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NITROX – More Oxygen for Longer Dives

Nitrox (EAN) is air in which the oxygen content is higher than the oxygen content in “ordinary” air. If in ordinary air (simplified) there is 21% oxygen and 79% nitrogen, with Nitrox the oxygen content exceeds 21%. Nitrox 32 (32% oxygen) and Nitrox 36 (36% oxygen) are most often used in recreational diving, while Nitrox with an oxygen content above 40% is used in technical dives.

Sooner or later, all divers start thinking about how they could stay underwater longer, have a safer dive, and feel less tired after diving, and one of the best solutions for this is diving with enriched air, which we call Nitrox or EAN


Advantages

The main advantage is the fact that Nitrox has a higher oxygen content and thus a lower nitrogen content. When diving with ordinary air, nitrogen from the air slowly dissolves in the blood. When, after a certain time at depth, the concentration of nitrogen begins to approach the critical limit, one should start with a controlled return to the surface, otherwise, decompression sickness can occur. Due to the lower content of nitrogen in Nitrox, the concentration of dissolved nitrogen in the blood is also lower, so you can stay at the same depth for a longer time, which is actually the biggest advantage of diving with Nitrox.

Other main advantages of Nitrox diving are associated with lower nitrogen – concentration:
– shorter time between two dives (less residual nitrogen)
– less fatigue after diving
– longer repeated dives
– greater safety
The biggest differences in time are when diving at depths between 15 and 30 meters. Let’s look at two examples:
– When diving with air at a depth of 26 meters we can stay for 25 minutes, while with Nitrox 32 that time is extended to 40 minutes.
– At a depth of 28 meters, a dive with air lasts 20 minutes, and with Nitrox 36-40 minutes.
For greater safety, some divers, especially those slightly older, dive with Nitrox in the same mode as if they were diving with air. In this way, diving safety is higher, but with higher consumption of Nitrox and special equipment.

An O2 analyzer is also essential for diving with Nitrox, but if you do not often dive with Nitrox, the staff at a diving senter will be happy to lend it to you


Dangers of diving with Nitrox

The biggest danger when diving with Nitrox is oxygen poisoning. At a partial oxygen pressure of more than 1.7 bar, there is a risk of oxygen poisoning. Therefore, in sport diving, we apply a safety limit of partial pressure of oxygen of 1.4 bar.
Oxygen poisoning can occur due to too deep dives. Namely, with Nitrox you do not dive deeper, you dive longer. This is very important to know when planning a dive, where you need to calculate the Maximum Operational Depth (MOD) and the Equivalent Air Depth (EAD) for the use of dive tables when planning a dive. In a specialist diving course with Nitrox, you will also learn to use tables, with which you can plan a dive for different types of gas mixtures (Nitrox).

What does MOD, i.e. maximum diving depth, mean? Due to the limitation of the partial oxygen pressure, with Nitrox you cannot dive as deep as you want, but you must first calculate the maximum diving depth for each percentage of oxygen in the gas mixture. You can check the MOD in the tables or calculate it using the formula:

MOD = (10 * PO2 / FO2) – 10

PO2 – partial oxygen pressure (bar, for sports dive = 1.4)
FO2 – percentage of oxygen in the gas mixture (i.e: 30 % = 0.3)

Example: MOD for planned dive with Nitrox 33 (33 % O2) with partial oxygen pressure 1.4 bar:

MOD (Nitrox 33 @1,4 bar) = (10 * PO2 / FO2 ) – 10 = (10 * 1,4 / 0,33) – 10 = (10 * 4,2424) – 10 = 42,42 – 10 = 32,42 m = 32 m

(the result is always the first lower value)
You can also plan a dive with Nitrox using dive tables, but you must first look for the value of EAD (Equivalent Air Depth) in special combined tables Nitrox – air or calculate it using the formula:

EAD = ( (1 - FO2) * (D + 10) / 0,33 ) -10

FO2 – percentage of oxygen in the gas mixture (npr: 30 % = 0.3)
D – depth (in meters), at which you want to dive with Nitrox

Example: With Nitrox 32 (FO2 = 0.32) you want to dive at depth of 29 meters (D) and use dive tables. EAD is, thus:

EAD = ( (1 - FO2) * (D + 10) / 0,79 ) - 10 = ( (1 - 0,32) * (29 + 10) / 0,79 ) - 10 = ( (0,68) * (39) / 0,79 ) - 10 = 33.57 – 10 = 23.57 = 24 m

(for the final result you should take the first higher (deeper) value)
The next danger is the length of time of diving and exposure to oxygen under increased partial pressure. For a partial pressure of 1.4 bar, the limit of one dive is 150 minutes, and the limit of all dives together in one day (24 hours) is 180 minutes.


Dive plan with Nitrox

When planning a dive with Nitrox, attention should be paid to the partial oxygen pressure, the time of an individual dive and the total time of all dives in one day, as well as the maximum diving depth (MOD) for the selected percentage of oxygen. Of course, when collecting their tank, each diver must use an O2 analyzer to check the mixture of gas in the diving tank.

You can also plan a dive with Nitrox using dive tables

When planning, it is very important that there are two divers with the same Nitrox in the bottle and that they both have a diving computer that supports diving with Nitrox, i.e. has the option to adjust the percentage of oxygen.
After the Nitrox analysis in the diving tank, each diver must affix a yellow sticker to the tank, on which the % of oxygen, MOD, date and his name are marked.


Equipment

When diving with Nitrox, we use customized equipment because there are two serious dangers due to the higher proportion of oxygen:
– greater possibility of oxidation of equipment
– higher risk of explosion
The dive tank, valve, and regulator must be “O2 clean” or “O2 ready”, as the remnants of lubricant or dirt could result in an explosion. Diving with Nitrox, in which the oxygen content is less than 40%, does not require special equipment (except for a diving tank), but it should be thoroughly cleaned (degreased) before diving with Nitrox. The regulator and octopus for Nitrox are green, and you will quickly notice the diving tanks by the green-yellow combination.

When diving with Nitrox, we use customized equipment


Diving with Nitrox – yes or no?

Diving with Nitrox requires a bit more money to refill diving tanks, maybe even an extra set of regulators, and there are some dangers. However, if you make a good plan and stick to it, then Nitrox will provide you with many benefits and advantages, with which you will enjoy more and dive longer and safer. So, the answer is very simple – sign up for a diving course with Nitrox and – have fun!


Text: Matej Ogorevc

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