Can you say Hernia!

[Rick Murchison]

There are several possible scenarios where a heavy tank can in fact put you out of buoyancy range.
(1) diving a thick wetsuit - the wetsuit will lose buoyancy as you descend, which must be compensated for with your BC. If your BC doesn't have the lift available you can end up negatively buoyant on the bottom with swimming up or hauling yourself up your only options.
(2) BC failure with wetsuit or no suit.
(3) Drysuit failure and inadequate BC lift available to compensate.
--------
When diving big steels, I either (1) use a drysuit and a BC with enough lift to handle the tanks (I can still get positively buoyant with either a BC or a drysuit failure), or (2) wear a BC that'll handle the tanks alone *and* carry a lift bag with sufficient lift to handle the tanks should I have a BC failure.
Under any circumstances, blaming the tank is off the mark.
Rick

 

[rcohn]

Dstang55,

It sounds like you're describing the triple death at WPB in January '98. This was extensively described on rec.scuba (basically beaten to death and far far beyond as usual) but it looks like the DejaNews archives are gone (at least temporarily) so I can't pull it up. I'm sure it was kicked around on Techdiver as well.

Ralph


Here are some of the topics from Techdiver if you want to wade through the "discussions" there.

http://www.aquanaut.com/bin/mlist/aquanaut/techdiver


Jan 14 1998 Missing tech divers in West Palm--to George Irvine
Jan 18 1998 3 missing in WPB Fl / Divers Supply "coverup"! FROM rec.scuba, sat pm
Jan 18 1998 Re: Added info re three missing in WPB / "Kick an IANTD instructor in the head--the lives you save will be his students !"
Jan 18 1998 Re: 3 missing in WPB Fl / Divers Supply "coverup"! FROM rec.scuba, sat pm
Jan 18 1998 3 missing divers in WPB. What may be scaring Divers Supply...
Jan 19 1998 TV 12 on 3 missing WPB Divers---Issue: Is there Culpable Negligence?
Jan 20 1998 Fw: Divers Supply - Press Release
Jan 20 1998 Re: 3 missing in WPB
Jan 21 1998 2nd Press Release by DS
Jan 21 1998 Re: 2nd Press Release by DS
Jan 22 1998 Re: Re.Beyond belief.W.P.B.dive accident
Jan 23 1998 Re: 2nd Press Release by DS
Jan 23 1998 Re: BAD NEWS: Fallout from the WPB tragedy
Jan 26 1998 Divers Supply thread from rec.scuba---What the real danger is...
Feb 2 1998 3 missing in WPB
Feb 6 1998 Re: Cool it on Divers Supply/ Here is the DANGER that needs to befixed...
Feb 18 1998 WPB Dive Tragedy- Update. One body just suurfaced..
Feb 19 1998 WPB Tragedy, Update #2
Feb 23 1998 Divers Supply, IANTD, Tom Mount and tragic technical diving

 

[Dstang65]

I suppose that is the story, like I said this is all second hand. I'm sure that tanks alone cannot be blamed for the incident. I was just trying to pass along a warning that I recieved from a member of the diving teaching community. Again I meant to cause no comtroversy.

 

[Rick Murchison]

Please don't shy away from controversy! It is often through a good spirited controversy that the truth, or a better idea, emerges.
So don't hold back - everyone's ideas and opinions are welcome.
Rick

 

[rcohn]

No controversy, I just thought you might be interested in some of the "facts" of the incident you were refering to.

Ralph

 

[turnerjd]

Originally posted by Rick Murchison
There are several possible scenarios where a heavy tank can in fact put you out of buoyancy range.
(1) diving a thick wetsuit - the wetsuit will lose buoyancy as you descend, which must be compensated for with your BC. If your BC doesn't have the lift available you can end up negatively buoyant on the bottom with swimming up or hauling yourself up your only options.
(

Rick,

on this point I don't agree with you - yes your solution is valid, but it doesn't depend on having a heavy tank. If you are diving in a thick wetsuit, you are going to need a reasonable ammount of TOTAL WEIGHT to get neutral (+some to allow for air use).

Now, if you use an aluminium tank, more of your total weight is on the weightbelt, and if you use a heavier steel tank you have less on the weightbelt. In both cases the TOTAL weight will be similar if the tanks displace the same ammount of water.

If you are neutral at the surface, the change in buoyancy from your suit being compressed will be the same if you have either steel OR aluminium tanks. It is simply the suit being compressed! (and hence it only depends on depth)

OK, so at depth, you have two variables, one is loss of suit buoyancy, and the other is the loss of the weight of the air you have used. both of these variables do not change with the tank material.

So, provided you are neutral at the start (or correctly heavy for air to be consumed) the tank material and size doesn't matter a damn for buoyancy during the dive. Getting a BCD that provides suitable amounts of buoyancy is a matter of knowing the weight of air you have in the tank, (the extra weight you have on your belt at the start of the dive) and the loss of buoyancy from your suit at depth (plus an added safety factor).

I have found that generally people I know that have learned with steel tanks generally don't like aluminium tanks simply because they have to wear extra weight with the aluminium tanks.

Tech diving using AL cylinders only is a bit of dogma that I would more than happily see dispensed with. UK technical divers generally tend to dive with steel cylinders, and don't seem to have any problem with them. In a sport that is supposed to rely on intelligent analysis of problems and risks to then provide a suitable solution this insistance on AL cylinders is completely unwarranted as the buoyancy change factors are independent of tank construction material.

Jon T

PS. If you are diving in a very thin wetsuit where heavy tanks would put you very negative at the surface, it is a different story, as in this case the total weight you need is much less, since you have less suit buoyancy to overcome. In this case it is quite likely that 4 steel tanks could make you 20Lbs negative at the surface! but obviously, with a thick wetsuit this is not the case, as you will need at least 20Lbs of weight to get neutral.

 

[Rick Murchison]

Sorry turnerjd.. I guess I wasn't quite clear on my point, which is that you can jettison a weightbelt to get positive, but not your tank.
Rick

 

[turnerjd]

Rick,

Thanks for that..... now you mention weightbelts it all makes purfect sense. Although, I would like to see the 'you must dive with AL cylinders' dogma disapear.

Jon T

 

[rcohn]

Since the Al vs. steel issue has come up I thought I'd copy the following which explains the logic behind the dogma that is so frequently repeated. Note that George is talking about doubles.

Ralph

http://www.aquanaut.com/bin/mlist/aquanaut/techdiver/display?46829,from

From: "George Irvine" <kirvine@safari.net>
Subject: Re: DIHUL, was: Fins question
Date: Sat, 24 Feb 2001 12:24:09 -0500

I keep saying it - weight yourself so that with little or no gas you can
hover at ten feet, and with full gas you can swim up with no inflation by
dropping something.

That covers it.

For tank choice in ocean, big heavy tanks are dangerous boat diving, so are
not my first choice. I'd rather add a stage and dive it dry , leaving my
back gas intact.

Cave diving is different in that you need more gas to go farther and the
decompression is in a safe environment,not open sea with all its vagaries.

 

[carlislere]

Back in the early 80's, we had an instructor that had come back from working in Hawaii for 5 years. He brought 2 US Navy steel 90 tanks with him. He brought them in for a fill and put them in this yellow plastic trash can with water that we used to keep the tanks cooled while filling.
I was much slimmer and lighter at the time. I filled the tanks, but when I tried to take them out of the trash can I couldn't get them over the top of the can to get them out!
I now have a Scubapro steel aloy 95, which is lighter than those old Navy tanks. To think they wore doubles with those old steel tanks and may still to this day!
RonC.