by Ron Kosmalski, sales manager, Clean Air Technology, Inc.
From electronics to medical applications to automotive interiors, avoiding the surface mars or product contamination that can happen in everyday manufacturing environments is the job of a cleanroom.
Cleanrooms are used in practically every industry where small particles can adversely affect the manufacturing process. These spaces vary in size and complexity, dependent upon the end user requirements. From industries such as medical device and life sciences to automotive, aerospace and defense, high quality standards and the need to reduce or eliminate potential contaminants are driving an increased use of cleanrooms in the plastics decorating and assembly segments.
Whether the soft-touch interior of a Jeep Grand Cherokee, a glossy black cellphone case or a welded microfluidic device, cleanrooms can be the difference between acceptable product and rejected scrap.
What is a cleanroom?
Understanding the role of a cleanroom requires an understanding of the particulates that exist in an everyday manufacturing facility. The ambient air outside in a typical city environment contains 35,000,000 particles per cubic meter in sizes of 0.5 micron and larger in diameter. These particles could be dust, airborne microbes, aerosol particles and chemical vapors. This level of particulate corresponds to an ISO 9 cleanroom, which is at the lowest level of recognized cleanroom standards. An ISO 1 cleanroom can reduce particles of that size to zero.
A cleanroom is a designated space where levels of contamination are reduced, while other environmental parameters – such as temperature, humidity and pressure – are controlled. The key component is the High Efficiency Particulate Air (HEPA) filter that is used to trap particles that are 0.3 micron 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.
Because human beings are a significant source of contaminants – think of skin, hair, clothing fibers – robotics often are used for decorating and assembly functions within a cleanroom environment. When human intervention is needed, manufacturing personnel who are 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 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 wearers body and contaminating the environment. The cleanroom clothing itself must not release particles or fibers to prevent contamination of the environment by personnel. Cleanroom 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 cleanroom garments used should reflect the cleanroom and product specifications. Low-level cleanrooms may require only 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 usually is 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 coverall, boots, gloves and complete respirator enclosure are required.
Cleanroom classifications
Cleanrooms are classified by how clean the air is within the contained space. In the US, Federal Standard 209 was developed and eventually progressed from 209A thru 209E. Classifications defined the number of particles measured in a cubic foot of air, and various sizes ranging from 0.1 micron through 10 micron were listed. Particles of 0.5 micron and larger were the standard in qualifying classifications. The metric nomenclature also is accepted in the most recent 209E version. Concurrently, European and British Standards were established, and most recently, the global contamination control community adopted the classifications of the International Standards Organization, with classifications ranging from ISO-9 up to ISO-1. The cleanroom classification standards FS 209E and/or ISO 14644-1 require specific particle count measurements and calculations to classify the cleanliness level of a cleanroom or clean area.
Cleanrooms are classified according to the number and size of particles permitted per volume of air. Large numbers like “class 100,000” or “class 10,000” refer to FED_STD-209E, and denote the number of particles of size 0.5µm or larger permitted per cubic foot of air. The standard also allows interpolation, so it is possible to describe e.g. “class 2000.” See Table 1.
Single-digit classifications 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 3,520 particles 0.5µm per m³. See Table 2. 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. As mentioned previously, ordinary room air is approximately class 1,000,000 or ISO 9.
Factors to consider in cleanroom design
The US Food and Drug Administration (US FDA) has defined cleanroom requirements in its standards for drug products, quoted here from the FDAs Guidance for Industry for Sterile Drug Products Produced by Aseptic Processing – Current Good Manufacturing Practice (http://www.fda.gov/downloads/Drugs/…/Guidances/ucm070342.pdf).
21 CFR 211.42(c) states, in part, that “Operations shall be performed within specifically defined areas of adequate size. There shall be separate or defined areas or such other control systems for the firm’s operations as are necessary to prevent contamination or mix-ups during the course of the following procedures: * * * (10) Aseptic processing, which includes as appropriate:
(i) Floors, walls and ceilings of smooth, hard surfaces that are easily cleanable;
(ii) Temperature and humidity controls;
(iii) An air supply filtered through high-efficiency
particulate air filters under positive pressure, regardless of whether flow is laminar or nonlaminar;
(iv) A system for monitoring environmental conditions;
(v) A system for cleaning and disinfecting the room and equipment to produce aseptic conditions;
(vi) A system for maintaining any equipment used to control the aseptic conditions.
In addition to defining the components of a cleanroom, there are a multitude of questions to consider when adding a cleanroom for decorating and assembly purposes, ultimately leading to an understanding of which standard must be met for the particular application that will be performed within the space. Questions could include the following:
- How much heat will be generated by the equipment operating within the space, and how is the equipment cooled?
- How many people will be working within the cleanroom?
- What are the normal temperature and humidity levels of the area in which the cleanroom will be contained? What temperature and humidity levels are required for the project?
- If hazardous or flammable materials will be utilized in any processes, what exhaust volume will be required?
- Do special requirements exist for lighting or room material construction?
- What types of data/communication or environmental controls need to be added to the space?
Cleanrooms facilitate high-quality plastic decorating and assembly operations by removing contaminants that could mar the surface, hinder the adhesion or destroy the required “aseptic appearance” of the final manufactured product.
Ron Kosmalski is sales manager for Clean Air Technology, Inc. Clean Air Technology, Inc. is a top design and build manufacturer and contractor for modular and portable cleanrooms. The company manufactures load-bearing wall and deck systems and application specific air handlers and filtration systems that are ideally suited for all controlled environments: cleanrooms, dryrooms and clean manufacturing facilities. Its fabrication capability allows for delivering site specific air cleanliness solutions. For more information, call 734.459.6320 or email [email protected].
