LeadTurn_SD
Contributor
Sorry, I'm not getting this. Why the bungee around your neck on your primary in the first place?
Ok, once more for the Marines in the audience ( ) :
Your backup 2nd stage is hanging just below your chin on a bungie. It has a shorter hose. Your primary 2nd stage is in your mouth. It has a longer hose.
Placing the bungied backup under your chin places it in a position you can instantly find it with your eyes closed, with either hand, and when correctly positioned and if you practice, with no hands.
1.) You donate the regulator from your mouth, the one you are breathing, to the OOA diver. You've guaranteed that the distressed diver gets a good, working reg. The longer hose makes sharing air much easier (you are not nose-to-nose like with a traditional length octo hose). It allows the 2 divers to actually swim freely.
2.) You breath off the backup 2nd stage, the one that is hung below your chin. It works, because you know that you will be the one breathing it in an an emergency so you maintain it, and you've tested it at least once before and during the dive!
I would never in a million years be confused for a DIR-compliant diver, but the long hose / bungied-backup is just a good way to share air. You can argue about how long the "long hose" needs to be for various environments, but the concept is valid for all environments.
Best wishes.