Steel tanks dangerous?

[Scared Silly]

Therefore, if you are properly weighted during a recreational dive and don't ditch any weight, the only weight you have to be able to swim up at the worst point in the dive is equal to the weight of the gas in the tank.

That is NOT true. One needs to account for the loss in buoyancy of their thermal protection at depth. That factor is significant for thick wet suits where in practical terms at depth (3-4 atm) the buoyancy is zero yet at the surface is 10 or more pounds.

One might be able to swim up the weight of their gas but many would struggle at depth to swim the weight of their gas plus another 10 or more pounds.

FWIW perhaps a decade or so there was a well document set of deaths of two divers who were diving very negative doubles in open water whilst wearing wetsuits. While their BCDs could compensate for the weight of the gas at the surface, the BCDs could not compensate for the weight of the gas and the loss in wet suit buoyancy at depth. They went way down to Davey Jones locker and did not come back.

 

[boulderjohn]

That is NOT true. One needs to account for the loss in buoyancy of their thermal protection at depth. That factor is significant for thick wet suits where in practical terms at depth (3-4 atm) the buoyancy is zero yet at the surface is 10 or more pounds.

One might be able to swim up the weight of their gas but many would struggle at depth to swim the weight of their gas plus another 10 or more pounds.

FWIW perhaps a decade or so there was a well document set of deaths of two divers who were diving very negative doubles in open water whilst wearing wetsuits. While their BCDs could compensate for the weight of the gas at the surface, the BCDs could not compensate for the weight of the gas and the loss in wet suit buoyancy at depth. They went way down to Davey Jones locker and did not come back.

You are correct in that I did not account for the wetsuit compression.

 

[fisherdvm]

I think some people believe that I am crying wolf. But to mentally think of problems for me is good. As I did have a partially leaky bcd due to poor attachment after a flight, that got worse after a dive. But by then the tank was near empty and it was easier to swim to the boat. I think it is good for a beginner to think about what he/she would do also if one jumped in with a deflated and disconnected bc - that the choice of steel or aluminum might limit your options in weight dumped. Thanks for the reminder that a wetsuit loses much of it’s buoyancy at depth.

 

[rsingler]

FWIW perhaps a decade or so there was a well document set of deaths of two divers who were diving very negative doubles in open water whilst wearing wetsuits. While their BCDs could compensate for the weight of the gas at the surface, the BCDs could not compensate for the weight of the gas and the loss in wet suit buoyancy at depth. They went way down to Davey Jones locker and did not come back.

You'd think, who wouldn't know that their bcd couldn't support their rig? That it was depending upon the added buoyancy of the wetsuit? But there you are. It happens. The buoyancy spreadsheet tool noted above includes a set of cells that show rig buoyancy alone, without what the diver provides via exposure suit. That will help you choose the correct wing/bcd lift, so that if you climb out of your rig to adjust something at the surface, it doesn't plummet to the bottom without you. Oops!

In this case, the failure to account for this was rather more serious. Very sad.

 

[rsingler]

I think some people believe that I am crying wolf. But to mentally think of problems for me is good. As I did have a partially leaky bcd due to poor attachment after a flight, that got worse after a dive. But by then the tank was near empty and it was easier to swim to the boat. I think it is good for a beginner to think about what he/she would do also if one jumped in with a deflated and disconnected bc - that the choice of steel or aluminum might limit your options in weight dumped. Thanks for the reminder that a wetsuit loses much of it’s buoyancy at depth.

Nah! @fisherdvm , this is a great thread! Just too scary a title, lol!

 

[tursiops]

I think it is good for a beginner to think about what he/she would do also if one jumped in with a deflated and disconnected bc - that the choice of steel or aluminum might limit your options in weight dumped.

I'd like to thonk that even more thought goes into hiw to avoid jumping in with a deflated and disconnected BCD. For better to prevent a problem rather than solve it.

 

[Scared Silly]

You'd think, who wouldn't know that their bcd couldn't support their rig? That it was depending upon the added buoyancy of the wetsuit? But there you are. It happens. The buoyancy spreadsheet tool noted above includes a set of cells that show rig buoyancy alone, without what the diver provides via exposure suit. That will help you choose the correct wing/bcd lift, so that if you climb out of your rig to adjust something at the surface, it doesn't plummet to the bottom without you. Oops!f

In this case, the failure to account for this was rather more serious. Very sad.

I think the real issue is that people do not realize that when it comes to wet suits that there is complete loss in buoyancy at depth. Tobin (from DSS) regularly notes (#130) that a BCD needs to be able to float your rig at the surface with full cylinders without you in it and be able to compensate for the loss in thermal protection buoyancy at depth. That might include the buoyancy loss in a wetsuit but also the loss in buoyancy due to a flooded drysuit.

 

[fisherdvm]

So as you go through your air trying to swim your negative setup to the surface the problem is self solving.

Buttt I often like to dive where hard bottom
Is 130 ft. So it is a good exercise to know your limitations before jumping in with a 120 steel, a good pony and NO smb or lift bags. The what if ? BC blew up at the surface with a stuck inflator? Dude with the spear just nicked your bladder?

 

[rsingler]

Buttt I often like to dive where hard bottom
Is 130 ft. So it is a good exercise to know your limitations before jumping in with a 120 steel, a good pony and NO smb or lift bags. The what if ? BC blew up at the surface with a stuck inflator? Dude with the spear just nicked your bladder?

Well, now you're exposing yourself to some justified criticism. It's one thing to say that IF my buddy left me, and IF my bcd is torn, and IF I forgot my SMB, that I'll have to jettison 4# and swim up 15# of weight until my wetsuit expands. That's planning. That's your third level of safety after your buddy and redundant buoyancy.
But if you are positing that you are STARTING your dive with no redundant buoyancy, and your profile lists you as Solo Diver, then I maybe think you deserve whatever criticism you get. Planning is a good thing. Planning with only one rescue option is not a good thing.

 

[northernone]

When I've been around recreational dive profile bcd failures, it's the buddy who helps.

Are we discussing self rescue techniques and redundancies as necessary for solo diving?