Quality of Breathing Gases at Fill Express

At Fill Express, we describe our breathing gases as Ultra Pure. On this page, we provide the information to substantiate that statement. Each quarter a certified independent testing laboratory tests gases at Fill Express. The information that follows describes the tests they perform and the quality of breathing gases at Fill Express. You may also examine a recent test report.

Links on this page: Breathing Gas Quality
Carbon Dioxide (CO2) Carbon Monoxide (CO) Odor	Oil and Particulate Matter Total Volatile Hydrocarbons Water Vapor (H2O)

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Breathing Gas Quality

Breathing gas quality is especially critical when using breathing gases in SCUBA diving. This is because, as depth increases, so does the partial pressure exposures to contaminants in the breathing gas. Industrial emissions, vehicle exhaust, combustion heating activities, and local environmental conditions can seriously degrade the quality of intake Air used during compression. Compressor equipment, malfunctions, poor maintenance or operational practices can also introduce contaminants into SCUBA cylinders. In order to assure good quality breathing gases, regular testing must occur.

In order to evaluate the results of tests, a comparison specification is required. There are several generally similar specifications for breathing gases, including the National Fire Protection Association (NFPA) 1500, U.S. Navy Diver's Air L-1, Federal Spec BB-A-1034 II A, and Compressed Gas Association (CGA) G-7.1-1997 Commodity Specification for Air. In our opinion, the appropriate specifications for evaluating breathing gases used in recreational SCUBA diving are:

The CGA Grade "E" quality verification level has become the specification most widely referenced for sport diving. CGA Grade "E" is generally considered to be the absolute minimum acceptable breathing gas quality for SCUBA diving, and many consider it to be too liberal. Filling an "Oxygen Clean" cylinder with CGA Grade "E" will introduce hydrocarbon contamination such that the cylinder is no longer considered O2 clean and may not be used for partial-pressure blending.
"Oxygen-Compatible" is CGA Grade "E" with reduced maximum acceptable carbon monoxide, hydrocarbon and particulate levels. The International Association of Nitrox Divers (IANTD) and American Nitrox Divers International (ANDI) created this designation for gases used in technical diving and gas blending. The U.S. Navy and the American Academy of Underwater Sciences (AAUS) have also issued "Oxygen-Compatible" specifications. All the "Oxygen-Compatible" specifications are similar but not identical. For the purposes of this discussion we'll use the IANTD "Oxygen-Compatible" specification.

Click the image at left to view a PDF of recent test results for breathing gas quality at Fill Express. Note the "<" (less than) symbol for levels of carbon monoxide, oil/particulates, and hydrocarbons means Fill Express gases are so pure, the results indicate levels below the detection thresholds of the tests. Breathing gas fills from dive shop compressors that are not regularly tested often do not meet even the Grade "E" specification, much less the "Oxygen-Compatible" specification. If there is no current test certificate posted at the fill station, you should consider carefully what its absence might indicate.

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Carbon Dioxide (CO2) -- CO2 levels in Air up to 10,000 ppm are not considered hazardous. However, compressed breathing gas with CO2 levels that are at the high end of this range can create problems while SCUBA diving. High CO2 levels in SCUBA diving can produce many of the milder symptoms of Carbon Monoxide poisoning, such as headaches and dizziness. In addition, high CO2 levels increase breathing rates and increase gas consumption during diving.

Parts Per Million	Gas Standard or Test Result
1,000 ppm	Allowed maximum for CGA G-7.1 Grade "E"
Less than 1000 ppm	Test results for Fill Express gases

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Carbon Monoxide (CO) -- CO, a colorless, odorless gas, ranks as the most dangerous compressed breathing gas contaminant. Headaches, dizziness, unconsciousness, or death can occur from exposure to even slightly elevated CO levels.

Parts Per Million	Gas Standard or Test Result
10 ppm	Allowed maximum for CGA G-7.1 Grade "E"
2 ppm	Maximum for IANTD "Oxygen-Compatible"
Less than 0.3 ppm	Test results for Fill Express gases

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Oil (condensable hydrocarbon mist/vapor) and Particulate Matter -- Inhaling hydrocarbon based oils from improperly maintained oil lubricated compressors can cause a serious inflammation of the lungs, known as lipoid pneumonia. Inhaling very fine particulate matter has been associated with respiratory and cardiac problems, infections and asthma attacks. Particulates also clog inlet filters of SCUBA regulator first stages, causing poor performance and increased breathing effort. The build up of oils and particulates in a SCUBA cylinder can provide the fuel and source of ignition for combustion inside the cylinder during filling, introducing the possibility of severe contamination.

Fill Express uses a food-grade synthetic lubricant which eliminates many of the health and safety concerns of oil lubricated compressors. Regardless of the type of lubricant, even with various filters, it is still possible for lubrication or fine particulates to be present in the compressed gases. These contaminants can condense on storage bank walls and in gas lines. Re-introduction into the gas flow stream from build up in storage banks can then occur at a later time. Sampling procedures involve connecting a filter assembly to a fill whip at our fill station and passing a known amount of a large volume of gas through a pre-weighed filter. The total weight of material trapped is then measured.

Milligrams Per Cubic Meter	Gas Standard or Test Result
5 mg/m3	Allowed maximum for CGA G-7.1 Grade "E"
0.1 mg/m3	Allowed maximum for IANTD "Oxygen-Compatible"
Less than 0.02 mg/m3	Test results for Fill Express gases

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Odor -- Because the sensory response of the human nose is highly variable and extremely sensitive to certain odors, evaluation of odor is highly subjective. Very clean breathing gases will sometimes be said to have an odor, when actually the smell of the sample is merely "different" than the ambient odors of the surrounding environment. Although not harmful, the presence of a pronounced odor in a breathing gas is unsatisfactory. Fill Express gases do not have a pronounced odor (the minimum reporting level for Trace Analytics is "None/Slight").

Rarely, a individual will report that a fill has a slight odor. Customers with a very sensitive nose may sense what some describe as a slight "fresh", "sweet", or "pine" odor. Experts have attributed this to components of oxygen compatible food grade lubricants used in compressors and used in lubricating the neck threads of cylinders and valves during assembly following visual inspections. However, we take any report of odor seriously, checking for pronounced odors in the output directly from our compressor, our storage banks and when possible, other cylinders filled in a similar time frame.

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Total Volatile Hydrocarbon Content -- Breathing hydrocarbons can interfere with oxygen intake, and short-term exposures are associated with mucus membrane irritation, nausea, vomiting, diarrhea, and confusion.

Several thousand types of organic gases and vapors can potentially be present in Air. Volatile organic contaminants can be manmade (e.g., gasoline vapor, exhaust fumes, cleaning solvents) or from natural biological activities (e.g., methane from organic decay). Because it is impractical to measure each type of organic contaminant present, they are measured as a group described as a Total Volatile Hydrocarbon Content (TVHC).

Parts Per Million	Gas Standard or Test Result
25 ppm	Allowed maximum for CGA G-7.1 Grade "E"
Less than 1 ppm	Test results for Fill Express gases, excluding methane

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Water Vapor (H2O) -- SCUBA breathing gases should be as dry as possible. As the temperature of a gas decreases, its ability to hold water as a vapor decreases. When the breathing gas reaches the dew point temperature, water vapor condenses into a liquid (water) or, if the temperature is low enough, solid (ice crystals). SCUBA gases must be dry enough to prevent malfunctions due to internal condensation or icing buildup caused by expansion cooling as the gas passes through regulators. Higher moisture content in gases at the pressures in SCUBA cylinders can also very significantly accelerate corrosion of the cylinder.

Parts Per Million/ Dew Point	Gas Standard or Test Result
24 ppm/-65 °F	Allowed maximum for CGA G-7.1 Grade "E"
7 ppm/-81 °F	Allowed maximum for mil-spec Aviators Breathing Oxygen (ABO), a reasonable benchmark for acceptable H2O content in breathing gases for SCUBA diving.
Less than 7 ppm/-81 °F	Test results for Fill Express gases

Note that whereas the difference between 24 ppm H2O and 7 ppm H2O may be significant to SCUBA equipment, it's extremely unlikely that humans can detect a difference during respiration. Regardless of the precise water content, any compressed breathing gas for SCUBA is going to seem very dry when inspired from the second stage of a SCUBA regulator.

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