Examining a practice-oriented test method with respect to the reproducibility of results
Carsten Moschner, Dastex Reinraumzubehör GmbH
Thomas von Kahlden, CCI-von Kahlden GmbH
It is indisputable that cleanroom garments are still one of the most important components of contamination control in the cleanroom. Apart from textile-related parameters, other factors, including fit of the garments, behavior of the user, clothing components and the undergarments, all affect particle delivery. The technical documentation for cleanroom garments, however, often just contains data referring to the selected textile. Since the test methods for important material properties such as particle retention capacity, water vapor permeability, electrostatic behavior, etc., are not standardized, the end user does not have the ability to compare the technical data of the respective suppliers with each other. Only results that are obtained under the same test conditions and methods are comparable with each other.
Comparability of data
Apart from the problems of comparability shown above, data usually refers only to the technical properties of materials that are not yet processed, i.e., to the fabric of the roll. At best, aging is simulated by cleaning the fabrics several times before the tests (e.g., fifty washing and drying cycles). Solid information as to the product properties after a complete piece of clothing and/or a clothing system has been manufactured from the materials is the exception and obvious effects like “positive pressure” and “thermionics” (under the cleanroom garments) are completely ignored.
Given the above, it is important to focus the mind of the users on the implications of positive pressure and thermioncs for cleanroom garments. Design of an approved, informative test method, and the resulting test expenditure, can prevent easy dissemination of information, but with this in mind we concentrated on an international recommended practice (IES-RP-CC003.2) for a comparative test method-the so-called Body-Box Test. Here, a practice-oriented approach forms the basis of its experimental setup, a short summary of which is shown below:
• A defined cleanroom size with a grill-plate floor contains only the test subject wearing the cleanroom garments to be examined.
• The test subject accomplishes a defined movement program in a given time frame.
• From the exhaust air (extracted from underneath the grill floor) air samples are taken, which are supplied to a particle counter.
Putting the method to the test
The particles delivered by the test subject need to be recorded and this is the “weak point” of the test method given in the recommendation, as the exact position of the particle counter is not defined. With undefined flow conditions in the exhaust air it is very probable that the results of measurement can vary greatly depending on the positionof the particle counter. Reproducibility is highly unlikely and the comparison between different cleanroom garment systems (with same test person and same test run) is therefore severely compromised.
Elimination of this weakness would give this test method the possibility of accomplishing meaningful user-oriented investigations. With given reproducibility, details of the clothing can be compared with each other, as can different cleanroom fabrics, different production methods, etc. Comparisons between disposable clothing and cleanroom garments become more informative and possible consequences of the “pump effect” with fabrics more impermeable to air compared to air-permeable materials may become apparent.