Bridgediver used the example of "why would the safety procedures used in ice diving be inadequate for any other PSD dive?" (Not singling you out Bridgediver, just using this as an example.) The safety procedures might not be inadequate, but they may not be optimal. I'm in south Georgia. We don't get much ice diving this way. Our dive and procedures should be planned based on the conditions we are diving, not what works in some other environment. The same as with the member who posted about overhead environments. The equipment and set-up should be based on what will work best for that dive, and we should always remain flexible to change to a different set-up if it is more benficial. The only absolute should be to rule out that which is unsafe and not worth the associated risk.
Where I'm coming from here is that in the past locking carabiners were still prefered for ice diving while snap shackles were recommended for the non-overhead type of diving (was also trying to get Blades to verify this is still the case first). The reasoning is that in an overhead you don't want to loose your line (I think we all can agree on that). My thinking is that if the locking carabiner is safe for ice diving why is it not safe for all other types of diving?
If ice diving is putting our divers more at risk than the other forms then perhaps we need to re-think procedures.
I agree that many don't have ice to worry about (lucky you!) but an overhead either soft or hard is still a hazard. Can you 100% of the time say that there will never be anything above you when you surface? (boats, docks, sub-surface debris, more entanglements floating mid water, fences, wire etc). Don't forget we are in zero vis to balck water (most of us) so you may not be aware of the overhead. Not everything is seen on the surface and/or before the dive.
This is why I'd prefer to keep the diver on a tether from the moment he steps in the water until he's out
Mud and Thal - Correct me if I'm wrong but your umbilicals are also used to haul you out of the water are they not? Ours aren't meant for life safety in the manner of supporting the weight of a person (even though the comrope can do that in a pinch - 5000lbs I believe it is?). No fall factors and 9:1 ratios are needed for our tethers
We also don't use it near as much as you guys so abrasion resistance I wouldn't think is that huge for us(?).
Our team also carries multiple EMS shears so if things really do go bad it takes a couple of seconds to pull them out and cut the comrope (it cuts easy with shears). BUT, it would be the very last thing we would ever try. It would have to be a very deliberate act to do if the diver thought there was no other choice - certianly not as reflexive as a quick release shackle and I think this is a good thing.
So I guess I'd never say never either

BTW - feel free to call me out anytime. I'm always trying to make things better for my guys but I don't know everything