What's the fastest O2 Fill you've ever seen?

DivnSapper

The following sounds like a Cale story coming straight out of Vance Harlow's OXYGEN HACKER'S COMPANION, but I did indeed witness this first hand:

So the story goes... I went down to the LDS on Saturday to get my 13cf AL cylinders filled with O2 and air.

The shop wasn't busy (actually empty) so I waited around for them to get filled up. The shop has a cascade of 4 O2 cylinders but they're not interconnected... so I'm lucky if I can get a 2000psi O2 fill (need a booster I know but that's off topic).

Anyways the shop tech hooks up the cylinder and proceeds to fill it up... he just opens the tank valves and away he goes... I'm talking 2000psi in less than a minute... I about crap my pants... I'm not sure if I should run, hide or take cover. He does this while holding the cylinder. He then closes the valves, undoes the whips and brings the cylinder over to me. It is a bit warm but nothing subtantial (much cooler than the one he just filled to 3000psi with air).

Feeling somewhat obligated (based on my own O2 transfilling knowledge or maybe that is ignorance?)... I mention to the guy "I think you supposed to try to keep that fill rate to around 200psi / minute to prevent an oxygen fire"... he brushes me off and states this is what he always does. They do indeed make a lot of Nitrox via PP Blending at the shop but I'm the only guy in town that takes pure high pressure O2 from him. The shop goes through 2-3 cylinders of oxygen a week... but based on what I witnessed Saturday... I think they are going to end up with a serious mishap!

I guess he can get away with this since he is not boosting or compressing the gas but rather just transfilling?

Just curious, what's the fastest O2 fills everyone else has seen and how often does this situation occur? It seems to me that my LDS is playing with fire!

Regards,
Ryan

nigelh

There was this incident when I forgot to check the needle valve was shut and blew a near empty 3L to about 150bar before I realised.

It was several years ago and holding a rather hot O2 cylinder tends to stick in the memory so I've never done it since.

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nigelh

cool_hardware52

How do you "cascade" if the supply bottles are not interconnected?

My guess is that your 13 cuft of pure O2 is the absolute worst case scenario, i.e. tiny bottle, 100%. The fill station operator likely has developed a false sense of security from PP blending nitrox into much larger tanks. Obviously with PP blending he needs to watch and control the pressure as the O2 is added.

If he insists on continuing the practice I'd find an excuse to be elsewhere when he fill's O2 bottles.

Tobin

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JS1scuba

ahhh the great discussion.

I routinely fill oxygen to 3500 psi (238 bar) and have boosted it as high as 4410 psi (300 bar). Haskel oxygen gas boosters will boost oxygen to 6000 psi.

Oxygen needs to be handled with care. But remember it's the "system" that is it being sent through and into that needs to be designed for oxygen service and clean for such.

Imagine for a moment transfering oxygen from the valve directly into a cylinder of exactly the same size where the valve opening on the supply and on the reciever are exactly the same size. The gas coming out of Supply will have its temperature drop while the temperature in the reciever is ambient and will cool (from incoming gas) and then reach ambient and possibly higher. In this case you can open the reciever first and then supply full bore. Hight to low to medium pressure transfer.

This by the way is how you handle a gas booster. Open supply, open reciever and all other valves full open ... THEN boost. IF you restrict the outlet of the booster to the reciever then you build up heat fast and have a dangerous situation. Once the pressure increases above transfil it will warm however Haskel boosters have an intercooler that drops the gas temperature to manage this. Only once the pressure reaches the service pressure will the temperature rise. Be careful with small cylinders. Boost, stop, cool, boost, stop cool. etc.

Gas temperature will only rise if you try to fit a fat boy into a small hole. Once the gas temp has risen it will take a while for it to come down UNLESS you have heat sinks on it (whole nuther discussion). The problem we have with transfilling into scuba bottles is going from High pressure big volume into high pressure small volume this is why the flow rate needs to be slow 60 psi per minute (4 bar). This is a nice, safe rate of transfer and the reciever should not get warm.

Will it blow up at 120 (8 bar) per minute ? Probably not. What about 240 psi (16 bar) ? Probably not. It all depends on how hot it gets and what junk is in the pathway.

I recently filled some iconel spheres for a client. Those little suckers get super hot by just looking at them. The temp in our fill area that day was 100F. We got a bucket with ice and put that little round wonder in there and filled away. 60 psi per min till equalized and then boost with all valves open. Perfect 3000 psi oxygen fill.

Will the tank monkey get away with transfilling 2000 psi in one shot .... sure he will .... till he doesnt. As an owner of a dive center let me give you one important piece of advice. Drop your cylinders off tell them what time you want to pick them up. Agree on that time and LEAVE. There is ZERO reason for you to ever be in the fill area. 1. you are not an employee and are exposed to hazards, 2. you WILL distract the tank monkey 3. read 1 and 2 again. Each dive center will do as they like as they always have. Unless it's a progressive operation (most are not) you telling the $7.50 / hr employee about oxygen handling is like trying to teach a pig to sing.

Off to make eggs housard ........

Cheers

JDS

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Joel Silverstein, VP COO
Tech Diving Limited a Division of Scuba Training and Technology Inc.

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Mixaddict

I often shake my head in disbelief at the lack of respect that various dive operations show for O2. The fact that "this is the way that we have always done it" does not change the fact that it only takes one mishap to ruin your whole day. After having a friend loose his life in an O2 filling operation, I have a whole new level of respect for O2 filling protocols. O2 makes most things around it burn quickly. Casual attitudes around O2 leads to deadly mistakes.

These knuckle heads that are casual about O2 filling can go their entire careers bending the rules, until the one time things go badly, and then everyone scratches their heads and wonders what could possibly have gone wrong. It doesn't cost that much more to O2 clean the system, set it up properly and then diligently follow the rules. If you don't follow the rules, you are irresponsible and a danger to yourself and those around you.

__________________
Randy Thornton (MixAddict)
Inspiration, Evolution,Hammerhead & Sentinel
CCR Instructor

AD_ward9

Actually, we do O2 fills in 20ms (1/50th of a second). So do quite a few others.

Not in the normal run of things of course, but there is an EN14143 test that requires 50 O2 pulses with a 20ms rise time. We use either 10 bar or 300 bar of O2 to drive that, depending on what we are testing. I attach a picture of the test rig, used in this particular case to test O2 injectors.

We do the test in heated water (60C typically), so the part under test is nice and hot, with a bronze buffer chamber to make sure there is no shortage of O2, and a trigger mechanism that opens a valve in 20ms. The pressure pulse travels down a tube of 5mm bore to build up energy, then goes into the injector, or cylinder, or whatever else we want to check for O2 compatibility. We normally use 50 of these pulses to check the item.

Whether you get an O2 fire depends on what the cylinder or other components are made out of. Things with 90 degree bends in them, or incompatible materials in the wrong place go up. For a cylinder to catch fire is something we have no had yet, but valves can go nicely if there is anything in them not made of brass.

The test is reasonably safe. All things are relative: boosting O2 to 300bar is much more hazardous. Both are done in a concrete ground floor room, and if the item is big like a whole cylinder, in a bunker.

Alex

Attached Images

O2 pulse tst.jpg (121.5 KB, 317 views)

cool_hardware52

You have all the fun. Let me say I appreciate your input here. The professional perspective on HP gas and HP O2 in particular is most welcome.

Tobin

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jeff h

IMHO and expierence the smaller bottles aren't as bad becasue they don't get as hot as bigger bottles. Not that filling them fast is a good idea, it's not.

If you doubt this then try an experiment with air (or don't). Fill a 6 cuft bottle in say 1 minute, then fill an 80 cuft bottle in a minute. Scary thought isn't it.

I've seen 6 cuft bottles filled in seconds by mistake several times. They get warm but not that hot. If you filled an 80 cuft bottle in under a minute it would be HOT and I wouldn't want to be in the same room when it happened.

The scariest O2 fill I ever saw was a steel 46 cuft bottle in less than a minute from 500 to 3000.

DivnSapper

Hey guys... thanks for the very detailed feedback and good suggestions... I agree with JDS' recommendation... I probably won't wait around for fills anymore... but noteworthy...$7.50/hr is a high paying technical salary here!

Correct... it's not a cascade but rather a series of individual cyliders arranged in an attempt to maximize the available O2 in the bottles.

Lastly, I guess I'm most surprised by the fact this is more of common experience than not... the poll really seems to suggest that rapid O2 fills (despite all the risks) may be a fairly common mistake.

Ryan

rjack

There is something "non-brass" in just about every scuba valve made - a nylon HP seat.

We have been discussing their "combustibility" over on TDS off and on for a couple months now.

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