Gradient Factors and Deep Stops

[bobidcstaff]

Hi everybody,
from what I've learned, the principle of Gradient Factors is that you have a "space" measured from 0 to 100% between the pressure of a saturated Tissue Compartment and the M-Value of the same TC. Is that correct?
So the idea is that when you ascent the TC becomes supersaturated and the GF increases (10%, 20%, ecc.). The trick is to maintain the GF below 100%. Right?
How does all this relate to deep stop planning?
From what I've understood, when you ascent, if you stop at an intermediate depth, the supersaturated (leading) tissue starts offgassing, so that after some time if you resume the ascent the same tissue will be less supersaturated. Is this the base of the deep stop theory?
Thank you!

 

[Diver0001]

Yes, you can see the safe (begs the question what is "safe") range for offgassing as having a "floor" and a "ceiling".

Gradient factors just move the floor and the ceiling to a slightly narrower range in order to simulate what other models were doing that calculated deep stops. In the intervening time we've seen research that suggest that deep ascent lines are not optimal so people are re-thinking how they set their gradient factors (especially the lower end) as a result.

R..

 

[boulderjohn]

How does all this relate to deep stop planning?
From what I've understood, when you ascent, if you stop at an intermediate depth, the supersaturated (leading) tissue starts offgassing, so that after some time if you resume the ascent the same tissue will be less supersaturated. Is this the base of the deep stop theory?

The deep stop theory actually has several origins, but the primary one is not based upon what you describe but upon the belief that stopping deep will control the growth of existing bubbles.

The theory was in its heyday a decade or two ago, and is not doing as well today. There is a growing belief that deep sTop advocates were stopping too deep, and the research that has been done in the last decade or so has not supported it. A decade ago, people were routinely using very low numbers for the lower gradient factors (like 20), which gives a relatively deep first stop. That number is creeping up among a number of divers today. I personally have gone to 50 for my GF low. For comparison, on a dive I did last weekend, my deepest stop was at 140 feet. If I had done exactly the same dive with a GF low of 20, my first stop would have been at 180 feet.

There are several very extensive and highly informative threads on this topic in the Tech diving forum here on ScubaBoard.

 

[CptTightPants21]

Remember that the gradient factors are percentages that apply conservatism to the original Buhlmann forumla and allow divers to "personalize" their decompression profiles. 100/100 GF would be the original Buhlmann formula, 100/110 would be a more aggressive than the original Buhlmann, something like 40/80 would be more conservative

Some information you may find helpful.
Gradient Factors | Dive Rite

 

[EFX]

Hi everybody, from what I've learned, the principle of Gradient Factors is that you have a "space" measured from 0 to 100% between the pressure of a saturated Tissue Compartment and the M-Value of the same TC. Is that correct?

Yes. Decompression algorithms will calculate the inert gas pressure in all TC's (for Buhlmann ZH-L16 this is 16 TC's). For each iteration of the program the highest pressure TC will be selected as the controlling TC (CTC).

So the idea is that when you ascent the TC becomes supersaturated and the GF increases (10%, 20%, ecc.). The trick is to maintain the GF below 100%. Right?

If the algorithm uses high and low GF's then the trick becomes staying below the GF-Hi. If GF-Hi is 80 then deco is calculated to keep the CTC's pressure below 80% of the surfacing m-value upon surfacing.

 

[rossh]

...
From what I've understood, when you ascent, if you stop at an intermediate depth, the supersaturated (leading) tissue starts offgassing, so that after some time if you resume the ascent the same tissue will be less supersaturated. Is this the base of the deep stop theory?
Thank you!

Yes correct. All ascents can be measured generically in the amount of supersaturation they involve. Deeper stops and GF Lo both lower the supersaturation amount in the early ascent, and the effect carries through all levels proportionally right up to the last stop.

Tissue microbubble growth (extra vascular) is directly related to amount of supersaturation levels, so that why supersaturation is controlled. Faster tissues can tolerate higher supersaturation, and slower tissues less. There is no hard ceiling on the absolute amount of tolerable supersaturation. Older deco models allow higher values than we do today.

Both GF Lo and VPM-B / bubble models are aiming to achieve the same thing - the argument is around how much is enough or correct.

Cheers.

 

[Diver0001]

Yes correct. All ascents can be measured generically in the amount of supersaturation they involve. Deeper stops and GF Lo both lower the supersaturation amount in the early ascent, and the effect carries through all levels proportionally right up to the last stop.

Tissue microbubble growth (extra vascular) is directly related to amount of supersaturation levels, so that why supersaturation is controlled. Faster tissues can tolerate higher supersaturation, and slower tissues less. There is no hard ceiling on the absolute amount of tolerable supersaturation. Older deco models allow higher values than we do today.

Both GF Lo and VPM-B / bubble models are aiming to achieve the same thing - the argument is around how much is enough or correct.

Cheers.

Well... Actually, Ross is partially correct in that the effect he is describing can be seen in the faster tissues. However, those tissues are not the ones experimentally implicated in developing DCS.

This paradigm has been thoroughly refuted. He knows it but he's having a very hard time accepting it. Every thread he participates in escalates into an avalanche of bull-****, so buckle up. Here we go again.

R..

 

[Tassi Devil Diver]

The original intent of deep stop theory was that by doing deeper stops you could reduce the length of shallow stops and reduce overall decompression time, which was found to be flawed as people started to get bent when following deco models that incorporated this deep stop theory. Deep stop theory was tweaked and the narrative behind deep stops amended by proponents of decompression models that incorporated deep stops along with the decompression models themselves. It has now been found by recent research that there is absolutely no benefit of deep stops and they are more likely to do harm than provide any decompression benefit.

 

[rossh]

Well... Actually, Ross is partially correct in that the effect he is describing can be seen in the faster tissues. However, those tissues are not the ones experimentally implicated in developing DCS.

This paradigm has been thoroughly refuted. He knows it but he's having a very hard time accepting it. Every thread he participates in escalates into an avalanche of bull-****, so buckle up. Here we go again.

R..

Then how do recreational divers get bent?? Because their only involved with fast tissue supersaturation. They don't have any slow tissue supersaturation involvement. The same can be said for those who blow through and ignore deco altogether (by miss adventure).

Excess supersaturation in tissues, both fast and slow, leads to injury.

You can see the conundrum you lot have backed yourselves into... pretending they don't count in one brand of deco, only to replace it with the same deco under a different brand. Rather hypocritical I think.


Of course, deeper stop style planning and bubble models have been the most successful deco approach in rec and tech dives for the last 15 years.

The biggest test bed of fast tissue supersaturation, is the rec diver who rides the limits, or has a few minutes of deco time, and their improved safety record in the last 15 years, comes from their increased use of slow ascents, and various forms of mid level short stops. All of this lowers the supersaturation levels in the faster tissues.

The original intent of deep stop theory was that by doing deeper stops you could reduce the length of shallow stops and reduce overall decompression time, which was found to be flawed as people started to get bent when following deco models that incorporated this deep stop theory. Deep stop theory was tweaked and the narrative behind deep stops amended by proponents of decompression models that incorporated deep stops along with the decompression models themselves. It has now been found by recent research that there is absolutely no benefit of deep stops and they are more likely to do harm than provide any decompression benefit.

That theory is not part of VPM. Never was. VPM follows the basic gas kinetic theories and formula (as used in every dive computer), which eliminates the possibility of the above.


However, It was taught in DIR classrooms......

.

 

[Scuba J7]

“Of course, deeper stop style planning and bubble models have been the most successful deco approach in rec and tech dives for the last 15 years.“