Blockage (2021)

A middle-aged man enters a staircase. The AI public addressing system warns for the time limit as the staircase is synthesized and safe for a limited amount of time at a safe oxygen level only. He walks down for quite some time, where he is not able to find an exit. Despite his tiresome effort and the suffocating conditions, he put himself together to go all the way back upstairs. Hence the entrance door can only open from the other side. Is there any way out?