Descending too fast??

[mono]

Is there any physiological aspects on descending too fast (apart from the obvious need to equalize)?

 

[Bob3]

The US Navy Diving Manual specifies a maximum descent rate but it goes largely ignored if diving plain air.

If you're diving air within normal recreational limits, clearing your ears is the only determining factor.

If you want to talk mixed gas it's a different story.

 

[Walter]

75 fpm is the max descent rate. Narcosis is more pronounced if you descend rapidly.

 

[mono]

I use EAN 21-40.
No Trimix.

 

[Dr Deco]

Dear mono:

Descent Rate

The gas loads in the tissues of the body are developed though tests with a defined descent rate. During ascent, the decompression risk is determined for this gas loads. If you descend faster than the test divers, you will have more dissolved nitrogen in your body. If you are one of these individuals who are sensitive to DCS, this increase in dissolved nitrogen could possibly make a difference.

That is the answer from a decompression point of view. As you indicated, clearing your ears is an entirely different matter.

Dr Deco :doctor:

Readers, please note the next class in Decompression Physiology :grad:
http://wrigley.usc.edu/hyperbaric/advdeco.htm

 

[Charlie99]

Dr Deco once bubbled...

The gas loads in the tissues of the body are developed though tests with a defined descent rate. .... If you descend faster than the test divers, you will have more dissolved nitrogen in your body.

Dr DECO: What about the effect of descent rate on narcosis?

Scientific studies been done?

Or reliable anectdotal evidence?

Or just scattered, unreliable anectdotal reports?

If descent rate does cause problems, what sort of rate or ppN2/min change cause problems?

Thanks in advance,
Charlie Allen

 

[Diver0001]

Dr Deco once bubbled...
<snip>

If you descend faster than the test divers, you will have more dissolved nitrogen in your body. <snip>

??? HUH ??? Maybe I'm just being daft but I can't see why this would be the case. Care to elaborate?

.... and what was the decent rate used for testing?

R..

 

[blackwater]

Accumulating more nitrogen on quicker decents will occur, not becuase of the Depths rate of change, rather because more time will be spent at depth. e.g. two diver giant stride off the boat, one sinks like a rock and waits at the bottom for his buddy, the buddy makes a slow decent.

The first buddy has more nitrogen because of the time spent waiting at the bottom for his buddy, make sense? so the effect is real, although admittedly not large for shallow dives.

The DSAT (PADI) RDP was derived/tested with a decent rate of 60 fsw/minute.

GT

 

[Dr Deco]

Hi Diver0001:

Blackwater has hit it on the nose. It is not actually the rate of descent, but rather the fact that the actual bottom time is longer. A dive to 90 FSW for 20 minutes will have associated with it a certain residual nitrogen designation. If one were to perform a descent at, say, 30 feet per minute, they would later ascend with a smaller nitrogen load than if they had descended at 90 feet per minute. The tables were not tested for the later, longer condition. Additionally, they were not tested for the muscular energy expenditure needed to drive you down that fast.

Dr Deco :doctor:

 

[Uncle Pug]

Waiting for your buddy to catch up????
More effort to drive yourself down that fast????
More nitrogen because your bottom time is longer????

We drop together at the same rate.
Double 104s don't need a lot of effort to sink.
Adjust your software for your preferred rate of descent.