What Is A Cleanroom?
01 November 2023

What Is A Cleanroom?

More than a room that is clean or a controlled environment, according to the ISO standard 14644-1 clean room definition, a clean room is defined as:

“A room in which the concentration of airborne particles is controlled, and which is constructed and used in a manner to minimize the introduction, generation, and retention of particles inside the room and in which other relevant parameters, e.g. temperature, humidity, and pressure, are controlled as necessary”

Minimizing the introduction, generation and retention of particles in a clean room is done in 3 ways:

  • Supplying the room with a large quantity of air filtered with high efficiency filters (HEPA filter or ULPA). The filtered air will dilute and remove particles, bacteria and chemicals from within the room. The air is also used to pressurize the room and ensure a non contaminated clean room air circulation
  • The clean room itself must be built with materials that do not generate contaminants, particles, or outgas airborne chemical and must also be easy to clean.
  • Clean room operators must wear garments that minimize dispersion of particles and micro-organisms generated by people such as hair, skin flakes, clothing fibers, etc. In fact, operator base contamination accounts for 70% to 80% of cleanroom contamination. To minimize the risk of contamination, the clean room operators will usually get dressed in a gowning room, also referred as anteroom. Air showers can also be used.


Maximising product yield, improving quality control and ensuring safety are common reasons to use a cleanroom. Cleanliness is only one of the aspects controlled within a cleanroom system. Cleanrooms can also control temperature, humidity, sound, lighting, and vibration when necessary.

The operations being conducted will determine which variables must be controlled. Here are some industries and applications that use cleanrooms:

  • Electronics, Semiconductors
  • Micromechanics
  • Optics
  • Nanotechnology
  • Biotechnology
  • Pharmaceutical
  • Sterile Compounding
  • Medical Devices
  • Food and Drink


Cleanrooms are classified by how clean the air is, according to the particle quantity and particle size per cubic meter of air.  Although several classifications exist, there has been an increasing trend to change from previous classification systems to the ISO classification system in ISO 14644-1.

The basis of cleanroom standards is the micrometer, micron in its abbreviated form. The image below compares the size of a micron with that of a human air (70 micrometers) and a grain of beach sand (90 micrometers).


The FS 209E states that the cleanroom’s class is determined by the particle concentration in one cubic foot of air. It measure the number of particles smaller than 0,5 micrometer in one cubic foot of room air. In a class 1 cleanroom system, there is 1 particle smaller than 0,5 microns. In a cleanroom class 1,000, there are  1,000 particles smaller than 0,5 microns, and so on.

To give you an example, a typical office building or room in your house has anywhere between 500,000 and 1,000,000 airborne particles of 0.5 micron or larger for each cubic foot of air. By taking another look at the 90 microns beach sand image above, can you imagine how clean a class 100 is?

The ISO class standard 14644-1 replaced the Federal Standard 209 classification in 1999 and it was then revised in 2015. Many companies continue to use the traditional Class 100, Class 10,000 and Class 100,000 terminology.


The cleanroom has three different occupancy states:

  • As built: installation is completed, the cleanroom is up and running but there are no equipment, materials or personnel inside
  • At rest: installation is completed and the cleanroom is up and running with the agreed upon equipment, without personnel inside
  • Operational: the cleanroom is functioning in the specified manner, with the specified number of personnel, working in the manner agreed upon


The regulations that apply to a particular cleanroom depend upon the application and processes taking place inside the room. Pharmacies with sterile compounding activities must follow USP 797 regulations. Other regulations include, but are not limited to, FDA, GMP and EMEA.

There are two types of cleanrooms, differentiated by their airflow systems:


Originally known as ‘turbulently ventilated’, the non-unidirectional air flow cleanroom receives clean filtered air through high efficiency air filters in the ceiling. The fresh air is mixed with the room air and removes airborne contamination generated by people and machinery. This process is done through air extracts positioned at the bottom of the wall. Depending on the industry as well as the cleanroom size, classifications up to ISO 6 can be achieved.

For higher and less stringent classifications such as an ISO 8 gray room, the air extracts can be positioned in the ceiling.


It’s a mistake to use the term laminar flow to describe this type of cleanroom. In physics and in engineering, laminar airflow does not apply to the cleanroom airflow. Unidirectional airflow cleanrooms use much more air than non-directional airflow cleanrooms. High efficiency filters are installed across the entire ceiling.

The air sweeps down the room in a unidirectional way, at a velocity generally between 0.3 m/s and 0.5 m/s. It then exits through the floor, removing the airborne contamination from the room. For a room of less than a 4-6 meters width, air extracts can be positioned on the side of the walls.

The unidirectional cleanroom is more expensive than the non-unidirectional type. This is because it can comply with more stringent classifications, such as ISO 5 or lower.