TDI Decompression Procedures question

[JohnN]

As a preamble, IMHO TDI course requirements are generally much more sensible than certain 'other' agencies.

But one of the bits in the Decompression Procedures class has me scratching my head:

Why-Oh-why?

8. Ascent reel with lift bag /surface marker buoy​

​

a. Adequate for maximum planned depth​

b. Minimum of 12 kg / 25 lb lift bag​

A lift bag is a crappy SMB, and a SMB is a crappy lift bag. What purpose is the lift bag supposed to serve?


TIA

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[Akimbo]

There is a huge gulf between crappy and useless. Both get the job done, especially when that job is getting your butt off the bottom with a failed wing and drysuit. As a recovering Brassaoholic, I consider lift bags essential equipment

 

[JohnN]

Thanks!

So the point is to protect against two points of failure?

Aren't there other single points of failure in the system?

(sorry, but I pretend to be an engineer sometimes)

 

[Akimbo]

…Aren't there other single points of failure in the system?...

Cylinder failure which takes you and your buddy out… maybe the boat too.

 

[decompression]

I explain the difference as well as the actual requirements for the course in my pre-course discussions.

 

[wedivebc]

I believe that the usage of lift bag is a generic term that includes SMBs. When I started tech diving I had never heard the expression SMB but used a lift bag to assist in staged ascent.

 

[JohnN]

Hard to find a SMB with 25lbs of lift

 

[Scott L]

There is a huge gulf between crappy and useless. Both get the job done, especially when that job is getting your butt off the bottom with a failed wing and drysuit. As a recovering Brassaoholic, I consider lift bags essential equipment

So, how would you execute such an ascent? Release gas from lift bag by tilting the bag sideways or monkey with the OPV? God help me if I am ever in that predicament.

 

[Jax]

Hard to find a SMB with 25lbs of lift

No, it's not. Here is a 50-lb, required when I was in wetsuit and doubles, and I routinely carry the XS Scuba 7' that is a 30-lb lift capability.

XS Scuba Surface Marker Buoy

So, how would you execute such an ascent? Release gas from lift bag by tilting the bag sideways or monkey with the OPV? God help me if I am ever in that predicament.

Not that bad, Scott, if you have a proper OPV, as is on the one above and the one I carry. Some say clip it to you, since it is your lift, now. Others say never. After hanging on it with my arm in the straps, I would clip it on my crotch ring.

You're off balance, have to monitor your ascent like crazy, and making your "deco stops" is a $%^&* . . . but when your life is at hand, you do it. Clipped off at the crotch, it's no so bad to reinflate the oral inflate.

Please understand, I was graceless and under- over- inflated and yo-yo'd, but I could bring myself to the surface pretty-safely if my wing and suit was gone. Hope I never have to do that in heavy seas.

 

[JohnN]

Awesome!!

that one makes sense to me