Cleanroom

A cleanroom is a controlled, contained space where provisions are made to reduce particulate contamination (i.e., dust, airborne microbes, aerosol particles, chemical vapors, etc.) and control other environmental parameters, such as temperature, humidity, and pressure. Cleanrooms have a controlled level of contamination that is specified by the number of particles per cubic meter at a specified particle size. Cleanrooms are used in many industries in which small particles have adverse effects, including the following:

• Manufacturing
• Research facilities
• Pharmaceutical
• Medical laboratories
• Electronic production
• Aerospace
• Nanotechnology production
• Optics and lens manufacturing
• Military applications

Air delivered to a cleanroom passes through filters that trap particles over a certain size. This includes the use of high-efficiency particulate air (HEPA), which prevents particles above 0.3 microns in size or Ultra Low Particulate Air (ULPA) filters. Cleanrooms employ laminar or turbulent air flow principles. Laminar, or unidirectional, air flow systems direct filtered air downward in a constant stream. It is typically employed across 100% of the ceiling to maintain constant, unidirectional flow.

Laminar or unidirectional cleanroom airflow.

A turbulently ventilated room receives clean filtered air through diffusers in the ceiling. This air mixes with the room air and removes airborne contamination through air extracts at the bottom of the walls. The air changes are normally equal to, or greater than, 20 per hour, which is much greater than that used in ordinary rooms, such as in offices. In this style of cleanroom, the contamination generated by people and machinery is mixed and diluted with the supply air and then removed.

Turbulent cleanroom airflow.

Proper cleanroom design encompasses the entire air distribution system, including provisions for adequate, downstream air returns. In vertical flow rooms, this means the use of low-wall air returns around the perimeter of the zone. In horizontal flow applications, air returns are required at the downstream boundary of the process.

Positive air-pressure cleanrooms are those in which the pressure is greater than the surrounding environment. This is achieved by pumping clean, filtered air into the cleanroom, generally through the ceiling. Positive pressure is used in cleanrooms where the priority is keeping any possible contaminants out of the cleanroom. As people enter and exit the cleanroom, the positive pressure causes air to flow out, preventing new contaminants.

In a negative air pressure cleanroom, the air pressure in the room is lower than the pressure outside of the room. Generally, this is achieved by filtering air out of the room. In most situations, air enters through filters near the floor and is then sucked out through filters in the room ceiling. Negative air pressure is used in cleanrooms when the goal is to keep any possible contamination from escaping the cleanroom. Windows and doors have to be completely sealed, and by having lower pressure, air outside the cleanroom is likely to flow into it rather than out of it. Negative air pressure cleanrooms are used in industries that manufacture pharmaceutical products and do biochemical testing; they are also used in hospitals to quarantine seriously contagious patients. Any air that flows out of the room has to first flow out of a filter, ensuring that no contaminants can escape.

People working wear specially designed clothing to trap contaminants naturally generated that could include airlocks, air showers, and/or gowning rooms. Typical clothing for cleanroom personnel can include the following:

• boots
• shoes
• aprons
• beard covers
• bouffant caps
• coveralls
• face masks
• lab coats
• gowns
• gloves
• hairnets
• hoods
• sleeves
• shoe covers

Cleanrooms are classified by how clean the air is, generally measured in the number of particles for a given size. There are regional standards, such as the federal standard 209 (A to D) in the USA, and a widely used series of classifications defined by the international standards organization (ISO). Both the international (ISO 14644-1) and US (FS 209E) cleanroom classification standards require specific particle count measurements and calculations to classify the cleanliness level of a cleanroom or clean area. ISO 14644-1 standards specify the decimal logarithm of the number of particles 0.1 µm or larger permitted per cubic meter of air. For example, an ISO class 5 cleanroom has at most 10⁵ = 100,000 particles per cubic meter, and ordinary room air is approximately class ISO 9 with 1,000,000 particles per cubic meter. Both FS 209E and ISO 14644-1 assume log-log relationships between particle size and particle concentration. Therefore, it is not possible to have zero particle concentration. Ordinary room air is approximately class 1,000,000 or ISO 9.

A table of the ISO 14644-1 cleanroom standards with the max concentration (#/m³) for a given size particle as well as the FS 209E equivalent shown for each:

Modular cleanrooms are freestanding environments that can be hard- or soft-walled. Hard-walled modular cleanrooms have a rigid construction with walls mounted between posts to increase volume for internal air pressure to help minimize contaminants. Soft-walled modular cleanrooms have curtains made of vinyl and are simpler to install and less expensive.

Portable cleanrooms, similar to soft wall modular units, are movable atmospheric and climate control enclosures. They are assembled or disassembled on site. Portable cleanrooms are useful for operations that require a basic measure of control over the environments in which their operations are conducted.