Standard ISO 14644-4 “Clean Rooms and Associated Controlled Environments Part 4 Design, construction and start-up” Annex E: Construction and Materials, defines: “The materials used in the construction of the installation should be selected and applied to meet the requirements of the installation, and should take into account the following:
- The cleanliness class
- Effects of abrasion and impact
- Cleaning and disinfection methods and frequencies
- Chemical/microbiological attack and corrosion
EU Guidelines for Good Manufacturing Practice for Medicinal Products for Human and Veterinary Use, Chapter 3 Premises and equipment indicates that “Premises and equipment must be located, designed, constructed, adapted and maintained to suit the operations to be carried out. Their layout and design must aim to minimize the risk of errors and permit effective cleaning and maintenance in order to avoid cross-contamination, build-up of dust or dirt and, in general, any adverse effect on the quality of products”
In the same way paragraph 3.9 on the same chapter says: “Where starting and primary packaging materials, intermediate or bulk products are exposed to the environment, interior surfaces (walls, floors and ceilings) should be smooth, free from cracks and open joints, and should not shed particulate matter and should permit easy and effective cleaning and, if necessary, disinfection”
2. MATERIALS AND QUALITIES
There are several options, regarding materials and qualities, which fit on these definitions, next we are going to identify these options with pros and cons..
1. Modular (panels)
Sandwich panel definition is “Material composed by means of an insulation core coupled to two external layers which could be metallic or non-metallic. Metallic ones are normally steel or aluminium. During the manufacturing process the external layers are prepared by bending or die cutting, in accordance with the desired shape, after that they are placed on a press machine and glued to the selected core by means of special glue. Once the panels are manufactured they are cutting on the selected length, piled up and packaged to be sent to site.”
The main advantage of this kind of material, besides insulation and surface finishing, is their ease of assembly and cleanliness. As a “dry work“, sandwich panels allow refurbishment and reparations with a low impact on the normal operation of the clean room. Normally modifications take short time, rubble and debris are easy to take away; in this way it is possible to continue the production work on adjacent areas with a slightly confinement of the refurbished area
On the other hand panel’s adaptability allows lay out modifications even during installation process with small additional cost.
Another advantage of this kind of wall (in the case of female-female connection) is the possibility of passing cables and tubing (electrical wires, air compressed tubing) through the connection tube; in this way it is not needed hard works or disassembling when replacing or installing new connections
Finally should be highlighted that these panels are self supported, so they do not need any structure or reinforced wall.
Among sandwich panels there are a wide range of options, but primarily there are two main groups in accordance with the material of the faces: lacked steel sheets and HPL (High Pressure Laminated) also called phenolic resin sheet. Both groups with several core materials: EPS (expanded polystyrene) XPS (extruded polystyrene), rock wool, PUR (polyurethane) (PIR polyisocyanurate). The total thickness depends on the required thermal and acoustic insulation and the total height of the romos
Metallic panels are probably the most commonly used on Clean Rooms, they are composed by two lacquered steel sheets of several thickness. The most recommendable thickness is 0,6 mm, it provides to the panel enough planimetry and hardness to be used in Clean Rooms; thinner sheets are nor recommendable, it allow to lower the material price cost but reduce dramatically the final quality
Regarding the other main material, HPL or phenolic resin sheets, the most common and recommendable thickness is 3mm.
Obviously, each type of panel has pros and cons. Metallic panels obtain better fire class than HPL panels. Depending on the core the fire classification ranges from Bs2d0 (worst case) with PUR insulation to A2s1d0 (best case) with rock wool, and a middle ground of Bs1d0 with XPS or EPS. Metallic sheet gives to the panel a high resistance which avoids surface cracks. On the other hand this kind of panels has a good stability against temperature and humidity changes.
HPL panels can achieve good fire class (Bs2d0) if the core is made of rockwool, with other core materials like XPS or EPS fire class is not so good. HPL sheets have a considerably surface hardness so that the panels are very resistant against scratches and bumps. Although HPL is more brittle than steel sheet it is easier to repair and it can be mended by means of appropriate filler and painting, unlike the metallic panel which once damaged is exposed to rust. Another advantage of HPL panel is the possibility to be cut and milling at site, it is possible to cut off the HPL panel and the edge is smooth and allow a clean and continuous sealing, unlike metallic panel in which the cut is rough and the sealing cannot avoid the rusting process and the edge has to be covered with profiles or cover plates.
In clean areas, with disinfection process by means of hydrogen peroxide, HPL panels remain unaffected after continuous cycles of disinfection, on the contrary metallic panels, depending on the thickness and quality of the lacquered, could be damaged after several decontamination cycles
With regard to the core insulation, the more common used are EPS (Expanded polystyrene), PUR (polyurethane) and rockwool.
Polystyrene is a light insulation, panels with EPS core are low weight but solid; this kind of insulation is the less particle shedding. Another advantage of polystyrene, both EPS and XPS (expanded or extruded), is the homogeneity, other injected insulations like PUR or PIR are not able to achieve this level of homogeneity. The only advantage of PUR and PIR is thermal conductivity. Whit regard to rockwool the main advantage is the reaction and behaviour against fire, besides the good fire reaction, with adequate thickness and density it is possible to achieve fire sector panels up to 180 minutes resistance. Thermal conductivity for rockwool is quite similar to polystyrene. Maybe the main disadvantage is the core is composed by pressed fibres, some of these fibres could be released; for this reason is recommendable to cover with adhesive tape all edges on the cut offs, in order to avoid fibre releasing to the surroundings (even in technical areas)
Apart from type of surface or material core panels also can be classified by the assembly system. Mainly there are three assembly types:
1. Male-Female: The sides of the panels have two type of shape: male with a protrurde edge and female with a grooved edge, both shapes fit each other in order to achieve a perfect joint. The main advantage of this kind of assembly is the good performance in terms of insulation, both thermal and acoustic. This is also very important for panels used in fire walls. The main disadvantage is that cables and tubing cannot go through the panel.
2. Female-Female: Both sides have grooved edges and the panels are assembled by means a square tube, made of PVC or aluminum. The tube provides a perfect alignment of the joint and at the same time, it could be used as conduit for cables or tubing. This kind of assembly provide better penetrability of the silicone sealant in the joint between panels, that makes the seal stronger and more homogeneous
3. Non-Progressive: This is a variant of female-female assembly. It allows disassembling any panel in any position without dismounting the adjacent. This is the main advantage, besides the use of the tube as conduit for small installations, like the standard female-female joint. The disadvantage is that each joint has two gaps to be sealed instead one gap as the other systems. In addition, it is a little expensive
2. Wall covered on PVC layer
This is another solution used for clean room walls. The finished is appropriate since PVC provides a continuous and non porous surface, and it does not shed particles. Joints between PVC sheets are heat sealing to keep the entire surface continuous.
This type of wall has some advantages such as good behavior under cleaning and disinfection procedures, it also allow to use the same PVC to cover floor and walls, that provide a continuous surface without any gap between wall and floor. That is a very adequate solution for washing areas. .PVC elasticity allows the use of the same material post forming in round shape corners and concave edges, without overlapping external profiles. Regarding fire sectorization, it depends on the wall material and thickness not on the PVC layer.
PVC is a hard material which made it impact resistant; it is not easy to break unless the use of sharp objects. Any case it is easy to repair, using a piece of the same material and hot welding.
The main disadvantages are its bad fire reaction and the risk of glue aging resulting in bubbles and parts of the PVC unstuck from the wall.
Since the PVC layer is supported by a wall any refurbishment on the clean room implies the inner wall demolition, normally composed of bricks, blocks or plasterboard, which means a big amount of debris and dust.
3. Wall covered with epoxi painting
This is a solution used for existing rooms built on traditional wall of bricks or plasterboard. Epoxi painting is a non porous material and it does not shed particles. It has a good behavior under cleaning and disinfection
procedures. Mechanical resistance depends on the wall material which means that cracks and fissures could be expected.
It is advisable repainting yearly, consequently maintenance could be expensive and like PVC, any refurbishment on the clean room implies dust and debris.
This is not a recommendable solution for high requirement áreas
4. Other coverings
There are other coverings like melamine resin, tiles, plastic painting… These finished cannot meet the cleaning and non-particle shed requirements used in clean rooms, therefore they are not recomendable.