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Air is the natural atmosphere of the earth--a nonflammable, colorless, odorless gas that consists of a mixture of gaseous elements (with water vapor, a small amount of carbon dioxide, and traces of many other constituents). Synthesized air is produced by combining pure oxygen and nitrogen and contains between 19.5 and 23.5 percent oxygen, with the balance nitrogen and with a major portion of the other components eliminated. Dry air is non-corrosive. Liquefied air is transparent with a bluish cast and has a milky color when it contains carbon dioxide.
Because air is a mixture, not a compound, it can be separated into its components. The most common method is the liquefaction of air by reducing its temperature to approximately -320 degrees F (-195.6 degrees C), then fractionally distilling to remove each of the constituents as fractions.
Air can be compressed at the point of use for most practical applications. To meet needs for air of special purity or specified composition (as in certain medical, scientific, industrial, fire protection, undersea, and aerospace uses), it is purified or compounded synthetically and shipped in cylinders as a non-liquefied gas at high pressures.
Atmospheric air also contains varying amounts of water vapor. For most practical purposes, the air composition is taken to be 78 percent nitrogen and 21 percent oxygen by volume, and to be 75.5 percent nitrogen and 23.2 percent oxygen by weight. The other "atmospheric trace gases" together compromise less than one percent. Trace impurity levels may vary with geographic locations or with proximity to industrial areas or highways carrying dense traffic. This composition remains relatively consistent in altitudes up to 70,000 feet.
Air meeting particular purity specifications has many important applications. Some of these applications include medical, undersea, aerospace, and atomic energy fields. It is also employed in self-contained breathing apparatus used by industrial, emergency response, and fire-fighting personnel, and as a power source for some kinds of pneumatic equipment.
Air may be compressed from the atmosphere and purified by chemical and mechanical means. It may also be synthetically produced from already purified major components nitrogen and oxygen.
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| DOT Name: |
Air, compressed |
| DOT Hazard Class: |
Nonflammable Gas (2.2) |
| DOT Label: |
Nonflammable Gas |
| DOT ID No.: |
UN 1002 |
| CAS No.: |
None |
| Valve Outlet: |
CGA 346, CGA 950 pin-indexed |
| Physical State in Cylinder: |
Gas |
| Toxicity: |
Non-toxic |
| Fire Potential |
Non-flammable |
| Chemical Name: |
Air |
| Molecular Weight: |
28.975 lb/mol |
| Specific Volume at 70°F and 1 atm: 13.346 ft3/lb (0.8333 m3/kg) |
| Specific Heat: 6.96 BTU/lbmol-deg F at 70 deg. F |
| Specific Gravity: |
1.000 |
| Gas Density: |
0.07992 lb/ ft3 @ 70 deg. F. 14.7 PSIA |
| Boiling Point: |
Temperature: -317.7 deg. F (-194.3 deg. C) Liquid Density: 54.60 lb./ft3 Latent Heat: 87.9 BTU/lb. |
| Critical Point: |
Temperature: n/a Pressure: n/a |
| Melting Point: |
Temperature: n/a Pressure: n/a |
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