To assist safety practitioners in the work of prioritizing preventative activities based on the stage of civil industry, it is necessary to identify the most common causes of accidents in the civil sector. Reports from official accident investigations are examined. For this aim, accidents are examined that were officially investigated by the Ministry of Cooperatives, Labour, and Social Welfare at the building sites of North of Iran (Mazandaran region) between 2013 and 2023. The percentage of causes in each of the several potential cause groups indicates a pattern of causation. There are notable correlations between the different cause categories and the phases of building and accident mechanisms. Depending on the accident's mechanism and the current building stage, there have been seen to be significant variances in accident causation. Prioritizing preventive measures to counter the most likely causes of each accident procedures and building stage should be done using these results.