measure the effects of newly implemented risk control options, as it needs to wait for accidents to happen to have sufficient data. Given the potential pitfalls of the quantification of risk as currently applied, it can be known that, unless a improved quantitative scheme is devised, a qualitative scheme might be more reliable, or at least less prone to problems than a quantitative approach. In other words, a qualitative approach may be better than a problematic quantitative one. B Risk Measurement and Quantified Risk Assessment a Risk Matrix and Risk index A risk matrix uses a matrix to divide the dimensions of frequency and consequence into categories. Each hazard is allocated to a frequency and consequence category, and the risk matrix then gives a form of evaluation or ranking of the risk that is associated with that hazard. Analytically, the IMO has introduced a 7 4 risk matrix, reflecting the greater potential variation for frequencies (7 indexes) than that for consequences (4 indexes). To facilitate the ranking and validation of ranking, consequence and frequency indices are defined on a logarithmic scale. The term risk index is established by adding the frequency (FI) and consequence (SI) indices. Combining the above two an index, the third index, the Risk Index (RI), is defined as: R F S (1) log R log F log S RI FI SI, (2) Then the Risk Matrix can be constructed, for all combinations of the Frequency and Severity Indices. By deciding to use a logarithmic scale, the Risk Index for ranking purposes of an event rated.remote. (FI=3) with severity.significant. (SI=2) would be RI=5. Hence, risk index is from 2 to 11, 10 in all RIs. According to given values in index table, one fatality is somehow equivalent to 10 severe injuries. Although something that can be debated, at least on ethical grounds, and constitutes a point, it is clearly showing the exponential law in quantifying description of frequency and consequence. And this solution approach is correct for quantifying description of little example events. 1495

The Risk Matrices are not used for decision making. However, they constitute a simple yet most important tool that is provided to the experts so as to accomplish the previously mentioned task of ranking of hazards. The matrices are simple to use. b. Probability Measures and ranking Some comments on probability notwithstanding, the explicit consideration of the frequencies and the consequences of hazards are typically carried out by the risk matrices. If these two definitions look similar, they are not exactly (the same?). In most FSA studies, frequency is given as the following fraction: Number of Casualties F (3) Total of Shipyears Probability is not the same as frequency, and zero collision in a harbor does not mean collision probability is zero. Only if the sample of event is large enough can their frequency be linked to their probability, whereas this is not the case for very infrequent events or for events for which there is insufficient data to calculate their frequency. Since there are no data in some definite problem, this does not mean that the relevant probabilities do not exist. Bayesian approaches have been suggested by some researchers for estimating probabilities of events for which few or no data exist to compute their frequency [16]. In the Bayesian approach, the probability distribution of an uncertain variable is systematically updated from a prior distribution (which is subjective) and via observations of the value of that variable (which are objective) as posterior distribution. More fundamentally, it is noted that the expression of these risk limits on an annual basis (instead, for instance, on a per voyage basis) does not account for the number of trips per year undertaken by a person who travels by ship, a number that may varies significantly and one that would surely influence the level of risk someone is exposed to. The ratio of 10 to 1 between the maximum tolerable risks for crew members vs. the equivalent risk for passengers implicitly assumes that the former category makes roughly 10 times more trips than the latter, for the acceptable risk to be equivalent on a per-trip basis. c. Risk Ranking and ALARP According to FSA guideline, FSA studied the individual risk and societal risk. Furthermore, environmental risk will be involved in the near term future. Usually Individual Risk is taken to be the risk of death and is determined for the maximally exposed individual, whereas Societal Risk is taken to be the risk of death and is typically expressed as FN-diagrams or Potential Loss of Life (PLL). Societal Risk is determined for the all exposed affairs, even if only once a year and is not a definite person and location. To be able to analyze further these categories of risk and their acceptance criteria, we must have a look at the levels of risk. According to Health and Safety Executive s Framework (HSE, United Kingdom) for the tolerance of risk, there are three regions in which risk can fall (HSE 2001). According to calculated outcomes risk can be classified into three different fuzzy categories, namely, negligible risk, risk as low as reasonably possible (ALARP) and intolerable risk. There is no single universal level of acceptable individual risk. IMO s guidelines provide no explicit Risk Acceptance Criteria (RAC). Current(ly) decisions are based on those ( )which were published by the UK Health & Safety Executive (HSE 1999). The IMO has adopted HSE s criteria that define the intolerable and negligible risk for a single fatality: FIGURE 1 RISK ACCEPTANCE CRITERIA AS TO HSE UK Incredible as it may seem, neither the IMO nor any other rule-making body has yet reached a conclusion on what the values of these numbers should be. But, the crucial issue of what are acceptable risk criteria for the safety of maritime transport is still an open question studied. The purpose of societal RAC is to limit the risks from ships to society as a whole, and to local communities (such as ports) that may be affected by ship activities. In particular, societal RAC are used to limit the risks of catastrophes affecting many people at the same time, since society is concerned about such events (high SI). Usually, societal risk is taken to be the risk of death and is, typically, expressed as an F N diagram (F 1 is the frequency of accidents involving one or more fatalities, Fig. 2). FIGURE 2 TYPICAL F N DIAGRAM [SEE MSC 81/18] In any event, it is clear that key analysis is necessary to define RAC and to ascertain if a better risk exposure variable can be found in maritime transport. If the expression of tolerable risk on an annual basis may present problems, the fact that the number of voyages (trips) was chosen as the most appropriate exposure variable for ship companies. Variables such as journey length or journey time may be more relevant for shipping, and this is something that should be examined. Needless to say, no similar issues have been thoroughly discussed thus far on the tolerable level of environmental risk. 1496

C. CBA and Decision-making based on risk The aim of FSA studies is that it can be used as a tool to facilitate transparent decision-making process. Thus, besides QRA, FSA also provides a clear justification for proposed regulatory measures and allows comparison of different option of such measures to be made based on Cost Benefit Analysis(CBA). As a decision making tool, CBA is also a vulnerable step, in the sense that it involves numerous assumptions on a great number of variables, and as a result runs the risk of wrong conclusions or even manipulation if these assumptions are not thoroughly justified. Its purpose is to identify and compare benefits and costs associated with the implementation of each RCO identified and defined in the practices. Some quantitative approaches have to be used to estimate and compare the cost effectiveness of each option in terms of the cost per unit risk reduction, such as Implied Cost of Averting a Fatality (ICAF) and can be expressed in two forms: Gross CAF and Net CAF. The QALY or DALY criterion can be used for risks that only involve injuries and/or ill health, but no fatalities. It can be derived from the GCAF criterion, by assuming that one prevented fatality implies 35 Quality Adjusted Life Years (QALY) gained. As a result, they are also used to calculate Cost per Unit of Risk Reduction (CURR) indicators. Net cost of variant application (costs) CURR (4) Possible risk reduction (benefits) It should be noted here that the reduction in risk (or R) is not measured as before- as the product of probability and consequence, but in terms of reduction in the expected number of fatalities once a specific RCO is put in place. This implies a rather narrow perspective, in the sense that, at least for the moment, only consequences that involve fatalities (and, by extension, injuries and ill health) is considered in this step. However, attempts to extend this approach to environmental consequences are currently under way. The dominant yardstick in all FSA studies that have been submitted to the IMO so far is the $3m criterion. And the $3m figure always probably is inquired. Although any numerical value could be criticized, the need for a numerical criterion is essential, and until now the problem in the FSA process is not the exact numerical criteria but the way that costs and benefits are estimated for subsequent evaluation against the criteria. Since decision making is a kind of management, on the basic of all definite criterions, transparent process is necessary. But nowadays the criterions including CBA indicators and NCAF have been under discussion. RCOs that was recommended based on mentioned always is a criticism. IV. PROPSAL OF RELATIVE RISK ASSESSMENT QRA is the most important step in the whole FSA method. It is connected with designing the computational model for risk estimation, based on the description of the influence diagram between ships and the environment. The identification of the risk resulting form hazards is made in Step 1. There are important scenarios indicated in the previous step being considered and the amount of risk occurring in each scenario is computed [9]. Through the analysis, factors which may have essential influence on the risk level are identified, and thus the attention is focused on the most important reasons for the risk. The main aims of this step are to generate and specify risk profiles, present them in a form which is important and useful for other steps and decision makers in Step 5, and finally to specify changes in the risk as a result of potential employment of the variants of risk control in Step 3. A. Relative risk assessment model Generally speaking, risk configuration for one, specific environmental hazard, based on the relative criterion of the determined severity natures, in association with the computing method of the risk matrix in the generic model can be established generally as a marine safety. n R R (5) i 1 i i where Ri denotes risk presented as a set of important parameters and i denotes weights of these parameters. In a summary, the severity of accident or incident can be viewed as the intergraded consequence and ranked according to Tab 3[7], which is the relative severity in the relative risk. TABLE 3 RELATIVE SEVERITY CRITERIA FOR VESSEL TRAFFIC NO Grade value Descriptions 1 Extra serious 50 teens fatalities 2 Very serious 10 many fatalities 3 Serious 6 single fatality or multiple severe injuries 4 Less serious 1 marginal injuries 5 Slight 0.1 small harm to people 6 Incident 0.05 no significant harm to people Taking relative relations and multiple hazards into consideration, the configuration of risk for m hazard sources in the investigated area during the analyzed period of time can be computed by using the risk parameters matrix and weights matrix as follows: R [ ( x ) ( x ) ( x ) ( x ) ( x )] i f m S m R m Sr m Rr m i f ( xm) S( xm) R( xm) S ( x ) ( ) r m R x r m j { F, S, R, Sr, Rr }; 1 1 i m; 1 j ji m i 1 i Where x is the calculated value of dependence degree under the five different factors: x the frequency, f T (6) 1497

S x the relative severity, S x the obligated severity r entailed by accidents, R x the nature of risks, and R x the obligated risk entailed by accidents. r represents respective weight parameters. Using the Bayes statics, the probability can be deducted based on historical data and modeling of influence diagram [12, 13, and 14]. The next step of formal safety assessment is to connect the most important factors of risk. Attention is focused on those which cause the highest risk level. First of all, they have to be analyzed taking into consideration the following coefficients: (1) high level of risk, (2) high severity, (3) high probability, (4) low confidence [15]. Next, all means of control are identified so that the control of risk, calculated in Step 2, could be possible. Taking into consideration either risks which occurred in the past or risk that could occur in the future, effective and practical variants of the control of the investigating domain are established. For each option, foreseen reductions in risk as after-effects of given possibilities are estimated. Finally, a register of all variants of risk control with effective risk reduction is gained, which is particularly analyzed in Step 4[9]. V. CONCLUSION The discussion of a/the vessel traffic risk has always been an important issue in the shipping industry [13, 16]. A lot of work has been done aiming to ensure ship safety navigation. This paper, with the overview of formal safety assessment approach, attempts to show how to improve the quantitative risk analysis and risk-based Decision making of the FSA approach. As a result, a relative risk assessment methodology was being held out. This method, verified in the cases of QRA [13], turns out to be feasible to work out the identified posterior probability by Bayesian learning, especially perception of accidents in the near future. ACKNOWLEDGMENT The research work was a part of work under the guidance of Shanghai Municipal Education Committee Research Project, with the contract number 09YZ252. The research was also partially supported by Shanghai Leading Academic Discipline Project, China under the contract number S30602. We want to thank some anonymous referees for their comments on an earlier version of the manuscript. [2] Kontovas Christos A., Psaraftis Harilaos N. (2009).Formal Safety Assessment: A Critical Review. Marine Technology, Vol. 46, No. 1, 2009, pp. 45 59 [3] Wang J. (2001). The Current Status and Future Aspects in Formal Ship Safety Assessment. Safety Science. 38 (2001)19 30. [4] Connell P Mc (2010). A Standards Based Approach to Operational Risk Management under Basel II. http://74.125.155.132/scholar?q=cache:euifbgk9ig0j:sch olar.google.com/ [5] SAI (2004) AS/NZS 4360: 2004 Risk Management and HB 436:2004 - Risk Management Guidelines - Companion to AS/NZS 4360: Standards Australia/ Standards New Zealand 2004 [6] Hu, S., Fang, Q., Xia, H. and Xi, Y. (2007). Formal safety assessment based on relative risks model in ship navigation, Reliability Engineering and System Safety 92(3): 369 377. [7] MEPC, M. E. P. C. (1997). Interim Guidelines for the Application Of Formal Safety Assessment (FSA) to the IMO Rule-making Processes, Technical Report MEPC/Circ. 335, International Maritime Organization, London. [8] MEPC, M. E. P. C. (2007). Consolidated Text of the Guidelines for Formal Safety Assessment (FSA) for use in the IMO rule-making process, MSC/Circ. 1023, MEPC/Circ.392, International Maritime Organization, London. [9] Mikulik, J. and Zajdel, M. (2008). Automatic Risk Control Based On FSA methodology Adaptation For Safety Assessment in Intelligent Buildings. Int. J. Appl. Math. Comput. Sci., 2009, Vol. 19, No. 2, 317 326 [10] Kaplan S, Garrick BJ(1981). On the quantitative definition of risk. Risk Analysis 1981; 1(1):11 27. [11] Ayyub BM, Beach JE, Sarkani S, et al. Risk analysis and management for marine system. Naval Engineers Journal, Issue 2, 2002, pp181-206 [12] Hu S; Cai C; Fang Q (2008). Risk Bayesian assessment approach to HOF-based ship operation in harbour. 2008 IEEE International Conference on Industrial Engineering and Engineering Management, IEEM 2008, p 1954-1960 [13] Hu S; Li X; Fang Q; Yang Z(2008). Use of Bayesian Method for Assessing Vessel Traffic Risks at Sea. International Journal of Information Technology & Decision Making. Volume: 7, Issue: 4 (December 2008) Page 627 638. [14] HSE (2001) Reducing Risk, Protecting People :HSE s decision-making process, Health & Safety Commission, 2001 [15] Skjong, R., E. Vanem, Ø. Endresen (2005). Risk Evaluation Criteria SAFEDOR-D-4.5.2-2005-10-21- DNV; 21 October 2005 [16] Devanney, J.W., III (1967) Marine Decisions Under Uncertainty, MIT Press, Cambridge, MA. REFERENCES [1] Soares, C. G. and Teixeira, A. P. (2001). Risk assessment in maritime transportation, Reliability Engineering and System Safety.74(3): 299 309. 1498