Used during the initial commissioning of a cleanroom and for routine periodic monitoring.
The 2019 revision added specific guidance for measuring particles down to the (as small as 0.01 µm). If you work with advanced materials or gene therapies, this is vital. Iso 14644-3.pdf
ISO 14644-3:2005 - Cleanrooms and associated controlled environments Used during the initial commissioning of a cleanroom
A "free" Iso 14644-3.pdf from a third-party blog is likely a pre-release draft. ISO does not authorize free distribution. Using a draft in a FDA audit results in a Form 483 observation. Iso 14644-3.pdf