BS EN ISO 14644-1:1999 covers the classification of air cleanliness in cleanrooms and associated controlled environments. This is based solely on the concentration of airborne particles. Only particle populations having cumulative distributions based upon threshold sizes ranging from 0.1μm to 5μm are considered for classification purposes.
According to the standard, airborne particulate cleanliness is designated by a classification number, N. The maximum permitted concentration of particles, Cn, for each considered particle size, D, is determined using:
Where: Cn is the maximum permitted concentration (in particles/m3 of air) of airborne particles that are equal or larger than the considered particle size.
Note: Cn is rounded up to the nearest whole number, using no more than three significant figures.
N is the ISO classification number (Not larger than 9). Intermediate ISO classification numbers may be specified, with 0.1 the smallest permitted increment of N.
D is the considered particle size in μm.
0.1 is a constant, with a dimension of μm.
The remainder of the standard specifies how users can demonstrate compliance. Annexes provide requirements for how the particulate cleanliness classification can be determined using a discrete-particle-counting light scattering instrument and on the statistical treatment of particle concentration data.
See other cleanrooms standards in the BS EN ISO 14644 series.
EN ISO 14644-1:1999
ISO 14644-1:1999