[1] - reference conditions 1 bar(a) and 20°C at 0% relative humidity
[2] - unless otherwise agreed or stated, reference conditions 7 bar and 20°C
[3] - measured according to ISO 8573-2 and ISO 8573-5
[4] - measured according to ISO 8573-2 ; measurement according to ISO 8573-5 optional
[5] - measured according to ISO 8573-3 and, if required, ISO 8573-9
[6] - measured according to ISO 8573-4
[7] - measured according to ISO 8573-8
[8] - measured according to ISO 8573-9
[9] - if particles greater than 5 µm have been measured, class 0-5 cannot be applied
[10] - liquid, aerosol and vapor oil content

The compressed air purity for the three major contaminants in compressed air, expressed as ISO 8573-1 purity classes, is stated in the following way:

     ISO 8573-1:2010 [ A : B : C ]

     where
     A - is the purity class for particles
     B - is the purity class for humidity and liquid water
     C - is the purity class for the total oil content

When a class for any of the three major contaminants is not specified, the designation shall be replaced by a hyphen, e.g.

     ISO 8573-1:2010 [ A : - : C ]

for a compressed air purity without any requirements to the humidity or water content.

When a specified contamination level falls within class X, then the highest concentration shall be given in round brackets, e.g.

     ISO 8573-1:2010 [ A : X(15) : C ]

for a maximum concentration of liquid water of 15 g/m³.

When a specified contamination level falls within class 0, IT IS MANDATORY to state the highest allowable concentration (which must be better than defined for class 1), e.g.

     ISO 8573-1:2010 [ 0(1000:100:1) : 0(-80) : 0(0,001) ]

or

     ISO 8573-1:2010 [ 0 : 0 : 0 ]

     Maximum particle content: 1000 pcs/m³ (0,1-0,5µ), 100 pcs/m³ (0,5-1µ), 1 pcs/m³ (1-5µ)
    Maximum humidity : -80°C  
    Maximum total oil content: 0,001 mg/m³

The designation itself is not defined for class 0, so it can be expressed in separate ways.

In case further contaminants should be specified, assuming an according measuring method is provided by the ISO 8573 series, these contaminants are additionally given as follows, e.g.

      ISO 8573-1:2010 [ 1 : 2 : 1 ]

      [SO2 ≤ 0,01 mg/kg]
      [CO2 ≤ 1 mg/kg]
      [CO ≤ 0,1 mg/kg]
       [ ≤ 5 CFU/m³]