Rebreather

[Sidediver77]

Hey guys, rebreather questions of the day. See if you can answer them.


1.) Can you go hypoxic from a dil flush

2.) Can I have a set point of 1.3 and ascend with that setpoint until I surface?

3.) If I'm checking my Po2 accuracy, why not just do a dil flush? Could I also use an 02 flush after ascending to 20 ft?

 

[JohnnyC]

1) Yes
2) No
3) Because a dil flush does not validate cells for linearity or current limitation.

 

[fsardone]

2. actually you can ascend to surface with set point 1.3, except that ppO2 cannot be above ambient pressure and therefore the reb will try maintaining the set point adding oxygen; so WHEN and not if you forget to switch to set point low, the reb will add oxigen making very difficult if not impossible to stay at depth between 6m and the surface.

 

[Sidediver77]

great answer I agree

 

[tbone1004]

1-if dil is hypoxic at the depth you flush. i.e. 10/70 at surface then yes. If the dil is breathable on OC, then no

2-maybe- it first depends on the fO2 in the loop and if that fO2 is not hypoxic. I.e. if you have EAN32 in the loop and it is 1.3 at 100ft, then yes you can make the entire ascent without adding O2. If you have a fO2 in the loop that equates to a ppO2 of less than .16 when you surface, then no. Typically that is only hypoxic dil mixes though. Also it depends on how long you take to ascent as you are dumping inert gas from your body back into the loop which artificially lowers the fO2 in the loop as you ascent. I.e. EAN32 at 100ft may end up as EAN 24 *random number btw* by the time you hit 20ft. If that number goes to less than 16, then you'll be hypoxic.

3- you O2 flush prior to descent to check for current limiting. Can't do that with dil, and people have died from failure to do this. You'll see 1.2 and want 1.3, keep adding O2 but it never gets there, go hyperoxic and die. O2 flush at 20ft would have shown that before you offed yourself. You also O2 flush when you get back to 20ft to get the inert gas out of the loop for deco efficiency. Don't O2 flush below 20ft, bad news bears