Cleanroom clothing
As cleanroom garments , clothing refers specifically to the circumstances of clean rooms is adapted. There are significantly higher demands on them than on normal work clothing. In addition to protecting people through clothing, the main task of cleanroom clothing is to protect the cleanroom contents from people. Humans pose the greatest risk of microparticles entering a clean room. They continuously secrete the smallest particles and host microorganisms . Without suitable protective measures, these can spread unhindered in the clean room and, in the worst case, lead to cross-contamination of the room contents to be protected. Humans represent 30–40% of all sources of contamination in a clean room. Special clean room clothing is used as a protective measure. It prevents airborne particles emitted by the employee from entering the room.
Properties of cleanroom clothing
Depending on the intended use, different requirements are placed on cleanroom clothing. These concern both the fabric and the workmanship and fit:
Particle retention capacity
Cleanroom clothing is of greatest importance as a filter between the human particle source and the cleanroom. Therefore, the particle retention capacity of the clothing and especially the fabric is important. The retention capacity of an uncoated fabric depends primarily on its porosity . The lower the porosity of the fabric, the better the particle retention capacity. However, this has a direct influence on the clothing physiological properties of the textile : the denser the fabric and thus the higher the particle retention capacity , the lower the wearing comfort (lack of air permeability). If the fabric is too dense, there is also the risk that body movements will cause a “pumping effect” that will allow larger amounts of particles to escape uncontrollably from the clothing openings ( cuffs on the arm and leg and head opening).
Particle migration behavior
Different layers rub against one another between the inside of clothing and the surface of the wearer's body. With this friction , particles and fibers can get through the cleanroom textile mechanically. This occurs more intensely, especially in dressing and undressing processes. The cleanroom fabric is designed in such a way that it stores these released particles and does not let them get into the environment. Therefore, contrary to the widespread assumption that it would be of secondary importance, cleanroom underwear is of decisive importance.
Abrasion resistance
The abrasion resistance of the fabric indicates its secretion of its own particles and fibers. If the strength of the cleanroom textile is too low, the environment will be exposed to abrasion after just a few wear cycles. Fabrics made from purely synthetic fibers (e.g. polyester ) meet these requirements significantly better than blended fabrics with a cotton content . For cleanroom clothing with lower requirements (e.g. ISO classes 8/9), polyester fabric is also used, in which textured yarns are used for reasons of comfort .
Electrostatic behavior
Due to the materials used, classic cleanroom fabrics tend to become electrically charged. During normal movements, the friction between tissue and tissue can lead to high electrostatic charges. In addition to the negative effects on many products, the carrier, acting as a magnet, attracts particles that can then reach the product to be protected, for example through the laminar flow . That is why many cleanroom textiles are given an antistatic finish . In order to maintain this protection over the entire life cycle of the textile, it is necessary to use special care procedures during decontamination .
Comfort
In addition to product protection, the wearing comfort of the cleanroom clothing is an essential decision criterion. Wearing comfort increases employee acceptance of the clothing; poor comfort can lead to an increased source of errors and reduced employee performance.
Decontaminability
Reusable cleanroom clothing requires effective decontamination after each wearing cycle. During this, the stored particles are washed out of the tissue. Therefore, depending on the particle retention capacity, the highest possible porosity of the textile is advantageous for decontamination. In addition to the fabric, the processing of the textile also has a major influence on the ability to be decontaminated. Items with pockets or puckered seams worsen the options. As a third point, the age of the tissue has an influence on the decontamination process. After a certain number of decontamination cycles, the fabric shows advanced fiber breakage, which also has a negative impact on the use of cleanroom clothing.
Sterilizability
People who work under sterile conditions in the clean room also need sterile clean room clothing. The tissue is usually sterilized by autoclaving or gamma radiation . Processes are not gentle on the material and therefore place special demands on the textiles (e.g. zippers, buttons, etc.).
Cleanroom clothing in disposable and reusable
Cleanroom clothing is offered as a disposable and reusable system. While disposable clothing tends to be widespread in many areas in Japan and the USA, reusable clothing is used much more frequently in cleanrooms in Europe. In the case of disposable clothing, the clothing is packaged with low particle content immediately after production and made available to the wearer ready for use. After the clothing has been worn once, it is disposed of and new clothing is used the next time you enter the clean room. Reusable clothing is more elaborate in terms of material and cut and is used several times. Depending on the intended use and contamination, reusable clothing can be reused up to 150 times. After the clothing has been used in the clean room, it is washed in a special decontamination process and freed from deposited particles. Then the clothing is packed ready for use and used again.
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Critical voices regarding the use of disposable clothing have increased in recent years. In addition to lower wearing comfort and a decrease in the wearer's ability to concentrate, the risk of particle entry through production conditions with a strong particle influence was also reported.
Decontamination and repair of textile cleanroom clothing
Decontamination of cleanroom clothing
Particles are deposited in the fabric of the cleanroom textile during use or storage outside the cleanroom atmosphere. This is favored by the porous structure of the textile. In order to empty this particle reservoir and to be able to use the cleanroom clothing again, the clothing item must be decontaminated.
As part of a professional decontamination process, the clothing is freed from particles in a washing process. The main difference to normal washing is that the focus here is on loosening and rinsing out the particles. Therefore, the water and the loading level are of increased importance. The decontamination of the cleanroom clothing must itself be carried out in a cleanroom.
After the particles have been rinsed out, the textile is then dried. Special dryers are used here. The air is supplied through a HEPA filter (high-performance particulate filter ), which filters out possible impurities in the added air.
Repair of cleanroom clothing
Like any form of clothing, cleanroom clothing also shows signs of wear and tear with continued use. Because of the cost of cleanroom garments, repairing it is often more economical than replacing it, taking into account the overall condition of the garment. Since particles and fibers are released during the repair process, a repair always requires another decontamination before the clothing is used again.
packaging
After the cleanroom clothing has been decontaminated, it is packed in special airtight film so that the textiles are not contaminated again during transport and when they are stored outside the cleanroom.
Cleanroom clothing for use in sterile areas is first packaged particle-free in sterilizable bags. These are sterilized in a further process step, for example by means of autoclaving .
Particle monitoring
Particle monitoring is an essential quality criterion for monitoring the successful decontamination of cleanroom clothing. The residual contamination of the decontaminated clothing is measured using defined measuring methods. For this purpose, a sample is drawn from the population depending on the requirements, which is then measured. The measurement result of this random sample provides information about the decontamination process and the success of the decontamination. Based on operational practicability and reliability, two measurement methods have established themselves in practice in Germany. These are used in parallel or as a substitute, depending on the requirements and the textile:
Helmke drum test
In the Helmke drum test, the item of clothing to be tested is placed in a drum, the loading side of which is partially open. As the drum rotates, the cleanroom textile to be tested is whirled around and during this movement releases possible particles that are still in the textile. The level of the particle density is determined and documented by means of an automated particle counter integrated in the drum. The test method is described in IEST-RP-CC003.3.
ASTM-F51.00 rapid measurement method
The ASTM-F51.00 measuring method is also often referred to as the suction meter method in practice. The item of clothing to be tested is clamped one after the other at 5 defined points in a device and air is sucked through the clamped textile areas. The air flowing through is then evaluated using a particle counter.
Individual evidence
- ↑ Absolutely particle-free cleanroom clothing reduces production rejects . Product protection in perfection - EPP . In: EPP . February 22, 2013 ( epp-online.de [accessed February 25, 2018]). Absolutely particle-free cleanroom clothing reduces production waste. Product protection in perfection - EPP ( Memento of the original from March 6, 2016 in the Internet Archive ) Info: The archive link was automatically inserted and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
- ↑ a b Influence of clothing
- ^ A b Lothar Gail, Udo Gommel, Hans-Peter Hortig: Clean room technology . 3. Edition. Springer , 2012, ISBN 978-3-642-19434-4 .
- ↑ disposable vs. Reusable cleanroom clothing
