Many air quality standards are required by industry or law, although they do not exist in any particular standards collectively. Some are stated formally by a variety of associations; others are understood verbally or traditionally. The following list covers almost all compressed air systems.

Plant air — There should be no liquid water or lubricants in the system. Particulates to the point of use should be <10 µm. There are no existing standards.

Instrument air — There should be no liquid water in the system. Pressure dew point is equal to or lower than 18° F below the lowest ambient temperature that the piping is exposed to. Hydrocarbons should be limited to <1 ppm condensables by volume, and particulates to the point of use <1 µm. The Instrument Society of America recognizes their ISA S7.3 standard.

CDA 100 — This standard is recognized by the microelectronics industry where air is used in contact with electronics components for cleaning or vapor absorption. Prior to CDA100, bottled and bulk nitrogen was used. It has been the intent to replace nitrogen with CDA 100 where the presence of oxygen is not a problem. There should be no liquid water in the system, the pressure dew point should be equal to or lower than –78° F, and hydrocarbons should be limited to no condensables. Particulate to the point of use should be less than 0.1 µm.

H1F and H1 FDA — The H1F standard applies where compressed air comes into contact with food in process. The standard is relative to the compressor lubricant having incidental contact. The standard is that there will be less than1 ppm of compressor lubricant per million parts of food. H1 standards are for the quality of compressor lubricants that may be used in a food processing environment, but may not have incidental contact with the food. The Food & Drug Administration publishes these standards.

Many other individual industry standards deal specifically with reactants to their process. One such requirement is no hydrocarbons or oils in any physical phase or state in a brewery. In aerospace testing, moisture content is typically measured as grains of moisture per pound of air.

Breathing air — There should be no liquid water in the system. Pressure dew point should be equal to or higher than 42° F, hydrocarbons limited to condensables <1 ppm, and carbon monoxide limited to <10 ppm. The carbon monoxide standard should be combined to include other potential inlet gases such as hydrogen sulfide, nitrous oxide, and other process byproducts, including some particulates (such as cotton dust as an example), which might be present in the atmosphere specific to the inlet of the system. Particulate to the point of use should be <1 µm. The Compressed Air & Gas Institute recognizes their Grade D standard. There is also a combined standard in OSHA regulation 29CFR1910 with Grade D. 29CFR1910 also includes standards for test and measurement of air quality.

Sterile air — There should be no liquid water in the system. Hydrocarbons should be limited to no condensables, microorganisms should be limited to less than 0.1 µm absolute, and particulate to the point of use: <0.1 µm. Final filter cartridges should be flash cleaned in place with process steam on a regular basis. This requires two in-situ filters with automatic valving, so that one filter can be cleaned while the other is on line. There is no existing standard.

R. Scot Foss is president of Plant Air Technology, Charlotte, N.C., which specializes in air system auditing and design. This series of articles is based on his book, Compressed Air System Solution Series. To order a copy, click here.