Question about deco stops when diving with air.

[Red Sea Shadow]

From now on, I want to learn how to calculate deco stops when diving with air on my own. How can I learn that? Do you know a site or book teaching about that? I want to know about that.

Deco diving needs hands-on training. Sites and books are not enough. And since you're new to this subject, sites are not recommended; a lot of misleading information.

 

[Red Sea Shadow]

I thought that you tech guys can help me out about planing the decompression stops when diving with air. I want to be extra safe in case of a compulsory deco stop. I like diving but do not want to die or become paralysed because of the decompression sickness. I want to know the rules firmly about the deco stops.

Then go for a Deco Proc course.

 

[boulderjohn]

The fact that you were "frightened" because you were 1 minute away from your NDL means that you were already diving beyond your limits.

While Lamont is certainly correct, the problem is amazingly common among divers. And by "the problem," I probably mean a couple of things.

Several years ago I was diving in the Galapagos with a buddy who was part of our group that made the trip together. I had never met him before the trip. He had logged hundreds of dives over a number of years of active diving in many places. During one dive while we were perhaps at 80 feet, he suddenly started heading hurriedly toward the surface. I followed, of course. When we were at about 25 feet I caught him and gave him a "What's up?" signal. With a look of near terror on his face, he showed me his computer (a Suunto). I stared at it for a while, seeing absolutely nothing problematic. I gave him a puzzled look and a "so what"" shrug. He almost shoved it in my face in response, and I returned the "I have no idea what the problem is" response, followed by a "can we get back to the dive?" gesture.

When we were back on the boat, he said excitedly, "I almost went into deco on that dive!" He explained that when he was at the depth at which he started his flight to the surface, he had seen that the computer was only giving him 3 minutes of no decompression diving, and he knew it would take him at least that long to get to the surface. When he showed me the computer in shallow water, he assumed I would see the NDL violation and be horrified. What I saw, of course, was that the computer had changed to giving him plenty of time due to his ascent. According to the computer, he still had quite a bit of pleasant diving time ahead of him.

I tried to explain it to him, but he would not listen. He just kept babbling--to everyone who would listen--about how he had narrowly missed going into deco.

I felt like slapping him across the face a few times to snap him out of it. I came close to that actually, although verbally.

Let me repeat what I said earlier. This man had logged hundreds of dives over a number of years. He had owned that computer for years.

Anyone who is that serious about diving needs to understand deco theory better than that, and if they are going to use a computer, they need to know how it works. I certainly hope all my newly minted OW students know more than that.

 

[AndyNZ]

While Lamont is certainly correct, the problem is amazingly common among divers. And by "the problem," I probably mean a couple of things.

Agreed.

On some courses that I teach, I will encourage students to put there computer into deco so they can see what it tells them and to ensure that they recognise it. That always comes with a caveat of do it on a dive where you have loads of gas, it's good conditions and do it as a group and look out for each other.

The first time to find out that you don't understand what your computer tells you to do is not when you really need to!

It's interesting in your example, John, that just a couple of signals would really help the communication. I always teach the "deco" signal and how it can be used....

 

[F106A]

I am a PADI OW diver. ... PADI OW divers do no deco dives. I have 55 ... dives.
...I was watching my buddy ... at around 125 fsw. ... he ... has 25 logged dives, went deeper ... I descended ... with him because he does not own a dive computer and was really careless about deco limits. We stopped around 125'. I forgot to check my dive computer for a while and was watching my buddy. .... Some time later I checked my computer and my eyes wide opened because we had 1 more minute to deco. I was really frightened and immediately warned my buddy and we started to ascend (and didn't) enter deco. Maybe I prevented something bad? I do not know ....
I do not know what to do ....

impulse,
What I'm writing will sound like a flame but that isn't the intent.
You sound like you're clueless. You have a healthy respect for DCS yet you went fairly deep without monitoring your instruments. You descended to your deeper buddy because, 1. "...he does not own a dive computer ..." Computer 101 stresses "no shared computers" in part because you may be at different depths for different times. So where is the logic in your, uh, logic? 2. "...he does not own a dive computer...." You do, why not use it as intended? 3. "(He)was really careless about deco limits." I suggest that maybe you were, too.

To quote Emil Faber: "Knowledge Is Good." And wanting to get educated about deco diving is good and can be an asset. But, if you're unaware/unconscious of your current status on a dive what makes you think you can offset it by possibly having a set of rules to implement and apply when the s--- hits the fan. Deco diving isn't a "I blew my NDL so I'll plug in my obligation numbers," but a fairly precisely planned dive.

Rather than look for advanced training (at the present), concentrate on doing your simple dives properly. If you're behind the power curve on the easy stuff you might not be able to handle the trickier stuff. Master the basics, build a solid skills foundation, then press on. HTH.
P.S. The other posters have made some good comments.

 

[Rhone Man]

The first time to find out that you don't understand what your computer tells you to do is not when you really need to!

In Mike Ange's book, Diver Down, there is a good story about a diver who puts his computer into deco for the first time, and it flashes a down arrow as the symbol for being in deco. In his narc'ed state, he assumes this means he has to go further down.

As Andy said, this is not an aspect of your computer you want to learn about on the fly (whilst narc'ed, or otherwise).

 

[TSandM]

In my OW class, I was taught, "Do not go into deco, and do not go into overhead environments." I came away with the idea that both were equally dangerous. They aren't.

You shouldn't go into deco, but what's REALLY important is not to panic if you do. It's a fixable situation. You do the time. If you don't have the gas to do the time, you surface and go on O2 and hope like hell you don't pay a price for what you did. If you are even halfway monitoring your status, you shouldn't have more than a minute or two or deco that you didn't do, and most likely, you'll be okay. I don't say this to condone going into deco. It's a bad idea. But far worse than being a minute over NDLs is panicking as a result and bolting for the surface.

Prevention is by far and away the better part of treatment; know before you go down what your expected bottom time at the proposed depth is, and then monitor your gauges to watch for that. But above all, if you are one minute into "deco", don't panic and bolt. Panic kills; deco is just more time you have to spend in the water, and if you have the gas to do it, it's not a horrible thing. On one of my staged decompression dives in the Red Sea, we did 20 minutes more deco than we needed to do, because we were twenty minutes from the boat, at 20 feet, and the reef was pretty . . . Where deco becomes frightening is if you don't have the gas to do it, or if your buddy doesn't have the gas to do it, which is why it's so strongly advised against for recreational dviers who are not given any tools with which to evaluate whether they have the gas to do some underwater stop time or not.

 

[Matt S.]

To the OP:

I won't bother to repeat what everyone else has said about dive planning and watching your instruments.

I will tell you what you might expect if you do go over your NDL by a tiny bit. I have exceeded my NDL by about one minute on two occasions. I was not worried, because I was with good buddies, had good communication with them, and we all had a ton of air left. On each occasion, I saw what was (possibly) coming a few minutes ahead of time, and just told my buddies, "hey, let's get moving, I am not diving nitrox doubles like you guys and it's time for me to turn around."

So what happens when you blow your NDL by about 1 minute at about 100 feet? Well, my computer tells me that I need to make a mandatory stop at 10 feet for about 1 minute... and the obligation had cleared long before I even got to 10 feet.

I don't intend to make a habit of exceeding NDL. Instead of exceeding NDL by one minute it would have been far better to be 1 minute more proactive in turning the dive! But it is important to know that a minor NDL violation won't turn in to a pumpkin. Do not be the diver boulderjohn was talking about and bolt for the surface. If you exceed your NDL by a minute, the computer is not going to order you to spend an extra twenty minutes under water.

See if your computer has a simulation mode, so you can run scenarios and see what to expect ahead of time. And be sure you understand how to read what the computer is telling you in the event you do need deco time.

 

[impulse]

Ok people, thanks for all the great information you provided and the detailed interpretation of my situation. What this topic taught me is that, I must take a class about decompression. This will be the wise decision. I know that intrusion of the NDL must be avoided but could happen forcedly or mistakenly. I know that a diver must not be forgetful but be awake and watch the insturments. But we are all humans and could somehow make a mistake or forget something to check. So I believe knowing more than you really need will always help when you are in a trouble. I believe it's valid about every aspect of life. Knowledge is always the power.

In my situation, I maybe narc'd maybe not yet I was in that situation and it could be worse. During when I was there, I really thought, oh god why I did not learn firmly about the deco rules in the first place.

Maybe carrying a small deco gas tank like nitrox must be obligatory for every diver. But I think this would change all the diving rules. Just a thought. May help to avoid health issues before they show up.

 

[Bubbletrubble]

Ok people, thanks for all the great information you provided and the detailed interpretation of my situation. What this topic taught me is that, I must take a class about decompression. This will be the wise decision. I know that intrusion of the NDL must be avoided but could happen forcedly or mistakenly. I know that a diver must not be forgetful but be awake and watch the insturments. But we are all humans and could somehow make a mistake or forget something to check. So I believe knowing more than you really need will always help when you are in a trouble. I believe it's valid about every aspect of life. Knowledge is always the power.

Yes, it sounds like a deco class might be helpful in your case. FWIW, I don't think taking a deco class is a quick-fix for being vigilant about checking depth and remaining gas pressure. Regardless of training level or experience, a diver should always know that critical information. I'm a recreational diver (no decompression dives) and in over 300+ dives, I can honestly say that I have never been surprised by my gauge readings. If I change depth during any phase of the dive, I check my depth gauge/computer. Every few minutes, I'll check my SPG. Alternatively, I'll feel for the stiffness of the HP hose (don't try this with the newer Miflex hoses). If I feel that I'm working harder than normal in the water, then I'll check my SPG more frequently. I also maintain my gear properly and do comprehensive pre-dive checks. On several occasions during a dive, when I look at my buddy, I make a cursory scan for any unusual bubbling that's coming off of his/her rig. My buddy does the same for me.

Maybe carrying a small deco gas tank like nitrox must be obligatory for every diver. But I think this would change all the diving rules. Just a thought. May help to avoid health issues before they show up.

Of all the reasons to carry a "small deco gas tank," avoiding "health issues before they show up" is not one of them. Check your gauges often. If this doesn't come "naturally" to you, train yourself to do it. If you have been trained to dive with a buddy, make sure that's exactly what you're doing. Always know where your buddy is because, after all, your buddy has your redundant gas source strapped to his back.

Have fun out there...and be safe.