In recent years, investigations into major incidents often highlight poor safety culture as one of the key causal factors. These investigations are often assisted by causal analysis tools that help to ensure that the investigation and the information captured are systematic. However, current causal analysis tools are not designed to analyze dynamic complexity of major incidents and safety culture, which arises from the interactions between actors and the temporal and spatial gaps between actions and consequences. This is because most causal analysis tools model events and causal factors linearly. In contrast, systems thinking, a discipline of seeing systems holistically, emphasizes the circular nature of complex systems, i.e. cause and effect are not distinguishable. This paper proposes that traditional causal analysis tools and investigation should be enhanced with the use of systems thinking tools. One of the systems thinking tools that is particularly useful in analyzing major incidents and safety culture is causal loop diagrams. The diagrams can be used to explain the systemic structure sustaining a safety culture and identify effective interventions to improve the safety culture and prevent a recurrence of a major incident. The paper demonstrates the use of systems thinking and causal loop diagrams through a case study on Bellevue hazardous waste ﬁre in Western Australia. The case study shows how different actors in the system, each acting in reaction to pressures that they are facing, produced and sustained a poor safety culture that was a major contributory factor to the ﬁre in 2001.