Maintenance strategies for cleanliness critical environments: fast setups, high efficiency, cost-minimised

In the aerospace industry, as in many other sectors, the question arises as to whether my product or process has to fulfil specific requirements, as otherwise quality or performance will be impaired, which in the worst case could even mean the success of the entire task, the failure of the product or the failure of a mission. Behind the many specifications to be fulfilled lies the fundamental question of whether my product/process/procedure/mission is critical to cleanliness. If this question is answered in the affirmative, it must first be clarified which type and level of contamination is to be controlled: particulate, chemical, biological contaminants, temperature/humidity ranges, electrostatic charges, vibrations, etc. To fulfil cleanliness specifications, the procedure is as follows: Firstly, the contamination-critical product (e.g. a product, a process, a sample, a material, medical/biological material or even highly complex flight hardware) is protected by trying to prevent contamination from reaching the cleanliness-critical product in the first place. This can be achieved by using a clean zone (operationally due to the reduction of contamination via containers, consumables, personnel, etc. or psychologically due to the reduction of carry-over to components by personnel), a Technically clean area (with the use of a protective enclosure without ventilation support) or a cleanroom (use of a protective enclosure including ventilation support). The next step is to ensure that no contamination is generated and released by the handling/process/storage technology used by means of suitable material pairings and a cleanliness-compliant equipment design, which could then be transferred to the cleanliness-critical product. For this purpose, databases with information on the cleanroom and cleanliness suitability of materials or even complex production or handling equipment are consulted. This represents the established procedures: Protection of the "cleanliness-critical item using cleanrooms". However, the previous logic is reversed in the case of maintenance of system technology during ongoing cleanroom operation. Here, the cleanroom, which was previously an aid to achieving cleanliness, must now be protected from the contamination of the maintenance process. The reason for this is that contaminants are released during maintenance that cannot be controlled by the classic cleanroom. Contrary to the original purpose of the cleanroom, even the contamination generated during maintenance work is now distributed across all previously cleanliness-controlled areas thanks to the prevailing cleanroom technology, especially when using turbulent mixing ventilation. This must be avoided by all means. The first remedy would be to switch off the clean air technology so that no maintenance-generated contamination migrates into the neighboring, cleanliness-controlled areas. Although this would contain the distribution, the neighboring areas would no longer be protected from contamination from outside. The second remedy is mechanical shading or a protective enclosure over the source of contamination. The third remedy is to combine a protective enclosure with a reversed ventilation logic. This involves creating negative pressure for the contamination-generating maintenance area in combination with filtration systems, which then release the filtered exhaust air into the ambient clean room with a higher level of cleanliness. These challenges are analyzed in more detail below using various maintenance strategies.