By Bruce Flickinger
End users need to juggle product and worker protection, comfort, utility, and cost-effectiveness in making the right choices about specialist laundries and cleanroom garmenting programs.
Any tailor will tell you that the signs of quality clothing can be found in the details, and the same can be said of cleanroom garments. In this analogy, companies such as Nitritex Ltd. (Newmarket, UK) are the high-tech haberdasheries, manufacturing cleanroom garments and apparel items to very high technical standards for customers operating a variety of demanding research and manufacturing environments.
“The construction of the garment is extremely important to ensure its effectiveness when worn in the cleanroom,” says Richard Bryant, Nitritex group sales director. “The fabric needs to be chosen carefully and be thoroughly technically specified to ensure it does not cause contamination in the finished garment. Each component–studs, thread, fabric, zippers–should be non-linting and made of non-plated stainless steel. Seams should be enclosed using continuous polyester thread at no less than 12 stitches per inch.” Garment edges usually are serged; that is, chain-stitched using two or more threads that form an overcast edge on a fabric.
Despite many advances in construction and fabric technology, the primary objective for cleanroom garment systems remains unchanged: to capture and entrain particles to prevent them from being dispersed externally and making contact with equipment or product. These contaminants largely are generated by the human body, including bacteria and yeasts, hair, dead skin cells, dandruff, and even elements such as sodium, potassium, chloride, and magnesium. It bears repeating here that people are the most significant source of contamination in cleanrooms and ancillary facilities.
But people also need to be protected, and a second but equally important function of cleanroom apparel is protecting workers from hazardous materials.
Risk assessments are used to ascertain the types and degree of worker protection required in a particular environment. Chemical splash protection is often needed, and difficult-to-control chemical flow or vapor eruption might warrant additional protection in some environments. Additionally, fire resistance is a concern for some applications, and awareness is heightened about OSHA/NFPA 70E requirements for protecting workers against potential arc flash events.
“The correct garment type is determined by the applicable technical standard, the type of cleanroom being operated, and the kind of work being carried out,” Bryant says. “We often provide on-site surveys to establish the correct garment type, along with training to assist wearers with the correct donning procedures to ensure that they adhere strictly to GMPs [Good Manufacturing Practices].”
Fabric options and tradeoffs
Garment considerations vary somewhat between industrial and life science cleanrooms. The former generally do not have a defined standard to work toward when choosing garments and must make the selection based upon the grade of cleanroom required or level of air cleanliness as defined by international standard. The life science or biopharmaceutical cleanroom, however, will have a more rigidly defined requirement for cleanroom clothing and its use as stipulated by GMP.
“Garments used in controlled environments share many common characteristics, such as compatibility with industrial laundering processes and low-particulation fabrics,” says Greg Winn, general manager, Controlled Environments Division, at White Knight Engineered Products (Charlotte, NC). “Carbon-grid fabrics are more commonly used in microelectronics applications because these customers will go to great lengths to control static buildup and/or discharge events. Pharma/life science customers must often maintain aseptic manufacturing conditions, so garments and materials undergo additional gamma sterilization or autoclaving procedures, which can significantly reduce material lifetime.”
Across all applications, key garment performance properties include air permeability, particle barrier efficiency, antistatic behavior, and moisture vapor transmission rate (MVTR). These speak broadly to a garment’s ability to both contain particles and keep the wearer comfortable. While all cleanroom garments need to meet technical specifications with regard to these properties, performance levels will vary and users need to assess carefully what criteria need to be emphasized while potentially compromising others.
An example is giving proper attention to worker comfort and mobility, which not only allows workers to carry out their duties throughout the day but also encourages compliance to the garment program. Cleanroom garments must permit the body to breathe, but the fabric’s breathability walks a fine line between comfort and contamination prevention: The body’s normal cooling process must be accommodated, but the airflow generated contains contaminants that can be transferred to the process or product. Lower MVTR and air permeability measurements mean lower potential for contamination but also reduced comfort for the wearer.
The fabrics used in making cleanroom apparel are largely polyester-based or 100 percent polyester weaves. Carbon matrices are used in some fabrics, and nylon and non-woven polyethylene materials are used in some special-purpose garment systems. The polyester weaves used in cleanroom garments are both hydrophobic and oligophilic and are constructed of very fine, tightly woven fibers. This creates small pore sizes for entraining skin flakes and other particles.
Sterilization, particularly gamma processing, will break down any fabric fiber to some extent. Polyester fabrics also are easily abraded by rough surfaces and are sensitive to extreme levels of acid or alkali and temperatures above 160