The Cart Block, Chestnut Court, Jill Lane,
Sambourne, Redditch, Warwickshire, B96 6EW
2025 © Copyright Airology Systems Ltd. All Rights Reserved.Company registration no. SC166192 VAT no. 670371639
How are Cleanrooms Classified?
Cleanrooms are classified according to the number and size of particles permitted per volume of air. We work with ISO, FED (Federal) and GMP cleanroom classifications.
The end-user determines the target classification for their cleanroom, towards which Airology can design and build a cleanroom with the appropriate technology.
ISO Standard Cleanrooms
The ISO 14644-1:2015 – ‘Classification of Air Cleanliness’ is the European standard for cleanroom classification, and is used throughout the UK and EU.
This sets out classes 1 – 9, with Class 1 being the cleanest and Class 9 having a similar air quality to any ordinary room.
The ISO Class stipulates the maximum allowable particles per cubic metre by size, as shown in Table 1 below. The cleaner the requirement, the more air changes per hour are required.
To Read This Table
This table shows that in an ISO 7 cleanroom, each cubic metre of air must contain:
- Fewer than (<) 2 930 particles which are greater than or equal to (≥)5 micron
- < 83 200 particles ≥1 micron
- < 352 000 particles ≥0.5 micron
US Federal Standard 209 (FED STD 209E) offers equivalent classes which range from 1 – 100,000 in steps aligned with ISO Classes 3-8. The FED class number refers to the maximum allowable particles >/=0.5 microns (μm) per cubic foot.
To discuss cleanroom classification requirements further, speak to one of Airology’s experts today. Call: 01527 894 279
Table 1: ISO Classes of Air Cleanliness by Particle Concentration & FED STD Equivalents
For each ISO class, this table shows the maximum allowable no. of particles ≥ each size per m³.
| ISO CLASS NUMBER | ≥0.1 µm | ≥0.2 µm | ≥0.3 µm | ≥0.5 µm | ≥1 µm | ≥5 µm | FED STD 209E Equiv. |
|---|---|---|---|---|---|---|---|
| ISO CLASS 1 | 10ii | iv | iv | iv | iv | v | viii |
| ISO CLASS 2 | 100 | 24ii | 10ii | iv | iv | v | Viii |
| ISO CLASS 3 | 1 000 | 237 | 102 | 35ii | iv | v | 1 |
| ISO CLASS 4 | 10 000 | 2 370 | 1 020 | 352 | 83ii | v | 10 |
| ISO CLASS 5 | 100 000 | 23 700 | 10 200 | 3 520 | 832 | iv, v, vi | 100 |
| ISO CLASS 6 | 1 000 000 | 237 000 | 102 000 | 35 200 | 8 320 | 293 | 1000 |
| ISO CLASS 7 | iii | iii | iii | 352 000 | 83 200 | 2 930 | 10,000 |
| ISO CLASS 8 | iii | iii | iii | 3 520 000 | 832 000 | 29 300 | 100,000 |
| ISO CLASS 9vii | iii | iii | iii | 35 200 000 | 8 320 000 | 293 000 | viii |
Notes to Table 1
i. All concentrations are cumulative, e.g. for ISO Class 5, the 10 200 particles shown at 0.3µm include particles 0.3µm or larger
ii. These limits require testing at large volume air samples. Sequential sampling may assist in air quality control.
iii. Concentration limits at this particle size are not applicable due to high particle concentration.
iv. Sampling and statistical limitations make classification requirements inappropriate for particles of this size.
v. Sample collection limitations for particles in low concentrations and sizes greater than 1µm make classification at this particle size inappropriate, due to potential particle losses in the sampling system.
vi. To specify this particle size in association with ISO Class 5, the macroparticle descriptor M (number of macro-particles per m3) may be adapted and used in conjunction with at least one other particle size.
vii. This class is only applicable while the cleanroom is in operation.
viii. There are no FED Class equivalents to ISO 1, 2 or 9.
GMP Cleanroom Classification
The Good Manufacturing Practices (GMP) facility grades for cleanrooms are in the range Grade A, Grade B, Grade C and Grade D. They stipulate ISO grades at rest and in operation, as well as necessary equipment, such as particle monitoring systems, and prohibited equipment, such as sinks and drains.
Table 2: GMP vs ISO At Rest & In Operation (EU GMP Annex 1. Rev. 2022)
For each grade, this table shows the maximum permitted number of particles ≥ each size per m³ at rest and in operation
| GMP Grade | At Rest ≥0.5 µm | At Rest ≥5.0 µm | At Rest ISO Class Equiv. | In Op. ≥0.5 µm | In Op. ≥5.0 µm | In Op. ISO Class Equiv. |
|---|---|---|---|---|---|---|
| A | 3520 | n/a | ISO 5 | 3 520 | n/a | ISO 5 |
| B | 3520 | n/a | ISO 5 | 352 000 | 2 930 | ISO 7 |
| C | 352 000 | 2 930 | ISO 7 | 3 520 000 | 29 300 | ISO 8 |
| D | 3 520 000 | 29 300 | ISO 8 | n/a | n/a |
Notes to Table 2
(i) Classification including particles ≥5.0µm is dependent on CCS (Contamination Control Strategy) or historical trends
(ii) End user’s risk assessment and routine data will establish operation limits for Grade D
More about cleanroom classification:
Regulating the concentration of airborne particles prevents contamination by minimising particles and microbes entering, remaining and multiplying within the space. Cleanrooms may also control other environmental factors like temperature, humidity, and light levels as needed.
Relationship between Contamination and Cleanroom Classification
Cleanrooms must be designed, constructed, and operated according to the cleanliness classification defined in ISO 14644-1:2015.
The classification required depends on the specific tasks performed within that cleanroom. Products that are highly susceptible to contamination need cleaner spaces. Once a classification is determined, the cleanroom must be maintained to meet the appropriate specifications for environmental factors such as:
- Cleanliness
- Temperature
- Humidity
- Pressure
- Number of air changes per hour
- Flow rate
When a cleanroom is constructed in a pristine environment using non-particulate materials, airflow is the primary influence on its cleanliness. Depending on the ISO class, a cleanroom will require between 5-580 air changes per hour to keep particulate levels consistently low.
Impact of Particle Size on Classification
The ISO class required depends greatly on the size of allowable particulate matter. This is the diameter of the particle measured in microns or micrometres (µm). Particulate matter is sometimes abbreviated to PM, with the diameter indicated numerically, e.g. PM5 refers to particulate matter greater than or equal to 5µm across.
For example: if a customer requires a cleanroom with fewer than 1000 particles per m3, they may opt for an ISO 6 cleanroom, as this requires less than 293 PM5/m3. However, ISO 6 allows up to 8,320 particles of 1 micron across, and 1,000,000 particles of 0.1 micron across (PM0.1).
Mistakenly classifying based on the wrong particle size would lead to inadequate cleanliness, so it is important to know what sizes of particles would cause contamination in your application.
Similarly, mistakenly identifying particle sizes when verifying cleanroom classification can cause errors. Mistaking 0.5-micron particles for 5-micron particles could mean the difference between ISO 5 and ISO 8, so the decimal place on an air quality meter is crucial to correctly classifying spaces.
Positive vs Negative Pressure in Cleanrooms
Most cleanrooms use positive pressure to keep contaminants from entering the room.
- Air is introduced through a fan-powered filter to remove particles, creating a slightly higher air pressure inside the cleanroom than outside.
- The air and any contaminants generated within the room are pushed down to the floor level, where vents allow them to flow out to the exterior.
- The pressure keeps most contaminants from entering through vents or when the door is open.
Negative-pressure cleanrooms are used to isolate substances, fumes or particles created during internal processes such as medical research or pharmaceutical development. This protects the space outside the enclosure.
- A fan pulls air and contaminants out of the room through a filter.
- This creates negative pressure inside the room, drawing new air in through venting.
- The force of air entering the room prevents contaminants from escaping.
Negative-pressure cleanrooms usually form part of a layout with multiple cleanrooms, with an anteroom immediately outside that is maintained at a higher pressure. This allows researchers to enter and exit without disrupting the environment.
Independent Cleanroom Classification
We require independent inspections and testing before use to verify that the cleanrooms we build are operating at the required classification. Read more about this on our Cleanroom Validation information page.
Our commitment to quality is evident in every project we undertake – delivering innovative class leading solutions for all our projects..
We work closely with clients from every sector of industry including pharmaceutical, medical, veterinary, catering, research, engineering, and technology fields.
Airology can provide a complete bespoke turnkey solution for your project, from concept to completion, focusing on the design, manufacture and construction of innovative cleanroom and controlled environment solutions.
7 key decisions when creating a cleanroom environment
1. Decide how it’s to be used
2. Decide how it should be classified
3. Decide on the right environment
4. Decide what size it should be
5. Decide how impurities will be extracted or filtered
6. Decide on the right lighting condition
7. Decide how secure your facility needs to be
Industries Covered…
Below are are just some of the main industries we service. We can work with companies in near enough all fields so please do not hesitate to get in touch with your requirements today!