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Decompression Diving Explained

Table of Contents

Sidemount and diving with twin tanks are gaining popularity.

This leads to longer dives and you will have to be careful about your No Decompression Limits (NDLs).

Most people are recreational divers and try not to go beyond their No Decompression Limits, but if something was to happen they still may go into “deco”.

On the other hand, tech divers go into “deco” on purpose as they go to greater depths and stay down longer than the average recreational diver.

Decompression Diving

No Decompression Limits (NDL)

In your Open Water Diver course, you should have learned about No Decompression Limit diving and why we do a safety stop at 15 feet (5M) for 3 to 5 minutes.

This is extra safety and is not technically required. The NDL is the amount of time you can stay underwater and get back to the surface without performing any decompression stops.

What is Decompression Diving?

Decompression diving (also called deco diving) means that you will intentionally go beyond your No Decompression Limits (NDLs) to have a longer bottom time at a certain depth. The way you could go into deco can vary.

You could spend an hour at 100 feet (30M) in a cave or 25 minutes at 148 feet (45M) waiting for thresher sharks. While you can go into deco and then do stops at certain depths as you return to the surface to “off gas” there are mental, physical, and logistical reasons why you would not spend 2 hours off-gassing.

When you go beyond your dive computer’s NDLs it opens up a lot more options on the different types of dives you can do.

You have the freedom to do more on a dive. Decompression dives that exceed the NDL will require a series of stops before you reach the surface. This will require additional training and courses for you to learn how to safely perform decompression dives.

What is a Decompression Stop?

When you dive you build up nitrogen. During a decompression dive, you build up an excessive amount of nitrogen, and it is no longer safe to ascend directly to the surface at any point during the dive.

You will need to give the body time to release the excess nitrogen from the body so you do not get decompression sickness.  

These are just like your safety stop in recreational diving. There are usually multiple decompression stops that may need to be completed at different depths for different amounts of time. 

Is There a Difference Between a Safety Stop and Decompression stop?

Yes, there is a large difference. A safety stop is recommended on dives but is not required to be completed, where a decompression stop must be performed.

If an emergency situation such as a free-flowing regulator and can’t be turned off, it may require an ascent directly to the surface.

If this is during a dive during an NDL dive in theory it is safe to do so without a safety stop. If that was a decompression dive you would have to share air with your buddy and wait.

All recreational dives are considered no-stop dives as you do not need to stop on your ascent.

When do I Need to do a Decompression Stop?

In most open water courses it is not even required any more for you to be able to do the math for a Recreational Dive Planner (RDP).

I always teach it if I have time as I think it is important in understanding what is said on your dive computer. Your dive computer will automatically calculate the no-decompression limit for you based on the current dive and all the dives you have done recently.

The more you are diving, the shallower the less bottom time you will have before you exceed your NDL.

A decompression stop must be completed any time a diver exceeds an NDL, whether it is on purpose or not.

How to Calculate Decompression Stops

If you are planning a dive that will make you go into deco, it is very important that your decompression stops are calculated, to make sure it is a safe dive.

There are too many variables and factors for me to be able to give you an exact way to calculate your deco stops by hand.

For example, the type of gas used (nitrox, helium, etc.) the length of the dive, the water temperature, the depth you are going and staying at, and your previous dives will affect the depth of each deco stop and the length.

Get a good dive computer that can calculate the deco stops for you and do the math on the fly in case something goes awry and you can follow your plan. A favorite of tech divers is the Shearwater, I am not a tech diver but have gone into deco before.

I use Suunto and that has never given me any issues. There are a lot of dive computers out there, make sure you get one that is trustworthy and test it before every dive.

I have made a table for you based on the recreational dive planner for an example but each dive computer will have algorithms they use and each company uses a slightly different one. They are all safe though and are quite conservative by tech diver standards.

Exceeded the No Decompression Limits by

Minimum Decompression Stop Time at 15 feet (5M)

Wait Time Before Your next dive

Less than 5 Minutes

8 Minutes

6 Hours

More than 5 Minutes

15 Minutes

24 Hours

What Happens if a Diver Doesn’t do a Decompression Stop?

If you do not decompress it can lead to decompression illness (DCI). There are a lot of symptoms that can be seen if a person is thought to have a DCI.

As you go to the surface even if ascending slowly, the body does not have enough time to release all the excess nitrogen.

This could cause bubbles to form in the blood and depending on where the bubbles form it can cause different issues.

Symptoms of DCI

These are the main symptoms of DCI but it is not limited to these:

  • Headache
  • Nausea
  • Fatigue
  • Rashes
  • Vomiting
  • Pain in the Chest
  • Issues Breathing
  • Unconsciousness
  • Joint Pain
  • Paralysis
  • Death

This is a scary list of symptoms, so plan your dive and try not to come up until you have gotten rid of the excess nitrogen. In the event you do have to come up to the surface quickly, with recognition of these symptoms and getting pure O2 is crucial. After that getting medical assistance and going to a chamber as fast as you will be key. Don’t push your limits, wear a dive computer and follow what it says.

What do Divers do During Decompression Stop?

I have only done a few of these for no longer than 10 minutes and it go boring. I was in open water and there is nothing to do besides practice your bubble rings (if you have ample air).

But I know some people diving to the bottom of the Blue Hole in Dahab, Egypt which is over 300 feet (92M). Some of these dives have decompression stops that take hours to complete.

Divers can play word games, tic-tack-toe, and hangman on their dive slates. If you have
Shearwater or another higher-end dive computer you can put on games on it. They also now have ones that can play podcasts or audiobooks.

If you are at a dive location that has shallow water, a deco stop can be a great time to look for macro in the muck. I also like to practice my bouncy skills and play games like passing a weight with your fins, or other fun skills.

Should I do Decompression Dives?

Decompression Diving

This is something you just do, you need training and should plan these dives out. If you are trained and capable then I see no problem with why you shouldn’t do them.

Deco diving is not inherently dangerous unless you have an underlying condition or don’t follow the guidelines.

If you do go into deco, and it happens by accident don’t freak out, it is ok, stay calm and follow your dive computer’s instructions.

How Deep Can I Dive Without Going Into Deco?

The recommended maximum depth for recreational diving is 130 feet (40M). This depth is the advanced open water course and the deep dive specialty.  If you stay within this range and follow your computer you should not have to make a deco stop. 

Training for Decompression Diving

Take a course, I am an instructor but still have done the side mount course and learned from other professionals that are experienced in this area.

It is not something to play around with.

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    My name’s Austin Tuwiner, a PADI Divemaster based in South Florida. With nearly 10 years of diving under my belt, I’ve accumulated the knowledge to help readers become better divers, buy their next piece of gear, and plan their dream dive vacation!

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