The quantitative risk assessment and consequence analysis by accident scenario in the process of EPS(Expendable Poly Stylene) reaction process are conducted. And the decision making process is studied followed by selecting various alternatives to safety management and facility improvement. The result are as follows; 1) The object of decision making through comprehensive risk assessment are the scenario which can cause four major accident, which are made by process analysis, work analysis and hazard identification. 2) Frequency analysis of ETA, FTA, HRA and consequence analysis of accident to each have been conducted. The each frequency values are yielded $9.2{ imes}10_{-5}/yr$ to scenarios $1, 8.2{ imes}10^{-4}/yr$ to scenario 2, $4.5{ imes}10^{-6}/yr$ scenario 3 and $1.8{ imes}10^{-7}/yr$ to scenario 4. The each scenarios have been conducted consequence analysis. 3) The calculated values have been obtained 4.00 to scenario 1, 3.25 to scenario 2, 2.43 to scenario 3 and 1.34 to scenario 4, as the weight value had been applied to the quantitative and normalized criteria of all components. As a risk criteria, scenario 1 have been selected, which is the most dangerous scenario as a result of ranking the scenario. 4) According to the importance of FTA and contribute to scenario 1, the cost-benefit values are yielded $8.05 imes10^5[￦/yr]$ to final alternative(Al), $1.55{ imes}10^5[￦/yr]$ to final alternative(A2) and $2.32{ imes}10^5[￦/yr]$ to final alternative(A3). As a result of final alternative(Al) has been selected, which is the most optimized alternative.