All About Cleanroom Air Change Rates

May 3, 2023

Figure 1. Air flow diagram – recirculating modular cleanroom

A cleanroom air change rate is how many times per hour the air in the cleanroom pass thru HEPA or ULPA filtration to clean the air of particles. The more times per hour the air is filtered the cleaner the room will be.

Cleanrooms are ISO classified by how many particles are allowed per cubic meter. Fed Std 209E is particles per cubic foot. In order to reach these cleanliness levels, the cleanroom industry standards committee specifies the number of air changes per hour thru the HEPA or ULPA filtration.

Design Requirements for Cleanroom Classifications
Criteria	Class 10 ISO4	Class 100 ISO5	Class 1000 ISO6	Class 10,000 ISO7	Class 100,000 ISO8
Air changes per HR/Min	500-600 / 8 to 10	300 to 480 / 5 to 8	180 / 3	60 /1	20 /0.33
Filter coverage %	90 – 100	60 – 70	20 – 30	7 – 15	4 – 5
CFM per square foot	85 – 90	36 – 65	18 – 32	9 – 16	4 – 8
Filter Efficiency	99.9997% ULPAs	99.997% HEPAs	99.997% HEPAs	99.997% HEPAs	99.97% HEPAs

Figure 2. Recommended cleanroom air changes per hour

The higher air changes per hour reduces the recovery time of the cleanroom when a door is opened to the outside and particles enter the cleanroom.

ISO 14644-1 Cleanroom Standards | Cleanroom Classifications
Class	Maximum Particles/m³						FED STD 209E equivalent
Class	>0.1 um	>0.2 um	>0.3 um	>0.5 um	>1 um	>5 um	FED STD 209E equivalent
ISO 1	10	2
ISO 2	100	24	10	4
ISO 3	1,000	237	102	35	8		Class 1
ISO 4	10,000	2,370	1,020	352	83		Class 10
ISO 5	100,000	23,700	10,200	3,520	832	29	Class 100
ISO 6	1,000,000	237,000	102,000	35,200	8,320	293	Class 1,000
ISO 7				352,000	83,200	2,930	Class 10,000
ISO 8				3,520,000	832,000	29,300	Class 100,000
ISO 9				35,200,000	8,320,000	293,000	Room Air

Figure 3. ISO 14644-1 cleanroom classifications

Cleanrooms are also particle tested “at rest” and “operational”. When a cleanroom is empty/at rest there are no sources of particles and the test will show the lowest amount of particles. When the cleanroom is “operational” tested there are people in the cleanroom operating machines and creating particles so the test typically show much greater amount of particles.

operational cleanroom, interior of cleanroom, people working in cleanroom — Figure 4. “Operational” cleanroom

at rest cleanroom, interior of cleanroom, no people in cleanroom — Figure 5. “At Rest” cleanroom

Summary: Cleanroom air changes rates refers to how many times per hour the cleanroom air is passed thru the HEPA filtration. The more air changes per hour the cleaner the cleanroom. An ISO-8/class 100k cleanroom requires 20 air changes per hour. A cleaner ISO-7/class 10k cleanroom requires 60 air changes per hour.

Property American Cleanroom Systems 2023

The author Anthony Chien has worked at American Cleanroom Systems for more than 10 years . He has more than 40 years of cleanroom experience. Anthony has a BS and MS in Electrical Engineering specializing in semiconductor manufacturing from the University of Illinois. American Cleanroom Systems is a design build modular cleanroom manufacturer based in Rancho Santa Margarita CA. It is expert in ISO-5 thru ISO-8 (class 100 to class 100k) modular cleanrooms for nutraceutical cleanrooms, pharmaceutical cleanrooms, medical device cleanrooms, and industrial cleanrooms.