Dan Kerem (2000) of the Israeli Navy Medical Institute, "I'll stress again that with pure oxygen diving, as long as your gear is okay and there is no CO2 buildup in the system, divers routinely dive for hours at 1.6 atm with no incidence of oxygen convulsion."
Perhaps. I have witnessed several exceedingly experienced divers all of who suffered respiratory difficulties (and in one case vision disturbance) after using their CCRs set to pO2 of 1.3 during two long dives a day for four days. They had to lay off diving for 24/36 hours. I have personally experienced mild discomfort towards the end of a single 4 hour CCR dive where I had pO2 set to 1.3. I now take Tom Mount's advice and dial it back to 1.2 or 1.1 for long dives, and even 1.0 if there will be many of them.