###### Abstract
This is a further issue that this paper intends to examine. A comparison with the consequences of the fire of a similar internal combustion engine bus (ICEB) also needs to be carried out. The aforementioned literature review also shows that the firefighting operations to extinguish a burning BEV are generally more challenging for rescue teams than those needed to address the fire of a similar ICEV, as the fire brigade (i) is forced to get closer to the burning vehicle to inject the suppression agent directly on the battery, thus preventing its reignition, and (ii) is exposed for a longer period of time to the high temperatures and toxic gas concentrations resulting from the fire, having to use a greater amount of suppression agent to deal with the BEV in flames. However, there has been limited research on quantitatively evaluating the safety of firefighters during a BEV fire in road tunnels. Even less research has been carried out on battery electric buses, thus representing an additional gap in knowledge. In light of these considerations, the scope of this paper is to contribute to filling the aforementioned gap of knowledge by quantitatively assessing the potential additional threat that a BEB--compared to a similar ICEB--might pose to the safety of the evacuees and firefighters when it catches fire in a road tunnel, which is also essential to understand if the current firefighter protocols in road tunnels are still valid or need to be adjusted to cope with the increasingly widespread use of BEBs. To achieve these objectives, the environmental situations in a tunnel in the event of a fire of a BEB or its ICEB counterpart were reproduced by setting up a 3D CFD modeling solved with the FDS tool version 6.7.3 [25]. The people evacuation process toward a safe place (i.e., emergency exits and tunnel parts) was simulated using the Evac code [26]. Furthermore, given that the environmental conditions inside road tunnels, apart from their geometry, depend on both the traffic flow and type of ventilation, the safety of the occupants and fire brigade in the event of a BEB fire was evaluated by considering the tunnel under conditions of congested traffic, as well as natural and mechanical ventilation. The scientific contribution of this study lies in the advancement of knowledge regarding the effects on the evacuees and firefighters due to a fire involving large battery electric vehicles, such as buses, in road tunnels. By providing accurate details on the fire-induced threats to the users of a naturally or mechanically ventilated road tunnel, this study can serve as a reference for tunnel management agencies. Specifically, it offers a better understanding of the BEB fire-related issue from a fire safety engineering perspective, assesses whether current firefighter protocols in road tunnels need adaptation, and supports more informed decision-making regarding the implementation of additional mitigation measures and/or traffic control strategies. The structure of the paper is as follows: the next paragraph presents a summary of the literature review. This is followed by a description of the geometry, ventilation conditions, material properties, and traffic characteristics of the road tunnel under investigation, as well as the fire source and escape scenario. After this, the proposed 3D CFD modeling and its calibration process are presented, together with the corresponding modeling of the evacuation process. Subsequently, the results obtained for both BEB and ICEB fires are shown and commented on, and appropriate comparisons are made to point out whether an electric bus powered by an LIB may worsen the environmental situations in the investigated tunnel.