Adding to Fredrik and Ali's posts -
I guess it comes down to how many failures you want to plan for..
I have tested the balance of a full rig by swimming up. I did a simulated ascent from 30M with stops of up to 5 mins at 6M.. not very long deco. I was able to do it - but it was tiring. It added CO2 to the mix in my body - and I am sure that it wouldn't be the cleanest deco imaginable.
Years ago I was taught the back-up process of using an SMB or lift bag as an alternate flotation device. I have to say it would have made the deco stops easier.
If starting from deep - you ride the partially inflated SMB up - keeping the dump valve uppermost and a hand on the string to control the ascent. (Much like using the wing dump.)
When you reach proper deployment depth release the SMB and "Climb" the string. You will need the surface marker for the boat.
Agreed it's not a DIR approach - and there are alternative ways a team could make this easier. (Emergency flotation sitting on your buddies for a start.) You also wouldn't get much out of one of the tiny DSMBs - and I'm not sure how you would deflate it anyway..
As with all emergency drills, it's only useful if practised. So as I don't practice it - I don't plan on doing it any time soon.. but it's useful to know it's there. You never know when multiple, safety-critical failures happen..
The truth is there somewhere...
