By Robert McIlvaine and Betty Tessien, The McIlvaine Company
In the December issue of CleanRooms, this column focused on the use of disposable garments. This month, the alternative-garments that are periodically laundered and reused-is explored. Reusable cleanroom garments have the potential for comfort and durability, and may reduce the cost per use while reducing waste. Reusable products can provide high-performance protection; however, cleanroom garments will deteriorate over time due to wear and the processing cycles of washing, drying and sterilization.
All garment systems must be worn correctly to be effective. There are many designs, providers and reprocessors available to meet the needs of varied cleanroom applications. One of the pharmaceutical industry’s main concerns in a cleanroom garment is sterility to decrease the bioburden in the cleanroom. Semiconductor manufacturers, on the other hand, are not concerned with sterility, but rather with particulate control. Because of these differences in requirements, the two industries have different preferences and needs with respect to cleanroom reusable garments.
Curt White of Aegis Environments (Midland, Mich.; www.microbeshield.com) notes, “Cleanroom reusable garments have evolved into unique and innovative systems utilizing design, fabric compositions, composites and finishes to meet the increasing demands for protection and comfort required by the ever-expanding end uses of cleanroom garments. These added functional needs are an outgrowth of a market trend that [regards] the cleanroom garment as an active component of a larger cleanroom environmental-control program.”
White continues, “Cleanroom garments have gone far beyond the historical function of preventing particle exposure, reaching into style and function. Comfort and increasing demand for more and more functional properties are higher on the needs list than in the past. Cleanroom garments must not release particles or fibers into the environment, yet must provide for the comfort of the wearer. They must also provide for the productivity and quality at the specific work site, for work processes, and for the products being produced. This challenge is being laid out as geometries for cleanroom processes decrease, nanoparticles become more common, and the manufacturing of personal electronics continues to explode. Concern over pandemics and foodborne illnesses is increasing the use of cleanroom garment systems for the protection of workers as well as for contamination control of products and environments.”
Reusable garments capture and entrain particles to prevent them from escaping into the cleanroom environment. Cleanroom personnel can contribute about 25 percent of the airborne particulate contamination in the cleanroom, according to Robin Howie of Robin Howie Associates (Edinburgh, Scotland). Of the millions of particle shed by the cleanroom worker, viable particles include bacteria, molds and yeast, and nonviable particles can include hair, dead skin cells and dandruff. Elements such as sodium, potassium, chloride and magnesium may also come from the human body. Loose fabric particles from clothing can also contribute to contamination. The higher the class of cleanroom, the greater the need for contamination control, ultimately leading to a full-body contamination-control suit.
Sterile environments require garments with fabrics that can withstand multiple processing and sterilization cycles. According to Jan Eudy of Cintas Cleanroom Resources (Mason, Ohio; www.cintascleanroom.com), “Cleanroom garments may be sterilized by electron beam (E-beam) sterilization, ethylene oxide (ETO) sterilization, gamma sterilization, or steam sterilization (autoclaving). Currently, gamma sterilization is the most cost-effective method of sterilization for cleanroom materials. However, for reusable cleanroom garments utilizing polytetrafluorethylene (PTFE) membranes, gamma sterilization and ETO sterilization are not an option because they degrade the polymer. Cleanroom apparel used in the U.K. and Europe may be steam-sterilized. Steam sterilization of cleanroom apparel can cause shrinkage and wrinkling of the reusable garment system. Additionally, there are cleanroom-compatible components that are not compatible with steam sterilization. Sterility validation of steam sterilization is performed per ANSI/AAMI/ISO 11134: 1993 for industrial facilities or ISO 13683:1997 for healthcare facilities. With gamma sterilization, the cleanroom garment launderer validates the gamma dose and provides documented evidence of the sterility assurance level (SAL). Audits of the contract sterilizer are also performed. All cleanroom materials used in sterile cleanroom manufacturing must undergo a quarterly dose-audit test and be validated for sterility assurance levels. Cintas, for example, has validated its sterile reusable garments to 10-6 SAL.”
In sterile environments, Richard Bryant of Nitritex (Suffolk, U.K.; www.nitritex.com) states that it’s recommended that cleanroom undergarments be used as an alternative to street clothes. These should be manufactured using nonlinting polyester barrier fabrics. The use of nonlinting polyester undergarments with a good coverall containment system will lower the number of particles carried into the cleanroom environment. Because particles are the main mode of transportation for microbes, a containment system should also lower the number of microbes carried into the controlled environment. The most comfortable choice will be a fabric with excellent wicking properties to allow rapid dispersion of perspiration.
John Smith of Precision Fabrics Group (Greensboro, N.C.; www.precisionfabrics.com) explains that, for pharmaceutical applications, “It has been shown that the number of bacterial colony-forming units is reduced using an antimicrobial. By doing so, the bioburden is reduced going into the laundering and sterilization steps. Even in less critical clean environments, the use of a nonmigrating antimicrobial can inhibit the growth of mildew and mold that can create odor over time. It is very important that the antimicrobial used not allow the mutation of bacteria to occur. The last thing we need is to inadvertently create a worse problem.”
The electronics and semiconductor industries do not focus on sterility, but rather on particulate and static control. Some processes require the garments to be static dissipative, containing electrostatic discharge properties (ESD).
Michele McSwain of TW CLEAN (Carlsbad, Calif.; www.twclean.com) remarks, “As electronic components continue to decrease in size, and as airborne, charged particles become a higher concern in cleanroom control, the attention to generation and management of electrostatics is increasing.”
The Electrostatic Discharge Association (www.esda.org), a primary training and investigation body in the development of standards and test methods for the industry on the subject of electrostatics, has recently published a technology road map, free for download on the Web site, highlighting the expected intolerance to static electricity based on input from major U.S. corporations. With the road map in mind, the ESDA has developed S20.201, a standard covering the essentials for developing a static-control program. Garments are a part of the total control program and are tested to STM2.1-1997 “for the Protection of Electrostatic-Discharge-Susceptible Items” (which is currently being updated).
Cleanroom garments made of clean, non-sloughing but insulative polyester fabric generate static charges whenever a wearer moves. The addition of carbon threads to the fabric provides a path for charges to migrate. A continuous path to ground at the garment level ensures that these free-floating charges are directed immediately to the ground and guarantees their elimination.
ESD garments should have a low propensity for triboelectric charging and a low resistance to fast dissipation in order to avoid charge accumulation. Microelectronic components can be damaged by static discharge. Also, microorganisms are known to develop on particles adhering to garments that have a static charge. This is unacceptable in pharmaceutical environments. It is therefore essential that the fabric utilized allow the garment to continually dissipate any static buildup.
Cleanroom garments are typically made from synthetic materials, which include nylon, polyester, polytetrafluoroethylene, polyvinylchloride and butyl or nitrile rubbers. These materials are electrically-insulating materials known as dielectrics, which can become electrostatically charged by friction.
Static dissipative fabrics typically incorporate a conductive carbon filament, which is less than 1 percent by weight of the finished material. The high-quality carbon fiber must be used and remain effective throughout the life of the garment and the washing cycles to ensure that the static dissipative qualities remain effective. The carbon fiber is woven into the fabric in either a grid or stripe format, providing a path for charges to migrate.
According to Jan Eudy, “ESD testing of cleanroom garments is based on application standards and is not cleanroom-specific. The Institute of Environmental Sciences and Technology (IEST) has a committee working to create ESD cleanroom-specific garment testing standards. Current tests include Static Decay FTM 4046, Surface Resistivity ASTM-D-257, NFPA 99-Static Decay Test (formerly NFPA 56A) and Surface Resistance of 50% RH ESD 2.1.”
Static dissipation will become increasingly important as nanoparticles, nanotechnology and further miniaturization become more common.
Fabric must be tested for weight, pore size, moisture-vapor transmission rate, tensile strength and surface resistivity. The construction of the garment is evaluated for entraining particles and durability. Validation of a reusable garment system will require an audit of the cleanroom laundry-service provider.
In 2003, the IEST published the recommended practices for garments, IEST-RP-CC003.3, Garment Considerations for Cleanrooms and Other Controlled Environments. This 48-page document, replacing the globally accepted CC003.2 version, studies fabric, cleaning, maintenance and garment configuration, selection and specification for various cleanroom applications in aseptic and nonaseptic cleanrooms and other controlled environments. The new version has an expanded section on fabrics, material properties and testing, and the design and construction of the apparel. Processing considerations for the user and processor are outlined. Particle penetration testing guidelines including pore diameter testing of fabrics using a body box, and Helmke Drum testing and microbial penetration testing are included. Classification tables describe cleanliness categories in particle size ranges of 0.3 to 0.5 micron.
Testing a garment for particulate follows industry standards and procedures set up by ISO, American Association of Textile Colorists and Chemists (AATCC), the Association for the Advancement of Medical Instrumentation (AAMI), and other organizations. ASTM F51-68 (American Society for Testing and Materials) is a standard method for sizing and counting particulate contamination in the size range of 5 microns or larger in and on cleanroom garments. This test is simple but time-consuming and less reproducible. A section of the garment is placed over gauze screen, one square foot in area, and is vacuumed using a filter paper holder. This testing method does not work for membrane garments, however. The Helmke Drum places garments in a rotating drum with an automatic particle counter that determines the particle density level. The Helmke Tumble test evaluates particles at 0.3 micron and larger. More recently, the Gelbo-flex test is used. Many labs provide these types of testing, as do many of the national laundry services. Third-party quality validation will involve ISO 9001:2000, ISO 13485 for medical device manufacturers and EC Certification for products sold in the European Union.
At the Royal Institute of Technology (KTH) in Sweden, a modified dispersal chamber has been used to study the protective efficacy of cleanroom clothing.2 No significant performance difference was seen between disposable clothing and the two sets of reusable clothing that were washed and sterilized once. The use of special cleanroom undergarments enhanced the filtration efficacy of both particles and colony-forming units. However, the number of colony-forming units generated did increase as the number of washing and sterilization cycles increased.
Many factors contribute to a cleanroom worker’s perception of comfort. Is the garment too hot or too cool? Is it too tight-fitting or, as was described in one survey, too loose, causing the workers to trip and fall.
The stiffness of the garment or-to use the industry term, the “hand” or general feel of the garment-is an important factor. Moisture vapor transmission rate (MVTR), the rate at which moisture is transmitted through the garment, is often used as a measure of comfort. MVTR testing models the ability of a garment to move perspiration away from the wearer and cool the body. MVTR is measured in units of grams/meters squared/24 hours. As a practical example, a vinyl raincoat has little moisture-vapor transmission, making the wearer very uncomfortable.
For the greatest user efficiency of reusable cleanroom garments, the correct design, size and fabric must be considered. Protective performance can be limited by penetration through fabrics, seams and fasteners, and by leakage between the garment and the body at seals, especially at the neck or wrists. Penetration through seal gaps can permit unhindered passage of large particles that would be unable to pass through the garment fabric.
Construction and durability
According to Bengt Ljungqvist, professor and head of the department of Civil and Architectural Engineering at KTH, the properties of the fabrics used for cleanroom clothing can be assessed by measuring air permeability, particle retention and pore size. The effectiveness of cleanroom clothing will deteriorate with factors such as aging, wear, washing, drying and sterilizing. Fabric strength and durability can be a factor of garment weight. Tongue Tear and Grab Tensile tests provide measurements of these qualities.
According to Robin Howie, the air permeability of seams and fasteners in many garments is much greater than that of the fabrics. Consequently, although the area of seam and fastener is typically less than 1 percent of the total area of the garment, the total flow of contaminated air through seams and fasteners can be much greater than through the fabric. Seam construction and components are part of the IEST recommended practice.
Seams must be bound using continuous polyester thread. No less than 12 stitches per inch should be used when sewing the garment. The seams should also be enclosed to ensure that no particles escape. Some designs, like GORE-TEX® cleanroom garments, are available with sealed seams that eliminate particle transmission through needle holes. Zippers should be made without coatings, which may break down, creating contamination. The pharmaceutical industry uses stainless-steel zippers, while the semiconductor industry, because of the risk-averse nature of loose metal contaminants, uses plastic zippers. If studs are used in the garment, they should be noncoated stainless steel or plastic. Some garment manufacturers purchase cuffs for the garments as a specialty knitted fabric. Other garments do not have knitted cuffs but rather snap or elastic closures made from the same material as the garment itself. Knitted cuffs may present the potential for breakdown and produce particles during the wash process, states Bill Steacker of Green Mountain Knitting (Milton, Vt.; www.greenmountainknitting.com). The firm currently has little demand for knitted cuffs used for cleanroom garments, though antistatic cuffs still are purchased. Others whom we interviewed commented that they purchase knit cuffs from suppliers with laboratory data indicating there is no breakdown, either mechanically or electrically, after years of use.
- ANSI/ESD S20.20-1999: Protection of Electrical and Electronic Parts, Assemblies and Equipment (Excluding Electrically Initiated Explosive Devices), ESD Association, 1999.
- Ljungqvist, Bengt and Berit Reinmuller. “Aseptic Production, Gowning Systems, and Airborne Contaminants,” Pharmaceutical Technology, May 2005.
Robert McIlvaine is president and founder of the McIlvaine Company, Northfield, Ill. The company first published “Cleanrooms: World Markets” in 1984 and has since continued to publish market and technical information for the cleanroom industry.
Betty Tessien is the cleanroom publications editor for the McIlvaine Company.
Reusable vs. disposable
In December, advantages of disposable garments were cited (see “Your Market Analysis,” CleanRooms, December 2005). Chuck Berndt, C. W. Berndt Associates, has offered a response to this article with comments pointing out the advantages of reusable clothing. For the full text of his response, visit the CleanRooms online discussion forum at www.cleanrooms.com.