Cleaning and Disinfection of Clean Rooms - Module 4
This page will give you detailed information on the new field of cleanroom cleaning. We recommend to study the slides presentation of the module first, as it provides the basics on cleanroom technology. For students and apprentices, the slides presentation of the module is available as a PDF file. Teachers should have a look at the summary of didactical components before downloading the original PowerPoint presentation from the restricted area. When you have used the module, we would appreciate your feedback submitted in the online evaluation form. Filling in the module evaluation form will help to improve the quality of the training course. The advanced learners will find on this page a detailed discussion on the strategies and techniques, used to keep a clean room clean.
What is a clean room?
Originally, clean rooms have been designed for the manufacturing of valuable high tech products like electronic computer chips and aerospace telescopes. The air in a clean room is subjected to successive steps of filtering i.e. it has been cleared from those dust particles that you can see when sunlight is falling into a room at a low ankle. The cleanliness and quality of clean room air is extremely important in this type of manufacturing, as a single contamination can destroy products worth millions of Euro. Filtering must be very effective in terms of the smaller particles being removed. The air is filtered by special HEPA filters (High Efficiency Particle filtering) that remove any particle bigger than 0.5 µm. For comparison, a bacterial cell has the size of 2 µm. Filtered air passes through the clean room from the ceiling to the bottom in a laminar flow (see image below).
The quality of air is denoted by the numbers of particles in the air after purification. Historically, clean rooms were denoted according to US Federal Standard 209, annex E as class 10,000, class 1,000, class 100, or class 10 clean rooms. The lower the number, the better the clean room. The value denotes the maximum load of particles per volume allowed (in this case the unit is 1 cubic foot, which is equivalent to 28,3 l). This standard however has been replaced by the DIN EN ISO 14644 standards with the ISO classes of based on the number of particles per cubic meter. Due to the removal of particles, and microorganisms, clean rooms successfully have been introduced into the food industry to improve the shelf life of products which can not be subjected to a final heating step or in which preservatives are not allowed. Aseptically filling of snacks and pastries – packaging in the absence of pathogenic organisms – nowadays improves both, the quality and the shelf life of such products.
Cleaning of clean rooms
Although a clean room only receives filtered and almost particle free air, it rapidly will be re-contaminated with particles introduced by abrasion from machines, foodstuffs, or by humans working in the clean room. The last point expresses the delicacy of the whole process of clean room cleaning. Cleaning services are performed by humans which at the same time are the biggest threat to the cleanliness of a clean room. Hence, cleaning of cleanroom correctly has been denoted as the “supreme discipline” for any cleaning enterprise.
To achieve such a goal, only a limited number of persons is allowed to stay in a clean room, provided they are using modern protective clean room garments. Only the use of fully protective cloth, overalls, hoods, face masks etc. 
will guarantee that the cleaner is not a permanent source of particles during the cleaning process. One should avoid activities like running or fooling around, as such activities might display gaps between the body and the protective cloth, through which particles may travel. Obviously, coughing and spitting are activities that do not belong into a clean room. So far, clean room cleaning has been conducted by in-company cleaning personnel, but due to an ongoing trend for outsourcing, more and more external providers will be able to tender for such contracts. Many of the experience in cleanroom cleaning is based on trial and error and the level of cleanliness necessary to achieve is intricately connected to the food producers requirements. Hence, we will not be able to present a final guideline how to perform cleaning in clean rooms.
The cleaning of cleanroom however follows the same principles as ordinary cleaning. As such it can be divided into gross cleaning and precision cleaning. Gross cleaning can be done with vacuum wet cleaners, squeegees, brushes, and sticky rollers and may be proceeded by dismantling of machines. If using vacuum cleaners, the main air flow must be directed outside the clean room or be filtered using ULPA (Ultra Low Particle) or HEPA (High Efficiency Particulate Air) filters. One should be aware that cleaning heads themselves must be cleaned regularly according to QM instructions. 
Precision cleaning requires special wipers and swabs, and the cleaning techniques need to be among the cleanest as possible. Often specially developed folding techniques will be applied before using cleaning wipers (see image on the left). Wet wiping is valuable because the liquid can dissolve and weaken bonds between the particles and the surface being cleaned. A damp wiper will have a greater affinity for particles than a dry wiper, but getting the wiper fully wet leads to some re-deposition of the particles on the surface. The cleaning should be finished by thorough rinsing with clean water in order to remove detergent residuals. Residual free surfaces are an important feature due to cross reactions between the sterilising agent and the detergent.
The cleanliness of clean room surfaces can be evaluated by e.g. UV light, sticky tape, rinse of the area and analysis of the liquid, followed by a chemical or microbiological assay. Designated clean room products only should be used for the cleaning of clean rooms. Ordinary cleaning items such as cotton mobs may not be introduced into a clean room, because cotton is known to release high number of particles upon application of mechanical forces. Mops, wipers, and other re-usable fabrics should be constructed in a way that particles are easy to remove in the laundering process. Mops manufactured of polyester fibres have a smoother surface from which particles are easier to remove. Depending on the requirements given by the food producer, buckets and wringers, mops, trash receptacles, wipers and swabs, cleaning and disinfecting solutions, dispensing bottles, stools, ladders, and vacuum cleaners may have to be disinfected or sterilised. Mops, wipers, and other re-usable fabrics must designed to survive common disinfection and sterilisation methods like chemicals, heat, or radioactive irradiation. In contrast to cotton, mops manufactured of polyester fibres generally would tolerate the energy applied by gamma sterilisation. Garments used in the cleanroom should be changed at least once per day and laundered in certified laundries (preferably using RABC based QM systems). Disinfection laundering processes should be preferred, and accompanied by measures to avoid re-contamination of the garment. Obviously, each enterprise will have to develop a specially tailored cleaning procedure which eventually will be integrated into the food producer’s HACCP based QM system. Due to the huge variety in the design of cleanrooms it will be impossible to give a certain recommendation how to adjust one’s standard procedures towards clean room cleaning. There are, however rules of thumb which can be applied to achieve a best practice of cleanroom cleaning. The second rule should be to discuss whether requirements derived from GMP controlled environments (GMP = Good Manufacturing Practice) are applicable for the type of clean room to be cleaned. Cleanroom cleaning according to GMP for instance may require the use of sterile solutions. Such solutions, however are much more expensive than normal grade products and represent a high potential to save customer's money. The only valuable advice to give here would be to study the literature (mainly standards like the VDI standard series 2083, DIN EN ISO standards 14644, and appropriate GMP guidelines). The problem of linting and particle release
Accordingly, protective clothing must be free of linting and function as a barrier towards bacteria and particles released from the human body during physical activities. Barrier textiles are constructed using very thin polyester fibres (image on the left shows a woven polyester garment with a carbon fibre), that can be woven into tight and light weight textiles. Cleaning agents and cleaning equipment must be proven for their ability of particle removal, and characterised by chemical stability to avoid the introduction of new particles into a clean room. Last but not least, personal hygiene measures and hygiene training (see module 1 and module 5) are necessary to avoid the introduction of microorganisms into such a delicate area.Disinfection and sterilisation of cleaning supplies
Final comments on clean room cleaning in a QM controlled environment
The first rule should be to develop a strategy of keeping the adjacent areas as clean as possible, e.g. by cleaning more often and more thoroughly the closer you get to the cleanroom. Contamination control may require frequent conventional cleaning of entrances, halls, and offices as well. Additionally, the changing rooms and the clean room need most careful and thorough cleaning. Due to the educational background in facility management, cleaning enterprises will be able so support customers in this type of strategic planning.