Which Floor in the Mist

I got on the elevator and ran into a man carrying a gas cylinder. I casually asked him which floor he was going to so I could press the button for him, but the man suddenly looked terrified, as if he had seen something horrifying. I was just about to ask him what was wrong when he immediately ran out of the elevator, saying I was crazy and that if I wanted to die, I shouldn't drag him into it. I was completely baffled—what was wrong with him? Could something happen in this elevator? So I set out on a journey to find the truth.