Hygienic Design Principles to Respect During Repair
Maintenance and repairs should occur according to the principles of proper hygienic design to ensure that safe food is produced once production is resumed. The following recommendations should be followed.
Design for Maximum Access
Equipment should be of such a design that cleaning or maintenance of it does not introduce food safety hazards, e.g., consideration should be given to eliminate or minimize the need for physical entry into the system. All equipment parts and components shall be readily and easily accessible for inspection, maintenance and troubleshooting. For that purpose, enough space and clearance should be provided around equipment, process and utility piping, equipment utility connections, etc.
Compatible Materials of Construction
Materials of construction used during maintenance and repair must be adequate to cope with the food product produced or process aids they are in contact with, as well as with the harsh conditions encountered in the food processing environment (detergent and disinfectant solutions, lubricants, etc.) (Moerman et al., 2014).
• Corrosion of metals, steels and alloys may result in leaks and impair the smoothness of the surface finish. This increase in surface roughness makes equipment materials of construction more prone to adhesion of food residues and bacteria. The latter finally can give rise to biofilms which could be very difficult to remove.
Immersion tests with metal coupons (Fig. 8.10) or specific equipment components (Fig. 8.11) allow evaluation of the effect of food products, detergents and disinfectants on the materials of construction used in the manufacturing of food processing equipment and utilities. Static immersion tests of the candidate materials of construction are rapid screening tests. The large numbers of welds and the numerous transitions from one metal to another make process equipment also very sensitive to
FIGURE 8.10 The compatibility of several materials of construction with detergent and disinfectant solutions can be tested in the laboratory by means of immersion tests conducted with coupons. Courtesy of Evapco Inc. Moerman & Fikiin, 2015.
FIGURE 8.11 Bearings made from different materials of construction were subjected to immersion tests in salt brine. Bearings No. 1, 2 and 8 are thin dense chrome plated; bearings No. 3, 5, and 7 are 400 series stainless steel; bearing No. 4 is coated; and bearing No. 6 is black oxide coated. Courtesy of John Butts, Land O’Frost, © 2016.
aggressive cleaning and disinfectant chemicals. Hence, if the plant item is to be welded, it is prudent to subject welded coupons to similar tests, as the weld metal and heat-affected zones may have different corrosion resistances in comparison with the unwelded material. To assess the risk of crevice corrosion, a testing procedure that involves the use of castellated washers is often used (Moerman and Partington, 2014; Moerman and Fikiin, 2016).
Several experimental parameters can be changed, such as temperature, detergent/disinfectant concentration, water quality (pH, hardness, etc.), application frequency, etc. It is recommended to perform “challenge tests” under forced conditions, which means that coupons are immersed for several days or even weeks in highly concentrated cleaning and disinfectant solutions, and, if necessary, the food product. At the end of this immersion period, coupons should be rinsed and dried to evaluate the effect of these cleaning and disinfection solutions. Parameters that can be measured are visual appearance, weight loss, thickness, hardness, etc.
The removal of the galvanizing and the release of zinc make galvanized steel unsuitable for application in the product contact and splash area, not least because zinc often contains residual traces of cadmium and lead as impurities. Painted steel never should be used in the splash zone or any other area where food is exposed, because paint may peel off and can splash/fall onto the food products (Fig. 8.12). Paints especially may create a health risk because they often contain toxic substances such as zinc, lead, cadmium, and phenolics. Paint surfaces used in nonproduct contact areas also may crack or flake, and must be repainted immediately.
Care must be taken when selecting a replacement part, because experience has shown that many items that were supposed to be stainless steel
FIGURE 8.12 This motor is constructed from mild steel, and is used to impart vibration to a perforated stainless-steel bed laden with food products. During hose-down operations, the cleaning agents and high pressure typical for traditional manual cleaning procedures have ruptured the physical integrity of the paint and allowed peeled-off paint to splash onto the cleaned conveyor bed. As a result, food products subsequently produced on this process line may become contaminated. Courtesy of Joe Stout, Commercial Food Sanitation LLC - Intralox, © 2016.
- 316L turned out to be 304. Packages containing these items were often marked and labeled as stainless steel 316L. Even 316L stainless steel tanks with inlet ferrules and manway collar in 304 stainless steel have been found. All the raw materials of construction that enter the factory, as well as purchased items, can be tested on their elemental composition using the nondestructive X-ray fluorescence method as a Positive Material Identification technique. By bombarding the surface of the test material with high-energy X-rays or gamma rays, secondary (fluorescent) X-rays emitted from the material can be detected. Each element in a material emits its own unique fluorescent X-ray spectrum, allowing it to be identified. However, commercially available portable handle-held XRF guns (Fig. 8.13) are quite costly and are limited in their ability to precisely and accurately measure the abundance of elements with atomic number Z < 11 (e.g., atomic number Z of carbon is 6). For this reason, XRF can’t be used to differentiate between stainless steel 316 and 316L. For small food manufacturers, the procurement of an XRF-analyzer can’t be justified due to its high cost. They still have to rely on certificates delivered by their vendors, although they still can qualify their vendors by hiring a contractor that is in possession of an XRF-analyzer and experienced in elemental analysis by this technological means.
- • Plastics must have good dimensional stability on exposure to high loads, corrosive chemicals, as well as high or low temperatures. Changes in dimension or shape, cracking, and breaking during operation may not occur, as they allow food residues access to areas where they will be
FIGURE 8.13 Quality technician doing Positive Material Identification on a stainless-steel vessel using an X-ray fluorescence gun. Courtesy of Holland Applied Technologies.
difficult to clean and pose a contamination risk. They must have high mechanical strength to withstand mechanical shocks, and resistance to aging, creep, brittleness, fatigue, erosion, etc. Excellent resistance to wear and abrasion is required in certain applications such as the transfer of solids, slurries or pastes (e.g., tomato concentrate). These food products may damage the plastic surface, promoting the accumulation of soils and the formation of biofilms, finally negatively affecting cleanability. The plastic material also must be chemically resistant to hydrolysis by steam, acids and alkalis, reducing and oxidizing agents, as well as cleaning agents and disinfectants. The equipment manufacturer should/can test the chemical resistance of the plastic material in the same way as described for metal, steels and alloys. They also must be tested on their thermal resistance (Partington et al., 2005; Moerman and Partington, 2014).
For use in the food contact area, it is important that plastics be odorless, nonporous, smooth and free from cracks, crevices, scratches, and pits, as they may harbor and retain product constituents and/or microorganisms after cleaning. Within the pores, microorganisms are also better protected against the bactericidal activity of disinfectants. And, spherical void expansion may cause changes in the chemical and physical properties of a certain plastic material, hence affecting its cleanability. In food contact applications, it is recommended to avoid additions into plastics, as additives incorporated in plastics may migrate into the product. But in addition to these additives, volatile remnants of monomers (e.g., styrene), oligomers, low molecular weight polymer fragments and certain organic solvents may leach from the polymer material into the food, inducing changes in the organoleptic qualities. It is recommended to delay any exposure of food to recently produced or processed plastics, so as to allow these plastics to release most of their chemical substances before application and during storage. Also, the first food batch should be sent to disposal.
While certificates of conformity are proof that the material is, in principle, safe for food contact and the component is made to specification, they are not evidence that the part specified is technically suitable for a particular application. It is good practice to require the supplier of plastic raw materials or components to provide documentation that the grade of material selected is certified for contact with the product in question (requiring studies to evaluate migration of specific substances).
• Rubber compounds are individually developed by the supplier, causing elastomers to differ greatly from one supplier to another. Rubber for food contact must comply with many different normative references (e.g., EN 1935/2004, BfR, FDA and 3-A), as well as the European Commission’s REACH Regulation (Regulation on Registration, Evaluation, Authorisation and Restriction of Chemicals). It is a major recommendation to avoid ingredients which are not chemically bonded, as they may be released in the food product). The rubber parts supplier should assist food manufacturers in selecting the most suitable elastomer for their specific operation. This selection must occur in function of the physical and chemical resistance characteristics of the different types of elastomers and the in-use process conditions. Degradation of elastomers by product, detergents, disinfectants, and thermal and mechanical stress proceeds much faster. Moreover, elastomers are more prone to microbiological degradation because they facilitate extensive biofilm formation more than plastic materials do (Moerman and Partington, 2014).
A typical symptom of this elastomer deterioration—mostly due to a combination of aggressive chemicals and elevated temperatures during cleaning processes—is hardening of the material, leading to loss of elasticity and eventually loss of sealing function. The result could be: physical contamination of the product with elastomer particles (consequence of abrading and break-up of the rubber material); leakage of lubricants or refrigerants; loss of bacteria tightness; permanent product and process contamination due to increased adherence and retention of dirt and bacteria in crevices; and insufficient cleaning and problematic disinfection. Moreover, ingress of liquids containing chlorides may occur under partially destroyed gaskets and seals, so that a high chloride concentration may subsist between damaged seals and adjacent metal, favoring crevice corrosion even in stainless steel. To ensure that the rubber remains in good condition, regular inspection is required. Routine replacement of elastomers must be done in function of the physical and chemical stresses imposed on the material.