# Safety Challenges in Battery Swapping Operations of Electric Underground Mining Trucks
## 2 Current Battery Swapping Methods for Underground Electric-Powered Trucks
One of the outtakes is that battery swapping for heavy-duty vehicles in public transport is considered an innovative business model for logistics companies. However, this study does not provide any insight into battery swapping for industrial and off-road heavy-duty electric vehicles. Nevertheless, this technology is developing rapidly, with around 400 battery swapping stations operated by several companies across China as of late 2023. No OH&S data on incidents are available in this study. With this in mind and underground mining conditions, Company 1 and Company 2 developed a solution for battery swapping in a dedicated single-entry charging chamber. The number and locations of the charging chambers in the mine are determined during the design stage. The size of the chamber will be sufficient to accommodate charging equipment and a specific number of batteries. However, Company 1 and Company 2 have different methods for removing the discharged battery from the BPM and installing the charged one. Company 1's charging station comprises charging equipment installed in the previously mentioned chamber, as well as an overhead crane which is used for battery handling. The crane supports are four steel beams forming the crane's operating area in a rectangular shape. Incorporating the crane into the charging station is a reasonable approach, since the mass of the battery pack for the underground trucks is over 5 tons. This OEM offers two options to arrange the charging stations. In the first option, BPM is parked in the roadway next to the chamber with the battery within the operating area of the overhead crane. The second option implies parking the BPM inside the chamber, also within the operating area of the crane, thus avoiding traffic blockage in front of the chamber. The described options are shown in Figures 1 and 2. Regardless of the option, the procedure comprises of following steps:  
* Parking the machine;
* Disconnecting the charged battery from the charger;
* Disconnecting the battery on the machine;
* Removing the discharged battery from the machine with the crane and laying it down in the chamber;
* Lifting the charged battery and placing it on the machine;
* Connecting the charged battery on the machine;
* Connecting the discharged battery to the charger;
* Driving the machine from the charging station. As can be seen, this procedure is straightforward and it does not require physical effort from the operator. Information provided by OEM is not clear on the required personnel for such a procedure, meaning that it is feasible for the truck operator to perform battery swapping without help, including operating the crane. Major OEM, Company 2, also uses a dedicated area for swapping and charging the batteries (charging station). It also took a different approach to battery swapping by equipping the machine with a mechanism for lowering discharged and lifting the charged battery (Figure 3), thus eliminating the additional external infrastructure (such as the crane). Figure 1: Battery swapping in front of the charging station (Company 1). Figure 2: Battery swapping inside the charging station (Company 1). Also, this mechanism eliminates manual battery connecting and disconnecting on the machine. Specific for this approach is that once the battery is lowered, the BPM loses its main power supply, and it can operate for a limited time and on very short distances on an auxiliary battery. The purpose of the auxiliary battery is to enable manoeuvering the machine from the lowered discharged battery to the charged one and to lift it onto the machine, which is all done within the charging station. This implies that such a charging station must be larger in comparison to one equipped with a crane, to enable moving the BPM inside the station.