Wipes for cleanrooms: how to select the best wipe for the job

Much has been written about the use of wipes in the electronics industry, but little or nothing about the requirements for wipes within life science cleanrooms. The assumption has also been made that life science requirements are very similar.

However, in reality the industries have very different requirements and the specification for one does not necessarily meet the needs of the other. This article will help pharma biotech users decide whether they are using the right kind of wipes for their application.

Electronics cleanrooms place their highest priority on removing particulates from the environment, through the use of sophisticated air filtering and HVAC systems. When it comes to cleaning surfaces or product, they require the wipe to remove any soiling, particulates or liquid without causing any abrasion to the surface. It is also essential that the wipe itself does not contribute any particulates to the environment, so the structure, composition and cleanliness of the material is very important. There are no requirements for control of microbial contamination within the room, so the wipes do not need to be used in conjunction with disinfectants and are not required to be sterile.

For pharmaceutical and biotechnology companies, the level of particulates, although important, is not necessarily as critical. Here, the primary concern is the application of a disinfectant and subsequent removal of microbial contamination. Consequently, the wipes need to be effective at removing non-viable particulates, capable of applying a disinfectant, and capable of the subsequent removal of viable contamination. It is also important the wipe does not contribute to the bioburden or generate additional particulates.

In direct contrast to electronics use, a surface resistance to the wipe may be desirable ­ this will enable the resulting physical action of wiping to break up the biofilm layer of micro-organisms. This action is known to be very important in the effective control of microbial contamination where removing the biofilm ensures the disinfectant can reach all surface organisms.

In Grade A and B areas it is essential that the wipes and packaging are sterile. Consideration should also be given to how easy they are to transfer in to the cleanroom and to ensure that the packaging does not generate any particles. In principle, the closer you get to product contact areas, the higher the grade of wipe needs to be.

Why wipe? The key reasons are: u Removal of physical soiling and residues. u More effective disinfection. u Convenience and ease of use. u Reduced environmental impact.

While HEPA filters and air handling systems can automatically maintain the required non viable particulate levels in the air, any surface contamination must be physically removed. Surfaces need to be cleaned before disinfection and the more efficient the cleaning cycle is at removing soiling and residues, the more effective the disinfection regime will be.

When disinfecting cleanroom surfaces or products for transfer, spraying with disinfectant and wiping is found to be much more effective than spraying alone ­ especially against bacterial spores. As already mentioned, this is because the action of wiping helps to break down the biofilm that protects organisms from the disinfectant. This is clearly demonstrated by the results of work carried out to assess the effectiveness of different liquid disinfection techniques1 (Table 1).

A sterile IPA impregnated wipe was significantly better against spore contamination than spraying alone. The best results were obtained using a separate stage of spraying and then wiping. And it made very little difference to this final result if wiping was followed by spraying.

There are certain key factors which need to be considered when choosing a wipe for use in your cleanroom ­ low levels of particulates are only part of the decision making process. u Does the wipe need to be sterile? u Would pre-impregnated wipes be more suitable? u Is the wipe compatible with the disinfectants used? u Does it need to be highly absorbent? u Is the packaging suitable for transfer into a Grade A or B room? u Will the material help remove the biofilm? u Are the wipes packaged in a suitable and cost effective quantity? u Are the wipes easy to access and use? u Are the wipes prepared and packed in a cleanroom?

Considering all these factors will allow you to choose the most suitable and most cost effective wipe for the different areas of your cleanroom.

There are many types of dry and impregnated wipe available ­ both sterile and non-sterile. For each application the user will need to decide what composition is preferred, determined by the level of particulates required, potential for product contact and cleanroom grade. Consideration also needs to be given to compatibility with the cleaning and disinfecting agents being used.

Very often users select a very high grade of wipe, when a more appropriate material would still fall within the acceptable limits for particulates and pose no threat to the quality of the product. For example, there may be no need to use wipes manufactured from a laundered material (where all particulates, chemicals and pyrogens have been removed) in a life science cleanroom.

Wipes materials

Knitted polyester with sealed edges is a high grade wipe, popular for product contact areas, as it has virtually no particulates and offers good resistance to abrasion and solvents. It is also more expensive.

A hydroentangled polyester/cellulose blend is an excellent solution for many applications, creating a robust, absorbent, low-particulate material. Many wipes are available made from a polyester/cellulose mix, so compare the specification of the different wipes, as particulate levels and absorbency can differ with the weight of the material. Also the percentage of polyester to cellulose and the method of entanglement can make a difference to the numbers of particles. Suppliers will be able to supply technical data including gsm, absorbency, wet and dry tensile strength, elongation, number of particles, number of fibres and extractable ions.

IES-RP-CC004.2 Evaluating Wiping Materials Used in Cleanrooms and Other Controlled Environments, published by the Institute of Environmental Science, provides test methods for comparing cleanroom wipes. This was developed for the electronics industry but some elements of the test method are relevant for life science cleanroom wipes.

Polyeurethane foam (sponge) is particulate free, non abrasive, highly absorbent and may be useful in specific situations. However it can be quick to release liquid when squeezed, reducing the operator's ability to control disinfection application, or more probably, a liquid spillage that may be hazardous.

Cotton and cellulose (tissue products) offer excellent absorbency but are relatively fragile and contain many particulates. These can rip easily and shed high numbers of both fibres and particles making them unsuitable for life science cleanrooms.

Sterile or non-sterile?

Wipes used in Grade A and B areas should be sterile prior to use. Some organisations buy non-sterile dry wipes and autoclave them. However there are potential drawbacks to this: u The sterility of the wipes can be difficult or time consuming to validate. u Autoclaving may alter the composition of the wipe material, rendering it structurally unsuitable. u Repacking requires valuable technician time, which could be spent more profitably on key activities. u There may be hidden costs associated with on-site sterilisation: extra workload, added production downtime and increased quality validation requirements.

Employing single-use items is best practice, minimising contamination risk. The purchase of gamma irradiated wipes at 25kGy, guarantees sterility and they are supplied with irradiation and sterility certificates.

High quality wipes are available from many suppliers, however they may not be packed ideally for a pharmaceutical cleanroom environment. If the wipes are sterile and provided in bulk packs, will wipes need to be thrown away at the end of each session? Would smaller, double bagged packs be more useful? The packaging itself should be low shedding and not generate particles on opening.

Is the packaging the wipes are provided in easy-to-open, especially when wearing a double pair of gloves? Some wipes packaging is provided with an aeasy tear' method of opening. This avoids the frustration of trying to tear open polyethene packaging or the need to take scissors into the cleanroom. Are the wipes packaged in such a way that they are easy to remove from the pack/pouch/tub without contaminating the wipe at the same time.

Vapourised Hydrogen Peroxide packaging is also available, which significantly reduces the aeration time during the decontamination cycle in gassing isolators.

If impregnated wipes are chosen, what format is most suitable for your application? This may be different in each area. In a preparation area, or low grade cleanroom, a plastic tub with low shedding aperture may be the ideal solution for quick and easy access to a large volume of sterile wipes. In the isolator or laminar flow cabinet, a resealable pouch of sterile wipes, which protects the wipes during the cleaning process, may be more suitable. Individually packed sachet wipes are also available.

Large mop wipes are supplied in small quantities in foil packs, which provide easy access for clipping onto mop frames.

Dry or pre-impregnated wipes?

Dry wipes may be preferable for clearing up spillages, or wiping down ato dry' surfaces after cleaning. Dry wipes also have the advantage of being versatile for use with different agents. Operator preference or process constraints can also be important. In addition, larger dry wipes may be needed for particular cleaning applications.

Pre-impregnated wipes can offer certain advantages. For example, in confined spaces or when trying to clean inside equipment, access with a bottle and a wipe can be difficult. In isolators or laminar flow cabinets it is not advisable to spray liquid that might seep inside equipment or pool in a difficult-to-reach area, as this could leave residues or cause damage, so an impregnated wipe offers a method of controlling the amount of liquid applied to the surface. An impregnated wipe can also be easier for an operator to handle, especially when items need to be picked up or manipulated to ensure successful disinfection.

Many disinfectants, alcohols notably, have low exposure limits, so the use of an impregnated wipe reduces the amount of disinfectant sprayed into the air, significantly reducing health and safety concerns relating to occupational exposure limits.

Pre-impregnated wipes also help to control the consumption of the disinfectant solution.

Choosing a pre-sterilised, pre-impregnated wipe from a manufacturer also eliminates any risk of incompatibility between the wiper material and the chemical disinfectant. This may be a particular issue where lower grade wipes, containing binders, have traditionally been used.

Large size sterile impregnated wipes for use with mop frames are also available. These offer a more suitable and environmentally friendly alternative to the traditional bucket and mop system.

Other advantages include: u They are the quickest and most convenient method of disinfecting large surface areas. u They save additional time by eliminating the need to mix concentrate into a solution or use a bucket system and remove the risk of dilution error. u There is no issue about where to obtain suitable water for dilution, a major inconvenience which has the potential of contamination if the water source is outside the cleanroom area. u The risk of cleaning fluid becoming contaminated is avoided. u The highly absorbent wipes remain wet throughout use, ensuring a consistent application of fluid to the whole surface area. u There is no need to dispose of unused disinfectant in the drainage system, making them much more environmentally friendly.

When choosing an impregnated wipe care must to be taken to ensure the wipe is not too saturated, but carries enough impregnate to provide an even and effective surface coverage of disinfectant.

Sterile impregnated wipes are available with IPA or denatured ethanol in different sizes. In addition, wipes are also available impregnated with a choice of sterile biocides, including sporicides, and neutral detergents.

Correct use of wipes

Once the correct wipe for the particular area or application has been chosen, all of its benefits can be eliminated if wiping is not carried out in a validated manner. Wiping or mopping should never be carried out in a circular motion as this causes the wipe/mop in its dirtiest state to be passed over an area which has just been cleaned. This point needs to be reinforced with operators, as a circular wiping pattern is the most comfortable and convenient according to studies2.

The correct technique is to wipe/mop towards you in straight horizontal lines, each time overlapping the previous one by 10­25percent. A contaminated wipe/mop should not be passed over an area that has just been wiped, unless in the case of a wipe it is folded and refolded to provide a clean surface. Usually quarterly folds are recommended but must be validated with each operator concerned, as a quarterly fold can lead to confusion as to which surfaces of the wipe have been used. In this case wipes folded in half should be used.

Surface wiping or mopping should be carried out from top to bottom, from back to front and from cleanest to dirtiest, changing the wipe at appropriate intervals.

Karen Rossington is with Shield Medicare Ltd, Farnham, Surrey, UK. www.shieldmedicare.com

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