Effect of oxygen with purity of between 90% and 99% is the same as far as biology and oxygen therapy are concerned. Purity of oxygen in capsule and PSA systems is as follows:

Purity of oxygen in PSA systems is between 90% and 96%. There are two international standards for oxygen. Pharmacopeias http://www.usp.org and ISO 10083 http://www.iso.org. In both standards, 90% to 96% purity is approved.

It has been noticed that level of purity of oxygen has been overvalued considerably while oxygen with 99% purity may not even have medical conditions too.

Oxygen should be pure from point of view of hygiene and oxygen therapy.
According to ISO 10083 standards (clause 8) pure oxygen

should have the following conditions:

• 90% to 96% purity
• 5 PPM CO content
• 300 PPM CO2 content
• 5 PPM Hydrocarbon
• -40 ºC Dew Point
• 0.5 Mg/m³ dust particles