Embarrassing Naivety

[MMM]

You did this bounce dive alone...?

Sounds like it was his job to check on the anchor if this was a paid charter and a DM working for tips, but - read a dozen death reports in Accidents forum and see what you think of you diving alone.

Don. given that I do shore dives in Coz alone frequently, and dive buddy-less on boat charters, we probably differ significantly on what "diving alone" means as well as associated risks. But in the situation described, a diver went to a fairly shallow depth of 50 feet (or so - vis unknown) for a very brief period of time with one or more qualified divers watching closely. Might just be me, but I don't see that as something that merits warnings of impending doom. You are probably more conservative than I.

 

[Diver0001]

I'll read the other replys in a minute so forgive me if I'm repeating things.

I'm assuming when I answer this that you planned these dives on the PADI RDP.

First dive was at a max depth of 40 feet, average was about 30 ft. Down for 60 minutes and did not do a safety stop.

Technically you didn't need to do a safety stop becuase you weren't within 3 groups of the NDL but for obvious reasons you should get in the habit of doing a safety stop whenever it's practical.

Second dive was after a 1 hour SI. The bottom was at 60 feet which was issue one, I was taught not to dive deeper than your previous dive?

Correct.

About reverse profiles: a couple of years ago there was some research done on reverse profiles and the conclusion was that the additional risk of DCS was negligable assuming the second dive wasn't more than (IIRC) 10-12 metres deeper than the first.

That said, it's a good diving habit to avoid reverse profiles. If you want to account for the additional risk factor in planning your dives then you can do what the OW books suggests you do with a dive in cold water... namely, plan your dive (determine your NDL) as if it were 4 metres deeper than you are actually going. You can apply this kind of "fudge factor" whenever you want to plan for extra conservatism using the tables.

Additionally, you could also extend your safety stop at the end of such a dive to more than 3 minutes. Maybe double it for additional off gassing before you surface.

The DM then asked me to check the anchor so I drop down to 50 feet and its not hooked in so I surface, tell him and then drop down to 15 feet and do a 3 minute safety stop. Now Im trying to figure out what to do since the 60 foot bounce dive confused my plans.

Bounce dives are another potential DCS risk factor. Avoid them and if you must make a bounce dive then make double sure that your ascent speed is well within limits. If you must make a bounce, then obviously doing it at the beginning of a dive, when there is less nitrogen in your system, is better than doing it at the end of the dive.

In the case you mentioned I'll tell you what I would have done, but that's not to say that this is what *you* should do.

I would have looked at the 50ft bounce as a big zig-zag in my profile and then gone and done the 60ft dive but added all of the bottom time from the bounce dive to the bottom time for the 60ft planned dive. Additionally, I would have backed off the NDL by 5 minutes or so (fudge for conservatism) and extended my safety stop from 3 to 6 minutes (another fudge for xonservatism).

Note: while I would personally feel comfortable doing this, there is no guarantees. You were adding a couple of potential DCS risk factors to your profiles (skipping safey-stop #1, bounce to 50ft and a reverse profile) so you were really doing things that the tables weren't tested to account for.

R..

 

[Lead_carrier]

I recently went on a 2 tank dive in San Diego and basically had to abort the 2nd dive due to ignorance and I was just looking for some clarification. First dive was at a max depth of 40 feet, average was about 30 ft. Down for 60 minutes and did not do a safety stop. Second dive was after a 1 hour SI. The bottom was at 60 feet which was issue one, I was taught not to dive deeper than your previous dive? The DM then asked me to check the anchor so I drop down to 50 feet and its not hooked in so I surface, tell him and then drop down to 15 feet and do a 3 minute safety stop. Now Im trying to figure out what to do since the 60 foot bounce dive confused my plans. I decide to spend 20 minutes at 30 feet and then do another 3 minute stop at 15 ft before surfacing. Basically Im wondering what my options were, can I dive deeper on the 2nd dive? How does the 60 foot bounce affect adjusted max bottom time? Was the bounce a bad choice? Any and all advice is greatly appreciated, even if you want to tell me how stupid I was.

The only non smart thing I see was doing the dms' job. Let him check the anchor, unless of course you were going to be tipped by him.

 

[Blackwood]

My concern would have been bubble pumping.

Yup, in particular the (repetitive) bounce dive -> descent to short 'safety stop' -> return to the surface

 

[Mr Carcharodon]

From the May 2006 edition of Undercurrent:

http://www.undercurrent.org/members/UCnow/issues/y2006/UC0506/reversediving_may2006.pdf

An other conclusion that could be drawn from that study is that if you go on a decompression dive, accumulate a large deco obligation, and then omit doing deco at all the chances of getting bent are high. That is not a useful way to draw a conclusion about reserve profiles however.

 

[webjr]

I'd be asking the operator why he even went to the shallow site first? Or were both dives at the same site?

 

[Coll]

The dives were at two different sites, as for the bounce dive, I did it and everything else with my buddy. In the future I would definitely not do the bounce. I was fortunate enough to make some bad choices, get through unscathed and learn from the experience as a result. Thanks very much for all the info and suggestions!

 

[DandyDon]

Don. given that I do shore dives in Coz alone frequently, and dive buddy-less on boat charters, we probably differ significantly on what "diving alone" means as well as associated risks. But in the situation described, a diver went to a fairly shallow depth of 50 feet (or so - vis unknown) for a very brief period of time with one or more qualified divers watching closely. Might just be me, but I don't see that as something that merits warnings of impending doom. You are probably more conservative than I.

It's very rare that anyone mistakenly calls me conservative about anything. I don't suggest solo diving for anyone, even tho I'm guilty of it myself - just read way too many dive death threads with that in common.

I am sure that in the event of unexpected gear failure, diver mistake, a hit or any other problem tho, you would probly be in better position for a self rescue than the original poster with 50-99 dives. The lazy DM sounds worthless, even tho we are dealing with only one side of the tale here.

 

[Doc]

Is there an echo in here?

 

[carrielsal]

I recently went on a 2 tank dive in San Diego and basically had to abort the 2nd dive due to ignorance and I was just looking for some clarification. First dive was at a max depth of 40 feet, average was about 30 ft. Down for 60 minutes and did not do a safety stop. Second dive was after a 1 hour SI. The bottom was at 60 feet which was issue one, I was taught not to dive deeper than your previous dive? The DM then asked me to check the anchor so I drop down to 50 feet and its not hooked in so I surface, tell him and then drop down to 15 feet and do a 3 minute safety stop. Now Im trying to figure out what to do since the 60 foot bounce dive confused my plans. I decide to spend 20 minutes at 30 feet and then do another 3 minute stop at 15 ft before surfacing. Basically Im wondering what my options were, can I dive deeper on the 2nd dive? How does the 60 foot bounce affect adjusted max bottom time? Was the bounce a bad choice? Any and all advice is greatly appreciated, even if you want to tell me how stupid I was.

This is definately the DM's job. If you're a paying customer, why should you be asked to screw up your dive profile to do his/her job.
Carrie