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De facto standards

All standard scuba regulators are compatible with air as well as Nitrox mixes which contain up to 40% oxygen. They will not require you to do anything differently or change anything. Regulators intended for use with Nitrox mixes above 40% oxygen, however, need to be oxygen cleaned.

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However Asian made regulators may not like this, need to check with the manufacturer.

O2 compatible grease and 0-ring

For recreational diving with Nitrox (oxygen concentration below 40%) :

 

Scuba Diver Experience:

  • A diver on the ScubaBoard forum shared their experience. They use silicone grease on all regulators except those exposed to very high O2 (80% to 100%).

  • For static hose O-rings, they use silicone spray during assembly (since these O-rings are not truly static during fitting rotation).

  • The dynamic HP O-ring in the balancing chamber of diaphragm first stages (e.g., Conshelf) is lubricated with silicone grease.

  • They dive Nitrox < 40% and have found that O2-compatible greases tend to separate over time, making them less effective as lubricants1.

 

Dive Gear Express:

  • The use of silicone grease with Nitrox is generally discouraged.

  • While the exact safety depends on the specific product formulation and gas pressure, as a practical rule, it’s best to avoid using silicone grease with Nitrox.

  • Silicone grease is a broad term for lubricants based on pure silicone oil (usually polydimethylsiloxane, or PDMS)2.

  • In summary, if you avoid using silicone grease on tank or DIN O-rings and limit its application to other parts, your practice should be safe. However, always exercise caution, follow manufacturer recommendations, and consider alternative lubricants like Christolube

Different opinions:

Two factions with divergent opinions have debated the question. ANDI, a Nitrox training agency, proposed that the scuba industry follow Compressed Gas Association guidelines: scuba gear and compressors using EAN with greater than 23.5 percent oxygen should require special treatment. One source of contamination would be simply the CGA Grade-E Air, the industry standard for normal scuba air; the allowable condensed hydrocarbon content is too high. Such a standard, however, would require any diver who planned to switch between Nitrox and compressed air to maintain separate scuba systems for each. That's too much to ask your average recreational diver to swallow.

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Most other agencies that certify fill stations and technicians lined up behind a cleaning threshold of 40 percent oxygen, meaning that systems using compressed air or EAN up to 40 percent did not need to be specially oxygen-clean. That would allow recreational divers using the common Nitrox mixes to use air, as well, with Nitrox-compatible regulators.

 

The Divers Alert Network held a workshop in November 2000 to resolve this debate, engaging most training agencies, several manufacturers and outside experts. DAN published a document saying the consensus was that 40 percent oxygen was an acceptable noncleaning threshold. Charlie Johnson says that the paper, which was not a transcription of the proceedings, left out many contrary arguments. He told Undercurrent that "Some experts outside the scuba industry say the 40 percent threshold is laughable. Some say it's criminally negligent. None say it's appropriate." Nevertheless, it seems to be the de facto industry standard.

In General:

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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!

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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.

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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.....)

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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.

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