Question about deco stops when diving with air.

[impulse]

Hello,

I am a PADI OW diver. And as you all know PADI OW divers do no deco dives. I have 55 logged dives.

During my last dive 5 days ago, I was watching my buddy taking photos at around 125 fsw. He was really bussy with taking photos. With the passion of taking photos, he, who has 25 logged dives, went deeper chasing a damn fish and I descended togather with him because he does not own a dive computer and was really careless about deco limits, we stopped at around 125 fsw, all the people in our group were at least around 16 fsw shallower, and they were watching a damn baracuda shoal. I forgot to check my dive computer for a while and was watching my buddy. The leader was watching us. Some time later I checked my computer and my eyes wide oppened becasue we had 1 more minute to enter deco. I really frightened and immediately warned my buddy and we started to ascend and the no deco time started to increase so we escaped from entering into deco. Maybe I prevented something bad? I do not know because I am not taught about how the decompression stops must done.

I do not know what to do If we entered into deco? Where to stop? Are the rgbm algorithm computers reliable about calculating deco stops?

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.

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.

Thank you.

 

[Rhone Man]

People vastly more experienced than me will come along soon to give their advice, but I will throw in my 2 PSI:

• Prevention is better than cure - if you keep an eye on your computer, and stay within your NDLs, you won't have a problem
• If you do exceed your NDL, don't panic. Your computer will tell you how high you can safely ascend to, and how long you need to stay there before you can surface (if your computer dies, go to 15' and sit there until you exhaust your gas supplies).
• Appreciate however, that you are not equipped for this, so abort the dive as soon as you become aware of the situation and go to that ceiling - don't hang around making it worse (but make sure you ascend at a safe pace - don't bolt).
• Non-technical divers often assume that decompression stops are some special skill (at least, I used to). All it really involves is hanging at a certain depth until the level of nitrogen (or other gases) dissolved in your tissues are low enough to ascend further.
• What technical divers spend much more time focusing on during their training is planning their gas consumption. Any idiot can sit at 15' waiting to ascend. What you train and plan for carefully is to make sure you are not sitting at 15' (or deeper) and you don't have enough gas to finish your stops.
• If it all goes really, really badly wrong and you have to go to the surface whilst your computer still shows you in deco - still don't panic. Firstly, you may not get a DCS hit at all - computers are just relying on algorithms. Secondly, if you do get a hit, it will rarely manifest itself immediately - 58% of symptoms take at least one hour, and sometimes as many as eight to manifest. You usually have time to get yourself onto oxyen and work out treatment options.

Hope that is useful. Lot's of people remonstrate about the folly of exceeding NDLs, but I suspect it actually happens more frequently than people admit. It certainly happened to me once or twice before I did any technical training.

 

[boulderjohn]

Good questions, and it is good to start learning about this.

First of all, there is absolutely no reason to panic being a minute from deco or a minute over deco. It can all be handled safely and relaitively easily--if you know what to do.

Your PADI OW class told you what to do in case you make such an error--the details are written on the back of your RDP. There are other ways that will get you back in the water sooner, though.

If you have a typical recreational dive computer, it will tell you what to do. The problem is that you have to know what it is telling you. The computer can give you all the details you need, but it won't help if you don't know what it is telling you. Get your manual out and read it carefully!

If you go a few minutes into deco, the computer will let you know in some way that you have a deco obligation. In that time frame, the deco obligation will probably be an extended safety stop at the normal safety stop depth. It will tell you when you are done. If you are only a minute or two over, it might not be much at all. When you surface, it will make you take a longer surface interval than normal.

If you violate your NDL by a more significant amount, it will make you stop for a while at a shallower depth. In some computers, it will indicate that you have a CEILING, a depth at which you should stay until it tells you to ascend again.

These features of your computer are designed to help you in case you violate NDLs in error. They are not intended for planned decompression diving. Some computers will work for planned decompression, but they should not be seen as a substitute for training in decompression theory. You should know how to plan decompression dives without a computer before you use one for that purpose. If you want to do decompression diving intentionally, take a class.

 

[rjack321]

Stay within no deco limits unless properly trained and equipped - the internets does not count.
Pay more attention to your gas and computer.
Avoid significant narcosis, your perceptions were narrowed to the point where you lost track of many issues on this dive. Do shallower dives, build experience slower.
Find a buddy with a better attitude.

 

[impulse]

Thanks for your answers. I know I must stay in no deco limits but you know knowladge is the most powerful friend. If I dive, I want to learn all the rules about that. Can you suggest me a book about the decopression theory? Taking a class about decompression diving is a smart decision. But before I take a class I would like to read a book about that.

 

[boulderjohn]

Thanks for your answers. I know I must stay in no deco limits but you know knowladge is the most powerful friend. If I dive, I want to learn all the rules about that. Can you suggest me a book about the decopression theory? Taking a class about decompression diving is a smart decision. But before I take a class I would like to read a book about that.

Deco for Divers, by Mark Powell.

 

[Web Monkey]

During my last dive 5 days ago, I was watching my buddy taking photos at around 125 fsw. He was really bussy with taking photos. With the passion of taking photos, he, who has 25 logged dives, went deeper chasing a damn fish and I descended togather with him because he does not own a dive computer and was really careless about deco limits, we stopped at around 125 fsw, all the people in our group were at least around 16 fsw shallower, and they were watching a damn baracuda shoal. I forgot to check my dive computer for a while and was watching my buddy. The leader was watching us. Some time later I checked my computer and my eyes wide oppened becasue we had 1 more minute to enter deco.

Decompression is "fuzzy" and depends on a lot of factors, including your personal physiology.

• Just because you're a few minutes into deco doesn't mean you're going to get bent, and
• Just because you're a few minutes under the no-deco limit doesn't mean you won't.

If you learn how to read your computer and pay attention to it, you'll probably be just fine.

Your buddy, however who not only doesn't use a computer, but apparently doesn't use a depth gauge, watch or tables either is just begging Darwin to come get him.

Terry

 

[TSandM]

The most important thing is to realize that there is no "bright line" where you are safe, and then you are not. Decompression programs draw a line and call that "no deco", but all dives are really decompression dives, in that you have to release some of the absorbed nitrogen before you can surface. In "no deco" diving, that release is accomplished by controlling the ascent rate. At some point, you have absorbed enough nitrogen that it is no longer safe (within whatever parameters the model uses) to proceed directly to the surface, and the ascent has to be prolonged further. At this point, you have to stop in the water where there is still enough pressure to keep nitrogen in solution, and allow it to leave your body before you reduce the pressure any more.

You should know that different computers will come up with different no-deco limits for a given depth, and they can vary by as much as ten minutes in some cases. Thus, that "going into deco" that you had on your computer might still be considered a no-deco dive by another. I am not saying this to tell you it's okay to overstay your limits. I am saying it to make sure that you understand that approaching your NDL limit means you need to do something constructive about your situation, but it is NOT an emergency. As you found, going shallower can rapidly give you a bit more time (although it's not advisable to continue to ascend bit by bit, as the computer counts down -- this is called "riding the computer" and is a good way to increase your DCS risk).

As already said, if you do go over the limit, your computer will have some mechanism for letting you know, and telling you what it expects you to do at that point. As John says, for very small NDL violations, it's usually a longer shallow stop -- and small NDL violations should be all you EVER have, or you are simply not paying enough attention to your gauges.

Above all, plan your gas consumption to allow reserves for emergencies. If you subscribe to the rock bottom strategy, you will have enough gas to do a prolonged shallow stop if one is required. As a wise instructor of mine told me, "You can fix bent, but you can't fix dead." The biggest lesson technical divers learn is to plan their gas so that they have enough for significant contingencies. You do not want to be trapped in the water by your decompression status, and watching your SPG tick down to zero!

You are certainly not the only person who has stayed at depth until they were "almost" in deco. I've done it myself. It's not always inattention, although it sounds as though that (and narcosis) played a role here. But things are okay if you pay attention, move shallower when you need to, and remain calm about the whole thing.

The Powell book is an excellent read. Better understanding of nitrogen dynamics leads to better choices.

 

[AndyNZ]

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.

Firstly, as John has pointed out.... deco isn't really something to be afraid of, it's just something that you have to learn to manage.

The problem with your thinking, though, is that doing dives that involve decompression stops is not just about knowledge. No offence intended to you, but typically a PADI OW diver is not going to have those skills to do decompression dives safely. You've got a few intermediate steps to think about, rather than just learning how to calculate stops.

Knowing the stops is one thing, being able to complete the schedule to the plan is another. How well can you hold your buoyancy? To my mind, you need to be able to hold a stop depth +/- 0.5m to be thinking about deco.

You also need to think about your gas, how much gas does it take? Deco on air sucks, it just takes too long - which means you need a lot of gas. It's real easy to rack up more deco than you have the gas to do without realising it if you don't plan your dive properly.

And what happens if the person you are diving with loses some of the their gas supply - either breathing too much or from failure? You need to be able to share gas whilst hitting your deco stops and holding them precisely.

Find a buddy with a better attitude.

Amen.

 

[lamont]

Some time later I checked my computer and my eyes wide oppened becasue we had 1 more minute to enter deco. I really frightened and immediately warned my buddy and we started to ascend and the no deco time started to increase so we escaped from entering into deco. Maybe I prevented something bad? I do not know because I am not taught about how the decompression stops must done.

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

Part of the problems is likely that you were narc'd enough for it to affect you emotionally, even though you might swear up and down that you "don't get narcd", which is one of the dangerous of newer divers diving to 100-125 feet. You are narc'd and one of the ways that it will affect you is that if the dive starts going sideways, you'll start getting into a panic (some of this is due to increased CO2 under stress which amplifies the narcosis, causing more stress, shallower respiration, and then more CO2 in a positive feedback cycle).

You should seriously think about backing off to dives above 100 feet until you get a bit more experience, and should shorten your bottom times at depth.

...

Having said that, the biggest issues that you're going to have with a little bit of deco as a recreational diver:

#1: At that depth, after long enough to rack up a deco obligation you probably have very little gas left. You need to be able to leave depth promptly and get to shallower depths promptly -- but *promptly* does *not* mean in a panic and blowing to the surface accidentally. You need to be able to leave in control. But you have to be able to promptly put the brakes on the gas consumption and decompression clocks.

#2: You need to be able to hold a stop, in open water, without a line for reference or stability and hold buoyancy at least at 15 feet +/- 5 feet (10-20 feet). If you successfully leave the bottom with a decompression obligation only to blow up to the surface without being able to hold a stop then you've put yourself at an elevated risk of DCS. Keep in mind, however, that on a recreational profile blowing off a couple minutes of deco accidentally is unlikely to kill or paralyze you. You'll most likely just feel like crap. If its clinicially significant you might get shoulder pains or skin bends or some other symptoms which might lead to a chamber ride, but you'll likely recover. So, if you do blow off deco, you need to be mentally prepared not to panic and to simply watch your symptoms on the surface and call the chamber for a ride if symptoms develop. A panic attempt to complete missed deco can lead to a ballistic ascent back down to the bottom attempting "IWR" and drowning or shunting of bubbles and a type 2 DCS hit. Do not attempt IWR as a recreational diver. Ever.

#3: You need to be able to manage your gas. One thing to realize is that even if you've got 20 minutes of deco to do at ~15 feet that its very little gas that you need, so you can do quite a bit of deco (and it doesn't hurt to do a little extra deco on a regular basis anyway -- for practice track how much gas you use during a 5 minute stop). However, you need to have that deco reserved, and you need to not put yourself into a position where you don't even have that much gas, and you need to be able to do an ascent quickly enough to leave yourself with enough gas for the decompression. If you're diving with a buddy who is also in deco, they're also probably low on gas as well, and you might need 2x the gas for them. Also, keep in mind that SPGs are unreliable near zero psi, and i own an SPG which reads 250psi on dry tanks. one of the reasons why you're supposed to be "back on the boat with 500 psi" is that you can't rely on the last 500 psi on your gauge actually be there.

#4: You need to be able to complete a gas share at your stop depth, with no line for reference without blowing off to the surface. Your buddy may run out of gas, and you need to be able to donate, and vice versa, even under the worst cirumstances.

So, all you need to be able to do is leave depth promptly, ascend to your stop depth and not drown, run out of gas or blowoff to the surface accidentally in the process. It is harder than it sounds though.

And clearly get a new buddy.