How often do most shops in your area require Nitrox tanks to be O2 cleaned?

[PhilEllis]

Oh and that's "peace of mind," not "piece of mind." Piece of mind is what Phil got.

Luckily, as a result of nature, a small piece of mind.

Phil Ellis

 

[wedivebc]

In spite of k-valve's unprovoked attack on Phil and his credentials, and you may be a tech divers k-valve but your facts are wrong. Grade e air is not acceptable for O2 clean tanks. The standard of condensable hyrdocarbons in grade E air is 5 ppm the standard for grade E+ or nitrox clean air is 0.1 ppm. The problem with condensable hydrocarbons is they accmumulate with each fill. As was mentioned earlier the big danger is in the valve which is not designed for O2 service in the first place and has the ability to cause quite amout of heat to build up in a rapidly opening valve. Combine that with accumulated hydrocarbons and some adiabatic complression and one day the valve goes boom. I know of at least one person who injured her hand when the valve on the tank she was opening blew. The risk is not the diver's to accept it is the poor shop employee who has to rely on the diver not to put crap in his tank and yet is at risk when ever they pp blend nitrox for you.

 

[redacted]

The risk is not the diver's to accept it is the poor shop employee who has to rely on the diver not to put crap in his tank and yet is at risk when ever they pp blend nitrox for you.

Given such a risk that the shop is unable to control in any practical manner, why do so many shops continue the practice of PP blending in tanks they are unable to control?

 

[PhilEllis]

Given such a risk that the shop is unable to control in any practical manner, why do so many shops continue the practice of PP blending in tanks they are unable to control?

Continuous production and banked storage of enriched air often involves problems that some shops cannot resolve. Membrane and continuous blending systems are sometimes expensive, and low volume shops can't recover that cost. In some cases, stores in shopping centers or crowded business districts have no where for the equipment. In our store, we have seriously considered moving to continuous blending. It presents space, equipment, and cost considerations we are looking at closely.

Partial pressure blending can be done safely. Dick at Global has designed well tested procedures, materials, equipment, and chemicals to do the job correctly. The processes they proscribe have stood the test of time and are laboratory verified. However, the divergence of attitudes about the importance of cylinder cleanliness present a problem to many of us. Many of us simply put policies in place to attempt to gain some level of control over the filling process....to protect ourselves from those who have been whistling in the dark with their mantra of "once clean - always clean". A good example is the re-clean requirement during annual inspection. To ease the pain for customers with this policy, we charge a lower fee for the "annual re-clean" service than that which would be in place for a cylinder that has never been placed in service for oxygen use. To be honest, we also "police" cylinders that come from any "known bad actors" in the area. Unfortunately, there are those who do not take hydrocarbons seriously, do not think cleaning is necessary, and frankly, don't possess the knowledge to know the difference anyway. We usually know who they are. We have, on occasion, refused fills when we have knowledge that the cylinder have been filled, cleaned, or inspected by the "known bad actors". A poster on this thread would not be the first to think that sticking a black light into a cylinder, and seeing no glowing, gives indication that all is well for oxygen service. We try to educate these types of people, but sometimes it is not an issue of education. They simply don't know or care, and they have no interest in changing their minds. They are the perfect candidates for home filling and we strongly encourage them to do just that.

Phil Ellis

 

[redacted]

Partial pressure blending can be done safely. Dick at Global has designed well tested procedures, materials, equipment, and chemicals to do the job correctly. The processes they proscribe have stood the test of time and are laboratory verified. However, the divergence of attitudes about the importance of cylinder cleanliness present a problem to many of us. Many of us simply put policies in place to attempt to gain some level of control over the filling process....to protect ourselves from those who have been whistling in the dark with their mantra of "once clean - always clean". A good example is the re-clean requirement during annual inspection. To ease the pain for customers with this policy, we charge a lower fee for the "annual re-clean" service than that which would be in place for a cylinder that has never been placed in service for oxygen use. To be honest, we also "police" cylinders that come from any "known bad actors" in the area. Unfortunately, there are those who do not take hydrocarbons seriously, do not think cleaning is necessary, and frankly, don't possess the knowledge to know the difference anyway. We usually know who they are. We have, on occasion, refused fills when we have knowledge that the cylinder have been filled, cleaned, or inspected by the "known bad actors". A poster on this thread would not be the first to think that sticking a black light into a cylinder, and seeing no glowing, gives indication that all is well for oxygen service. We try to educate these types of people, but sometimes it is not an issue of education. They simply don't know or care, and they have no interest in changing their minds. They are the perfect candidates for home filling and we strongly encourage them to do just that.

Phil Ellis

In the name of safety, why does the small shop that can't justify one of the fancier systems, do PP blending in a couple of their own separate bank tanks and then fill nothing more than 40% into customers tanks? How much more would that cost than the apparently dangerous operation of directly filling 100% O2 into customer's tanks.

 

[danktex]

In the name of safety, why does the small shop that can't justify one of the fancier systems, do PP blending in a couple of their own separate bank tanks and then fill nothing more than 40% into customers tanks? How much more would that cost than the apparently dangerous operation of directly filling 100% O2 into customer's tanks.

It all comes down to the investment of money and space. Both of which are at a premium in any small business. Especially when PP blending, when done properly, has a pretty good track record.

 

[mike_s]

Honestly? I don't feel like looking all over the Internet to gather a fact here and there and piecing it all together for ya'll. You know you won't find it in any O2 Service Manual. We won't find it in guidelines developed by PADI or SSI. They make policies that support their affiliates. I don't blame them for that. It's a smart business plan. They want to O2 clean our tanks as often as they can.

Here are the points I tried to make:

1. I stated earlier in this convoluted mess that it doesn't matter how well you O2 clean a tank, it's going to be contaminated with the first fill that has any air in it, Grade E or otherwise. That said, you don't have to have a perfectly clean tank to do a safe O2 fill. It doesn't matter if there is a very small amount of contaminant.

2. The fact is that tanks don't have to be perfectly clean. I'm not saying that some yahoo can walk in with an old tank and that we should VIP it and call it good for oxygen use. The OP stated that his tanks were cleaned less than a year earlier. If they were cleaned properly and there hasn't been a catastrophic failure with the valve or neck o-ring, the tank hasn't been breathed down to near zero psi, or low grade air introduced then it's going to be clean enough for O2 service.

3. If a tank has been recently O2 cleaned we will be able to see any relevant contaminants with a good, quality VIP and a UV light. What is likely to get into a tank that is well-maintained? Nothing but gas. Now if someone is stupid and let's the gas out to lube the neck o-ring with motor oil we'll be able to see that.

4. I don't know you, but if you fill tanks with oxygen you know that you fill them slowly to avoid heating. Heating usually occurs by friction where the gas has to go around or through something too quickly. Like through the tank valve or tubing leading through the fill station. The build up of contaminants in valves is what is concerning because that's where most friction occurs. I didn't say don't clean your valves. I'm just talking about the tank and tanks don't have a bunch of tight turns that cause friction. The gas is usually heating before it's even introduced to the tank then continues to heat depending on how fast you fill it and how much pressure you apply. Anyone who fills a tank with a gas no more stable than pure oxygen should be looking out for this.

5. Once the gas enters the valve on the way out through the dip tube that's a whole new ballgame. But the tank? No. A minute bit of contaminant in a tank that you can't see with with a quality VIP (emphasis on the word quality) and UV scan isn't going to cause the dive shop to burst into flames. Not gonna happen.

Now that I've said all of that I still think even the best maintained tank needs to be O2 cleaned on some kind of schedule. I just don't think it is necessary for all tanks to have an annual O2 cleaning, and I don't think you have to tumble them if there isn't a good reason to do it.

Now if ya'll want to go find a bunch of research to dispute that knock yourselves out. I'm not going to go find any to contradict what is found. Research is a funny thing...there is something out there to dispute about anything you want to argue about. It's all up to the researcher and if and how much they are biased. I'm not interested in a debate. I've given my 2 cents. Take it for what you will. Do with it what you'd like. I'll continue to do what works for me...you all can continue to do what works for you.

I still don't see anything in all that babble to backup your earlier statement that if a UV light doesn't show anything that is "clean enough for o2 use".

 

[texdiveguy]

I regards to a UV light being used in the process of evaluation of the O2 clean status of a scuba cylinder, it IMO is just another 'tool' that is available in helping detect some trouble areas that may require additional attention in the cleaning process.

For all us home and scuba shop O2 cleaners there is no such thing as a 100% O2 clean anything, just not possible in these environments, but we can get close enough to allow us the safety margins needed to properly fill blends as needed.

 

[mike_s]

I regards to a UV light being used in the process of evaluation of the O2 clean status of a scuba cylinder, it IMO is just another 'tool' that is available in helping detect some trouble areas that may require additional attention in the cleaning process.

I agree with you that it might detect something (if the tank was dirty)... but that's not what he said.

He said that if the UV light shows nothing, then the tank is clean enough for O2 use.

I don't many folks that would agree with that being true.

reference:

UV light testing. Anyone who can do a decent VIP on a tank should be able to see most indications that would point toward a required O2 cleaning. After that, use a UV light to look for other contaminants that fluoresce. If nothing shows then the tank is clean enough for O2 use.

 

[PhilEllis]

I agree with you that it might detect something (if the tank was dirty)... but that's not what he said.

He said that if the UV light shows nothing, then the tank is clean enough for O2 use.

I don't many folks that would agree with that being true.

reference:

The following is a quote from a paper titled "Inspection of Scuba Gear by Ultraviolet Light" by Dr. Dick Boyd and Greg Kent.......

APPLICATIONS OF UV-A LIGHT INSPECTIONS: Unfortunately, UV-light is NOT infallible as applied for hydrocarbon detection. Many modern chemical products DO NOT fluoresce and therefore cannot be sensed by UV A-light methods. Two diving-related examples of non-fluorescing materials are synthetic compressor oils and most silicone grease compounds. Among diving technicians, these chemicals are recognized as the most likely contaminants to pervade scuba oresce. Consequently, GMC does not recommend UV-inspection of dive tanks after oxygen-cleaning. If the presence of the most common pollutants cannot be confirmed by UV-A, the purchase and use of a tank VIP Blacklight costing many hundred of dollars makes no sense! Many military and research organizations agree with this point, and no longer mandated Blacklight inspections for all types of oxygen equipment.

You can argue with these guys, it just makes your argument look silly.

Phil Ellis