Planned deco on a recreational dive?

[cneal]

So whats the difference between 1 minute of ndl and 1 minute of deco?

I have been told one minute of deco is a rounding error.

 

[Bob DBF]

I find this cynical and I disagree. Most people tend to shy away from things that are potentially dangerous if they "don't know what they don't know". There is nothing wrong with that. You might call it "fear, uncertainty and doubt" but I would call it wisely respecting your limits and comfort zone.

Actually I found that respecting my limits and comfort zone was the most important thing I learned in diving, and try to pass that on to new divers I meet that are trying to progress faster than their skills develop. I attribute my longevity diving to making the right choices, mostly, when confronting unknown situations.

So why do *I* think most people avoid doing simple deco dives? I think they do so because they recognize, perhaps passively, that it's a complication with (to them) unknown risks and they probably estimate that "it's not worth it".

It is a simple deco dive until it isn't. At that point you need experience and training, without that it it can be anywhere from an interesting to a fatal day.

If someone decides that they want to take the limits of their current training and experience seriously then it's really rude to mockingly say (at least that's how I read it) that they must be suffering from Fear Uncertainty and Doubt. Personally, as an instructor and a technical diver, I fully respect people's choices in these matters.

Fear Uncertainty and Doubt can be your best friends, and can keep you from making a very poor choice.


I rarely do deco anymore, the fact that I learned back in the 60's when there was one hell of a lot less known is one reason, and I have little desire or need to train as a tech diver at my advancing age now. Times change and I would think that taking advantage of the knowledge and technology we have today is a lot better than the DIY deco course I had back in the day on j-valve double 72's.



Bob

 

[boulderjohn]

Times change and I would think that taking advantage of the knowledge and technology we have today is a lot better than the DIY deco course I had back in the day on j-valve double 72's.

One of the things people forget when comparing the two eras is that the the fatality rate on scuba was MUCH higher then than it is now. The most well known attempts to study dive fatalities started in 1970 (for North America), and those annual results were always included in a section of the annual DAN report. The total number of dive fatalities annually from 1970-1980 were much, much higher than in recent years. That is despite the fact that there are probably several times as many divers today than there were then, and we are much better at getting information about dive fatalities now than we were then--meaning the newer numbers are probably more accurate than the older ones.

The fact that scuba is so much safer today can be attributed to a number of reasons, including better equipment, but one of those reasons is almost certainly the fact that we know a lot more about things like decompression theory, and we have added a number of standard practices into our diving that make it safer. To give you one example of the difference, according to Sheck Exley's book on cave diving, in 1976 at least 26 people died while diving in caves in Florida alone. Exley's book established safe cave diving practices, and cave divers embraced it. Today there has to be at least 100 times as many cave divers world wide than there were in 1986, but you would have to go back about a decade to get a total of 26 deaths world wide, not just in Florida.

 

[Fastmarc]

I truly find it astonishing that it is being recommended here that it is ok for divers who are recreational trained do deco diving.

 

[wbatten1]

So whats the difference between 1 minute of ndl and 1 minute of deco?

A 25% increase in the risk of getting decompression sickness. It's not worth it.

 

[dumpsterDiver]

Some people misunderstood some posts I made on this topic few weeks ago. In them, I said that I used a Shearwater computer in tech mode while doing recreational dives, and in that mode with the settings I use or technical dives, it will put me into deco when others are still within NDLs. I also said that when it puts me into deco, it is telling me I need to do a 1 minute stop--less than a standard safety stop. If I go a couple more minutes into deco, I get to stop for the full 3 minutes. I don't worry about it. The worst thing that could happen is that I might have a catastrophic gas loss while doing that stop (highly unlikely) and have to surface before it is done. Under those circumstances, I will almost certainly have no ill effects.

That is for unplanned deco. If I am planning to go into deco, then I have the opportunity to deal with the potential for a catastrophic gas loss ahead of time by having a redundant gas source. That's a pretty simple precaution to take, and it would be silly not to take it. I have the training to do decompression, and all I need is the appropriate equipment to do it safely.

I find your comments about the dangers of decompression diving to be off the mark. It is surprising to me that a technical dive instructor would promote this kind of attitude (“I don’t worry about it” ) for a recreational dive situation where the diver is accruing 3 minutes of required decompression penalty.

More specifically, you are claiming that should you go a little into deco (without any redundancy which is required by agency standards, it seems), the worst that could happen is that you might run low on air at a shallow stop and have to blow off a minute or so of deco.

The sort of grossly simplistic thinking you put forth is something I would expect from an open water student, not from a tech instructor.

As I have mentioned before, I have no technical training, but it is quite obvious to me that a much, much more serious problem which MIGHT arise on a decompression dive - would occur AT DEPTH not at 10 feet. This is something that I WORRY ABOUT. In other words, the WORST CASE SCENARIO IS NOT A PROBLEM AT 10 FEET!

If a recreational diver (who has entered into the required decompression “zone) is carrying no redundant gas supply (something you have no problem with) and has an air supply failure (at depth) and is unable to secure an alternative breathing gas source, then the only remedy is going to be a rapid ascent – with zero air. The ability to maintain a safe ascent rate of 30 feet per minute (let alone the deco or safety stop) is going to be compromised or eliminated for just about everyone.

The problem with “lite” decompression diving is not carrying enough gas or being able to control buoyancy to some rudimentary degree, but the ability to survive a loss of gas -at the worst possible time.

Once the diver has completed a normal (slow and careful) ascent and has reached the deco stop depth of 10 or so feet, the consequences of (the loss of a gas supply) resulting in the blowing off a minute (or 3) of deco are much less troubling.

If the same thing happens at 125 feet.. The situation is drastically (and obviously) very different.

Since this is the “BASIC SCUBA” section of the forum, I think the weakness in your argument should be explicitly addressed.

 

[Beau640]

Agree agree agree. Like a said a few pages ago some of the replies are nuts. Like I said before, people would be going hog wild if someone advocated for "lite" cave diving. There is no lite deco.

 

[KenGordon]

I find your comments about the dangers of decompression diving to be off the mark. It is surprising to me that a technical dive instructor would promote this kind of attitude (“I don’t worry about it” ) for a recreational dive situation where the diver is accruing 3 minutes of required decompression penalty.

More specifically, you are claiming that should you go a little into deco (without any redundancy which is required by agency standards, it seems), the worst that could happen is that you might run low on air at a shallow stop and have to blow off a minute or so of deco.

The sort of grossly simplistic thinking you put forth is something I would expect from an open water student, not from a tech instructor.

As I have mentioned before, I have no technical training, but it is quite obvious to me that a much, much more serious problem which MIGHT arise on a decompression dive - would occur AT DEPTH not at 10 feet. This is something that I WORRY ABOUT. In other words, the WORST CASE SCENARIO IS NOT A PROBLEM AT 10 FEET!

If a recreational diver (who has entered into the required decompression “zone) is carrying no redundant gas supply (something you have no problem with) and has an air supply failure (at depth) and is unable to secure an alternative breathing gas source, then the only remedy is going to be a rapid ascent – with zero air. The ability to maintain a safe ascent rate of 30 feet per minute (let alone the deco or safety stop) is going to be compromised or eliminated for just about everyone.

The problem with “lite” decompression diving is not carrying enough gas or being able to control buoyancy to some rudimentary degree, but the ability to survive a loss of gas -at the worst possible time.

Once the diver has completed a normal (slow and careful) ascent and has reached the deco stop depth of 10 or so feet, the consequences of (the loss of a gas supply) resulting in the blowing off a minute (or 3) of deco are much less troubling.

If the same thing happens at 125 feet.. The situation is drastically (and obviously) very different.

Since this is the “BASIC SCUBA” section of the forum, I think the weakness in your argument should be explicitly addressed.

I think the importance of being a good buddy and having a good buddy belongs in basic scuba. The buddy is the mitigation for equipment failure at depth whether or not deco is due. Whether you have spent 17 minutes or 21 minutes at 30m a direct out of air rush to the surface is not advised.

Most of what John talked about in his post is not 'real' deco but deco imposed by setting a computer to a quite conservative mode. I think there are different problems with this, knowing when it starts to be 'real' and getting blasé about deco obligations

 

[RainPilot]

If @boulderjohn had had a Zoop on his other wrist, he would not have put it into deco. The question then arises, is this a deco dive or not. In a situation like this it creates a grey area, I personally do not believe that it constituted a deco dive at all but in the case where the same thing happened to me, I chose to obey the Perdix. I was still out before the other divers, who were all in before me, and on their second dive of the day where I was on my first.

To be clear: they were in deeper, earlier, longer than me and had a mandatory safety stop for 3 minutes at 5m but still in NDL on 2nd dive. I had a mandatory 1 min stop at 6m, the other stops all cleared on the ascent well before they were reached. If none of them were in deco then physiologically there is no chance that I was.

I have no problem with John's statements at all.

As a side note, if I choose to use the GF99 feature to control my ascent, is that not using a computer within its design limits? If the GF99 remains below 90-95 (which correlates to some of the more aggressive DC NDL limits) then surely we are never in actual deco and the stops become "stepped safety stops" in effect?

 

[dumpsterDiver]

If @boulderjohn had had a Zoop on his other wrist, he would not have put it into deco. The question then arises, is this a deco dive or not. In a situation like this it creates a grey area, I personally do not believe that it constituted a deco dive at all but in the case where the same thing happened to me, I chose to obey the Perdix. I was still out before the other divers, who were all in before me, and on their second dive of the day where I was on my first.

To be clear: they were in deeper, earlier, longer than me and had a mandatory safety stop for 3 minutes at 5m but still in NDL on 2nd dive. I had a mandatory 1 min stop at 6m, the other stops all cleared on the ascent well before they were reached. If none of them were in deco then physiologically there is no chance that I was.

I have no problem with John's statements at all.

As a side note, if I choose to use the GF99 feature to control my ascent, is that not using a computer within its design limits? If the GF99 remains below 90-95 (which correlates to some of the more aggressive DC NDL limits) then surely we are never in actual deco and the stops become "stepped safety stops" in effect?

Wow another instructor who thinks that the loss of gas at a deco stop is worse than loss of gas on the bottom during a recreational, unplanned deco dive which is conducted without a redundant gas supply.

Have you ever done a CESA with zero air from 100 or 125 feet? Just curious if you have actual experience in something similar.