This thesis provides background information on DFS carried out by the government in an effort to reduce the accident rate, cases of DFS in other advanced countries to study their risk detection, risk assessment, risk control measures, and cases in which application of DFS during the designing phase succesfully led to reduction of the accident rate. Till now, the focus has been on incident responses after the occurance of accidents, it describes the importance of considering safety during the desining process through safety results and cases.