THE BALANCE BETWEEN MARINER'S ABILITY AND OCCURRENCE OF MARITIME ACCIDENTS
Hiroaki KOBAYASHI (Tokyo University of Mercantile Marine, Japan)
Abstract: Training of Bridge Team Management is recognized to be effective for improving safety of navigation. Techniques required in the Bridge Team Management must correspond to the techniques to realize the safe navigation. The necessary techniques in a bridge team can be clarified based on the consideration of reasons why bridge teams are organized.
The objectives of a bridge team organized by plural persons are to expect the realization of higher technical level than the level of a single officer. When the expected technical level cannot be realized, it is said that the Bridge Team Management is insufficient. The reasons why the required techniques cannot be attained should be studied. They are necessary techniques in a bridge team and it is training objectives on Bridge Team Management that the necessary techniques in a bridge team should be learned.
In this paper, the necessary techniques in a bridge team are defined as communication and cooperation based on the concept mentioned above. Furthermore, ship-handling operated by a bridge team causing a risky situation are shown with handling examples when the necessary techniques are not attained.
This paper proposes the basic concept on the future training of Bridge Team Management.
The objective of Bridge Team Management is to establish safe navigation. In this paper, rationality on effects of the Bridge Team Management for safe navigation is shown. Conditions of maintenance of safe navigation are discussed based on the relation between necessary techniques and attainable techniques. As the relation contains uncertainty of human functions and a change of navigation environment, this concept is capable to be used for understanding the causes of accidents widely. Applying the concept, we can clarify not only the effect of a bridge team but also the necessary techniques for attaining the function of a bridge team. The necessary techniques in Bridge Team Management are discussed with the some results of training on Bridge Team Management.
2. DISCUSSION ON CONDITION OF ACCIDENTS OCCURRENCE
Accidents are caused by many kinds of factor. Before discussing each factor in detail, it is needed to discuss the condition of accidents occurrence from point of global view relating to the factors on accidents. It is mentioned frequently that over 80% of the causes of accident are human behavior. On the other hand, it is also common knowledge that the degree of safe navigation may be changed by the condition of navigational environments.
The concept on the condition is proposed in this paper based on the relation between the difficulty of navigational environments and human ability that decide the human behavior. Firstly, the condition of navigational environment relate to following items,
- Maneuvering characteristics of own vessel
- Water area for navigation
- Weather and sea state
- Traffic condition
(kinds of traffic vessels and the density)
- Rule of road
Fig. 1 shows the probability of degree of navigational difficulty. "µΕ" shown by line "b" indicates the mean difficulty of the water area. The mean difficulty can be changed by the condition of relating factors mentioned above. Mean traffic density and average weather conditions correspond to them. In case of a wide water area and low traffic density, the mean difficulty will be low shown by line "b". On the other hand, all of the factors mentioned above are not constant. They may change uncertainly. The probability of difficulty can be change caused by the condition of relating factors. They are the change of traffic density in term of time and weather conditions and so on. The distribution on probability becomes to narrow when a separation scheme and restriction of traffic vessels are applied. The probability changes from condition "A" to condition "C" in Fig. 1.
Secondly, characteristics of human ability on ship handling are discussed. The ability that human operator shows is changed by following factors,
- Mariner's license rank
(relating to the elapsed time of standing watch)
- Tension (relating to the time of watch)
Fig. 2 shows the probability of degree of human ability "µH" shown by line "a" indicates the mean "a" treatment ability that is decided by mariner's license rank and their experience. In case of high rank of the license and the long experiences, the mean ability becomes high shown by line "b". Human dose not always show same ability. It is a common that it may be change in term of time. The factors that make the change of ability are fatigues and tension. In case of high tension, he shows higher ability than normal ability. Point "α" in Fig. 2 indicates this situation. Under the condition of fatigue or drunken, he shows lower ability than normal ability Point "β" in Fig. 2 indicates this situation. Human error may occur in these situations.
Fig.1 The probability of the degree of navigational difficulty
Fig.2 The probability of the degree of human ability
Table 1 The awareness level of the brain
It is said that the awareness level of the brain is divided into 5 categories shown in Table 1. Human keep the situation in Phase II for long time in which normal information processing can be accomplished. Human cannot keep the situation in Phase III longer than 5 or 10 minutes in which higher information processing that is proper, high speed and accumulate processing can be done. Probability curve in Fig. 2 shows this probability of human processing ability. The situation at point α cannot be kept for long time.
Support systems for ship handling being developed in recent days should be developed based on these human characteristics that are changeable human ability. One of objectives of support systems is to support the human operator when his ability becomes a low accomplishment. Another one is to support him when he has to carry out higher information processing for long time. Furthermore it is well known that support system should accomplish tasks that human cannot carry out. Though some of the support systems have been developed to assist the normal function that can be done by human in normal situation on the condition that human has to be normal situation, these kinds of function should not be needless ones.
2.2 Accident Occurrence and its Condition
In this section, the relations between the accident occurrence and its conditions are discussed. It is often observed that a human having lower ability carried out handling in a situation of high tension with feeling difficulty, but the handling under the same condition can be done easily by a human having higher ability. The difficulty of handling ship should not be decided only by the condition of navigation, but it is also decided by human ability. The conditions of accident occurrence relate to the combination between the condition of navigational environments and the human ability. Fig. 3 shows the relation between the ability required by environment to accomplish safe navigation in the condition and the human ability that can be carried out by the human. The line with an incline of 45 degrees indicates the equivalent condition between them. Normal navigation is carried out in the condition of higher part of this line. In the lower zone of this line, it shows a dangerous situation to occur an accident. This area shows that the ability required by the navigational environment needs higher than the ability accomplished by the human.
Fig. 4 shows the situation of Fig. 3 with the contents of Fig. 2 and Fig. 3. In case of the condition with both ability being ,average shown as situation "A", the safe navigation can be expected. As mentioned above, the situation of human and environment may not be same and they may fluctuate. The ability required by environments may become high temporary caused by the change of weather and the concentration of traffic vessels. This condition is shown as situation "B". Safe navigation cannot be accomplished by mean human ability at this situation. If human realizes higher ability with tension, the situation can be moved to the situation "C", and navigation will become safety again. On the other hand, although the navigation environment is mean situation, human ability shows lower one by the fatigue or lack of tension. This situation shown by D is also dangerous situation.
The navigational safety defined by both condition of human ability and required ability navigational environment
The fluctuation of safety degree relating to the probability of human ability and required ability
By analyzing results on marine accidents, it is often difficult to recognize the necessary reasons which lead to the accidents. In other words, although the similar situation often happens daily, it is the fact that no accident occurs. So it is reasonable thought that the accident may happen when the unusual events occur simultaneously. It is statistic event. One of the situations that scare happen is shown by situation F in Fig. 4. In this condition, the ability required by the navigational environment becomes extremely high while the human ability goes down temporary.
The probability on fluctuation of human ability and navigational environment are now studying, they will be present shortly.