The effects of moisture on molecular sieve oxygen concentrators.

Molecular sieve oxygen generating systems are receiving extensive laboratory and flight evaluation. Assessment of the molecular system has generally been conducted in the laboratory using clean dry air. In aircraft, however, the molecular sieve generator is supplied with engine bleed air which may not always be totally free of contaminants and water. Recent studies using bed washout technics have shown that the molecular sieve units, with 50% of the beds deactivated with water, still function normally with respect to product gas flow and O2 concentration. By utilizing the technics described in this paper, the moisture content or state of hydration of the molecular sieve can readily be determined.

Molecular sieve generation of aviator's oxygen: Performance of a prototype system under simulated flight conditions.

The molecular sieve method of generating an enriched-oxygen breathing gas is one of several candidate onboard oxygen generation (OBOG) systems under joint Army-Navy-Air Force development for application in tactical aircraft. The performance of a nominal two-man-capacity molecular sieve oxygen generation system was characterized under simulated flight conditions. Data are given on the composition of the molecular sieve-generated breathing gas (oxygen, nitrogen, carbon dioxide, and argon) as a function of inlet air pressure, altitude, breathing gas flow rate, and ambient temperature. The maximum oxygen concentration observed was 95%, with the balance argon. At low demand flow rates and certain conditions of pressure and altitude, the argon enrichment factor exceeded that of oxygen giving a maximum argon concentration of 6.6% with the balance oxygen. The structural integrity of the unit was verified by vibration and centrifuge testing. The performance of the molecular sieve unit is discussed in the context of aircraft operating envelopes using both diluter-demand and 100% delivery subsystems.

Relation of breathing oxygen-argon gas mixtures to altitude decompression sickness.

A 95% oxygen-5% argon breathing mixture produced by a molecular sieve generator was shown to be similar to a 95% O2-5% N2 mixture for breathing during 1-h exposures at 7,620 m (25,000 ft) or 10,972 m (35,000 ft), as determined by the detection of proportionate numbers of intravascular bubbles in the pulmonary artery of dogs. Comparable results were obtained with 95% O2-5% He or 100% O2. The partial pressures of a 5% mixture at 7,620 and 10,972 m were 14.1 and 8.6 torr, respectively, and were apparently low enough so that the nonmetabolizable gases did not result in differences in the incidence of intravascular bubble formation or decompression sickness. Argon at the 10% level showed a nonsignificant trend to produce more bubbles. Individual susceptibility or resistance to form bubbles was observed with the different gases. Denitrogenation with either 5 or 10% mixtures of the inert gases was quite effective, as shown by a reduction in the number of intravascular bubbles detected.

Molecular sieve oxygen generating system: the argon question--a brief review.

The molecular sieve oxygen generating system (MSOG) is currently being considered as a replacement for liquid and gaseous stores on aircraft for the supply of aviator's breathing oxygen. Incorporation of onboard oxygen generation in aircraft not only increases system safety but also minimizes logistic requirements. However, a unique characteristic of the MSOG is that it concentrates not only oxygen but also argon in the process of removing nitrogen from engine bleed air. Maximum concentrations produced by present systems are in the order of 95% oxygen and 5% argon. These results have precipitated numerous questions relating to the physiological effects of argon in the product breathing gas. This report reviews the current literature concerning argon as a minor constituent (less than 10%) in gas breathing systems and recommends studies prior to human compatibility testing of the molecule sieve oxygen generating systems.