“Fairly” Uncontrolled Ascent - Please help me understand what went wrong

[CD24]

Do you recall how much air you had remaining in your tanks and what depths you were at when you started to ascend?

 

[KristenK]

Well......you'd hear the inflator.

I'm going with empty Al80. They can get floatier than we thin

Assuming you're properly weighted to start with, sounds like a stuck inflator. They can be sneaky and stick intermittently or slow filling. If your BCD is five years old it's entirely possible the inflator mechanism (or at least the internal cartridge) needs replacing. I wouldn't assume the inflator was replaced when your regs were serviced unless you know otherwise. From what I can see Cressi uses its own (rather than generic K valve) inflator mechanism. That's too bad since they can be harder/more expensice to find/replace. You may need to wait until you get home to get sorted but I strongly recommend you go with a generic K valve inflator (and compatible hose assembly) since they're ubiquitous-cartridges are $15-or carry a spare Cressi unit on your next trip. I change out the K valve inflator cartridge before every big trip and carry a couple of spares.

In the near term-before your next dive-connect the BCD to the LPI hose and hit the up button hard for two seconds and release. Wait ten minutes. If the BC keeps inflating, even a little, it's a stuck inflator. You won't necessarily hear it if it's a slow fill. If it doesn't fill at first, it could be an intermittent stuck inflator. Try the test a dozen times. After each give it a while to see if the BC keeps filling. Trying another reg on your BCD is also one way to test whether the inflator is the problem. If it is, swap out the inflator if possible. Don't bother replacing/servicing the o rings. Just chuck the inflator (or at least the internals). Swap them out from time to time prophylactically-hint: your service tech will not likely do this unless requested.

Free flowing regs are another matter. If the seconds are free flowing it's likely they are either hot tuned (below spec) or the IP is above spec, or both. BTW, even if the IP is out of spec, it's not likely the cause the uncontrolled BCD filling since second stages would likely free flow massively before that. Besides, the buoyancy problem occured well into the dive. If the problem was an out of spec reg it would show up late in the dive they way you describe. However, it's possible you have multiple problems (some combination of first stage IP out of spec, second stage cracking pressure out of spec, stuck inflator). At the least, I would have your IP and seconds checked and adjusted if out of spec.

This is very, very helpful. It really helps me learn my equipment more thoroughly, which I need to do in order to be a great diver. Thank you for the detailed and easy to follow answer.

 

[KristenK]

Do you recall how much air you had remaining in your tanks and what depths you were at when you started to ascend?

Over 1000 psi on both. First dive was around 40 feet when I realized there was an issue. Second dive was around the same. (I’m too tired to go look on my computer.)

 

[MidOH]

Could be runaway inflation of the air already in the bcd.

That air expands as you go up. Al80 is getting light. Waves splashing and bubbles all over me.

End result: I'm doing my safety stop up side down kicking hard to go down. Once my fins broke the surface, I gave up.

Solution. At the end of my dive, or anytime I go up shallow, I dump air, and fin up.

I stay negative during my safety stop, and my whole climb back to the boat. If I stop finning, I sink.

 

[Fishdip]

Could be runaway inflation of the air already in the bcd.

That air expands as you go up. Al80 is getting light. Waves splashing and bubbles all over me.

End result: I'm doing my safety stop up side down kicking hard to go down. Once my fins broke the surface, I gave up.

Solution. At the end of my dive, or anytime I go up shallow, I dump air, and fin up.

I stay negative during my safety stop, and my whole climb back to the boat. If I stop finning, I sink.

To me this sounds like a bad habit. No every dive site will have something to hold for a safety stop. On top of that swimming to the boat like that could end bad if you get a bad cramp or a fin comes off. I would recommend learning to control your buoyancy at any depth and at any point in the dive.

 

[VikingDives]

I'm going to offer two other options:

1. Incorrect intermediate pressure (IP) from the first stage. Given that things "free flow easily" that could be the problem.

2. Malfunctioning LPI. I've seen LPIs that have a "slow leak" into the bcd and on ascent, the slow leak is enough to cause an uncontrolled ascent.

@KristenK I'm betting on an equipment issue.

 

[gordonscuba]

I don't think it's related to the tanks' buoyancy. The tank had 1000 psi in both cases. I assume the OP has been underwater at 40 feet and roughly 1000 psi before in the same gear, and not had this happen. Also, the second dive added weight. The only other way to get so positive, so quickly, is that something is inflating the BC. I agree with @VikingDives as to the most likely causes. I also agree with @rx7diver that, as a temporary measure, you can stop this from happening by keeping the LP inflator hose disconnected, and doing all inflation orally. That would allow you to finish your vacation, and then get your gear serviced at your LDS.

Also: the manual dump valves which are directly on the BCD usually vent gas faster than the top button on the hose, and if you start an uncontrolled ascent, be prepared to simultaneously dump gas from the direct BCD valve and disconnect the LPI hose. Then once you reverse the ascent, orally inflate to restore neutral buoyancy. Make sure you can locate the manual dump valve and LPI quick-disconnect easily from muscle memory.

 

[happy-diver]

I am a good diver, although only 120 dives, and can’t figure out what happened. I think it was equipment related. I have an Aqualung Micron and a Cressi BCD. I’ve been diving with both for 5 years without any problems.

These are great odds well done feel good get back in the water and be ready, you can't buy such experience

It is a very fine line, staying vertical pulling on your shoulder dump, or a duck dive and using the bottom one

 

[Russjstewart]

I know steel tanks have been mentioned earlier, but….. does the op normally use steel and has moved to AL for the trip and have their been any changes in wetsuits/ thermal protection

 

[Edward3c]

Hello everyone, I’m on a dive trip in Turks and had two upsetting dives this morning. I am a good diver, although only 120 dives, and can’t figure out what happened. I think it was equipment related. I have an Aqualung Micron and a Cressi BCD. I’ve been diving with both for 5 years without any problems.

Dive started fine. At about 45 mins the first dive and 35 mins second dive I started ascending. I dumped all my air, using dump valves and the shoulder dump. I squeezed the bcd the best I could to get air out. Nothing worked. I grabbed the safety stop bar and even that wouldn’t keep me down.

I will say my second stage and octopus free flow fairly easy. I have no idea if this has anything to do with it.

My weights are fine. I even added 2lbs the second dive. Sank like a rock and knew I was overweighted.

No one on the island services equipment (that’s not their own rental gear.) I’m switching to rentals tomorrow. But meanwhile my confidence has been shaken and I have 3 more dive days to go (and Philippines in January.) Not fun.

Thank you for your knowledge and help!

My first thought was the mass of the cylinder was different from what you normally use. Second, the salinity of the oceans is not constant, it may be more salty than you’re used to.