The biggest source of contaminants in any industry is air. In order to minimize the amount of particles floating around, production processes are moved to a cleanroom.
The design of a cleanroom is completely aimed at controlling these airborne particles. The particles are periodically measured using particle counters which comply with ISO 21501-4 standards and meet the requirements of both 21 CFR part 11 and ISO14644 et GMP Annex 1.