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All About Cleanroom Air Change Rates

mayo 3, 2023
recirculating modular cleanroom
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.

Requisitos de diseño para clasificaciones de salas limpias
Criterio Clase 10 ISO4 Clase 100 ISO5 Clase 1000 ISO6 Clase 100,000 ISO8
Cambios de Aire por HR / Min 500-600 / 8 to 10 300 to 480 / 5 to 8 180 / 3 60 /1 20 /0.33
% de Cobertura por Filtros 90 – 100 60 – 70 20 – 30 7 – 15 4  – 5
CFM por pie Cuadrado 85 – 90 36 – 65 18 – 32 9 – 16 4 – 8
Eficiencia de Filtro 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 Estándares de salas limpias | Clasificaciones de salas limpias
Clase Máximo de Partículas/ft³ ISO Equivalente
>0.1 um >0.2 um >0.3 um >0.5 um >1 um >5 um
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.

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