During the dive, you use a gas cylinder with breathing gas. At the beginning of your diving adventure you will only use ordinary air. However, it doesn’t stop there. There may be other breathing gases in the dive cylinder, and nitrox is one of the most popular. Today I will explain to you what enriched air is.
Nitrox, Enriched Air Nitrox or EAN, Oxygen Enriched Air are the names of the same gas mixture. They are used to determine breathing mixes with increased oxygen content. As you probably know, in the air we have about 21% oxygen, 78% nitrogen in oxygen, and 1% other gases. For different types of dives, mixes with different oxygen levels are used. Different gas will be used by recreational divers and another by technical divers.
Nitrox is a serious threat to life and health for people who are not properly trained. We need oxygen for life, but it can be dangerous. Therefore, you cannot use an EAN cylinder unless you have been trained to do so. The gas you have in the diving tank is compressed, i.e. injected under high pressure. During the dive, you breathe gas under increased pressure and this increased pressure can be dangerous for untrained people.
Therefore, all diving cylinders that contain gas other than air must be marked. Remember that you must not use a gas cylinder other than your level of training. Even if they are on the same boat, it doesn’t mean that they are meant for you. If in doubt, always ask your instructor.
As I said before, all diving cylinders that have a non-air breathing mix must be specially marked. Nitrox cylinders are marked in green and yellow. Usually it is a large sticker informing that there is enriched air inside. It is important that the sticker is large, clear, visible from all sides to all divers. You can see this label below.
You already know what a sticker for a diving cylinder should look like. Now let’s tell ourselves what information should include such a sticker. In the picture below you can see what a professional rating label looks like.
Each diving tank that is filled with enriched air should contain the following information:
As you can see, it is mandatory to sign the tank with the name of the person who will dive with this tank. This is very important because each diver is responsible for analyzing the gas in the tank. What we teach at the Enriched Air Nitrox course is, among other things, making the correct mix analysis.
An oxygen analyzer is used for this purpose, which is able to provide the exact percentage of oxygen in the analyzed gas. It is worth noting that every diver should compulsorily analyze the gas before starting each dive. Remember – you are responsible for your safety. No one else.
MOD, Maximum Operating Depth, i.e. maximum operational depth. This is the maximum depth allowed for a given breathing mix. MOD specifies the depth in meters or feet for which the partial pressure of oxygen reaches the maximum allowable value.
This is very important for your safety, because exceeding the maximum partial pressure can lead to oxygen poisoning. In recreational diving, the maximum permissible oxygen partial pressure is 1.4 ATA for normal (recreational) diving and 1.6 ATA for decompression stops.
The MOD can be calculated using the following formula:
MOD – Maximum Operating Depth
FO2 – percentage of oxygen in the mixture
PpO2max – maximum assumed oxygen partial pressure
When calculating the MOD, always use a value less than the permissible value. The higher value of 1.6 ATA is used in emergency situations or during decompression stops. After calculating the MOD for various gases, it can be seen that the higher the oxygen content of the breathing mix, the lower the maximum depth.
|Breathing mixture||MOD (1.4 ATA)||MOD (1.6 ATA)|
|Air 21%||56 m.||66 m.|
|NITROX 32%||33 m.||40 m.|
|NITROX 36%||28 m.||34 m.|
|NITROX 50%||18 m.||21 m.|
|Oxygen 100%||4 m.||6 m.|
According to PADI standards, the maximum oxygen content in the breathing mix can be 40%. This is the limit that applies to recreational divers. Enriched air diving qualifications can be obtained at the PADI Enriched Air Nitrox diving course. You can do this course in one or two days.
After completing it, you’ll get a nitrox diver license. With this license you can use enriched air with an oxygen content in the range of 22% – 40%. In practice, however, you will most often use EAN32 and EAN36.
The biggest tangible benefit that nitrox gives us is the possibility of extending the dive time. During recreational diving with the use of nitrox we are less exposed to the occurrence of decompression sickness. Part of the nitrogen is replaced with oxygen, and thus a smaller amount of nitrogen dissolves in our tissues. Theoretically, diving with nitrox is safer when it comes to the possibility of decompression sickness.
I have already mentioned that nitrox 32% and 36% is the most popular gas among recreational divers. I think that this popularity is largely due to both its availability in diving bases and affordability.
The use of enriched air allows you to extend your dive time, but at the same time limits the maximum depth at which you can dive. Remember the general rule – the higher the oxygen content, the lower the maximum depth. This is clearly seen in this table, where the maximum depth for various types of gases is given:
|Depth / Gas||AIR 21%||EAN 32%||EAN 36%|
|18 meters||56 minutes||95 minutes||125 minutes|
|22 meters||37 minutes||60 minutes||70 minutes|
|30 meters||20 minutes||30 minutes||35 minutes|
As a recreational diver you will use enriched air in line with what you have learned during the course. However, it is worth mentioning that these are not all nitrox mixes used in diving. We can distinguish several types of enriched air:
Cold nitrox is a gas with an oxygen content in the range of 21% to 40%, intended largely for recreational divers. To use such mixtures, the equipment must be oxygen compatible, i.e. made of oxygen resistant materials. Most regulators are ready to work with such gas.
Hot nitrox contains from 40% to 100% oxygen and is mainly used by technical divers to perform decompression. When using hot nitrox, the equipment must meet aerobic purity requirements. Special regulators are used for this type of gas.
Now you know what enriched air is and how it differs from ordinary air. Is it worth diving with nitrox? In my opinion, most definitely. The reduced nitrogen content will allow you to stay underwater longer. And could there be anything better than an extra dozen or so minutes in the underwater world?
If you want to go on a vacation to a warm country for diving, you want to spend as much time as possible underwater, right? This is what allows you to dive with enriched air. Why would you not use it?