What is class zero?
ISO 8573-1 class zero
The 1991 ISO 8573-1 edition of the air quality standard established five purity classes: 1 through 5.
The class 1 specified an oil concentration of more or less 0.01 mg/m3 at 1 bar(a) and 20°C. Conformance to class 1 was sometimes called "a technically oil-free solution". However, only oil aerosols and liquids were considered. Below 35°C, vapors could be ignored, when, in fact, the quantity of vapors may be higher than aerosols.
Some manufacturers still use the old edition to promote their machines.
In 2001, the standard was revised to address the needs of applications where air purity is essential. These include industries such as pharmaceuticals, food and beverages, electronics, automotive paintings, textiles. In these cases, risk of contamination must be excluded to avoid severe consequences: spoiled or unsafe products, production downtime or damage to brand and reputation.
The 2001 revision established a more comprehensive outlook by specifying the measurement of total oil content, as opposed to the earlier edition which called for the measurement of aerosols and liquids alone and not the vapors, below 35°C. Moreover, to the existing purity classes 1 through 5, a new and more stringent class was added: ISO8573-1 CLASS 0.
ZD compressors have been certified CLASS 0 as per ISO 8573-1 by an independant organisation, the TÜV.