This part of ISO 14644 covers the monitoring of air cleanliness by particles in terms of concentration of airborne nanoscale particles. For monitoring purposes, only populations of particles with a lower size limit of 0.1 microns (100 nm) or less – “nanoscale” – are considered. The monitoring given in this document is for use mainly in “operational” states. NOTE 1 – to entry For the purposes of this document, reference will be made to “nanoscale particles”, which here signify all nano-objects having one (nanoplate), two (nanofibre) or three (nanoparticle) dimensions in the nanoscale. NOTE 2 – to entry It should be noted that the actual behaviour of particles in the cleanroom depends on their sources and physical behaviour. NOTE 3 – to entry Health and safety considerations are excluded from this document.