Hygienic design is very important when planning and designing machinery and facilities in the food and drugs industry. It refers to the easy-to-clean design of parts, components and production machinery. Hygienic design results in machines with a closed design that have little dead space and are easy to clean. It is particularly important when handling solids because solids, unlike liquids, can be distributed throughout the entire building by the ventilation system, from surface to surface and from person to person if the solids are not handled properly or are handled open. At the same time, there is a risk of product cross-contamination which in accordance with the EU GMP Guidelines must always be avoided. The design of the machinery to be used is extremely important in this context and should be taken into account at an early stage of planning.
The designer must first of all consider the parts of the machine that will have direct contact with the product. These parts have the highest priority when it comes to hygienic design. The designer must then consider the parts without product contact, as well as the working environment. The requirements affecting these areas are less stringent.
The following points apply in general to hygienic design of machinery:
The internal parts of a machine, i.e. the "product contact surfaces", must be free of dead space and easy to clean. Internal fittings in the machine parts should be avoided because they prevent simple cleaning. This is, however, difficult to realise when working with solids.
When filling an API, for example, it may be necessary to crush agglomerates after drying, which requires the installation of a crusher with a sieve. Representative samples are taken from the product using a sampler. The product is then filled into intermediate or final containers using a precise metering system. All of this requires a considerable number of mechanical parts and many fittings in the product flow.
As a result, it is not always possible to use a CIP system for cleaning. In practice, WIP processes (washing in place) are used, which involves the critical machine parts being dismantled and manually recleaned after automatic pre-washing. The critical parameters must be checked prior to and during the cleaning validation and documented in the cleaning SOP.
If the machines have to be opened during the production process, hygienic design should not be limited to the product transfer systems and processes. Cleanrooms especially, where specific requirements apply to the cleaning of machinery and surfaces, must have as few additions, cable bushings etc. as possible.
The design of the area where emptying or filling takes place is also important because of the close proximity to the product and the increased risk of contamination. It must also be taken into consideration whether a monofunctional or multifunctional system is being used. The cleanroom class (A, B, C or D) is also important. Each area requires its own individual design which must be defined and documented in the user requirements specification during the early stages of planning. The following aspects are important for a hygienic design of the outside of the machine:
The panelling of added components such as e.g. drives, should be moved from the production to the technology area. This also simplifies the servicing and maintenance of the machine.
Problems that occur in practice often result from mistakes made during the planning phase. The issue of supply and discharge of solids is often only taken into consideration after planning of the room or building has been completed. The rooms or buildings are already under construction before the supply and discharge of solids is planned for. During API production, for example, the reactors and crystallisers are usually installed on the upper floors, the centrifuges on the middle floors and the dryers on the lower floors. Equipment inlet and outlet heights for the solids feed must be taken into consideration, because the input materials are sometimes delivered in large containers. These aspects must also be considered when designing machines for manufacturing medicinal products.
When the solids feed is not taken into consideration, the solids can sometimes no longer be supplied or emptied using gravity. They must then be supplied to the machines using transport systems (e.g. pneumatic conveyor systems) in order to feed the solid to the reactors or load a tablet press, for example. When emptying dryers and centrifuges in API production and blenders in medicinal product manufacture, a pneumatic conveying system must also be used if the room ceiling is not high enough.
The design of solid transfer systems is often not covered in enough detail during the planning phase. Open pipes, open cable ducts and an inadequate design of the machine surfaces are frequently encountered, so that the machine is often difficult to clean.
The room design is another weak point. Most APIs are filled in a classified room after drying, but the design of the room is often inadequate. There are often weaknesses in the wall design and spatial planning with GMP-compliant transitions in particular.
Skan AG, Allschwil, Schweiz
Applying the Principles of Hygienic Design to Solid Dosage Forms explains all important design characteristics for hygienic design, using the example of different types of connections, feeding and dosing systems, and cleanroom installations.
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