What is a clean room?
Often used in manufacturing or in scientific research, a clean room is a controlled environment where the levels of contaminants such as dust, bacteria, oil dust and chemical vapors in the air remain low. Strictly speaking, cleanrooms have a level of contamination controlled by a specified number of dust particles of a certain size in a cubic meter of air. Each cubic meter of air in the outside environment of a typical city contains 35,000,000 dust particles with a diameter greater than or equal to 0.5 microns, corresponding to ISO 9 clean room standards, the lowest standard for a clean room.
Overview of Cleanrooms
Cleanrooms are used in most industries in which small dust particles can have a negative effect on the production process. They vary in size and complexity, and are used extensively in industries such as semiconductor manufacturing, pharmaceuticals, biotechnology, medical devices and life sciences, as well as demanding manufacturing processes such as aerospace, optical equipment, military and energy.
A cleanroom is any given space that includes elements provided to reduce contamination by dust particles and control other environmental parameters such as temperature, humidity and pressure. The key component of the clean room is the "High Efficiency Air Particulate Filter" (HEPA) used to filter dust particles with a size of 0.3 microns or larger. All air supplied to cleanrooms must pass through HEPA filters, and in many cases where strict cleanliness is required, "Ultra Fine Particulate Air Particulates" (ULPA) are used.
Employees selected to work in cleanrooms undergo rigorous training in pollution control. They enter and exit the cleanroom through airlocks, airshowers and/or changing rooms, and they must wear special clothing designed to trap contaminants naturally produced by the human skin and body.
Depending on the cleanliness level or function of the clean room, the employee's clothing may be just a lab coat and head covering or it will be a multi-layered full-body outfit equipped with a breathing mask for clean rooms with strict requirements.
Clean room clothing is used to prevent components from falling from the human body and polluting the environment. The cleanroom garment itself must not emit dust particles or fibers to prevent contamination of the cleanroom air. This form of human-caused pollution can degrade manufacturing processes, for example in the manufacture of semiconductors or pharmaceuticals, and it can cause cross-contamination between healthcare workers and patients.
Cleanroom attire includes boots, shoes, apron, beard cover, head cover, coveralls, mask, gown, gloves, hair cover, hood, sleeves and shoe covers. The type of cleanroom clothing used will reflect the standard level of the cleanroom and product. Low-level cleanrooms will likely only require special shoes with soft soles that do not create dust or dirt. However, the shoe sole must not be slippery because safety is always a priority. Cleanroom attire is often required every time entering a cleanroom. Class 10,000 cleanrooms may require only jackets, hoods, and boots. For Class 10 cleanrooms, a thorough changeover procedure with a full-body zip-up suit, boots, gloves, and respirator will be required.
Principles of clean room air circulation
Cleanrooms maintain a particulate-free atmosphere through the use of HEPA or ULPA filtration using the principle of laminar or turbulent air flow. A laminar flow system, or unidirectional flow, will blow air directly through the filter from top to bottom continuously. Laminar flow air systems are typically blown across 100% of the ceiling to ensure a steady unidirectional flow is maintained. The laminar flow principle is often applied to mobile work stations (LF hoods), and is applied to clean rooms with ISO-1 to ISO-4 standards.
A properly designed clean room encompasses the air distribution system, including an adequate supply of return air at the end of the air flow. In a room with vertical air flow, a wall-mounted return vent surrounds the entire perimeter of the room. In rooms with horizontal airflow, the system will request air return at the corresponding end. The use of ceiling return air vents is not appropriate in clean room design.
Clean room level
Clean rooms are classified according to room cleanliness. In US Federal Standard 209 (A to D), the number of particles greater than or equal to 0.5µm is measured per cubic foot of air (ft3), and this number is used to classify cleanrooms. This measure also applies to the most recent version 209E of the Federal standard. Federal Standard 209E applies domestically in the United States. The newer standard used is "TC 209" quoted from the "International Standards Organization". Both standards classify clean rooms by the number of particles measured in the laboratory air. Clean room standards FS 209E and ISO 14644-1 both require the measurement and calculation of particle counts to assess the cleanliness of a clean room or clean space. In the UK, the BS standard requires 5295 is used to classify clean rooms. This standard has almost been replaced by BS EN ISO 14644-1.
.Clean rooms are classified based on the number and size of particles allowed in a unit of air volume. Large parameters such as "class 100" or "class 1000" in FED 209E standard refer to the number of particles larger than or equal to 0.5 µm in one ft3 of air. This standard can also be interpolated, so it is also possible if we say a clean room is "class 2000".
Small parameters according to ISO 14644-1 standard, calculated according to the logarithmic function to base 10 of the number of particles larger than or equal to 0.1 µm in one m3 of air. For example, according to ISO 5 standard, the number of particles greater than or equal to 0.1 µm will be 105 = 100000 particles/m3.
Both FS 209E and ISO 14644-1 assume a log-log relationship between particle size and particle density. For that reason, there is no such thing as zero particle concentration. The air in a typical room is equivalent to class 1000000 or ISO 9.
Source: https://www.cleanairtechnology.com/cleanroom-classifications-class.php
Abridged translation: Khanh An
