In my story, I have need of a gas or gaseous compound that will knock out anyone who inhales too much of it and then kill them if they don’t reach clean air in a few minutes. I know of many gasses that are lethal upon inhalation and others that knock you unconscious upon inhalation, but is there some sort of substance that will knock you out then kill you?
Time is a factor here and ideally I need my characters to pass out within minutes of inhaling a concentrated amount of the substance, but death can come however fast after the initial inhalation. To get an idea, I would like my characters to be dead within fifteen minutes of inhalation in a concentrated amount.
Is there anything we know of in real life that fits under this description?
(Side note: I wouldn’t be too upset if it weren’t, but if said gas were flammable that would be amazing :p)