## 4 Efficiency Management
### Description of Symbols  
The symbol descriptions contained in this article are shown in Table 2.  
Considering that the longer the time of contact with hazardous waste materials, the higher the risk to the workers, it is stipulated that the workers should especially deal with the recovery of hazardous waste materials in a certain period of time, and give priority to the treatment of hazardous waste materials in a certain period of time. Work can also be carried out after the specified time is exceeded, but due to the increase in working hours, the time period exceeded may generate additional operational risks, and safety satisfaction will be discounted. Therefore, a fuzzy time window is proposed to reflect such a real situation, and the risk of the operator is described by the fuzzy processing method of the service time window. A safety satisfaction function is proposed, and then the risk weight is combined to describe the overall risk of the hazardous waste recycling network. The safety satisfaction function is represented by Equation (1):  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Symbol** & **Description** \\ \hline \(I\) & Set of hazardous waste collection points, \(I=\{1,2,\cdots,n\},i\in I\) \\ \(I\) & Set of hazardous waste treatment center point, \(J=\{1,2,\cdots,m\},j\in J\) \\ \(N_{v}\) & The actual number of vehicles \(v\) in use \\ \(V\) & Set of hazardous waste transport vehicles, \(V=\{1,2,\cdots,k\},v\in V\) \\ \(R_{i}\) & Number of people handling hazardous waste at collection point \(i\) \\ \(a_{i}\) & The amount of hazardous waste materials at the collection point \(i\) \\ \(x_{ijv}\) & The amount of hazardous waste materials transported from collection point \(i\) to treatment center \(j\) through vehicle \(v\) \\ \(d_{ij}\) & Distance from hazardous waste collection point \(i\) to treatment center \(j\) \\ \(c_{1}\) & Transportation cost \\ \(C_{0}\) & Loss cost of vehicle volume \(v\) \\ \(G_{i}(T_{ip})\) & Safety satisfaction function \\ \(Q_{v}\) & Load capacity of vehicle \(v\) \\ \(p_{v}\) & Vehicle \(v\) travelling speed within the shipyard \\ \(s_{j}\) & Treatment capacity of hazardous waste materials in treatment center \(j\) \\ \(T_{ip}\) & The time when vehicle \(v\) arrives at collection point \(i\) \\ \(t_{iv}\) & Loading of vehicle \(v\) to collection point \(i\) takes time \\ \(\omega_{i}\) & Risk weight coefficient of safety importance of collection point \(i\) \\ \(c_{3}\) & Storage cost \\ \([ET_{iou},ELT_{ip}]\) & Expected time interval \\ \([RET_{ip},RLI_{ip}]\) & Tolerance time interval \\ \hline \hline \end{tabular}
\end{table}
Table 2: Symbol description details.  
\[G_{i}(T_{iv})=\begin{cases}(T_{iv}-RET_{iv})/(EET_{iv}-RET_{iv})&T_{iv}\in[RET_{iv}, EET_{iv})\\ 100\%&T_{iv}\in[ET_{iv},ELT_{iv})\\ (RLT_{iv}-T_{iv})/(RLT_{iv}-ELT_{iv})&T_{iv}\in[ELT_{iv},RLT_{iv})\\ 0&T_{iv}\in[0,RET_{iv})\cup[RLT_{iv},\infty)\end{cases} \tag{1}\]  
In Figure 5, we present the fuzzy time window, which depicts the safety satisfaction of collection point operators based on the vehicle's arrival time within the dedicated time \([EET_{iv},ELT_{iv}]\) for hazardous waste disposal. If the vehicle arrives within the expected time frame, the safety satisfaction of the collection point operators at its highest level is 100%. However, if the vehicle arrives earlier or later than the expected time, it will lead to a reduction in safety satisfaction, gradually decreasing as the gap between the vehicle arrival time and the expected time increases. The arrival time window constraint \([RET_{iv},RLT_{iv}]\) represents the tolerable range for the collection point in terms of vehicle arrival time. If the arrival time falls outside the expected range and beyond the tolerable range, the safety satisfaction is reduced to 0.