What are the ISO classes of air cleanliness by particle concentration?

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ISO 14644-1:2015(E)

Table 1 – ISO Classes of Air Cleanliness by particle concentration

ISE Class Number (N) Maximum Allowable concentrations (particles/m3) for particles equal to and greater than the considered sizes, shown belowa
0,1 μm 0,2 μm 0,3 μm 0,5 μm 1 μm 5 μm
1 10b d d d d e
2 100 24b 10b d d e
3 1,000 237 102 35b d e
4 10,000 2,370 1,020 352 83b e
5 100,000 23,700 10,200 3,520 832 d, e, f
6 1,000,000 237,000 102,000 35,200 8,320 293
7 c c c 352,000 83,200 2,930
8 c c c 3,520,000 832,000 29,300
9g c c c 35,200,000 8,320,000 293,000


  • a All concentrations in the table cumulative, e.g. for ISO Class 5, the 10,2000 particles show at 0,3 μm include all particles equal to and greater than this size.
  • b These concentrations will lead to large air sample volumes for classification. Sequential sampling procedure may be applied; see Annex D.
  • c Concentration limits are no applicable in this region of the table due to very high particle concentration.
  • d Sampling and statistical limitations for particles in low concentrations make classification inappropriate.
  • e Sample collection limitations for both particles in low concentrations and sizes greater than 1 μm make classification at this particle size inappropriate, due to potential particle losses in the sampling system.
  • f In order to specify this particle size in association with ISO Class 5, the macroparticle descriptor M may be adapted and used in conjunction with at least one other particle size. (See C.7.)
  • g This class is only applicable for the in-operation state.

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