Nitrox

[pops]

Can someone please give me a link or two that will explain nitrox in general terms? I'm a new diver, 57 years old and in good shape, marathon shape. I've been told I should use nitrox because of my age. I have other questions too, like is plain air just a 21% nitrox mix? If you calibrate a nitrox computer to 21% will it be an air computer? I understand what increased O2 levels does to grease etc but can a nitrox setup be used for air but not vice versa? or does equipment have to be cleaned and setup whenever switching from one to the other? And can you get nitrox in the diving islands - carib etc? If I switch over completely to nitrox is travelling screwed?

 

[Spectre]

If you search for 'nitrox', you'll probably find a lot more information here. But to hit a couple of your questions directly.

like is plain air just a 21% nitrox mix

No. Air is 20.9% O2, 79% Nitrogen, and .1% trace gases. 21% nitrox is 21% O2, 79% nitrogen.

If you calibrate a nitrox computer to 21% will it be an air computer

Yes.

can a nitrox setup be used for air but not vice versa?

It depends. Is your nitrox setup cleaned to handle over 40% O2? Is your tanks O2 cleaned? If your tanks are O2 cleaned, you don't want to put regular air in, but rather "hyper" air or "clean" air, which has that .1% removed.

If your tanks are not O2 cleaned, you can still use nitrox, but you have to banked nitrox. Banked nitrox is nitrox that has already been blended, so what is going into your tank doesn't exceed an O2 content of 40%.

The problem with banked nitrox vs. partial pressure fills, is that the equipment used to bank nitrox tends to be a little expensive, and therefore they charge more [e.g. around here, ~ $16 a tank for banked nitrox, whereas partial pressure blended cost ~ $8 a tank].

Regarding travelling. Most likely 'switching' to nitrox is only tanks; since everything else is getting the nitrox from the tanks and therefore it's going to be under 40%. If your travelling with everything but your tanks, the rest of your gear will be fine with air or Nitrox. Since you're now nitrox certified however, if they've got a nitrox bottle, you can dive that instead.

 

[Aquamaniac]

Spectre once bubbled...
..............

No. Air is 20.9% O2, 79% Nitrogen, and .1% trace gases. 21% nitrox is 21% O2, 79% nitrogen.

Hmmm, apart from being a little pedantic, Im not so sure about that, and granted, I dont know who is mixing your gas,BUT.....

How do they get rid of the .1% Trace gases?
Most of the places I get fills still use air (hydrocarbon free) and O2

Therefore it would be 21/78.9/.1 (rounded off)

Dave

 

[SDAnderson]

Can someone please give me a link or two that will explain nitrox in general terms?

Concise, comprehensive, understandable:
Alan Wright's "Nitrox FAQ's"

I'm a new diver, 57 years old and in good shape, marathon shape. I've been told I should use nitrox because of my age.

Sooner or later you'll hear nitrox referred to as "geezer gas." Anecdotally, breathing EAN mixes seems to reduce after-dive tiredness. I'm 47 and it's one of the reasons I usually use EAN when diving.

I have other questions too, like is plain air just a 21% nitrox mix?

Sort of. Plain air is 21% oxygen and so is EAN21. In the real world, however, nitrox fills are hyper-filtered to remove carbon compounds and excess moisture. Caution needs to be exercised crossing equipment back and forth between "plain air" fills and nitrox fills.

If you calibrate a nitrox computer to 21% will it be an air computer?

Yes.

I understand what increased O2 levels does to grease etc but can a nitrox setup be used for air but not vice versa? or does equipment have to be cleaned and setup whenever switching from one to the other?

Spontaneous combustion is one of the biggest worries when using (and especially when mixing) high O2 concentration gases. There is a lot of arguing that goes on about equipment preparation and cleaning for nitrox diving, but here's my .02: for recreational EAN mixes (less than 40% O2), only tanks need to be O2 prepped and cleaned. Regulators do not. In theory, if you are going to fill your tanks with premixed (banked) EAN40 or less, then you shouldn't need to O2 prep and clean your tank, either. In the real world, however, EAN tanks should always be O2 prepped and cleaned and dedicated because the day will come when you (or the local dive shop) want to mix EAN in your tank. Anything over EAN40 requires both tank and regulator to be O2 prepped, cleaned and dedicated. Because the standards for filtering "plain air" are much lower than for EAN, any gear used for air can no longer be considered O2 ready and will require cleaning before being returned to O2 service.

And can you get nitrox in the diving islands - carib etc? If I switch over completely to nitrox is travelling screwed?

Nitrox is more or less readily available in any area where there is a substantial amount of diving going on, especially in the Carribean. If you're diving recreational EAN mixes (below 40%) you don't need to prep, clean and dedicate your regulators, so you should not have any problems.

Hope this helps.

Steven

 

[Uncle Pug]

Pops get nitrox certified... all of your questions will be answered in the class and you won't be sorry. Nitrox is not just for geezers... it allows an increased safety margin, increased bottom times (especially on subsequent dives) and shorter surface intervals between dives. There are trade offs between these advantages... more of one advantage means less of another... but the advantages are definitely worth it IMO.

I dive standard EAN32 (enriched air nitrox at 32% O2) for all dives <110fsw. And I'm not a geezer... well... maaabye....

 

[SimonN]

I've been told I should use nitrox because of my age.

By a shop wanting to sell you a course? upset:

If you are marathon fit, then age has SFA to do with it, you are probably in better shape to go diving that your average diver. The generalisation about age pretty much come down to fitness.

Do a course though. Nitrox is a good gas and you will (depending on which course and the instructor) probably learn more about dive physiology than on any other single course (I did on the ANDI CSU).

I have other questions too, like is plain air just a 21% nitrox mix?

Yes.

If you calibrate a nitrox computer to 21% will it be an air computer?

Yes and one reason to get a nitrox computer to begin with.

I understand what increased O2 levels does to grease etc but can a nitrox setup be used for air but not vice versa? or does equipment have to be cleaned and setup whenever switching from one to the other?

It is not so much an air/nitrox thing that is the problem, but whether your gear is going to come into contact with a very high percentage of O2 at anytime.

Tanks

(Probably) most nitrox fills are done using partial pressure blending. Partial pressure blending is when the tank is filled to X psi of pure O2 and then topped off with triple filtered air. Since, the tank and valve come in contact with high pressure pure O2 they need to be O2 clean.

If filled using continuous blending or from nitrox banks the tank and valve only come into contact with the mix that you require, not pure O2, so in theory they do not need to be clean.

The air component of the mix must be triple filtered. Usually, normal air is only double filtered). This is where Nitrox 21, EAN21 or SafeAir 21 come in. It is normal air in respect to decompression, but has, theoretically again, been triple filtered.
Getting a fill from a non-triple filtered source means that technically your tank is no longer O2 clean. However, you tend to get to know where to get good fills in your local area.

I clean all my tanks though even though most of the time I just dive on air. It is not expensive and why would I want to breath from dirty tanks and valves?

Overall, spare a thought for the shop monkey pumping HP O2 into your tanks!

Regulators

ANDI reckon that any equipment coming into contact with more than 23.5% O2 hould be O2 clean - apparently this is the standard in the gas industry. Other agencies say only equipment used with more than 40% O2 needs to be cleaned.

Personally, I have four regs and three have an order of choice for which I'll use and one of my regs is for EAN50 or more. I'll soon be purchasing another reg that will only be used on EAN50 or more as well. I wil then have one reg I'll use on anything up to 40% and not worry about it. 2 regs I'll use up to 40% and not use on unknown tanks and 2 regs I'll keep clean to the max.

And can you get nitrox in the diving islands - carib etc? If I switch over completely to nitrox is travelling screwed?

At the end of the day, it depends on who you believe. Personally, for mixes of 40% O2 or under I don't worry about it.

 

[Jim Baldwin]

The easy answer is that Nitrox is enriched air. Normal air has 21 % Oxygen. To make Nitrox , oxygen is added and increases the percentage. Most recreational divers use standard mixes of 32 most common and 36 next most common.

The basis behind Nitrox is that it reduces your Nitrogen uptake and in theory you are less likely to develop DCS as compared to diving air.

Because you're breathing a higher level of oxygen a dive on 32 %to 80 feet will only feel like a dive to 60 feet on air.

Many divers use Nitrox to increase their bottom time and decrease their surface interval.

With Nitrox and a good dive computer you can nearly double your bottom time as compared to air and a dive table.

A standard air computer could be used while diving Nitrox but you would get no additional bottom time.

A Nitrox computer is programable to the mix you are using and calculates your nitrogen buildup based on the information you input. Most nitrox computers allow you to program them from 21 to 50 percent.

I have an Oceanic Data Max Pro Plus air intergrated dive computer and when you turn it on it automatically defaults to 21 % air, You have to go through a series of functions to change it to Nitrox.

When you dive Nitrox you are suppose to check the percentage in each tank yourself with a meter to make sure that the markings are correct.

If you were diving 36 percent Nitrox and thought you were diving air and went to 120 feet you would probably go into a seizure and drown.

The theory is that older divers should dive Nitrox since their bodies don't process things as quickly and this would reduce the chance of Decompression Sickness.

A good basic Nitrox class from your local dive shop should help with some of your questions.

Hope this helps.

Jim Baldwin
jbaldwin@cox-internet.com

 

[ghosty_old]

If you were diving 36 percent Nitrox and thought you were diving air and went to 120 feet you would probably go into a seizure and drown.

Jim i am extrmely new to this nitrox thing so forgive me if i sound stupid or if i didn't read your post clearly. Im not sure i understand this quoted statement. Now in your post you said using 32 % a dive to 80 feet would feel like a dive to 60 feet on air. Now if you were using 36% wouldn't a dive to 120 feel like a dive to 100 or 95 on air. So why would one go into a seizure and drown.

If anyone else can answer this or help me out, please do.
thanks

 

[Genesis]

The other part is the O2 exposure.

Partial pressure of a gas is equivalent to the percentage of the gas in the mix times the pressure in atmospheres.

Now, with that said, if you dove to 120' on 36% Nitrox, your PO2 would be 1.67. This is above the generally-accepted "safe" limit of 1.6, at which point an Oxygen-tox-induced seizure is likely to result.

The question is WHEN will it result?

Immediately? Probably not. But it might!

Even safer is a PO2 of 1.4.

It is generally though that an acute O2 seizure cannot occur at PO2s of under 1.3 (but I do not intend to "push" the O2 clock to find out!)

Nitrox is a mixed bag. You get less Nitrogen loading, therefore you can stay down longer, but since you replace the Nitrogen with Oxygen, which is toxic at a too-high partial pressure, you must be aware of the"floor" - or maximum depth - you can safety use your particular mixture at.

This is, in fact, THE greatest risk with Nitrox, and the one that you MUST understand to use it safely.

 

[Aquamaniac]

Genesis once bubbled...
Nitrox is a mixed bag. You get less Nitrogen loading, therefore you can stay down longer, but since you replace the Nitrogen with Oxygen, which is toxic at a too-high partial pressure, you must be aware of the"floor" - or maximum depth - you can safety use your particular mixture at.

This is, in fact, THE greatest risk with Nitrox, and the one that you MUST understand to use it safely.

I wonder if there is a way to replace the nitrogen with another gas? Then you could lower the O2 AND the Nitogen!!!!!

Boy THAT would be a safe gas!!!!

Dave