For using an exit bag anyways, the optimal flow rate is 15 LPM according to the PPH, which is a good resource if you're considering this method. You might also find valuable insights from folks on the intert gas thread. If you're looking into a HOOD device, the recommended flow rate is generally higher—around 25 LPM, according to the PPH. I am sure the people more in the know on this method than me would also happily chime in on the megathread if you asked (but try to search for the info first but if you can't find it by browsing or using the search feature I bet someone would steer you where to find it).
This flow rate is important for a few reasons: (1) it helps create a near-zero oxygen environment, (2) prevents CO2 buildup, which triggers the hypercapnic alarm, and (3) it ensures that oxygen cannot enter the opening of the exit bag. It's advisable to make sure your tank can provide sufficient flow for about 40 minutes, which is a good safety measure, even though death is expected to occur much sooner. This gives you some leeway to ensure everything works as intended.
If someone had the funds and skill level for it, then the SCBA set up looks primo.
GasMonkey had a rather incredible set up. I am just not sure if everyone has that much time, money, and expertise to pull it off (especially the funds side, sounds pretty expensive to source that gear).
Regarding the Respiro ReBreather device, you should search around a bit as it sort of sounds (I am not an expert in this area by any means at all) the device sounds like it was unreliable [
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4] and I recall the PPEH even mentioning no confirmed reports of successful use for that device. Unless you just meant the generic term rebreather mask in which case you will also find discussions about the risks of those and the seal and risk for failure doing that. If someone is confident in their skillset I suppose there are different ways to approach the inert gas method but the exit bag seems to be somewhat the most straighforward and accessible to folks anyways.
This thread may be also be useful for your educational purposes.
Exit bag and inert gas megathread which will probably have a lot more folks more hip to this method able to steer you on the right course. The exit bag route certainly seems the most simple, when it ventures into things like SCBA gear the level of technicality, and cost, definitely goes way up.
Given you are talking about a few different ways, look into the optimal flow rates for each so you can make the best decisions based on whatever you are deciding. When done right the inert gas method certainly sounds quite peaceful to me!
With whatever you decide, I hope you find everything you are looking for.
