: Probably not a relevant figure. You'll probably get bored with staying
: upside-down before you could build up that high a level.

i just wonder what is the relevant variable. the issue is how long(or # breaths) will it take. the more bored i may get the bigger safety margin.

: More often you'ld move about 2 to 3 liters of
: air in and out on each breath.
: More like 40 to 48, since we aren't expecting maximum lung effort.

makes good sense, website below confirms this:
http://pirate.shu.edu/~jenkinmi/ALI_Stuff/myweb2/LungVolumes.htm

exercise uses abt 3 l. so a 2 l. guess for crunched up upside down sounds ok.

: Another problem would be the length of the hose. If it is more than 3 or 4
: feet long (and I suspect it might be aobut that long) then it really
: doesn't matter how good the air is in the sealed chamber. You'll keep
: building up the level of carbon dioxide in the hose. If the volume of the

if snorkel is 3/4in i.d. and 36in long(this is quite long) get abt 16 cu in. which is abt 15% of a 2 litre breath. a factor, but not a real big one.

what's the driver and at what %, tho'?