Many events with catastrophic consequences occurred over past decades. One of them was the disaster in Bhopal. A weak safety culture is mentioned as a one of the causes of this tragic event. It is a generally accepted fact that the level of safety culture has to be continuously evaluated and improved to avoid the occurrence of such situations in the future. This paper introduces a new method Assessment Tree Method (ATM) allowing for quantitative estimation of the level of safety culture in an organization. The ATM enables the determination and quantification of the key aspects of safety culture on the basis of assessment trees. The structure of the trees is analogical to fault tree, a commonly used tool for the analysis of accidents. The assessment process is based on the guided interviews. As a result, a deeper insight is gained and effective identification and elimination of weak points in safety culture enabled. Next, the level of safety culture is calculated taking into account the results obtained for key safety aspects specific for a given organisation as well as their weights of importance. The ATM was tested for the evaluation of safety culture at the university department. There were twenty students, and three staff members responsible for safety, participating in the study. The six key aspects of safety culture were identified: knowledge & skills; awareness; flow of information; monitoring & control & supervision; management commitment and continuous improvement. On the basis of the obtained results it was concluded that the level of safety culture is high and some recommendations were given to make it even better. The most important advantages of the proposed method are quantification and simplicity enabling assessment of a broad scope of the specific aspects of safety culture. The proposed method could be used for the standardised benchmarking of the different organisations. (C) 2015 Elsevier Ltd. All rights reserved.