Beep beep going into decom :-( or :-)

[blackice]

Hi there, recently my dives have started pushing the no-deco times on my computer, I have then been getting 4-13 minutes accent time, most of which I do at 4-5meters.

Many people in our group went into decom when we did a double wreck dive, we all did our required stops.

We are all diving single tanks, and I made sure I had 1000psi before I went in to decom. Is this a problem?

Is it mainly a matter of ensuring that I have enough air to meet the decom requirements and then some for safety.

Or are other things happening in my body that I'm not aware of?

At what point do I have to move to doubles (would still get decom time) or move to Trimix gases and decom/stage bottles.

=-)

 

[DA Aquamaster]

I would not do any form of overhead diving without a redundant air supply and adequate training. Period.

For deco diving I would plan on a minimum of a pony bottle with enough air to ascend and complete any required deco for the dive. Depending on your air consumption this would be 19 to 30 cu ft MINIMUM.

Deco diving on a single tank is fine, until you get a free flow or similar problem that leaves you with no air and some required stop times that you will end up having to skip with a possible DCS hit. I have personally never felt that relying on a buddy as a redundant air source was a good idea - they are invariably not around when you need them or are short of air when you both need it.

Being 38 and no longer the 21 yr old Marine I was when I started diving, I am conservative on stop times and add a minute or two to the 30 and 20 ft stops and do a minimum of 3 minutes at 20 feet even if it is not reuired and then add 3-5 minutes to the 10 foot stop. I also do a deep stop for 1 minute at 1/2 my max depth. It's probably overkill on conservatisim but it beats getting bent.

I dive independent doubles to ensure enough air to complete the dive with a healthy reserve even with a total air loss from one tank. In deco diving it does not take long to realize that there is nothing a pony bottle can do that a set of properly configured doubles can not do a lot better and safer.

I also usually have a tank hanging off the boat at 20' with Nitrox 70 that can be brought up and clipped again at 10'. It is rigged as a stage bottle and can also be clipped to me or another diver if required or more convenient.

When the ascent line is used, a saftey tank gives me the option of using Nitrox 70 during the 20' and 10' stops for what amounts to accellerated decompression. Using standard air tables, nitrox tables or a computer and normal stop times, this accellerated deco provides another saftey margin. Nitrox 70 is also about optimum for shallow deco stops as it gives most of the benefit of 100% O2 without taking as large a bite out of the CNS clock. Even with a saftey tank, you need to plan on carrying adequate air to complete the dive safley in the event that you cannot locate the ascent line. It's nice to have but dontl include the air or nitrox it contains in your dive planning.

A separate deco bottle with Nitrox 50 (used on ascent from 70' to the surface), Nitrox 70 (used on ascent from 40' to the surface) or 100% O2 (used from 20' to the surface) is also worth considering to either accellerate deco or add a saftey margin, but it requires advanced training and specialized equipment.

I also have emergency oxygen on the boat and regard it as a neccesary saftey item as well.

Unless you are properly trained and equipped, I would really avoid getting into deco situations at all. If your deep diving is 130ft or less, getting Nitrox certified may extend your bottom time and alleviate your need for deco diving. Nitrox certification is also a good first step toward more technical dive training.

Trimix is about as advanced as you get in diving and it requires extensive training before you are even qualified to enroll in a trimix course. Trimix also has some downsides in terms of high cost, the need for additional thermal protection to prevent you from getting chilled while breathing trimix, and in terms of the potential for increased deco time on shallow dive profiles. Trimix shines at depths below 150-170 ft but at shallower depths it is often not worth the costs and compromises involved.

 

[Jonathan]

seriously consider some additional training if you want to go beyond your NDL.

13 minute time to surface without proper provision (training and equipment) can lead to serious consequences. We are not just talking about just missing the mark here....

Safe diving
Jonathan

 

[DiveTub]

13 Minutes of deco with no redundent Air source and no Deco training, relying on a computer sure sounds like a good way to get very bent.

Why not go do some technical training so you don't die ?

 

[blackice]

Thanks for the advice, we don't plan to do decom dives (not yet any way). And I just wanted to know what the deal is, sure the computer doesn't think it's a great idea (neither does my wife!)

I am planning on taking AdvNitrox /Decom Procudures in the next 6 months and I'm starting to dive with more like minded divers that would like to extend beyond AOW dives.

Yes training is part of the plan and I like the idea of learning more. So for now no more deco dives until they are planned.

Cheers.

 

[Jonathan]

we don't plan to do decom dives

Trying not to sound harsh - and we've all probably been there - but it does not sound like you plan your dive at all.

Even if it is the worst plan in the world "plop down, swim about a bit come up when we are low on air" if you computer is coming close to NDL time to go up 5m.

If you can't you are too far in that wreck.....

Jonathan

 

[blackice]

First up we weren't IN the wreck,

I personal was only incurred 4 mins deco, others were worse off . ie the 13 min guy.

I was paying close attention to the computer and wanted to see what was on the other side of 0. Yes it told me to accend to a saftey stop , which I did.

Where I waited for the required 4mins + 2 more for safety's sake (and mine).

We were following a DM and they pushed further (ie 13mins) but once my com said deco , we headed up.

I was just wondering if others had had this happen before, as I had never had it happen in 70+ dives, but on that dive 5 people went beyond the limits.

Not something planned, and yes there was a plan - but deco was never discussed!

I will in the future avoid pushing the 0 limit and stay within the NDL, but like you say it happens, as long as you are aware, in control, your buddy is aware, etc ... you try not to do it again .

 

[fins wake]

Trying not to sound harsh - and we've all probably been there - but it does not sound like you plan your dive at all.

I don't wish to be rude (and hope it isn't taken that way) but I agree entirely with Jonathan. 13 minutes of deco is actually a serious obligation, which indeed requires serious training and serious equipment.

Even if you're only on 1-2 mins deco regularly, or even just at the NDL limits, it means you're regularly pushing your NDL tables (and all your previous training and experience) to and beyond the limits. There is serious risk of decompression injury here. Remember that most computer manufacturers specifically excempt decompression diving (although it's possible on their computers of course). On some computers, you'll be using algorithms specifically tested in NDL conditions. You're extending the projections and alfa-testing it yourself ... and what if your computer gives up mid-dive? Let alone you run out of gas or similar?

There are many ways to skin a cat and I respect DA Aquamaster's knowledge and his efforts to provide good tips. However, there are pros and cons to everything, including independent doubles (requires discipline and careful breathing down of each tank) and to leaving your stage bottle on the line (in case you lose it, just as Aquamaster himself correctly writes). Of course, stage bottles aren't strictly required on simple dives with properly configured doubles ...

In general, on even a basic course (such as Adv Nitrox) you'll learn the theory and - more importantly - the practicalities of simple deco dives (yes, I know Adv Nitrox is not a deco course, strictly speaking) under instructor supervision.

Do yourself a favour, blackice, go that route and start planning your dives now. All the best!

 

[blackice]

Read carefully, I did not have 13 mins deco only 4, you may say that both is bad - yes but 4 mins is a hell of a lot better than 13! and consider that the computer normal give you a 3min stop this does not seem not extreme!

Not good but not so off the scale as to continue to cut me down. Like I have said I know this was pushing limits, I know it's not ment to happen and I know that I need more training if I wish to do deco dives.

But I find it hard to believe that no one else has EVER done that before.

I did also say that this is the first time it has happened in over 70 dives and I have no plans to do it again.

 

[fins wake]

Read carefully, I did not have 13 mins deco only 4,

'Twas read carefully. I was replying to the original post:

recently my dives have started pushing the no-deco times on my computer, I have then been getting 4-13 minutes accent time, most of which I do at 4-5meters.

This implies that you regularly get 13 mins deco times, which are then handled haphazardly at different stop depths.

and consider that the computer normal give you a 3min stop this does not seem not extreme!

True, but there's a world of difference between a recommended safety stop and a compulsory decompression stop. Personally, I always take a minimum 3-minute safety stop on all my dives, however shallow. Note, however, that by tacking this 1 minute deco stop above and beyond the safety stop, you're no longer in NDL territory and not "within the margins of the envelope". That doesn't mean you will get decompression illness if anything goes pearshaped, just means you well might ...

Like I have said I know this was pushing limits, I know it's not ment to happen and I know that I need more training if I wish to do deco dives.

Excellent. I think we all reacted to the 'recently my dives have started pushing'-statement ...

But I find it hard to believe that no one else has EVER done that before.

Oh yes, guilty as charged (although only once, M'lord, and I had a large tank and it was a nice tropical reef dive with extremely long decompression long after the computer had cleared ... 'onest!) This was a while ago. Since then I have done further technical training.

I did also say that this is the first time it has happened in over 70 dives and I have no plans to do it again.

I'm not the scuba police ... *shivers*

To each his own. Decompression diving is actually a natural step for a wreckie, but it requires serious training and equipment, that's all. Peace out, man! =-)