Diving with gradient factors for a new recreational diver

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HomeBarista

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After about 30 dives I've fallen in love with diving and want to pursue the hobby more actively. Unfortunately, I'm a worrying personality, risk averse, and despite being a decent swimmer and a triathlete, I'm not a natural when it comes to diving and buoyancy control. I want to find ways to enjoy the sport more safely, especially as it relates to DCS risk.

DAN vignettes, ScubaBoard (especially advanced scuba), and talks like Pollock's and Marroni's have been invaluable in my safety pursuit. Most recommendations are fairly straightforward and applicable on all/most dives. As I read through the forums and research articles, however, I come to the conclusion that using conservative gradient factors with multiple stops instead of the popular 3 minute safety stop at 5m (15ft) is a good idea for minimizing risk. But is it practical to do, especially for an inexperienced diver without a regular dive buddy?

So here we go:
Do the safety benefits of multiple safety or deco stops (and diving with conservative gradient factors) outweigh the awkwardness and inconvenience of having to do them on recreational dives? Is it practical?

The pros:
  1. safety - deeper than 5m stops seem to reduce bubble and DCS risk in recreational dives (somewhat significantly).
    FWIW, I don't want the discussion to get mired in whether deep stops are good or bad, but my reading of the journals is that while "too deep" is not good, some deeper than 5m stops are good for reducing bubbling in recreational divers. FWIW, for most recreational dives these seem to be at the deepest in the 12 to 9 meter (40-30ft) range depending on the dive profile and gradient factors chosen.

The cons:
  1. Different (i.e. more conservative) safety / decompression protocol that (almost) everyone else in a real life recreational dive group
    1. stops different that the 5m / 3 min safety stop - both deeper and shallower stops
    2. longer total stops time
    3. (with conservative factors) high likelihood of decompression time while everyone else is in NDL
    4. (with conservative factors) lack of clarity how to handle emergencies while having deco time while others are in NDL
  2. Having to convince the group to follow a different more conservative protocol - not very likely or practical
  3. Separating from the group by a few meters for a stop - I guess this is an outright bad idea for a new diver, a diver without a regular buddy, might be against the manual, and I don't expect it would be tolerated by many dive masters
  4. A more expensive dive computer
  5. Complexity
What do you kind and knowledgeable folks recommend for someone in my situation? Is it a bad idea for a newbie diver to try to dive with multiple stops and conservative gradient factors?
 

drk5036

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I think without technical dive training, it's not really smart or feasible to do "deco stops" on a rec dive. The main problem I see is that you could potentially consider that the stops can be ignored, since you aren't "actually" in deco. However, in this case then, how do you know if you truly ARE in deco (as in, a direct ascent to the surface is likely to cause injury) or not? Basically, the readout on your computer will no longer reflect reality, and you might then not believe it, making the whole situation too complicated.

My suggestion? This is what I do:
1) dive with a shearwater so you have access to your "surfaceGF", or what your % nitrogen loading is if you were magically transported to the surface.
2) set the gradient factors to low conservation (GF95), so that you aren't going to be running into deco far before your other diving mates.
3) keep an eye on the SurfGF. When you get to your safety stop, track it until it goes below 75 (equivalent to the high conservatism setting).

Now you effectively have the best of both worlds. Your computer isn't lying to you, saying "you're risking serious injury by surfacing now!" on a relatively benign dive, but you can also track your nitrogen loading so that you can offgas to a high degree before surfacing. I know a couple of people on here who effectively dive this way.
 

JXT71

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Do you personally feel like the typical 3min @ 5m is insufficient for you? Are you feeling ill at the surface or later in the day? Some red flag like that? If not, I'd say no - all this isn't practical.

I don't think anyone will fault you for having concerns for your own safety, but before diving into deco theory maybe start with more experience and confidence underwater. Get to the point of comfort where buoyancy control isn't a key issue, and you can instead spend your dive time casually looking around. If you're actually following agency rec limits your dive profile can look like this |____| and you shouldn't be getting DCS with all the conservatism already applied. That safety stop is NOT a decompression stop - this is recreational diving. If you haven't done nitrox class, go for it and make sure the optional dives are included, although with the research you've hinted at, you can probably teach the class by now.

I think both your video links mentioned not following your computerblindly. That's fine, but take that opportunity to learn about your computer and understand what it's telling you and how you set it up. Actually plan your dives and compare what your computer says to what a dive table says - one of them will be more conservative (or maybe your buddy's plan is).
If you're gonna worry about something now, worry about establishing good dive planning and execution habits, not decompression.

Also for the bit about being tolerated by divemasters - I can recall a few dives I was called in specifically to address special concerns like this for one or more divers in a group. No one will appreciate it being brought up at the last second, but if they're aware of it ahead of time it shouldn't be an issue.
 

rongoodman

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As a new diver with admitted buoyancy issues, I don't think you need the distractions of unnecessary "deco stops". There's a long discussion about safety stops going on right now over in the basic forum and it isn't something there's really much debate about. They're a good idea, but in the end, they're optional for NDL dives. I've been diving Shearwaters for years and for recreational dives, just set the conservatism to Medium(45/85) and forget about it. Getting nitrox qualified will increase your NDLs and make your shorter/shallower dives more conservative. Staying flat in the water will lessen the chances of popping up too fast and give you the option of finning back down should you begin to do so. While it isn't as likely with dive computers running Buhlmann GF, with many if you set the conservatism too high and are unable to hold or complete the subsequent required deco stops, the computer will lock up and be useless for the next 24 hours.
 

Angelo Farina

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If you do not plan to exceed 32-34m, my suggestion is to use Nitrox-32 instead of air, while diving with people using air, and leaving your computer set to air. You will not need to have slower ascent than the others, while having a significantly reduced risk of DCS. It is just marginally more expensive to get Nitrox instead of air. Worth the risk reduction!

In the rare case when you conduct a recreational dive deeper than 34m, and depending on your certification, you should adopt a different strategy. My recreational certification (CMAS) allows for a max depth of 50m, with "light deco on back gas". And I agree with you that, for a dive, say, to 42m, it is better to plan and equip for diving with a number of deco stop.
"Riding" the NDL to the edge of it, "hoping" of not going in the need of deco stops, is much more risky.
So, when diving beyond 32-34m (and often even just around 30m) I prefer to plan for multiple deco stops (starting at 9m for deep dives, and at 6m for depths in the range 30 to 40m).
As the deco is planned with the group of divers, all will agree to stop at deepest planned depth for the first stop. Then people compare their computers, and the duration of the stop is the longer one among the group. Thereafter all of you move to the next stop, and again the longer stop is performed (depending on different settings and different dive profile, the diver commanding the first longer stop could be different by the diver commanding the last deco stop).
Here in Europe most diving clubs and training centers (we do not rely usually on "shops" here) train recreational divers for performing planned deco stops. Instead, US-based commercial agencies, working usually with "shops", tendentially only train recreational divers to stay within NDL. This caused the bad practice of "riding the NDL"; that is, exposing your body to the very edge of the limit between requiring deco stops and being able to ascend directly to the surface. I agree with you that this is not "safe enough" for me. I prefer to plan a deep dive with significant conservatorism, planning a number of deco stops, and behaving accordingly (which also means carrying a redundant independent air source, so that a direct ascent to surface is never required in case of failure of the main air supply).
I evaluate that recreational deco diving, if planned and conducted properly, is definitely more safe than "riding the edge of the NDL".
 

jadairiii

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You are a recreational diver. Focus on buoyancy control and dive will within the recreational limits. GF's should be the last item on your mind right now.

Think of it this way, you just learned to drive, you dont need to know how to set up the springs of your car for Daytona.
 

blue sky

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Theoretically speaking, if you make a 30 minute dive to 90 feet breathing air and decide to make a deep safety stop at 30 feet, will you still be on gassing nitrogen? Or off-gassing?

Same situation but breathing 32% oxygen.

IMHO, I don't think the pressure gradient delta is great enough to off-gas and that nitrogen on gassing will continue but be less than at 90 feet.
 

sheeper

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you are going down a rabbit hole that you are not ready for. Focus on basic recreational diving. The questions you are posing are in the realm of technical diving. Taking a class from a competent tech instructor will answer those questions for you.
Deco stops are by definition technical diving and should not be done without proper understanding and training.
 

tbone1004

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@HomeBarista

Couple things that may seem to go around the world a bit, but I'll try to have this be somewhat linear.

You seem to be confusing some of the things that have been said regarding gradient factors and decompression with conservatism settings used to adjust NDL's.
Historically the conservatism settings are used to adjust the NDL on any given dive with a diver choosing a setting via a letter or number of a/b/c 1/2/3 etc. that was tied to whatever algorithm they were using. Often this was actually done by telling the computer you were at altitude, sometimes by changing the gradient factors, but all were intended on having the dive stay within NDL. Some divers, myself included don't use NDL as any sort of limit for our diving and discussions around that may have been a source of confusion. If it was, then my genuine apologies as I have tried to make it clear that it is a paradigm shift that tends to occur one you have been decompression certified and it changes your perspective on how you conduct your dives since NDL is no longer a variable in your dive planning.

Addressing each of your points in order.

"Safety"
If you use the gradient factors that people like Pollock and Mitchell have said they use personally *50/70*, you have to be at 100ft for about 45 minutes before the computer is going to give you a 30ft stop and you will have a total deco obligation of 24 minutes. That is not something you should be even remotely considering. If you use 30/70 which is the default setting on a Shearwater in Tec mode *I think the Peregrine and Rec mode is 40/85*, then you're down there for ~25 minutes, but the research has shown that that the GF-Lo is probably too low so I wouldn't recommend going down that rabbit hole. If you believe in the research they've done, then consider using the GF's that they personally use when diving. I don't, but I follow their logic and use 60/80 which I know from my diving is perfectly suitable for my body.

Cons
1-different stop profile. If you have your dive plan done before the dive starts, you'll know roughly what your stop profile looks like and you will be able to brief your dive buddy. Ascent plans are done together, you don't leave your buddy. If you have wildly different thoughts about ascent strategies, either one of you needs to get over it and change, or you need to find a different buddy. Don't leave your buddy.
I wouldn't consider longer stops that a con other than getting bored, BUT you do need to make sure you have all of that time planned into your gas consumption.
In an emergency, you need to know things like what GF99 is doing and if you have mandatory stops left but your GF99 or SurfGF is letting your surface, better to be bent than dead, the boat should have O2 on the top and you can always go back down or find a chamber, but this is why things like planned decompression need to be done after you have a solid understanding about decompression.

2-good luck

3-don't leave your buddy, and if the dive plan is to stay as a full group, then the whole group is your buddy.

4-the Deep6 Excursion will have custom GF's very shortly and is quite inexpensive. The Peregrine at $500 is not what I would consider expensive either.

5-agreed.

Is it a bad idea? At your level absolutely. If you want to dive more safely, then feel free to use the gradient factors to adjust your conservatism, but stay within NDL's where you are just heading up to your precautionary/safety stop sooner than everyone else vs. trying to turn recreational NDL dives into decompression dives by running really conservative profiles.
 

rongoodman

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Theoretically speaking, if you make a 30 minute dive to 90 feet breathing air and decide to make a deep safety stop at 30 feet, will you still be on gassing nitrogen? Or off-gassing?
According to Buhlmann, the answer would be "it depends on which compartment you're talking about". The faster compartments which were fully saturated by the time you began your ascent would be off-gassing due to the decreased pressure at the safety stop, while the slower compartments might still be ongassing, although at a slower rate, because they hadn't had enough time to become saturated yet.
 
https://www.shearwater.com/products/peregrine/

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