When considering a dual bladder wing, the first question is “Why would a diver need one?” and the second is “How do I use it?”
Back in the 1980’s cave divers were using two Dive Rite Classic Wings (it was the only 60 lb wing at the time) when they needed more lift for staging or just for added reassurance when diving deep caves in a wetsuit. Wreck divers, who typically were diving in colder water, used their drysuit as emergency backup inflation. In the 1990’s, technical diving grew and wreck divers began using multiple wings for extra lift in case of emergency. Wreck divers began finding that a drysuit was not good backup for heavy double steels along with steel travel/deco bottles so they also began using the dual bladder wing.
Dive Rite and OMS both introduced dual bladder wings to give divers a more streamlined solution for backup inflation. Everyone was happy, but now we get into the management problems of how safely and effectively dive a dual bladder.
The first quandary is how to route the hoses on the backup bladder. When divers were using two wings the most common method was to put the inflation hoses back to back and bungee the hoses together to have everything at your fingertips. However, dual bladder wings have the backup inflator behind the diver’s right shoulder, rather than the left, so now there is a hose on each shoulder. For awhile, this seemed to work; then the diving community began seeing issues.
I can’t help but remember one of Billy Dean’s talks on equipment management. He called it the triangle of influence (TOI), starting at the neck draw a triangle from shoulder to shoulder down to just above the navel. In this area should only be items needed for life support, primary and secondary regulators and BC inflation. Everything else should fall outside this area so it doesn’t interfere with survival needs.
Issues began arising as confused divers began clipping the backup inflator on a dual wing in front of their right shoulder, within the TOI. They believed this provided easy access in case of emergency. However, in reality we have seen more issues with divers using the backup inflation when it was not necessary, which results in a buoyancy issue that is potentially dangerous. In a stressful situation that requires the use of inflation; many divers will use the backup inflation because it is the first button they can get their hands on. If the primary bladder has not failed, divers now have a bigger issue because they have gas in both bladders. At some point during the situation, if they forget to vent one or the other, further stress is created with out-of-control buoyancy.
This is the reason all our current Dive Rite dual bladder wings have the back up inflation hose oriented so it clips into a D-ring on the belt or on the bungee of the wing, behind the shoulder down and away from the TOI. It should be treated like any other piece of back up equipment and not positioned so it can mistakenly be used when not necessary and lead to more issues that can make a small problem a major issue. I welcome comments on this.