Why is Nitrox better for diving and how deep can you dive with Nitrox?
Using Enriched Air Nitrox (EAN) is not the answer for all dives, but over a certain depth it makes for an extended no decompression stop dive time. But Nitrox diving has its limits and there are pros and cons to using EAN.
What is Nitrox scuba diving?
Before I explain further about why Enriched Air Nitrox is better for diving in certain circumstances. Plus taking a look at the pros and cons of Enriched Air Nitrox, for those who are not familiar with the term ‘Nitrox‘, let me explain further.
What does ‘Nitrox’ mean?
The term Nitrox actually refers to any gas mixture composed mostly of nitrogen and oxygen. Atmospheric air, is approximately 78% nitrogen, 21% oxygen.
Most divers know that when we refer to the term ‘Nitrox Dive‘, this is actually an enriched level of oxygen (I explain this further below).
In the Oxford dictionary, the word ‘Nitrox’ is defined: ‘A mixture of oxygen and nitrogen used as a breathing gas by divers, especially a mixture containing a lower proportion of nitrogen than is normally present in air, to reduce the risk of decompression sickness.’
What does Nitrox mean in diving?
In the above definition in the Oxford Dictionary, they focus on the reduced proportion of Nitrogen, rather than the increased proportion of Oxygen.
Scuba divers who use Enriched Air Nitrox focus on the Oxygen content, rather than the reduced nitrogen. Whilst the benefit of diving on Enriched Nitrox Air is mostly derived by the lower amount of Nitrogen, it is the level of oxygen that is important.
Why is the oxygen level in Enriched Air Nitrox important?
The reason why the level of oxygen in Nitrox is so important is due to the fact that oxygen becomes toxic at depth. Normal atmospheric air, which contains approximately 21% oxygen, becomes toxic at around 60 metres (198 feet). When this percentage of oxygen is increased the depth at which the oxygen becomes toxic reduces.
The most common use of nitrox mixtures which contain oxygen in higher proportions than atmospheric air, is in scuba diving. This is where the reduced partial pressure of nitrogen is advantageous in reducing the nitrogen uptake in the body’s tissues. Thereby extending the practicable underwater dive time by reducing the decompression time.
What is the difference between Nitrox and Air?
‘Nitrox’ refers to any mixture of nitrogen and oxygen. Whereas ‘enriched air‘ refers to mixtures of oxygen and nitrogen that contain more than 21% oxygen.
The Nitrox that is used in recreational scuba diving is between 21 and 40% oxygen. As the oxygen content increases, so does the percentage of nitrogen decrease in direct proportion.
How deep can you dive with nitrox
How deep you can dive with nitrox depends on the percentage of oxygen.
But using the most common nitrox mixes of 32% and 36%, the deepest you can dive using these nitrox mixes in 33 metres (110 feet) on 32% and 28 metres (90 feet) on 36% nitrox.
There’s no doubt that Nitrox does limit your dive depths, but being limited to 33 metres isn’t a bit deal. There are plenty of great dives to this depth, in fact for the last 10-15 years I’ve not dived deeper than 30 metres myself.
It therefore depends on the type of diving you want to do. If you wish to do some very deep dives to 40+ metres (130+ feet), then nitrox may not be for you.
But if you’re interested in extending your dive time at more sensible dive depths, then you may wish to consider taking a nitrox training course.
Why is Enriched Air Nitrox used in diving?
A mixture known as nitrox is used to reduce the risk of decompression sickness by substituting oxygen for part of the nitrogen content.
However, one of the ‘Cons‘ or using Enriched Air Nitrox (EAN) is that breathing EAN can lead to Hyperoxia (see below). This is due to the high partial pressure of oxygen, if used on too deep a dive for too long a time.
Now you understand why enriched air nitrox is used in scuba diving, it’s worth taking a look at a table of how the higher levels of oxygen affect your bottom times.
One of the main ‘Pros’ of using Enriched Air Nitrox is how it increases bottom time. This is better explained by way of a table.
DM: Depth Metres
DF: Depth Feet
B21: Minutes of bottom time on 21% Oxygen BSAC Tables
P21: Minutes of bottom time on 21% Oxygen PADI Tables
N32: Minutes of bottom time on 32% Oxygen
N36: Minutes of bottom time on 36% Oxygen
1:40 Po2 LIMIT: The partial pressure limit of oxygen is exceeded at that depth (see "How does oxygen toxicity occur" below).
The depths and times in this table have been based on BSAC/PADI air dive tables and the National Oceanic and Atmospheric Administration NOAA nitrox tables. This has been done for comparison purposes only and this should not be used to plan or carry out your dive. Please use the tables associated with your diver training or use a dive computer for your dive times. 32% and 36% oxygen mixes are used for comparison, as these are the most common nitrox mixes used by nitrox divers.
Where nitrox really benefits scuba divers is on dives of 20 metres (66 feet) and above. Below this the air mixes of nitrox become expensive and arguably wasteful. For example, if you look at the dive time associated with a 15 metres (50 feet) dive, it’s likely that your air will run out way before you reach the 215 minutes of no decompression stop time using 36% oxygen mix.
Myths around Enriched Air Nitrox
There are some myths surrounding the use of enriched air nitrox. One such myth is that Nitrox is for deep diving, but it’s not.
Myth #1 about Nitrox – Nitrox is for deep diving
The first myth about nitrox is some think that it’s for deep diving, when it’s not. If you read on below, you’ll see that oxygen becomes toxic at depth. Nitrox is about increasing the oxygen content. This means your diving depth reduces…not increases.
This is how the Divers Alert Network put it:
Today, nitrox mixes are readily available and prepared across a range of concentrations. It has a lot to offer divers, but it isn’t magic; rather, it’s a useful tool that provides benefits if used correctly. When diving according to air tables or using the air setting on a dive computer, nitrox can reduce decompression stress on a diver. When used with an equivalent air depth, this safety margin is lost, but bottom time can be extended.Divers Alrert Network – Nitrox
The myth therefore that nitrox lets you dive deeper is a dangerous misconception. You must therefore be sure to get the necessary training and gain the appropriate certification before you use nitrox on a dive.
Myth #2 about Nitrox – Nitrox reduces your air consumption
Your air consumption when scuba diving depends on several factors. These include the depth you dive, how good you are at controlling your buoyancy and your buoyancy control device, plus how fit and healthy you are before you dive.
None of the above factors have anything to do with the percentage of oxygen contained your air mix. Your air consumption will therefore be the same regardless of whether you increase the percentage of oxygen or not.
Myth #3 about Nitrox – Diving on nitrox is safer than diving on air
People who claim that diving on nitrox is safer than diving on air is more myth than truth (but see my pro of using nitrox and age). Whilst you could argue there’s some truth to this, as you don’t build up the same levels of nitrogen in the body when diving on EAN, which in itself isn’t unsafe, safety is more about your approach to diving.
Diving on nitrox enriched air requires you to follow the same strict safety rules and procedures as you would if you’re diving on atmospheric air. If you’re diving on Nitrox, things can still go wrong and if you don’t follow safe diving practices, you are just as likely to get into trouble.
Myth #4 about Nitrox – You’re less tired when you dive on nitrox
Diving on nitrox and being less tired may be a “half-truth”. The reason behind this thought is based on the physiological effect of the build-up of nitrogen in our bodies as we dive more. This may be particularly true when diving to excess on a liveaboard.
It’s argued that there’s a certain amount of weariness you feel when nitrogen accumulates in your body tissues. However, when you’re diving on Enriched Air Nitrox, you breathe in less nitrogen. Therefore your body tissues absorb less of it.
It’s possible therefore, diving using EAN may reduces the tiredness of multiple dives. But this is quite difficult to prove one way or another.
Pros and cons of nitrox diving
The pros and cons of nitrox diving have already been touched upon in this article, but let’s take a closer look at these in more detail.
The pros of using Enriched Air Nitrox when scuba diving
The following are what are considered pros of using nitrox for scuba divers:
Pro #1 of using Enriched Air Nitrox
Extended bottom times on dives up to the depth limit of the oxygen mix used, see above table. For example, a dive to 30 metres (100 feet) using a 32% mix is increased from 20 minutes to 30 minutes, which is a 50% increase in time. Although if you use a 40% mix to 24 metres (80 feet), your bottom time is increased from 30 minutes to 74 minutes.
Pro #2 of using Enriched Air Nitrox
In theory, using nitrox reduces the risk of decompression sickness. This is on the basis that your body takes on less nitrogen during the dive where the percentage of nitrogen is less. However, the risk of decompression sickness should never be a problem when diving, as you should always dive to the appropriate tables or use a dive computer whether you use nitrox or not.
Pro #3 of using Enriched Air Nitrox
You reduce your surface interval times when using nitrox, as you breathe in less nitrogen and therefore less nitrogen is absorbed by your body and tissues on your dive.
Pro #4 of using Enriched Air Nitrox
Feeling less tired. It is argued by some that due to the fact your body takes up less nitrogen when diving on nitrox enriched air, you feel less tired. However, the jury is still out on this pro of using EAN.
Pro #5 of using Enriched Air Nitrox
As you age, your body becomes less efficient at the various processes that go on inside the body. This could be argued the same for nitrogen release after a dive. It could therefore be argued that it would be safer to dive using nitrox as you get older. This is only my theory.
Pro #6 of using Enriched Air Nitrox
If money isn’t a problem, you could use nitrox to increase your margin of safety when you dive. You could plan your dives as if you’re using air, but dive using a nitrox mix with a higher oxygen content. This will dramatically reduce any risk of decompression sickness.
The cons of using Enriched Air Nitrox when scuba diving
The following are what are considered the cons of using nitrox for scuba diving:
Con #1 of using Enriched Air Nitrox
It’s expensive. In comparison to a regular air fill, a nitrox fill is more expensive. Not only that, you also need to buy an air testing kit to check your nitrox mix.
Con #2 of using Enriched Air Nitrox
The higher the percentage of oxygen mix of nitrox, the greater the depth limit on your dive. See the above table.
Con #3 of using Enriched Air Nitrox
Mixing gases and testing them is a bit of a faff and you need to make sure you check the mix before you dive to avoid problems. However, once you’re used to checking your gas mixes this does become easy.
Con #4 of using Enriched Air Nitrox
If your diving buddy doesn’t use of have nitrox when they’re diving, the benefits you gain will not be achieved, as you’ll need to dive to your buddy’s dive profile and not yours.
Con #5 of using Enriched Air Nitrox
Nitrox is not always available where you dive and is not always available on liveaboard boats. Check this before you book your liveaboard or resort trip.
Con #6 of using Enriched Air Nitrox
If you already have a dive computer before you learn to dive with Nitrox. And if your dive computer isn’t one that can handle nitrox, you”ll need to buy a new nitrox-ready dive computer at further cost.
An aside to nitrox diving
As an aside, I’ve been diving since 1990 and never done a nitrox course and not dived using nitrox in all that time. This has never stopped me from doing all the dives I’ve done around the world.
Often times I’m on a dive boat somewhere in the world and I’m paired-up with a dive buddy. It’s very rare that I’ve been with a diver who is either nitrox trained or on a boat that offers nitrox. But this has never compromised my dives…so far!
However, this might be just me. It may be similar to when I did most of my UK diving in a semi-dry suit. This was until one of my dive buddies insisted that I try his drysuit. Up to then I never fully appreciated the benefits of diving in cold waters using a drysuit. But afterwards, I immediately rushed out and purchase a DUI drysuit. Since then I’ve always dived in the UK using a drysuit.
It might be that if I try nitrox, I may get hooked. I may then actively seek out nitrox dive boats and resorts instead. I welcome your comments below.
How does oxygen toxicity occur?
As you dive deeper, the partial pressure increases, which is explained using Boyle’s Law alongside Dalton’s Law.
Dalton’s law states that the total pressure of a gas is equal to the sum of the pressures of its component gases. Whilst the components that make up the gas you breath underwater don’t change, the pressure does as you descend.
Within the recreational scuba community and as recommended by the National Oceanic and Atmospheric Administration (NOAA), generally a maximum oxygen partial pressure of 1.4 atmospheric absolute (ATA) is recommended.
The ATA on atmospheric air or the maximum operating depth (MOD), where the oxygen content is 21%, is exceeded at approximately 60 metres (198 feet).
However, when the composition of your breathing gas is changed, the MOD needs to be adjusted accordingly.
Using the same 1.4 ATA (1:40 PO2) limit:
- 32% Nitrox mix has an MOD of 112 feet.
- 36% Nitrox mix has an MOD of 95 feet.
What happens when the ATA limit is exceed?
The result of breathing increased partial pressures of oxygen, where the ATA is exceeded, is referred to as Hyperoxia or ‘Oxygen Toxicity’.
Hyperoxia occurs when the cells, tissues and organs in your body are exposed to an excess supply of oxygen. Or where oxygen at a level which is higher than normal partial pressure of oxygen.
The body is affected in different ways by Hyperoxia. This depends on the type and length of exposure. Central nervous system toxicity is caused by short exposures to high partial pressures of oxygen.
What are the symptoms of Hyperoxia?
Symptoms of oxygen toxicity as a result of Hyperoxia can include disorientation, respiratory problems, or myopia, which is an eye disorder causing nearsightedness. Prolonged exposure to higher than normal partial pressures of oxygen can result in oxidative damage to your cell membranes.
The symptoms produced from breathing high concentrations of oxygen for extended periods have for good or for bad been studied on animals. In the majority of cases these studies reported the occurrence of irritation, congestion and edema of the lungs. In certain circumstances this even led to death following prolonged exposures to enriched oxygen.
The moral of the story is to be careful about your depths when diving using Enriched Air Nitrox.
How much does nitrox certification cost?
Now that you’ve read about nitrox and the pros and cons of diving with nitrox, you may be wondering how much does nitrox certification cost?
During both courses you’ll learn about the mixture of air and how the different levels of oxygen and nitrogen affect you. You be taught about increased bottom time, which comes from the equivalent air depth (EAD) principle.
You will also get to practice analysing oxygen content in your scuba tank. Plus you’ll learn how to set your dive computer for diving with enriched air nitrox.
The cost of certification will depend on which course you do. But as an estimate you likely to pay around $100-150 for this course.
I hope you enjoyed this article about what are the advantages of nitrox diving
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