Did everything right ( I think) still, buddy got bent??

[DiveBandit]

Hi everyone. I'm always learning from reading about what happens to others in this forum. I thought it was time to contribute something myself. I felt this would be good for the near miss section rather than the accident section mostly because we kinda dodged what could have been a fatal bullet.

Last weekend My son and I dove Friday, Saturday, and Sunday for an IANTD advanced nitrox/deco class.

Friday at 6:20pm we did a quick dive to 33 feet to calculate our sac rate. Dive lasted 24 minutes.

Saturday at 3:00 pm we did a dive to 108 feet averaging 65 feet for 35 minutes, a SI of 18 minutes and then a 2nd dive to 35 feet averaging 22 feet for 40 minutes.

Sunday at 5:00 pm we did a dive to 131 feet averaging 47 feet for 62 minutes, a SI of 11 minutes and then a dive to 57 feet averaging 27 feet for 25 minutes. After a SI of 5 minutes we went back down to 21 feet for about 3 minutes just to retrieve our deco bottles.

My son declined to mention that he experienced pain in the knee joints on the 2nd dive sunday which went away after we went down to 57 feet. Monday night he told me he had leg pain that was getting worse since Monday morning, and by Tuesday afternoon he was on his way to Orlando to do a 5 hour dive in the Chamber.

In the end I'm left to wonder why. We did everything by the book (except for the short SI's) we did deco stops using 50% EANx even though our computers said we didn't need to. The instructor and myself didn't bend? I just don't get it.

I really need to understand what happened here because I don't want this to happen again for obvious reasons. So far all I can come up with is that I need to do future deco dives and maybe even all future dives extremely conservative?

Some things I considered in trying to figure this out.
1. first deco dives we've ever done.
2. bent diver said he was cold at the end of the dive.
3. both buddy and I are a tad over weight (but fairly fit).
4. SI's were probably too short.
5. there was a lot of flucuation in depth on the 2nd dive Sunday.
6. should have brought the deco bottles up after the 2nd dive rather than going back down for them and doing what was essentially a bounce dive ??

thank you everybody in advance for your constructive criticisms

Dave.

 

[z3r0c00l]

I dont know how your dive plan could have worked - I assume it was computer based, but all of those SIs are painfully short - even your later shallow dives became decompression dives, and serious ones at that. Using 50-50 decomp gas should be less about saving time on these kinds of dives (rec. decompression under 1 hour total decomp time) and more about making you safe. I would use 50-50 or leaner EANs as air, and live a long healthy life. Am I too conservative? I would pose that question to your buddy.

If this was a class, did someone check your plan and-or guide you in your SIs?

The only suggestion I can make is be very conservative - always. Welcome to decompression - I personally do decompression with this kind of buffer - round up to the next depth, next time, and next surface interval. Some people think I am crazy (computer divers) and just wasting air and dive time, but bent divers lose lots more dive time.

I have to say your sunday dive schedule seems a bit much to me. After your 131 ft decompression dive, doing a 57 ft dive after only 11 minutes seems a bit much. What kind of decompression did you do on the 57 ft dive?

Also, if you feel bends pain you should abort the dive right away. There is a huge danger in compressing bubbles and then letting them grow again. That knee bend could have become a brain bend after going to 57 ft. In a few instances, guys got pain starting to go up, and had to stop. They basically got stuck underwater.

 

[Walter]

Dave,

You didn't mention if you were diving tables or computers and which ones.

If you were diving tables, 108 ft for 35 minutes puts you on a staged decompression dive with a 2 minute stop at 20 feet followed by a 21 minute stop at 10 feet. I don't know if you made the required stops, but you followed it up with a 35 ft dive for 40 minutes. As an L diver (assuming you made the 2 decompression stops), your max bottom time at 35 feet was 39 minutes. You should have made a 2 minute stop at 10 feet.

The next day, you dived to 131 feet for 62 minutes. This exceeds anything I've been able to find online (I have the full tables at home, so I can get you better info later), so for the purposes of discussion, let's assume your actual depth was 130, not 131. That dive required three stops, 6 minutes at 30 feet, 24 minutes at 20 feet and 61 minutes at 10 feet. Leaving you a Z diver on the tables. After 11 minutes you were still a Z diver and as such you had an RNT of 122 minutes for a dive to 57 feet. Added to the 25 minutes and the 3 minutes (If your surface interval is less than 10 minutes, it's the same dive.) you have a TBT of 150 minutes. That would require a 48 minute stop at 10 feet.

I'm frankly surprised you both weren't seriously hurt with such a profile. I'm glad you're both OK.

 

[tedwhiteva]

IMO, your Sunday schedule was too agressive, espcially with the short SIs and espcially if there was a lot of fluctuation in any of the dives (caves?)

 

[z3r0c00l]

I'm frankly surprised you both weren't seriously hurt with such a profile. I'm glad you're both OK.

Along those lines, my question really is: in a class, didnt someone check your plan?

 

[Rick Inman]

6. should have brought the deco bottles up after the 2nd dive rather than going back down for them and doing what was essentially a bounce dive ??

In general, I don't like the bouncing for stages myself. Maybe in this case it wasn't a contributing factor, but I think it's a bad habit to get into. If I can't bring a stage up (for whatever reason) I'll ask my buddy to surface with it, or support crew to retrieve it, or I'll leave it until I'd done a reasonable SI.

There are a few times I can remember where we've actually abandoned some sort of gear on the bottom and retrieved it on a different day. It's just stuff.

Frankly, I'm surprised your instructor promoted this practice.

Of course, I also don't like the short SI's as a trained practice.

 

[dlent]

Read this article: Bounce diving

 

[Ice9]

Read this article: Bounce diving

Good points in this article. I hadn't thought of it that way before...

 

[lamont]

After a SI of 5 minutes we went back down to 21 feet for about 3 minutes just to retrieve our deco bottles.

gue.com/Expeditions/WKPP/Decompression/nobounce.html

 

[Sonofasailor]

you might want to have a PFO test (both of you) since you started deco diving. if you are not familiar, it is called the patent foramen ovale, you can google and look it up on the DAN website. I'd also add that there is evidence both ways suggesting that having a PFO does/and does not affect off-gassing nitrogen.