Method How much helium needed to make sure I can die

[Babycaca]

I bought a 22L balloon helium tank but I heard about it may neutralized with O2,so I order another 50L one and make sure it's 99.999% purity,problem is,is 50L enough to flow in the bag (slowly) for at least like 15-20 mins for me to die,also how can I avoid breathe in my own Co2? It would be a nightmare to struggling in a plastic bag sober

Please help, I can't wait to get off this train asap