PART III PROCESS SAFETY
2. Hygienic Design
2.2. Building design
Good hygienic building design should minimise the possibility of infestation by insects, birds, animals, micro-organisms, any accumulation of dust, surface water or condensed water or product. These events are all factors that create the poten- tial for microbial growth and therefore the risk of contamination.
First of all, when a new production facility is planned, risks from neighbouring facilities and activities creating possible contamination sources, such as waste water treatment plants, farms, heavy chemical industries, nearby rivers, canals or other open water areas etc. have to be taken into account.
Building design includes aspects of zoning, construction elements, utility installations, air and water related aspects.
2.2.1. Zoning
To minimise contamination, dry and wet areas should be separated and washing and drinking facilities should not be placed in production areas. Short product routing without crossings together with good equipment location schemes can prevent contamination risks involving raw material, intermediate and end-product handling, waste management, equipment operation and personnel activities.
The classification and separation of areas according to hygienic and cleaning requirements (see Figure 5) is a very effective measure to avoid contamination. In general “Basic” or “Low” hygiene zones are areas with no or closed production.
Medium hygiene zones are areas with partly open production. High hygiene zones are areas with open production.
Each of these zones can be classified, according to the cleaning requirements, into “wet”, “controlled wet” and “dry cleaning”. Where “controlled wet” is defined as the use of a controlled amount of water, which is then followed by a drying process.
Zoning means the exclusion and restriction of unwanted items together with the definition of areas and barriers. This implies knowledge of product and process (what is to be prevented). Zoning must be logical and practical for all concerned. Furthermore, zoning must be affordable and the rules must apply for everyone and everything. Training of the personnel is essential. For each zone specific rules for installation, personal behaviour and cleaning procedures should be defined. The different zones should be made clearly visible, especially the perimeters where personnel and traffic will cross. Furthermore, the direction of air, personnel and products must be clearly defined. Zones may temporarily have their classification level changed in cases such as for maintenance or cleaning purposes.
Packaging materials, replacement parts, stockrooms for technical supplies and also maintenance workshops should be located in separate areas, but not in a pro- duction area.
Barriers between zones are extremely critical and must be monitored. These barriers may be walls or simply lines on the ground, drains, air filters, windows
Cleaning requirements controlled wet wet
hygienic requirements
dry
yard, parking area
bottle washing
opent filling powder filling
closed filling milling
offices, store store
Bw
Mw
Hw Hcw Hd
Mcw Md
Bcw Bd
FIGURE5. Examples for classification of areas according to hygienic and cleaning require- ments (Duffey et al., 2003). B ... basic hygiene zones, M ... medium hygiene zones, H ...
high hygiene zones, w ... wet cleaning, cw ... controlled wet cleaning, d ... dry cleaning.
through which materials may be transferred, etc. Access points for products and personnel, air and utilities, as well as traffic conditions must be systematically reviewed To set appropriate rules to ensure that the appropriate hygienic level requirements are met. Access point includes doors, windows, holes of any size, ventilator openings, drains, etc. For example, material transport from a zone M to a zone H using a conveyer belt should not be carried out with one single belt, but with two. At the boundary the material is transferred from one belt to the other, and a laminar air flow at the boundary prevents the entry of contamination to zone H. A typical example is where bottles and containers are cleaned in a zone M and then transferred to a zone H for filling.
Elevators are classified in the lowest hygienic level due to the non-accessible spaces in the shaft above and below the elevator and air drafts created in the shaft that cause airborne dust movement and can be a major source of contamination.
Elevators should never connect different zones if they have not been fitted with additional measures such as airlocks. and the area under the elevators should be monitored very carefully. If different hygienic zones are accessible by stairs or elevators, air locks must be installed.
2.2.2. Construction elements
Interior building element surfaces should be non-electrostatic (stainless steel preferred to polymers), but should be smooth, have round corners and have good accessibility for cleaning. Materials that are resistant to cleaning agents and dis- infectants, if required, should be used. The use of mould resistant or disinfectant containing paints is not recommended, because micro-organisms can develop resistance when constantly exposed to disinfectants.
Platforms and walkways are difficult to design hygienically and therefore their use should be minimised. All parts should be easily accessible for inspection, maintenance and cleaning. The framework should be constructed from open pro- files and all hollow structures, horizontal ledges and pockets should be avoided.
If ledges are unavoidable, they should have a slope of 45˚. Walkways over open processes should be avoided, because soil and foreign material may be transferred into open equipment located underneath when people walk across the platforms.
Framework should not be mounted directly on to floors that are inevitably uneven, but should be mounted with a rubber seal between the floor and the framework to ensure a tight fit. Double ceiling constructions should not be used, as they also accumulate dust and form hollow inaccessible cavities.
Sufficient sloping of floor surfaces should be provided for drainage in wet zones To prevent stagnant water formation. Floor coverings have to prevent mois- ture getting under the floors and should be rounded upwards at the base of the walls. When tiles are applied, all junctions should be made of non-porous mate- rial to prevent moisture penetration into the walls.
Any drainage must be separated from an open processing area. Drains should always be placed as far as possible from processing equipment. It should be noted that water locks may create air if there is a pressure differential over the water
lock. Any bubbling can generate aerosols. Drains and channels should not be present in completely dry areas. When wet cleaning procedures are utilized in a dry production area, the drains should be tightly covered and kept dry during pro- duction. The reason being that when there is no water in the drains to form a water lock, there then is direct access to the sewer system.
The number of windows should be minimised in processing areas. Window frames should not be made of wood. Windows should not open and have no or 45˚ sloped sills and ledges. If windows do open to the exterior, they must have insect screens which should be easily accessible, cleanable or replaced regularly.
No untreated standard glass should be used for windows, lightings and other fixings in open processing areas due to problems of detection of fragments when this material breaks.. Polymer material like polycarbonate or strengthened glass should preferably be used.. If, however, standard glass were used, it should have a protective film on its surface to prevent shattering on breakage.
As doors can be a source of pest infestation and dust accumulation they should be completely flat, without any hollow body and seals around doors should be avoided. An ambient pressure differential would be preferred. If seals are unavoid- able, they should be checked regularly, because they deteriorate with time.
Insulations against noise or condensation should be avoided as much as pos- sible, as they can retain moisture and harbour micro-organisms. A better but much more expensive alternative is a so-called hot/cold room concept (see Figure 6), which means that equipment which needs to be heated or chilled is installed in a separate room, where the walls, ceilings and floors of the room provide the insu- lating boundary. However, if insulation is required, no perforated or electrostatic materials should be used; they should be water tight and must be removable for inspection and cleaning. Insulation should be placed on the side of the wall located in the area of lower hygienic requirements.
FIGURE6. Example for a hot/cold room concept.
Light sources should preferably be watertight and integrated into ceilings and walls in a way that avoids any dust accumulation (see Figure 7). Light sources are not to be placed above open processes, since if damaged, broken fragments will fall into open process equipment.
2.2.3. Utility installations
Inappropriate positioning of utility installations is a major source of contamina- tion by dust and condensation (see Figure 8).
Hygiene risk Horizontal surfaces
Water tight integrated Correct
Slope Soil
Ploycarbonate instead of glass
FIGURE7. Examples of lighting.
FIGURE8. Example of inappropriate piping.
hygiene risk correct
full tray
Hollow body
Acoustic insulation open ends
funnel
electric wires
grid or sheet, one-layer, sloed or vertical horizontal grid
FIGURE9. Examples for electrical cabling.
Pipes should run in separate and accessible gangways and enter the process area through the ceiling. If this is impossible, open trays that are sealed to walls or to ceilings should be used. These trays should be designed hygieni- cally to minimise presence of horizontal ledges, crevices or gaps where inac- cessible dirt can accumulate. Pipe lengths should be as short as possible and should never be installed above open production lines, because drops of con- densate may contaminate the product. Exterior surfaces of pipes that traverse walls should have water and air tight contact with the wall, when the wall sep- arates areas with different hygienic requirements. If both sides of the wall are in the same zone, water and air tightness is not essential, but any opening should be large enough for access and cleaning. Special attention must be paid to avoid dead space especially for connections, couplings, seals, valves and sensors.
Trays for electrical cabling should be sloped or vertical mounted grids con- taining only one layer. Cable funnels should be avoided because they are hol- low bodies (see Figure 9). If they cannot be avoided for some reasons, the ends should be closed and sealed and able to be easily opened for inspection and cleaning.
2.2.4. Air related aspects
Air contains microscopic particles of dust and micro-organisms, either alone or attached to dust particles. Therefore air is a potential contamination source in food processing. There are different types of air quality to consider as environ- mental (ambient) air, process air and instrument air.
Ambient air should flow from higher to lower hygiene areas and from lower to higher dust loaded areas. In a high hygienic area, additional measures such as
air filtering (EN 779, 2003) and operating under conditions slightly above atmos- pheric pressure are necessary.
Process and transport air should only be drawn in at a single location, being at least 3m above the ground level and at least 10m away from any exhaust dis- charge point (VDI 6022, 2002).
For instrument air the outlet has to be carefully positioned away from open and dry products to avoid formation of dust.
2.2.5. Water related aspects
Water is a vital medium used for many different purposes in the food industry.
The safe storage and distribution of water in food factories is described in detail in EHEDG Doc. 27 (2004) while the hygienic re-use of processing water in food plants is referenced in a Codex Alimentarius discussion paper (1999).
Stagnant water should not be allowed to exist on floors, plant and equipment surfaces after wet cleaning. Sufficient drainage must be provided if wet cleaning is required.
To prevent contamination risks water quality control is very important.
Water quality for different use should be specified and quality control proce- dures should be established. Pipes for different water qualities should never have connections. In general the following water qualities are used: Product water is used as an ingredient, for transport purposes, cleaning/disinfection and for rinsing equipment surfaces in direct contact with the product. Utility water is used in a secondary process like heating/cooling, cleaning and fire fighting, where no direct contact with the product will occur and potable water is for personnel use.
In food factories the proliferation of Legionella spp. is of particular concern.
This bacterium causes severe respiratory illness (Legionnaires’ Disease) when inhaled from contaminated aerosols. Hygienic design to prevent the growth of this bacteria consists of avoiding the presence of stagnant water, the formation of aerosols and the use of the right design and placement of equipment like cooling towers, evaporative condensers, domestic water systems, pressure jet- ting systems, can/bottle washing systems, emergency showers; fire sprinklers, fountains, garden hoses and sprinklers, spray humidifiers and air washers, machine tool cooling units, conveyor lubrication, etc. where water tempera- tures in the range of 20-45˚C may be found. The prevention, risk assessment and control of Legionella spp. bacteria is described in detail in EHEDG Doc.
24 (2004).