In the absence of sufficient cabin altitude, and failure of supplemental oxygen, is there any case to be made for emergency breathing techniques?
.....and exactly
what are you going to breathe, pray tell?
...as someone who has (deliberately) come off oxygen at 25,000 cabin altitude in an aircraft - momentarily - let me tell you that the first thing you will do is cough uncontrollably like a 200 a day addict....
....emergency breathing techniques? Don't think so....