What is a Decompression Dive? Deco Diving Guide

Last Updated: February 8, 2023

For most recreational divers, going about 30 meters down is the most anyone can tolerate, but sometimes people want to go even deeper than that. For this, a decompression dive will be necessary. A decompression dive is a technical diving technique that requires training and precise planning.

While the following discusses the overall basics of a decompression dive, it is advisable to undertake professional training courses. Regardless, this is a fascinating process and important to familiarize yourself with if you are thinking about doing it.

What Does it Mean to Decompress when Diving?

In laymen’s terms, a decompression dive, also called a deco dive, is a technical dive performed by experts trained in being able to withstand depths of more than 40 meters. 40 meters is the maximum limit a normal person can go into the water, otherwise called the No Decompression Limit (NDL).

Therefore, this is a planned submersion into water with the intention and knowledge of exceeding the NDL in a safe and smart way. This is because the design of the human body doesn’t have the capacity to handle the pressure and lack of oxygen inherent in deep sea waters.

Deep Water Diving Arrangements

But people can do such dives when they undertake the correct measures in safety for the best experience possible. Such dives can involve all kinds of unusual underwater adventures. For instance, this could involve spending an hour at 30 meters (100 feet) or even 20 minutes at 50 meters (90 feet).

The Human Body when Deco Diving

When the human body goes into deeper waters, it releases and absorbs gasses due to an increase or decrease in pressure from the changes in depth. The deeper into the water, the quicker the body absorbs gasses. So, these must release before coming back up.

Without preparation and training, an average human runs into serious physiological and health risks. Failing to decompress can result in Decompression Injury (DCI). This happens because there’s far too much nitrogen left in the body.

When there’s an excess of nitrogen, it can cause bubbles to develop in the blood stream as well as in other body areas. In many cases, these bubbles can block the flow of blood. The ensuing symptoms can include:

How to Plan a Decompression Dive

The best and most effective way to avoid potential issues is to create and follow a dive plan. But, there can never be enough emphasis on the fact that you should complete certified training at a qualified facility. Here, they’ll give you all the information you need to accurately plan a deco dive and execute it safely.

Depth Will Determine Gas Required

The first thing you have to think about is how deep you want to dive into the water. Knowing this will help determine the kind of gas you’re going to need for a re-breather. This is the device deep divers carry on their back with a mouthpiece that they use to intake artificial air.

In many cases, you’ll need Nitrox but you may also need Trimix. Both of these simulate atmospheric air that we breathe on dry land. Nitrox is the typical mix of nitrogen and oxygen, appropriate for many deep diving situations.

But, diving beyond 60 meters may mean you should use Trimix. This will blend helium into the mix of oxygen and nitrogen which lowers the narcotic effects that can occur with Nitrox. Recreational dives usually use only oxygen to simulate atmospheric air.

Time Determines Amount of Gas Needed

Then there’s the question of how long you want to spend underwater at your determined depth. This will be a major factor in how much time you will need to decompress before you can come back to the surface as well as how fast you can go into the depths of the water.

The depth and length of time will then determine how much gas you will consume from the tank for the duration of the dive. Plus, you should devise a contingency plan. So, ensure you have more than enough for the duration of the journey. This will come in handy in case any unforeseen events should happen.

Other Pertinent Calculations

Planning a dive involves using decompression theory and applying it to calculations before you go diving. This is because there is a limit to how deep can someone dive before they can come straight back to the surface.

This means dives beyond 40 meters will have to have certain stops, called decompression stops, on the way down and coming back up. These decompression stops will be more important for returning to the surface, indicating the speed and time it should take.

Using Modern Tech

Doing such a thing will help acclimate the body to the experience of ocean pressure in relationship to breathing artificial oxygen and nitrogen. You can calculate your personal limits manually or you can use modern technology. There are a host of dive computers and watches, calculators and other gadgets that makes planning easier, faster and more accurate.

A digitized meter you sync with your personal computer is the most advisable. But there are many devices and computer applications that help with planning and executing various types of decompression dives. These should be able to give real-time readings during the dive.

They will indicate things like how much gas you’ve used, how long you’ve been in the water, how far down you’ve gone and how much time you should take to return to the surface. Later, you’ll be able to compare your planning calculations with what actually occurred. This will provide for even more accurate results the next time you want to dive.

Decompression Stops

The largest and most important aspect to planning a deep dive is the decompression stops. When someone goes underwater, there’s an excess amount of nitrogen that gets accumulated. This means it’s dangerous to directly ascend during any point of the dive.

The body must have time to release the excess nitrogen in order to prevent sickness. Decompression stops are something akin to safety stops done during regular recreational dives. However, safety stops are for emergencies and executed only once prior to coming back to the surface.

Various Depths Will Have Different Stops

For decompression stops, various depths will require a certain number of stops before coming back up. As a general rule, the deeper you are, the longer it will take to come back to the surface because the number of stops you’ll have to make along the way will also increase.

At What Depth Do You Decompress?

There are many factors involved with calculating the depths at which to decompress. This is why using technology and taking a certification training program are essential.

As with a recreational dive’s safety stop before resurfacing, there is one with deeper dives as well.

The first stop occurs at the halfway point on the way to the surface. So, if someone dives 40 meters, the first decompression depth will be at 20 meters. How many stops occur after this will depend on the diver, their endurance, strength and experience.

You can use the Recreational Dive Planner (see example below) to calculate the no-decompression limit. A deco stop must be completed any time NDL is exeeded, whether planned or not.

Beginners versus Experienced Divers

Beginners should do a stop about every 10 meters on their way back up. But, more seasoned divers can clear the distance, stopping short at five meters. These stops are only for a minute or two. But they add safety and acclimatization.

However, there are some depths that will require hours of decompression time before a person can return to the surface. This will be especially true if a diver spends a considerable amount of time under the water. So, another aspect to the decompression stop is the amount of time required to decompress before coming up to the surface.

Due to a number of variables, such as the type of gas used (pure O2, nitrox, helium), the length and depth of the deco stop can be different on each dive. Diving computers are a great help in calculating and planning deco stops.

Dive Tables & Computerized Aids

There are dive tables available. However, it’s better to use a dive computer for these calculations. While the tables are a good guide, they are not foolproof. The training school should provide these tables. While taking the classes, they will instruct you on how to exactly calculate the proper stops.

Final Thoughts

Nothing displays the wonder and beauty of the earth like experiencing deep sea diving. It allows us to see things beyond what we can view on the surface of the water.

Planned deco diving allows for almost any underwater purpose. It’s useful for exploring old shipwrecks, examining sunken archaeology or studying fish. While the human body can only handle about 40 meters deep into the sea, it is possible to go much deeper than that.

But, no one should attempt decompression diving blind. While going beyond the NDL isn’t often an issue, it does take planning and training to do it right. Any failure or misstep in the process can result in serious health issues that include death.

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