Fig.2 shows this chaining process of mistakes based on human factors. However, trouble will not occur if this chain of mistakes can be broken before errors in operation or behavior occur.

　

Fig. 1 Definition of human error [1]

　

(3) Certain personal and environmental factors can induce mistakes as a background to occurrence of human error. Such personal and environmental factors include human relationship in the work place, working time, personal characteristics, the health condition of the person, work characteristics and environment conditions around worker. etc. These might include, for example, the environmental condition or state of mind of the worker or sometimes a desire to omit certain work process in order to complete a task more quickly. These personal and environmental factors that act as backdrop to the occurrence of human error are directly related to human factors. It is already well recognized that improvement of such personal and environmental factors is very important to preventing the occurrence of human errors

　

Fig. 2 Chain of mistakes due to human factors

　

It is generally recognized that the human factors shown above normally differ between inexperienced and skilled workers. SRK Model advocated by Rasmussen shown in Fig. 3 can assist in understanding these differences.

　

Fig. 3 SRK Model advocated by Rasmussen [2]

　

Rasmussen stated that human behavior can be categorized into three levels: behavior based on skill, behavior based on rules, and behavior based on knowledge. One of these three types of behavior will be selected depending upon sensuous incentive, knowledge gotten by education or training, work condition requested, necessary action and so on. For example, a skilled worker can select his task immediately by taking short cut to automated sensitive behavior pattern based on his memory of relevant skill. However, the behavior of an inexperienced worker will be taken through identifying information, selecting and deciding task, planning task and behavior, selecting tool stored for task and sensitive behavior pattern. Moreover, a person who is undergoing training will take his behavior through the route of behavior based on rule.

These categorized three types of behavior are connected with three types of human error categorized by Reason [2] from a viewpoint of processing information in brain;

(1) Mistake: Error that is occurred in judging wrong balance with external information.

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