You said in your post that you are using a helium mix as well. This information was posted as to diving on 100% pure oxygen, no mix. Meaning that you can not safely dive while breathing off of an o2 bottle as the original poster was asking.
The information is laid out in the US Navy Dive Manual Volume 2. I recommend you examine it and see that it is clearly documented there.
Here is the exact quote from part of it. It is several pages long, so I have only inserted the important pieces:
"From the air we breathe, oxygen is the only air used by the body. The other 79% is used to dilute the oxygen entering the body. Sometimes 100% oxygen is used for shallow diving operations and certain phases of mixed gas diving operations. However, breathing pure oxygen under pressure may induce the serious problems of oxygen toxicity."
Examine it for yourself. If I am wrong let me know so I can stop teaching my classes wrong information, and I can correct my instructors who taught me.
