"Accidental" deco with 1-day group, what to learn?

[DevonDiver]

It's easy to be nonchalant about DCS as a novice diver.... and that's partly the fault of the dive industry.

Entry-level scuba courses do their utmost to 'sell' diving as a safe and fun activity. Dive professionals are also in the business of selling divers more diving. Being 'real' about the risks isn't good for sales. The 'real talk' doesn't become transparent until much later, usually.

Scuba diving is a statistically safe activity. That said... many millions of dives are conducted each year. That means...statistically...and in reality... many hundreds of divers get rushed to recompression chambers around the globe annually.

There's nothing on a 'fun dive' that warrants risking life in a wheelchair... especially not an "extra" few minutes underwater gained by pushing NDLs to the limit (or buying a less conservative computer that simply re-defines where those NDLs stand).

Dive to X depth for Y minutes and you have Z risk of DCS.

A conservative computer, versus an aggressive computer, merely defines where in a grey zone that Z is deemed acceptable. It's not black or white.

I fully understand that if a diver has limited opportunity to dive, then their instinct is often to cram as much underwater time as they can on their vacation etc. There are potential consequences to pandering that instinct.

I mean... seriously... just how awesome is that last 5 extra minutes of a dive?

People want to get their 'moneys worth' from a dive. I get it.... and the focus is entirely on the time they spend underwater. I think that's short-sighted.

Getting your 'moneys worth' from a dive is where a dive operator shows you an amazing time underwater and keeps you safe. A great guide dive will show you more in 30 minutes than a crappy dive guide will show you in 45 minutes. A great dive guide will entertain you and educate you. THAT is value for money. Not some d1ckhe@d divemaster who'll risk putting you in a wheelchair in the hope that appealing to people's tendency towards instant-gratification will swell their tips from the trip...

DCS is just not 'frightening' enough... is it? It's very hypothetical from a novice diver perspective (and some not so novice divers...). But dive enough and you'll see it happen... to you or someone you're with.

DCS and other hyperbaric maladies don't trigger an instinctive fear response... like, for instance, you'd get in other outdoor sports like rock climbing, parachuting or white water kayaking. It's hard to gauge risk when you don't get an instinctive, sensory warning of something that can kill you.

Run out of air underwater and you're likely to soil your wetsuit. Aggressively push your off-gassing tolerances and you won't even break a sweat. The more you get away with it, the more silly it seems to fear it... it becomes some sort of 'old wives tail'.... except it's not.

Conservatism is good. Keeping dives shorter and shallower is prudent. As competency grows, don't get more aggressive with the diving... get more intelligent about how, when and why you can extend your limits. Nitrox is good... if used to extend dives conservatively. It's no benefit if it's just another means to make dives more aggressive...and retain the same risks for an extra little bottom time..

Technical diving is the final step... complete freedom to dive as long as you'd ever want. People think tech is just about diving deep... it's not. Technical diving opens up your options for really long and really safe dives....

 

[kalleth]

It's easy to be nonchalant about DCS as a novice diver.... and that's partly the fault of the dive industry.

<snip>

There's nothing on a 'fun dive' that warrants risking life in a wheelchair... especially not an "extra" few minutes underwater gained by pushing NDLs to the limit (or buying a less conservative computer that simply re-defines where those NDLs stand).

I fully understand that if a diver has limited opportunity to dive, then their instinct is often to cram as much underwater time as they can on their vacation etc. There are potential consequences to pandering that instinct.

Andy, I think at this stage we're singing from the same hymn sheet. I like to think of myself as a conservative diver precisely because I never, ever want to get DCS, and I *am* scared of it. But conservatism, taken to extremes, would mean not diving altogether, right?

My instinct is never to cram as much underwater time as possible, but to possibly normalise my time underwater to put it more in touch with what's permissible at an acceptable level of risk. Your posts have opened my eyes to ensuring that I make an informed decision on that point before buying a new computer, and really understanding what the algorithms mean before I do so -- so I thank you for that.

I don't, as I mentioned above, see "buying a less conservative computer" as any kind of solution to the incident I've related, it's a side issue which has been informed by many dive masters and instructors who I've dived with regularly and trust telling me that the Suuntos are "overly" conservative, but I will now try and understand what that means before I use that knowledge to inform the choice of another computer.

I don't have any interest at this stage in taking a "technical" course, or in extending my diving so that I'm regularly in a situation where I have a ceiling preventing me from surfacing (almost) immediately and safely if I experience a problem. I do, however, want to take a couple more courses that will help me gain more experience -- combined with diving more regularly -- at how to dive safely, recreationally, within my own personal limitations.

Thanks again for your detailed responses.

 

[DevonDiver]

Training agencies very seldom here about such non-training incidents directly from the diver involved. And, agencies have more than a little difficulty acting on information supplied by a third party, when the 'offending' dive operation denies that such a behavior occurred.

Courses are easier to audit... there's set performance standards, training standards and instructor standards to comply with. Course participants are given QA forms to email back.

Fun diving... it's just not covered by the agency QA process. It only ever becomes an issue when an incident report is submitted to the agency. Who is supposed to submit those reports?.... the instructor/center. Of course... it's not in the interest of the instructor/center to highlight incidents that happen under their duty of care.... there's no benefit for doing it.... and possible risks. So the only time that agencies hear of incidents is if an incident causes injury or death...and the lawyers get involved. ONLY THEN do the agencies want to hear every detail of the incident....

Agencies do have 'membership standards' for their 'professionals'.... but these aren't specific nor auditable. They aren't black or white standards. There's no list of prohibitions to apply. Divermasters are taught, by the agencies, how to brief and supervise dives. Nobody seems to care if they apply what they were taught. Nobody seems to care if divemaster are poor 'role models' and advocate - in words or actions - very unsafe diving practices.

I'd love to see every dive center having to prominently display a QA 'poster' from their respective affiliated agencies. That poster should list an agreed set of safe diving practices....and the standards, service and duty-of-care that the agency vouches for with that dive center. There should also be the email address and/or phone number for customers to contact the agency to report any instance where the dive center, and their staff, didn't supply those safe diving practices. You know the type of deal... "How's my driving? Call......"

 

[rjack321]

One thing that almost never gets talked about on group dives is "what is your NDL for the upcoming dive?" and "where are we going to do the safety stop" (and how long)

I know a few agencies encouraging this but they are still very much in the minority. I think its an embarrassment that briefings focus on how to get down and what to see and do on the bottom, with almost no consideration of when to leave or the ascent. 2 of the most important things to discuss are how much gas do you have and when are we ascending.

Would you climb a mountain with no briefing on how to get down?

 

[rongoodman]

1. I'm considering buying a slightly less conservative computer -- not ridiculous like Shearwater but perhaps a Scubapro/Oceanic set to a slightly more conservative setting. I have to think about whether I'm comfortable with that first.

What does "ridiculous" even mean? You can make the Shearwater, or any other computer running Buhlmann GF or VPM, as liberal or conservative as you like. What GFs (or conservatism in the case of VPM) you choose is up to you. And these algorithms are well documented and widely available, so you won't be making guesses about how some piece of proprietary software works.

 

[DevonDiver]

What does "ridiculous" even mean? .

From a novice diver perspective, I'd guess it means that those computers allow sufficient flexibility for the diver to set algorithm parameters that'd actually let them hurt themselves.

No safety net.... except your knowledge.

I once met a guy who thought VPM-B conservatism was like Suunto RGBM conservatism... and he was setting VPM-B '0' assuming it was the de-facto 'norm'.,,,, he didn't like "conservatism"....and pesky dive computers that cramped his expectations.

 

[geoff w]

Your Suunto is working exactly the way it's supposed to. I've had a Vyper for over 10 years (actually a few, because periodically the depth sensor just decides to crap out and then it's just trash), and also have a Shearwater Petrel. Since my Vyper is in a console, I dive with both the Vyper and Shearwater. My Vyper is set to normal conservatism (which is very conservative), my Petrel set to moderate conservative in recreational mode

On deep dives, sometimes my Vyper shows more NDL time than my Petrel on the first dive. On subsequent dives, the Vyper is always way more conservative. I always complete the time both computers show before surfacing

When we were diving in Maui on nitrox and our guide was on air (he had a Zoop, so essentially the same computer), and we were running up against NDL times, I asked him how he kept from going in to deco mode. He just said he set his computer to 36% nitrox when he dived air. That gives some idea how conservative the Suuntos are

When your Suunto goes in to deco mode, if you start ascending soon you'll find you get credit for the ascent and chances are you'll just end up doing your safety stop

The good news is you picked up valuable knowledge and experience for future dives with similar profiles and situations

 

[DevonDiver]

On deep dives, sometimes my Vyper shows more NDL time than my Petrel on the first dive. On subsequent dives, the Vyper is always way more conservative. I always complete the time both computers show before surfacing

I can't remember off the top of my head... but on a non-repetitive/non-multi-day 30m/100ft dive #1, Suunto RGBM equated to ZHL16 at around GF90. On a second 30m/100ft dive, after 65 min SI, RGBM equated to around GF70.... there's your 'reduced gradient' in action.

Try matching your ZHL to the RGBM once you hit bottom depth (GF Hi is adjustable in-water on Shearwaters..) on a range of dives.

RGBM is accounting for micro-emboli persistance post-dive, rather than just tissue half-times. It's also calculating based on those persistent bubbles growing on repetitive dives.... which is predicted more dramatically than a straightforward "I have ___ residual nitrogen and I will add ____ more nitrogen on this dive".

Odd though.... how some divers rave about deep stops because of "those important bubbles" then bitch about those algorithms giving more conservative repetitive dives because of the same bubble considerations... LOL

He just said he set his computer to 36% nitrox when he dived air. That gives some idea how conservative the Suuntos are

It gives an idea of how moronic some dive pros are. Why didn't he just leave it in gauge mode instead?

When your Suunto goes in to deco mode, if you start ascending soon you'll find you get credit for the ascent and chances are you'll just end up doing your safety stop

That entirely depends on the controlling tissue compartment. Which, in turn, entirely depends on your prior repetitive and multi-day diving schedule.

I've seen divers get very caught out due to complacency that deco would clear on ascent.

I proved this to a friend before. I dived nitox, but left my Vyper set for air for demo purposes. On the 3rd dive of the day... only16m deep, it went into deco mode. We ascended very slowly. By the time I reached 3m it had accumulated nearly 20 minutes of deco. Not cleared... as my mate had assumed (bet me...).

Also... bear in mind that Suunto's ADD the 3 minute safety stop to the overall TTS. So... if you're reading 4 minutes deco... then it's only actually 1 minute of deco, then it'll switch back to no-deco and give the routine 3 min safety stop. This misleads some divers into thinking that 'minimal deco clears always on ascent'. Suuntos aren't actually that good at clearing deco on ascent.... RGBM uses a tight 'deco zone'....and it's relatively inefficient in clearing below that depth (compared to some other deco models).

 

[fmerkel]

When we were diving in Maui on nitrox and our guide was on air (he had a Zoop, so essentially the same computer), and we were running up against NDL times, I asked him how he kept from going in to deco mode. He just said he set his computer to 36% nitrox when he dived air. That gives some idea how conservative the Suuntos are

OMG! a professional that is even more of a Suunto renegade than we are! Shudder......

Once again fellow divers this is not an approved computer tweak, Suunto approved modification, or a ScubaBoard sanctioned procedure.

 

[DevonDiver]

Suunto's are a really bad choice for dive pros working aggressive multi-day diving schedules..... or a really good choice.... depending on whether you're the type to dismiss that nagging shoulder ache to 'climbing boat ladders and hauling tanks' or not...