Maritime industry has intended to standardize to collect data of marine casualties and incidents in order to reveal safety measures not to repeat them. This paper suggests proper items for the investigation of human factors that are recognized as most important causes. Studies on a navigation showed that many factors increase difficulty of maneuvering situations and navigator' action and there is not the definite border between danger and safety. Useful information for safety measures is what factors affect risk of navigators' action and how. Navigators' internal and external conditions bring their behavior and action, which are recognized as performance shaping factors. We listed up ninety-five important elements considering safety measures, and evaluated their effects for a navigator's performance. We suggested multivariate-analysis for extracting relations beween elements to control for safety management.