# Application of Digital Twin in Handling and Transportation of Hazardous Chemicals
## 2 Literature Review
### Applicability of DT in the Safety of Hazardous Chemicals  
In terms of technical application, [PERSON] et al. have developed a framework to accurately identify the abnormal static situation of personnel in indoor scenes. It is based on IoT and DT. They developed relevant algorithms to improve monitoring accuracy and eliminate false alarms in this framework [16]. As for present applications in handling and transportation, [PERSON] built a framework of DT which comprises ML and a prognostics algorithms model used to predict the risks of pipeline system emergency [17]. DT has been applied in the field of petrochemical industry [18], just as in the field of hazardous goods. [PERSON] et al. designed a DT platform for 3D and real-time georeferenced visualization of container parks and the location of hazardous containerized freight [19]. Additionally, [PERSON] displayed digital technologies and their benefits that have been incorporated into the exploration, production, and transportation of oil and gas products in Russia [20]. Extending to hazardous waste process, [PERSON] aimed to solve the multiunit linkage optimization problem under the framework of DT technology [21]. [PERSON] summarized the DT application in transportation infrastructure: railway, highway system, bridge and tunnel, pointing out the drawbacks at the same time [22]. [PERSON] illustrated how to construct a port management system based on DT and its implementation steps, furthermore, the function of this system is discussed, mainly focused on risk prediction, environment protection, data sharing and information communication, cargo handling and transportation, container terminal operation [23]. DT has application prospects in the handling and transportation control of hazardous chemicals. Firstly, as of the first half of 2021, there are more than 13,000 hazardous chemicals logistics enterprises in China, with a total of more than 575,000 transportation vehicles. The establishment of this system based on DT technology will fully integrate all kinds of information and provide a visual interface to show the operation links. It is necessary to further study various virtual risk scenarios. Secondly, a realistic problem has been raised in that there are so many risk scenarios in the hazardous chemical handling and transportation process, it involves a lot of different infrastructures, such as LNG terminals and chemical plants, etc. Although the number of them is huge, the construction and layout of their internal structures follow the national unified standards, and the transportation vehicles are governed by the same authorities as roads at all levels [5]. If the structures are modularized in the system, and then connected by 'assembly', this will reduce the burden of modeling. Thirdly, sensors are widely distributed in all positions of hazardous chemical production units. During transportation, the tanks of these vehicles are equipped with traditional sensors, such as temperature and pressure sensors and liquid-level manometers and GPS, and improved sensors offering more detailed monitoring of vehicle status are installed on it [24]. Figure 1 displays the diversity of sensors in the hazardous chemicals monitoring system. Concerning driver fatigue detection, many scholars are deepening the research on this issue. [PERSON] discussed all the techniques concerning driver fatigue detection, introducing all kinds of sensors, and how machine learning and big data techniques are used in this process was shown as well [25]. Heterogeneous sensors installed on the tank were used to evaluate the status of the vehicle synthetically. The environment in the station is more complex, and chemical leakage detection sensors are often equipped and interlocked with the actuator to control the emergency shutdown of the valve [26; 27]. Based on the sensor data, the gas diffusion is further rehearsed and the risk assessment is carried out [28].