Race to the Depth, Slow descend vs Fast descend

[Remy B.]

Before I start, please try to stay on the topic, ignore my lack of experience and try to make a informative answer so I can learn from your perspective, I understand better a informative explanation with the most facts taken in account, than comments of you have less than 100 dives and you will die.

I have notice that fast descent don't suit me well, it makes me anxious, specially when I don't see bottom.

it makes me breath very fast and I feel very uncomfortable, this is with Deco or NDL dives, and when I go slow everything go fine, my deepest Tec dives I have done here in Curacao, one 10 days ago from a boat and fast descent which it produced a new uncomfortable result of my first Tunnel Vision starting just around 30m, after we reached the target depth 56m, I started to breath slower and the dive proceeded normal, unfortunately we missed the target at 50m of some small wrecks due to the current.

Yesterday, I went to another dive site to another small wreck at 52m, on this dive I had another buddy, and I told them that I wanted to descend slow and explained my unrest with fast descents, he had no problem with that and we executed the descend and further dive as planned.

Now I have "almost" same dives to compare to, 56m vs 52m / 15min BT vs 18min BT, same bottom gas, the, same temp, same visibility, the biggest difference fast vs slow descend.

I have done other dives with same results but those had been in cold waters of different temperatures and bad visibility with some meters difference, where I can compare fast vs slow descent, with the same results of being uncomfortable when descending fast and normal enjoyable when slow.

It is a fact that, it still are to few dives to compare, but I know my self and pay a attention on my self and surroundings during all my dives and note how I felt and what happen and write it down.

If I'm lucky I will repeat the dive where we miss the two small wrecks at 50m, this time I will let my buddy to descent slow and report back how it went.

After you know some of my background of how do I feel between fast and slow descent, my question are - -->Have you encounter the same ?
>Will it impact less your body N2 uptake descending slower and allowed to adjust/adapt it self better to uptake the N2 ?( excuse me if this is a ignorant question )
>Is it just me with my particular physiology that don't like the fast descents or adjust/adapt/reacts slower ?

Thanks for your informative interventions and time.

 

[Centrals]

Fast descend will almost certainly bring narcosis on me.
Too fast a descend also means I would have to spend extra min or two longer than planned at the bottom. BTW, I only use BT for my baby tec dive.

 

[flyboy08]

Are you clearing your ears before entry and then every 5 ft or so? I'm thinking this could be an equalization issue. 56m? That's pretty deep for an OW diver....you have AOW training or greater!

 

[Remy B.]

Are you clearing your ears before entry and then every 5 ft or so? I'm thinking this could be an equalization issue. 56m? That's pretty deep for an OW diver....you have AOW training or greater!

I'm constantly clearing, I have TDI, AN-DP-Helitrox for whatever that means.

 

[DevonDiver]

Fast descent brings several problems.

CO2 narcosis is particularly relevant to fast descent, as any CO2 retention issues will be exacerbated as narcosis by the rapid spike in PPO2.

CO2 is significantly more narcotic than nitrogen and it's all to easy to cause CO2 build-up/retention in the kitting and water-entry phase of a technical dive... especially in challenging water conditions and if inexperienced /inefficient as a tech diver.

Carbon Dioxide, Narcosis, and Diving | Global Underwater Explorers

Hidden Killer: Understanding Carbon Dioxide Toxicity

Evaluating the Narcotic Properties of Breathing Gasses (pdf)

CO2 narcosis often (I believe) presents itself as "dark narc", with symptoms of agitation, psychological stress elevation, panic sensations and increased respiration demand.

I've seen, first-hand, several instances of individuals aborting technical dives due to "dark narc" on reaching bottom depth... and in every instance the diver concerned was breathing heavily prior to, and during, descent. Descent speeds were moderate-fast (at, or exceeding 15m per minute).

Secondly, it's known that (in extreme diving) descent speed / rapid compression significantly effects the onset of several hyperbaric maladies, such as HPNS and Compression Arthralgia. These aren't considerations for most of us, but it's prudent to remember that there's a lot of issues not understood or known in diving science... and rapid descent/ compression and/or rapid spike in varied gas partial pressures, even at moderate depths, could pose issues as yet unidentified.

 

[Trailboss123]

I have a number of diving friends and myself that will experience early onset narcosis symptoms (sometimes at 20M or 65ft), accompanied by anxiety and perceptual narrowing when descending to deeper depths too quickly. This is made worse in dark/low visibility conditions. Slow descents result in better outcomes for us- the better the visibility, the better also.

 

[PfcAJ]

Point scooter toward the bottom. Pull trigger.

 

[dumpsterDiver]

How are you descending?

In some situations, for example drift diving (while trying to reach a precise location), it is pretty much essential that you descend rapidly and vertically.

If you are pulling/swimming yourself down an anchor line and fighting a current, then it is obviously going to involve more work, more Co2 generation and will have a tendency to "absorb your attention" - more so if you are weak, scared or inexperienced. In that type of scenario, it is important to go at a reasonable pace and not over-exert yourself on the descent.

Also, as others mentioned.. it is pretty much accepted that rapid descents are correlated with increased narcosis.

I can descend about 170 feet per minute when making a free descent in clear water with no reference, but I also allow myself to get heavy on descent and try to limit my inhalations to less than maximum until i have reached a good freefall speed. A streamlined vertical position is also important in minimizing exertion and maximizing descent speed. Freedive fins help too, if you can't afford a scooter.

 

[boulderjohn]

Let's say you are planning a deep dive (300 feet) for 15 minutes using desktop software. That software assumes by default a 50 FPM descent rate.In that case, you reach the bottom in 6 minutes, with an average depth of 150 feet for the first 6 minutes of your dive. After your 15 minutes of planned bottom time, your average depth is 240 feet.

Let's say instead you descend at a rate of of 100 FPM. In that case you reach the maximum depth in 3 minutes, with an average depth of 150 feet for the first 3 minutes of your dive. After your 15 minutes of planned bottom time, your average depth is 270 feet.

Let's say instead you descend at a rate of of 30 FPM. In that case you reach the maximum depth in 10 minutes, with an average depth of 150 feet for the first 10 minutes of your dive. After your 15 minutes of planned bottom time, your average depth is 200 feet.

Think that would make a difference?

OK, you aren't going to 300 feet, but the point remains.

 

[Bennno]

Before I start, please try to stay on the topic, ignore my lack of experience and try to make a informative answer so I can learn from your perspective, I understand better a informative explanation with the most facts taken in account, than comments of you have less than 100 dives and you will die.

I can tell you exactly what's happening here, but it's not the answer you wanna hear:
You get nervous because deep decends are new to you - feeling uncomfortable increases your breathing rate, both of which enhances the narcosis (whether you're aware of it or not, tunnel vision at 30m tells me you're narced, it doesn't really matter whether it's caused by N2 or CO2 at this point) - being on air below 50m/170' with little to no prior deep air experience doesn't help in that situation.

I'm not saying any of the other posts were wrong, but I can almost garantee you, the anxiety is caused by the lack of experience, making the anxiety the crux of the issue.

Here is what you can do about it:
Do a few decends to 30m or 40m and see how it feels and only dive deeper once you feel 100% comfortable. Than do a couple of dive to 45ish, how does that go? Than 48 or 50... but don't progress to the deeper decends until you have this stuff down.

Nobody said, 'less than 100 dives and you will die'; however, a bunch of people HAVE killed themselves diving deep or air! Starting out anxious 'occupies' part of your mind and stress factors like these can greatly decrease you metal capacity. The amount of dives is less important than the level of comfortability. Being aware of your metal state is important.
I know you said you don't want this answer, but it doesn't work that way... it is what is. It take time.