Sigh.
I've tested CO2 (dioxide method) and it's sort of painless just funny accelerated breathing takes place during inhalation is a bit uncomfortable but tolerable anyway. Now I think about a reliable setup to deliver the gas straight in a closed atmosphere prolly gonna soon fill up my 0.5L CO2 tank at a local gas filling station, i'd calculated the cylinder has capacity for 1-2 minutes of gas flow, it's enough to do the job given no gas escapes from the mask.