Here's An Interesting Question Dr D

[ingreevox]

Today , my buddy and I did a dive in the Delaware water gap. The total depth was 11 feet.
Say we stayed over the alotted PADI time limit, and required a safety stop.
What Depth would we do it at?

We are already above 15 feet!
Thanks in advance!

 

[DocVikingo]

Not really a concern as at 11' you wouldn't be able to stay down long enough to exceed NDLs.

Best regards.

DocVikingo

 

[scubasean]

ingreevox once bubbled...
Today , my buddy and I did a dive in the Delaware water gap. The total depth was 11 feet.
Say we stayed over the alotted PADI time limit, and required a safety stop.
What Depth would we do it at?

We are already above 15 feet!
Thanks in advance!

I'd wonder what you thought was the allotted PADI time limit....and how you arrived at the conclusion. (I can't recall, but think that the PADI table doesn't list an NDL for 20 ft. If it did, as doc said you would have an NDL around 100 minutes, and wouldn't likely have enough air to stay down that long.)

Sean

 

[ScubaRon]

You can stay down at 11' for 100 min. on about half a tank!
However I think you have your tables confused. PADI uses a 205 min. non-deco time at 35', so at 11' you would be more likely to have something like 400 minutes. Probably still doable with a double tank, but why would you want to.

ScubaRon

 

[ingreevox]

My buddy and I had just completed a very shallow dive, and it was a hypathetical we batted around.

Thanks Dr D and everyone else for your answers.
We had kinda figured that it wouldnt matter, due to air, but it was interesting enough to ask!
Thanks!

KEEP BREATHING!

 

[Charlie99]

It varies from deco model to model a bit, but there is a depth to which you can do a saturation dive (infinite length), then have immediate ascent and still have low probability of getting bent. Typical depth on air is about 22'-25' in today's models. It was 33' for Haldane.

If you look more closely at the PADI RDP special rules, you will see that they limit average depth to 22-1/2 feet.

 

[Dr Deco]

Dear SCUBA SOURCE Readers:

Depth and DCS

The depths for first detection of Doppler bubbles are shallower than for DCS, as one would imagine. For a saturation dive, Eckenhoff et al measured about 11 fsw.

For DCS, the depth appears to be about 20 feet. These all required a dive of longer than 24 hours.

Dr Deco :doctor:

References :book2:

Ikeda T, Okamoto Y, Hashimoto A. Bubble formation and decompression sickness on direct ascent from shallow air saturation diving. Aviat Space Environ Med. 1993 Feb;64(2):121-5.

Eckenhoff RG, Olstad CS, Carrod G. Human dose-response relationship for decompression and endogenous bubble formation. J Appl Physiol. 1990 Sep;69(3):914-8.

 

[pipedope]

I have done lots of dives 10-15 feet deep that lasted for 2 to 6 hours with no problems.
Usually I surface somewhat slowly because I am tired from fighting with the dredge or other equipment for all of that time.
The bright side is I get to pick up a nice paycheck.

 

[Frank O]

Dr Deco once perfused...
The depths for first detection of Doppler bubbles are shallower than for DCS, as one would imagine. For a saturation dive, Eckenhoff et al measured about 11 fsw.

For DCS, the depth appears to be about 20 feet. These all required a dive of longer than 24 hours.

Thanks for the concise information. In reading it, I was reminded of a diver's story of her experience with DCS and PFO on another board:

http://www.deeperblue.net/article.php/368/29

Although this individual had done dives to ~25 meters before the event for which she was treated -- and acknowledged issues with water temperature and post-dive exertion (lugging a set of doubles) -- she or her doctors seemed to feel that she had been accumulating DCS-related damage on "every" dive she had ever been on, even the shallow ones to the 7-meter (23-ft) range. She interpreted this as being due to her apparently fairly significant PFO.

When I mentioned this scenario (diver with PFO thinks she is getting DCS symptoms in relatively short dives to ~20 ft) to you briefly at your recent seminar, I believe you said you thought that even with a PFO DCS was fairly implausible at that depth/time; but the issue might be a non-DCS but PFO-related issue that could be exacerbated by diving. Am I remembering that correctly?

 

[DeepTechScuba]

If you look in the NOAA Diving Manual, you will see that NDLs start at an EAD of 25 ft.

For dives of 20 ft or less, your dive time is unlimited, and you may ascend to the surface anytime without a deco or safety stop.

NAUI, SSI, and PADI all teach that any dive shallower than 40 ft should be treated as a 40 ft dive, or something similar to this concept. By referring to the NOAA dive tables, you can see that this concept is fallacious. However, it is conservative.

Dr Deco pointed out that the story is different for saturation diving, which requires pressurization for more than 24 hours. 24 hrs x 1.61 ATAs x 60 min/hr x .075 RMV = 1,739 cu ft of breathing gas, so if your scuba tank(s) can hold 1739 cu ft, then uhhh you MIGHT run into a problem at 20 ft depth.

Otherwise, you should be fine down to an EAD of 20 ft for a long, long, LONG time on scuba.