Feasibility and effectiveness of vertical evacuation of patients with chronic respiratory disease for tsunamis: A prospective study in a coastal area of Okinawa Prefecture, Japan

This study aimed to determine the feasibility of vertical evacuation of patients with chronic respiratory disease living in a tsunami inundation area in Okinawa Prefecture, Japan. The participants included 34 patients with chronic respiratory disease at Public Hospital A and Private Hospital B in Okinawa Prefecture until April 2023 and March 2024, respectively. The 6-min walk test and stair climbing test were measured to determine walking and stair ascending speeds. Walking speeds were used to determine horizontal evacuation time from home to the designated evacuation site for comparison with the estimated tsunami arrival time. The time required for vertical evacuation to suitable buildings was calculated using walking and stair ascending speeds. The mean grace time from the occurrence of the earthquake to the start of horizontal evacuation was significantly shorter than the grace time to the start of vertical evacuation time ( p = 0.003). No significant difference was observed in the expected success rates when the evacuation was started immediately after the earthquake. However, when the evacuation was started later than 20 min after the earthquake, the expected success rates were significantly higher for vertical evacuation than for horizontal evacuation (20 min; p = 0.007, 25 min; p = 0.009, 30 min; p = 0.011). The results show that vertical evacuation is more effective for tsunami evacuation than horizontal evacuation and is feasible for patients with chronic respiratory disease. Thus, vertical evacuation should be included in individual evacuation plans for those who require support for tsunami evacuation.