O2 diving

Question
Can you dive on pure O2?  A colleague has said that you can but I thought that O2 was toxic in the water.  Please can you confirm this for me.

Answer
Thanks for your question and it is a good one.

Yes, you can dive on any mixture of air and oxygen, even up to 100% oxygen.  The maximum operating depth of 100% O2 is 20 feet (6 meters) (with a ppO2 of 1.6) however.  Breathing 100% below that depth would likely resulting in CNS O2 toxicity and likely drowning.

In Nitrox classes, you learn how to breath mixes up to 40% and properly calculate the maximum operating diving depth of the mix, establish a safe ppO2 of 1.4, and calculate an exposure time to that mix in order to reduce the risk of a CNS hit.

In advanced Nitrox and decompression diving courses you learn how to use mixes up 100% to enhance nitrogen elimination during decompression stages of the dive.

Note that special equipment procedures are also mandated when breathing mixes greater than 40%.  Also note that there is no benefit to breathing 100% O2 under the water for normal recreational diving.

Have fun diving, Jesse