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

[kalleth]

Hey there! First post, mainly because I'm looking for some advice on what happened today

I'm a PADI AOW with deep cert on holiday in Malta with about 75 logged dives before today. I'm here visiting family, but I decided while they were working I'd go diving to while away the hours, with a local dive shop. I've done this before a few times in Mallorca, Florida and now here in Malta, twice -- though this shop was new to me, and today was the first time I've used them.

They're a PADI 5* / tecrec and instructor training shop.

I generally dive on holiday in warm water, not in the UK recently, and I'd consider myself a competent, conservative vacation/occasional diver, usually -- but I am not a "tec diver" or an "advanced diver". I'm calm in the water, rarely get flustered, and I'm rarely the person in any group with the highest gas usage.

As luggage space is a factor, I take my own computer (suunto vyper, ~8y old regularly serviced) and a prescription dive mask, and rent the rest from whatever dive shop I'm joining for the day.

To the dives themselves; today we visited a wreck that sits in between ~25 and 35m. We dove it the first time around well within our ND limits -- entered the water on 220 bar, left with 70, on a 15L tank. Impressive vis, really enjoyed the dive.

Then we took a 1h surface interval and the instructor (acting as a guide -- there were 3 other clients, me, and the instructor, total of 5 -- nobody was taking a course) briefed the second dive, which was to include light penetration where an exit route was always visible. I was a little worried about ND limits as he said we'd first look under the keel at ~35m. I didn't mention anything about them at this point because we were all diving computers.

The dive began as the first dive of the day did, a reasonable swim at ~8m out to the wreck, then dive down to the keel, have a look around, and rise up to ~28m for the penetration. At this point I have 6 minutes remaining on my computer of ND time and pointed this out to the guide, who understood and 'okayed' me. I am fine with the dive at this point, everything is going great. Air remaining ~170 bar.

We penetrated through to an area where I remained in view of the "chimney" style exit, the other three members of the group and the guide descended a level (about 3 or 4m away from me, the guide was always in view) to swim around the large room for a moment. At this point I check my computer and have one minute of ND time remaining, which I signal to the guide. He makes the "okay" sign, and tells me to stay where I am.

I am getting somewhat nervous at this point, but I remain calm and wait.

One minute later, my computer beeps, and I signal using my little finger (the sign we had agreed in the prebrief -- i've not been trained on it, as far as I can remember, but some googling says this is a 'deco' sign). The guide again "okays" me, and tells me to wait.

I watch the "ascent time" creep up on my computer to 6 minutes, then 9 minutes, eventually reaching 20 minutes with a 3m ceiling. During this time I am signalling with my little finger, tapping my computer, but I'm not sure how to signal beyond that as I've not had training on decompression diving (nor, really, do I want to yet). The guide then swims up after gathering the rest of the group, the guide reaches me, and we exit the wreck with about 130 bar in my tank.

We subsequently swim back to our entry/exit point, and then spend ~25 minutes decompressing at 5m (after a 10min swim at 8m) before surfacing. I left the water with 60 bar remaining, after a total dive time of 74 minutes. I'm pretty cold in a 3mm suit at this point, and I need a pee. My computer was clear before I ascended, and I have no adverse symptoms of DCI/DCS now, 4 hours after leaving the water. I think I'm fine (I decoed as instructed, I'm sure I am....)

I guess I have some questions for some more experienced divers;

1. I know I should have been more assertive in ending the dive as soon as I felt uncomfortable once I reached zero time left on my computer. Would a "thumbs up" signal have been appropriate then?
   
2. After leaving the water, the german clients didn't seem fazed by the deco, saying "this is normal for a wreck on air at this depth". Should I have been expecting it, even though it wasn't briefed as a deco dive, and everyone was aware of my cert level, given this was a repetitive dive on air to a deeper wreck?
   
3. Is this normal (leading question, I know) at the more technical dive centres? There's a certain amount of trust (as an occasional diver) I place in the dive masters leading a dive when I dive alone with a "pick-up" group. I perhaps naively assumed that PADI -- at this 5 star certified centre -- would prevent this from happening, and I'd be diving within my comfort zone, to the level I'm qualified doing.

I'm generally a very conservative diver and this is the first time I've put my computer into deco mode, and I'm in no rush to do it again -- especially not with a single tank, no stage bottle, buddies who i've never dived with before and rental gear I'm not familiar with. Really, any advice is welcome -- including "you donut, why didn't you end the dive!".

 

[Steve_C]

You did the correct thing in clearing your computer.

NDL is the result of a bunch of computer models and approximations. Your Sunnto is probably one of the most conservative computers that exist. I currently have a ZOOP as my backup and a more recently purchased Scubapro computer. On two dives two days ago. On dive 1 to 85 feet and most of the time at 60-70 ft the computers were about the same. Did a 53 minute total dive time. Slow assent, safety stop, and a 55 minute SI. On dive two to the same depths they started to differ. Toward the end of the second dive the scubapro had well over 10 minutes of NDL and the ZOOP was about out of NDL. Plenty of air. Made the decision to dive the SP. Started up the anchor with the scubapro showing a few minutes of NDL still left and the ZOOP showing 10 minutes of mandatory deco. Did a slow assent and when I got to 20ft the scubapro was showing 90 minute of NDL and the ZOOP was still requiring 10 minutes of deco. Did my safety stop and since my buddy still needed a couple more minutes I did some of the ZOOPS. Since I was not diving again for 24 hours anyway and I know my SP is not an aggressive computer I did not bother to clear the ZOOP. We were last ones up and the boat was waiting. This was on 30%.

The point of all this is that it is very likely that the DMs knew that you were within NDL by their computers and that you had enough air to clear your Sunnto before getting back out of the water. So the dive was a bit more aggressive than you are used to but not a deco dive by many divers computers. Sounds like you handled it well. If in fact, that is what they were doing they should have explained that to you ahead of time to reduce anxiety (and get your approval).

Personally I like having a conservative computer like the ZOOP and a moderate computer. They give me more information especially on a second dive. I usually clear both but I find it helpful on the second dive to get more information.

 

[fmerkel]

Yeah, Suunto..... short SIT interval with an moderately aggressive profile. It notifies you it doesn't like that behavior. It's a well known issue and debated to dust (just do some searching in the forum). Whether you LIKE it or not is up to you, some think it's wonderful, other think it kinda sucks. There is no right or wrong answer.

My wife runs her Vyper on 26% (diving air) to sorta match my UWATEC Aladin 2G. We've had dives where she had 12 minutes of deco and I had 12 minutes of no deco at the same time.
I carry a Suunto Favor (air only) as a backup and I've bent the hell out of it a couple times when the UWATEC was fine, and it's algorithm seems to be a bit more liberal than the Vyper.

 

[Fin Finder]

Your experience is not uncommon. I have a friend who told an almost identical story after a guided dive in Florida.

Too often these "guides" do the dive they want to do, not what their client wants to do.

Pre-dive communication is critical in any guided dive situation, in my opinion.
Glad you're ok. So, for now, you gained some valuable experience without consequences.
How to handle an unexpected decompression obligation should be part of advanced training, in my opinion.

And don't blame Suunto. Personally I like diving on the conservative side.
Nineteen years of diving Suunto and I've never been bent... officially.

After leaving the water, the german clients didn't seem fazed by the deco, saying "this is normal for a wreck on air at this depth".

On a cycling tour of Spain a German couple doing the same route kept stopping me and asking to look at my map. After about the fifth time this happened I asked why didn't they just get their own map. Their response was, "Ha. We don't need a map".

 

[Soggy_Diver]

Hi Kalleth,

I also dive a Sunnto and agree with what Steve_C has said above.

But, I avoid situations where the dive guide is driving my dive profile,if there is any chance of getting into deco or getting low on air. So I either dive with a guide that I know in advance is very conservative; or I dive with my buddy, with the plan that we can leave the group and ascend when we are ready based on our air and ND time; of if I am following a guide with no specific known buddy, then I do only shallow "swim around the reef" type dives.

 

[toby43]

Square things, sit in the kitchen, thats it; tables. Dive planning for the use of.

 

[LordElrond]

Around here (Italy/France) most divers like to go deep, so everyone doesn't care about a bit of mandatory deco, even if outside their training limits, and it seems there is a "don't ask don't tell" policy. Not that I approve of that...

You had about 750 liters of air remaining, enough to bring a (calm) buddy to surface, so no big deal, especially since computers' NDL are very conservative.
Why don't you dive nitrox?

 

[Caveeagle]

To the OP: I hate "group dives", When the DM told you to "wait there"..it sounds a little like you were sort of on your own in an over-head environment. Add to that, being uncomfortable with the dive plan and pushing NDL past your comfort zone.. (if I got that right)
You should have given the 'Thumbs Up' signal and made it clear you wanted to end the dive. I agree that you were not in any real danger from deco, but it sounds like you were not comfortable.

If there had been an issue with another diver.. Would you have been asset to help? ..Or an additional accident risk, if the whole thing went sideways?

Also, this sounds like the perfect dive profile for Nitrox. Especially when diving out as a single add-on diver. It would give you a lot more flexibility on types of dives you can do, with a better margin of safety.

...My wife runs her Vyper on 26% (diving air) to sorta match my UWATEC Aladin 2G. We've had dives where she had 12 minutes of deco and I had 12 minutes of no deco at the same time.
.

Wow.. fudging up on your Po2? I know that diving Nitrox with an air computer is just fine as long as you respect the MOD, but I have never heard of this approach. So your viper is tracking her dive as if you only had 74% N2. What would you do if your Uwatec went Tango-Uniform? I know.. you would probably be ok just adding another 10m to your safety stop. ...But are you sure?

 

[Colliam7]

Very interesting post. Thank you for sharing the experience here on SB! Several thoughts come to mind.

Too often these "guides" do the dive they want to do, not what their client wants to do.

An excellent point. And (unfortunately), these 'guides' do it because of frank ignorance a misplaced confidence, such as:

The point of all this is that it is very likely that the DMs knew that you were within NDL by their computers and that you had enough air to clear your Sunnto before getting back out of the water.

This does happen - they know the site, they have probably done the dive dozens (or more) times before, etc. And, from my perspective, that doesn't make it right - for the customer. You were, frankly, put in a rather compromising position. It is one thing to accumulate 5 minutes of calculated 'deco' obligation at depth, which almost always clears on the ascent. But, you accumulated 20+ minutes, per your post, which didn't clear on the ascent. And, required you to stay down for ~25 minutes to clear the computer. Play out possible scenarios: What if you had not had enough gas? What if there had been an underwater emergency that thwarted the DMs plans to have everybody stay down and clear their computer?

I agree that Suunto algorithms are generally conservative. That doesn't mean they are wrong. I usually dive with 2 computers, a Suunto and another, less conservative Liquivision. There are selected times when I will follow the less conservative computer, when they diverge. But, I also often dive my Suunto alone, and I follow it when I do.

As to what you might have done differently: it is a difficult call. Personally, I think you should have been more aggressive in ending the dive. But, that is not a criticism, just an observation, in hindsight (which is always wonderful). It is NOT within the domain of authority - or competence for that matter - for a dive guide to intentionally ignore a situation where a diver's computer is racking up a calculated deco obligation on a recreational dive. Simple as that.

I know a number of dives guides across a number of Caribbean resorts. (I don't know any in Malta, nor have I dived there.) Many of them are very experienced, in terms of the sheer volume of their diving . They are good people, I enjoy diving with them when the occasion arises. And, for the most part, the majority of them also do not know jack about decompression. The take-away lesson: next time you are in a similar situation - preparing for a guided, deep dive: have a chat with the guide on the surface before the dive. Let them know that you are going to follow your computer if you run out of NDL. It is your dive, your computer, your health.

 

[Storker]

Your Sunnto is probably one of the most conservative computers that exist.

...for short SIs, reverse profiles and/or omitted safety stops. For normal profiles with good SIs, it isn't particularly conservative. First dive of the day, square profile, the Suunto's NDL squares pretty well with the PADI RDP.

If you like some extra conservancy when other factors than max depth and bottom time indicate a somewhat less ideal profile, a Suunto is great for you. If you don't care about that extra padding under those conditions, not so much.