2airishuman
Contributor
Can you share any details? I wasn't aware they could cause problems. I can't think of anything that seems reasonable other than someone using it as a stage to extend a dive and getting bent. What happened?
I've brought them up in other threads. There have been at least two similar fatalities, probably more. The specific accidents are starting to blur together in my head but here's what I remember.
Accident A. A diver using a back-mounted pony cylinder mistakenly started the dive with his (primary) tank valve shut but did not realize his mistake because he inadvertently began the dive on the pony cylinder regulator. Diver was observed performing a standard predive check by breathing the regulator while watching the SPG. During the predive check, the SPG reading appeared normal because the primary regset was charged and shut off before the dive. OOA accident ensued when pony cylinder was exhausted. Diver was unable to reach the primary cylinder valve and did not have a buddy nearby.
Accident B. A diver using a back-mounted pony cylinder completed all usual predive checks and started a dive correctly. At some point during the dive, he lost his primary regulator and performed an arm sweep to locate and retrieve it. The regulator so located was actually the pony cylinder regulator but diver did not realize this. OOA accident ensued when pony cylinder was exhausted. Diver never switched back to the primary reg, reasons unclear due to lack of witnesses, conjecture was that the diver was so convinced that it was his primary air supply that failed that he was trying to switch to the pony and never made an effort to locate and use the primary.
These were fatalities.
The lessons that I have taken from these accidents are:
- A poorly thought through pony configuration adds risk to the dive. Even smart, experienced divers can conclude that a configuration is safe when it is not.
- Slung ponies are inherently safer than backmounted ponies, because identical configurations have been in use a stage bottles by technical divers over the past 20 years, and the risks and configuration tradeoffs are well understood based on their use in millions of actual dives. (As an aside, the only fatality that I'm aware of that was blamed on a stage bottle was an entanglement event involving a stage bottle with all-metal rigging on the lower band that could not be cut loose. This is easy to avoid by using braided cord to attach the stage band to the bolt snap, which is now the standard practice)
- When using a backmounted pony, it is vitally important to be able to identify which regulator is connected to the pony cylinder, quickly and reliably, under all reasonably foreseeable dive conditions. (I do not believe hose or regulator color or texture, alone or in combination, are sufficient to identify the reg, because sometimes it's dark and I'm wearing gloves. It is unclear to me what steps the divers in these accidents had taken to make the regulators identifiable, but they were experienced divers who thought they were getting it right)
- Clear agency guidance is overdue. PADI, NAUI, SSI, SDI, DAN, etc., should be providing evidence-based, experience-based guidance on how to use these tools since their use has become widespread in the general recreational diving community and the hazards are now known.