Nitrox Tank

[halocline]

Sorry, I don't really understand the part about when blending. What do you mean "Oxygen Clean" Why does exposing the tank to 100% Oxygen differ from normal gas? How is it cleaned? I have 2 new tanks, would something still have to be done differently to "clean" them?? Thanks!!

You should do a search about oxygen cleaning, you'll find all sorts of material about it. The suggestion about taking a nitrox class is a good one too; any nitrox class (which you'll need to get nitrox fills) should have a good explanation about high pressure oxygen use.

The basic explanation is that handling high pressure O2 can have some risk of explosion, so there are special environmental requirements for its use. A scuba tank that will be filled with 100% O2 has to be carefully cleaned of any hydrocarbons, (is that the right word?)including the valve, and special greases and o-rings must be used in the valve. The materials used are designed to resist ignition and to be durable in exposure to high pressure 100% O2.

The only time a scuba tank and valve is exposed to 100% O2 in recreational nitrox use is when it is filled by blending 100% O2 and highly filtered air (more highly filtered than the industry minimum for breathing air) in the tank itself. That's called 'partial pressure' blending. Many smaller shops still do this, although the trend is going towards pre-blending nitrox in larger tanks or blending systems, which means your tank never is exposed to pure O2.

 

[scubadiver888]

Sorry, I don't really understand the part about when blending. What do you mean "Oxygen Clean" Why does exposing the tank to 100% Oxygen differ from normal gas? How is it cleaned? I have 2 new tanks, would something still have to be done differently to "clean" them?? Thanks!!

For fire to occur you need three things: oxygen, heat, fuel. This is the fire triangle. If you reduce or eliminate any one of these three things, you reduce or eliminate the chance of fire. In a scuba tank, the fuel would be contaminants. The higher the oxygen content, the lower the contaminants must be. If the oxygen level is at or below 40%, the standard method for cleaning a cylinder is sufficient. However, the more the content is above 40%, the lower the contaminant levels must be.

Partial pressure blending is done by filling a cylinder with 100% oxygen part way then filling the rest of the cylinder with air. For example, if I wanted to have 32% oxygen or EAN32 in an AL80 cylinder, I would fill the cylinder to approximate 418 PSI with 100% oxygen then I would fill the rest of the cylinder with air until it reached 3000 PSI. Essentially, 418 PSI 100% oxygen + 2582 PSI air = 32% oxygen.

Because the cylinder holds 100% oxygen during the blending process, the cylinder must be a lot cleaner than standard cylinders are cleaned. This is called oxygen clean.

Some shops will pre-mix nitrox and fill your cylinder with 32% oxygen. For this method, your cylinder is never exposed to higher than 40% oxygen and you don't need to oxygen clean it. Every shop is different so you'll have to talk to your shop to see if they use partial pressure blending. If they do, you need to have your cylinder oxygen cleaned.

Additionally, there is something called 'oxygen clean air'. This is normal air but it has been filtered to remove more contaminants. At shops which do partial pressure blending, they will use oxygen clean air and 100% oxygen. This will help to keep a cylinder oxygen clean. Other shops which use pre-mixed nitrox or only fill with air might not use oxygen clean air. If you get a fill from a shop without oxygen clean air, every fill you get increases the amount of contaminants in your cylinder. At some point there will be enough contaminants to cause a fire if you use partial pressure blending. Bottom line, if you use a shop that does partial pressure blending, it is usually safer to not use shops which pre-mix nitrox or do air only fills.

 

[scubadiver888]

The only time a scuba tank and valve is exposed to 100% O2 in recreational nitrox use is when it is filled by blending 100% O2 and highly filtered air (more highly filtered than the industry minimum for breathing air) in the tank itself. That's called 'partial pressure' blending. Many smaller shops still do this, although the trend is going towards pre-blending nitrox in larger tanks or blending systems, which means your tank never is exposed to pure O2.

In my province I don't know anyone who does pre-mixed nitrox. All the shops, big or small, do partial pressure blending. Many of the big shops do a lot of trimix. Most technical divers use different trimix blends depending on the dive and conditions plus they all want 50% and 100% oxygen for the final deco stop. This means all the trimix shops keep 100% oxygen around for them. It is just easier to partial pressure blending nitrox if your shop is set up for trimix.

Bottom line, don't assume just because the shop is large they will bank nitrox. It depends on the area you are diving in.

 

[ajduplessis]

Really? The dive shop won't give you a fill unless they cleaned the tank themselves even if it's got a sticker on it? According to your logic, then a shop tech won't fill a tank that has not been visually inspected or hydro'd by them because they would be foolish to trust any other. Maybe he shouldn't be intimate with his significant other unless she provides proof of a recent STD panel because she could be lying. Maybe the dive shop owner won't eat food he hasn't prepared himself because who knows what could be in there? Maybe when he gets his car back from the shop he's going to put it up on a jack to make sure the work was done properly?

Regs do not have to be 02 cleaned when used with recreational diving Nitrox mixes. Tanks DO need to be 02 clean when used with recreational diving Nitrox mixes.

If you use normal unfiltered air in your tank it will be need to be cleaned again prior to be filled with Nitrox (depending on whether it's banked or blended of course).

Somebody needs to go back through Nitrox class again and hint, it's not me!

:cool2:

You need fuel, O2 and heat/ignition to have a fire/explosion. Do you argree?

Let say you want to make EAN32. You add 28 bar O2 and top it of with AIR to 200 bar. That gives you a 200 bar EAN32 mix. Do you agree?

If you fill an empty no-O2 clean tank with O2 at a very slow rate like you always should (this means no heat or ignition source), meaning you only have 2 of the 3 "items" to start/sustain a fire. Please explain how this is going to end up in a fire/explosion?

Please also explain how recreational nitrox require a O2 clean tank and valve but not the regs?

I would suggest you redo your nitrox course.

 

[rongoodman]

In my province I don't know anyone who does pre-mixed nitrox. All the shops, big or small, do partial pressure blending. Many of the big shops do a lot of trimix.

Northern Tech Divers in Kinsgston banks 32%, luckily for me, since none of my tanks are O2 clean except for deco bottles.

 

[JollyWaffl]

Please also explain how recreational nitrox require a O2 clean tank and valve but not the regs?

Because only the tank and valve come in contact with O2 > 40%. The regs only ever come in contact with the EAN32 mix in your tank, never the pure O2 that you started with.

Or are you worried about contaminants on the DIN fitting being transferred from a non-cleaned reg to a cleaned valve? I haven't taken a nitrox course yet, so dunno if this would be a problem.

 

[idocsteve]

You need fuel, O2 and heat/ignition to have a fire/explosion. Do you argree?

No, because scuba tanks that are contaminated and then filled with pure oxygen have been known to explode in the absence of heat/ignition. If they didn't well then there would be no point in having tanks 02 cleaned in the first place.

Let say you want to make EAN32. You add 28 bar O2 and top it of with AIR to 200 bar. That gives you a 200 bar EAN32 mix. Do you agree?

I'm not ashamed to admit your calculations are over my head but I'll take your word for it. That much being said I don't see the relevance here.

If you fill an empty no-O2 clean tank with O2 at a very slow rate like you always should (this means no heat or ignition source), meaning you only have 2 of the 3 "items" to start/sustain a fire. Please explain how this is going to end up in a fire/explosion?

I don't know the chemistry/physics/mechanics behind why a scuba tank may explode if it has contaminents and those contaminents come in contact with pure oxygen under pressure but I don't think there's any question about that, again, that's the entire purpose behind cleaning tanks that are certified for use with Nitrox. No need to reinvent the wheel here..

Please also explain how recreational nitrox require a O2 clean tank and valve but not the regs?

This has been very nicely explained by another poster.

I would suggest you redo your nitrox course.

Why? Are you hoping to get a 2 for one deal? I passed my course.. you on the otherhand.. it's a bit shakey from where I sit..

 

[boulderjohn]

You need fuel, O2 and heat/ignition to have a fire/explosion. Do you argree?

Heat/ignition is not necessarily a requirement in the presence of pure O2.

Please also explain how recreational nitrox require a O2 clean tank and valve but not the regs?

As said above by someone else, the regs do not normally come in contact with pure O2 or even a very high concentration of O2. In technical diving, O2 clean regs are used whenever the diver is doing deco on high O2 concentrations, typically 50% and above. There have been some scary stories of contaminated regs reacting when the gas first goes through the system.

 

[Slamfire]

I remember reading somewhere (or maybe it was hearing it in a class), that you do not need an explosion to be harmed by a tank that's not O₂ clean. When the unclean part gets the sudden high pressure O2 flow, there is a chance of contaminants microflashing (mini burn / mini explosion). When this happen harmful toxic gases are produced (eg carbon monoxide or other hydrocarbon vapors). Breathing these toxic gases at depth is very dangerous and could even be life threatening. This situation is very dangerous because the mini explosions are not necessarily big enough to be easily noticed. So it is best to take prevention having your gear O2 clean and opening valves slowly so that pressure changes are not that sudden.

 

[fdog]

Good one!
Unfortunately, LDS knowledge of O2 protocols and how they relate to Nitrox is a free-for-all....anything goes depending on the shop.

If I could make the Thanks button work, I'd click it...

So here ya go. <insert click noise> THANKS



All the best, James