About Cleanrooms
Here we share our knowledge, competence and many years of practical experience with cleanrooms.
Our "About Cleanrooms" aims to give you insight and overview through general descriptions, thumb rules, tips, and recommendations.
If you have a specific project in mind, please get in touch with us for a informal talk.
Main Souce: Cleanroom Technology: Fundamentals of Design, Testing and Operation, 2nd Edition 2010 William Whyte
What is a cleanroom
ISO standard 14644-1-4 defines a cleanroom as:
“A room in which the concentration of airborne particles is controlled, and which is constructed and used in a manner to minimize the introduction, generation, and retention of particles inside the room, and in which other relevant parameters like temperature, humidity, and pressure, are controlled as necessary.”
Minimizing the introduction, formation and retention of particles in a cleanroom is done in 3 ways:
- Supplying the room with a large volume of air filtered with high-efficiency filters (HEPA or ULPA) to dilute and remove particles, bacteria and chemicals inside the room. The air is also used to pressurize the room, ensuring that no contaminated air flows into the cleanroom.
- The cleanroom itself must be built with materials that do not generate pollutants, particles or airborne chemicals and must also be easy to clean.
- Cleanroom operators must wear garments that minimize the spread of particles and microorganisms generated by operators, such as hair, skin flakes, clothing fibers, etc. Note that operators make up the majority of cleanroom contamination.
Another way to explain a cleanroom is that it is a engineered and designed area that allows for precise control and monitoring and designed to regulate:
- Pressure
- Filtration
- Airflow
- Temperature
- Humidity
Who need a Cleanroom?
The need for controlled conditions in production can be due to several factors, including:
- A customer may require your products to be produced under controlled conditions.
- Your products may require high, fine or uniform production to function properly.
- It may be that the industry requires a certain standard to be followed.
- These may be national or regional rules which means that specific standards must be followed.
Whatever the reason, it’s important to understand the requirements and rules that apply to these controlled conditions, often referred to as cleanrooms.
The operations and processes performed in the cleanroom determine which variables to control.
Cleanliness is only one of the aspects controlled in a cleanroom. Cleanrooms often also control temperature and humidity.
Here are some industries and applications that use cleanrooms:
- Pharmaceutical products
- Sterile compounding products
- Hospitals
- Medical Devices
- Biotechnology
- Cosmetics
- Food and drink
- Fine electronics
- Micromechanics
- Nanotechology
- Semiconductors
- Optics
- Aerospace
- Defence
- Laboratories
- Universities
- Toxics, dust and more, that you want to keep inside the room
If you are in doubt whether your production is covered by cleanroom requirements, please contact us
Classifications
ISO 14644-1-4
Cleanrooms are classified primarily by how clean the air is, according to the amount and size of airborne particles per volume of air.
Although several classifications exist, there has been an increasing trend to move from previous classification systems to the ISO classification system in ISO 14644-1-4 2015. Current versions are:
- 14644-1 : 2015
- 14644-2 : 2015
- 14644-3 : 2019
- 14644-4 : 2022
Other rules
The rules that apply to a particular cleanroom depend on the application and processes taking place inside the room.
Pharmacies with sterile compounding activities must follow the rules in USP 797, 800 or 825.
Pharmaceutical production normally follows EU GMP (A, B, C, D).
Other regulations include, but are not limited to, regional, national and international regulations such as
FDA and EMEA.
Please contact us, if you want to know more about cleanroom classifications.
Cleanroom conditions
The need for controlled conditions in production can be due to several factors, including:
- A customer may require your products to be produced under controlled conditions.
- Your products may require high, fine or uniform production to function properly.
- It may be that the industry requires a certain standard to be followed.
- These may be national or regional rules which means that specific standards must be followed.
Whatever the reason, it’s important to understand the requirements and rules that apply to these controlled conditions, often referred to as cleanrooms.
The operations and processes performed in the cleanroom determine which variables to control.
Cleanliness is only one of the aspects controlled in a cleanroom. Cleanrooms often also control temperature and humidity.
If you are in doubt whether your production is covered by cleanroom requirements you are welcome to contact us
Airflow & ventilation in cleanrooms
There are two types of cleanrooms, which differ according to their ventilation method:
Non-unidirectional airflow Cleanroom
The non-unidirectional airflow cleanroom receives clean air filtered through high-efficiency HEPA/ULPA filters in the ceiling. The fresh air is mixed with the room air and removes airborne pollution generated by people and machines through air extractors placed at the bottom of the walls.
Depending on the operations performed in the cleanroom and its size, classifications up to ISO 6 can be achieved with this ventilation method.
However, for higher and less stringent classifications such as an ISO 8, air extractors can be placed in the ceiling.
Airflow & ventilation in cleanrooms
Unidirectional airflow Cleanroom
High efficiency HEPA/ULPA filters are installed throughout the ceiling. The air sweeps vertically into the room unidirectionally and exits through the floor, removing airborne contaminants from the room.
Since unidirectional airflow cleanrooms use more air and more filters, it is more expensive than non-unidirectional, but can comply with more stringent classifications, such as ISO 5 and the more stringent ISO 4, ISO 3, ISO 2 and ISO 1.
Please Contact us if you have any questions about cleanroom ventilation.
Cleanroom qualification
New Clean rooms are classified according to the purity of the air in them. The cleanroom class is the cleanliness level that the room meets, according to the amount and size of particles per volume of air.
The primary authority is the ISO classification system ISO 14644-1. This standard includes these cleanroom classes: ISO 1, ISO 2, ISO 3, ISO 4, ISO 5, ISO 6, ISO 7, ISO 8 and ISO 9.
ISO 1 is the “cleanest” class and ISO 9 is the “dirtiest” class. ISO 9 is still cleaner than a normal room. The most common ISO classes are ISO 7 and ISO 8.
The old Federal Standard 209 (FS 209E) includes these cleanroom classes: class 100,000; 10,000; 1,000; 100; 10; 1. This standard was replaced in 1999 by ISO-14644-1. It was withdrawn in 2001, but it is still used to some extent.
Cleanrooms must also follow industry-specific and regional standards. As mentioned, EU GMP (ABCD) applies to pharmaceutical products and USP (795, 797, 800, 825) to compound pharmacies.
See table for appoximal comparision.

| ISO 14644-1 | FS 209E | EU GMP |
|---|---|---|
| ISO 3 | 1 | |
| ISO 4 | 10 | |
| ISO 5 | 100 | A-B |
| ISO 6 | 1,000 | |
| ISO 7 | 10,000 | C |
| ISO 8 | 100,000 | D |
ISO Class - Particles, Size
The basis for cleanroom standards is the micrometer, µm, which is the size of the particles to be filtered. As mentioned earlier, cleanrooms are classified by how clean the air is and by the amount and size of particles per volume of air.
The cleanroom classification table below shows the maximum concentration limits (particles / m3 air) for particles equal to and greater than those shown.
Some classifications do not require certain particle sizes to be tested.
Below find the maximum limits per class and size according last version 14644-1 2015
| ISO Class | ≥ 0.1 µm/ m3 | ≥ 0.2 µm/ m3 | ≥ 0.3 µm/ m3 | ≥ 0.5 µm/ m3 | ≥ 1 µm/ m3 | ≥ 5 µm/ m3 |
|---|---|---|---|---|---|---|
| ISO 1 | 10 | 2 | 0 | 0 | 0 | 0 |
| ISO 2 | 100 | 24 | 10 | 4 | 0 | 0 |
| ISO 3 | 1,000 | 237 | 102 | 35 | 8 | 0 |
| ISO 4 | 10,000 | 2,370 | 1,020 | 352 | 83 | 0 |
| ISO 5 | 100,000 | 23,700 | 10,200 | 3,520 | 832 | 0 |
| ISO 6 | 1,000,000 | 237,700 | 102,000 | 35,200 | 8,320 | 293 |
| ISO 7 | - | - | - | 352,000 | 83,200 | 2,930 |
| ISO 8 | - | - | - | 3,520,000 | 832,000 | 29,300 |
| ISO 9 | - | - | - | 35,200,000 | 8,320,000 | 293,000 |
Air change per hour (ACH)
Air purity is achieved by passing the air through HEPA and ULPA filters.
The more often the air passes through HEPA filters, the fewer particles remain in the room air.
The air volume filtered in one hour divided by the room volume gives the number of air changes per hour (ACH)
For GMP (A, B, C, D) cleanrooms, it is a rule of thumb to use:
- 5-10 ACH in GMP D rooms
- 10-15 ACH in GMP C rooms
- 20-25 ACH in GMP B rooms with Laminar Air Flow
- 30-35 ACH in GMP A rooms with Laminar Air Flow
Below table with some rule of thumb for ACH for fine electronics (dust)
| ISO 14644-1 | ACH (dust) | Air Flow |
|---|---|---|
| ISO 5 | 240-360 | Laminar |
| ISO 6 | 90-180 | Ceiling - Wall |
| ISO 7 | 30-60 | Ceiling - Wall |
| ISO 8 | 15-25 | Ceiling - Ceiling |
| ISO 9 | 2-4 | Ceiling - Ceiling |
Cleanroom Design
Depending on the class of cleanroom you want to achieve, it is important to make room also for airlocks/exteriors, which prevent the migration of particles from outside into the cleanroom.
The rule of thumb is when moving towards a cleaner room (for example, from ISO 7 to ISO 6,) you need to move throug a airlock. In reality, however, you can move to a cleaner class with fewer airlocks with the appropriate ACH.
- PAL is a personel air lock
- PASL is a personel air shower lock
- MAL is a material air lock
- MASL is a material air shower lock
Some rull of thumbs:
- PAL and MAL are used into ISO 7 and ISO 8
- By lower and more strict classes we recomend always to use PASL and MASL.
However this depends on the process taking place inside the cleanroom, the size of the cleanroom, the number of people working in the room, the equipment in the room, etc.
That’s why you should always get help from a cleanroom consultant who can create the optimal layout for your specific needs.
HVAC & ACH
HVAC calculations requires a mix of technical skills, understanding of the particle-generating potential of the process and experience.
It is crucial that you talk to a HVAC specialist who has experience with cleanrooms.
ISO 14644-1:2015 does not specify ACH for each cleanroom class because it depends on many factors. It can only tell you the result to aim for: the maximum concentration limits for particles.
However, the ISO purity level (ISO 8, ISO 7, ISO 6 and ISO 5) gives a hint about the required ACH range.
A cleanroom with activities that generate few particles versus one that generates many airborne particles, even though both are ISO 7, does not require the same ACH.
Various recommendations ACH ranges and intervals can be found on the Internet.
This can be summarised to the following rule of thumb for fine electronics, etc. (dust)
- ACH 10-30 for ISO 8
- ACH 30-65 for ISO 7
- ACH 80-150 for ISO 6
- ACH 200-450 for ISO 5.
For EU GMP A-D, it is a rule of thumb to use:
- ACH 5-10 for GMP D
- ACH 10-15 for GMP C
- ACH 20-25 for GMP B
- ACH 30-35 for GMP A
If there is a significant generation of particles in the process, or many
people in the room, the higher number is selected in the range of the area.
Note that the ACH above is only a rule of thumb!
ACH must be calculated by an HVAC engineer based on experience and understanding of the particle generating potential of the specific processes.
We are always ready to assist you.
HVAC considerations
Some other elements that affect the required airflow are mentioned below.
- Cleanroom layout
- Number of people working in the cleanroom
- The equipment in the room
- Use of fume cupboard or similar. (air extraction)
- Lighting
- The pressure difference
- Outdoor temperature and humidity
Cleanroom layout
The air volume in the cleanroom will affect the required airflow and air exchange. The bigger the room, the more air you need. The width, length and height of the classified spaces and their layout must be used for HVAC calculations. One way to save costs is therefore to lower the ceiling.
Number of people working in the cleanroom
The airborne contamination in a cleanroom depends to a large extent on the activities in the room, and thus the staff. Staff are responsible for most of the particles generated in a cleanroom. The HVAC system must therefore take into account the number of people working in the room at the same time. The more people working in the cleanroom, the more airflow is needed to get rid of the contaminants. Cleanroom staff usually wear clothing to limit contamination. Therefore, it is important to maintain a comfortable environment for staff (heat, humidity, etc.)
The equipment in the room
For example, the equipment generates heat and dust. The heat increase generated by the equipment inside the cleanroom is used to determine the required cooling. The equipment in the room, together with the product manufacturing, generates dust that must be removed with the right amount of air.
Use of fume cupboard or similar. (air extraction)
A fume cupboard or the like needs a constant supply of air. This air supply must be included in the cleanroom’s HVAC calculations.
Lighting
The required lighting affects the heat generated inside the cleanroom and therefore the required cooling.
The pressure difference
The pressure should be higher in more strictly classified rooms so that the air leaks towards the less clean rooms. Positive pressure prevents dirty air from entering the cleanroom. In a clean room with negative pressure, the opposite occurs; the airflow must be greater in the adjacent room.
Outdoor temperature and humidity
If air can be recirculated in the cleanroom, the outside weather will only slightly affect the HVAC system. However, the air filling can go up to 100% of fresh air for cleanrooms working with hazardous products. In these types of cleanrooms, HVAC systems are more complex.
In winter, for example, HVAC systems need to take outside air down to -30°C in winter, warm it up to 20°C, remove the humidity and bring it back into the room again and again.
We are always ready to assist you.
Note
The above helps you to understand the basic differences between an ISO 5, ISO 6, ISO 7 and ISO 8 cleanroom according to ISO 14644-1.
Please note that this information is provided for educational purposes only.
The definitions in this "About Cleanrooms" are simplified to aid understanding.
If help is needed related to a Cleanroom project, you are always welcome to contact us if you have any questions about the design of your cleanroom.
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