what is a decompression dive?

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birdwrasse

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i haven't been diving too long, and seem a little foggy on the "decompression dive." i know that recreational diving typically is above 130ft, and as of right now i am not planning to go deeper, but what happens if you do?

other than the amount of air one has to breath, if i go below 130, what happens on my dive computer? does it tell me i've gone too far? i know i can set it to "guage" mode and just follow the numbers...

how do i get to a point where i can learn the skills with a decompression dive?

when i went to catalina a month ago, everything i wanted to see was above 60 ft and from what i hear, same is true for the tropical dives spots like cozumel...

just for clarification.

thanks,


--carlos
 
Any dive where you can't make a slow and safe ascent directly to the surface without stopping is a decompression dive.

From the DAN wesite...Decompression Diving -- Diving exposure requiring staged in-water stops before ascent to the surface.

Are you certified? Do they not teach decompression diving when getting certified??
 
well you have a long way to go before your doing decompression diving if your wanting to learn first you have to go advance open water then you can learn deco. in nitrox and advanced nitrox as well as deep air diving courses when your doing deco.. your in a new feild of diving your in a tech. level there are many types of diving that involve deco. you in cave diving deep air diving as well as many many more things im just having a brain fart to many left over bubbles should have deco.ed longer
 
Hi there Carlos -

I'm somehow not surprised anymore that OW divers don't know what trivial stuff like decompression is.

Deco dives are where your tissues become saturated enough in nitrogen during a dive that you must stop and off gas at a decompression stop before reaching the surface or risk getting bent: you are in effect diving with a ceiling above you. You have to fix all problems that occur while underwater.

Deco dives can occur at any depth below 10 metres: its a factor of pressure and time and theres a thing called dive tables that can help you avoid going into deco.

You can of course get bent when inside your no deco limits.

Once you go into deco on a dive most computers will sound an alert and tell you to ascend to your first deco stop depth and will display how long you must spend there. Some cheap ones just freeze up and say error.

Of course, if you are doing deco dives you should be planning your stops and air consumption (used and reserve) before you get in the water - not just blindly following your computer.

Just setting your computer to gauge and diving below 140, with no knowledge of deco requirements or gas planning, with a single tank on air, is a sure fire way to end up as a statistic.

To learn how to do a deco dive I suggest you get a lot more dives in, do nitrox, rescue and then, when ready, do advanced nitrox and deco procedures. However it sounds like you need to get some more experience first.

Safe diving.
Cheers,
Rohan.
 
Carlos, I am very surprised at your question. You say that you haven't been diving too long. This leads me to think that you've recently completed your open water certification. If that is true, the concept of decompression (especially in the context of how to perform a NO-decompression dive) should really be fresh in your mind.

Knowing how to use dive tables and stay within no-decompression limits is a seriously important part of scuba diving. Without this knowledge, you could really hurt yourself. If you do not remember how to calculate no-decompression limits, PLEASE review this information in your class materials, and go over it with your instructor if you have questions. Take a refresher class if its been a while since your class.

If you have not completed a certification class and are borrowing a friends' equipment to dive, be aware that if you "mess up"…which is very easy to do when doing repetitive diving, you could become seriously injured. You could end up with paralysis or even die from decompression illness.

Please do yourself and your loved ones a huge favour and get properly trained to dive.
 
Every dive is a decompression dive. It just depends how much and how long.

As soon as you 'pressurize' your body underwater Nitrogen begins to be 'compressed' into your body. This means it has to 'decompress' to come out as you relieve the pressure on your body when surfacing. What's important is how much Nitrogen has 'compressed' and how long it will take to 'decompress' without 'fizzing' and forming lots of nasty bubbles in your tissue and blood (imagine a shaken, quickly opened soda bottle)
Normal recreational dives talk about NDLs. Basically these are the time limits that your body can deal with and 'decompress' itself from if you do a normal slow ascent according to what you were taught. If you go past these limits then your body absorbs more Nitrogen than it can safely expel in this way and you need to make special 'decompression' stops to allow your body the time to get rid of the gas without fizzing and forming bubbles (imagine opening the soda bottle VERY slowly so that the pressure escapes but WITHOUT any bubbles forming - you have to do that very slowly right?)
It's all simply a question of degree - all dives make you absorb gas and then lose it again, it's just a question of whether that process is built into the dive so you don't really have to think about it, or whether you need to know it and plan the extra stops.
 
Anytime you descend to increased pressures breathing gas mixtures that contain inert gasses like nitrogen or helium your tissues will absorb increased levels of those gasses and will offgas on ascent. So...any dive is a decompression dive unless you find some way to keep that gas that has escaped the rest of us.

We need to do a slow enough ascent that allows that gas to be given back at a rate that won't damage our body. At low levels of absorbtion, a normal ascent works. At greater levels we have to be more deliberate about the ascent and spend more time at it.

Depth and time, as well as the mix being used (the partial pressure of the inert gas) combine to determine the theoretical amount of absorbtion so you don't have to ge below 130 to get in a situation where you are must stage your ascent.
 
All dives are decompression dives. I think you are referring to the types of dives where you overstay recreational dive limits. But even staying within recreational limits you still decompress...You are off gassing nitrogen. You can stay within the dive table limits, but if you shoot to the surface instead of ascending at 30...some still say 60 ft/minute you still risk getting bent because you did not allow enough time for off gassing. Anytime you are under pressure you are compressing. When you ascend you are decompressing. During this time you have to allow the nitrogen time to come out of solution at a safe rate, otherwise you become a shaken up soda bottle. Beyond the recreational limits, as I think you are talking about, it's a matter of additional time you have to stay at certain depths to allow for the nitrogen to come out of solution. But that is all about time. All dives are deco dives. I would'nt suggest using gauge mode on your computer. It basically becomes a bottom timer in that mode.
 
This is all true... My instructor taught the principles of Deco Diving in my OW class, he went over the basics and why certain things must be done. Most realistic (and worthy) dive computers will go into Deco mode if the NDL is exceeded. However, I don't think that most rec dive computers are meant to be used as Deco computers, rather they merely are able to calculate the correct deco procedure (ceiling, time, etc) to get you back to the surface safely. My Suunto Mosquito will enter deco mode when the NDL is exceeded---beep and flash---tell me what depth to ascend to immediately, how long to stay there, then the next highest depth, how long etc. Once you surface, I think the mosquito makes you do a 12 hour surface interval before it will turn itself back on again--just as a precaution (I THINK).
 
rocketry:
Once you surface, I think the mosquito makes you do a 12 hour surface interval before it will turn itself back on again--just as a precaution (I THINK).
I'm also not sure but I've also heard similar stuff about Suuntos (I have a Vyper). I only ever pushed it into a couple of minutes deco on a last dive of the day once. The next morning it was fine - I've got no idea if it would have let me do a night dive the evening before! :D
Actually - first it showed me a couple of minutes deco but by the time I'd (slowly) ascended to my ceiling it immediately cleared. It was all very 'on the edge'.
 
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