Oh yes, as you know I am quite familiar with CNN911Fakes. I'm also familiar with Chev4206, who has to be the most deliberately offensive Youtube user of all time. In fact, they are so similar that I'm not sure they're not sock puppets of the same person. However CNN911Fakes seems slightly more gracious at times.
I hadn't seen your discussion with him on diving mixtures. Pure oxygen is actually quite toxic at high pressures, above about 2 atm or so. So while it is useful in helping N2 outgas from your body, it cannot be safely used below a depth of about 9 m. Its partial pressure must be limited, which at greater depths can only be done by adding diluent gases such as N2, He and even H2.
This was not understood by the WW2 German divers who were breathing pure O2. The British divers defending Gibraltar made use of this fact by taking their German opponents down until they went into convulsions. Apparently this property of pressurized oxygen was a tightly held British secret during the war.
The comments are in Hunchy's
Moon Hoax Yes vid.
I told CNNetc that some diving rigs do use pure oxygen but they're expensive, complex, and require specialized training to use safely. I didn't even bother going into the computerized rigs that adjust the partial pressures of an oxygen-nitrogen-helium mix according to depth, since he denied even the concept of partial pressures.
It is surprising how quickly oxygen becomes toxic at increased pressures. Back when I was doing sport & rescue diving I never went below about 100 ft (3 atm absolute) which is well within limits for air but would almost certainly kill you as dead as a hammer in short order if you were breathing pure oxygen.
I even told CNN that he didn't have to take my word, he could just call his local hospital and talk to any respiratory therapist - they would tell him the same thing about partial pressures, but he did his usual thing of ignoring that in favor of twisting what I told him and, IMO, deliberately pretending not to understand what I was saying. I eventually got bored with him and dropped it; I can only argue with a fencepost for so long before dozing off.
That's interesting about the German/British divers. I hadn't heard that.