Same Reg for both air and nitrox

[YoungCousteau]

I am just learning nitrox. I am looking to buy a regulator. I have heard two things from many different people, one side says that If I use a regulator with nitrox, that regulator should only be used for nitrox from that point on. The other side says that as long as I stay under a 40% mix I can swap between air and nitrox. I would appreciate any help that anyone could give me.

Thanks

Mike

 

[DiveTub]

Depends on the country
But as long as you are using less than 40% then you should be able to use the same Reg for Air and Nitrox, check with the manufacturer to be on the safe side.

Anything over 40% should have Nitrox clean regs only used for clean Air Fills.

Remeber a clean Air (Nitrox) fill is anything that has been filtered to meet clean Air Standards in your country. So you can get a Clean 21% fill to use with your Nitrox clean Regs.

 

[Detonate]

"The other side says that as long as I stay under a 40% mix I can swap between air and nitrox."

That's the side I swing with.

Same thing goes for Tanks, O-Rings, etc... From what I understand, when the O2 content is above 40%, that is when it can spontaneously combust, and things need to be O2 cleaned, certified or whatever....

I'm sure someone can explain it better, but just so you know I use all the same gear with Air or Nitrox.

 

[Genesis]

This applies ONLY to mixes under 40% - that is, what "recreational Nitrox" covers. This DOES NOT APPLY to mixes over 40%, and definitely does not apply to mixes richer than 50/50!

You really SHOULD use Hyperfiltered air in any TANK that is going to be used for recreational Nitrox, and you PROBABLY should consider O2-cleaning it and the valve at least annually.

The reason is that someone MAY, in the future, partial-pressure blend into your tank. If they do AND there are hydrocarbons or other contaminents in there (Grade-E air has some contaminents) you could get an ignition event in the TANK during the PP filling, and that would be EXTREMELY ugly. The consequence could either be a nasty dose of CO in the tank or worse, an explosion or fire.

A regulator will only see the "mixed" percentage of O2. That will be under 40%. While there is a theoretically-enhanced risk of an oxygen fire in a regulator at that mix, the risk is extremely low. It is NOT zero - however, its not zero even with AIR!

So, take common-sense precautions. Open valves SLOWLY - ALWAYS. NEVER have any part of your body in the ejection plane of a HP seat on a regulator (the cap over the HP seat) nor over the bonnet of a tank valve when you open valves. Crack them SLOWLY, do not slam them open.

There are people who will tell you that you must specially clean and treat regulators for non-air mixtures - including recreational Nitrox. IMHO, they're full of it, with a couple of exceptions. The specific exceptions are:

1. Aluminum regulators. SP and a few others have made them as an "ultra-light" gimmick. I would NOT use enriched gasses with them, as aluminum will burn furiously in an enriched atmosphere. Bad news.

2. Titanium regulators. These are iffy for recreational Nitrox IMHO, and absolutely verboten for mixes over 40%. The problem is the same as that of AL - it'll burn in high FO2 mixtures!

3. ANY regulator or tank that has been lubricated with silicone. There is no reason on God's Green Earth to do that these days, with Christolube being readily available. O2-compatable greases are better lubricants than silicone anyway, and the miniscule amount used makes the cost issues a non-event. I've rebuilt over a dozen regs (firsts and seconds, all mine) over the last month or so (annual time) and didn't even significant dent a 1/4 oz tin of the stuff (about $2-5 worth!) If your reg manufacturer or tech is still using silicone for lube, fire him/her/them and find a new one.

There is a controversey about O-ring material compatability. Here's the straight poop as I've been able to determine it after extensive material study on the matter:

1. Buna-N (rubber) O-rings are marginal for low-temperature (defined as under about 200F) O2. They will oxidize faster than in air and degrade and leak more quickly than they would in ordinary air. This can contribute to shorter-than-normal rebuild requirement intervals.

2. Viton O-rings are somewhat better for low-temperature O2. They will maintain their stability better under high FO2s, and are a BIT harder to ignite (requiring higher temperatures to flash) BUT if they do flash they release nasty ("one breath and you die") combustion byproducts. Viton also has crappy abrasion resistance, which makes it a really poor choice for dynamic (moving) applications - like HP and LP piston O-rings.

3. EPR and Polyurethane are almost as good as Viton in terms of O2-resistance, BUT they both have excellent abrasion resistance as well. This makes them a better choice, IMHO, than Viton for dynamic applications. They're ALSO cheap (unlike Viton), which means that they make an excellent "all around" replacement for Buna-N - to the point that unless there's a real good reason NOT to use them, you may as well. (If you're using a factory "kit" then this is moot, since they supply them - but if not.....)

For everyone who says that Buna is unsuitable for O2 you'll find someone else who says its actually preferrable, as the risk if you DO get ignition is lower than it is with Viton! Specifically, aircraft O2 systems (which do route high pressure pure O2!) tend to have almost exclusively Buna-N O-rings all through it.

 

[rescuediver009]

The simple solution to all this is that when you want to dive nitrox with your regs, you are ok as long as you stay under 40%. The air that is going in your tank should be clean and grease free anyways. Most regulator brands advertise that their regs are up 40% O2 compatible. Only when you want to use a reg for over 40% (deco etc.) then you have to use O2 compatible o-rings.
As far as tank are concerned, they must be cleaned and labelled as soon as they are converted to nitrox. The reason is that most facilities use partial pressure blending. This means that they add the O2 and then the air, so at one point your tank is exposed to 100% O2. Your regs never reach this level, thus they only need to be cleaned for over 40%.

 

[YoungCousteau]

Thanks for all the great information. I doubt that i will be using any mixes over 40% in the near future. But it is good to know the details. I finish my nitrox class this week and hope to try it out this weekend.

thanks again

Mike

 

[rescuediver009]

Depending on your age and physical condition you may notice some reduction in post dive fatigue. this also depends on your mix choice. Where I notice the biggest difference is in the reduction of surface intervals when diveing between 70 and 100 ft. Otherwise nothing else.