This study proposes a Policy, Process, Personnel and Incentive (3P+I) framework which may help project managers manage construction site safety. A postal survey of contractors in Singapore was conducted to test the framework. It is found that site accidents are more likely to happen when there are inadequate company policies, unsafe practices, poor attitudes of construction personnel, poor management commitment and insufficient safety knowledge and training of workers. It is recommended that project managers pay more attention to the important factors identified in this study to help them enhance performance at construction sites and reduce the frequency of accidents.