## 5 Case Study
### Description  
The issues explored in this study arose from an in-depth study of a large shipyard in China. During the fieldwork, we identified coordination needs related to reverse logistics and on-site HSE management, which led to the development of this study. In S Shipyard, the primary sources of hazardous waste, specifically waste paint barrels and waste paint slag, are generated during the coating process. This process can be divided into four distinct stages: steel pretreatment, segmented coating, dock coating, and wharf completion coating. The entire ship construction process is monitored, and each operational stage occurs in different areas, such as the steel plate yard, the cruise ship painting platform, and the dock area. This necessitates the recycling of hazardous waste from each area to a designated treatment center for professional disposal. To enhance operational efficiency, the logistics center is tasked with vehicle allocation, ensuring that vehicles are dispatched uniformly from a central location to each collection point for hazardous waste transport. Figure 6: Flowchart of the discrete crow search algorithm. In actual shipyard practice, safety equipment and vehicles need to be regularly inspected and maintained as part of strict on-site safety management protocols. Thus, situations such as vehicle breakdowns or safety equipment failures during transport, which could lead to the disruption of operations, were not considered in this study. After completing a task, vehicles proceed directly to the next assignment without returning to the logistics center. Figure 7 illustrates the process of hazardous waste management and recycling in shipyards. Due to restrictions on confidentiality during the construction of China's first domestically constructed large cruise ship, the case study in this paper is based on some of the real data from the cruise shipyard, adjusted to take into account the operating conditions common to large shipyards. That is, the data used in this study come from field research and existing records in shipyards, supplemented by industry common sense to ensure representation. The approach balances the requirement for confidentiality with the need to maintain reproducibility and relevance. There are six hazardous waste collection points in the factory. One logistics center is represented by S, and one hazardous waste treatment center, denoted as E. Operators are assigned to recycle hazardous waste materials within specified time frames, maintaining optimal satisfaction levels throughout operations. Details regarding node information and vehicle-related parameters are provided in Tables 3-5 and illustrated in Figure 8.  
The risk weight coefficient of safety importance was derived from on-site investigations and field studies conducted at shipyards. Factors such as different production processes, the nature of materials involved (e.g., toxic gases, flammable substances), and the varying coverage areas of work zones were considered. Based on these practical observations and expert judgments, the coefficients were assigned to reflect the relative safety risks in different areas. This approach ensures that the weighting captures real-world conditions specific to shipyard environments.