## 3 BBN Model Structuring and Verification for a Grounding Accident
### Qualitative and Quantitative Background Knowledge  
Maritime transportation is a complex socio-technical system that is often influenced by economic pressures. At the coarse level of organization of the baseline BBN model structure, grounding impact factors are divided into human, organizational, external, and technical factors. Each factor has subfactors and each of them can affect a number of other factors. Subsequently, coarse-level factors are refined into detailed variables suitable for implementation into the BBN framework (terms factor, variables, nodes are used interchangeably throughout the paper, though they represent a single concept.) In maritime transportation, accidents caused by human error are most common. Existing data and research to date shows that 43% to 96% of all marine casualties are caused by human error. According to [31], human factors cause 67.6% of maritime grounding accidents. The nodes relating to human error and organizational segments are deliberately emphasized in the model. Human factors are part of a scientific discipline that deals with the study of human abilities (perception, mental state, etc.) and its limitations in relation to the system [27]. The term \"human factor\" is often confused with the term \"human error\". According to [32], various authors' use of different definitions makes it extremely difficult to identify difference between human error and human factor. According to [33], human error is an intolerant activity or deviation from normal behavior whose boundaries are defined by the system and as such is a direct cause of a maritime accident. According to [34], the human factor is the root cause of a maritime casualty. According to the definition used by authors in their work, the human factor consists of organizational, group and individual factors that affect maritime safety. In this paper, the term \"human error\" is used as the immediate cause of a marine casualty caused by human behavior. Organizational factors reduce the risk of maritime accidents as human experience can significantly reduce the likelihood of a maritime accident by knowledge and use of safety measures. Technical factors refer to equipment like hardware, software, and vessel construction. Statistically, 20% of maritime accidents are caused by technical factors [35]. External factors refer to variables related to hydrometeorology, weather, traffic distribution, navigation in shallow water and special caution area navigation. Identified factors are organized to form a causal network structure according to the subjective opinion of the expert. It is necessary to include expert knowledge at the point of structuring because most of the databases of maritime accidents do not provide causal relations, but only enumerated statistical information on different factors and consequences. The disparities in the organization of statistical data extends to the quantitative aspect of BBN modeling. According to [36], statistical data adds to the uncertainty of the model, as this data are often incomplete or not properly investigated. For example, it is known that a certain number of accidents are not regularly reported and as such do not undergo official statistical processing nor inclusion in the databases. Additionally, real accident data collected without proper investigation often do not include the chain of events that causally led to marine accidents, thus event ordering as potentially useful information for modeling is not available. Due to the above data limitations, including the relatively small samples in the statistical realm of rare events and inconsistent information organization, existing statistical data were supplemented with expert estimation of parameter values in the model. Statistical data were used to assign a priori values of the following factors: time and hydrometeorological factors. Human node values and parts of organizational factors are taken from other sources [9; 26; 36].