ISO cleanroom class
The cleanliness classification ISO 14644-1 assigns a room, from ISO 1 to ISO 9, by the maximum concentration of airborne particles at or above stated sizes. Each class number allows ten times the particles of the class below it, and the classification says nothing about airflow, temperature, or pressure.
Also called ISO 14644-1 class, cleanroom classification, ISO 7 cleanroom, ISO 8 cleanroom
What is an ISO cleanroom class?
An ISO cleanroom class is the ISO 14644-1 rating of how few airborne particles a room holds, from ISO 1, the cleanest, to ISO 9. ISO 7 allows 352,000 particles of 0.5 micrometers and larger per cubic meter, and ISO 8 allows 3,520,000.
ISO cleanroom class: how it works
The class limit at any particle size comes from one formula, Cn = 10^N × (0.1/D)^2.08, where N is the class number and D is the particle size in micrometers. A certifier samples air at a number of locations set by the room's floor area, counts particles at the sizes chosen for the class, and compares every location with the limit. The room holds the class it meets, in the occupancy state that was tested.
Where you meet the term
- In a sterile compounding suite, where USP 797 requires ISO 7 buffer rooms and ISO 8 or cleaner anterooms.
- In the FDA aseptic processing guidance, which uses ISO 5 for critical areas and ISO 7 or ISO 8 for supporting rooms.
- In ASHRAE's data center contamination guideline, which recommends keeping data halls at ISO 8.
How to check it
- Read the classification report. The report names the class, the particle sizes counted, the occupancy state, and the date, and a room is classified only in the state that was tested. Owner check
- Count particles at the required locations. A certifier uses a calibrated particle counter at the number of locations ISO 14644-1 sets from floor area and compares each location's result with the class limit. Technician
Figures you will see
| Condition | Figure | What it tells you |
|---|---|---|
| ISO 5 at 0.5 micrometers and larger | 3,520 particles per cubic meter | Read against the model documentation |
| ISO 7 at 0.5 micrometers and larger | 352,000 particles per cubic meter | Read against the model documentation |
| ISO 8 at 0.5 micrometers and larger | 3,520,000 particles per cubic meter | Read against the model documentation |
ISO cleanroom class: what it is not
- An ISO class is not an air change rate. ISO 14644-1 sets particle limits only, and every air change figure attached to a class comes from a regulation or a recommendation.
- A room classified at rest is not classified in operation. People and processes release particles, and the operational count can be far higher than the at-rest count.
ISO cleanroom class questions
What does Class 100 mean in ISO terms?
Class 100 comes from the withdrawn United States Federal Standard 209E and corresponds to ISO 5. The FDA aseptic processing guidance still pairs the old and new names, describing Class 100 as ISO 5, Class 10,000 as ISO 7, and Class 100,000 as ISO 8.
How many sample locations does ISO 14644-1 require?
The number of sampling locations comes from a table in ISO 14644-1:2015 based on the room's floor area, and every location has to meet the class limit. Larger rooms need more locations, and the certifier's report lists where each sample was taken.
Is ISO 9 cleaner than ordinary room air?
ISO 9 allows 35,200,000 particles of 0.5 micrometers and larger per cubic meter, a limit ordinary indoor air can fall within. The classes that carry HVAC design consequences start at ISO 8 and run cleaner.
Where this definition comes from
Written from standards body publication, government guidance material held in the HVAC Bench evidence record. Where a document limits a definition to certain models, that limit is repeated here rather than generalised across a brand.
- ISO 14644-1:2015, Cleanrooms and associated controlled environments, Part 1: Classification of air cleanliness by particle concentrationClassification of cleanrooms by airborne particle concentration only, using Cn = 10^N x (0.1/D)^2.08 particles per cubic meter for class N and particle size D in micrometers, giving 3,520 per cubic meter at 0.5 micrometers for ISO 5, 352,000 for ISO 7, and 3,520,000 for ISO 8, with classification stated for the as-built, at-rest, or operational state. The standard sets no air change rate, air velocity, or ceiling filter coverage for any class.
- Guidance for Industry: Sterile Drug Products Produced by Aseptic Processing, Current Good Manufacturing PracticeFDA guidance recommending a positive pressure differential of at least 10 to 15 pascals between adjacent rooms of differing classification with doors closed, outward airflow sufficient to minimize ingress when doors open with door-open time strictly controlled, at least 12.5 pascals from an aseptic processing room to adjacent unclassified space, airflow for at least 20 air changes per hour as acceptable for ISO 8 supporting rooms, a critical area velocity of 0.45 meters per second (90 feet per minute) plus or minus 20 percent, and HEPA filter leak testing at installation and at intervals such as twice a year for the aseptic processing room.
- General Chapter 797, Pharmaceutical Compounding, Sterile Preparations2023 revision, official 1 November 2023, for sterile compounding: at least 30 air changes per hour of HEPA-filtered supply in ISO 7 buffer rooms and anterooms and at least 20 in ISO 8 rooms, with at least 15 of them supplied by the HVAC system through HEPA filters; a minimum positive pressure differential of 0.020 inches of water column between the buffer room and anteroom and between the anteroom and unclassified space, monitored continuously; rooms maintained at 20 degrees Celsius or cooler and 60 percent relative humidity or below; and certification of primary and secondary engineering controls every six months.
- 2011 Gaseous and Particulate Contamination Guidelines for Data CentersASHRAE TC 9.9 recommendation that data centers be kept clean to ISO 14644-1 Class 8, achievable by continuously filtering room air with MERV 8 filters and filtering air entering the data center with MERV 11 or preferably MERV 13 filters; that relative humidity be kept below 60 percent so settled dust with a low deliquescent relative humidity does not become conductive; and that gaseous contamination stay within modified ISA-71.04 severity level G1.