Typically used in manufacturing or scientific research, a cleanroom is a controlled environment that has a low level of pollutants such as dust, airborne microbes, aerosol particles, and chemical vapors. To be exact, a cleanroom has a controlled level of contamination that is specified by the number of particles per cubic meter at a specified particle size. The ambient air outside in a typical city environment contains 35,000,000 particles per cubic meter, 0.5 mm and larger in diameter, corresponding to an ISO 9 cleanroom which is at the lowest level of cleanroom standards.
Cleanroom Overview
- Cleanrooms are used in practically every industry where small particles can adversely affect the manufacturing process. They vary in size and complexity and are used extensively in industries such as semiconductor manufacturing, pharmaceuticals, biotech, medical devices, and life sciences, as well as critical process manufacturing common in aerospace, optics, military, and the Department of Energy.
- A cleanroom is any given contained space where provisions are made to reduce particulate contamination and control other environmental parameters such as temperature, humidity, and pressure. The key component is the High-Efficiency Particulate Air (HEPA) filter that is used to trap particles that are 0.3 microns and larger in size. All of the air delivered to a cleanroom passes through HEPA filters, and in some cases where stringent cleanliness performance is necessary, Ultra Low Particulate Air (ULPA) filters are used.
- Personnel selected to work in cleanrooms undergo extensive training in contamination control theory. They enter and exit the cleanroom through airlocks, air showers, and/or gowning rooms, and they must wear special clothing designed to trap contaminants that are naturally generated by the skin and the body.
- Depending on the room classification or function, personnel gowning may be as limited as lab coats and hairnets, or as extensive as fully enveloped in multiple-layered bunny suits with self-contained breathing apparatus.
- Cleanroom clothing is used to prevent substances from being released off the wearer’s body and contaminating the environment. The cleanroom clothing itself must not release particles or fibers to prevent contamination of the environment by personnel. This type of personnel contamination can degrade product performance in the semiconductor and pharmaceutical industries and it can cause cross-infection between medical staff and patients in the healthcare industry for example.
- Cleanroom garments include boots, shoes, aprons, beard covers, bouffant caps, coveralls, face masks, frocks/lab coats, gowns, gloves and finger cots, hairnets, hoods, sleeves, and shoe covers. The type of cleanroom garments used should reflect the cleanroom and product specifications. Low-level cleanrooms may only require special shoes having completely smooth soles that do not track in dust or dirt. However, shoe bottoms must not create slipping hazards since safety always takes precedence. A cleanroom suit is usually required for entering a cleanroom. Class 10,000 cleanrooms may use simple smocks, head covers, and booties. For Class 10 cleanrooms, careful gown-wearing procedures with a zipped cover all, boots, gloves, and complete respirator enclosure are required.
ALSO READ: Clean Room Validation Requirements
Cleanroom Air Flow Principles
- Cleanrooms maintain particulate-free air through the use of either HEPA or ULPA filters employing laminar or turbulent air flow principles. Laminar, or unidirectional, air flow systems direct filtered air downward in a constant stream. Laminar air flow systems are typically employed across 100% of the ceiling to maintain constant, unidirectional flow. Laminar flow criteria are generally stated in portable workstations (LF hoods) and are mandated in ISO-1 through ISO-4 classified cleanrooms.
- 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, it require the use of air returns at the downstream boundary of the process. The use of ceiling-mounted air returns is contradictory to proper cleanroom system design.
Cleanroom Classifications
- Cleanrooms are classified by how clean the air is. In Federal Standard 209 (A to D) of the USA, the number of particles equal to and greater than 0.5mm is measured in one cubic foot of air, and this count is used to classify the cleanroom. This metric nomenclature is also accepted in the most recent 209E version of the Standard. Federal Standard 209E is used domestically. The newer standard is TC 209 from the International Standards Organization. Both standards classify a cleanroom by the number of particles found in the laboratory's air. The cleanroom classification standards FS 209E and ISO 14644-1 require specific particle count measurements and calculations to classify the cleanliness level of a cleanroom or clean area. In the UK, British Standard 5295 is used to classify cleanrooms. This standard is about to be superseded by BS EN ISO 14644-1.
- Cleanrooms are classified according to the number and size of particles permitted per volume of air. Large numbers like "class 100" or "class 1000" refer to FED_STD-209E and denote the number of particles of size 0.5 mm or larger permitted per cubic foot of air. The standard also allows interpolation, so it is possible to describe e.g., "class 2000."
- Small numbers refer to ISO 14644-1 standards, which specify the decimal logarithm of the number of particles 0.1 µm or larger permitted per cubic meter of air. So, for example, an ISO class 5 cleanroom has at most 105 = 100,000 particles per m³.
- Both FS 209E and ISO 14644-1 assume log-log relationships between particle size and particle concentration. For that reason, there is no such thing as zero particle concentration. Ordinary room air is approximately class 1,000,000 or ISO 9.
ISO 14644-1 Cleanroom Standards
BS 5295 Cleanroom Standards
Cleanroom Air Flow Principles
- Cleanrooms are facilities designed for conducting research or manufacturing products that require extremely clean environments. Typically, cleanrooms employ a broad range of techniques to prevent air particles, bacteria, and other contaminants from entering the workspace, often using employee dress code and washing, pass-thru lockers and chambers, and intensive detail to cleaning.
- However, one of the major forces keeping a cleanroom particle-free is the air filter system. Cleanrooms employ many different types of filters, including HEPA filters and ULPA filters, but two standard airflow patterns are consistently used: laminar flow and turbulent flow.
Cleanroom Basics
- Cleanrooms are necessary for various kinds of scientific research that require particle and bacteria-free environments. For example, when scientists grow cultures, it is important to reduce the introduction of other bacteria so that results will not be compromised. Manufacturing various kinds of products like microprocessors also requires a particle-free environment, because even a human hair contacting the small chips of a microprocessor can inhibit or destroy functionality.
- Cleanrooms are either hard- or soft-walled. A hard wall cleanroom is a permanent structure or part of a larger permanent structure, while a soft wall cleanroom can be transported or augmented depending on requirements, and primarily exists within a larger, permanent structure. Modular, soft-wall cleanrooms are needed for medical emergencies or when smaller runs of environment-sensitive materials are produced within a larger facility.
- Cleanrooms are graded depending on how clean the air in the facility is. There are two standards used for this determination: the ISO and United States federal standards. ISO grades are numbered sequentially, advancing from 1. A cleanroom graded ISO 1 contains ten or fewer particles per 0.1 micrometer cubed area. A cleanroom-graded ISO 2 contains 100 or fewer particles per 0.1 micrometer cubed area. The rest of the series features the amount of particles rising by a factor of 10 per level. US federal standards are numbered 10, 100, 1000, etc., with the lower class number representing a cleaner facility. Class 1 cleanrooms have one or fewer particles per 0.5 micrometer cubed area. Class 10 cleanrooms have 10 or fewer particles per 0.5 micrometer cubed area. Ascending class grades rise by a factor of 10.
- Because people often work in cleanrooms, they are required to follow dress and behavior guidelines to limit the amount of particles they will bring into a cleanroom or particles they will shed while working in the environment. Workers must change from street clothes into specially designed outfits, often with full hood coverings, gloves, and breathing masks. Workers must also enter through an air shower to eliminate remaining particles on the cleanroom suit, and then pass items into the cleanroom through a small chamber that prevents outside air from entering the clean environment.
Cleanroom Air Filtration
- Cleanrooms employ air filtration to limit the particles in the environment's air. Typically, this is through the use of either a highly efficient particulate air (HEPA) or ultra-low particulate air (ULPA) filter. These filters can remove roughly 99.9 percent of all microparticles in room air by applying either laminar airflow or turbulent airflow techniques to the environment air.
- Laminar air flow refers to air that flows in a straight, unimpeded path. Unidirectional flow is maintained in cleanrooms through the use of laminar airflow hoods that direct air jets downward in a straight path, as well as cleanroom architecture that ensures turbulence is lessened. Laminar air flow utilizes HEPA filters to filter and clean all air entering the environment. Laminar filters are often composed of stainless steel or other non-shed materials to ensure the amount of particles that enter the facility remains low. These filters usually compose roughly 80 percent of the ceiling space. Cleanrooms employing laminar air flow are typically referred to as Unidirectional Airflow Cleanrooms.
- Non-unidirectional airflow cleanrooms utilize turbulent airflow systems to clean particulate air and maintain a clean environment. While laminar airflow filters are often a component of turbulent airflow systems, they are not the only systems employed. The entire enclosure is designed to use laminar flow and random, non-specific velocity filters to keep the air particle-free.
- Turbulent airflow can cause particle movement that can be difficult to separate from the rest of the air, but non-unidirectional airflow systems count on this random movement to move particles from the air through the filter.
