Question Shearwater Teric (GF40/85) goes into DECO on first dive (max depth 25.9m, avg depth 17.6, duration 48mins)

[lowwall]

The OP was using the Shearwater rec default of 40/85, so no problem there.

IMO, high default GFs, even x/95, is fine for an NDL dive. As long as you don't take that all the way to the surface unless it's an actual emergency. In which case you should take it a lot easier on your next dive if you aren't skipping it entirely.

We need to keep in mind that the calculated GF during a dive assumes your max allowable ascent rate all the way up without a safety stop. Spend a little time in the shallows and do your safety stop and none of your tissues will be loaded near their theoretical maximum when you surface.

If you don't want to push it, then fine. Just stay away from your NDL during the dive. But I'd rather know my actual limit in case something super cool shows up rather than set my GF artificially low and have to make a decision on whether to leave early or turn it into an impromptu deco dive.

 

[scubadada]

Follow your SurfGF

 

[lowwall]

Follow your SurfGF

If you've shelled out for a Shearwater

 

[rsingler]

Oh @rsingler

The DSAT decompression algorithm runs close to a GF high of 95, at least on the 1st clean dive. It has been used by many, many divers for about 35 years. Are you saying it is unsafe, or something else?

@scubadada , I'm saying that IMO, under certain circumstances, it's unsafe.
The circumstances:
a) bucket list vacation dive trips do LOTS of repetitive dives; in this we are a lot more aggressive than 30 years ago;
b) safety stops are still regarded as optional;
c) no one pays ANY attention in OW training to the final rate of ascent from 15 feet.

The OP was a PERFECT example (and I'm not picking on him). Hit NDL, ignored computer to provide for buddy, unknown final ascent rate and continued diving later in the day.

Folks get away with this all the time.
Folks having been diving DSAT for decades.
But why have deep stops gone away?
Why are folks talking about Integrated Sum of Saturations?
Why the attention to the bloom in GF99 from 15' up?
Why are Buhlmann computers now almost standard? And custom GF's?

As you know, we've been learning. And if it's good for tech divers (not to mention Dr. Simon Mitchell in many circumstances) to dive xx/70, then how do we explain that DSAT is okay for 2-3 dives, but maybe not for 40 in a week? And if 50/70 is good for 40 dives in a row (this is me talking) maybe I should dive 50/70 all the time.

It's tough to integrate anecdotal experience ("been divin' this way for years!"), with the not so rare cases of DCS in either formal studies or ScubaBoard anecdotes.

So if someone says (in the Basic Forum), "You're advocating something way too conservative!", I'll take that hit. I dive 50/70. Having been trained, I go into brief deco a lot on dive trips. And it clears on the way up, or during a 5- minute safety stop, and the DM's never ask because my Shearwater doesn't lock me out. But I'd rather surface with a GF of 40-70 on my 30th dive of a trip than anything higher. And I NEVER (short of OOA) surface with a GF of 95. Ever. That comment was what lit my fire.

Just my opinion. One of many opinions. But given this forum, I felt compelled to speak for conservatism, because it's never cramped my style with my buddies. No one ever says, "Oh, he's always the first one up because his GF is so low." Doesn't happen that way. I'm usually one of the last ones up because I'm taking my time offgassing safely and leisurely.

 

[Blackcrusader]

c) no one pays ANY attention in OW training to the final rate of ascent from 15 feet.

This. When I was in the Maldives a nice couple were asking me why I was always the slowest diver to ascend from the safety stop. I take more than a minute or two.
I asked them what the ascent rate is? They realized that when safety stop was done a lot of divers just fin up to the surface and not ascend slowly. Now they go slowly like I do. I just checked my last dive it took me 2 minutes 30 seconds to go from 5m to surface. That's a tad slow but it's certainly safe.

 

[Jai Bar]

I apologize beforehand for the following harsh words: you are a dangerous diver. To yourself, your buddy and also unsuspecting dive master.

Why use a diving computer if you are going to ignore what it tells you? You can as well leave it on the boat or back home and dive freely...

If you don't trust it, dont know what are the meanings of all these settings (e.g. Gradient factors), then perhaps you need a more simple computer that does not require any user interaction? But instead, you omitted the deco obligations the computer has calculated for you, ended the dive because your wife had stomach upset- I wonder if she did know that you are in deco and have to do safety stops? You were lucky, because the worst could have been that she would have to take care of you in the deco chamber - with her stomach still upset. Or, you could have forced unintended deco stops for her and dive master, only Neptune knows if they had enough gas left to keep company for the decompression stops you surprised them into.

Then you ask if it is normal 25.7m maz depth on air, 48 minutes? If you ignore the computer and, say, consult the old diving tables, what story do you think the tables would have told you?

And it gets worse: you omitted deco and then followed by erasing the nitrogen load by flashing a new firmware and then continued diving!? Seriously???

I can quote Vance Harlow's Oxygen hacker's companion (about Oxygen cleaning, but also relevant for ignoring decompression stops): "It's one of those things that you may get away with ten or a hundred times, but if on the thousandth time it blows up in your face you're going to feel pretty stupid in those last micro-seconds."

If I was your buddy and then you surprise me with "oh, so sorry, I need X minutes deco stops" I'd be pissed as hell and never dive with you again. If you'd signal and show me your NDL is running short, I would be proud of you and signal back to start ascending a little to shallower depth.

So, not being all negative, what should you have done?

1. Plan the dive. Know beforehand the max depth and duration, multilevel accordingly to dive site and sea conditions to end the dive with reserve just in case- who knows- your computer plans some deco obligations for you.
2. Know your computer, understand how it works, once in a while look at this pesky "NDL" value and when it begins to creep towards less than 10 minutes (or whatever) *communicate* this (e.g. shoe the darn screen to buddy, dm) and let them know it is time to ascend a little wee.
3. If something went wrong, do the requested stops
3.1. if had deco stops, or skipped them for whatever reasons- communicate this to crew, hydrate, breath 100% oxygen just for precaution, be attentive for whatever signs
3.2 Consider skip diving 24 hours. A Suunto would have locked you anyway just for this very same reason.
4. DO NOT erase the computer! For the sake of Hyperbaric chamber, they need this information for treatment planning.
5. Consider Nitrox for the type of diving you mentioned
6. Learn your SAC or air consumption rate, so you can have an idea when begin ascent to end dive with reserve. If you are using Air Integration, you can set in Shearwater to show the remaining time to reserve if you keep at current depth.
7. Communicate your status with buddy (and dm if there is one). Also be aware of their NDL and remaining gas status. This is your obligation towards your buddy.
8. You are diving for fun, nothing is worth risking you life in a reckless manner.
9. If you dove air because no nitrox certification, by all means do. I suggest also master diver or even better dive master.

Again, forgive me for harsh words, I do hope that you learnt a lesson, made you a better diver, and that you keep diving more frequently so you won't need refreshers in the future.

Perhaps it can help others who happen to find this thread with similar questions.

 

[Jai Bar]

Folks get away with this all the time

And again, Van Harlow's Oxygen hacker's companion: "It's one of those things that you may get away with ten or a hundred times, but if on the thousandth time it blows up in your face you're going to feel pretty stupid in those last micro-seconds."

Moreover, each folk is different. Weight,.physical condition, perhaps PFO, tiredness, hydration condition, age, whatever.

 

[Blackcrusader]

If you've shelled out for a Shearwater

If you bothered to read up on the features and settings and learn what your Shearwater is telling you rather than deciding during the dive the Shearwater must be wrong lol

 

[boqurant]

Fortunately a lot of this can be avoided by RTFM and trusting your tools. Good on OP for asking the questions though, and the responses here seem useful!

Obviously not everyone has time to really dig down into a subject, but I figure in a sport where the consequences are so serious, it behooves one to read up and research as much as possible about your tools, techniques, activities etc etc. Scubaboard is a fantastic resource

 

[tursiops]

b) safety stops are still regarded as optional;

That depends on the operator. For example, they are mandatory for Cayman Divers (LCBR and CBBR) and you even sign a waiver before diving that you will do them.