The Science Behind Cleanrooms: What Keeps Them Clean?
Author: Anthony Chien
Figure 1. ISO-7 medical device cleanroom
To make cleanrooms clean the cleanroom are built using HEPA filtration, non-particulating materials, airlocks, and non-particulating flooring. In addition, cleanroom personnel follow special rules such as wearing cleanroom garments, no eating or drinking, and wipe down the cleanroom on regular basis. Finally, cleanrooms monitor the cleanliness of the room using particle testing and biological settling plates.
1. Cleanroom design elements that make the cleanroom clean:
Cleanroom use HEPA filtration to remove particulates from the air. HEPA is “an acronym for "High Efficiency Particulate Air [filter]" (as officially defined by the U.S. Dept. of Energy). This type of air filter can theoretically remove at least 99.97% of dust, pollen, mold, bacteria, and any airborne particles with a size of 0.3 microns (µm).” HEPA fan filter units have fan attached to HEPA filter assembly to push the air thru the filter (figure 2) . The HEPA fan filter units are placed in ceiling of cleanroom (figure 3) so the only air entering the cleanroom is clean air thru the HEPA fan filter units.
Higher class cleanrooms can also use ULPA filters. ULPA stands for Ultra Low Particulate Air. ULPA filters are denser than HEPA filters, so they are 99.999% effective at removing particulates 0.12-micron diameter or larger. The HEPA fan filter units are placed in ceiling of cleanroom (figure 2) so the only air entering the cleanroom is clean air thru the HEPA fan filter units.
Figure 2. HEPA fan filter unit Figure 3. Recirculating modular cleanroom with HEPA fan filter units in negative pressure plenum
Cleanroom have Air lock/Gown room to prevent particles from entering the cleanroom every time the door is opened. The airlock prevents 96% of particulates from entering the cleanroom. The room also provides a clean space for personnel to put on their cleanroom garments – which also stops particles from entering the cleanroom.
Figure 5. Cleanroom epoxy flooring
Only non-particulating materials used for cleanroom construction
1. Modular cleanroom walls have Melamine, vinyl, FRP, or painted aluminum surfaces. Standard construction gypboard walls must be painted with epoxy paint.
2. Only special vinyl coated cleanroom ceiling tiles are used in cleanroom ceilings. Standard commercial ceiling tiles will particulate.
3. Special sealed lights are used in cleanrooms to keep particulates from leaking into cleanroom from plenum.
4. Cleanrooms have special flooring requirements. Not only must the flooring be non-particulating, but it must be easily cleanable and durable since in medical device and pharmaceutical cleanrooms it is subject to frequent cleaning with harsh cleaning agents. Acceptable flooring materials include Industrial VCT, epoxy, heat welded vinyl, heat welded vinyl with integral cove. The type of flooring selected depends on cleanroom classification, industry of user and expected cleaning regimen.
Figure 6. Cleanroom Air shower
5. Some cleanrooms use Air showers as last step before personnel enter cleanroom. The purpose of the air shower it to blow off any particulates on the outside of personnel cleanroom garments with HEPA filtered super clean air.
2. Cleanroom personnel rules to prevent them from introducing particulates into the cleanroom. These include:
Always wear cleanroom garments when inside cleanroom
No eating or drinking in cleanroom
Cleanroom doors always kept closed after entering cleanroom
Wipe down all cleanroom surfaces on regular basis
Wipe down all equipment before bringing into cleanroom
Do not bring cardboard or other particulating material into cleanroom.
3. Cleanrooms must be cleaned on a regular basis to keep them clean.
Figure 7. Cleanroom garments for ISO-5 cleanroom
Daily or weekly cleaning is done to remove an particulates that may have settled on walls, work surfaces or floor.
Industrial cleanroom are typically wiped Isopropyl wipes or Simple Green.
Pharmaceutical and medical device cleanrooms often use more aggressive cleaning agents like bleach, spore-clean, De-ton, perchloric acid to attack microbial or mold contamination.
Figure 8. Cleaning tools
4. Regular Cleanroom Testing
Cleanroom are typically tested internally weekly or monthly with annual 3rd party testing. The cleanroom is tested to ensure it meets the ISO 14644-1 cleanroom classification. Viable testing is also done to ensure cleanroom meets sterility requirements. Regular testing is an important part of keeping a cleanroom clean. Testing will show if there are contamination problem and allow the cleanroom user to address the problem.
A. For cleanroom classification - the test is for non-viable particles. For ISO 14644-1 each cleanroom classification has a maximum number of particles of a certain size per cubic meter. These measurements are taken using a laser particle counter
ISO 14644-1 Estándares de salas limpias | Clasificaciones de salas limpias
Clase
Maximum Particles/m³
ISO Equivalente
>0.1 µm
>0.2 µm
>0.3 µm
>0.5 µm
>1 µm
>5 µm
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
Figure 9. ISO 14644-1 Cleanroom classification table
Figure 10. Laser particle counter for cleanroom testing
B. Cleanroom viable testing is for live organisms. Typically, samples are collected using settling plates with some type of media. The plates are placed in the cleanroom at specific locations for 4 hours and then are then sent off to analytical labs for incubation and measurement.
Figure 11 . Settling plates for cleanroom viable particle counts
Conclusion
The science of making cleanrooms include using HEPA filtration, non-particulating materials, airlocks, and non-particulating flooring. In addition, cleanroom personnel follow special rules such as wearing cleanroom garments, no eating or drinking, and wipe down the cleanroom on regular basis. Finally, it is important monitor the cleanliness of the room using particle testing and biological settling plates to identify problems and address them.
Property American Cleanroom Systems 2023
The author Anthony Chien has worked at American Cleanroom Systems for past 11 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 pharmaceutical cleanrooms, medical device cleanrooms, and industrial cleanrooms.
Frequently Asked Questions (FAQs)
Q: What are the requirements for a clean room?
A: Cleanrooms require HEPA filtration to remove particles from the air thus making the room clean. Other common requirements of a clean room include air locks to prevent particle from entering the clean room when the door is opened, gown room for personnel to put on cleanroom garments and positive pressure.
Q: Who invented the cleanroom?
A: Willis Whitfield from Sandia Labs designed the first laminar flow cleanroom in 1960 to address quality problems in manufacturing of nuclear weapon parts.
Q: Why do some cleanrooms have raised floors?
A: Class 100 cleanrooms with tight temperature and humidity requirements use 100% HEPA ceiling coverage and raised floors to ensure that there is vertical laminar air flow in every area of the cleanroom. The raised floor is perforated and allows air to pass through to return air chase beneath.
Q: Why do cleanroom personnel wear bunny suits inside cleanrooms?
A: Humans give off huge amounts of particles. The bunny suits encapsulates the particles to reduce the amount of particles the operators introduce into the cleanroom.
Q: How does a cleanroom air shower work?
A: The air shower blows off the already bunny suited operators with high velocity HEPA filtered air to reduce amount of particles the operators bring into cleanroom.
Q: How long will a cleanroom last?
A: With proper maintenance there is no limit on how long a cleanroom can last. However items like HEPA fan filter units are typically replaced sometime after 5 years and HVAC after 10-15 years.
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