What are some of the unique dangers in a 1200' dive, as compared to a 800' dive?

[kr2y5]

In one of the other threads, someone mentioned that a 1200' dive is a totally different game than an 800' dive. I thought that was interesting, and I was hoping to learn more, for no other reason than intellectual curiosity. Unfortunately, most of the other threads degenerated into bashing the diver's motives, so I thought I would start a new one, in which we could focus less on the motives, and more on just exchange of pure, dry knowledge, to help less knowledgeable divers like myself better understand some of the specific reasons why the risk going from 800' to 1200' increases so greatly. I'm sure some of the reasons are obvious to everyone, but there are probably some that aren't, so maybe it's worth spelling them out, and there's a chance that some of us will even learn something in the process.

Some of the specific things that caught my eye were, the deviation of actual deco requirements from the model, and the possibility of lung damage. Unfortunately, nobody posted any specifics, I would grateful if someone, who knows more could help us understand that. It was also mentioned that logistics grow exponentially, I can see why that would be. I'm sure there are more interesting details that the majority of us here aren't aware of, perhaps some of the deep diving gurus among us could share...

 

[Patoux01]

HPNS is the first thing I'd think of.

 

[100days-a-year]

The depth.

 

[cerich]

making sure the tab for the gas and boat ride is settled pre dive versus post dive

 

[wedivebc]

Not professing to be an expert at anything but it would seem diving within the limits of OC gas usage and time spent doing deco would force one to make risky choices as far as oxygen and helium exposure.
Given an unlimited gas supply and a warm comfortable environment to deco in one could reduce higher oxygen exposure and deco on a gas less hostile to living tissue. Remember that oxygen is actually really bad for you in high doses.

 

[dreamdive]

Increased depth causes increased gas density - (there is only so much you can overcome with helium. )
Increased gas density = increased work of breathing
Increased work of breathing can lead to CO2 retention
Increased CO2 can lead to death

 

[rossh]

In addition to above:

Equipment limitations. Along with increased gas density, is the breathing equipment that was designed and tested for use in the 1 to 10 ATA depth ranges. It may not function quite so well at 36 ATA.

 

[Akimbo]

HPNS is the first thing I'd think of.

And compression arthralgia, they go hand-and-hand. You can eliminate HPNS and compression arthralgia, but it will take about 20 hours to reach 1200'. That in turn will require around two weeks of decompression so you may as well stay a while.

… Equipment limitations. Along with increased gas density, is the breathing equipment that was designed and tested for use in the 1 to 10 ATA depth ranges. It may not function quite so well at 36 ATA.

This is much more of a limitation for rebreather divers than OC Scuba, OC surface supplied, or surface-processing totally-closed circuit divers that are the norm for Saturation Divers — but your point is well taken. You can buy the same demand regulators that deep sat divers use that are tested to 1600' on breathing machines:

Scuba Regulators | Kirby Morgan

The other side of the coin is a rebreather can provide optimum PPO2 where OC divers would need a lot of different mixes during descent and ascent plus the ability to consistently switch to the gas that won’t kill you.

There is another factor working against Scuba divers; breathing rates. Commercial divers condition themselves to breathe deep and as fast as they want to ensure good lung ventilation (plus compensate for the added dead-air space in their hats). They have unlimited gas supplies, multiple gas banks for backup, and professional diving supervisors on the surface to manage them. Oh, and they don’t pay for the gas.

Scuba divers train themselves to develop breathing techniques that use minimal amounts of gas, for obvious reasons. The trouble is the “minimum” to adequately ventilate CO2 at 200' isn’t even close to the minimum rate required at 1200'.

This problem is further compounded by Trimix used to reduce, but not eliminate, HPNS symptoms at these depths. That added Nitrogen also adds quite significantly to the gas density.

Let’s not forget one of the oldest problems for divers. Hypothermia. Drysuits are OK for a limited amount of time but punching a hole in it will probably kill you past the point of no return to 1200'. Remember you can’t plan on very good coordination that deep due to HPNS and compression arthralgia. You don’t have to be that clumsy to tear a seal on a good day. And then there is the respiratory heat loss problem of long exposures to rich Helium mixes. Every exhalation blows off a lot of calories from your core given the higher thermal conductivity and a lung area of about an acre. That’s a big heat exchanger. Early pioneers of sat diving developed pneumonia in 600' after as little as half an hour of breathing gas at sea water temperature. Granted, they were not in the tropics, but they weren’t under the ice either.

Sat divers use hot-water heated wetsuits with 2½ gallons/minute at 110° F, gas heaters, and keep the chamber shirt-sleeve comfortable at about 90° F. It would take a lot of candy bars generate that many kilocalories.

 

[KathyV]

This article about the possible dangers of deep dives may be of some interest; but it doesn't go anywhere near the extreme depths that Doc Deep for trying to successfully dive.

How Deep is Too Deep?

 

[PeterNBiddle]

In one of the other threads, someone mentioned that a 1200' dive is a totally different game than an 800' dive. I thought that was interesting, and I was hoping to learn more, for no other reason than intellectual curiosity. Unfortunately, most of the other threads degenerated into bashing the diver's motives, so I thought I would start a new one, in which we could focus less on the motives, and more on just exchange of pure, dry knowledge, to help less knowledgeable divers like myself better understand some of the specific reasons why the risk going from 800' to 1200' increases so greatly. I'm sure some of the reasons are obvious to everyone, but there are probably some that aren't, so maybe it's worth spelling them out, and there's a chance that some of us will even learn something in the process.

Some of the specific things that caught my eye were, the deviation of actual deco requirements from the model, and the possibility of lung damage. Unfortunately, nobody posted any specifics, I would grateful if someone, who knows more could help us understand that. It was also mentioned that logistics grow exponentially, I can see why that would be. I'm sure there are more interesting details that the majority of us here aren't aware of, perhaps some of the deep diving gurus among us could share...

Great question - thanks for asking it!


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