Originally Posted by Sawatch Rescue
Keep in mind that there is no difference in your buoyancy if the water is inside or outside of your bibs (or waders) as long as you are still in the water. To put it another way, you can completely fill a pair of waders and other than the bulk and reduced range of motion you won't feel a change in buoyancy. Add a pfd to the equation and you maintain what could be considered an acceptable level of safety.
We actually extensively tested a variety of wader combinations in a controlled whitewater environment a few years back and were a bit surprised at the results. The water in the waders only became an issue when our test subjects reached shallow water and the shore where they had to spill the water from the waders to maintain maneuverability.
Specifically relating to the OP, in close to 30 years in the whitewater industry I have never heard of an issue with the safety of dry suit bibs when used in conjunction with a dry top (or without for that matter but I can't picture a situation where you would want drysuit bibs and not a dry top...)
Did you publish anything relating to this study?
Of course, the water in your bibs/waders won't affect your buoyancy, but it sure as hell will affect your ability to actively swim away from obstacles or into eddies. It also seems that recovery of swimmers into a raft would be a whole lot more difficult if they have waders full of water on. Imagine self rescuing onto an inverted raft with 80 pounds of water sloshing around in your waders.
I don't think that waders are the death trap that some people think they are, but it does seem like they would be quite a hazard in a rescue scenario. In fact, I can't really think of much you could do to help yourself or others if you were wearing sacks of water on your legs.
I know, wading belts, pfds and dry tops are pretty effective in keeping the bulk of the water out in short, calm swims, but I don't see how any of those things are really going to stop your waders from filling up in a long rough swim.