McIlvaine et al. (1992) outline air-flow considerations for cleanrooms.
When maximum particle reduction is sought, air velocity through the cross-section of the room normally is maintained at 90 feet (approximately 27.5 meters) per minute with a uniformity within plus or minus 20 percent throughout the undisturbed room. In certain applications where user requirements permit, air velocity in vertical laminar flow rooms may be reduced below the 90 fpm level. Any significant reduction in velocity can increase both the clean down time and the possibility of cross-contamination between work locations. The elimination of particles from the work area is essential to ensure cleanliness, sterility and functional requirements.
The following general outline can be used to determine the velocity throughout a room and is based upon desired cleanliness level:
(High Velocity)
Class 1100 fpm
Class 1072 to 100 fpm
Class 10072 to 100 fpm
Class 1,00025 to 30 fpm
Class 10,0007 to 15 fpm
Class 100,0002 to 7 fpm
Change rate is calculated on the basis of average uniform velocity expressed as fpm times 60 divided by ceiling height equals exchange rate.
