UK How cleanroom classes work
Cleanroom classes grade a controlled room by the number of airborne particles it contains. ISO 14644-1 is the international standard: each class sets the maximum number of particles at or above a given size in one cubic metre of air, and each step up the scale allows ten times more particles than the one below. ISO 1 is the cleanest and ISO 9 is only slightly cleaner than normal room air.
The limits come from a formula. For class N and particle size D in micrometres, the maximum concentration is 10N × (0.1 / D)2.08 particles per m³. In practice everyone uses the table of rounded values in the standard, and a room is classified at one or more particle sizes chosen to suit the process, most often 0.5 µm.
A class is only meaningful with its occupancy state. ISO 14644-1 recognises three: as built, with the room complete but empty of equipment; at rest, with equipment installed and running but no people; and in operation, with normal work under way. A room might be ISO 5 at rest and ISO 7 in operation.
ISO 14644-1 class limits
The table gives the maximum particles per cubic metre at three common sizes, with the nearest class from the old US system. A dash means the standard does not set a limit at that size for that class.
| ISO class | ≥ 0.1 µm | ≥ 0.5 µm | ≥ 5 µm | Former FS 209E |
|---|---|---|---|---|
| ISO 1 | 10 | – | – | – |
| ISO 2 | 100 | – | – | – |
| ISO 3 | 1,000 | 35 | – | Class 1 |
| ISO 4 | 10,000 | 352 | – | Class 10 |
| ISO 5 | 100,000 | 3,520 | – | Class 100 |
| ISO 6 | 1,000,000 | 35,200 | 293 | Class 1,000 |
| ISO 7 | – | 352,000 | 2,930 | Class 10,000 |
| ISO 8 | – | 3,520,000 | 29,300 | Class 100,000 |
| ISO 9 | – | 35,200,000 | 293,000 | Room air |
The old Federal Standard 209E counted particles of 0.5 µm per cubic foot, so Class 100 meant no more than 100 such particles per cubic foot. It was withdrawn in 2001 but the names are still widely used.
Which industries use which class
Each process chooses the class that keeps its product within tolerance. Typical uses are:
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ISO 3 to ISO 4. Semiconductor wafer processing and lithography, usually inside mini-environments rather than whole rooms.
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ISO 5. Aseptic filling, sterile compounding hoods, and semiconductor and optics processes, often under unidirectional airflow.
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ISO 6. Semiconductor back-end work, precision optics, hard disk and some medical device production.
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ISO 7. Electronics and PCB assembly, medical device manufacturing, pharmacy compounding and the background room around ISO 5 zones.
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ISO 8. Packaging, gowning rooms, food and cosmetics production, and general controlled areas.
EU GMP grades and how they map
Sterile medicine manufacturing in Europe uses EU GMP Annex 1, which defines Grades A to D. Each grade has a particle limit at rest and in operation, plus microbial limits that ISO classes do not cover:
Grade A is ISO 5 at rest and in operation, for high-risk operations such as aseptic filling. Grade B is ISO 5 at rest and ISO 7 in operation, the background to Grade A. Grade C is ISO 7 at rest and ISO 8 in operation. Grade D is ISO 8 at rest, with the in-operation limit set by the manufacturer.
US practice for sterile drugs follows the FDA aseptic processing guidance, which uses ISO classes directly. Our guide to ISO 7 cleanrooms covers the most common manufacturing class in more detail.
How a cleanroom is classified
Classification is a particle count to a set procedure. ISO 14644-1 sets the minimum number of sample locations from the room’s floor area, the volume of air to sample at each location and how to judge the results. Every location must meet the limit. ISO 14644-2 then sets how the room is monitored between classifications, with a full requalification typically at least once a year.
The count is taken with an optical particle counter, and the result applies to the occupancy state in which it was measured. Changes to the room, its air handling or its processes usually call for a new classification.
What cleanroom classes mean for equipment
The tighter the class, the more closely every object in the room is treated as a particle source. Computers and displays inside a classified room should be fanless with no vents, sealed at the front to at least IP65, and finished in materials that tolerate alcohol and other disinfectants. In ISO 5 zones, equipment is often kept outside the critical area altogether or mounted flush in the wall.
Our guide to clean room computers explains how fanless design, sealed surfaces and mounting change from ISO 8 to ISO 5. Our stainless steel panel PCs suit operator stations in classified rooms.
Quick answers on cleanroom classes
Cleanroom classes: common questions
What is the cleanest cleanroom class?
ISO 1. ISO 1 allows no more than 10 particles of 0.1 µm per cubic metre. In practice, ISO 1 to ISO 3 conditions are created in small enclosed mini-environments for semiconductor work.
What is a Class 100 cleanroom?
The old US name for ISO 5. Under FS 209E, Class 100 allowed 100 particles of 0.5 µm or larger per cubic foot. ISO 5 sets 3,520 per cubic metre, which is roughly the same concentration.
What cleanroom class is used for semiconductors?
Usually ISO 3 to ISO 5 at the wafer. Front-end lithography and wafer processing need the cleanest air, often in sealed mini-environments inside a less strict room. Back-end assembly and test typically run at ISO 6 to ISO 8.
Are ISO classes and GMP grades the same?
No. GMP grades set particle limits that match ISO classes, but they also set microbial limits and separate at-rest and in-operation states. A GMP grade is a wider requirement than an ISO class.
How are cleanrooms classified?
By counting airborne particles. A certified particle counter samples air at locations set by ISO 14644-1, and every location must meet the class limit at the chosen particle sizes.
We supply fanless, sealed panel PCs and displays for classified rooms, with the finish and mounting matched to the class and cleaning regime, and integrate and test each system before it ships. Tell us the class and how the room is cleaned, and we will recommend the system to suit.