BREATHING AIR SPECIFICATIONS
This is only a partial list of the specifications that we routinely work with.
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© 2000 Analytical Chemists, Inc. Analytical Chemists, Inc 7535 Convoy Ct. San Diego, CA 92111 Voice & FAX (800) 466-8898 Rev 01/01
COMMENTS REGARDING AIR PURITY SPECIFICATIONS.
- We use Total Volatile Hydrocarbons rather than the misnomer “Total Hydrocarbons” because the test can only detect volatile or vaporized hydrocarbons (not oil mist). (This is true for all laboratories, not just ours.) The absence of a Total Volatile Hydrocarbon check in CGA Grade D removes an important indicator from the discovery process, therefore we run that test on every sample. See also our section on Laboratory Methods.
- Oxygen content in air from ordinary compressors will always be 20.95% unless it is improperly prepared synthetic air, or compressor air intake located in a compartment deficient in oxygen. For example, oxygen deficiency could occur in a ship’s cargo hold or a leak in an air liquification area. Air compressors cannot by themselves increase or decrease the oxygen content of air.
- Nitric Oxide and Nitrogen Dioxide in compressor air can occur only from welding, carbon arc search- lights and, high temperature combustion gases in the immediate vicinity of the compressor intake. The possibility of their presence in compressor air at significant levels is extremely remote. Sulfur dioxide can only come from combustion of sulfur compounds (such as a gasoline engine or catalytic converter). (In our opinion, inclusion of these 3 contaminants in this specification would only be reasonable if your compressor is located near a steel foundry, oil refinery, or a large combustion source, and you operated your compressor without any molecular sieve filters.) Note the most recent (1985) version of Federal Specification BB-A-1034 no longer requires a check for these compounds.
- CGA Grade J has been erroneously used by some labs as the specification for air used to prepare Nitrox. Compressor air will never be able to meet the criteria. If your lab recommends it, you should use a smarter lab. The CGA adopted this specification only for instrument air – not compressor air. By the way, the term “Modified CGA Grade J air” is a misnomer. If you look closely at it, you will see that every part is modified so much that it bears no resemblance to the original CGA Grade J.
- Nitrous oxide (laughing gas) is not part of the Medical Air specification, but it is a common hospital anesthetic, and could accumulate near a compressor We have checked one hospital where this actually occurred. We believe that it should always be included in a program that checks medical air.
- Odor is a very important test which is essentially the first line of defense for a diver. The fact that the observation is subjective does not detract from its importance. Strong odors are an immediate warning of danger and are not acceptable. Compressor air (except Navy air) usually has either no odor or a very slight odor (depending on the maintenance of the compressor).
- The Dew Point specification for USN Diver’s air is only appropriate when compressor air is run through a dryer system. Limits given are as of September 2000.
- Dew Point is primarily a cold climate concern, however, read about tropical air in our section on moisture. Values in parentheses are typically specified by the end user. The CGA “suggests” -64 ºF as a reasonable dew point as long as the dew point is no warmer than 10 ºF below the coldest anticipated ambient temperature. It seems like a simple rule, but it may require consideration of the effect of expansive cooling in the first stage regulator of very high pressure tanks. (We measure Dew Point in your sample (+32 to –75º F), but values for critical applications below – 40 ºF are always best done on site with a NIST traceable dew point meter because of sampling considerations.
- Halogenated Hydrocarbons are organic compounds that contain one or more of the following atoms: Fluorine, Chlorine, Bromine or Iodine. Chlorofluorocarbons (CFCs) contain one or more atoms of Chlorine plus Fluorine. We understand that the Canadian specification has a 2 ppmv limit on each chlorofluorocarbon: Trichlorotrifluoroethane, Dichlorodifluoromethane, and Chlorodifluoromethane.
- Specification Sources: (a) Post Painting of Recompression Chambers is per NAVSEA PI 00C3-PI-001; (b) Pure Oxygen (Aviator’s Breathing) is per Mil-O-27210 Type 1; (c) US Navy Air specification for Nitrox preparation is per USN Diving Manual, Vol. 2, Chapter 10, Table 10-2; (d) NASA Safety Manual Chapter 5; (e) ANDI (American Nitrox Divers International); (f) IANTD (International Association of Nitrox and Technical Divers; (g) AAUS (American Academy of Underwater Sciences.)
- No industry wide consensus exists for non-military Oxygen Compatible Air (OCA) Specifications. Our version of “Modified CGA Grade E” takes into account all existing specifications for OCA, effective analytical protocols, safety and practical concerns. The “oil mist + particulate” acceptance level of 0.2 mg per cubic meter was chosen to take into consideration the weight changes which are due only to normal uncertainties in weighing filters. (See also our section on Bad Science.) Considerations of particle size and quantity are based on NASA criteria for Oxygen systems.
- Moisture specifications are not fixed; they are relative to regional temperatures and/or client’s needs. For example, the US Navy only requires that air meet a dew point criterion in specific situations. CGA does not have rigorous Dew Point Requirements; it only offers suggestions that can be modified by the client. If in doubt see current booklet: CGA G-7.1 (1999). Medical air must be wet (Dew PT +32F.)
Contact our local service center if you are unable to resolve a contamination issue. Contact us if you need the name of a technical specialist located in your area.