Handsaws aren't going to kickbak when they catch a little twig eh?
I AM self-employed (OSHA does not apply to me) and grandfathered in to one-handing a chainsaw. I one hand all the time... and so do the best production climbers I know. Crossing hands while one handing is a very bad idea as per an earlier post... Keeping the saw sharp is important as a dull saw will tend to jump on contact. Also good trigger control and timing so the saw is running at a good rpm upon contact is importnant...
Finishing cuts with a handsaw sounds good, but is time consuming over the course of many cuts... Proper positioning and saw control and visibility will get the job done safely. When there is any doubt, tie it or finish with a handsaw.
And all new climbers should be trained to use two hands on a saw. Safety must trump production... that's a given when learning to climb... so the question is when does a climber become experioenced enough to one hand..
There was a thread at AS showing a video of a climber with a few years experience needlessly waiving a saw over his head like a flag with one hand while holding on to his climbing line with the other hand. I was the only voice over there at the time that seemed to think that was a problem. That climber was repeatedly and needlessly one handing the saw while reaching for cuts from awkward positions... That is NFG and not what I Am talking about as a safe practice... So I understand the rule and why it is important..
I just shot a video of a highly experienced production climber pushing over a 12 inch top with one hand whiel he finished the cut with the other. The problem was, he dutchmaned the notch, so once the kerf closed the hinge siezed and he had to keep psuhing until the hinge broke. It is all very clear in the video. Now if he had cut a clean notch he could have made the backcuut and put the saw away, and then used two hands to push the piece over. Even though I thought the cut was safe, it was unnecessary and someday he could get in trouble from not cutting a clean notch, though probably not from that cuasing the need to one-hand... I'll talk to him about it when we look at the video together.