https://www.airgas.com/medias/Airgas-Compressed-Gas-Cylinder...
The have a volume in cubic feet specified, multiply by the 165 bar that's what's typically used to see how much space it will fill. Looking around our house there's a very odd-shaped closet under the stairs that would be difficult to measure. Of the more typical places the smallest room in the house is a closet. 6' x 5' (minus a 1' x 1' chunk that I believe contains an air duct) x 8' = 232 cubic feet. Suppose you dump 232 cubic feet of material into it--you'll displace half the air which gives a time of useful consciousness of 20-30 minutes. Not good enough. Let's try doubling that, now we end up with a time of useful consciousness of 30-60 seconds. That's probably enough. That's 2 cylinders at 137 pounds each. Or if you use aluminum, 3 cylinders of 90 pounds each.
I was trying to meet your request for an option that came as close as possible to just flicking a switch.
> Step into a room, step inside a pod, press a button, pod closes, press another button to replace the air with nitrogen, done.
I know of a friend of a friend who did this on his own. If you are of sufficient capacity to step into some place and press a button then you are able to buy or make this equipment on your own and do it yourself.
> I'm sorry, but 'life is precious' is a religious view, even if you call yourself 'atheist'.
And some religious people also believe that taking care of Earth's natural environment is also a religious duty. That doesn't make it a religious view, it makes it a general moral view that is shared between some religions and some atheists. The justification for a moral view is what makes it religious or secular.
> Humans have killed each other since they evolved from Australopithecus
And how many of these deaths have been because of religious beliefs? I think enough of them to say that killing people for moral reasons is a religious view, even if you call yourself 'atheist'.