Construction industry is playing the most important role in the economic development not only in Turkey, but also in all developing countries. Turkish construction industry has reached its climax in the last 20 years with 7.4% share in total employment and 11.5% growth in terms of GNP in recent years. Parallel to this growth, there has been an increase in the number of occupational accidents in Turkish construction industry as well. Small or middle scale residential projects have a big share in the industry and majority of fatal accidents usually occur on such work sites. This study focuses on compulsory investments of small or middle scale residential building construction projects such as safety staffing costs on-site, formal safety training courses, PPE, safety facilities and fee for laboratory examinations in employment procedures of workers. Based on these subcomponents of OHS measures, an extensive literature review has been made to single out specific risks and the measures to prevent those risks. These specific parameters are then incorporated into an existing computer program, which had been originally designed to calculate direct construction costs only. By calculating and making a budget for the cost of prevention at the beginning of construction projects, it provides a better understanding of safety costs during a building construction project implementation. Thus, it helps efforts to reduce loss of workers' life and the mitigation of safety costs arising from severe injuries, fatalities, administrative procedures, legal obligations and litigation costs and expenses. The efficacy of the developed computer program is also tested on a construction project. The results reveal that the percentage of compulsory OHS costs to the direct construction costs is 5.15%, and OHS cost per unit area is approximately 8.47 USD/m(2).