Quote: (Originally Posted by
Freef)
What happened? Did you post an incident report?
I wasn't a member of Rebreather World back then, I just read the posts
Thus I did not file any incident posts. Plus, I did not want to look stupid
, but maybe this will help someone else!!!!
I was experimenting with different gas mixtures and flow rates in an attempt to maximize my bottom time. I never liked the fact that I was depth limited by my mix - If what I was actually breathing was not as rich as what the tank held. I made several spreadsheets (to do the math for me) and began to input the mix, flow rate, and usage to determine a new EAN (this was suppossed to be what was in the loop).
My biggest mistake was in the amount of gas used. I was calculating by volume rather than what was actually metabolized. I found it very hard to estimate these figures using a SCR that vented.
My loop was always much higher than expected, but my dives were planned with a bottom depth that would yield a max PO2 of 1.5 in the event of calculation errors (full tank flow and FO2)
On the dive in question, I was diving a max depth of 72 ft. to a wreck that I was very familiar with. I was using 60% ( which would actually breath as 44%, 1.5Lpm usage) and my MOD was 72ft. Max PO2 @ 72ft was 1.4 I thought that all was fine. When I hit the sand at 72ft my PO2 was 1.9 I began to ascend, at 65' (still above the wreck) my PO2 was 1.7. I did about 15 minutes there before aborting and ascending.
PO2 of 1.9 scared the crap out of me. All of my training tells me 1.6 is the absolute maximum. I was even nervous about 1.7
Did I mention this: When I got home and rinsed and disinfected my gear,
I had connected the input hose to the wrong orifice, It was still on the 32% and not the 60%. This doubled the flow. Remember, distraction will kill me too.
The problem with my calculations was this: I was figuring usage as "volume of gas used" (1.5Lpm) and it should have been "volume of O2 used" (.23Lpm). This makes a big difference in the actual loop mixture and the resulting PO2 at depth.
That was my last attempt at experimenting and decided I needed and OXY and Uwatec to be sure. I still never felt safe and decided to bite the bullet and buy a CCR. I spent almost 2 years researching and studying Rebreather before picking an instructor and buying a unit. I am still waiting for technical training though.
If I never see a PO2 over 1.2 again, that is fine by me!!!!!!!!!!!!!!!!!
Even at the expense of proving my braindeath, I hope that this post may prevent another from doing the same thing