How long do we have before we fizz up?

[SPEEDSTER]

that's basically what I thought, however, aquatec's response threw me a little from my basic understanding of deco procedures. I took it to mean that once you began the offgassing, your body was more prone to keep offgassing at that rate. therefore, if you surfaced from 40' after doing some deco, you would have significantly less time to get into the surface chamber. thank you for the informative response, as usual.

as for the complete chaos after missing big deco obligations, I'm glad I've never been witness to one, and certainly hope to keep it that way.

mike

 

[Scuba]

Dr. Deco,

We see in this procedure a definite demonstration that being supersaturated does not cause DCS. There are also question of micronuclei and the growth of these nuclei by inward diffusion of nitrogen. This growth process requires time, and that short duration for growth can be utilized to repressurized the divers in a deck decompression chamber. As the time before repress is extended, the situation can rapidly turn into a disaster

A question out of curiosity. Do all divers who surface supersaturated develop DCS over time if not treated? What %?

 

[Dr Deco]

Dear Scuba:

Supersaturated

No, not all divers who are supersaturated will develop DCS. The is true because we know that if you breathe for only a few seconds at one foot of depth, some dissolved nitrogen will be in you tissues, but you will not develop DCS. What seems to mater is the degree of supersaturation. The dose of dissolved nitrogen does not become sufficient to result in DCS unless you are saturated at about 18 fsw. Any supersaturation less than this will not result in “the bends.” Gas embolism from a ruptured lung is a different matter.

Haldane’s Metastable State

The original concept of JS Haldane was that if the dissolved gas were not above a sufficient partial pressure, then gas bubbles would never form. This limit was referred to as the metastable limit. In actuality, the “limits” do not exist whether it concerns the boiling of water, or the crystallization of sugar, et cetera. To form decompression gas bubbles in the real world of the pressures we encounter, it is necessary that the micro gas bubbles be present to start with.

A diver is really a gas-in-water emulsion where decompression is concerned. Without the nuclei, you could rise to the surface from saturation at six miles below the surface.:mean:

Where do these nuclei come from? The everyday movement of our tissues is the origin. This produces cavities (and hence the process of cavitation) in the water. If these are large enough, they can grow with supersaturation.. This degree of supersaturation is a pressure change in a saturated diver from 20 feet to the surface. Likewise, it is seen when someone goes from sea level to an altitude of 15,000 feet.

This requires micronuclei of about 2.5 microns in radius. Bigger ones do not exist in our bodies (at least in any quantity). Thus, no, not all supersaturation will result in the bends.

Dr Deco :doctor:

 

[pt40fathoms]

Am I missing something here?

In a chamber, pressurized to 40', breathing O2.

Would this not result in Oxygen toxicity?

The last time I checked, anything over 1.6pp O2 would result in me having a very bad day. That would mean that they would only be able to pressurized to 6 metres or about 20'.

What am I missing here?

 

[Dr Deco]

Dear pt40 fathoms:

Oxygen Toxicity

You are quite correct is noting that this depth seems pretty scary on oxygen. The difference is that, for this decompression technique, we are talking about a resting diver in a dry place on a ship. This is different from in-water decompression at that depth.

The tables are designed to minimize the problem of pulmonary oxygen toxicity, and the safe habitat will minimize the problem of CNS toxicity.

In a sense, on can think of this style of decompression as employing a treatment table to reduce the effects of a blowup. In a physiological sense, the differences are only that one is very controlled and the other is totally by accident. Preparation and proper timing will result in a highly successful decompression with one and possible death in the other scenario.

Dr Deco :doctor:

 

[madmole]

Surface deco has been banned in European commercial diving for many years

Too many hits and osteoporosis resulted

 

[rmediver2002]

The partial pressures of O2 are very high indeed and the divers are observed for symptoms of O2 toxicity throughout the procedure...

Remember that when conducting treatment tables we are giving 100% O2 at even greater PP O2 (60 FSW)

To help to off-set the chance of O2 hits we have sceduled air breaks (for both treatments and surface decompression) , time spent breathing chamber air before resuming 100% O2. This helps to decrease the chance of CNS O2 but of course does not eliminate it completely.


Jeff Lane