>>12749298ok I'll explain
the American gas chambers use nitrogen to suffocate the convicts
suffocating means you replace 100% of the air with inert gas
you need to prevent air from seeping in, which means you need good seal and overpressure
the Nazi gas chambers used hydrogen cyanide to poison Slavs and Jews
poisoning means you need only about 0.01% of air to be hydrogen cyanide
you don't have to care about air getting in or out because it's opens to the outside and you need very little amount of gas - by the time it stars to leak out, everyone is dead already
Prisons sometimes also used hydrogen cyanide, but because gas chamber is inside, you still need to prevent any leaks
otherwise you're poisoning inmates and guards inside the prison (a building with very poor ventilation)
