The characteristics of team communications are important since large process systems such as nuclear power plants, airline, and railways are operated by operating teams. In such situation, inappropriate communications can cause a lack of situational information and lead to serious consequences for the systems. As a result, the communication characteristics of operating teams should be understood in order to extract meaningful insights to address the nature of inappropriate communications. The purpose of this study was to develop a method to evaluate the characteristics of team communications based on social network analysis and compare them with the frequency of inappropriate communications. In order to perform the analysis, verbal protocol data, which were audio-visual recorded under training sessions by operating teams, were used and interfacing system loss of coolant accident scenarios were selected. As a result of the study, it was found that the frequency of inappropriate communications decreased when more operators perform the same types of role as other operators, since they can easily and effectively back up each other. Also, the frequency of inappropriate communication is decreased for teams which provide a relatively large communication content that acknowledge or confirm another communication content. (C) 2013 Elsevier Ltd. All rights reserved.