How often does a clean room need to be certified?

A clean room is a controlled environment with low levels of pollutants such as dust, airborne microbes, aerosol particles, and chemical vapors. Clean rooms are designed to maintain extremely low levels of particulates, in the range of just a few parts per million or even parts per billion. The primary goal of a clean room is to prevent contamination of processes or products that could be ruined by particulates, organisms, or vapors.

Clean rooms are used extensively in industries like semiconductor manufacturing, biotechnology, pharmaceuticals, medical devices, aerospace, and healthcare. For example, clean rooms enable the production of microprocessors that require nanoscale precision. In healthcare, clean rooms prevent medical products like implants and surgical tools from being contaminated.

To ensure clean rooms meet the highest standards of cleanliness for their intended use, they undergo certification by qualified professionals. Certification validates that a clean room’s specifications for factors like air purity, temperature, humidity, pressure, and particle counts have been met. Clean rooms must be recertified regularly to confirm they continue operating within established parameters.

What is a Clean Room?

A clean room is a controlled environment designed to maintain extremely low levels of pollutants like dust, airborne microbes, and aerosol particles (Wikipedia, 2022). Clean rooms are utilized in a variety of industries where environmental control is critical, including manufacturing, scientific research, and healthcare.

Clean rooms use High Efficiency Particulate Air (HEPA) filters and other technologies to regulate temperature, humidity, airflow patterns, and pressure. Staff wearing protective clothing minimize the introduction of contaminants. The cleanroom environment allows precision work when even microscopic particles could ruin experiments or processes (Angstrom Technology, 2022).

Clean rooms are classified by the number of particles of a certain size permitted per volume of air. For example, a Class 100 clean room allows no more than 100 particles of 0.5μm or larger per cubic foot of air (Colandis, 2022). More stringent classifications have smaller allowable particle concentrations.

Clean Room Classifications

Clean rooms are classified according to the number and size of particles permitted per volume of air. The primary standard for this classification is the ISO standard ISO 14644-1. This standard specifies the maximum allowable concentrations of airborne particles for various cleanroom classifications from ISO Class 1 to ISO Class 9.

ISO Class 1 cleanrooms have the highest air purity levels, allowing no more than 10 particles of 0.1 μm or larger and 2 particles of 0.2 μm or larger per cubic meter of air. On the other end of the scale, ISO Class 9 cleanrooms permit up to 352,000 particles of 0.1 μm and 832 particles of 0.5 μm or larger per cubic meter (ISO Standard Clean Room Information).

As the ISO class number increases from 1 to 9, the air purity standards decrease. Each doubling of the class number allows for double the number of permitted particles per volume of air. So an ISO Class 5 cleanroom can have 100 times as many allowable 0.1 μm particles as an ISO Class 3 cleanroom. The higher numbers correspond to “dirtier” or less strictly controlled environments.

Different cleanroom classes are suited for different purposes. More sensitive industries like pharmaceuticals and medical device manufacturing utilize ISO Class 5 or cleaner rooms. SEMI-conductor manufacturing generally uses ISO Class 6-7 cleanrooms. Aerospace and disk drive manufacturing employ ISO Class 7-8 cleanrooms. Assembling and testing processes may use ISO Class 8 or 9 cleanrooms (Clean Room Classifications).

Why Certify Clean Rooms?

Cleanroom certification is critical to ensure the room meets the required standards for its classification level. According to American Cleanrooms, cleanroom certification ensures that facilities adhere to industry specifications and regulatory requirements. Proper certification verifies that contamination control measures are effective so sensitive processes can be completed safely.

Cleanrooms used for manufacturing pharmaceuticals, medical devices, or other products requiring sterile conditions must meet strict particulate limits. Regular certification confirms the cleanroom continues operating at the necessary cleanliness level over time. Meeting established ISO standards provides quality assurance and protects product integrity.

Cleanroom certification validates that air filtration, pressurization, temperature/humidity, and other parameters meet specifications. Certifying cleanrooms is not just recommended, but required by regulators in many industries. Routine testing and certification confirms ongoing compliance with guidelines and reassures customers that products are manufactured in controlled, high-quality environments.

Certification Process

The certification process for cleanrooms involves thorough testing by accredited professionals to ensure the facilities meet the proper ISO classification standards. This testing focuses on critical environmental factors like particle counts, airflow patterns, pressure differentials, temperature, and humidity.

To measure particulate levels, certified technicians will use specialized particle counters that use laser optics to detect and count particles down to .1 μm in size. The particle counts taken at designated locations are compared to the maximum levels dictated by the target ISO class. For example, an ISO Class 5 cleanroom must show no more than 3,520 particles (.5 μm or larger) per cubic meter.

Airflow is also carefully examined during certification. Unidirectional laminar airflow from the ceiling to the floor is essential in cleanrooms to sweep away particles. Technicians will use anemometers and smoke tracers to map the airflow patterns and identify any turbulent or dead air zones. Pressure gauges are employed to verify the cleanroom maintains positive pressure relative to lesser classified adjoining spaces to prevent contamination from entering.

All of these environmental factors are rigorously tested and monitored during the certification process to validate cleanrooms comply with ISO standards.

Initial Certification

Initial cleanroom certification is performed before the cleanroom begins operation. It verifies that the cleanroom’s design specifications, materials, and installation meet the required cleanliness classifications. Initial certification confirms that the HVAC system, airflow patterns, room pressurizations, filtering systems, monitoring systems, gowning procedures, and all other aspects were implemented correctly according to the original cleanroom design.

After construction is completed, a certified testing agency performs thorough tests and inspections. Airflow visualization tests using smoke assess proper airflow patterns. Particle counters measure particulate concentrations for comparison with ISO standards. Microbiological assays test for bacteria or airborne organisms. Surface sampling checks for particles on critical surfaces. Testing is performed in an empty cleanroom and throughout the defined clean zones surrounding it. Once initial certification is complete, the cleanroom can begin normal operation.


The Basics of Cleanroom Testing & Certification

Routine Recertification

After the initial certification, cleanrooms require routine retesting and recertification to ensure they continue meeting ISO standards. The frequency of routine recertification depends on the cleanroom classification and intended use.

For ISO Class 5 environments or cleaner, such as those used for pharmaceutical manufacturing or semiconductor fabrication, recertification is recommended every 6 months at minimum. More frequent testing, such as quarterly or even monthly, may be required for the highest-grade cleanrooms to validate ongoing contamination control [1].

For cleanrooms above ISO Class 5, annual recertification is typically sufficient. Testing every 6-12 months can confirm that air filtration, room pressurization, gowning procedures and other contamination controls continue functioning properly over time [2].

More frequent routine retesting may be advised based on criticality of use, after major facility changes, or if previous certifications uncovered issues needing correction.

Recertification After Modifications

Cleanrooms often undergo changes and modifications to layout, equipment, HVAC systems, or other aspects. According to experts, any major modifications in the cleanroom require recertification [1]. This ensures that the cleanroom’s integrity has been maintained after the changes.

Examples of modifications that would warrant recertification include:

  • Changes to the cleanroom layout or footprint
  • Adding or removing walls or doors
  • Installing new equipment like biosafety cabinets
  • Upgrading or altering the HVAC system
  • Modifying air filtration systems
  • Changing airflow patterns

After any major modification, a full recertification is needed to validate that proper cleanroom conditions have been maintained. Partial recertification may be acceptable for minor changes. However, the best practice is to fully recertify the cleanroom’s integrity after any significant layout, equipment, or HVAC alterations [2].

International Standards

There are several key international standards that govern cleanroom certification:

ISO 14644 is the primary ISO standard that specifies airborne particulate cleanliness classifications for cleanrooms and associated controlled environments. It includes requirements for particulate matter, airflows, air filtration, temperature, humidity, noise, vibration, electrostatic discharge and more. ISO 14644 has multiple parts covering cleanroom operations, testing methods, metrology and terms/definitions.

The EU Good Manufacturing Practices (GMP) Annex 1 provides guidelines for manufacturing sterile medicinal products. It covers cleanroom requirements for aseptic processes as well as environmental monitoring, disinfection, clothing and training.

FS209E is the Chinese national standard for cleanrooms, with requirements largely consistent with ISO 14644. However, there are some differences in terminology and particulate limits.


In summary, the frequency of clean room certification depends on the classification level and purpose of the clean room. ISO standards recommend certifying ISO Class 5-7 clean rooms every 6 months, while ISO Class 8 clean rooms can be certified annually. More stringent cGMP and GMP guidelines require certification every 6 months regardless of classification. After major modifications or breaches, clean rooms should be re-certified to ensure standards are still met.

Maintaining proper clean room certification is essential for industries like pharmaceuticals, medical devices, and microelectronics where controlling contamination is critical. Allowing clean rooms to operate without routine evaluation can lead to quality issues, regulatory violations, and threats to product or patient safety. By following a scheduled certification program, companies can continuously verify their facilities meet the required cleanliness levels.