Liquid Nitrogen (LN2)
NOT Nitrogen Gas (as in tanks)—LIQUID Nitrogen. LN2 is cheap, abundant, and easily available everywhere and anywhere, from your local ice cream equipment supply shop, local university chemistry stockroom, dry ice supplier, specialty chemical store, industrial/medical gas shops. Welding Supply shops chief among them, always on tap. Who the hell has the money and patience to work with massive gas nitrogen tanks, complex hoses, valves, regulators, and all of these complex apparatuses, fittings, complex calculations plus dealing with exit airbags or what not Too many variables and headaches.
With Liquid Nitrogen, you just need a cryogenic container off Amazon for $100 and a confined space. That's it. Full stop.
LN2 evaporates from liquid to gas at an expansion rate of 1:700 liquid to gas unit ratio. So 1L of liquid nitrogen rapidly expands to 700 Liters of Nitrogen gas. 6L of LN2 would only weigh a few pounds and would be enough to displace the entire atmosphere in a large vehicle, or double its internal pressure.
With a large enough quantity inside, it could blow out a car's windows if you poured the LN2 from the dewar onto styrofoam pails inside. Exposed to room temperature, the liquid-gas expansion rate would rapidly increase the internal pressure without a small vent exhaust aperture.
Nitrogen is very dangerous because it doesn't set off the body's hypercapnic response alarm system, so you won't feel panicked or like you're going to die. Industrial accidents often occur with LN2 leaks where bystanders peacefully pass out within a breath or two. Then another goes into the rescue the first, becoming a second casualty, and then a third, and then a fourth, and a fifth, until enough bodies pile up.
Right to die advocates heralded Nitrogen as one of the most peaceful means of euthanasia, in harmony with the thousands of peaceful N2 euthanistic modes of death acclaimed by the scientists who've witnessed them first-hand. They die in a few breaths with a smile in peace.
All you need is a one-person pop-up tent you can get on Amazon for $40. Why not even a body bag? The ideal setting would be in a vehicle with the window cracked just a bit or or any confined space and leave a little vent hole for the composite atmospheric air to exhaust out. Because nitrogen will be both colder and heavier than oxygen, it will begin filling up the confined space from the bottom up as it evaporates from liquid to gas. It's like filling up a swimming pool from bottom to top, forcing out the air out from the bottom up.
Liquid Nitrogen is legal to purchase, possess, and use to do whatever you wish with; no special licenses or regulatory approval. All you need is an approved cryogenic container ($100 on Amazon) and take it to your local welding shop. You can even make Ice Cream with it, as a last meal if you will. Just Google and print out a liquid nitrogen ice cream recipe, take it to your nearest welding shop with the container and they'll fill you up for a few bucks - like at the gas station. No questions asked. They're a business, and you're a paying customer. Cheaper than bottled water too, at only $2 bucks a Liter.
Please be mindful to leave a note to first responders warning of a HazMat Oxygen Deficient Environment, so people don't die going in to rescue you.
Just uncork the Dewar, pour the LN2 into a styrofoam container in a confined space, and snuggle tight in a sleeping bag, peacefully expelling yourself into non-existence. If you don't have a small closet, just get a body bag on Amazon for $35, decant the Dewar into a styrofoam cooler at the far inside (so you don't spill any and freezebite your feet) and leave the zipper an inch open for the oxygen to vent out. A caveman could do it.
You could also buy one of those small plastic one-person pop-up tents for a few bucks, cut a vent hole atop it, and enjoy the last few minutes of a final sunset before your lights go out for good. Go somewhere far away out to the Grand Canyon, abandoned Lighthouse, meadowlands or wherever remote parts of Nature beholds your sight, with not a soul around to spot you in sight. Why not even your local cemetery in the dead of night?
Just in case you should post a HazMat (or ☢ warning) Keep 500 Feet Away Warning Note posted around you so in case you're found they'll run away faster than the speed of wisdom away from you, instead of rushing in rescue towards you. I'd run with Godspeed faster than Speedy Gonzales if I ever saw a BioHazard or Radiation Warning sign like that with the fear of Satan in me away.
I'd be five hours late by the time rescuers would be cleared to go anywhere near you after having to fly in a special HazMat team to test and clear the area as safe out of an abundance of caution.