Evolving Thoughts on Deep Decompression Stops

[boulderjohn]

A few months ago I met with a couple former tech students for a cave dive, and one of them told me with amusement of his dive the day before. He had randomly joined a group that included a technical instructor, and when that instructor learned that he used a GF Low of 50, he gave him a very worried "You're gonna die!" lecture about how important it is to do a first stop much, much deeper than that. That instructor can to a large extent be excused for not knowing anything about the way thinking has been changing over the last decade, because there really is no good, reliable resource for topics such as that. I wrote a blog about it a year again which I described going through a 10 page Google search in which I found 15-year old information repeated as if it were brand new and almost no articles whatsoever describing any of the thinking of the last decade.

That thinking has been quite robust, as was evidenced by a number of threads in different dive forums over the years, including on ScubaBoard.

I decided that I would try to help the situation out by writing a more accurate summary, and I enlisted the help of Dr. Simon Mitchell, who gave me a lot of good information and corrected my wording when it was necessary. Karl Shreeves of PADI was also quite helpful. It was just published yesterday, and I hope someone will find it helpful. Here it is.

Evolving Thought on Deep Decompression Stops

I am not a scientist. I do not do research. When the debates get hot and heavy, I let the people who know more than I carry the load while I watch carefully and try to learn. I am just a diver who would prefer to come back alive after every dive, but more than that, I want my present and former students to come back alive after every dive. I hope that making this information more readily available will help the technical diving community.

 

[JBFG]

Well written and very concise. I don't know enough about deep stop to comment anything meaningful but to me, it make sense to not stop "Deep".

 

[RVBldr]

Good article, I read that earlier this morning and I might have to re-think my GF settings.

 

[Nirvana]

Great article, @boulderjohn. A very nice summary of the current thinking on deco strategy, besides being serving as an index of recent scientific writing on the matter.

Just a small note: on the first paragraph of the "History of the Deep Stop" section, there is a spelling error. The name of the creator of RGBM is written as "Bruce Weinke", while it should be "Bruce Wienke" (see the cover of his book).

 

[dmaziuk]

You've a typo: "Suunto RGB" in the last sentence of "Fraedrich Study".

Also, something I recently played with: -- Buhlmann's M-values, left side is fast tissues, front is surface, back is at 7 bar. You can see how disproportionately far up the far left corner is, that's fast tissue oversturation at first stop. It's no surprise if bringing it down with lower GF Lo/deeper stops looks like a good idea.

 

[Johanan]

Thank you for the article! Some thoughts to listen to:

 

[Jared0425]

I think the ultimate goal is to keep the bubbles in us the same microscopic size as we go up. So whatever works.

 

[Nirvana]

I think the ultimate goal is to keep the bubbles in us the same microscopic size as we go up. So whatever works.

I believe the whole point of the article was to show that not everything works as people once thought, and that some strategies once thought to be an improvement may actually aggravate the risk profile of the dive.

 

[Manatee Diver]

Just an observation, weren't Pyle stops implemented back when the acceptable ascent rate was 60 fpm? So could it be possible that the positive effects from the 1-2 minute Pyle stop resulted from the fact that it slowed the overall ascent rate?

 

[dmaziuk]

Just an observation, weren't Pyle stops implemented back when the acceptable ascent rate was 60 fpm? So could it be possible that the positive effects from the 1-2 minute Pyle stop resulted from the fact that it slowed the overall ascent rate?

It's not impossible, but ascent time and rate usually get factored in. So e.g. if at 60 fpm you hit an M-value at 18 m, you'll get the stop at 18 m. If, on the same ascent but at 30 fpm you hit an M-value at 12 m, you'll get the stop at 12 m instead. In other words you'd have to mis-calculate your profile, or blow your safe ascent rate in order for it to work as you say. I think -- ICBW and all the usual disclaimers, of course.