ISO 14644-1 defines the classification of air cleanliness in cleanrooms and associated controlled environments exclusively

in terms of concentration of airborne particles. Only particle populations having cumulative distributions based on threshold

(lower limit) particle sizes ranging from 0,1 μm to 5 μm are considered for classification purposes.


  1. a) All concentrations in the table are cumulative, e.g. for ISO Class 5, the 10.200 particles shown at 0,3 μm include all particles equal to and

greater than this size.

  1. b) These concentrations will lead to large air sample volumes for classification. Sequential sampling procedure may be applied; see Annex D.
  2. c) Concentration limits are not applicable in this region of the table due to very high particle concentration.
  3. d) Sampling and statistical limitations for particles in low concentrations make classification inappropriate.
  4. 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.

  1. 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.).