A Practical Guide to ISO 14644 Part 1 Cleanroom Classification
Cleanrooms are designed to control contamination. Even a tiny airborne particle can damage a microchip, contaminate a sterile medicine or affect a sensitive laboratory process.
This is where ISO 14644 Part 1 becomes important. The standard defines how cleanroom air cleanliness is measured and classified using airborne particle concentration.
For cleanroom engineers, facilities managers and contamination control specialists, ISO 14644 Part 1 forms the foundation of cleanroom compliance.
This guide explains how the standard works, how classification is determined and why it matters across industries such as pharmaceuticals, semiconductor manufacturing and biotechnology.
What ISO 14644 Part 1 Covers
ISO 14644 is a global series of standards for cleanrooms and controlled environments.
Part 1 focuses specifically on classification of air cleanliness based on particle concentration.
In simple terms, the standard defines how clean an environment is by measuring how many airborne particles exist in a cubic metre of air.
Key elements covered in ISO 14644 Part 1 include
• cleanroom classification levels from ISO Class 1 to ISO Class 9
• particle concentration limits
• particle size ranges used in testing
• sampling requirements for certification
• statistical methods used for classification
The classification system applies to environments where contamination control is critical.
Examples include
• pharmaceutical manufacturing
• semiconductor fabrication
• aerospace engineering
• medical device production
• nanotechnology research laboratories
Why Cleanroom Classification Matters
Cleanroom classification allows organisations to demonstrate that their environment meets contamination control requirements.
Without a recognised classification system, it would be difficult to compare cleanroom performance across facilities or industries.
ISO 14644 Part 1 provides a consistent framework that allows
• engineers to design appropriate cleanroom systems
• auditors to verify compliance
• regulators to assess contamination control
• manufacturers to protect sensitive products
For example, sterile pharmaceutical manufacturing may require an ISO Class 5 environment, while semiconductor wafer processing may require even stricter particle limits.
Understanding ISO Cleanroom Classes
ISO 14644 Part 1 defines nine cleanroom classes.
Each class specifies the maximum number of airborne particles permitted per cubic metre of air.
Lower class numbers represent cleaner environments.
Cleanroom classification table
| ISO Class | Typical Environment |
|---|---|
| ISO 1 | Advanced nanotechnology labs |
| ISO 2 | Semiconductor research facilities |
| ISO 3 | Microelectronics manufacturing |
| ISO 4 | Precision optics and wafer fabrication |
| ISO 5 | Pharmaceutical sterile production |
| ISO 6 | Medical device manufacturing |
| ISO 7 | Pharmaceutical packaging areas |
| ISO 8 | Clean manufacturing environments |
| ISO 9 | Typical indoor air |
Most industries operate between ISO Class 5 and ISO Class 8 depending on product sensitivity.
Particle Size and Measurement
ISO 14644 Part 1 classification is based on particle size and particle concentration.
Particles are measured using optical particle counters.
These instruments draw in air samples and detect particles based on light scattering.
Typical particle sizes measured include
• 0.1 micrometre
• 0.2 micrometre
• 0.3 micrometre
• 0.5 micrometre
• 1.0 micrometre
• 5.0 micrometre
A micrometre is one millionth of a metre.
For comparison
• a human hair is about 70 micrometres wide
• bacteria may be around 1 micrometre
• smoke particles may be smaller than 0.5 micrometres
Cleanroom testing focuses on particles that could contaminate products or processes.
Maximum Particle Limits
Each ISO cleanroom class has defined particle limits.
The table below shows maximum particle concentrations in a 1m3 sample for selected particle sizes.
| ISO Class | ≥0.1 µm | ≥0.2 µm | ≥0.3 µm | ≥0.5 µm |
|---|---|---|---|---|
| ISO 1 | 10 | 2 | 0 | 0 |
| ISO 2 | 100 | 24 | 10 | 4 |
| ISO 3 | 1000 | 237 | 102 | 35 |
| ISO 4 | 10000 | 2370 | 1020 | 352 |
| ISO 5 | 100000 | 23700 | 10200 | 3520 |
| ISO 6 | 1000000 | 237000 | 102000 | 35200 |
These limits are based on the ISO classification formula.
The ISO 14644 Part 1 Particle Formula
The cleanroom classification system is derived from a mathematical formula.
The formula is
Cn = 10^N × (0.1 ÷ D)^2.08
Where
Cn represents the maximum permitted particle concentration
N represents the ISO classification number
D represents particle size in micrometres
This formula allows particle limits to be calculated consistently for different particle sizes.
The approach ensures that classification levels scale logically between ISO Class 1 and ISO Class 9.
Cleanroom Certification Testing
Cleanroom classification is verified through formal testing.
Testing is typically performed by trained cleanroom professionals using calibrated particle counting equipment.
Key steps in cleanroom certification include
1 sampling location calculation
2 particle counting measurements
3 statistical analysis
4 classification verification
Sampling locations are determined by the floor area of the cleanroom.
The standard provides formulas that calculate how many measurement points are required.
Each location must meet particle limits for the cleanroom classification to pass.
Testing may occur
• during initial cleanroom commissioning
• during periodic requalification
• after modifications or maintenance
Professionals who specialise in this process often undergo formal training such as the CTCB-I Cleanroom Testing certification available through the CCN courses page
Industries That Depend on ISO 14644 Classification
Cleanroom classification plays a critical role in many sectors.
Pharmaceutical manufacturing
Sterile medicine production requires tightly controlled environments to prevent microbial contamination.
Semiconductor fabrication
Microchips contain features smaller than many airborne particles. Even a single particle can damage a semiconductor wafer.
Medical device production
Implants, surgical instruments and diagnostic equipment often require contamination controlled manufacturing.
Aerospace and optics
Satellite sensors and high precision optical systems must be produced in controlled environments to avoid performance defects.
Biotechnology and research laboratories
Many laboratories rely on cleanroom environments to protect experimental integrity.
Key Changes Introduced in the 2015 Revision
ISO 14644 Part 1 was revised in 2015.
The update introduced several important changes.
Removal of the previous 95 percent statistical confidence calculation
The revised standard simplified classification by removing the older statistical method used in earlier versions.
Improved sampling guidance
The revision clarified how sampling locations should be calculated.
Refined particle size limits
Some particle limits were adjusted to reflect modern contamination control requirements.
Alignment with modern cleanroom technology
The revision recognised advancements in particle counters and monitoring systems.
For engineers and facilities managers, the 2015 revision simplified certification procedures while maintaining strict contamination control standards.
ISO 14644-1:2015 is currently under review.
Cleanroom Monitoring and Ongoing Compliance
While ISO 14644 Part 1 defines classification, maintaining that classification requires continuous monitoring.
Airflow performance
filtration efficiency
room pressurisation
particle monitoring
All play a role in maintaining cleanroom conditions.
Ongoing monitoring requirements are addressed in ISO 14644 Part 2.
Cleanroom professionals must ensure that environmental conditions remain within acceptable limits between certification tests.
Training and Cleanroom Competence
Understanding cleanroom classification requires technical knowledge of contamination control, particle measurement and cleanroom operations.
Professional training is therefore an important part of maintaining compliance.
Courses such as the CTCB-I Cleanroom Testing programme offered by the CCN help professionals develop expertise in cleanroom testing, certification and environmental monitoring.
More information about these courses can be found here
Why ISO 14644 Part 1 Remains the Foundation of Cleanroom Classification
ISO 14644 Part 1 provides the global foundation for cleanroom classification.
By defining particle concentration limits and testing methods, the standard allows organisations to demonstrate that their environments meet strict contamination control requirements.
From pharmaceutical production to semiconductor manufacturing, cleanroom classification plays a vital role in protecting products, research and patient safety.
For cleanroom professionals, understanding ISO 14644 Part 1 is an essential step in ensuring that controlled environments operate reliably and remain compliant with international standards.
ISO 14644 Part 1 FAQs
What is ISO 14644 Part 1?
ISO 14644 Part 1 is the international standard that defines cleanroom classification based on airborne particle concentration.
How is a cleanroom classified?
A cleanroom is classified by measuring airborne particle concentration using particle counters and comparing results with ISO class limits.
What particle sizes are measured in cleanrooms?
Common particle sizes include 0.1 micrometre, 0.3 micrometre, 0.5 micrometre, 1 micrometre and 5 micrometres.
How often are cleanrooms tested?
Cleanrooms are typically tested during commissioning and then requalified periodically to ensure continued compliance. In the UK we have a suggested frequency table in ISO 14644-2:2015
Which industries use cleanrooms?
Industries include pharmaceuticals, semiconductor manufacturing, biotechnology, aerospace engineering and medical device production.
Blog by Toni Horsfield
