Questions about filtration

[nadwidny]

How so? I tend to not trust this kind of claim. What basis do you have for making it?

I test compressed breathing air and medical O2 for a living. Compressed breathing air standards here in Canada allow 10ppm methane. That's both for Z180 (fire depts, etc) and Z275 (divers). Medical O2 (the stuff that most of us use for PP blending) allows either 25 or 50ppm, depending on which standard is being used. I asked a buddy of mine who is a chemical engineer for Praxair why there was a higher level of methane in "pure" O2 as compared to air and he said that it's because they can't filter the stuff out when making O2.

Typically our air samples come in at ~2ppm of methane. I had a 99% O2 sample the other day from a hospital drawn from their bulk tank that had 25ppm methane-not an unusual amount.

So what is the big deal about Grade "E" air? The shops I've been to take it as a matter of religion that if your tanks are O2 clean, filling them even once with Grade "D" air hopeless contaminates them.

Because the Grade D standard is so liberal as to be useless. Although IMHO the same goes for Grade E when compared to the standards here.

And if methane is used as a marker for general hydrocarbon contamination, what would be the source given the oil/particulate level is held to the spec'd level ?

I'm not sure who would be using methane as a marker for hydrocarbon contamination. That's pretty stupid. Methane is natural and exists everywhere and can't be filtered out.

 

[JohnN]

I'm not sure who would be using methane as a marker for hydrocarbon contamination. That's pretty stupid. Methane is natural and exists everywhere and can't be filtered out.

I got that from the reference to the "E" and "D" standards link

Methane is an odorless, colorless gas naturally present in air. It occurs naturally in the atmosphere at a concentration of about 2 ppm. It is the simplest lower molecular weight hydrocarbon.

Levels at or below 25 ppm are considered safe to breathe. Methane by itself is not known to be toxic at levels up to 50,000 ppm, but can act as a simple asphyxiant if it displaces enough oxygen. At 50,000 ppm and higher, the biggest danger posed by methane is it flammability.

Being the simplest lower molecular weight hydrocarbon, methane is the easiest to measure and therefore the most common lower molecular weight hydrocarbon tested for. There are several thousand lower molecular weight hydrocarbons (benzene, toluene, ethylbenzene, xylene, methanol, isobutane, acetone, propane, etc.), making it impossible to check for the presence of them all. It was for these reasons standardizing bodies originally chose methane, or 'total methane equivalents', to represent the entire group.

Methane, and all of the other lower molecular weight hydrocarbons, are separated from higher molecular weight hydrocarbons in air quality standards and given a separate limit because of the different effect they have on the body. Higher molecular weight hydrocarbons are typically used as lubricants in compressors and for lubricating various breathing equipment components. They are more likely to remain stable at a given temperature and pressure, and are tested under the separate category 'oil mist'.

The lower molecular weight hydrocarbons are more likely to vaporize under the same condition, thus earning the familiar expression 'volatile organic compound'. Unlike oil mists and droplets, which generally do not pass beyond the lungs, volatile organic compounds are gaseous in form at room temperature, allowing them to pass through the lungs, absorb into the blood stream, and become widely distributed in the body, including the brain. The lethal concentration of toluene exposure, for example, is estimated at just 1,900 ppm for one hour. The short-term and long-term toxicity of all volatile organic compounds is not yet fully known, but they are capable of acting like an anaesthetic with undesirable side-effects. Some side-effects are cardiac irritability, predisposing one to arrhythmia and sudden cardiac death.

The presence of any volatile organic compounds is abnormal. It indicates something is wrong with breathing air production or storage and should be investigated. Besides being potentially toxic and flammable, they can also degrade breathing air gear and filter performance, which can result in other dangerous conditions.

FWIW, the other hydrocarbons they cite (benzene, toluene, ethylbenzene, xylene, methanol, isobutane, acetone, propane, etc.) are all higher, not lower molecular weights, not to mention mixing up ketones with alcohols, with benzene rings. Sigh. . .

 

[nadwidny]

Interesting but I don't see how they can use methane levels as a marker for anything else. I suspect that the methods of analysis available when the standards were originally written were not as discriminating or as accurate as the methods available today. With our method of analysis we can identify the different hydrocarbons (methane looks different than propane which looks different from gasoline which looks different from diesel, etc). We can see normal levels of methane but elevated levels of other compounds, if present (very, very rare by the way).

I can see how the presence of VOC's can indicate other problems, but the "methane as a marker" thing doesn't make sense to me.

 

[opie712]

IM not sure if this has got off topic or what but my question was I have seen where people are blending with just the PO filtration which is grade"D" is that adequate filtration who mixing gas or should I upgrade my filter to a tower where it will produce OCA

 

[Wookie]

And I think that the answer was that grade D air is fine for breathing at the surface in a hood, but if you are subject to the elevated partial pressures of scuba diving, you need to have grade E air. Oxygen mixes fine with grade D air, so if you are in a sandblast hood or level 4 containment biohazard facility, Grade D nitrox is fine. If you are putting it in a scuba cylinder, it needs to be grade E or better.

 

[opie712]

And I think that the answer was that grade D air is fine for breathing at the surface in a hood, but if you are subject to the elevated partial pressures of scuba diving, you need to have grade E air. Oxygen mixes fine with grade D air, so if you are in a sandblast hood or level 4 containment biohazard facility, Grade D nitrox is fine. If you are putting it in a scuba cylinder, it needs to be grade E or better.

Thanks wookie if the question was answered IM sorry I didn't understand it your post was the info I was looking for much appreciated

 

[JohnN]

And I think that the answer was that grade D air is fine for breathing at the surface in a hood, but if you are subject to the elevated partial pressures of scuba diving, you need to have grade E air. Oxygen mixes fine with grade D air, so if you are in a sandblast hood or level 4 containment biohazard facility, Grade D nitrox is fine. If you are putting it in a scuba cylinder, it needs to be grade E or better.

I'm still confused. If that comparison of Grade "D" vs "E" air is accurate (Compressed Air Quality Test: Grade D, OSHA 1910.134), where is the issue (particularly if O2 contains methane at or near the thresholds specified by Grade "E")?

--------------------- detail added --------------------------------

So the more I look into this, the more this looks like a total mess. In addition to the OSHA "D" and "E", there is "Modified E" where the definition seems entirely up to whoever is making the specification.

Here is a chart from Trace Analytics:

https://www.airchecklab.com/service...a-sport-diving-compressed-air-specifications/

[h=2]SCUBA / Sport Diving - Selected Air Quality Specifications[/h]
Air Quality Specification	THC	CO	CH4	CO2	H2O	DP, °F	O2	N2	OIL	ODOR	Other
CGA G-7.1-2011 Grade E (0)	25	10	N/A	1000	24	-65	20-22	N/A	5	None/Slight	N/A
CGA G-7.1-2011 Grade E (1)	25	10	N/A	1000	N/A	N/A	20-22	N/A	5	None/Slight	N/A
CGA G-7.1-2011 Grade E (2)	25	10	N/A	1000	N/A	N/A	20-22	N/A	5	None/Slight	N/A
CSA Z180.1-2013 (>2216 psig)	5 (T)	5	10	600	27	-63	20-22	N/A	1	None/Slight	Halogenated Hydrocarbons, ppmv	Atmospheric Dewpoint, °C
5	-53
Enriched Air Nitrox - 1995 & CGA G-7.1-2011 Grade E(2)	25	10	N/A	1000	N/A	N/A	(O)	N/A	0.1	None/Slight	N/A
Nitrox Technologies 36-2001	25	10	N/A	1000	N/A	N/A	(O)	N/A	5	None/Slight	N/A
ANDI Oxygen Compatible Air-1994	25	2	N/A	500	128	-40	20-22	N/A	0.1	None/Slight	No. Particles > 2 µm Diameter
None
IANTD Oxygen Compatible Air-2003 (I)	25	2	N/A	1000	N/A	N/A	20-22	N/A	0.1	None/Slight	N/A
Oxygen Compatible Air-1994 (A1)	25	2	N/A	500	128	-40	20-22	N/A	0.1	None/Slight	No. Particles > 2 µm Diameter
None
Oxygen Compatible Air-2003 (I)	25	2	N/A	1000	N/A	N/A	20-22	N/A	0.1	None/Slight	N/A
THC = Total Gaseous Hydrocarbons, ppmv CO2 = Carbon Dioxide, ppmv O2 = Oxygen, volume % N2O = Nitrous Oxide, volume % CO = Carbon Monoxide, ppmv H2O = Water, ppmv N2 = Nitrogen, volume % Odor = Odor as supplied by customer CH4 = Methane, ppmv DP = Dew Point, °F at 0 psig Oil = Oil Mist & Particulate, mg/m3 HS = Halogenated Solvents, ppmv
(0) This specification is for applications where the CGA G-7.1 SCBA requirement for water content is employed. It combines the stricter limits of the Grades L and E. (1) This specification is intended for applications that do not require a water content specification. CGA G-7.1-2011 has no water content limit for Grade E, for which the typical use is listed as SCUBA air. As allowed by CGA G-7.1-2011, Table 1, Note 6, water content is not specified nor reported. Note 6: "The water content of compressed air required for any particular QVL [grade] can vary with the intended use from saturated to very dry." Water ppmv and dew point is not reported. (2) This specification is intended for applications that do not require a water content specification. CGA G-7.1-2011 has no water content limit for Grade E, for which the typical use is listed as SCUBA air. As allowed by CGA G-7.1-2011, Table1, Note 6, water content is not specified but is reported. Note 6: "The water content of compressed air required for any particular QVL [grade] can vary with the intended use from saturated to very dry." Water ppmv and dew point is reported. (A1) This specification for oxygen compatible air is taken from ANSI/CGA G-7.1-1989 Grade E as modified by American Nitrox Divers International (ANDI) in their document Standards and Recommendations for Users, October 1994. (I) This specification for oxygen compatible air is taken from ANSI/CGA G-7.1 Grade E as modified by International Association of Nitrox and Technical Divers (IANTD) in their document Blending Standards, 2003. (O) Oxygen varies according to limit requested by customer. (T) Does not include methane.
Air & Gas Specifications referenced above may be viewed and/or purchased from: ANDI - American Nitrox Divers, Int'l • CGA - Compressed Gas Association • CSA - Canadian Standards Association • IANTD - International Association of Nitrox & Technical Divers, Inc.

At first blush, it looks like CGA decided to drop the methane component, so their Modified E(1) and E(2) looks identical to OSHA "D" to me and CGA E(0) only adds a moisture/dew point specification.

I'm forced to conclude that unless you look at the analysis report on the last sampled air, Grade "E", Grade "D", Grade "E" modified doesn't mean crap

 

[Wookie]

I'm still confused. If that comparison of Grade "D" vs "E" air is accurate (Compressed Air Quality Test: Grade D, OSHA 1910.134), where is the issue (particularly if O2 contains methane at or near the thresholds specified by Grade "E")?

I'm forced to conclude that unless you look at the analysis report on the last sampled air, Grade "E", Grade "D", Grade "E" modified doesn't mean crap

I happen to agree with you. The nitrox technologies spec for nitrox specifies 32+.5% oxygen for their nitrox spec. I happen to have a Nitrox technologies membrane system, so that's the spec I used to use, but sometimes I make 36%, sometimes 28%, depending on client needs. I asked Trace to remove the spec on O2 content, and they wouldn't, so I asked them to widen the range from 32+.5% to 21% to 40%. They were happy to comply. Now, I test for CGA Grade E, CGA OCA in the air compressor and CGA OCA and Nitrox Technologies 32% (Modified) in the Nitrox compressor. Actually, I test banked gas, as then there isn't a question of when I changed the filters.

The point is that Trace will analyze to any specs you want. It's up to the operator to determine if their air is any good. Most operators don't have a clue as to what the specs or requirements are, so they blindly trust Trace (or TRI) to make the determination for them.

I do know a fella who routinely CBs 80% through his mariner. He comes to me when he has carbon inside the filter tower and pieces of charred filter in his cylinders. You buy them books and you buy them books....

 

[swamp diver]

I have been reading through some old threads regarding nitrox continuous blending right now the only filter I have on my bauer compressor is the PO filter, some was saying that they were blending with only the PO filter and just doing more frequent filter changes. Im almost 100% positive that my filter bauer brand said grade D and LF website confirms theirs is grade D. I was under the impression that isn't adequate filtration for o2, am I wrong you don't need OCA air to continuous blend that the PO would be enough. if the PO isn't enough would a 16" or a 33" tower work.

Oxygen compatible air is used to partial pressure blend nitrox and you don't need OCA output unless you plan to take your tanks to another fill station which will pp blend. If that is the case your compressor must produce OCA whether it is pumping air or nitrox in order to keep your equipment O2 clean.

OCA requires you to follow one of the OCA standards which is not Grade E air. For OCA the condensable hydrocarbon (aka liquid oil mist) is lowered from 5 mg/m3 to 0.1 mg/m3 which minimizes any contamination of the tank or valve with oil mist. If your compressor does not meet the 0.1 mg/m3 oil mist and particulate specification then you should restrict that tank to pre-mix only when away from home. The tank will not be O2 clean.

Here are several OCA standards but the common theme is a much tighter oil and particulate specification.
Oxygen Compatible Air

---------- Post added November 8th, 2014 at 11:41 PM ----------

Interesting but I don't see how they can use methane levels as a marker for anything else. I suspect that the methods of analysis available when the standards were originally written were not as discriminating or as accurate as the methods available today. With our method of analysis we can identify the different hydrocarbons (methane looks different than propane which looks different from gasoline which looks different from diesel, etc). We can see normal levels of methane but elevated levels of other compounds, if present (very, very rare by the way).

I can see how the presence of VOC's can indicate other problems, but the "methane as a marker" thing doesn't make sense to me.

Methane is not used as a proxy marker of compressor contamination but rather it is the reference against which the lab measures the other potential VOC compounds in the sample. If using the GC/FID for example methane is measured as a one which relates to the number of carbon atoms. Pentane would would produce an output of 5 if the analyzer is calibrated to measure in 'methane equivalents', heptane a 7, etc. They could measure in xylene equivalents as some standards do for TVHC reporting. Essentially the FID counts the number of carbon atoms but the result is not the absolute concentration of pentane rather the number is simply relates to methane equivalents and tends to overestimate the true value which is a good thing when you are screening a sample for VOCs.

The GC/FID methodology is the best option for screening a sample when multiple unknown volatile hydrocarbons may be present. Infrared spectroscopy is another methodology used to screen samples for VOCs. In the US the value is reported as total volatile hydrocarbon (TVHC) which includes methane whereas in Canada we subtract the methane off the TVHC result to give 'non-methane hydrocarbons' (NMHC) (TVHC = NMHC + methane).

None of this has anything to to with methane being a marker for other volatile hydrocarbon contamination produced by the compressor.

Most labs (mandatory in Canada) if they see a TVHC > ~ 5 ppm will use a secondary analytical method like GC/MS to formally identify the VOC(s) in question and quantity it.

---------- Post added November 8th, 2014 at 11:58 PM ----------

How so? I tend to not trust this kind of claim. What basis do you have for making it?

Oxygen is made by fractional distillation so air is cooled to about -200 C and then the liquid air enters a tank with a heater in the bottom to warm the air just above the boiling point for nitrogen which then is collected as a gas. Methane has a boiling point very close to oxygen so the ambient air methane ends up being concentration in the oxygen fraction.
http://2.bp.blogspot.com/-kqdpwOIoFpQ/TZ2s_Y75vII/AAAAAAAAGJI/k3pKAZ4eHQ4/s1600/IMG.jpg

Nitrous oxide or 'laughing gas' also concentrates in the oxygen fraction which is why there is a spec for this compound in many of the diving and aviator oxygen standards. Elevated levels of N2O can be found downwind of recently manure fertilized farmer's field.
Nitrous Oxide Emissions | Climate Change | US EPA

---------- Post added November 9th, 2014 at 12:06 AM ----------

I test compressed breathing air and medical O2 for a living. Compressed breathing air standards here in Canada allow 10ppm methane. That's both for Z180 (fire depts, etc) and Z275 (divers). Medical O2 (the stuff that most of us use for PP blending) allows either 25 or 50ppm, depending on which standard is being used.

Typically our air samples come in at ~2ppm of methane. I had a 99% O2 sample the other day from a hospital drawn from their bulk tank that had 25ppm methane-not an unusual amount.

Do you work for Maxxam Analytics or RPC which are the only two accredited labs in Canada because both the most recent versions of CSA Z180.1-13 and Z275.2-11 state an accredited laboratory shall be used?

In Z275.2 breathing oxygen is allowed to have 30 ppm of methane absolute and in the medical gas standard Z7396.1-12 they allow 100 ppm of methane and 5 ppm of nitrous oxide for oxygen.

 

[nadwidny]

Do you work for Maxxam Analytics or RPC which are the only two accredited labs in Canada because both the most recent versions of CSA Z180.1-13 and Z275.2-11 state an accredited laboratory shall be used?

I am with AirChekLab in Alberta. As of this past September we are also an accredited lab with the SCC, so that makes 3.