This paper proposes a new quantitative method of supporting business decision-making while investing safety related facility and service. This method suggests the priority of investment relevant to safety within limited budget, so most possible hazards can be removed or the company may not invest money for the acceptable hazards depending on the budget. The typical theory that risk is equivalent to the multiplication of frequency and severity, given by CCPS (Center for Chemical Process Safety) in American Institute of Chemical Engineers (AIChE), is modified to consider more detailed classifications. The criteria of decision are determined by the manager's survey. Computation of R matrix results the priority of investment and the investment is finally chosen by the decision criteria. This method is proved to be effective in reducing safety accidents by proper management through the analysis of real accident data of a Korean petrochemical company for using Yonsei Safety Information Management System (ySIMS). We collected 5500 accident data for one and a half year by using the 'detailed classification sheets' including more than 60 accident cause types. As a result of applying this system to the company, the number of accidents of class A and B was significantly reduced in 6 months after the systematically chosen investment by 70% and 62% that was from 33 to 10 and from 122 to 47, respectively. The aim of this study is to manage safety accidents properly and to prevent major accidents from petrochemical industry.