Why do people add a few minutes to their last deco stop?

[rjack321]

On a Great Lakes charter a few years ago a bunch of us are dekitting our CCRs on the back deck when "Diver B" comes up the ladder. He's still standing thigh to knee deep in the lake. Its July, calm and the surface is relatively warm in Lake Huron.

Diver B: Hey guys could you help me with my fins? My arm starting hurting on the way up.
Us: Dude what are you flooded? No? What are you doing here? You still have O2 and scrubber? Drop back down if you can.
Diver B: Oh ok I'll drop in to 20ft
Us: One of us should watch him, yeah
Extra diver splashes

10-15 mins later, Diver B is on the ladder again, extra diver behind them

Diver B: Better than it was last time
Us: Just better?
Diver B: Yeah better but still started aching at 10ft
Us: Why did you keep ascending??!?
Diver B: I dunno
Us: Go back down silly your watcher buddy is still there

15-20 mins later, Diver B is on the ladder again

Us: (preemptively) Still hurt?
Diver B: No not this time
Us: Phewww

If it *hurts* stop watching to your computer and stay where you are longer! Going up is almost for sure going to make it worse. Or repeat the previous stop (barring OOA). It was a ~45min deco kind of dive and Diver B ended up doing about 75-80mins of deco in multiple pieces.

 

[Nick_Radov]

Yes, I know all of that.
I'm questioning calling this pseudo-scientific, and producing just guesses.
Seems like hyperbole....
I'd of thought you could do better.

Unfortunately we can't do better. The deco algorithms that most of us use have only undergone limited scientific validation, especially when it comes to deep or repetitive diving. For most tech diving it's a mix of science, guesswork, and experience. Seems to work well enough, and if we want to do these dives at all then we just have to accept that our approach isn't truly scientific.

 

[tursiops]

Unfortunately we can't do better. The deco algorithms that most of us use have only undergone limited scientific validation, especially when it comes to deep or repetitive diving. For most tech diving it's a mix of science, guesswork, and experience. Seems to work well enough, and if we want to do these dives at all then we just have to accept that our approach isn't truly scientific.

You appear to be in the camp of "it's not perfect so it is mostly guesswork and definitely not science."
How are you with weather forecasts?

 

[happy-diver]

Like this?

I figured out that if you eat a lot of mustard, pee will have nice neon tone to it. Producing some quite astonishing effects both in water and out of it.

 

[Nick_Radov]

You appear to be in the camp of "it's not perfect so it is mostly guesswork and definitely not science."
How are you with weather forecasts?

Two days ago the weather report for my Zip code said it was clear and there was a slight chance of rain much later that night. I went right out to walk the dog and we got soaked in a downpour 5 minutes later.

Empirically deco models seem to work pretty well most of the time. But occasionally someone gets an "unearned hit" and no one can reliably explain why...

 

[tursiops]

Two days ago the weather report for my Zip code said it was clear and there was a slight chance of rain much later that night. I went right out to walk the dog and we got soaked in a downpour 5 minutes later.

Empirically deco models seem to work pretty well most of the time. But occasionally someone gets an "unearned hit" and no one can reliably explain why...

So the weather forecasts are to be dismissed as pseudo-science and just guesses?
I agree, our deco models DO work pretty well MOST of the time. Isn't that a better point to focus on? Their continued denigration as "just guesses" is foolish.

 

[SpeedyJ]

You appear to be in the camp of "it's not perfect so it is mostly guesswork and definitely not science."
How are you with weather forecasts?

To even compare the two shows a lack of desire to understand the nuance of @Nick_Radov 's post. Just the private weather forecasting industry in the United States is an industry larger than DEMA claims the total GDP impact of scuba diving and snorkeling. ($11.6B vs. $11B)

Add in government agencies and non-government research, and you have a whole heap of money trying to predict the weather with research, modeling, and observation. Just NOAA alone has 17 satellites that cost nearly $5B orbiting the earth and providing good quality quantitative data to researchers for modeling.

I doubt I could even come up with a number for how much is spent each year researching decompression globally. My guess is you could fit everyone studying decompression on divers this year around the globe on a 737, and more than likely on a regional jet with no space for their carry-on luggage.

Do you really think that a handful of human experiments with extremely limited scope, some tests on animals in labs, and empirical observations is even remotely akin to the wealth of scientific effort put into weather forecasting? It wasn't that long ago that Pyle Stops were the rage in deco, are you positive we're right this go round?

 

[tursiops]

To even compare the two shows a lack of desire to understand the nuance of @Nick_Radov 's post. Just the private weather forecasting industry in the United States is an industry larger than DEMA claims the total GDP impact of scuba diving and snorkeling. ($11.6B vs. $11B)

Add in government agencies and non-government research, and you have a whole heap of money trying to predict the weather with research, modeling, and observation. Just NOAA alone has 17 satellites that cost nearly $5B orbiting the earth and providing good quality quantitative data to researchers for modeling.

I doubt I could even come up with a number for how much is spent each year researching decompression globally. My guess is you could fit everyone studying decompression on divers this year around the globe on a 737, and more than likely on a regional jet with no space for their carry-on luggage.

Do you really think that a handful of human experiments with extremely limited scope, some tests on animals in labs, and empirical observations is even remotely akin to the wealth of scientific effort put into weather forecasting? It wasn't that long ago that Pyle Stops were the rage in deco, are you positive we're right this go round?

We've been doing deco research for over a century -- in multiple countries -- and the results have pretty much converged on a set of models that are remarkably good and can even be tuned to your special needs/physiology/dive, if you want. [Pyle stops were strictly anecdotal and have pretty much disappeared...because of science.] My point is that the occasional deficiencies of a deco model do NOT suddenly put them in the realm of pseudo-science and guesses, which is what my original post #28 was complaining about.
By the way, by most any measure the skill of deco models is higher than the skill of weather forecasts....

 

[admikar]

Like this?

View attachment 819302

That looks more like Warhammer

 

[SlugLife]

I'm talking specifically about adding extra time to the last stop before starting the ascent to surface

Being closer to the surface, you also benefit from lower air consumption. The most likely or common place for a deco injury to occur is when you actually surface.

By adding more time to your last stop, you be more conservative and gas-efficient at the same time.