Almost out of air after descending against a strong current

[BDSC]

From the story above.

I was last in a group of 4 (two buddy pairs) plus our guide (a highly experienced instructor)..............There wouldn't have been anyone behind me to notice

 

[phoenix31tt]

being last should not be a reason for nobody to notice...

what happens in the case of an emergency?

first, last or middle my eyes always go to my buddy multiple times before i hit the bottom

 

[clownfishsydney]

If the current was indeed 1.5 knots, then you probably should not have been diving it. Two knots is undiveable unless doing a drift dive. Anything over 1 knot is very hard work (I am talking about anchored dives). Even 0.5 knot is hard work for an unfit person. Learn to work out when currents are too strong and make the decision to not dive. I know of a number of deaths that would have been prevented if people had not dived in currents that were too strong for their gear configuration and/or experience level. I have even seen very experienced divers come undone in high currents.

 

[Mike]

I personally find the explanation of a free flow in a 1.5 knt current to be hard to believe.

As much as wants to be said at how 'deadly' a 1.5 knot current is.... it's a typical drift dive current, not a life robbing ripping current. At 1.5 knots you'd have easily heard the free flow. 1.5 knots is not a mask ripping, water roaring in your ears current. If the current was that strong it had to been more than 1.5 knots.

It's been recorded that Michael Phelps swims at an olympic level of 3.2 knots.

According to fin manufacturers a decent in shape diver can swim 2.2-2.4 knots but not sustained

Less than average shape diver can do 1.0-1.5 knts

A 1.5 knot current is not a killer, a pin you against something until you drown, a ripper of gear... if you count 1 mississippi, 2 mississippi in a 1.5 knot current an object would have passed about the length of your outstretched arm from finger tips to shoulder

It's good you caught the low tank when you did, with proper buddy protocols in place I don't see you being in any danger what-so-ever on this incident. You would have simply breathed off your buddies second reg to the short distance to the surface.

• Currents pose special risks. I wasn't aware that an alternate could free flow from the pressure that the current puts on it. If I had been aware that it was a possibility, I would have checked on it frequently to make sure the purge valve wasn't facing straight forward. I would also have been more likely to notice a funny sound.

I don't think you should change your former beliefs, they are still accurate, unless of course you were in much more current than was described.

 

[dorkito]

some other lessons learned:

- look at your buddy once in a while during descent, even if they are behind you.
- practice deploying an smb from depth in case the situation arises again.

Agreed on both points.
- My buddy did check a couple of times, but mostly at the beginning. The guide did as well. I signaled OK each time since I was feeling great and everything was in control. Or so I thought. I should have checked my gauges- stupid (ignorant might be a better word)!
- I only just bought an SMB+reel that week. I practiced in the pool the day before with an instructor just before we left for the trip. My first attempt was a complete disaster. If I had tried that for the first time sharing air while drifting I might have killed us both. I'm going to work on this a lot. It's a huge hole in my skill set.

Some other thoughts/reactions:
- I am considering taking GUE fundies in a few months. I could see myself switching to the alt on necklace + primary on long hose method. Seems to have a lot of advantages. One is that a free-flowing alternate would be impossible not to notice
- The 1.5 knots was a rough estimate. That was based on how quickly we made our journey overnight versus how quickly the boat can usually cover that distance (it's done it many, many times). So the current could easily have been stronger on the dive. The jellies were ripping apart if they hit the rope or another diver's arm or whatever. I was thinking of the film "Gravity" as it was happening. If you've seen the film, you'll know what I mean. The current was strong enough that my mask was pushing uncomfortably against my face. The top part was really smashing into my forehead- more than uncomfortable, it downright hurt.
- There was a lot of sound. Some of it was the current, but the bubbles from the divers below were blowing into my face as well. Given that the line was so close to horizontal, I guess that's also an indicator that the current was quite strong.
- We were all pretty relaxed on the descent. We had a descent on another wreck the day before in a similar current, but I don't think it was as strong. Our guide (an instructor- PADI MSDT) talked to our group at length about the need to relax and just use your arms to gently pull yourself along. Finning is just a waste of energy and air. That was on my mind the whole time. I was totally focusing on relaxing. That's why I don't think I blew through my air. Another data point to consider. In August we dove Crystal Rock in Komodo, which is known for a strong current. Negative entry and fin, fin, fin down as fast as you could to avoid getting blown away. It was an all-out effort and, frankly, scary. When I got to the bottom I was as out of breath as if I had been doing wind sprints. It was a little deeper and I blew through 50 bar. I was amazed that I went through so much. My lesson learned there was make sure you check when you get down, you might have used more air than you thought. I guess that was really only 1/2 a lesson learned
- There is something to be said for not diving in those conditions. My wife chose not to do the second dive. I'm glad I did though. Without the air problem (whatever the cause) it wasn't all that hard, and it was very rewarding on several levels. I could have done without the jellies though. Much worse on the second dive, and I got some really nasty hits.
- Regarding descending on a line versus drifting down, the vis wasn't great, probably a little over 5 meters. Hard to tell, but not great. I chatted with the guide who set the hook, and he said he basically couldn't see the wreck until he was landing on it. That sounds more dangerous to me.

 

[TSandM]

I'm not sure how fast a Dive X-tras Sierra can go, but it can go fast enough to make a regulator freeflow. The flow out of Ginnie Springs can make a regulator freeflow. I believe that this happened to the OP. The only other reasonable explanation was that the OP didn't check the tank pressure before diving, and was unaware that he had a partially empty tank to begin with. I think his description of a relaxed descent pulling down the anchor line is accurate -- he made the point of assuring us that he wasn't nervous or frantic. To go through the entire contents of ANY reasonable-sized tank just on descent, requires a consumption rate that is off the wall. In fact, if you assume an Al80 (fairly small tank) and a 6 minute descent (pretty slow) to 100 feet (fairly deep), you are talking a FOUR cubic feet per minute consumption to end up at 50 bar at the bottom of the anchor line. I have never seen anyone achieve that breathing -- I hope I never do!

 

[Steve_C]

Comparing drift dive and anchored is irrelevant. With a drift dive your velocity relative to the water is small. With an anchor it is the water velocity. It it the Delta V that matters in this case. The speed also usually varies with depth so the surface speed does not tell the full story.

Personally low viz and high current at depth, sounds more like work then fun to me.

 

[drbill]

I may have missed something, but how deep was the dive? Hard for me to understand a drop of 150 bar (2,250 psi) on a recreational descent. A 1.5 knot current is a pretty decent one but why was the drop made against the current instead of dropping up current? I've experienced currents more than twice that velocity and they were PITAs in two cases, but then I've got massive tree stumps for legs (good German ones).

As Lynne said, a detuned reg would help limit free flows. I honestly can't remember the last time any of my regs free flowed. I do keep them slightly detuned yet have had no trouble breathing them at depths to 200 fsw (they are Mk10/G250s).

 

[Mike]

No drop. A descent down an anchor line, to less than 60 ft.

The descent was down an anchor line to a wreck. We got to the end of the rope (depth about 18 meters)

 

[dorkito]

No drop. A descent down an anchor line, to less than 60 ft.

Right. The guide who set the hook drifted down, and that sounded like it way, way beyond my experience level.

---------- Post added October 29th, 2013 at 01:26 PM ----------

The only other reasonable explanation was that the OP didn't check the tank pressure before diving, and was unaware that he had a partially empty tank to begin with.

Checked, double-checked, triple-checked the moment before entering the water. Gauge showed 200 bar. Guage is practically brand new and seemed to function correctly before and after that. So I'm as sure as I can be that the tank was full. I think we can safely conclude that free flow is what did it. Where else could the air have gone? Impossible to breath that much, as you say. Even breathing my hardest in Komodo I only burned through 50 bar. It couldn't have gone out though the BC. Seal on first stage is fine. There is nowhere else to go.