To ensure optimal cleanroom performance, evaluate air flow design and frequency of air changes. Cleanrooms are classified according to the number and size of particles permitted per volume of air in a specific amount of time. There is a relationship between cleanroom class ratings and the room’s air changes per hour. For a cleaner room rating, more air exchanges become necessary. For example, a typical ISO 7 room will have 60-150 changes of air per hour, while an ISO 6 room will have 150-240 changes. All areas within a cleanroom should have similar air changes each hour to ensure required performance.
The right balance of filter systems and air returns must be maintained to create positive air pressure inside the cleanroom. Positive air pressure produces an outward air movement, preventing the inflow of contaminants and assisting in expelling particles generated by workers and equipment.
Cleanroom air flow performance can be upgraded in a cost-effective manner by adding fan-filter modules (FFM). For example, FFMs cover approximately 5-15% of an ISO 8 cleanroom ceiling. Upgrading to an ISO 7 cleanroom requires 15-25% ceiling coverage, and covering 25-40% of the ceiling changes the room to ISO Class 6.
This cleanroom tip, which appeared in the May/June 2015 issue of Controlled Environments, was submitted by Kevin Weist of Clean Air Products in Minneapolis, Minn. www.cleanairproducts.com