Diving below sea level

[SandShark]

Hi Everybody,
New to the forum and making my first post. I have, what I believe is a dive safety related question about diving below sea-level. OK, I know most of you that read this will say: "Duh? Diving below sea-level is a no-brainer as long as you use the accepted dive tables!" However, my question concerns diving where you enter the water at a site which is located below sea-level (cave diving comes to mind here). I regularly dive in the Siwa Oasis in Egypt which is located on the edge of the Great Sand Sea (or Sahara Desert, which is an oxymoron by the way....Sahara is the Arabic word for desert), which is situated between 10 and 50 meters below sea-level depending on the location.

Recently I was assisting the Egyptian Underwater Archaeology Department in conducting surveys of 4 springs/wells with Roman remains in them and after spending about 4.5 hours underwater on air over 5 dives with 45 minute to 1 hour surface intervals between dives, I starting experiencing symptoms which one could possibly be associated with DCI. All dives had been conducted at depths of 8 meters or less. As there are no dive doctors out in the desert, I was put on 100% O2 for approximately an hour when most of the symptoms subsided to a large degree. Upon returning to the town of Siwa I was taken to see the local doctor who promptly said I was okay (imagine that!). Although, to be fair to the doctor, when he was told that I had been diving in the area he admitted that he didn't understand dive physiology.

My question here is: Is there a "penalty" for starting a dive which has a water entry located below sea-level? As I am not an altitude diver or cave diver I haven't received the training for diving at different altitudes. Although if I can find a Altitude Diving or Cave Diving instructor here in Egypt I'll gladly sign up for the course!

My way of thinking on this goes like this....and please correct me if I am wrong, standard dive theory states that for every 10-meters below sea-level we add 1 ATA. So therefore, at 20-meters below sea-level for example, the air on the surface of the earth should be more dense (at 3 ATA). Add to that, diving an additional 8-meters should put a diver at close to 4-ATA which is off-the-charts using the RDP/ERDP. Especially considering that on the 8-meter dive I had a bottom time of 76-minutes.

Being as that all dives conducted during the trip were at less than 10-meters water depth, we did not worry about reverse profiling as long as we had the previously mentioned surface intervals. Average dive depth for all other dives were 3.5 meters (92 minutes), 5 meters (48 minutes), 6.2 meters (28 minutes), 4.6 meters (54 minutes), with the 8-meter dive being after the 5-meter dive.

All dives consisted of underwater photography and recording of archaeologically important features, cleaning of site features, artifact recovery and documentation, and use of air-lift/hydro-lift equipment so there was quite a bit of physical work being conducted on each dive.

Anyway, any information that you can provide on "reverse-altitude" diving would be greatly appreciated.

Thanks,
Mike

[Mako]

Very interesting question...
I am an altitude diver and I don't see any problem surfacing below the sea level. The difference should go towards safety and not increase risks of decompression sickness. What you should care about is what happened after surfacing. Are you going up a deep well using a lift? Even that should still be ok... as long as you don't ascend 1000m or the speed is still normal. ;-) If the cave is hermetically closed and you feel a depressure by opening it that could be a problem...
I believe more that you were dehydrated, staying in Siwa at this period of the year is very dehydrating... you can almost not drink fast enough what you sweat and the air is so dry that you don't even feel it. Your urine should be transparent, if it is yellow you should drink more! This is quite a challenge in Summer staying in Siwa! I had quite a few times guests on the boat in Egypt who had similar problems because they were dehydrated. Also exercise during and after the dive can be a cause try to get surface help to carry and help reduce your efforts.
But you did the right thing, Oxygen to a higher percentage as possible is the best you can do. I recommend 100% O2. Don't delay, the earlier you take it the better.
If you don't feel any pain now this means the O2 treatment was the right thing! Otherwise the pain will stay or increase.
Make sure you drink enough and definitely reduce your efforts!
If you still feel pins and needles or pain don't dive again and visit a hyperbaric doctor. Do the same if you experience again discomfort after the next dive.
If you have any more detail about the situation don't hesitate to write again.
The right procedure for a decompression sickness is 100% oxygene lying down during the transportation to the recompression chamber where the specialist can care for you.