Some thoughts on recent posts, but may only be relevant for the UK. I feel it's way easier to source N2 in the US.
Note, this is my intended method. I'm not suggesting anyone do any of this or giving anyone advice on how to ctb. It's just my plan for my own ctb.
I can only get small disposable tanks delivered online, so I'm getting four. I found most online delivery companies sell the small 2.2 litre tanks without asking any questions. 2.2 litres = 220 lites gas. Four tanks = 880 litres. One for testing, three for ctb. The downside: I'll need three regulators and those things cost. I'll also need three tubes. Feed all three into the bag then divide PSI for one tank at 15 lpm by three for a flow from each tank of 5 lpm. Combined the trio of tanks provide 15 lpm and a total 660 litres which is about 44 minutes of gas time. Conversion charts for lpm to PSI can be googled.
The tricky part (I assume as I'm still waiting on delivery of my tanks) will be turning on all three valves to the right flow rate in quick succession but those extra 4 minutes beyond the recommended 40 should suffice for this fiddly bit and 40 minutes is the 'safe' estimate. In reality I'll pass out in 10 to 15 seconds and be dead within ten to twenty minutes depending on how much oxygen contaminates proceedings.
I'm going to check specs on N2 purity carefully though! Here in the UK 99% pure N2 is only available as laboratory grade and restricted to business purchase only but certain air con suppliers provide small, purer tanks. They seem to be more stringent on who they sell to and why though.
This method is pricey but I think it solves a lot of the accessibility issues involved with procuring industrial size tanks and either transporting them or getting them shipped, at least here in the UK.
Note: the test tank is to double check flow rate inflates the bag in 60 seconds as I'm not confident using the regulators. If settings need tweaking I don't want to waste the 660 cbm N2.
I'm not testing purity with the spare canister. Inhaling N2 is extremely dangerous if not done correctly. I already failed once with too small a tank/wrong technique, revived before ten minutes and now have brain damage. I've learned the hard way not to get this method wrong. It is technically the trickiest peaceful option but also the gentlest and fastest. The hard part is setting it all up then overcoming SI. Believe me when I tell you, pulling the inflated bag down and starting to breath was almost impossible because I was in no doubt (at the time) it was going to kill me. Still not sure how I managed to beat the SI. I just blanked my mind when I pulled down the bag then, as I breathed, kept focusing on my reasons for leaving the world. It was brutally hard. Breathing deep or regularly was very hard as I was anxious and shallow breathing with quick shaky breaths.
Preparation approaching ctb: I tried twice at night. First time I watched my favourite show: Breaking Bad, last episode to calm my nerves then resolved to go after the last episode. Had a final vape, set everything up then started but couldn't bring myself to pull down the bag.
Second time, also at night, drank heavily and took diazepam. Managed to pull down bag and breathe but yanked bag off when I started to feel tingling in extremities and tunnel vision (after about 7 seconds).
Third time, woke up at 6am in state of despair as I do most days and was utterly resolved to do it. This time went all the way but previous two attempts had depleted gas and I didn't have enough left (had only one 2.2 litre tank, though airflow was too low also so it took a long time to finally pass out and those were long minutes. A lot of fear and shallow breathing, shaking, but I was determined and SI didn't stand a chance). I will do my next attempt the same way. Wait until I'm so desperate to ctb I do it with conviction.
If anyone is wondering how it feels, it doesn't. At least, I have no memory of the transition from awake to unconscious but then I do have brain damage. I slur my words, struggle to talk in coherent sentences and feel dizzy. Also have weird burst blood vessels in my fingertips and toes that look like varicose veins. I don't know what that is.
As far as I recall I was breathing shallow and quick, feeling very mild sense of suffocation (like you get if you wear just the bag without gas) then oblivion and reviving to find I the bag clinging to mouth and the panic/asphyxiation effect of breathing CO2. Couldn't remove the bag for a while as my hands were clawed. I had numb lips, headache, nausea, disorientation, dizziness and felt very cold. Didn't notice the slurring and cognitive effects until I tried to talk to someone much later.
I think, based on what others have said, my N2 was contaminated with CO2 hence the mild sense of anxiety and shallow breathing but it didn't nullify the hypoxia and it wasn't unbearable like if you try to just suffocate yourself.