A clean room is an environment where air born particulates are controlled through an exchange of highly filtered air, and through minimization of activities that generate particles. A clean room is an enclosed space in which airborne particulates, contaminants, and pollutants are kept within strict limits, ordinarily utilized as a part of assembling, including of pharmaceutical items or logical research, and in addition aviation semiconductor building applications. In industry, clean rooms are used in the manufacture and servicing of hardware such as integrated circuits (IC s) and hard drive s. In biotechnology and medicine, clean rooms are used when it is necessary to ensure an environment free of bacteria, viruses, or other pathogens. The electronic, high-tech, semiconductor, pharmaceutical, aerospace, medical and many other industries depend on clean room technology. As products such as cell phone circuit boards become smaller, the chance of contamination in manufacturing becomes higher. For pharmaceutical companies, clean, safe and contaminantfree products are imperative to manufacturing and distributing a viable product. In addition, the temperature and humidity may be controlled. Clean room specifications for particulate matter (such as dust) are defined according to the maximum allowable particle diameter, and also according to the maximum allowable number of particles per unit volume (usually cubic meters). For non-particulate contaminants, the maximum allowable density in terms of microbes per cubic meter, or molecule s per cubic meter, is specified. Four fundamental rules apply to clean rooms. First, contaminants must not be introduced into the controlled environment from the outside. Second, the apparatus within the controlled environment must not generate or otherwise give rise to contaminants (for example as a result of friction, chemical reactions, or biological processes). Third, contaminants must not be allowed to accumulate in the controlled environment. Fourth, existing contaminants must be eliminated to the greatest extent possible, and as rapidly as possible.
Managing a Clean Room
Personnel selected to work in clean rooms undergo extensive training in contamination control theory. They enter and exit the clean room through airlocks, air showers and/or gowning rooms, and they must wear special clothing designed to trap contaminants that are naturally generated by 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. Clean room clothing is used to prevent substances from being released off the wearer’s body and contaminating the environment. The clean room 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. Clean room garments include boots, shoes, aprons, beard covers, bouffant caps, coveralls, face masks, frocks/lab coats, gowns, glove and finger cots, hairnets, hoods, sleeves and shoe covers. The type of clean room garments used should reflect the clean room and product specifications. Low-level clean rooms 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 clean room suit is usually required for entering a clean room. Class 10,000 clean rooms may use simple smocks, head covers, and booties. For Class 10 clean rooms, careful gown wearing procedures with a zipped cover all, boots, gloves and complete respirator enclosure are required.
Air Flow Principles
Clean rooms maintain particulate-free air through the use of 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 is generally stated in portable work stations, and is mandated in ISO-1 through ISO-4 classified clean rooms. Proper clean room 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 requires the use of air returns at the downstream boundary of the process. The use of ceiling mounted air returns is contradictory to proper clean room system design.
Clean rooms are designed to maintain positive pressure, preventing “unclean” (contaminated) air from flowing inside and less-clean air from flowing into clean areas. The idea is to ensure that filtered air always flows from cleanest to less-clean spaces. In a multi-chambered clean room, for instance, the cleanest room is kept at the highest pressure. Pressure levels are set so that the cleanest air flows into spaces with less-clean air. Thus, multiple pressure levels may need to be maintained. A differential air pressure of 0.03 to 0.05 inches water gauge is recommended between spaces. In order to minimize disruptions to these cascading pressures when doors are opened, air locks are often specified between rooms of differing ISO cleanliness levels. Automated fan controls simplify pressure balancing by allowing fan speed adjustments at a centralized console panel.
Clean Room Standardization
In the United States, Federal Standard 209E (FED-STD-209E) was used until the end of November 2001 to define the requirements for clean rooms. On November 29, 2001, these standards were superseded by the publication of ISO specification 14644-1. Typically, used in manufacturing or scientific research, a clean room 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 clean room 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 micron and larger in diameter, corresponding to an ISO 9 clean room which is at the lowest level of clean room standards. Clean rooms 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 clean room. 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 clean room by the number of particles found in the laboratory’s air. The clean room 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_STD209E 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 metre 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. The table illustrates the percentage of ceiling coverage recommended for each cleanliness class, again as a range:
Clean Room Applications
Clean rooms 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 device and life sciences, as well as critical process manufacturing common in aerospace, optics, military and Department of Energy. A clean room is any given contained space where provisions are made to reduce particulate contamination and control other environmental parameters such as temperature, humidity and pressure. Filters are used to trap particles that are 0.3 micron and larger in size. All of the air delivered to a clean room passes through standard filters, and in some cases where stringent cleanliness performance is necessary, Ultra Low Particulate Air (ULPA) filters are used. Clean room systems can be used in a wide variety of applications. Clean room applications range from small laboratories to gigantic clean rooms in the automotive or aerospace industry. The requirement for contamination or environmentally controlled manufacturing is becoming more and more prevalent across a variety of industries and markets: alternative energy, e-cigarettes, ion lithium batteries, solar and more. Some of these emerging clean room applications are to support technology and process advancements in traditionally non-clean process applications. Others are in response to changes in regulatory requirements. And yet others are to support breakthrough disruptive technologies and new markets. The table 1 gives a view for some of the real-world applications of clean rooms.
The figure 1 shows some of the industries which need clean room and the cleanliness class generally applied therein:
Clean Room Guidelines
– Protect the clean room environment against human contamination
– Not to generate contamination
– Protect people against solid or liquid hazardous substances and biological hazards
– Allow heat exchange, and air and moisture vapour permeability for the wearer’s comfort
– Provide consistently high two-way protective performance, by virtue of being limited-use. – People are the most serious source of particle emission in a clean room. Regular clothing can expose products or processes to material particle shedding, residues and foreign particles. Effective particle barrier clothing functions as a personal filter that protects clean rooms from contamination by people.
– At the same time, some clean room work requires the protection of people from hazardous substances, such as liquid or solid chemicals or biological agents. These hazards occur not only in chemical, pharmaceutical and microbiological environments, but even in the production of computer chips or when painting under clean room conditions. Traditional clean room clothing simply does not provide adequate personal protection.
– Both clean room clothing and chemical protective clothing need to meet the same basic criteria for use in a clean room: The material must be lowlinting, the design must be sufficiently tight, and the danger of collecting particles on the surface of the garment must be minimized.