Lynne, I think this is a huge point the "redundant lift crowd" dont really consider.
If they actually needed 40 or more pounds of lift to be neutral, and suddenly lost the lift of the wing --they would in all liklihood fail to even slow their descent if not ALREADY standing on the bottom. If plummeting, they would have huge task loading issues for the deployment of a lift bag, and may even experience ear clearing pain and damage , which would serve to even worsen the task loading of the deployment. And then there is the risk of the lift bag getting away from them after it becomes positive and begins heading upward---they lose the bag, if they can't hang on to it....how many have the bag clipped to them so that if they let go of it, it could not escape them?
At least with wetsuit and double 80's, you can easily swim the rig to the surface with no wing whatsoever. There can be no uncontrollable plummeting.
I dont know why some divers have such a desire to use heavy steel tanks....when the 80 al works so much better, and is so inexpensive.