728 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS objectives. Nevertheless, hygienic operating procedures require a high stand- ard of attention to a wealth of detail and many aspects will be discussed in this monograph. The extent to which the advice offered here needs to be applied in a particular manufacturing process will depend on the scale of production, the susceptibility to contamination of the formula concerned, and the extent of inoculation with contaminants to which it might be exposed if precautions are insufficient. For example, suggestions are given with regard to plant sterilization whether or not the plant needs to be sterilized before each batch of product is manufactured should be deter- mined by the microbial status of the resulting material. Microbiological quality control should always serve as the guide to the success of manu- facturing hygiene and as the warning-light to show when more stringent precautions are needed. 3.2 Hygienic methods Precautions should be taken to prevent micro-organisms from con- taminating a product at the various stages of manufacture. Even if a pre- servative is incorporated, there is still a risk that its antimicrobial capacity may be overwhelmed. Hygienic methods, are, in essence, procedures for maintaining a high standard of cleanliness but the necessary precautions are not obvious to everyone and are easily overlooked or misunderstood. The foremost need is, therefore, to inculcate the correct attitude into all operative and supervisory staff, with periodic re-education in the subject so that slipshod habits do not develop. There are also numerous points con- cerning factory and plant design where attention to detail will help to limit contamination. A vigilant attitude needs to be persistently maintained to avoid a sudden upsurge of contamination it often happens, for example, that current production needs call for modification of plant lay-out without delay and this may well result in serious contamination if the hazard is not recognised. The typical hygienic problems associated with cosmetic manu- facture may be exemplified thus: 3.21 Air and water are often important sources of contamination. 3.22 Any arrangement of plant or operating procedure that would allow dust to enter the product will also encourage airborne microbial contamin- ation. 3.23 Stagnant residues of product in the plant between the processing of successive batches may well lead to multiplication of micro-organisms. 3.24 Efficient cleaning and sterilization of plant is desirable, but bad plant design can make this difficult or virtually impossible.

HYGIENIC MANUFACTURE AND PRESERVATION 729 3.3 Factory and plant design Design of the building in which plant is to be housed should ensure that walls, floors and ceilings have smooth, non-absorbent and easily cleaned surfaces with no hidden corners or ledges in which dust and dirt will collect. Provision should be made for efficient ventilation, preferably by means of filtered air giving a positive pressure with respect to the surround- ing atmosphere. The building should be designed as far as possible so that personnel moving from one area to another do not have to traverse the production floor. Changing rooms should be kept apart from the production area and lavatories should not connect directly with either changing rooms or production areas. Adequate washing facilities must be provided. The design of manufacturing plant should be such that stagnation of product residues in pipes, joints, pumps, pressure gauges and valves cannot occur these are some of the places where serious contamination is most likely to develop. Stainless steel of high quality is undoubtedly the most suitable material for the fabrication of pipe-work, but other construction materials may be satisfactory so long as they can be effectively cleaned and sterilized. Plastic hose is quite suitable when new but requires frequent examination for defects and for accumulation of residues on roughened surfaces. Pipe runs need to be kept as short as possible, avoiding right- angled joints in order to facilitate cleaning they should never run com- pletely horizontal but always slope towards a venting point. Complete and thorough removal of product residues is essential if machinery is to be left idle for even a short space of time. Joints in pipes should be made by welding or with plastic seals interchangeable dairy-type fittings are satisfactory but the packaging of pipework joints with hemp and grease is highly undesirable. Flexible piping offers the advantage that it may be disconnected, cleaned and sterilized between runs. Dead ends in pipework and traps in the lines must be avoided as far as possible, e.g. a by-pass to another plant or filling machine will serve as a "dead end" and lead to stagnation if it is only used occasionally. Adequate provision should be made so that sterilization either by steam or chemical means can be accomplished it is essential to provide a range of points at which steam or fluid may be vented, to ensure that air locks in the plant do not interfere with efficient cleaning and sterilization. All parts of manufacturing equipment likely to come in contact with the product should preferably be constructed of smoothly-finished stainless steel vessels should be double-jacketed to allow for heat sterilization and equipped with well-fitting lids capable of excluding dust particles and bacteria from the surrounding atmosphere.