How Is Cleanroom Cleanliness Measured?

by Technical Air Products

fan filter unit

One frequently asked question about cleanrooms is: How is cleanroom cleanliness measured? Companies that invest in cleanrooms want to know that they will be able to achieve their cleanliness specifications and also expand their capabilities if needed further down the road. Here we will define cleanliness and explain how fan filter units (FFUs) operate to achieve it. 

How Is Cleanroom Cleanliness Measured? 

A cleanroom is a controlled environment that limits the concentration of airborne particles to specification. That specification will vary based on the purpose of the room, but pollutants like dust, pollen, airborne microbes, and aerosol particles are filtered out to create a clean environment.

There are different cleanroom classes and they are determined by the air flow in the cleanroom.

The above chart shows the different classes of cleanrooms. They have specific parameters. For example, an ISO 5 cleanroom cannot have more than 3,520 particles >0.5 microns per cubic meter. To achieve an ISO5 cleanliness rating, the cleanroom airflow must be unidirectional and exchanged through a HEPA filter 240-600 times per hour. 

In order to achieve any level of cleanroom cleanliness, the cleanroom must have a clean physical design with materials that do not shed particulate matter. It must also have an airflow of filtered air that works to dilute the particulate matter present and force dirty air from the cleanroom. 

Fan Filter Units Create Airflow and Maintain Cleanliness

The way this is achieved is by using fan filter units (FFUs). There are different models of FFUs and they can utilize either HEPA or ULPA filters. A High Efficiency Particulate Air (HEPA) filter is 99.99% efficient at 0.3 microns. An Ultra Low Particulate Air (ULPA) filter is 99.999% efficient at 0.1 microns. This means it removes 99.999% of particles with a minimum particle penetration size of 100 nanometers.

Fan filter units filter air at between 90 to 100 feet per minute. This creates laminar airflow within the cleanroom, but it is not disruptive to the activities of people or objects within the room. Laminar airflow happens when all of the air within a space is moving in the same direction at the same velocity. Adding fan filter units will make the cleanroom cleaner by filtering out more particulate matter from the air. 

Measurements of particulate levels are taken with a particle counter at various points throughout the cleanroom. This is how cleanliness is determined. Not all areas of the cleanroom have to be filtered to the same standard. In fact, it’s common practice to have separate areas for gowning, for example. However, areas with more stringent cleanliness requirements must be kept separate to maintain the necessary standard. 

Many organizations choose to use modular cleanrooms instead of stick-built cleanrooms because they are easy to install and control, simple to maintain, and they can be added on to if the organization needs to expand its operations later on. Technical Air Products offers both softwall and rigidwall cleanrooms as well as the components and accessories necessary to make them operate, including FFUs. Please take a moment to go through our products to see what would best serve your cleanroom needs. 

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