•Using the ConAC framework, 1.039 causal factors were identified in 176 construction accidents.•Factors most identified were worker actions, risk management and immediate supervision.•Worker actions is the outcome of many other causal factors.•Immediate supervision is a key causal factor connecting management and worker actions.•Risk management is a key causal factor and strongly connected to immediate supervision and worker actions. The aim of this study was to add to the relatively sparse literature on accident causality in the construction industry by identifying frequent causal factors and connections between causal factors. Using the Construction Accident Causation (ConAC) framework, 176 relatively severe construction accidents investigated by the Labour Inspection Authority in 2015 were analysed. The seven factors most identified were (in rank order): (1) worker actions, (2) risk management, (3) immediate supervision, (4) usability of materials or equipment, (5) local hazards, (6) worker capabilities, and (7) project management. A set theoretic approach was used to identify causal connections between causal factors. Risk management, immediate supervision and worker actions were found to be key causal factors and strongly connected. The analyses identified seven causal factors consistently connected to worker actions, for example immediate supervision and local hazards. Immediate supervision was found to be strongly connected to both worker actions and risk management, underlining the importance of the supervisor controlling unsafe conditions/acts and planning the work to reduce risk. Strong connections were also found between risk management and immediate supervision, and between risk management and worker actions. Risk management and immediate supervision is to a large degree about planning and risk control at different levels, underlining the importance of risk being addressed at different levels and by different actors in construction projects.