Cleanrooms are uniquely designed to keep a workspace clean from particles and contaminants, but how does it do that? There a number of physical components that keep a cleanroom working - and we’ll cover those - but cleanrooms also use physics to keep particles away from your workspace.
Two words: positive pressure.
So how does that work?
First, let’s cover how a cleanroom is physically built and structured to understand how physics plays a role.
The Structure Of A Cleanroom
Cleanrooms are built with 4 areas in mind:
- The outside environment
- Ancillary areas
- Clean zone
The air is brought in from the outside environment to be cycled through the Air Handling Unit (AHU) and corresponding filters into the appropriate rooms. This is the physical structure of the cleanroom that allows for the positive pressure to remove particles from the air and keep the room clean.
So, when we look at the physical structure of a cleanroom, it resembles a human body. You have the outside environment which interacts with the ancillary areas - and on the human, this would be the skin that protects their internal organs from the outside world. Then the clean zones would be the internal organs that need to remain clear of bacteria and external influences to remain clean.
Now, inside the cleanroom, we have the filters which serve as lungs. The air goes through the filters to enter the bloodstream and diffused to the rest of the body. The Air Handling Unit (AHU) is the heart, which moves the air (blood) throughout the whole body, utilizing centrifugal fans (arteries and veins) to get the blood where it needs to go.
Ultimately, it comes together as one working component that keeps the insides clean and operational.
The Building Materials For A Cleanroom
Because of the nature of the work done in a cleanroom, they must be able to be sanitized thoroughly and easily. You do have some choices for your cleanroom walls to dictate the appearance of your cleanroom, but the material should be nonporous and easily sanitized.
These materials can include glass, aluminum, stainless steel, vinyl-coated gypsum, and polycarbonate. Not only do these materials fit the criteria of being easily cleaned and non-porous, but they can also be constructed with an interior honeycomb pattern.
This honeycomb pattern in the wall makes the wall lighter so it’s easier to install and saves on material and installation costs. They can also be customized to fit the appearance of your facility.
The Air Handling Unit In A Cleanroom
The heart of the cleanroom is the Air Handling Unit (AHU). It not only hosts the filters that keep the cleanroom clean, but it also uses fans to push the cleaned air into various parts of the cleanroom, similar to the blood vessels throughout your body. It’s the critical component of how cleanrooms work.
Without the AHU, there is no cleanroom.
AHUs use a centrifugal fan to move the air around the room. Unlike normal fans, which move air straight through them, centrifugal fans are designed to redirect airflow. This allows the room to continually circulate air into different areas of the room and through different filters.
Circulation is an important part of keeping the air clean - which is why cleanrooms use a lot of air. But, most importantly, that circulation keeps the air passing through filters, specifically HEPA and ULPA filters.
Cleanrooms work by using High Efficiency Particulate Air (HEPA) filters to sift particles out of the air as it enters the room. HEPA filters are 99.97% effective at eliminating contaminants from the air, such as dust, pollen, bacteria, mold, and other airborne particles.
Particles the size of 0.3 microns are defined as a HEPA filter’s Most Penetrating Particle Size (MPPS), which means that larger particles will be caught by the filter at a much higher rate. However, HEPA filters can potentially filter out smaller particles as well.
Most cleanrooms will use HEPA filters, as they are highly effective and readily available; however, some cleanrooms used for more sensitive production may also use ULPA filters.
Cleanrooms also work by using Ultra Low Penetration Air (ULPA) filters in certain instances to sift out even finer particles. An ULPA filter’s MPPS is 0.12 microns. They have an efficiency of 99.9995%.
They aren’t necessary for every cleanroom and are an added expense at the initial build and during upkeep. Also, because they are more restrictive, using an ULPA filter leads to higher energy cost and stronger fans needed. But they are an excellent idea in cleanrooms used for highly sensitive products, such as microprocessors.
The Power Of Positive Pressure
So now we know how the body of the cleanroom works, but how does it use physics to keep the room extra clean?
Simple. It uses positive pressure.
Essentially, this means that the air inside the cleanroom is at a higher pressure (it has more kinetic energy in it) than the air outside the room. Because the world naturally tries to be in a state of equilibrium, the room tries to make the pressure even with that outside of the room. So air is constantly leaving the room and taking particles borne in the room with it - another reason cleanrooms use a lot of air and circulation.
Also, because air is always leaving the room, no new air is entering naturally. Only the air being forced in through the AHU (and cleaned through the filters) is being entered into the cleanroom environment.
Imagine a tea kettle being heated on the stove. As the water heats up, that heat translates to the molecules in the water having more kinetic energy, which means they’re moving more. As they move more, bouncing off the inside of the tea kettle (and visibly seen as boiling), that increases the pressure within the tea kettle. Eventually, the pressure rises to the point where the water has to escape because there’s nowhere else in the tea kettle for it to go. So it blows through the spout of the tea kettle. At that point, nothing is able to enter the tea kettle because the only way in and out (the spout) has steam rushing out of it.
The inside of the tea kettle has positive (more) pressure than the outside environment and, to create equilibrium, the air from inside had to exit the kettle.
While your cleanroom won’t be heated to a boiling point, the same principle applies. The pressure inside the room remains positive so the air is forced from the room to the outside world, preventing any new particles from entering.
And that’s the physics behind how a cleanroom works.
The Maintenance To Keep A Cleanroom Working In Perfect Conditions
Every cleanroom should have its particles monitored regularly to make sure the AHU is still doing its job. Here at Lighthouse Worldwide Solutions, we provide top-quality particle counters to make sure your cleanroom is staying clean utilizing real-time monitoring or certification.
Cleanrooms are required to be certified frequently to make sure it's still performing correctly. The frequency of the certification depends on its use, though. These certifications are done by taking a sampling of the air and using a particle counter to examine the sample.
While this practice is the bare minimum for certification, if your industry is producing aseptic or sterile products (such as pharmaceuticals or semiconductors), we highly recommend the real-time monitoring solution. In this situation, your cleanroom would be consistently monitored and you would be alerted if the air cleanliness is threatened. This means that your cleanroom is constantly being monitored while in use to make sure it is performing at optimal levels consistently and the risk of product contamination is significantly reduced.
Interested in learning more about how a particle counter and real-time monitoring can improve your cleanroom? Contact us today.