Floors and flooring systems must be able to withstand the roughest treatment of any structural component in a cleanroom. Kathrin Kutter, Market Segment Manager Industry, nora systems, Germany, looks at criteria for their selection.
Contamination control is critical to ensure product quality is maintained and research work is a success in controlled environments. But the diversity of cleanroom use requires a careful selection of production equipment and materials. Materials with the lowest possible potential for contamination should be chosen at the early stages of the cleanroom planning procedure and this is particularly important for the selection of floorings.
When choosing floorings, it is necessary to take account of the whole production process during cleanroom planning procedures and to define the specific requirements of floorings to meet the needs of these individual processes.1
The internationally accredited regulations ISO 14644 and GMP guidelines offer initial indications for the selection of cleanroom-suitable materials. To comply with ISO 14644-4, for instance, surfaces such as floorings should have low particle emission behaviour and a non-porous surface. They need to be anti-slip and able to withstand dynamic loads. Floors also need to be resistant to any process media, cleaning agents and disinfectants. In addition, they need to offer appropriate ESD protection properties.2
The GMP guidelines add to this specification the requirement for a smooth, dense surface without cracks or open joints, and easy but effective cleaning and disinfection properties.3
The requirements of floorings or surfaces as stipulated in the ISO or GMP guidelines can be regarded only as a first approach to selecting the most suitable material. The differentiation between cleanroom and cleanliness suitability of materials as stipulated in the soon-to-be-published VDI 2083-17 (draft) offers additional approaches.
Generally, each industry sector places focus on a different type of contamination. This approach is not sufficient, however, in the pharmaceutical industry where more criteria need to be considered. Here, the suitability of materials must take into account the complete production process including all its peculiarities. Besides airborne particle contamination, regard must also be given to airborne molecular contamination (acids, bases, dopands, condensables and other VOCs), cleanability, resistance to chemicals and microbial metabolic potential of cleanroom materials, to name a few.4
No matter which option is eventually chosen, the wall-to-floor connection must be smooth and crevice-free to allow proper and easy cleaning, for example, through the use of modelled coving. Joints are to be avoided as they present a hygiene risk. The choice of flooring systems that meet these requirements may vary considerably.
Coating-free surfaces
An important selection criterion is the quality of the flooring’s surface. Additional surface coatings or sealers must be reviewed critically as they often present a weakness. These surfaces tend to separate from the base under the influence of tribologic strains caused, for instance, by rolling transport containers or walking personnel, thus causing airborne particle contamination.
Contamination control is critical to ensure product quality is maintained and research work is a success in controlled environments
Partially loosened or damaged coatings can also present ideal places for biological growth, which cannot then be disinfected or cleaned properly. Nora rubber floorings, for example, do not need any kind of coating. Thanks to a state-of-the-art production process, these floorings offer an extremely dense and non-porous surface that is particularly resistant to abrasion. They are also easy to clean and disinfect, providing durability and a high level of hygiene.
Another risk can arise from even the smallest cracks in the flooring’s surface, which can be caused by movements and cracks within the subfloor. Unlike inflexible, hard floor coatings, permanently resilient rubber floorings can compensate for these cracks to a certain extent.
ESD protection
Depending on products and processes, significance might be assigned to ESD protection. Floor coatings with components such as conductive additives that are blended on site rely considerably on the floor installer’s professional quality. The permanently reliable functionality of conductive or dissipative floor coatings can be achieved only if the conductive additives are distributed evenly during the application process.
Other floorings rely on conductive additives that are bound physically or chemically into the flooring material during its production in the flooring factory. These additives are usually more evenly distributed within the flooring and permanently effective.
Regardless of which system is chosen, any final surface coatings or sealers are best to be avoided as they may have a negative influence on the flooring’s conductive functionality.
The flooring’s ergonomic features are not to be neglected. Cleanroom personnel carry out a lot of work while standing or walking. Unlike hard floors, permanently resilient rubber floorings relieve joints and spine stress and contribute to ergonomic workplaces and a higher working comfort, which in turn has a positive effect on concentration and efficiency.
| Table 1: Relative importance of different criteria for various sectors | |||||
| Airborne particle contamination | Emission of molecular contamination | Electrostatic properties | Cleanability | Chemical resistance | |
| Pharmaceuticals | ++ | 0 | + | ++ | ++ |
| Biotechnology | + | + | 0 | ++ | ++ |
| Medical devices | + | 0 | + | ++ | ++ |
| Food industry | + | + | 0 | ++ | ++ |
| Photovoltaic | + | + | + | 0 | 0 |
| Semiconductor | ++ | ++ | ++ | + | + |
| Microsystem technologies | ++ | + | ++ | + | + |
| Legend: ++ = stringently required + = recommended 0 = not generally required, case by case review recommended. (Source: VDI 2083 – 17 (draft), 2012) | |||||
Unified testing methods
The material properties mentioned so far are all criteria that need to be evaluated. Material selection also needs to take into account: installation on floor screed, raised or hollow floors, resistance to static and dynamic loads or repair options, and this increases the complexity of the selection process.
Until recently, it was possible to compare floorings and flooring systems only with regard to their general suitability for industrial applications with the help of the manufacturer’s technical data. Unified testing methods to determine the cleanroom or cleanliness suitability did not exist.
Together with representatives from industry such as nora systems, the Fraunhofer Institute for Manufacturing Engineering and Automation IPA has achieved ground-breaking development work. Within the framework of the industrial alliance CSM, testing methods and validation schemes have been developed not only to verify the cleanroom and cleanliness suitability of materials, but also to allow their comparison. Among these testing methods is the determination of particle emission behaviour to assign a material to the air cleanliness class in accordance with ISO
14644-1. In addition, molecular emissions (VOC) or outgassing, respectively, and the resistance to microbial metabolic potential and chemicals are determined as part of the cleanliness suitability verification.
Surfaces such as floorings or flooring systems are now being tested under unified testing methods, and their results are being documented in a consistent fashion. This simplifies the comparison of floorings considerably – an important consideration since subsequent flooring corrections are both time-consuming and expensive.
References
1. Dr. Ing. Dipl.-Phys. Udo Gommel, Dipl.-Ing. (FH) Frank Bürger: VDI Society for Building and Building Services Engineering: Cleanroom Technology: 14th VDI Conference, Nürtingen, Germany, on 26 and 27 October 2011, Düsseldorf: VDI press, 2011 (VDI report 2125)
2. DIN EN ISO 14644-4:2003-06
3. EG GMP Guidelines (Guidelines for Good Manufacturing Practice) Part 1: 2006
4. Reinraumtechnik (VDI book), Lothar Gail, Udo Gommel and Hans-Peter Hortig, Springer Berlin Heidelberg, Germany, 2012
