Dr. Roger Eltringham, Anaesthetist, Gloucestershire Royal Hospital, Gloucester.
Edited by D. R.

A reliable source of oxygen is essential wherever oxygen or ozone therapies are considered. Oxygen is traditionally supplied in cylinders which are both bulky and expensive. In isolated areas transportation of cylinders is difficult and many clients attempting to use oxygen in their homes find difficulties associated with obtaining oxygen and storage of pressurized oxygen tanks not appealing, dangerous or impossible. In many parts of the world the supply of oxygen may fail altogether leaving the user of ozonation system without any means how to produce pure ozone.

Atmospheric air consists of approximately 80% nitrogen (Atomic weight 14.00674) and 20% oxygen (Atomic weight 15.9994). An oxygen concentrator uses ambient air as a source of oxygen by separating these two components. In the oxygen concentrator the nitrogen is absorbed by the Molecular Sieve when under pressure and released from the Molecular Sieve when the pressure is released. This process is based on a property of Zeolite^® granules to selectively absorb nitrogen from compressed air. (Zeolite is a trade name for one of the special granulated materials which can be used as a fill for Molecular Sieve). Atmospheric air is entrained by the concentrator (Fig 1), filtered and raised to a pressure of 20 pounds per square inch (P.S.I.) by a compressor. The compressed air is then introduced into one of the canisters containing Zeolite granules where nitrogen is selectively absorbed leaving the residual oxygen available for patient use. After about 20 seconds the supply of compressed air is automatically diverted to the second canister where the process is repeated enabling the output of oxygen continue uninterrupted. While the pressure in the second canister is at 20 P.S.I. the pressure in the first canister is reduced to zero. This allows nitrogen to be released from the Zeolite and returned into the atmosphere. The Zeolite is then regenerated and ready for the next cycle. By alternating the pressure in the two canisters so that first one and then the other is at 20 P.S.I., a constant supply of oxygen is produced while the Zeolite is continually being regenerated. Individual units have an output in range 1/ 4 to 5 liters per minute [LPM] with an oxygen concentration usually in range of 90 - 95%.

Routine maintenance consists merely of changing the filters at regular intervals as directed by the manufacturers and this can be easily achieved using skills available locally. Providing these recommendations are observed the unit requires no other attention and will continue to function for many years. With its record of dependability, ease of maintenance and minimal running costs the initial purchase price is usually considered an excellent investment and will rapidly lead to great savings of money.