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.
