Gas - Tanks

Yes and no; this simple question has a complex answer because there is no widely recognized scuba diving standard for what constitutes suitability for oxygen service. Hypothetically, the equipment we sell could be used with oxygen if we describe it as Nitrox Ready, otherwise you should assume air only service. However, from the point of view of stringent U.S. aerospace guidelines and Compressed Gas Association handling standards for oxygen, nothing in general use in recreational diving is suitable for oxygen service. Using oxygen for diving requires you to make an informed decision to accept for yourself the risks of handing the oxygen. To help form your opinion about the answer read our article About Oxygen Disclaimers.

According to our suppliers, their Nitrox Ready products are oxygen compatible and oxygen clean from the factory, prior to initial use, for compressed gases greater than 23.5% oxygen. (Air is defined as containing from 19% to 23.5% oxygen.) However, most suppliers in the dive industry specify their Nitrox Ready products for use with gas mixtures containing a maximum of 40% oxygen as the upper limit. Although controversial, some dive industry professionals are of the opinion that Nitrox Ready products do not have to be dedicated to oxygen service and may be used interchangeably with CGA Grade "E" air as long as the Nitrox Ready product never contacts gas mixtures in excess of 40% oxygen.

To better understand the issues associated with handling oxygen rich compressed gas, please read Understanding Nitrox Ready.

Since Air is defined by the CGA as containing 19% to 23.5% oxygen, describing nitrogen-oxygen gas mixtures up to 23.5% as Nitrox is just an obscure way of describing ordinary Air. Gas mixtures greater than 23.5% oxygen are what most people assume to be Nitrox, and of course there is also pure Oxygen. To avoid conflict with various dive supplier labeling and any misunderstanding about exactly what constitutes Nitrox, Dive Gear Express sometimes uses the phrase "suitable for service with compressed gases containing greater than 23.5% oxygen" to describe products that are both oxygen compatible and oxygen clean prior to initial use, especially in reference to cylinders and valves.

There are several versions of a dive tank VIP decal for sport Nitrox & Oxygen service that is widely available to anyone who wishes to purchase them online from Amazon and eBay. They typically have a punch out described as "cleaned for PREMIX oxygen content 22% to 40%". We will be blunt and clearly state these decals are meaningless; they have no provenance and reference no standards as well as being dangerously inaccurate. Local dive shops following best practice will not normally honor this type of VIP decal.

"Oxygen clean" is described as: the flow path and material surfaces which meet standards for absence of contaminates that can become a source for ignition. There are no diving-related industry-wide consensus or peer reviewed standards for the handling of the specialty compressed gases used in diving. So the dive industry has to fall back on the standards and guidelines of other industries. In the US, they are established and maintained primarily by the Compressed Gas Association (CGA). The CGA states that equipment and systems handling any gas in excess of 23.5% oxygen by volume shall be cleaned as if the gas was PURE oxygen. The CGA pamphlet G4.1 "Cleaning Equipment for Oxygen Service" describes the methods for cleaning and then testing the cleanliness of equipment used with oxygen.

Our suppliers tell us their cylinders and valves are oxygen clean from the factory. The CGA states that equipment handling any Nitrox mixture in excess of 23.5% oxygen shall be cleaned to their standard as if the gas is 100% oxygen, there is no lesser standard. That means all SCUBA tanks sold and assembled by Dive Gear Express that we label as Nitrox Ready on our VIP decal, prior to initial use, are oxygen clean from the supplier; we have done nothing to change that condition. Nitrox Ready tanks are not just 'kinda sorta clean' or 'premix clean', they are oxygen clean to CGA standards. For more information please read About Oxygen Disclaimers.

In rare cases, a shop will insist on some form of after-market "cleaning" before agreeing to fill a tank not sold by them. They have that right, but we want you to know that no such service can make a new empty cylinder and valve marked Nitrox Ready from Dive Gear Express any more oxygen clean.

Our suppliers tell us their equipment described as Nitrox Ready is already oxygen clean from the factory. The Compressed Gas Association standards state that equipment handling any Nitrox mixture in excess of 23.5% oxygen shall be cleaned to their standard as if the gas is pure oxygen, there is no lesser standard. That requirement is why Nitrox Ready equipment has already been oxygen cleaned by the manufacturer. SCUBA equipment is labeled 'NITROX READY' or '40% MAX OXYGEN' instead of 'Oxygen Service' because the manufacturers are managing the risks, both to your safety and their liability, associated with oxygen-related fires and explosions by specifying their SCUBA products for use only with breathing gas mixtures no more than 40% oxygen.

Nitrox Ready and Oxygen Service equipment from our suppliers is not just 'kinda sorta clean' or 'premix clean', it is oxygen clean. The practice by shops and individuals of aftermarket cleaning for new dive equipment that is already oxygen clean from the factory is pointless at best and dangerous if done improperly. Prior to initial use, no amount of aftermarket cleaning can make a Nitrox Ready product more oxygen clean nor can cleaning it ever override the manufacturer specified limits. The manufacturer can't stop you from using their equipment with breathing gases and pressures that exceed their specifications, but doing that requires you to make an informed decision to accept for yourself the risks of handing the oxygen.

Our oxygen compatible O-rings are typically made of fluorocarbon elastomer (aka fluoroelastomer, aka FKM, aka FPM) A-Type material. FKM is the designation for a class of fluorocarbon based synthetic rubbers as defined by ASTM standards, equivalent to FPM by ISO standards. Originally developed by DuPont under the name Viton, FKM is a high performance elastomer with excellent resistance to oxygen. In a few specific cases our O-rings might be described as made from a different oxygen-compatible material, for example EPDM.

Many people refer to any and all oxygen compatible O-rings as "viton" in the same manner that the Kimberly-Clark brand name Keenex has become synonymous with tissues. However, Viton™ is now The Chemours Company trademark brand name for their fluoroelastomers and use of the brand name requires joining their licensing program. Chemours is not the only company that manufactures FKM products and there are different types intended for various different applications. Counterfeit and mislabeled FKM A-Type material O-rings are so widespread that Dive Gear Express makes up our own kits using O-rings supplied through trustworthy channels. We use the generic terms fluorocarbon elastomer or FKM to describe our O-rings, not the brand name Viton.

There is no reliable visual inspection method to determine O-ring material composition, only specialized materials testing equipment can make that determination. Acrylonitrile butadiene rubber elastomers (aka NBR, aka Nitrile, aka Buna-N) are considered to have good resistance to oxygen with a 15 year shelf life. Fluorocarbon elastomers (aka FKM, aka FPM, aka Viton™) are considered to have excellent resistance to oxygen, with an essentially unlimited shelf life. To ensure specific composition, O-ring material must be specified at time of purchase and then segregated from other O-rings.

There are no O-ring color coding standards and thus color or appearance is not an indication of the material or quality. O-rings are available in nearly any color, although most commonly seen in black regardless of material. Even though most fluorocarbon O-rings are black, the loose FKM O-rings sold by Dive Gear Express are oxygen compatible and usually brown or green; simply to make them easily distinguishable from more common NBR O-rings which are usually black. However, O-rings inside equipment (valves, regulators, hoses, service kits, etc.) are almost always black regardless of material. O-ring materials also can not be distinguished from each other by their surface appearance, more a function of the manufacturer than the material. NBR is incorrectly said to have a shiny surface and FKM a matte surface. This is not a reliable indicator, and certainly not true if the O-ring has been lubricated.

Just to be clear, the COLOR and SURFACE APPEARANCE of the O-ring is MEANINGLESS regarding their compatibility with oxygen.

Yes. Many divers are surprised to learn the SCUBA industry convention of using fluorocarbon elastomers (FKM or FPM, aka Viton™ o-rings) with Nitrox is not a matter of oxygen fire safety. The introduction of Nitrox in recreational diving included a recommendation to use FKM for seals in gas blending equipment whose wetted surfaces contact pure Oxygen. This was frequently confused with the very important safety requirement for oxygen cleanliness (i.e. the absence of readily combustible materials); creating a mistaken but widely held belief that FKM is also somehow related to safety of Nitrox for diving equipment such as SCUBA regulators and cylinder valves.

FKM is no more 'safe' in Nitrox diving applications than ordinary synthetic nitrile rubber (NBR aka Buna-N). While FKM has a slightly higher temperature of ignition at {~ 900°F | 500°C} than NBR at {~ 750°F | 400°C}, nearly any material can still serve as fuel in the kindling chain to an oxygen fire that will reach {~ 5000°F | 2700°C}. The reason for preferring FKM in high oxygen content applications is because the service life is typically longer than NBR, i.e. FKM is more resistant to oxidation than nitrile rubber although FKM also exhibits a tendency to swell slightly in high-pressure oxygen. While FKM o-rings theoretically outperform NBR o-rings, in practice there is no safety reason to prefer them in Nitrox SCUBA life-support applications such as regulators and valves given the periodic service requirements of such equipment.

Regardless, Dive Gear Express specifies oxygen compatible and oxygen clean products whenever possible, and we only use O2 compatible O-rings and lubricants in equipment service. Any products we identify as Nitrox Ready or Oxygen Service will meet industry standards for both oxygen compatibility and oxygen cleanliness prior to initial use.

The short answer is NO. The longer answer is it depends on the exact product formulation and gas pressure but as a practical matter the answer is still no. Silicone "grease" is a generic term for a variety of lubricant formulations that are based on some form of pure silicone oil, most commonly polydimethylsiloxane (PDMS). While pure PDMS itself is a chemically inert inorganic substance that is not combustible; in order to make the little tub or spray can of generic 'scuba lube', the PDMS is mixed with thickeners and/or organic solvents that typically are readily combustible. Lubricant contamination in high pressure compressed gas equipment is a frequent cause of oxygen fires. In general, lubrication in oxygen service applications should be avoided whenever possible. Oxygen service applications in SCUBA that require lubrication must use specialized (and relatively expensive) lubricants, typically based on polytetrafluoroethylene (PTFE) or polychlorotrifluoroethylene (PCTFE) compounds.

It is true that in low pressure Nitrox applications such as regulator second stages and rebreather loops, the type of lubricant is pretty much irrelevant to oxygen fire safety. Occasionally, the desire to minimize use of expensive oxygen compatible lubricants can lead to the erroneous assumption that inexpensive silicone lubricants might used in ambient or low pressure applications that are in close proximity to high pressure applications. However, the high tack and adhesion property of silicone lubes also makes them very migratory and difficult to completely remove. In practice, we find silicone lubrication on the low pressure side of equipment will eventually be transferred to the high pressure side such as a first stage connector or valve outlet. Never use silicone lubricants with electrical contacts, even though this is an often suggested practice. Silicone products will react with plastics and other contaminates to form insulating films and silicone carbide compounds which can cause intermittent connections in low-current applications such as rebreather oxygen sensors. When multiple lubricants are available, there is also the very real increased risk of inadvertently applying the wrong lubricant. In practice, if lubrication is required it is best to only use oxygen compatible lubricant consistently throughout all equipment in service with Nitrox regardless of pressure.

Dive Gear Express avoids silicone lubricants in our facility, using only oxygen compatible lubricants for all SCUBA applications that require lubrication. Any products we identify as Nitrox Ready or Oxygen Service will meet industry standards for both oxygen compatibility and oxygen cleanliness prior to initial use.

DOT regulations currently limit the oxygen fill pressure of aluminum and composite cylinders to 3,000 psi at 70F. There are no similar DOT fill pressure limits for compressed oxygen gas in steel cylinders, but as a practical matter pure oxygen fills exceeding 3,000 psi are highly unlikely, regardless of cylinder composition or service pressure. In the US, almost all bulk compressed oxygen available to local dive shops is aviation grade in steel DOT-3AA-2400 cylinders with a CGA-540 valve at a service pressure of 2,640 psi. Since most oxygen fills by local dive shops are done using the cascade method, a typical local dive shop pure oxygen fill in a rebreather or decompression cylinder will be between 1,800 psi and 2,400 psi unless the shop has an oxygen booster.

The DOT considers any gas containing more than 23.5% oxygen to be pure oxygen for the purposes of handling. Thus, knowledgeable fill station operators will not fill aluminum cylinders with Nitrox higher than 3,000 psi. This means the 3300 psi "compact" or "neutral buoyancy" aluminum SCUBA cylinders will receive a short fill. Again, there are no such restrictions on Nitrox in steel high pressure SCUBA cylinders with a service pressure of 3442 psi. Although there are some older steel SCUBA cylinders with a service pressure of 3500 psi, recent DOT regulations limit the transport of such cylinders to a maximum fill pressure of 3442 psi as well.

We offer two different gas boosters suitable for applications with recreational diving; both are compressed air driven, air cooled, non-lubricated, reciprocating piston, single action single stage type. The DGX Gears X-30 is a value priced oxygen booster that is suitable for light duty usage. The faster Haskel MSB-9000 is a premium quality oxygen booster manufactured in the USA that is suitable for heavy duty usage in mission critical applications. A benefit of the Haskel booster is additional cooling provided by routing the cold exhausted drive air through a jacket surrounding the gas compression barrel.