## 4 Results  
We assessed the risks involved in each of the four tasks for the concrete cutting stage--the main target of management within the shield concrete structure decontamination and decommissioning processes described above. We calculated the level of risk by work, structural risk, and job risk, as well as the total risk. Here, the risk is roughly estimated to be in the range of 0 to 100, which indicates the minimum and maximum values when the frequency and depth are either at their lowest or highest. In addition, slight differences may occur depending on the weight; here, a larger number indicates greater risk. Table 11 presents the risk assessment results for each task. The risk was assessed in terms of the structural and job risk items that could be generated for that type of work. We derived the converted value by assigning the weight for each task determined by the expert interview to the overall score. The assessment by work type revealed the levels of risk to be in the following order: residual concrete removal (54.17), cutting with wire saw (21.21), wire saw installation (9.74), and wire saw transport (3.99). Table 12 presents the risk assessment results for each type of risk. The assessment results of structural risk were greater for collapse (22.55) than for drop (13.64), whereas job risks were assessed in the following order: fall (58.08), eye attack (38.25), jam (26.74), and electric shock (18.39). In the integrated assessment of structural and job risks, fall (58.08) was considered the most dangerous. The overall level of risk for job risks was high. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline  
Table 13 presents the risk assessment results by work and risk type. The difference between the risk assessment by risk type above and that shown in Table 13 is that even for the same risk type, the assessment is divided into different items for different work stages. According to the work-risk type assessment, the total risk was evaluated as 25.17. The breakdown shows that the risk of eye attacks (66.75) and falls (58.08) in residual concrete removal were high, whereas drop (3.23) and collapse (3.34) in wire saw transport were relatively low risk activities. The risk assessment can be plotted to compare the results of all the items at a glance, as shown in Figure 3a-c. The work-specific/risk type-specific/work-risk type-specific risk assessment graphs evaluated above are analyzed as follows. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Category** & **Item** & **Conversion Value** & **Dimension Ranking** \\ \hline Total risk & & 25.17 & - \\ \hline \multirow{6}{*}{Wire saw transport} & Collapse & 3.34 & 16 \\  & Drop & 3.23 & 17 \\  & Jam & 5.41 & 15 \\ \cline{2-4}  & Collapse & 10.33 & 10 \\  & Drop & 7.94 & 12 \\  & Jam & 14.61 & 9 \\  & Electric shock & 6.06 & 14 \\ \cline{2-4}  & Collapse & 29.22 & 8 \\  & Drop & 29.75 & 7 \\  & Eye attack & 9.74 & 11 \\  & Jam & 30.28 & 6 \\  & Electric shock & 7.08 & 13 \\ \hline \multirow{6}{*}{Remove residual concrete} & Collapse & 47.32 & 4 \\  & Eye attack & 66.75 & 1 \\ \cline{1-1}  & Fall & 58.08 & 2 \\ \cline{1-1}  & Jam & 56.67 & 3 \\ \cline{1-1}  & Electric shock & 42.03 & 5 \\ \hline \hline \end{tabular}
\end{table} 
Table 13: Risk assessment results by work and risk type. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Category** & **Item** & **Conversion Value** & **Dimension Ranking** \\ \hline Risk assessment by & Collapse & 22.55 & 1 \\ structural risk & Drop & 13.64 & 2 \\  & Mean value & 18.10 & - \\ \hline \multirow{6}{*}{Risk assessment by job risk} & Eye attack & 38.25 & 2 \\  & Fall & 58.08 & 1 \\ \cline{1-1}  & Jam & 26.74 & 3 \\ \cline{1-1}  & Electric shock & 18.39 & 4 \\ \cline{1-1}  & Mean value & 35.37 & - \\ \hline \hline \end{tabular}
\end{table} 
Table 12: Risk calculation results by risk type. First, the risk assessment results by work type revealed the high level of risk involved in removing residual concrete.