Thomas is the Director of Training for PADI Asia Pacific as well as a PADI Exmainer, Course Director and TecRec IT. In this article he answers a FAQ by explaining PADI’s philosophy on backing up buoyancy control devices during open circuit TecRec training.
Many tec diving risks either don’t exist in recreational diving, or are more severe than in recreational diving. These risks include drowning due to failed BCD and back up buoyancy control while diving heavily weighted with equipment. It is also possible to drown in heavy gear due to entering the water with all your cylinder valves closed (due to an improper predive check) and sink, unable to inflate your BCD or breathe.
The philosophy and requirement in regards to backup buoyancy control is that the student must have reliable means for controlling buoyancy and maintaining decompression stops in mid-water with a failed primary BCD. During the PADI TecRec courses these skills are also put into practice. Whether you need a double bladder BCD (sometimes called “double wings”) depends on the dive requirements. In all cases, you should have back up buoyancy. If, for example, dropping your weights in the event of BCD failure would still leave you substantially negative, then a double bladder BCD might be the best way to go. But, you still want the simplest rig that does the job. Typically, if you’re in a dry suit with lighter cylinders, that may provide adequate back up buoyancy control and a single bladder can be appropriate. The heaviest cylinders can weigh too much to use a dry suit reliably for back up buoyancy control, or you may be diving in a wet suit. In those cases, the double bladder BCD provides the back-up you need. If you dive in several environments, you may find you need both single and double bladder BCDs, using whichever one fits the circumstances.
In cases where the student is carrying a relatively small quantity of overall weight (e.g., a single cylinder only) one source of buoyancy control may be acceptable at the instructor’s discretion, provided that there is a reliable alternative method for maintaining decompression stops, such as ascending along a mooring line or decompressing on the bottom if topography allows. However, a lift bag or DSMB is not considered a reliable method of backup buoyancy control.
There are several manufactures who are offering dual bladder BCD’s including the Hollis SMS100D, DiveRite Horseshoe dual bladder (BC2074-DUAL), Dive Rite Dual Nomad Wing, OMS Tesseract, ScubaPro X-Tek Horseshoe Twin Wing, Apeks WTX6R Double Comfort, EZDIVE Tech Scuba Diving Wing BCD or IST JT65H 65Lbf Double Bladder Twin-Tank Bcd.