deep stops or not

[TSandM]

Superb post, Dale.

I believe some of the perseveration over DCS risk comes from the fact that OW classes go quite heavily into DCS (while ignoring gas management). When you combine that with the fact that most new divers are going to have some muscle or joint pain from unaccustomed activities, you create a lot of worry. Your post makes it simple: The risk of DCS is low if you stay relatively shallow and keep your dive times reasonable.

 

[DaleC]

Yes, and learn as you go slowly. The way dive tourism is geared doesn't help. It isn't uncommon for people to log little or no dives throughout the year and then go do 21-28 dives in a week on a live a board. I get the time management issues but still think it's crazy. On a recent trip to Port Hardy my friend and I were trying to do every dive offered but I jammed out because it wasn't feeling fun. They persevered, but were almost in tears due to exhaustion. For better or worse, I'm just not that driven any more.

One thing I did experience early on was something I called fuzzy headedness and undue fatigue. I used to almost fall asleep driving home from the dives but rarely if ever experience it now. I dove EAN for a while and thought that might be alleviating it but I gave that up a few years ago (except for some charters). In retrospect I think it was nervousness/stress, working too hard and popping up too fast from 15-0.

 

[String]

If you're going into deco ascending from 25-30 to 18m, you're ascending too slowly.

This is a very good point and often skipped. Admittedly we're in the "basic" SCUBA section but there is some overlap. Recreational agencies tend to push the slow ascent (PADI's SAFE - Slowly Ascend From Every Dive for example) and for shallow no-stop dives this is good, sensible safety practice.
However, it breaks down once you go deeper and start flirting with NDLs (and breaks down completely once you start going into deco).

Ultimately if you're on-gassing your goal is to get out of that area and into an off-gassing area as quickly as possible. THEN you slow your ascent. There is such an ascent as a too-slow ascent if by taking a long long time to shallow you actually take on MORE inert gas thereby increasing your tissue loading and reducing your NDL/adding to your deco.

A lot of people transiting to tech diving get caught out first by how fast the ascents are (9m/min for example FEELS really fast to start with when you're used to 2-3m/min recreational stuff). The ultimately goal is to stop on-gassing and start off-gassing as quickly as possible so mandates a certain minimum ascent speed.

A "good" profile would typically be a fast (10m/min maybe) ascent from the bottom to the off-gassing floor then a gradually decreasing rate from there towards the surface. Combined with deep and shallow stops.

 

[gcarter]

This is a very good point and often skipped. Admittedly we're in the "basic" SCUBA section but there is some overlap. Recreational agencies tend to push the slow ascent (PADI's SAFE - Slowly Ascend From Every Dive for example) and for shallow no-stop dives this is good, sensible safety practice.
However, it breaks down once you go deeper and start flirting with NDLs (and breaks down completely once you start going into deco).

Ultimately if you're on-gassing your goal is to get out of that area and into an off-gassing area as quickly as possible. THEN you slow your ascent. There is such an ascent as a too-slow ascent if by taking a long long time to shallow you actually take on MORE inert gas thereby increasing your tissue loading and reducing your NDL/adding to your deco.

A lot of people transiting to tech diving get caught out first by how fast the ascents are (9m/min for example FEELS really fast to start with when you're used to 2-3m/min recreational stuff). The ultimately goal is to stop on-gassing and start off-gassing as quickly as possible so mandates a certain minimum ascent speed.

A "good" profile would typically be a fast (10m/min maybe) ascent from the bottom to the off-gassing floor then a gradually decreasing rate from there towards the surface. Combined with deep and shallow stops.

What agency teaches this ascent rate? I was taught 60 ft/min (18 m/min) from depth slowing to 30 ft/min (9 m/min). I have never seen 2-3 m/min recommended anywhere.

Edit: the max rate recommendation switches at 60 ft / 18 m. I know these are maximums, but I rarely see rec divers ascending slower.

 

[dmainou]

18 m per minute is a lot. 9 is the recommended. Still most people trying to go really fast average about 6.

The reason to go really slow on the really shallow bit of the dive is because that is where the greatest change in pressure is.

You half your pressure in the last 10 m.


Sent from my GT-I9300 using Tapatalk

 

[String]

"as slow as possible" is taught. 18m/min is taught as an absolute maximum ascent rate (PADI RDP anyway, no idea about other agencies tables). None teach slowing 18-9 once at 10m as far as im aware.

From experience most recreational dives end up at 2-3m/min average ascent rate getting to the surface and most guides ive seen end up hitting around that speed even from depth with only 1-2 min NDL remaining.
They just take the "slow ascent" as black and white without understanding or thinking about the deco theory or physics behind it.

 

[dreamdive]

If any of you are diving Gradient Factors on say a Shearwater, your ascent rate has to be 30 ft/min in order to stay true to that GF! Many people don't know that.

A slower than 30 ft/min ascent will increase your TTS. There is nothing wrong with that, as long as you have enough deco gas.

Too slow an ascent rate will have you load your tissues unless you change from 10 ft stops to 1 foot stops (like a "diver on the line") which will decrease your decompression time.

 

[lowviz]

...//... (like a "diver on the line") ...//...

Haven't heard that term for a while. (Do you dive a VR3?)

In that light, why isn't a microbubble stop considered to be a "deep stop"? -always wondered that...

 

[dreamdive]

Haven't heard that term for a while. (Do you dive a VR3?)

In that light, why isn't a microbubble stop considered to be a "deep stop"? -always wondered that...

Replaced my VR3 quite a while ago! Using Shearwater predator now, but the concept is the same, nevertheless. As to your other question, replied to your PM.