During our checkout dive for the Deep Diving section of our SSI AOW course last fall, one of the instructor's buddies came alone for the dive and to keep an eye on us. The instructor and his friend were buddies, while I had my own.
We get in the water and start to descend to the bottom 85-90 feet below. As we all collect around 85 feet, someone grabs my octo (at this time, I had a regular 36 inch octo hose attached in the golden triangle). I turn around, and it's the instructor's buddy, huffing and puffing on this Sherwood octo. His Odin is dangling next to him, free flowing. I grab the guy's BC and get an OK from him, then I tap my buddy on the shoulder and let him know I'm ascending now. I make eye contact with the OOA guy and we start to ascend, he's dragging me up a bit fast computer says around 65-70 fpm.
At 45 feet, the guy drops the octo and bolts to the surface. I continue ascending at my current rate, skip the safety stop, and meet the guy on the surface to check on him and find out what happened. Apparently he wasn't getting the air he wanted from the Odin, and he was freaking out and damn near hyperventilating on my Sherwood when he zoomed to the surface. He started breathing on his Odin at the surface and I took him down to 30 feet for a couple of minutes, then up to 15-20 where we sat for about 20 minutes waiting for the other divers to finish.
Lucky for us, we were both ok. In retrospect, I should have taken more time at the bottom to make sure this guy was calm and ready for an ascent.. he was completely freaking out when we started to go up. This also is one of the reasons I adopted the long hose design.. the 36" octo wasn't long enough for us to be face to face comfortably while he sucked down the air, which added to the anxiety of the situation. Now I tell everyone I dive with to simply grab my primary (but please alert me first ) when it's an emergency. This was my first (and so far only) actual emergency OOA situation.