This paper proposes a human factors analysis method that contains a cognitive process model, a human factors analysis technique and a marine accident causal chain focused on human factors. In this paper, the cognitive process model that can be used as a tool to identify unsafe acts, decisions or conditions is discussed in detail, and 18 towing vessel collision accidents are analyzed to identify related unsafe acts. Then the human factors analysis technique which is based on the well-established human factors frameworks such as SHELL model and Reason's Generic Error Modeling Systems (GEMS) framework is used to identify underlying factors that cause those identified unsafe acts to occur. Lastly, in order to derive the optimum safety barriers, the marine accident causal chains are used.