- Email: [email protected]
Improving the design of floors
9 Improving the design of floors B. Carpentier, Agence FrancËaise de SeÂcurite Sanitaire des Aliments, France
9.1
Introduction
We will here mainly consider the design of floors intended for greasy and/or wet food processing areas where they have to fulfil many requirements to be suitable. Because flooring materials are not food contact surfaces, some may consider that flooring materials are not of paramount importance to obtain the best microbial quality of food product. However, all cleaning systems disperse viable microorganisms in both water droplets and aerosols (Holah et al., 1990), allowing microorganisms to reach food and food contact surfaces. As slipping is one of the main causes of accidents at work, flooring materials need to be rough. Add to these the fact that gravity carries most of the soiling and microorganisms down, and it can be seen why flooring materials are usually more microbiologically contaminated than other inert surfaces of food processing premises. Finally, floors are places where Listeria monocytogenes is very likely to be found (Cox et al., 1989; Nelson, 1990). For all these reasons, great attention should be given to the choice and then to the application of a flooring material. The aim of this chapter is to give non-specialists some explanations of what the flooring materials for food processing premises are and to describe what properties are suitable for food processing areas.
9.2
What are floors made of?
9.2.1 The substrate The material that supports flooring, called the substrate or the floor base, has a great impact on the quality of the flooring material. It is either an existing one,
Improving the design of floors
169
which has to be properly prepared, or a new one, which has to be properly constructed and prepared before applying the flooring in order to allow a good adherence of the latter. It must be dry (a concrete slab must be let to dry for a minimum of 28 days but this time may be far greater if climatic conditions are not optimal) and able to prevent humidity reaching the impervious flooring. It must be capable of withstanding all structural, thermal and mechanical stresses and loads that will occur during service and it must be sloped sufficiently in order for liquids to flow to the drains. This is recommended for resin-based floors as well as for ceramic tiles, even though, traditionally, ceramic tiles are applied on a flat substrate, the slope being given by the screed. Particular attention must be given to joints that are an integral part of the floor system. Nevertheless, it is not the purpose here to detail all the construction rules regarding the substrate. For further information see Timperley (2002). 9.2.2 Flooring Two families of flooring materials are recommended for food processing areas: ceramic tiles and resin-based floors. Polyvinyl chloride (PVC) sheets are considered unsuitable because they are too easily worn. They can become cracked after the fall of a knife or other sharp object. Ceramic tiles Ceramic tiles are made of clay that after shaping is subjected to high temperature. They are manufactured products of constant quality and have been produced for centuries. Vitrified unglazed ceramic tiles are recommended for food processing areas. They are highly resistant to the main constraints that can be encountered in food processing premises, especially to heat shocks. The vitrified tiles can either be pressed (in which case they are usually square or hexagonal) or extruded (they are always rectangular). Dimension tolerances of the pressed tiles are better than those of extruded ones, allowing thinner joints. Resin-based flooring materials The first resin-based flooring, the acrylic cementitious systems, appeared in food industry premises during the 1960s and around two decades later synthetic resin flooring was also proposed, with the prospect of achieving a high standard of hygiene because those floorings are seamless. However, a high degree of technical skill is necessary to obtain in situ a good final product (only to be applied by a trained operative). As this has not always been respected, there have been many problems with such floors. Resin-based floors are obtained by application of a mortar made of a mix of one or more organic or inorganic binders, aggregates, fillers and additives, and/ or admixture, and can be classified according to the nature of the binder(s) used. There are two families of binders: synthetic resins and the hydraulic binders. The first ones are organic polymers comprising one or more components that
170
Handbook of hygiene control in the food industry
react with a hardener at ambient temperature, whereas the hydraulic binders, as cement or lime, need water to harden. Hydraulic binder The hydraulic binder used in the construction of flooring material is cement. The main drawback of the use of hydraulic binders is the high porosity due to water evaporation during hardening. The addition of a synthetic polymer reduces porosity, increases the mechanical resistance and reduces cracking risk. Cement can be used in polymer-modified cementitious screed that is defined as a `screed where the binder is a hydraulic cement and which is modified by the addition of polymer dispersion or re-dispersible powder polymer with a minimum content of dry polymer of 1% by mass of the total composition, excluding aggregate particles larger than 5 mm' (Anon, 2001a). Examples are the acrylic-modified cementitious systems that are the main systems used in the meat industry in France. The main and great advantage of such floorings is that they can be applied onto a damp substrate. Cement is also used in association with resins, such as epoxy resin and polyurethane. In those cases, resin content is around 5% by mass of the total composition. In such floors, cement is more a filler than a binder, which is why they are considered to belong to the synthetic resins family. Synthetic resins Epoxy resins are the more frequently used synthetic binders, followed by polyurethane and methacrylate resins. Polyester resins are seldom used, to the author's knowledge, in the food industry. Characteristics of the different resins change according to the formulation used. The formulation may be changed to adapt to such non-optimal installation conditions as temperature, relative humidity or time available prior to being put into service. Specific formulations proposed may have consequences on the resistance of the final product. It is therefore difficult to give precise rules on curing. The final floor system must be allowed to cure according to the manufacturer's instructions. These generally require 1±3 days at 15±20 ëC before trafficking and 3±7 days before washing, before contact with chemicals or before any ponding tests and high traffic loads (Anon, 2001b). The only resin that clearly escapes this general rule is polymethylmethacrylate (PMMA), also called methacrylate or methylmethacrylate. It is characterised by a very short time prior to putting in service: 2 hours. It can be applied at low temperature (ÿ10 ëC). However, this resin possesses a strong odour at installation that can irreversibly alter food products present nearby. The climate above the uncured resin should be maintained at least 3 ëC above the dew point. The substrate humidity must also be correct. It must, for instance, be smaller than 3% for an epoxy resin, or 7% for polyurethane±cement flooring. Aggregates Aggregates are granular materials that do not contribute to the hardening reaction of the mortar. Roles of aggregate depend on their size and abrasion
Improving the design of floors
171
resistance. Small aggregates that may be called fillers have many roles. Among those are reducing shrinkage and increasing the mechanical resistance. Such aggregates are often made of sand with high silica content (SiO2 or quartz, 7 on the Mohs scale). Hard aggregates are used to increase resistance to abrasion. Those may be aluminium oxide (Al2O3 or corundum, 9 on the Mohs scale), silicon carbide (SiC, commercial name carborundum, 9.5 on the Mohs scale). It may happen that hard aggregates lead to an accelerated wear of shoes and of brushes used for cleaning. Large aggregates are used to increase slip resistance. Primer A primer (one or two coats) is most generally used to aid the adhesion of the final flooring and to seal and consolidate the surface of a porous substrate. It consists of a liquid product, which is often a solvent-based epoxy, applied to a substrate. Coats Anti-slip resin-based floorings can be obtained by one-coat or multicoat systems. Multicoat systems that are the more frequently proposed are thin flooring (2±5 mm) made of a self-levelling mortar on which large aggregates are sprinkled. One or two coats and then one or two finishing coats can be applied. These finishing coats are very thin, which is why they have a poor durability (1 or 2 years). Such finishing coats can be interesting when they fill the bubble gas holes but their role should not be to maintain large aggregates necessary to slip resistance. One-coat systems, also called monolithic systems, are made of mortar in which all the aggregates are mixed prior to application. The maximum diameter of the aggregates must be smaller than the third of the flooring thickness (Pollet, 2000). They are thicker (4±12 mm) and the large aggregates necessary to obtain slip resistance are often better maintained. Gas removal Gas bubble holes are highly undesirable for hygienic considerations (see below). Surface-active agents can be added to avoid or decrease their formation during polymerisation of resin-based floors. There is also prickle roller, called heÂrisson in French (hedgehog), that is used when the mortar is in the fresh state to release entrapped gas bubbles. In some flooring, such as polyurethane±cement, it is very difficult to remove gas bubbles and to prevent their formation. One important measure is not to apply such flooring when room temperature is increasing. 9.2.3 Jointing Ceramic tile jointing A jointing material should completely fill the gap between to ceramic tiles right up to the top edge of the tile as shown on Fig. 9.1. This is often not done
172
Handbook of hygiene control in the food industry
Fig. 9.1
Unhygienic and hygienic jointing.
although it is technically possible. The gap must be as small as possible and applicators must wait (for instance around 1 to 2 hours at 18±20 ëC for an epoxy grouting), so that the grout has begun to cure, before the first cleaning of the floor. The jointing material has to absorb dimensional variations of tiles. That is why the better tolerance dimensions of pressed tiles, allow a joint around 5± 7 mm wide instead of 6±10 mm for extruded tiles. The smallest joints may be obtained when ceramic tiles are laid in a synthetic resin bed and then subjected to vibration. However, it is not advisable to have joints smaller than 5 mm because it will be impossible to fill them down to the bottom, as tiles for industrial purpose are thick. A high diversity of grouting products is available (epoxy, vinyl ester, etc.) and descriptions of all of them are not possible here. The choice of system is governed by the chemical stresses expected on the floor surface. Cement grouts are not suitable for food processing areas because they are highly porous, acid sensitive and have a poor durability when subjected to mechanical stresses. In addition, a simple epoxy grouting will not resist the acidic conditions of some food factories such as dairy factories and an anti-acid grouting must be chosen. Other joints Among all the joints necessary in the construction of floors are: construction or day joints, expansion joints, movement joints, and isolation joints. All the joints in the subfloor or floor base should be carried through overlay material and filled with a suitable sealant. Joint fillers have to be flexible and are therefore not as capable of withstanding heavy loads or aggressive chemical as the adjacent floor finish. They must be changed when worn.
Improving the design of floors
9.3
173
Requirements for flooring materials
9.3.1 Slip resistance In France and the UK, with little variation from year to year, around 20% of all workplace injuries leading to working days lost are caused by falls on the same level (slips, trips, etc.). This cause of injuries ranks second after accidents during manual handling. These injuries are also responsible for 20% of all working days lost, 20% of accidents leading to a permanent incapacity to work and 2% of the fatal injuries (Leclercq and Tissot, 2004). A high risk of slipping exists in the food industry because wet and/or greasy floors are frequent, especially where meat is processed. In slaughterhouses, slipping is the cause of 16% of occupational accidents. In order to decrease slipping accidents, anti-slip floors are necessary. Wearing anti-slip footwear is also necessary but not sufficient and, as for all risks at work, collective measures against accidents must always be taken before individual measures. Unfortunately, anti-slip properties of floors are obtained by increasing surface roughness, while smooth flooring materials, supposed to be the more cleanable ones, are therefore not appropriate. By contrast, efficient cleaning of the floors is necessary to decrease both their slipperiness and their microbial load. Regulation According to the European Directive 89/391/EEC employers are responsible for implementing a process of prevention of accidents and other work-related health problems based on nine principles. This process of prevention is based on a hazard assessment. The hazards that cannot be avoided must be evaluated (principle 2), and must be combated at source (principle 3). Collective protective measures must be taken before individual protective measures (principle 8). Appropriate information must be given to employees (principle 9). For instance, an effective cleaning procedure to remove greasy soil and to obtain the correct durability of the floors must be known by employees. Employees must also be instructed not to run. Surface texture There is a general awareness that smooth floor surfaces are slippery, especially when wet and/or greasy, and that rougher surfaces are safer, but it is only in the past two decades that scientific research has been conducted on the impact of roughness on underfoot friction (Chang et al., 2001). GroÈnqvist et al. (1990, 1992) proposed three roughness factors that seemed to determine the anti-slip resistance of contaminated floors and footwear: (1) the macroscopic structure (e.g. profile asperities); (2) the microscopic roughness (e.g. Ra, the arithmetic mean roughness) and (3) the microscopic porosity of the floor. Harris and Shaw (1988) from the Health and Safety Executive (UK) proposed the Rz (previously called RTM) which is the average of the single peak-to-valley heights of five adjoining sampling lengths. Rz can be measured by a portable and inexpensive profilometer. For this reason, it is appreciated for measurement of roughness in
174
Handbook of hygiene control in the food industry
the field (Chang et al., 2001). More recently, the roughness peak height, also called mean levelling depth, Rpm, which is the mean value of the levelling depths of five consecutive sampling lengths, became the preferred roughness parameter of the Health and Safety Executive (Anon, 1999) and of Chang and Matz (2000), cited by Chang et al. (2001). 9.3.2 Hygiene As written in the introduction paragraph, flooring materials may be a reservoir of microorganisms. The pathogen Listeria monocytogenes, which is frequently found on floors, can even become persistent in food industry premises (Giovannacci et al., 1999; Miettinen et al., 1999; Chasseignaux et al. 2001). Lawrence and Gilmour (1995), using RAPD (random amplified polymorphic DNA) and multilocus enzyme electrophoresis as typing methods, found two coexisting L. monocytogenes types widespread on food contact surfaces, floors and drains during an extended period. These bacterial types were also found in the cooked poultry products for at least one year. This highlights the potential for persistent strains to cross-contaminate processed foods. Regulation In the European Directive 93/43/EEC, it is stipulated that floor surfaces must be maintained in a sound condition and they must be easy to clean and, where necessary, disinfect. This will require the use of impervious, non absorbent, washable and non-toxic materials and require a smooth surface up to a height appropriate for operations unless business operators can satisfy the competent authority that other materials used are appropriate. European regulations will replace the European Directive 93/43/EEC and many sector-specific Directives on foods of animal origin. They will be applicable as of 1 January 2006. The text concerning floor in the 852/2004 regulation is very similar: floor surfaces are to be maintained in a sound condition and they must be easy to clean and, where necessary, disinfect. This will require the use of impervious, non-absorbent, washable and non-toxic materials unless food business operators can satisfy the competent authority that other materials used are appropriate. Where appropriate, floors are to allow adequate surface drainage. Surface texture The study by Mettler and Carpentier (1999) on the impact of surface texture on the hygienic properties of flooring materials showed that gas bubble holes, which are frequently found on resin-based flooring materials, are not cleanable (Fig. 9.2). Indeed a smooth polyurethane-based flooring material containing
Improving the design of floors
Fig. 9.2
175
Cross-section of a resin-based flooring material showing gas bubble holes.
many gas bubble holes appears to be, after cleaning, the most contaminated material of those having been inserted in the floor of a cheese-processing site. Furthermore, a significant linear correlation was observed between the number of spherical holes and the cleanability as assessed by a laboratory test. Masurovsky and Jordan (1958) and Holah and Thorpe (1990) have also observed that surfaces which at first glance appeared to have a readily cleanable, smooth surface but were, however, very difficult to clean, were precisely characterised by the presence of small holes when surfaces were examined in more detail. These crevices do not give any slip resistance and are therefore very undesirable. The easiest way to detect such a defect is to observe the material under a stereomicroscope (Fig. 9.3) at 40 magnification. The observation allows also seeing cracks often found around aggregates, holes left by removed aggregates, `spongy' aggregates, very deep crevices and other texture defaults. Under the stereomicroscope, it is also interesting to test with a simple metallic point the anchorage of the aggregates. If they are easily removed by manual handling of the metallic point, it means that they will be easily removed when subjected to the `in-house' mechanical stresses. Such flooring will not maintain their slip resistance and will be difficult to clean. Around 50% of the flooring materials (resin-based or ceramic tiles) received at our laboratory presented such obvious texture defaults visible under the stereomicroscope. Unfortunately, observations are not measurements and in some case, there may be some difficulty in interpretation. In order to reject or accept a flooring material for a food processing area, it is proposed that the observation should be done by at least three trained persons, who should all reach the same conclusion. Roughness measurement at the microscopic level could be a way to further characterise material cleanability. Mettler and Carpentier (1999) explored
176
Handbook of hygiene control in the food industry
Fig. 9.3
Stereomicroscope for viewing texture defaults.
different roughness parameters at two cut-off wavelengths (2.5 and 0.8 mm) and looked for correlations between those parameters or combinations of parameters and the contaminations that remained after cleaning of six flooring materials inserted for four weeks in a cheese processing site. Asperities taken into account by parameters calculated with the cut-off wavelength of 2.5 mm gave lower correlations, suggesting that there is a threshold value for the diameter of asperities under which the soil is not removed by the mechanical action of the hygiene procedure. This corroborates the finding of Taylor and Holah (1996), who observed that the gross topographic irregularities of floor were not responsible for their cleanability performance. The Mettler and Carpentier study showed that Rvk, the reduced valley depth that characterises the depth of the inwardly directed portion of the surface profile, was a better parameter than Ra. As slip resistance is supposed to be linked with other roughness parameters, it should be possible to select cleanable materials with high slip resistance.
Improving the design of floors
177
Connection between floors and walls In the past, it was mandatory in France to have a rounded angle between floors and walls. For this purpose, rounded angle pieces were sometime just stuck at the connection between floors and walls. Most of the time humidity and soil were able to reach the back part of such pieces, which rapidly became highly contaminated. Now it is necessary to have cleanable sealed junctions between floors and walls. For resin-based flooring or polymer cementitious systems, it is possible to construct a rounded angle with the same material as the one used for the flooring. In addition, ceramic rounded baseboards may be used; they must be sealed in the wall and in the floor in the same way tiles are sealed, using a correct jointing material. Cleaning and disinfection of floors Efficient and frequent cleaning and disinfection operations are necessary to prevent microbial contamination reaching a high level. Between two hygiene operations, the floors should be, if possible, maintained in a dry state. Cold is a common way to decrease growth rate of bacteria, but dryness is also a good measure. All the ways used to decrease relative humidity, water spills, water drop and condensation are good. For instance, flooring must be sloped properly to allow water to drain out; the slopes of the floors must be around 1.5±2% depending on the length of fall. It is also advisable to have cleanable stainless steel drains in the middle of the rooms, so the distance for water to drain is short. The water used for the cleaning and disinfection operations may be highly contaminated with, for instance, Pseudomonas species. Microorganisms transported from inert surfaces of the food processing area may contaminate ends of the ducts used for cleaning (spray nozzle, hose). It has been shown that a Pseudomonas putida organism was able to spread by 40 cm within 8 days, i.e. 5 cm per day, upwards in a fixed and straight up duct (GagnieÁre et al., 2004). To prevent such a contamination the end of the water ducts should be immersed in a disinfectant solution between two hygiene operations. Floor and jointing material suppliers must give information to the end-users about the compatibility of their products with detergents and disinfectants. For instance, acrylic modified cementitious systems do not tolerate any acidic products. Acidic products attack those floorings so that they return to the colour of the new ones but with formation of crevices that are uncleanable. It is also necessary to have information on the compatibility between chemical products that may accidentally spill on the floor, such as peracetic acid or hydrogen peroxide, which are highly corrosive products. As flooring materials must be rough to increase their slip resistance they are, of course, not as easy to clean as really smooth materials. An efficient mechanical action is necessary. Using a squeegee cannot be considered as a mechanical action; furthermore, squeegees may be highly contaminated and if they are used to remove excess water, they must be immersed in a disinfecting solution after use. Scrubber brushes or pressure water jets (the use of the latter is no longer recommended because they produce more contaminated aerosols and
178
Handbook of hygiene control in the food industry
water droplets than scrubber brushes) are necessary. Of course, brushes must be clean before use and be soft enough not to damage the floors. 9.3.3 Performance requirements It is necessary to have a durable floor adapted to the effective service characteristics of the food processing area. The main constraints are: mechanical shocks, heavy weight, pressure jet, chemical agents, thermal shocks, wear, shifting and rolling. Falls of heavy objects, knives and other sharp objects may lead to cracks in the floor. Cracks allow water to infiltrate under the floor, which will progressively detach from the substrate. A high thickness of the floor is necessary to reach a good resistance to mechanical shocks and to thermal shocks. The smallest acceptable thickness depends of the size of the aggregates. For a resin-based floor, 3 mm appears to be a minimum but a thickness of 5 mm is strongly recommended. It is of course difficult to know the thickness of a resin-based floor when the application is finished. That is why it is strongly recommended to check whether the right quantity of ingredients has been used by counting the number of bags used at the end of the application. In the case of litigation, core borings may be performed to check the minimum and mean thickness announced. Ceramic tile resistance to thermal and mechanical shocks is higher when the ratio area/thickness is small. The thickness of ceramic tiles adapted for food processing areas ranges from around 8.5 to 20 mm, but for industrial premises with high traffic load a minimum of 12 mm is recommended. Chemical constraints are essentially linked to the food processed and to the cleaning and disinfecting products used on the flooring materials, but also to the equipment. Sugar, butter, whey and milk products, blood and urine are substrates for microorganisms present on flooring materials. Cleaning and disinfection do not remove or inactivate all microorganisms (Mettler and Carpentier, 1998). Their metabolism leads to the formation of very aggressive acid, e.g. lactic acid formed by lactic acid bacteria. Flooring materials also have to withstand cleaning products such as alkaline, chlorinated-alkaline and acid products (when mineral soil has to be removed) and disinfectants. Peracetic acid and hydrogen peroxide, frequently used to disinfect equipment, are very corrosive and can accidentally spill on the floor.
9.4
Test methods
9.4.1 Slip resistance `Over 70 machines have been invented to measure slip resistance (Strandberg, 1985), none of them accurately represents the motion of a human foot and at present, there is no generally accepted method of measuring slipperiness' (Chang et al., 2001). The diversity of methods used at present leads to different, sometimes contradictory, floor classifications (Tisserand et al., 1995). This is why it is so difficult to select a method to produce a European standard. It is well
Improving the design of floors
179
recognised that to prevent slipping accidents it is necessary to use two complementary methods for assessment of the slip-resistance of floors in the laboratory and in the field (Leclercq et al., 1994). Among the numerous laboratory methods to compare new surfaces are the ramp test and tests based on the evaluation of a coefficient of dynamic friction between an oiled surface and an elastomer (as the one chosen by the French National Institute of Research and Safety). The ramp test (German standards) is conducted by two people. They each in turn face downhill with an upright posture, and walk forwards and backwards on the floor surface. During the test, the test person gradually increases the gradient of the floor surface until an (acceptance) angle is reached where the test person either slips or becomes so insecure as to refuse to continue the test. To assess slip resistance in the field where surfaces are often worn and soiled, the French National Institute of Research and Safety uses a portable device developed in Sweden by Ohlsson, called the portable friction tester (PFT). It is based on the continuous evaluation of a coefficient of dynamic friction over a variable distance between the surface to be tested and an elastomer. 9.4.2 Hygiene The European Hygiene Engineering and Design Group (EHEDG) Tests Method Subgroup is about to produce a guideline document on the testing of the hygienic qualities of flooring materials. Two test methods are proposed: a surface water absorption test and a cleanability test. The surface water absorption test is based on a test derived from the National Swedish Institute for Materials Testing, Test Regulation CP-BM-2/67-2 (Determination of water transmission under pressure) as described by Taylor and Holah (1996). The method involves sealing a container onto the floor sample and filling it with water to a depth of 10 cm. After 24 h the level of water is examined to see if there has been any absorption into the surface. Ten samples are assessed and all should pass the test (zero absorption) for the surface material to be deemed suitable for use in food factories with respect to water absorption. This test is designed to assess the uptake of large quantities of water (millilitres) into very porous materials. It is not intended to assess the small water absorption of the whole material. This is measured by weighting floor test plates (resin-based) or whole ceramic tiles before and after having been immersed in boiling water for 2 hours. The second test, a cleanability test, is based on the method used by Mettler and Carpentier (1999). Results of the latter study showed that contamination after cleaning of flooring materials inserted in the floor of a cheese site was linked to their cleanability and not to their disinfectability. That is why a tracer of the microbial soil (a biofilm), spores of Geobacillus stearothermophilus, which are not sensitive to alkaline cleaning products, are used to assess the removal of the biofilm. One-day biofilms of Pseudomonas fluorescens containing spores of Geobacillus stearothermophilus are developed on test
180
Handbook of hygiene control in the food industry
Fig. 9.4 The Gardner washability machine adapted to perform a cleanability test on 4 2.5 cm2 test plates.
plates and subjected to a mild cleaning. The latter consists of a submersion in a 0.01M solution of NaOH followed by a mechanical action provided by 37 reciprocal movements of a scouring pad moved over the plate surface by a Gardner washability machine (Fig. 9.4). After rinsing, residual spores are detached by sonication and counted after growth on Shapton and Hindes agar. Based on the residual spores counts on the test plates and on plates of the control material, flooring materials are classified as more, as or less cleanable than the control material. This test is not intended to accept or reject a flooring material. Only the presence of crevices, cracks or gas bubble holes, etc., observed under a stereomicroscope is considered a criterion to reject a flooring material. 9.4.3 Material resistance European standardised test methods in accordance with the Construction Products Directive 89/106 EEC have been produced by the CEN committees `Floor screeds and in-situ floorings in buildings' (TC 303) and `Ceramic tiles' (TC 67) to assess the flooring products or the system's performance.
9.5
Construction of floors
The recommendations needed for the construction of a floor are not provided. For this subject see the sources of further information below. It can be very useful to use questionnaires to check for all the points that need to be examined before choosing a flooring material and before beginning construction. Such questionnaires can be found in the French `Guide des reveÃtements de sol' from
Improving the design of floors
181
the Caisse nationale d'assurance maladie des travailleurs salarieÂs (Liot et al., 1998) or in the British `Guidelines for the design and construction of floors for food production area' (Timperley, 2002). The time necessary for the construction of a floor encompasses preparation of the subfloor, time for application and time to full cure. End-users often ask for a rapid construction and particularly for a possibility of rapid repair or rapid refurbishment. This decreases the choice of flooring material but, unfortunately, some applicators reduce the construction time at the expense of the quality. In addition, for most resin-based floors, the right relative humidity, temperature and humidity of the substrate are to be respected to obtain a good final product. That is why it is of prime importance to choose a qualified company with trained employees.
9.6
Future trends
Two of the most important future trends should be a better respect of the state of the art when applying flooring materials and the systematic checking to ensure the absence of gas bubble holes and other texture defaults. The suppliers of resin-based flooring systems are continuously innovating to formulate improved products. However, those new formulations are trade secrets. The AFFAR (the French association of formulators and applicators of resin-based floors) has announced new resin-based floors able to withstand high temperature (more than 100 ëC) and others that are able to adhere to wet substrate with short curing times. Among other possible trends is antimicrobial flooring. Although some few suppliers propose antimicrobial resin-based floorings, no antimicrobial effect has ever been demonstrated in such floorings, to our knowledge. Only PVC floorings, which are not considered suitable for food processing areas (see above), and which all contain an antimicrobial product because PVC is a substrate for fungal microorganisms, have a proven antimicrobial effect (Carpentier, unpublished results). Anyway, if antimicrobial resin-based flooring could ever exist, it would have to be cleaned and disinfected as other floors. Indeed, antimicrobial material may reduce microbial contamination when wet, but cleaning and disinfection allow for further decrease of surface microbial contamination. The application of ceramic tiles in resin bed is increasing, especially in the dairy industry. It allows withstanding higher variation of temperature, humidity, etc. and smaller joints.
9.7
Sources of further information and advice
9.7.1 Slip-resistance and accidents at work · European Agency for Safety and Health at Work: http://europe.osha.eu.int/. This website provides statistics of accidents at work in the EU.
182
Handbook of hygiene control in the food industry
· Health and Safety Executive (UK): a paper from Richard Morgan giving the priorities in the food and drink industry may be downloaded from http:// www.east-anglian-fishnet.org.uk/docs/oct99.rtf · An information sheet updates HSE booklet `Slips and trips ± Guidance for the food processing industry' with consideration of the roughness parameter Rpm impact on slip resistance of flooring materials: Food sheet no. 22: http:// www.hse.gov.uk/pubns/fis22.pdf
9.7.2 Resin-based flooring · EFNARC (European Federation of producers and applicators of Specialist Products for Structures) was founded in March 1989 as the European Federation of national trade associations representing producers and applicators of specialist building products. Two interesting documents are available at their website: `Specification and guidelines for synthetic resin flooring' and `Specification and guidelines for polymer-modified cementitious flooring as wearing surfaces for industrial and commercial use'. A free downloadable pdf copy of those guides is available from http:// www.efnarc.org/efnarc/publications.htm · A French written document of Pollet (2000) from the Scientific and Technical Center for Construction (CSTC) (http://www.cstc.be, website in French and Flemish, English is in preparation): `Les sols industriels aÁ base de reÂsine reÂactive' (technical note 216) give some information on resin-based floors, description of tests to assess their performances, recommendations on joints and construction and help in choosing an industrial flooring system. · AFFAR, the French association of formulators and applicators of resin-based floors has a website (French only) http://www.affar.asso.fr with information on the new technologies, help in choosing the right resin-based flooring, etc.
9.8
References
(1999), `Preventing slips in the food and drink industries-technical update on floors specifications', Health and Safety Executive information sheet: Food sheet no. 22. HSE Books, Sudbury. ANON (2001a), `Specification and guidelines for polymer-modified cementitious flooring as wearing surfaces for industrial and commercial use', EFNARC (European Federation of producers and applicators of Specialist Products for Structures), Farnham. ANON (2001b), `Specification and guidelines for synthetic resin flooring', EFNARC (European Federation of producers and applicators of Specialist Products for Structures), Farnham. CHANG W-R and MATZ S (2000), `The effect of filtering processes on surface roughness parameters and their correlation with the measured friction, Part I: Quarry tiles', Safety Sciences, 36, 19±33. CHANG W-R, KIM I-J, MANNING D P and BUNTERNGCHIT Y (2001), `The role of surface ANON
Improving the design of floors
183
roughness in the measurement of slipperiness', Ergonomics, 44, 1200±1216. and ERMEL G (2001), `Molecular epidemiology of Listeria monocytogenes isolates collected from the environment, raw meat and raw products in two poultry- and pork-processing plants', Journal of Applied Microbiology, 91, 888±899. COX LJ, KLEISS T, CORDIER JL, CORDELLANA C, KONKEL P, PEDRAZZINI C, BEURNER R and SIEBENGA A (1989), `Listeria spp. in food processing, non food and domestic environments', Food Microbiology, 6, 49±61. GAGNIEÁRE S, AUVRAY F. and CARPENTIER B (2004), `Vitesse de progression d'un Pseudomonas putida Gfp+ dans une conduite contamineÂe par un aeÂrosol', Poster presented at the National Congress of the French Society for Microbiology, Bordeaux (France), 10±12 May. GIOVANNACCI I, RAGIMBEAU C, QUEGUINER S, SALVAT G, VENDEUVRE JL, CARLIER V and ERMEL G (1999), `Listeria monocytogenes in pork slaughtering and cutting plants use of RAPD, PFGE and PCR-REA for tracing and molecular epidemiology', International Journal of Food Microbiology, 53, 127±140. È NQVIST, R, ROINE, J, KORHONEN, E and RAHIKAINEN, A (1990), `Slip resistance versus GRO surface roughness of deck and other underfoot surfaces in ships', Journal of Occupational Accidents, 13, 291±302. È NQVIST, R, HIRVONEN, M and SKYTT, E (1992), `Countermeasures against floor GRO slipperiness in the food industry', Advances in Industrial Ergonomics and Safety, IV, 989±996. HARRIS, GW and SHAW, SR (1988), `Slip resistance of floors: users' opinions, Tortus instrument readings and roughness measurement', Journal of Occupational Accidents, 9, 287±298. HOLAH JT and THORPE RH (1990), `Cleanability in relation to bacterial retention on unused and abraded domestic sink materials', Journal of Applied Bacteriology, 69, 599± 608. HOLAH JT, TIMPERLEY AW and HOLDER JS (1990), `The spread of Listeria by cleaning systems', Technical memorandum 590. The Campden Food and Drink Research Association, Chipping Campden. LAWRENCE LM and GILMOUR A (1995), `Characterization of Listeria monocytogenes isolated from poultry products and from the poultry-processing environment by random amplification of polymorphic DNA and multilocus enzyme electrophoresis', Applied Environmental Microbiology, 61, 2139±2144. LECLERCQ S and TISSOT C (2004), `Les chutes de plain-pied en situation professionnelle', INRS ± HygieÁne et seÂcurite au travail-Cahiers de notes documentaires, 194, 51± 66. LECLERCQ S, TISSERAND M and SAULNIER H (1994), `Assessment of the slip resistance of floors in the laboratory and in the field: two complementary methods for two applications', International Journal of Industrial Ergonomics, 13, 297±305. LIOT J-P, CARPENTIER B, LECONTE A.-M, FAU G, VETTER F and SAULNIER H (1998), `Guide des reveÃtements de sol reÂpondant aux criteÁres `HygieÁne ± SeÂcurite ± Aptitude aÁ l'utilisation' pour les locaux de fabrication de produits alimentaires', Caisse nationale d'assurance maladie des travailleurs salarieÂs (CNAMTS), Direction des risques professionnels, Paris. MASUROVSKY EB and JORDAN WK (1958), `Studies on the relative bacterial cleanability of milk-contact surfaces', Journal of Dairy Science, 41, 1342±1358. METTLER E and CARPENTIER B (1998), `Variations over time of microbial load and CHASSEIGNAUX E, TOQUIN MT, RAGIMBEAU C, SALVAT G, COLIN P
184
Handbook of hygiene control in the food industry
physico-chemical properties of floor materials after cleaning in food industry premises', Journal of Food Protection, 61, 57±65. METTLER E and CARPENTIER B (1999), `Hygienic quality of floors in relation to surface texture', Transaction of the Institute of Chemical Engineers, 77, 90±95. È RKROTH KJ and KORKEALA HJ (1999), `Characterization of Listeria MIETTINEN MK, BJO monocytogenes from an ice cream plant by serotyping and pulsed field gel electrophoresis', International Journal of Food Microbiology, 46, 187±192. NELSON JH (1990), `Where are Listeria likely to be found in dairy plants?', Dairy, Food and Environmental Sanitation, 10, 344±345. POLLET V (2000), `Les sols industriels aÁ base de reÂsine reÂactive. Note d'information technique 216', Centre scientifique et technique de la construction. Bruxelles (Belgium). STRANDBERG L (1985), `The effect of conditions underfoot on falling and overexertion accidents', Ergonomics, 28, 131±147. TAYLOR JH and HOLAH JT (1996), `A comparative evaluation with respect to the bacterial cleanability of a range of wall and floor surface materials used in the food industry', Journal of Applied Bacteriology, 81, 262±266. TIMPERLEY A (2002), Guidelines for the design of floors for food production areas (second edition), Guideline no. 40. Campden and Chorleywood Food Research Association Group, Chipping Campden. TISSERAND M, LECLERCQ S and SAULNIER H (1995), `Exigence pour une norme de mesure de la glissance des sols', Cahiers de notes documentaires, 159, 191±198.
9.1
Introduction
We will here mainly consider the design of floors intended for greasy and/or wet food processing areas where they have to fulfil many requirements to be suitable. Because flooring materials are not food contact surfaces, some may consider that flooring materials are not of paramount importance to obtain the best microbial quality of food product. However, all cleaning systems disperse viable microorganisms in both water droplets and aerosols (Holah et al., 1990), allowing microorganisms to reach food and food contact surfaces. As slipping is one of the main causes of accidents at work, flooring materials need to be rough. Add to these the fact that gravity carries most of the soiling and microorganisms down, and it can be seen why flooring materials are usually more microbiologically contaminated than other inert surfaces of food processing premises. Finally, floors are places where Listeria monocytogenes is very likely to be found (Cox et al., 1989; Nelson, 1990). For all these reasons, great attention should be given to the choice and then to the application of a flooring material. The aim of this chapter is to give non-specialists some explanations of what the flooring materials for food processing premises are and to describe what properties are suitable for food processing areas.
9.2
What are floors made of?
9.2.1 The substrate The material that supports flooring, called the substrate or the floor base, has a great impact on the quality of the flooring material. It is either an existing one,
Improving the design of floors
169
which has to be properly prepared, or a new one, which has to be properly constructed and prepared before applying the flooring in order to allow a good adherence of the latter. It must be dry (a concrete slab must be let to dry for a minimum of 28 days but this time may be far greater if climatic conditions are not optimal) and able to prevent humidity reaching the impervious flooring. It must be capable of withstanding all structural, thermal and mechanical stresses and loads that will occur during service and it must be sloped sufficiently in order for liquids to flow to the drains. This is recommended for resin-based floors as well as for ceramic tiles, even though, traditionally, ceramic tiles are applied on a flat substrate, the slope being given by the screed. Particular attention must be given to joints that are an integral part of the floor system. Nevertheless, it is not the purpose here to detail all the construction rules regarding the substrate. For further information see Timperley (2002). 9.2.2 Flooring Two families of flooring materials are recommended for food processing areas: ceramic tiles and resin-based floors. Polyvinyl chloride (PVC) sheets are considered unsuitable because they are too easily worn. They can become cracked after the fall of a knife or other sharp object. Ceramic tiles Ceramic tiles are made of clay that after shaping is subjected to high temperature. They are manufactured products of constant quality and have been produced for centuries. Vitrified unglazed ceramic tiles are recommended for food processing areas. They are highly resistant to the main constraints that can be encountered in food processing premises, especially to heat shocks. The vitrified tiles can either be pressed (in which case they are usually square or hexagonal) or extruded (they are always rectangular). Dimension tolerances of the pressed tiles are better than those of extruded ones, allowing thinner joints. Resin-based flooring materials The first resin-based flooring, the acrylic cementitious systems, appeared in food industry premises during the 1960s and around two decades later synthetic resin flooring was also proposed, with the prospect of achieving a high standard of hygiene because those floorings are seamless. However, a high degree of technical skill is necessary to obtain in situ a good final product (only to be applied by a trained operative). As this has not always been respected, there have been many problems with such floors. Resin-based floors are obtained by application of a mortar made of a mix of one or more organic or inorganic binders, aggregates, fillers and additives, and/ or admixture, and can be classified according to the nature of the binder(s) used. There are two families of binders: synthetic resins and the hydraulic binders. The first ones are organic polymers comprising one or more components that
170
Handbook of hygiene control in the food industry
react with a hardener at ambient temperature, whereas the hydraulic binders, as cement or lime, need water to harden. Hydraulic binder The hydraulic binder used in the construction of flooring material is cement. The main drawback of the use of hydraulic binders is the high porosity due to water evaporation during hardening. The addition of a synthetic polymer reduces porosity, increases the mechanical resistance and reduces cracking risk. Cement can be used in polymer-modified cementitious screed that is defined as a `screed where the binder is a hydraulic cement and which is modified by the addition of polymer dispersion or re-dispersible powder polymer with a minimum content of dry polymer of 1% by mass of the total composition, excluding aggregate particles larger than 5 mm' (Anon, 2001a). Examples are the acrylic-modified cementitious systems that are the main systems used in the meat industry in France. The main and great advantage of such floorings is that they can be applied onto a damp substrate. Cement is also used in association with resins, such as epoxy resin and polyurethane. In those cases, resin content is around 5% by mass of the total composition. In such floors, cement is more a filler than a binder, which is why they are considered to belong to the synthetic resins family. Synthetic resins Epoxy resins are the more frequently used synthetic binders, followed by polyurethane and methacrylate resins. Polyester resins are seldom used, to the author's knowledge, in the food industry. Characteristics of the different resins change according to the formulation used. The formulation may be changed to adapt to such non-optimal installation conditions as temperature, relative humidity or time available prior to being put into service. Specific formulations proposed may have consequences on the resistance of the final product. It is therefore difficult to give precise rules on curing. The final floor system must be allowed to cure according to the manufacturer's instructions. These generally require 1±3 days at 15±20 ëC before trafficking and 3±7 days before washing, before contact with chemicals or before any ponding tests and high traffic loads (Anon, 2001b). The only resin that clearly escapes this general rule is polymethylmethacrylate (PMMA), also called methacrylate or methylmethacrylate. It is characterised by a very short time prior to putting in service: 2 hours. It can be applied at low temperature (ÿ10 ëC). However, this resin possesses a strong odour at installation that can irreversibly alter food products present nearby. The climate above the uncured resin should be maintained at least 3 ëC above the dew point. The substrate humidity must also be correct. It must, for instance, be smaller than 3% for an epoxy resin, or 7% for polyurethane±cement flooring. Aggregates Aggregates are granular materials that do not contribute to the hardening reaction of the mortar. Roles of aggregate depend on their size and abrasion
Improving the design of floors
171
resistance. Small aggregates that may be called fillers have many roles. Among those are reducing shrinkage and increasing the mechanical resistance. Such aggregates are often made of sand with high silica content (SiO2 or quartz, 7 on the Mohs scale). Hard aggregates are used to increase resistance to abrasion. Those may be aluminium oxide (Al2O3 or corundum, 9 on the Mohs scale), silicon carbide (SiC, commercial name carborundum, 9.5 on the Mohs scale). It may happen that hard aggregates lead to an accelerated wear of shoes and of brushes used for cleaning. Large aggregates are used to increase slip resistance. Primer A primer (one or two coats) is most generally used to aid the adhesion of the final flooring and to seal and consolidate the surface of a porous substrate. It consists of a liquid product, which is often a solvent-based epoxy, applied to a substrate. Coats Anti-slip resin-based floorings can be obtained by one-coat or multicoat systems. Multicoat systems that are the more frequently proposed are thin flooring (2±5 mm) made of a self-levelling mortar on which large aggregates are sprinkled. One or two coats and then one or two finishing coats can be applied. These finishing coats are very thin, which is why they have a poor durability (1 or 2 years). Such finishing coats can be interesting when they fill the bubble gas holes but their role should not be to maintain large aggregates necessary to slip resistance. One-coat systems, also called monolithic systems, are made of mortar in which all the aggregates are mixed prior to application. The maximum diameter of the aggregates must be smaller than the third of the flooring thickness (Pollet, 2000). They are thicker (4±12 mm) and the large aggregates necessary to obtain slip resistance are often better maintained. Gas removal Gas bubble holes are highly undesirable for hygienic considerations (see below). Surface-active agents can be added to avoid or decrease their formation during polymerisation of resin-based floors. There is also prickle roller, called heÂrisson in French (hedgehog), that is used when the mortar is in the fresh state to release entrapped gas bubbles. In some flooring, such as polyurethane±cement, it is very difficult to remove gas bubbles and to prevent their formation. One important measure is not to apply such flooring when room temperature is increasing. 9.2.3 Jointing Ceramic tile jointing A jointing material should completely fill the gap between to ceramic tiles right up to the top edge of the tile as shown on Fig. 9.1. This is often not done
172
Handbook of hygiene control in the food industry
Fig. 9.1
Unhygienic and hygienic jointing.
although it is technically possible. The gap must be as small as possible and applicators must wait (for instance around 1 to 2 hours at 18±20 ëC for an epoxy grouting), so that the grout has begun to cure, before the first cleaning of the floor. The jointing material has to absorb dimensional variations of tiles. That is why the better tolerance dimensions of pressed tiles, allow a joint around 5± 7 mm wide instead of 6±10 mm for extruded tiles. The smallest joints may be obtained when ceramic tiles are laid in a synthetic resin bed and then subjected to vibration. However, it is not advisable to have joints smaller than 5 mm because it will be impossible to fill them down to the bottom, as tiles for industrial purpose are thick. A high diversity of grouting products is available (epoxy, vinyl ester, etc.) and descriptions of all of them are not possible here. The choice of system is governed by the chemical stresses expected on the floor surface. Cement grouts are not suitable for food processing areas because they are highly porous, acid sensitive and have a poor durability when subjected to mechanical stresses. In addition, a simple epoxy grouting will not resist the acidic conditions of some food factories such as dairy factories and an anti-acid grouting must be chosen. Other joints Among all the joints necessary in the construction of floors are: construction or day joints, expansion joints, movement joints, and isolation joints. All the joints in the subfloor or floor base should be carried through overlay material and filled with a suitable sealant. Joint fillers have to be flexible and are therefore not as capable of withstanding heavy loads or aggressive chemical as the adjacent floor finish. They must be changed when worn.
Improving the design of floors
9.3
173
Requirements for flooring materials
9.3.1 Slip resistance In France and the UK, with little variation from year to year, around 20% of all workplace injuries leading to working days lost are caused by falls on the same level (slips, trips, etc.). This cause of injuries ranks second after accidents during manual handling. These injuries are also responsible for 20% of all working days lost, 20% of accidents leading to a permanent incapacity to work and 2% of the fatal injuries (Leclercq and Tissot, 2004). A high risk of slipping exists in the food industry because wet and/or greasy floors are frequent, especially where meat is processed. In slaughterhouses, slipping is the cause of 16% of occupational accidents. In order to decrease slipping accidents, anti-slip floors are necessary. Wearing anti-slip footwear is also necessary but not sufficient and, as for all risks at work, collective measures against accidents must always be taken before individual measures. Unfortunately, anti-slip properties of floors are obtained by increasing surface roughness, while smooth flooring materials, supposed to be the more cleanable ones, are therefore not appropriate. By contrast, efficient cleaning of the floors is necessary to decrease both their slipperiness and their microbial load. Regulation According to the European Directive 89/391/EEC employers are responsible for implementing a process of prevention of accidents and other work-related health problems based on nine principles. This process of prevention is based on a hazard assessment. The hazards that cannot be avoided must be evaluated (principle 2), and must be combated at source (principle 3). Collective protective measures must be taken before individual protective measures (principle 8). Appropriate information must be given to employees (principle 9). For instance, an effective cleaning procedure to remove greasy soil and to obtain the correct durability of the floors must be known by employees. Employees must also be instructed not to run. Surface texture There is a general awareness that smooth floor surfaces are slippery, especially when wet and/or greasy, and that rougher surfaces are safer, but it is only in the past two decades that scientific research has been conducted on the impact of roughness on underfoot friction (Chang et al., 2001). GroÈnqvist et al. (1990, 1992) proposed three roughness factors that seemed to determine the anti-slip resistance of contaminated floors and footwear: (1) the macroscopic structure (e.g. profile asperities); (2) the microscopic roughness (e.g. Ra, the arithmetic mean roughness) and (3) the microscopic porosity of the floor. Harris and Shaw (1988) from the Health and Safety Executive (UK) proposed the Rz (previously called RTM) which is the average of the single peak-to-valley heights of five adjoining sampling lengths. Rz can be measured by a portable and inexpensive profilometer. For this reason, it is appreciated for measurement of roughness in
174
Handbook of hygiene control in the food industry
the field (Chang et al., 2001). More recently, the roughness peak height, also called mean levelling depth, Rpm, which is the mean value of the levelling depths of five consecutive sampling lengths, became the preferred roughness parameter of the Health and Safety Executive (Anon, 1999) and of Chang and Matz (2000), cited by Chang et al. (2001). 9.3.2 Hygiene As written in the introduction paragraph, flooring materials may be a reservoir of microorganisms. The pathogen Listeria monocytogenes, which is frequently found on floors, can even become persistent in food industry premises (Giovannacci et al., 1999; Miettinen et al., 1999; Chasseignaux et al. 2001). Lawrence and Gilmour (1995), using RAPD (random amplified polymorphic DNA) and multilocus enzyme electrophoresis as typing methods, found two coexisting L. monocytogenes types widespread on food contact surfaces, floors and drains during an extended period. These bacterial types were also found in the cooked poultry products for at least one year. This highlights the potential for persistent strains to cross-contaminate processed foods. Regulation In the European Directive 93/43/EEC, it is stipulated that floor surfaces must be maintained in a sound condition and they must be easy to clean and, where necessary, disinfect. This will require the use of impervious, non absorbent, washable and non-toxic materials and require a smooth surface up to a height appropriate for operations unless business operators can satisfy the competent authority that other materials used are appropriate. European regulations will replace the European Directive 93/43/EEC and many sector-specific Directives on foods of animal origin. They will be applicable as of 1 January 2006. The text concerning floor in the 852/2004 regulation is very similar: floor surfaces are to be maintained in a sound condition and they must be easy to clean and, where necessary, disinfect. This will require the use of impervious, non-absorbent, washable and non-toxic materials unless food business operators can satisfy the competent authority that other materials used are appropriate. Where appropriate, floors are to allow adequate surface drainage. Surface texture The study by Mettler and Carpentier (1999) on the impact of surface texture on the hygienic properties of flooring materials showed that gas bubble holes, which are frequently found on resin-based flooring materials, are not cleanable (Fig. 9.2). Indeed a smooth polyurethane-based flooring material containing
Improving the design of floors
Fig. 9.2
175
Cross-section of a resin-based flooring material showing gas bubble holes.
many gas bubble holes appears to be, after cleaning, the most contaminated material of those having been inserted in the floor of a cheese-processing site. Furthermore, a significant linear correlation was observed between the number of spherical holes and the cleanability as assessed by a laboratory test. Masurovsky and Jordan (1958) and Holah and Thorpe (1990) have also observed that surfaces which at first glance appeared to have a readily cleanable, smooth surface but were, however, very difficult to clean, were precisely characterised by the presence of small holes when surfaces were examined in more detail. These crevices do not give any slip resistance and are therefore very undesirable. The easiest way to detect such a defect is to observe the material under a stereomicroscope (Fig. 9.3) at 40 magnification. The observation allows also seeing cracks often found around aggregates, holes left by removed aggregates, `spongy' aggregates, very deep crevices and other texture defaults. Under the stereomicroscope, it is also interesting to test with a simple metallic point the anchorage of the aggregates. If they are easily removed by manual handling of the metallic point, it means that they will be easily removed when subjected to the `in-house' mechanical stresses. Such flooring will not maintain their slip resistance and will be difficult to clean. Around 50% of the flooring materials (resin-based or ceramic tiles) received at our laboratory presented such obvious texture defaults visible under the stereomicroscope. Unfortunately, observations are not measurements and in some case, there may be some difficulty in interpretation. In order to reject or accept a flooring material for a food processing area, it is proposed that the observation should be done by at least three trained persons, who should all reach the same conclusion. Roughness measurement at the microscopic level could be a way to further characterise material cleanability. Mettler and Carpentier (1999) explored
176
Handbook of hygiene control in the food industry
Fig. 9.3
Stereomicroscope for viewing texture defaults.
different roughness parameters at two cut-off wavelengths (2.5 and 0.8 mm) and looked for correlations between those parameters or combinations of parameters and the contaminations that remained after cleaning of six flooring materials inserted for four weeks in a cheese processing site. Asperities taken into account by parameters calculated with the cut-off wavelength of 2.5 mm gave lower correlations, suggesting that there is a threshold value for the diameter of asperities under which the soil is not removed by the mechanical action of the hygiene procedure. This corroborates the finding of Taylor and Holah (1996), who observed that the gross topographic irregularities of floor were not responsible for their cleanability performance. The Mettler and Carpentier study showed that Rvk, the reduced valley depth that characterises the depth of the inwardly directed portion of the surface profile, was a better parameter than Ra. As slip resistance is supposed to be linked with other roughness parameters, it should be possible to select cleanable materials with high slip resistance.
Improving the design of floors
177
Connection between floors and walls In the past, it was mandatory in France to have a rounded angle between floors and walls. For this purpose, rounded angle pieces were sometime just stuck at the connection between floors and walls. Most of the time humidity and soil were able to reach the back part of such pieces, which rapidly became highly contaminated. Now it is necessary to have cleanable sealed junctions between floors and walls. For resin-based flooring or polymer cementitious systems, it is possible to construct a rounded angle with the same material as the one used for the flooring. In addition, ceramic rounded baseboards may be used; they must be sealed in the wall and in the floor in the same way tiles are sealed, using a correct jointing material. Cleaning and disinfection of floors Efficient and frequent cleaning and disinfection operations are necessary to prevent microbial contamination reaching a high level. Between two hygiene operations, the floors should be, if possible, maintained in a dry state. Cold is a common way to decrease growth rate of bacteria, but dryness is also a good measure. All the ways used to decrease relative humidity, water spills, water drop and condensation are good. For instance, flooring must be sloped properly to allow water to drain out; the slopes of the floors must be around 1.5±2% depending on the length of fall. It is also advisable to have cleanable stainless steel drains in the middle of the rooms, so the distance for water to drain is short. The water used for the cleaning and disinfection operations may be highly contaminated with, for instance, Pseudomonas species. Microorganisms transported from inert surfaces of the food processing area may contaminate ends of the ducts used for cleaning (spray nozzle, hose). It has been shown that a Pseudomonas putida organism was able to spread by 40 cm within 8 days, i.e. 5 cm per day, upwards in a fixed and straight up duct (GagnieÁre et al., 2004). To prevent such a contamination the end of the water ducts should be immersed in a disinfectant solution between two hygiene operations. Floor and jointing material suppliers must give information to the end-users about the compatibility of their products with detergents and disinfectants. For instance, acrylic modified cementitious systems do not tolerate any acidic products. Acidic products attack those floorings so that they return to the colour of the new ones but with formation of crevices that are uncleanable. It is also necessary to have information on the compatibility between chemical products that may accidentally spill on the floor, such as peracetic acid or hydrogen peroxide, which are highly corrosive products. As flooring materials must be rough to increase their slip resistance they are, of course, not as easy to clean as really smooth materials. An efficient mechanical action is necessary. Using a squeegee cannot be considered as a mechanical action; furthermore, squeegees may be highly contaminated and if they are used to remove excess water, they must be immersed in a disinfecting solution after use. Scrubber brushes or pressure water jets (the use of the latter is no longer recommended because they produce more contaminated aerosols and
178
Handbook of hygiene control in the food industry
water droplets than scrubber brushes) are necessary. Of course, brushes must be clean before use and be soft enough not to damage the floors. 9.3.3 Performance requirements It is necessary to have a durable floor adapted to the effective service characteristics of the food processing area. The main constraints are: mechanical shocks, heavy weight, pressure jet, chemical agents, thermal shocks, wear, shifting and rolling. Falls of heavy objects, knives and other sharp objects may lead to cracks in the floor. Cracks allow water to infiltrate under the floor, which will progressively detach from the substrate. A high thickness of the floor is necessary to reach a good resistance to mechanical shocks and to thermal shocks. The smallest acceptable thickness depends of the size of the aggregates. For a resin-based floor, 3 mm appears to be a minimum but a thickness of 5 mm is strongly recommended. It is of course difficult to know the thickness of a resin-based floor when the application is finished. That is why it is strongly recommended to check whether the right quantity of ingredients has been used by counting the number of bags used at the end of the application. In the case of litigation, core borings may be performed to check the minimum and mean thickness announced. Ceramic tile resistance to thermal and mechanical shocks is higher when the ratio area/thickness is small. The thickness of ceramic tiles adapted for food processing areas ranges from around 8.5 to 20 mm, but for industrial premises with high traffic load a minimum of 12 mm is recommended. Chemical constraints are essentially linked to the food processed and to the cleaning and disinfecting products used on the flooring materials, but also to the equipment. Sugar, butter, whey and milk products, blood and urine are substrates for microorganisms present on flooring materials. Cleaning and disinfection do not remove or inactivate all microorganisms (Mettler and Carpentier, 1998). Their metabolism leads to the formation of very aggressive acid, e.g. lactic acid formed by lactic acid bacteria. Flooring materials also have to withstand cleaning products such as alkaline, chlorinated-alkaline and acid products (when mineral soil has to be removed) and disinfectants. Peracetic acid and hydrogen peroxide, frequently used to disinfect equipment, are very corrosive and can accidentally spill on the floor.
9.4
Test methods
9.4.1 Slip resistance `Over 70 machines have been invented to measure slip resistance (Strandberg, 1985), none of them accurately represents the motion of a human foot and at present, there is no generally accepted method of measuring slipperiness' (Chang et al., 2001). The diversity of methods used at present leads to different, sometimes contradictory, floor classifications (Tisserand et al., 1995). This is why it is so difficult to select a method to produce a European standard. It is well
Improving the design of floors
179
recognised that to prevent slipping accidents it is necessary to use two complementary methods for assessment of the slip-resistance of floors in the laboratory and in the field (Leclercq et al., 1994). Among the numerous laboratory methods to compare new surfaces are the ramp test and tests based on the evaluation of a coefficient of dynamic friction between an oiled surface and an elastomer (as the one chosen by the French National Institute of Research and Safety). The ramp test (German standards) is conducted by two people. They each in turn face downhill with an upright posture, and walk forwards and backwards on the floor surface. During the test, the test person gradually increases the gradient of the floor surface until an (acceptance) angle is reached where the test person either slips or becomes so insecure as to refuse to continue the test. To assess slip resistance in the field where surfaces are often worn and soiled, the French National Institute of Research and Safety uses a portable device developed in Sweden by Ohlsson, called the portable friction tester (PFT). It is based on the continuous evaluation of a coefficient of dynamic friction over a variable distance between the surface to be tested and an elastomer. 9.4.2 Hygiene The European Hygiene Engineering and Design Group (EHEDG) Tests Method Subgroup is about to produce a guideline document on the testing of the hygienic qualities of flooring materials. Two test methods are proposed: a surface water absorption test and a cleanability test. The surface water absorption test is based on a test derived from the National Swedish Institute for Materials Testing, Test Regulation CP-BM-2/67-2 (Determination of water transmission under pressure) as described by Taylor and Holah (1996). The method involves sealing a container onto the floor sample and filling it with water to a depth of 10 cm. After 24 h the level of water is examined to see if there has been any absorption into the surface. Ten samples are assessed and all should pass the test (zero absorption) for the surface material to be deemed suitable for use in food factories with respect to water absorption. This test is designed to assess the uptake of large quantities of water (millilitres) into very porous materials. It is not intended to assess the small water absorption of the whole material. This is measured by weighting floor test plates (resin-based) or whole ceramic tiles before and after having been immersed in boiling water for 2 hours. The second test, a cleanability test, is based on the method used by Mettler and Carpentier (1999). Results of the latter study showed that contamination after cleaning of flooring materials inserted in the floor of a cheese site was linked to their cleanability and not to their disinfectability. That is why a tracer of the microbial soil (a biofilm), spores of Geobacillus stearothermophilus, which are not sensitive to alkaline cleaning products, are used to assess the removal of the biofilm. One-day biofilms of Pseudomonas fluorescens containing spores of Geobacillus stearothermophilus are developed on test
180
Handbook of hygiene control in the food industry
Fig. 9.4 The Gardner washability machine adapted to perform a cleanability test on 4 2.5 cm2 test plates.
plates and subjected to a mild cleaning. The latter consists of a submersion in a 0.01M solution of NaOH followed by a mechanical action provided by 37 reciprocal movements of a scouring pad moved over the plate surface by a Gardner washability machine (Fig. 9.4). After rinsing, residual spores are detached by sonication and counted after growth on Shapton and Hindes agar. Based on the residual spores counts on the test plates and on plates of the control material, flooring materials are classified as more, as or less cleanable than the control material. This test is not intended to accept or reject a flooring material. Only the presence of crevices, cracks or gas bubble holes, etc., observed under a stereomicroscope is considered a criterion to reject a flooring material. 9.4.3 Material resistance European standardised test methods in accordance with the Construction Products Directive 89/106 EEC have been produced by the CEN committees `Floor screeds and in-situ floorings in buildings' (TC 303) and `Ceramic tiles' (TC 67) to assess the flooring products or the system's performance.
9.5
Construction of floors
The recommendations needed for the construction of a floor are not provided. For this subject see the sources of further information below. It can be very useful to use questionnaires to check for all the points that need to be examined before choosing a flooring material and before beginning construction. Such questionnaires can be found in the French `Guide des reveÃtements de sol' from
Improving the design of floors
181
the Caisse nationale d'assurance maladie des travailleurs salarieÂs (Liot et al., 1998) or in the British `Guidelines for the design and construction of floors for food production area' (Timperley, 2002). The time necessary for the construction of a floor encompasses preparation of the subfloor, time for application and time to full cure. End-users often ask for a rapid construction and particularly for a possibility of rapid repair or rapid refurbishment. This decreases the choice of flooring material but, unfortunately, some applicators reduce the construction time at the expense of the quality. In addition, for most resin-based floors, the right relative humidity, temperature and humidity of the substrate are to be respected to obtain a good final product. That is why it is of prime importance to choose a qualified company with trained employees.
9.6
Future trends
Two of the most important future trends should be a better respect of the state of the art when applying flooring materials and the systematic checking to ensure the absence of gas bubble holes and other texture defaults. The suppliers of resin-based flooring systems are continuously innovating to formulate improved products. However, those new formulations are trade secrets. The AFFAR (the French association of formulators and applicators of resin-based floors) has announced new resin-based floors able to withstand high temperature (more than 100 ëC) and others that are able to adhere to wet substrate with short curing times. Among other possible trends is antimicrobial flooring. Although some few suppliers propose antimicrobial resin-based floorings, no antimicrobial effect has ever been demonstrated in such floorings, to our knowledge. Only PVC floorings, which are not considered suitable for food processing areas (see above), and which all contain an antimicrobial product because PVC is a substrate for fungal microorganisms, have a proven antimicrobial effect (Carpentier, unpublished results). Anyway, if antimicrobial resin-based flooring could ever exist, it would have to be cleaned and disinfected as other floors. Indeed, antimicrobial material may reduce microbial contamination when wet, but cleaning and disinfection allow for further decrease of surface microbial contamination. The application of ceramic tiles in resin bed is increasing, especially in the dairy industry. It allows withstanding higher variation of temperature, humidity, etc. and smaller joints.
9.7
Sources of further information and advice
9.7.1 Slip-resistance and accidents at work · European Agency for Safety and Health at Work: http://europe.osha.eu.int/. This website provides statistics of accidents at work in the EU.
182
Handbook of hygiene control in the food industry
· Health and Safety Executive (UK): a paper from Richard Morgan giving the priorities in the food and drink industry may be downloaded from http:// www.east-anglian-fishnet.org.uk/docs/oct99.rtf · An information sheet updates HSE booklet `Slips and trips ± Guidance for the food processing industry' with consideration of the roughness parameter Rpm impact on slip resistance of flooring materials: Food sheet no. 22: http:// www.hse.gov.uk/pubns/fis22.pdf
9.7.2 Resin-based flooring · EFNARC (European Federation of producers and applicators of Specialist Products for Structures) was founded in March 1989 as the European Federation of national trade associations representing producers and applicators of specialist building products. Two interesting documents are available at their website: `Specification and guidelines for synthetic resin flooring' and `Specification and guidelines for polymer-modified cementitious flooring as wearing surfaces for industrial and commercial use'. A free downloadable pdf copy of those guides is available from http:// www.efnarc.org/efnarc/publications.htm · A French written document of Pollet (2000) from the Scientific and Technical Center for Construction (CSTC) (http://www.cstc.be, website in French and Flemish, English is in preparation): `Les sols industriels aÁ base de reÂsine reÂactive' (technical note 216) give some information on resin-based floors, description of tests to assess their performances, recommendations on joints and construction and help in choosing an industrial flooring system. · AFFAR, the French association of formulators and applicators of resin-based floors has a website (French only) http://www.affar.asso.fr with information on the new technologies, help in choosing the right resin-based flooring, etc.
9.8
References
(1999), `Preventing slips in the food and drink industries-technical update on floors specifications', Health and Safety Executive information sheet: Food sheet no. 22. HSE Books, Sudbury. ANON (2001a), `Specification and guidelines for polymer-modified cementitious flooring as wearing surfaces for industrial and commercial use', EFNARC (European Federation of producers and applicators of Specialist Products for Structures), Farnham. ANON (2001b), `Specification and guidelines for synthetic resin flooring', EFNARC (European Federation of producers and applicators of Specialist Products for Structures), Farnham. CHANG W-R and MATZ S (2000), `The effect of filtering processes on surface roughness parameters and their correlation with the measured friction, Part I: Quarry tiles', Safety Sciences, 36, 19±33. CHANG W-R, KIM I-J, MANNING D P and BUNTERNGCHIT Y (2001), `The role of surface ANON
Improving the design of floors
183
roughness in the measurement of slipperiness', Ergonomics, 44, 1200±1216. and ERMEL G (2001), `Molecular epidemiology of Listeria monocytogenes isolates collected from the environment, raw meat and raw products in two poultry- and pork-processing plants', Journal of Applied Microbiology, 91, 888±899. COX LJ, KLEISS T, CORDIER JL, CORDELLANA C, KONKEL P, PEDRAZZINI C, BEURNER R and SIEBENGA A (1989), `Listeria spp. in food processing, non food and domestic environments', Food Microbiology, 6, 49±61. GAGNIEÁRE S, AUVRAY F. and CARPENTIER B (2004), `Vitesse de progression d'un Pseudomonas putida Gfp+ dans une conduite contamineÂe par un aeÂrosol', Poster presented at the National Congress of the French Society for Microbiology, Bordeaux (France), 10±12 May. GIOVANNACCI I, RAGIMBEAU C, QUEGUINER S, SALVAT G, VENDEUVRE JL, CARLIER V and ERMEL G (1999), `Listeria monocytogenes in pork slaughtering and cutting plants use of RAPD, PFGE and PCR-REA for tracing and molecular epidemiology', International Journal of Food Microbiology, 53, 127±140. È NQVIST, R, ROINE, J, KORHONEN, E and RAHIKAINEN, A (1990), `Slip resistance versus GRO surface roughness of deck and other underfoot surfaces in ships', Journal of Occupational Accidents, 13, 291±302. È NQVIST, R, HIRVONEN, M and SKYTT, E (1992), `Countermeasures against floor GRO slipperiness in the food industry', Advances in Industrial Ergonomics and Safety, IV, 989±996. HARRIS, GW and SHAW, SR (1988), `Slip resistance of floors: users' opinions, Tortus instrument readings and roughness measurement', Journal of Occupational Accidents, 9, 287±298. HOLAH JT and THORPE RH (1990), `Cleanability in relation to bacterial retention on unused and abraded domestic sink materials', Journal of Applied Bacteriology, 69, 599± 608. HOLAH JT, TIMPERLEY AW and HOLDER JS (1990), `The spread of Listeria by cleaning systems', Technical memorandum 590. The Campden Food and Drink Research Association, Chipping Campden. LAWRENCE LM and GILMOUR A (1995), `Characterization of Listeria monocytogenes isolated from poultry products and from the poultry-processing environment by random amplification of polymorphic DNA and multilocus enzyme electrophoresis', Applied Environmental Microbiology, 61, 2139±2144. LECLERCQ S and TISSOT C (2004), `Les chutes de plain-pied en situation professionnelle', INRS ± HygieÁne et seÂcurite au travail-Cahiers de notes documentaires, 194, 51± 66. LECLERCQ S, TISSERAND M and SAULNIER H (1994), `Assessment of the slip resistance of floors in the laboratory and in the field: two complementary methods for two applications', International Journal of Industrial Ergonomics, 13, 297±305. LIOT J-P, CARPENTIER B, LECONTE A.-M, FAU G, VETTER F and SAULNIER H (1998), `Guide des reveÃtements de sol reÂpondant aux criteÁres `HygieÁne ± SeÂcurite ± Aptitude aÁ l'utilisation' pour les locaux de fabrication de produits alimentaires', Caisse nationale d'assurance maladie des travailleurs salarieÂs (CNAMTS), Direction des risques professionnels, Paris. MASUROVSKY EB and JORDAN WK (1958), `Studies on the relative bacterial cleanability of milk-contact surfaces', Journal of Dairy Science, 41, 1342±1358. METTLER E and CARPENTIER B (1998), `Variations over time of microbial load and CHASSEIGNAUX E, TOQUIN MT, RAGIMBEAU C, SALVAT G, COLIN P
184
Handbook of hygiene control in the food industry
physico-chemical properties of floor materials after cleaning in food industry premises', Journal of Food Protection, 61, 57±65. METTLER E and CARPENTIER B (1999), `Hygienic quality of floors in relation to surface texture', Transaction of the Institute of Chemical Engineers, 77, 90±95. È RKROTH KJ and KORKEALA HJ (1999), `Characterization of Listeria MIETTINEN MK, BJO monocytogenes from an ice cream plant by serotyping and pulsed field gel electrophoresis', International Journal of Food Microbiology, 46, 187±192. NELSON JH (1990), `Where are Listeria likely to be found in dairy plants?', Dairy, Food and Environmental Sanitation, 10, 344±345. POLLET V (2000), `Les sols industriels aÁ base de reÂsine reÂactive. Note d'information technique 216', Centre scientifique et technique de la construction. Bruxelles (Belgium). STRANDBERG L (1985), `The effect of conditions underfoot on falling and overexertion accidents', Ergonomics, 28, 131±147. TAYLOR JH and HOLAH JT (1996), `A comparative evaluation with respect to the bacterial cleanability of a range of wall and floor surface materials used in the food industry', Journal of Applied Bacteriology, 81, 262±266. TIMPERLEY A (2002), Guidelines for the design of floors for food production areas (second edition), Guideline no. 40. Campden and Chorleywood Food Research Association Group, Chipping Campden. TISSERAND M, LECLERCQ S and SAULNIER H (1995), `Exigence pour une norme de mesure de la glissance des sols', Cahiers de notes documentaires, 159, 191±198.