An evacuation experiment was carried out at the Äspö Hard Rock Laboratory in March 2018 to investigate human behaviour during evacuation in underground facilities via escape routes with long ascending tunnels. The objective of the experiment was to collect data that could be used as a basis for evacuation risk and safety assessments in underground tunnels and other large infrastructure projects related to e.g., mining. In total, 32 participants individually ascended the 907 m long tunnel with an inclination of 14%. During the evacuation, each participant's walking speed, vertical walking speed, heart rate and estimated physical exertion was documented. The measured walking speeds were found to be higher than the walking speeds obtained in previous experiments, but the vertical walking speeds were lower. The strategy of 44% of the participants was to adjust their walking speed to a pace they thought could be maintained over a longer distance. The results of this experiment show that the walking speed decreased as the level of perceived exertion increased. Moreover, the results indicate that the walking speed and the level of perceived exertion stabilized during the movement along the tunnel. © 2022 The Author(s)