Fast Descents?

[Frog]

Hi.

I dont want to sound too ignorant here but is it much better to keep surface interval acivity to a minimum? For example after ascent would it increase the chance of getting dcs if there was a long (100-300 metres) service swim to follow. Cheers

 

[Dr Deco]

Dear Frog:

Yes, vigorous surface activity is a predisposing factor to DCS. This has been known experimentally since the 1940s. A surface swim would be a generator of micronuclei. An easy swim of a short distance is most likely fine.

Activities such as long swims, and climbing ladders with full gear is quite stressfull. So are activities such as moving heavy scuba tanks.

The other side of the coin is true, however. While vigorous musculoskeletal actives can generate nuclei, physical activity also increases blood flow. Therefore, one wishes to avoid straining and vigorous activity but ALSO wishes to avoid complete inactivity such as sleeping during the surface intervals.

It is a bit of a tug of war! :mean:

Dr Deco

 

[old_mike]

i was under the impression that rapid descents at least with helium based mixes were correlated with High Pressure Neurological Syndrome. Of course, this may not be a problem on the standard tropical vacation dive to 60 fsw.

 

[scubadoc]

Mike is correct in that rapid descents can cause HPNS but this refers to diving on a helium mix and is at 600+ feet.

NOAA has the following to say about HPNS:

"At diving depths greater than 600 fsw (183 msw), signs and symptoms of a condition known as the high pressure nervous syndrome (HPNS) appear and become worse the faster the rate of compression used and the greater the depth or pressure attained. HPNS is characterized in humans by dizziness, nausea, vomiting, postural and intention tremors, fatigue and somnolence, myoclonic jerking, stomach cramps,
decrements in intellectual and psychomotor performance, poor sleep with nightmares, and increased slow wave and decreased fast wave activity of the brain as measured by an electroencephalogram (Bennett et al. 1986)."

Fred Bove's text relates that the following things can occur with a rapid descent:
Barotrauma, transient caloric and alternobaric vertigo, hypercapnia(high CO2) with attendant cerebral symptoms due to rapid compression of alveolar gas, hypoxia in mixed gas diving (not in air diving)in the first few moments of the dive, oxygen toxicity - again in mixed gas diving with a diver inadvertently breathing a gas mixture with a high oxygen content, slight nitrogen narcosis - aggravated if the descent is rapid. (pp.325 - 333t)

NOAA's new Diving Manual (21-10) states that rapid descent endangers due to 'barotrauma and impact with bottom features in shallow waters'. 'Uncontrolled descents in deep water may be complicated by nitrogen narcosis and O2 poisoning, rapid air consumption and subsequent drowning'.

 

[BetterLateThannever]

Do people really dive that deep? Now that I mention it..what is the deepest a scuba diver can safely venture?

Jimbo

 

[old_mike]

the one thing that tends to limit depth in an unforgiving way is oxygen toxicity. If the partial pressure of O2 rises much higher than 1.6 than one is playing Russian roulette. Here in Southern California, we recently lost a diver who was doing an air dive to 280-300 fsw. The max depth on air would be 218 fsw, /w/o exceeding the 1.6 atm ppO2 limit. Of course, there are those who believe that a max working ppO2 of only 1.4 or even 1.2 is safer, thus the max depth for these folks on air would be 187 fsw. Of course, this ignores narcosis, CO2 buildup and all sorts of other horribilia that could occur /w/ deep air diving. The late Sheck Exley and some others have gone to 900 feet or more, and there are folks in So Cal that go to 300 fsw or deeper and of course the Florida cave divers who also go very deep. Some French commercial divers have ventured as deep as 5,800 feet (if my info is correct). For my part, the sunlit shallows are where i spend most of my time, life is much too good to venture that deep if you know what i mean.

BTW, with wall dives, its easy to surpass your planned depth if one doesn't watch their descent rate. All it takes is a glance at a cool sponge formation or a distant shark or sea turtle and the next thing you know, you are at 150 and falling <: (

 

[Dr Deco]

Dear readers:

As far as deep depths go, I believe that the deepest for humans is about 2200 feet in a hyperbaric chamber with helium and oxygen mixtures.

In France, pigs went to 5,000 feet in a laboratory chamber dive, and they were returned safely to the surface. This was not a dive made by humans, however.

Dr Deco

 

[old_mike]

Halcyon or Dive Rite wings that is!

It would be interesting to know what sort of physiological effects the pigs had suffered. Also, it would be interesting to see what sort of effects would be manifest in an organism more like humans...say for example, those genetically engineered mice or perhaps some Rhesus monkeys.

I take it that there is some sort of barrier that is preventing humans from breaking the record any further? If i recall correctly (which is not likely the case here) that feat of going to 2000 fsw was done quite some time ago??

 

[DiverDave]

http://www.divingheritage.com/moderncomexkern.htm

 

[DiverDave]

http://www.onr.com/user/zacaton/