Nitrox fills

[fantasea]

Honestly, there’s been so much debate (even behind the scenes) for the last decade or more on the use and filling of ‘enriched air’ versus ‘regular air’, and there never seems to be a law or something that stands undisputed or unchanged (like absolutes on DCS – there are no absolutes). As dive operators, even we were told misinformation from other colleagues and industry sources in the past, and now, just when you think you know something, it changes all over again.

Why can’t training agencies and divers all think of air as simply EAN21 or EAN22? We don’t think that this would confuse anyone if training agencies began their teaching curriculums for their beginning Open Water Divers with that simple mindset. This would seem to make transitions over to Enriched Air Nitrox, Tri-Mix, and other mixed gas learning much easier.

DOT standards on the subject may/will change next year, and then change again. Then they’ll change once more. It is hard to comment on their justifications. We don’t wish to knowingly break any laws.

By PADI standards (we cannot speak for other training agency standards), we can say the following:
It is crucial that no one accidentally confuse a tank of enriched air for a tank of normal air. Enriched air tanks are clearly marked to identify them as enriched air tanks. One method for blending enriched air requires putting pure oxygen in the cylinder and adding oxygen compatible air, this is called “partial pressure blending”. Because the tank valve and interior will be in contact with pure oxygen, if partial pressure blending will be used, the cylinder must meet oxygen service standards, even though the final enriched air blend may have less than 40% oxygen. (Standard scuba cylinders don’t typically meet oxygen service requirements until those standards/procedures have been applied.) Enriched air cylinders filled by other blending methods may not have to meet oxygen service standards, depending upon manufacturer recommendations, local law or local practice, but the cylinder must still be dedicated to assure proper markings.

Enriched air cylinders have standardized stickers and/or tags and color-coding generally agreed upon by the international dive community. These markings assure that you can readily identify an enriched air tank, determine its contents, and determine whether the cylinder can be used for partial pressure blending:
1. Yellow cylinders should have a 10cm/4 inch green band around the tank shoulder with yellow or white lettering reading “Enriched Air”, “Enriched Air Nitrox”, “Nitrox”, or similar designation.
2. Non-yellow cylinders should have a 15cm/6 inch band around the tank shoulder. The top and bottom of this band should be a yellow 2.5cm/ 1inch band, with the center 10cm/4 inches green – again with the same lettering/label as above.
3. Enriched air cylinders should have a dated annual visual inspection sticker (decal) stating that the cylinder has been serviced and inspected for enriched air use. The sticker should also indicate if the cylinder does or does not meet oxygen service standards for partial pressure blending.
4. Enriched air cylinders should have a contents sticker (decal) or permanent tag. This sticker/tag should be, at a minimum, list the oxygen content of the blend the cylinder currently holds, the fill date, the maximum depth for the blend, and the name of the person who analyzed the oxygen content to verify the blenders analysis (this should be the diver who will use the tank). Stickers and tags are replaced/rewritten when you have the cylinder refilled by the blender.
5. Besides the markings above, local laws and regulations may require additional or modified markings on enriched air cylinders. Some areas have recommendations or requirements that an enriched air cylinder be used within a given period, such as 30 days, and the cylinder may be marked accordingly.

The use of duct tap in addition to the markings above is a great idea for help in clear and easy identification at the surface and below, especially when staging.

We are in no way saying that this is a perfect system or the only system that should be used for air/enriched air use. We rest assured that as diving continues to develop, many new and useful ways of marking, analyzing, diving, transporting, storing, and maintaining scuba cylinders will continue to develop and improve.

Funny though, in some places we’ve seen outside of the US, the only marking that a tank is enriched air is a green colored valve cap!