Diving below sea level

[anzac65]

Um, it's a trick question, right? All my diving is below sea level!

 

[Thalassamania]

I agree with Don. By asking the question you state your lack of cave dive qualifications in general - and, a mile below sea level, please. IF this is hypothetical... then none of us really know, because none of us experienced cave divers have actually made that dive.

It's simple physics, it's the same as working from a shallow habitat, a dive many people have made, many times.

 

[victor]

I expect you could get a significant difference between a low and a high preasure area.
e.g. Diving in the centre of a huricane is the equivalent of diving at altitude.
and Diving in a high preasure zone is the equivalent of starting a dive at below arbitary sea level.

When you get a line squall storm front crossing you can get a significant preasure difference in a very short time which I guess might be the equivalent of going up in an aeroplane.

 

[daniel f aleman]

It's simple physics, it's the same as working from a shallow habitat, a dive many people have made, many times.

Go for it, but not in a cave 5000 feet below sea level.

 

[Thalassamania]

Go for it, but not in a cave 5000 feet below sea level.

I don't cave dive, but from a decompression standpoint, which is the conversation here, pray tell why not?

 

[Dr Deco]

Hello repodisk:

This one actually took some looking into. It is just hypothetical, as you will see below.

Temperature

The temperature would be high – about 189 F. This is by calculation only as there are no mines that deep currently. (This is taking the average increase as 35 c degrees /km). Temperature increases in African diamond mines make conditions very difficult (so I read).

The water in the cave would be in temperature equilibrium with the walls and would likewise be this hot. You would soon become pooched – I mean poached.

Pressure

Air pressure at 1 mile down is about 17.9 psi. This is also by calculation, as I do not believe it has ever been measured.

Diving under these conditions would be similar to an underwater habitat. You would need to make corrections for the new depths. This is commonly encountered in commercial diving, but I do not know of recreational tables for this purpose.

All things considered, it is truly a Jules Verne type of experience encountered only in Journey to the Center of the Earth.

Dr Deco :doctor:

 

[Thalassamania]

Pressure

Air pressure at 1 mile down is about 17.9 psi. This is also by calculation, as I do not believe it has ever been measured.

Diving under these conditions would be similar to an underwater habitat. You would need to make corrections for the new depths. This is commonly encountered in commercial diving, but I do not know of recreational tables for this purpose.

All things considered, it is truly a Jules Verne type of experience encountered only in Journey to the Center of the Earth.

Dr Deco :doctor:

Many deco programs permit you to change the storage depth. For this problem (forgetting about the need for a cold water suit like you use in a reactor) you’d just change to storage depth to about 6 feet.

 

[jeelan]

Hello repodisk:

This one actually took some looking into. It is just hypothetical, as you will see below.

Temperature

The temperature would be high – about 189 F. This is by calculation only as there are no mines that deep currently. (This is taking the average increase as 35 c degrees /km). Temperature increases in African diamond mines make conditions very difficult (so I read).

The water in the cave would be in temperature equilibrium with the walls and would likewise be this hot. You would soon become pooched – I mean poached.

Pressure

Air pressure at 1 mile down is about 17.9 psi. This is also by calculation, as I do not believe it has ever been measured.

Diving under these conditions would be similar to an underwater habitat. You would need to make corrections for the new depths. This is commonly encountered in commercial diving, but I do not know of recreational tables for this purpose.

All things considered, it is truly a Jules Verne type of experience encountered only in Journey to the Center of the Earth.

Dr Deco :doctor:

The deepest mines in South Africa's Witwatersrand region are between 3km and 3.5km in depth (1.8miles to 2.18miles) and i believe a new mine has recently opened that plans on delving to 5km (3.15miles).

Ave temp at this depth is 70C (158F) but is kept at about 100F through heavy of commercial air conditioning equipment. Dont know about pressure at this depth. As a rule, air temp increases by about 30C for every 1km below the surface. Pressure increases too but at a much more slower rate, although the pressure on the rocks increases by about 300bar for every 1km of depth.

see www.drd.co.za - a mining company in South Africa with some mines that are at 3km depth or more.

see also www.xstrata.com - another mining company which has recently opened a mine in Canada that goes 3km plus.

Cheers
Jeelan

 

[MDImike]

Hi All,
OK, I know that this is an old post but it addresses the subject matter that I would like to address. Jeelan's post brings up a good question concerning dive computers (or better yet, dive tables for sub-sea level dive entry).

I own and run a dive company that regularly dives in Roman-era springs and wells in the Siwa Oasis which is between 10 and 20-meters below sea level. I recently experienced a suspected bout of DCI after diving on these wells and spring with the Egyptian Supreme Council of Antiquities-Department of Underwater Archaeology (SCA-DUA). I had assisted the SCA-DUA team in conducting archaeological surveys of 5 "Ain's" (wells or springs) and located many Roman artifacts. Within two hours of completing my last dive of the day I experienced the typical DCI symptoms of crinkling in the shoulders and pain in my elbow joints. I had conducted 5 dives throughout the day with a maximum depth of 8.2 meters on the first dive and ending with 92 minutes of bottom time (last dive was the longest) at 3.2 meters while conducting excavation/bottom sediment removal. TBT for the day was 4 hours 26 minutes with the longest SI being 3 hours between the 2nd and 3rd dives). All dives were 8.2 meters or less. Using the TDI/DSAT tables, PADI Wheel, and PADI ERDP, I should have been well within NDL at sea-level.

Not a cave-diver here (I dive in a desert which just happens to be below sea-level) and am also not an altitude diver (I guess I should take the course?). Am looking for some feedback and maybe a technical reference or two for diving with entry points below sea-level.

Any info that you can provide would be greatly appreciated...
Mike

 

[Charlie99]

You can ignore the altitude since you say that the wells and springs are only 20 or 30 meters below sea level.

The atmospheric pressure difference between sea level and your location is smaller than the normal day to day barometric pressure difference at sea level due to high pressure and low pressure weather systems passing by.

Most dive tables consider anything less than 300m/1000' altitude as being close enough to sea level that the sea level tables apply. Your 10 or 20 meter altitude change is much less than this, and it doesn't really matter that you are a tiny, tiny bit deeper than sea level.