Uncontrolled ascent today from 40ft - advice sought

[IrishPaul]

Hi all,

Couple of questions.

I did two dives today; at an altitude of 1700 ft, freshwater lake, in a 7mm wetsuit, standard Aluminum tank.

The first lasted 31 minutes with max depth of 65 ft.

1 hour 10 minutes of SI was followed by a dive of 24 minutes with a max depth of 69 ft.

On the first stop we did a slow ascent from 40 ft, then the 3 minute safety stop at approx 20ft.
During this dive, I was weighted with 30lbs lead, which I found to be a bit too much. During the safety stop I was kicking to stay at 15-20ft.


For my second dive, I reduced the weight to 24 lbs lead. Descent was slower, but I felt I had more buoyancy control (fin pivots were great, could control ascent and descent by breathing).

We had planned to so a safety stop again, but as I ascended to 20 ft, I could not stop myself, even with my BC deflated, the hose in the vertical position and my thumb on the deflator. I effectively missed my safety stop, but was able to get back down to maybe 5ft for a minute. At this point, I feel that I was not fully exhaling, as I was slightly panicked.

So, my questions are:

1. I am a little paranoid about missing my safety stop, (especially since the lake is 1700 ft above sea level)but I am hoping that the depths and time at them will mean that any side effects are unlikely. Any input here would be appreciated.

2. Can one stop such an ascent? On my next dive (assuming similar gear, tank, water etc) I will increase the weight to 28 lbs and see how that goes.

3. I am therefore wondering, for a beginner diving to 60-70 ft, is it better to be slightly overweighted, to help cope with the extra buoyancy of an Aluminum tank at the end of the dive?


Sorry about all the questions, but I am quite concerned at my inability to stop my ascent today!

Thanks,
IP

 

[Scott L]

Ideally, one tests the weighting of their rig with 500psi in the cylinder before diving with new or an altered gear set-up. You should be able to remain at eye-level on the surface if properly weighted. It is certainly a better system than guessing. At some point soon, you should learn to ascend in the horizontal position, which will greatly aid in controlling a problematic ascent...

 

[IrishPaul]

That's a good point. I will see if I can bring a 3rd tank with low air and test weighting at that psi reading. Thanks.

 

[JahJahwarrior]

The best would be to have tested out the weighting on the first dive.

You could use zip ties to hold several pounds of your weight, say 6 ( 3 2 pounders) on some cheap brass bolt snaps. At your safety stop on the dive, get neutral, then hand off one weight at a time to your buddy, getting neutral each time. Easy way to find the optimal weight.

Which brings me to the second point, your kicking on the first dive. Why not simply add more air to your wing, to stay neutral?

 

[Scuba_Noob]

A change of six pounds between one dive and the next is pretty significant without any change in gear (e.g., changing from AL80s to Steel 100s). Usually, I like to keep my weight changes around three pounds or less.

I'd say that you should monitor yourself for any symptoms of decompression illness for a few hours because usually symptoms hit within the first six or so hours after a dive (if it hits, call DAN). How slow was your ascent? If it was less than 60ft per minute, and you were not holding your breath (i.e., breath normally, exhaling on ascent), with your dive profile, you should be fine.

If you want to slow down such an ascent, you can flare your body out to increase the surface area (like a starfish) and also dump as much air out as possible.

My opinion is that being slightly overweighted is better than being underweighted. You can always fin up (and/or inflate your BCD), but it's hard to fight downwards. You should do a buoyancy check at the end of your next dive at 500psi.

You mention that in the first dive, you were finning up to maintain your depth at the safety stop. Why not just fill your BCD a little? Also, are you wearing a drysuit? If so, you may not be releasing all the air from the drysuit while ascending.

As a side note, I have no experience with altitude diving.

 

[Dsix36]

There is absolutely nothing wrong with being paranoid about missing a safety stop. They are designed into the dive to add a level of safety to you dive. Missing a safety stop does not mean that you are going to get the bends. However if you ascent is uncontrolled to the pont that you are ascendinf too fast, then problems can/will occur.

There is no way to stop such an ascent when you are in a heads up position if you have vented all the gas from your BC. To stop or slow the ascent you will need to be head down and use your fins to keep from ascending too fast.

Being overweighted to cope with a tank that is empty is NOT overweighted. If you can not maintain a 20' stop and then do a slow and controlled ascent to the surface, you are too light and need more weight.

Of course lung volumn plays an important part in this too.

 

[TSandM]

I think what you learned was that doing a real weight check is better than trying to do it by guess. You don't have to do a weight check with an empty tank -- you can weight yourself neutral at the surface with a full one, and then add a pound for every 13 cubic feet of gas you intend to use from your tank. (In the case of an Al80, that's five pounds.) If you do this, you don't have to know the buoyancy characteristics of your tank at all, because the weight check takes care of it.

You can definitely swim down several pounds of positive buoyancy, but it's a lot of work. From the sounds of things, you were more positive than that . . . generally, if you're only off by a pound or two, you're just a little light at the safety stop. If your neoprene had rebounded enough at 40 feet (2.2 ATA) to make you uncontrollably buoyant, you were significantly underweighted.

As far as having to swim at your safety stop -- are you doing your ascents by going vertical, and emptying your BC? In that case, if your tank isn't nearly empty, you WILL be a little negative at 15 feet. The only time you'd expect to be perfectly neutral there is if you are at 500 psi (or whatever low pressure you planned your weighting for) and your wetsuit had fully rebounded. And notice that, if you do your weight check at the surface, you WILL be a little negative at 15 feet, from neoprene compression.

 

[bl6394]

When I was taking my Adv Open Water Class (or technically Specialty Diver class - since I only had about 13 dives logged) - we lost our instructor in Bonne Terre mine doing our navigation drill. Me and my buddy wondered around the mine down to a depth of about 70 feet and 30 minutes before we were low on air - thoroughly lost - and decided to surface... Doing a free ascent with my buddy - we got up to about 35 feet - when I started to get too buoyant (7mill suit - heavily weighted). I hit the deflate button - or so I thought - and went up even faster. I REALLY mashed the button - and went up like a rocket. My computer claimed the last recorded ascent rate was 194 feet / minute... (Important to hit the DEFLATE button - not the INFLATE button.)

Once back on the surface - we found the instructor - and followed him back to the dock. I was pretty paranoid about the ascent rate - and the skipped safety stop - but had no ill effects.

It sounds like you abused your body much less than I. Safety Stops are discretionary ( but highly recommended.) Your body is complicated - and one can't make an absolute determination about when you will get bent - or won't. But my guess is you'll probably get away with this.

I had a hard time with the 7 mm wet suit - but if you make small adjustments to your buoyancy sooner - rather than later; you'll be less likely to get a runaway ascent.

Being over-weighted generally will lead to carrying too much air in your BC - which contributes to buoyancy and trim issues. I'd suggest you take a tank with about 500 psi to a pool - and see how much weight you need to easily stay down at 15 feet in your configuration. Another way to check weight is to see how much weight you need to float at eye level with full tanks, all of the air our of your BC, and fully exhaled.

Safe diving!

Bjorn

 

[bleeb]

Concur with the other posting that the best thing would be doing a more accurate weight check.

However, as a sanity check, for an average sized male who's not carrying a lot of body fat, 24 lbs in fresh water is on the verge of being high enough that I'd go back to make sure I did the weight check correctly, although less so, if you're bigger or carrying a lot of 'bioprene'. Was that a single piece wet suit? And I'm assuming you were wearing hood, gloves and boots.

 

[IrishPaul]

Thanks to all.

I was ascending in a vertical position, releasing air from my BC with my left hand. I did try to get vertical, head down and try to fin back down, but I was at the surface before I could manage it.

On my first dive, I was kicking to stay at 15 feet, as I did not want to air my BC up too much and ascend.

I will work more on buoyancy using the techniques suggested.