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To understand time gaps during bus evacuation to conduct high-quality risk analysis of tunnel fires, this study collected time gaps from the Hsuehshan tunnel fire in Taiwan, experimental bus evacuations, and observed bus alighting. Based on the analysis of Hsuehshan tunnel fire, two situations were manifested: one wherein the bus passengers alighted normally as if it was a usual bus experience with no urgent requirement to evacuate (evacuees one to seven) and another associated with an urgency to evacuate (evacuees 8–19). We applied the results of the analysis in the Hsuehshan tunnel fire incident to investigate the time gaps from experiments and observations by dividing it into two groups: non-urgent and urgent. Statistical analyses were performed to investigate suitable probability distribution curves to describe the time gap distributions. The lognormal and gamma distributions show relatively good performance in approximating time gap data in non-urgent and urgent situations. Moreover, when comparing the time gaps of bus evacuation during the Hsuehshan tunnel fire accident, the urgent and non-urgent group time gaps corresponded to the assorted Stage II (52%) and Stage I (65%) of the Hsuehshan tunnel fire, respectively. • Time gaps of bus evacuation during a tunnel fire were investigated. • Bus-alighting time gaps were clarified as two main types (non-urgent and urgent). • Time gaps can be approximated by lognormal or gamma distribution. • Time gap distribution was compared with time gaps in an actual incident. [ABSTRACT FROM AUTHOR]