"Riding your Computer Up" vs. "Lite Deco"

[DevonDiver]

Deep stops for deco dives is hotly debated but is confused by definitions.

It's most just 'hotly' debated by those who don't understand that modern dual-phase algorithms don't represent the simplistic and unilateral 'Pyle' type stops that saw some brief interest over a decade ago, before being discredited by studies.

Even PADI has removed deep stops from its tech curriculum now..

Deep stops versus 'deeper' stops generated by dual-phase models isn't hard to get your head around. The critical practical difference is that modern algorithms account for slow tissue on-gassing and deal with that in the shallow deco phase.

IMHO, putting deep stops onto recreational diving instruments was nothing more than a gimmick. What's inexcusable is that, on many such computers, deep stops are an either/or option versus safety stops.

 

[DevonDiver]

Decompression Theory | Links and Resources | Technical Scuba Diving

I am curious why you have this hanging around though...
DEEP STOPS
B.R. Wienke
NAUI Technical Diving Operations
Tampa, Florida

So people can understand the historical context and educate themselves on the premises of that concept.

At the time, it was leading work and garnered much attention. Decompression theory advances ceaselessly... so it's important to note publishing dates when reading such articles.

 

[lowviz]

I do not think deep stops for recreational profiles are valuable. ...//...

I agree based on personal experience. Where I dive (ocean, back bay, or deep quarry) I am guaranteed a very long drive back home. The aches and pains (if any) and degree of tiredness will present in a very predictable pattern. Deep stops appear to have no effect on this. However, dumpsterDiver's usual level of exertion is unlike mine, so I can't speak to his observations.

...//... For me it is a way to approach dives with a very conservative dive computer that hopefully gives me safer dives with reasonable bottom times.

Well, that's exactly where I'm going with all this. It is common practice to find the most aggressive PDC and run it right up to the NDL to get the greatest bottom time allowable. I believe that setting your PDC to a high level of conservatism and doing the stops (up to ~15 minute obligation) is far safer and easier on your bod. Problem is, the agencies can't touch this procedure. They would be putting recreational divers into deco! Yet another "slippery slope" problem that forces a less than optimal directive on their recreational divers...

...//... IMHO, putting deep stops onto recreational diving instruments was nothing more than a gimmick. What's inexcusable is that, on many such computers, deep stops are an either/or option versus safety stops.

If I understand that (and it appears to be clearly written), you are saying that if a diver started his ascent when he hit his NDL and did his deep stop, then his mandatory safety stop is no longer mandatory???

 

[RainPilot]

I agree with tbone regarding the deco on a high conservatism vs NDL on a low.

The other day I did a 30m dive with a mate, it was his first deep dive and we went out to a small benign wreck here to have a look. We joined onto the second dive of the two tanker the other guys on the boat were doing. I calculated rock bottom, had 2 tanks on SM with my friend in standard single BM so lots of gas spare.

I had inadvertently left my Perdix in tech mode on a GF of 40/70 and about 10-12 min into the dive I saw i was approaching NDL fast. Now I know from the UTD min deco tables that NDL for 30m on 32% is 30 min, I was far from that, I also watched all the PADI guys on their 2nd dive still happily tootling around. I checked my buddies DC and he still had a fair chunk of time till NDL which corresponded to my 30/30 reference.

What to do? I wasn't sure how to change GF in mid dive so I decided to just dive the stops the SW gave me and see how it went. I also had the tables and buddies DC as a sanity check. I went into a 8 min deco stop at 10m indicated, when we hit rock bottom at around 25 min runtime we ascended. The 10m stop cleared on the way up and then I had a 3 min stop at 6m. While the others all did their safety stop at 5m in the swell, we sat at 6m and the stop cleared 2 min in.

Was this a "deco dive"? I chose to treat it as such and was quite happy to do so, but in reality I was in the "algorithm buffer zone" that seems to exist between multiple brands of computers and conservatism settings. I believe that what i did was safer than setting the highest GF I can on a rec computer and then riding it up with no safety stop, which would fall within the limits of rec diving as per most agencies.

That all being said, i really don't know how insurance companies would view this. It doesn't matter how reasoned and sensible we are, if the "book" says no deco and your DC says deco, they will make a concerted effort to avoid payout im sure.

 

[KenGordon]

. Problem is, the agencies can't touch this procedure. They would be putting recreational divers into deco! Yet another "slippery slope" problem that forces a less than optimal directive on their recreational divers...

Just choose your diving educators more carefully. Outside of the PADI centric world second level divers are taught how to do deco dives. So if you are qualified to 30m you are qualified to do a deco dive. People discuss maximum stop times before getting in. Some only like to do no stop dives, some might say 5 minutes of stops, 10 minutes or whatever. They do not feel the need to take a couple of extra cylinder and risk oxygen toxicity mistakes. Redundant gas is provided by the buddy.

 

[boulderjohn]

I had inadvertently left my Perdix in tech mode on a GF of 40/70 and about 10-12 min into the dive I saw i was approaching NDL fast.

This leads us to the overwhelming question looming in the background of this thread, a question I am almost afraid to mention it because of the potential reaction.

When I am recreational diving, I use a Perdix, and I have never bothered to take it out of tech mode. I don't even know what it looks like in recreational mode. You bet it runs out of NDL well before the others, but if you ascend immediately after going into deco, you will find that when it does, it requires a one minute decompression stop at safety stop depth. Sure, if you stay in deco long enough at depth it will run all the way up to 3 minutes (like everyone else) and even beyond, but when it first goes into deco while in tech mode, it is really at the beginning stages of calling for a real safety stop.

So let's say you are on the boat crew supervising divers who were warned "This is a no deco dive!" before they went in the water. When they all come out and get back on the boat, do you check their computers to see if they went into deco? What would you say if you did and found that they guy with the Perdix went into NDL and did 2 minutes of deco, as opposed to the people with recreational computers that did not go into deco but did a 3 minute safety stop? What would you say if the guy with the Perdix did 4 minutes of deco?

But it does not have to be a tech computer. If you are diving an ultra conservative Suunto recreational computer, go into deco, and ascend immediately, there is a good chance it will clear on ascent. It may just require a 3 minute stop. It may extend that stop to 4-5 minutes, something you might be doing anyway.

I think you might be seeing where I am going. As a tech instructor, I don't have any qualms about going into deco on a supposed recreational dive. I know when it is getting serious, and I know my limits on gas supplies. I sometimes carry a deco bottle on recreational dives, and I guess the crew assumes it is a pony bottle. (They look pretty much the same except for the MOD marker the crew never asks about.) I can handle that light deco, and the boat crew will never know of my transgression. (It is also likely, since they know me, that they don't care what I do.)

So what is the level of training and experience you need to be able to do all of this? The PADI Tech 40 class teaches light deco (up to 10 minutes) within recreational ranges, exactly what we are talking about here. Is that sort of training necessary for this kind of diving? Will boat crews publicly adapt policies that enable light deco for those with the proper credentials?

 

[redacted]

If you are a lite deco proponent, what is your plan if there is an emergency recall. Do you blow off the deco or do you make the boat wait (or leave you)?

 

[scubadada]

If you are a lite deco proponent, what is your plan if there is an emergency recall. Do you blow off the deco or do you make the boat wait (or leave you)?

This is an interesting question and a reasonable argument to not allow deco with a rec group. Light deco could certainly disrupt a recall or increase the risk of DCS if the obligation is blown off. Increasingly, divers with doubles or RBs are diving off the same boats as rec divers and, under appropriate circumstances, are being offered the option of doing a single long dive or 2 shorter dives. The former option could very significantly delay surfacing after the 1st rec dive. I'm not at all sure how operators are dealing with this question but would like to hear from those who have experience with this issue.

I have never been part of an emergency recall, however, on one occasion, there was an OOA/near drowning while I was still down on a wreck. Fortunately, my boat was able to leave immediately and arranged that I be picked up by another boat in the immediate vicinity. Obviously, this would not always be possible.

 

[KenGordon]

If you are a lite deco proponent, what is your plan if there is an emergency recall. Do you blow off the deco or do you make the boat wait (or leave you)?

This is what helicopters and lifeboats are for

You need a plan for the dive, that includes a maximum run time or the boat will be calling the coastguard for a lost diver. If something nasty happens before the divers are up then the boat has to wait or risk those still in the water for the sake of the casualty. How that is managed depends on local conditions.

I do not think a skipper who left a boat load of divers behind would be getting much repeat business.

Really there is not a binary difference between a no stop dive and a deco dive as the stops depend on the algorithm chosen and only approximate the body. While there is a tendency to increased risk with duration not all longer/deeper dives are riskier and in particular not all shorter/shallower dives are safer.

Who are these people on boats that 'check' computers? I don't think you can tell with mine if I was in deco or not.

 

[Vicko]

A few months ago someon on reddit someone asked why I would not recomend going into tec diving. I posted a dive profile to 65 meters on air, I was attacked for not diving a Perdix (but a suunto, that i mostly use to piss off tec divers online), using air for deco, and having only 20 minutes bottom time. Now I have a question, since that was not a tec dive, did i die while reading comics at 6 meters for 40 minutes?

Except the survival rate, what's the difference between a tec dive and a planed diet deco with backup gas?