How long can air sit in a tank?

[Deep South Divers]

$4 air fills in Georgia? Where is this? I'm in South Carolina, right next to Savannah, GA.

At $4 per fill, that barely covers the cost of electricity and filters, oil, and maintenance of our compressors. At $4 per fill, I'd be happy to sell my compressors off and just let someone else fill my tanks.

I suspect that if a business is giving away free fills or doing $4 air fills, then they aren't maintaining their compressors properly... I mean, why would they spend anywhere from $2k to $20k for an average dive shop compressor system to MAYBE cover operational costs or actually pay to fill your tanks? I suspect that they're shortcutting somewhere to make a $4/fill business model fly.

Please provide shop name and contact information so that I can go get my tanks filled there. I'd enjoy testing their gas. If it tests well, I'll bring my tanks to them and sell my compressors and pay off a few loans that I have.

FWIW, when someone asks me for a fill, I charge $10 for air. My air is tested modified J grade (or the lower "E" grade if they want it), every fill is cold and at 105% capacity, and filled in six minutes from empty, so virtually immediately.

If someone wants to complain about a few dollars per fill, then I point them up the road to the $5/fill dive shop where their gas tastes like an oil refinery.

Funny... Nobody complains about price any more.

 

[Doc Harry]

At $4 per fill, that barely covers the cost of electricity and filters, oil, and maintenance of our compressors. At $4 per fill, I'd be happy to sell my compressors off and just let someone else fill my tanks.

Having your own compressor is usually never about saving money, it's about convenience.

 

[sarahdive]

Is there any difference between filling your tank through a fire department over having a dive shop do it? My dive shop costs $15 but my local fire department costs $8. When I have 4 tanks to fill I like that savings. And their inspections and Hydro's are cheaper too....
Don't get me wrong, I love my dive shop but it's so expensive for everything it makes it hard to go back.

 

[flots am]

Is there any difference between filling your tank through a fire department over having a dive shop do it?

That depends on how clean their air is.

Air that's just ducky to breathe at 1ATA (in a burning building) might not be OK at 100', depending on the contaminants and their level.

Just because it's OK for the FD doesn't make it OK for you.

Now lots of FDs have awesome compressor setups, but many don't. The catch-22 is that the places with great air have great maintenance and probably money, which means that they probably also have risk-management people that won't let them fill outside tanks.

The places that let you come on in and fill your own are likely to be the places where you shouldn't be doing it.

flots.

 

[Deep South Divers]

Not inherently. For example, there's no legal difference or quality of air difference just because one place is a dive shop and the other a fire department. Both pump "E" grade breathing air as a minimum unless otherwise stated.

Some dive shops (not fire departments) have gotten into "nitrox" fills, more accurately called "enriched air" or "EANx." These compressor systems can be "hyperfiltered," even further improving the quality of the air pumped, which is designed to improve safety for use when adding oxygen to air. "Hyperfiltering" is as simple as taking the "E" grade air already coming out of the compressor and passing it through another series of filter mediums, which purifies the air even further. This hyperfiltered air is called "JJ" grade or "modified J" grade air. There is no advantage to it except when using it to mix with high pressure oxygen for EANx or trimix applications... And even then, only in an effort to reduce fire hazard during the mixing process. There is no advantage from a diver's perspective in terms of usable depth, NDL, or reduced particulate toxicity.

Once mixed, the breathing gas is no longer called "air," but is called "gas," or "mix." Often divers doing more advanced dives will refer to all breathing gasses - even air - as "mix" or "gas" to denote that it may or may not be air (about 21% O2, 79% N) in their cylinder.

...So yes, there can be a difference in quality of air from these sources if the dive shop is hyperfiltering their air for mixing with oxygen ("nitrox" or "trimix"), but not from a practical diver's perspective... Assuming, of course, that the compressors are both maintained properly.

The biggest difference from place to place - regardless of what sort of establishment it is - is the maintenance level of the compressor... Which has a direct effect on the quality of the gas. Aside from hyperfilters, all breathing air compressors pump "E" grade air so long as they are maintained properly.

Most compressor maintenance boils down to changing filters on a proper interval. There should be a record of this. Ask to see the maintenance record. Filter-change requirements vary widely, and can be as often as every 6 hours of compressor use, but can be as high as thousands of hours. Obviously, to know proper changing intervals, a compressor would have to have an hour meter on it, and there isn't always one. This is a red flag to me.

...Another red flag is a general compressor condition. Is it sitting in a puddle of oil? Are there spider webs on it? Is it kept outside to be rained on? Someone who cares about the quality of their breathing gas is going to be particular about their compressor's appearance as well. A dirty compressor is an indication of someone who doesn't care - or doesn't know any better.

The only other difference that I can think of is convenience. With the fire department, are they offering immediate fills or do you have to leave them there for filling, meaning that a fill will cost you two trips? Is one more local than the other?

Having said all of this, many fire departments don't allow for their compressors to be used for non-fire department use. That is, many divers can't get fills from them unless they work there. Liability is often blamed for the reasoning. If your local fire department is filling tanks, then consider yourself lucky to have a choice on where to go for fills.

$15 is a LOT of money for an air fill. $8 is cheap. My gut feeling is that I would beware of both places and really look at the quality of the gas - and service - of both, and spend the extra money if you're actually getting something for the difference. If not, then get your fills from the cheaper of the two.

 

[Luis H]

Actually the requirements for SCBA and other surface breathing air is grade “D” not grade “E” (per OSHA and NFPA codes). That being said any good breathing air compressors will meet or exceed grade “E” (if it is maintained properly), but the difference is that they may not test it to grade “E” if it is not used for Scuba.

I know the Navy SCBA compressors and many fire departments only test to grade “D”.

---------- Post Merged at 10:42 PM ---------- Previous Post was at 10:37 PM ----------

Is there any difference between filling your tank through a fire department over having a dive shop do it? My dive shop costs $15 but my local fire department costs $8. When I have 4 tanks to fill I like that savings. And their inspections and Hydro's are cheaper too....
Don't get me wrong, I love my dive shop but it's so expensive for everything it makes it hard to go back.

If they are actually selling air, you can ask them if they meet grade "E" requirements. Just tell them you are using it for Scuba diving (not for paint ball) and they should know.

 

[Deep South Divers]

Not exactly.

During the testing process, the lab simply reports what is in the gas tested. There is no "test to a certain grade." The results are simply compared to graded values and therefore judged as "grade E" or "grade D" or whatever. If someone is telling you that "they only test to grade D," they don't understand the testing process. If they tell you the gas "failed grade E standards," that's another story. But that doesn't really happen. I've never seen it unless something is seriously wrong... Like there was a puddle of oil in the scuba tank to begin with. Or the filter hasn't been changed in 150 hours of operation, when it should have been changed in 10... AND the compressor is being used while in a small room filled with diesel smoke.

"Grade E" air is simply "grade D" air with stricter oxygen content, less hydrocarbons, and less water content. The ANSI/Compressed Gas Association (CGA), the ones who created the "grade D" and "grade E" standards, created "grade E" "for all compressed air stored in air cylinders, e.g., SCBA tanks or large breathing air cylinders" (cited from ANSI/CGA). According to OSHA regulations (taken from OSHA 1910.134(i)(4)(ii)), "Cylinders of purchased breathing air have a certificate of analysis from the supplier that the breathing air meets the requirements for Grade D breathing air; and the moisture content in the cylinder does not exceed a dew point of -50 deg.F (-45.6 deg.C) at 1 atmosphere pressure." In other words, "grade E" air. I suspect that the terminology of "grade E" would have been used by OSHA rather than "grade D with less water content" had it been a standard at the time of OSHA's writing.

...Which would be consistent with my experience with OSHA using outdated regulations to govern the workplace... And adding to a lot of confusion for those trying to adhere to it's standards.

What's all of this mean to the layman? It means that if a fire department is filling either scuba or scba tanks, they, too, have to use "grade E" air at the very least, as per ANSI/CGA standards, AND as per OSHA standards, although they didn't actually call it "grade E" because "grade E" wasn't yet invented when they wrote the standard.

...Which is why compressors today that fill tanks (not hookah compressors - which are what use a "grade D" standard because they don't fill tanks and therefore operate at lower pressure) all are "grade E" compliant and use filters that will result in "grade E" quality air at a minimum.

...So if someone is telling you that they "only test to grade D," then they are mistaken. And if someone is actually filling tanks with air that does not at least meet "grade E" standards, then they are not ANSI/GGA or OSHA compliant. I suspect that they wouldn't be NFPA compliant either, and could possibly be in violation of the law (depends).

Bottom line: If anyone is filling tanks and using a commercially available compressor and commercially available filter and is maintaining the equipment to specification, it's a safe bet that it's "grade E" or better unless there is something REALLY wrong.

 

[Luis H]

Thanks for the response… I am glad you are quoting some specs.
This is definitely not my area of expertise. I just occasionally have to cover for one of my coworkers when we have to test the shipboard SCBA compressors.

The air test is sometimes done at the lab, but it is often done with a field test kit. I don’t do any of the testing, I am just the engineer observing the technician and I have actually not even been present when they do the air quality testing.

I may be wrong, but my understanding is that the field testing kits are only a pass/ fail and only for grade “D”.

I have also seen reports from the lab, but I can’t remember exactly what they reported.

What I do recall very clearly is that the SCBA compressors are not authorized to be used for Scuba air. I have no dough that the SCBA compressors aboard all the new classes of Navy ships will meet or exceed grade “E”, but I have no way of proving it since the air is only tested to grade “D”. These are brand new Bauer head compressors custom assembled to meet shock requirements and I am sure they are using the best filter system, but they are not “approved” for grade “E”. I know the immediate reaction is that the Navy is behind the times… and that is partially true, but not exactly.

 

[Deep South Divers]

All of the field test kits that I've used aren't actually test kits at all... They're sampling kits. A sample is taken and then sent into the lab for thorough analysis.

In Googling "field test kit grade D" I found these: Air Quality Kits, Respiratory Protection, Respirators, Breathing Protection Notice that there are NO "grade E" test kits available here... Only "grade D." It suggests that "grade E" isn't something that is tested in the field, and a perfect reason why the USN would not be able to test any further than "grade D" in the field, assuming that they wanted to perform the pointless exercise of seeing if their "grade E" required gas can pass a "grade D" field test.

I am surprised to find on that page a "grade D" test kit available for high pressure compressors, which are going to be the ones used to fill SCBA and SCUBA bottles. Notice that most of them are for low pressure "hookah" compressors only. That's because the regulation (ANSI/CGA/OSHA and maybe NFPA) is to only use "grade E" or better when filling high pressure (in this case, "high pressure" denotes anything more than about 300 psi) tanks. Perhaps this is the unit that you guys are using.

I also found this: Compressor Supply & Consumables - Air Test Kits These are also called "field test kits," although they aren't test kits at all... They're merely sampling kits that you use to obtain a sample of the gas to be analyzed, and then send it into a lab for a thorough analysis. Notice that there is a "grade D" test kit for low pressure compressors (like on hookahs or "surface supplied" air such as a Brownie's Third Lung and other unbottled gas) and a "grade E" test kit for high pressure compressors like those used to fill SCUBA and SCBA bottles.

In your case where sometimes the air is tested for "grade D" and sometimes for "grade E," I would have complete confidence that the compressor was always "grade E" compliant as long as the maintenance (which means mostly filter changes) was kept up with... And with a "grade E" pass, I have no idea why they would not allow the compressor to be utilized for SCUBA bottles. The fittings are different on each of the bottles... Perhaps it is a plumbing issue. Or perhaps they simply don't want SCUBA bottles and SCBA bottles to be mixed in the same vicinity onboard the ship.

 

[sarahdive]

I've learned so much here, thank you all for commenting. My husband and I are volunteer EMT's and the 02 tanks we use on the rigs are filled at the fire department (right next door). When we go over there to fill our SCUBA tanks I'll be sure to make note of the overall looks of the compressor set up and ask them about the Grade of their air. I learned about nitrox in my class but at this point it's not something I'm using or plan on using. Maybe down the road though.