Thanks for the detailed reply. I just want to bump this thread again, because I am hoping that somebody has some information on carbon monoxide in particular. Will combining formic and sulfuric acid to produce carbon kill me faster than the nitrogen? 40 minutes is a long time, and I am concerned about somebody trying to stop me. And will it induce pre-death side effects, like a headache?
You shouldn't just combine formic and sulfuric acid to produce carbon monoxide. You need the right set up. The gas produced needs to filter through water otherwise you'll breathe in caustic fumes which will literally strip the inside of your lungs and lead to a horrific, painful death.
I haven't done a bunch of looking into CO. I'm assuming you're planning to do this in a room, closet, etc (I would think these would be considered large compared to a traditional exit bag). In a large area like that it will take a while for the gas concentration to get high enough to even make you lose consciousness. If it even does reach the right concentration. Considering that one of the main side effects of CO poisoning is headache, I would say this is likely. I remember reading about a survived attempt with CO where they were found and woke up with a splitting headache. I can't remember exactly which one, but they used something to help them fall asleep, which I would think eliminates the headache prior to death. Also, no, for any form of gas asphyxiation it's recommended that you have 40 minutes in the low oxygen environment. Being completely honest, unless you're incredibly desperate and want to risk failure, I would stick to the methods that have been proven.
Nitrogen is not an easy method. If you don't research it thoroughly and get it right (the right valves, gas release, type of bag etc.) you'll mess it up and wind up with brain damage. There's a wealth of information on this site and in the PPH to help you, but it's still very complicated. More than just getting a N tank, hooking it up to a bag and putting the bag on your head. You need the right purity of N, the right amount, the right regulation valve, the right flow of gas etc. Even then people fail because the bag slips or the gas runs out or the valve flow is too fast or too slow.
CO isn't a painless peaceful death by all accounts. There's a lot of survivor accounts that suggest it's one of the worst ways to ctb. You're paralyzed but tortured to death basically so you can't escape. My ctb of choice was CTB using barbecue grills, but I abandoned the idea after researching as there are just too many variables. You need a certain level of saturation for one thing and you can't test that without a very expensive meter that isn't even a handheld device, you need a degree in engineering to hook it up to a laptop and the ability to make sense of the data. Then there's the amount of briquettes, the time you leave it to smoulder, whether you sit with it or leave it in the space then get in once levels are high enough etc. If you sit with it, death will be very slow and painful. If you get in there's a risk you'll release the fumes when you open a door or whatever. It's a minefield and the risk of brain damage is very high if you fail, and most intentional attempts with CO fail through lack of testing and research. Again, use the search tool on this site and do your research really thoroughly. Go into this blind and impulsively and you'll get badly hurt.