Cleanroom cleaning options: what is right for your scenario?

Cleanrooms and labs, along with the furnishings and equipment housed inside them, require regular cleaning. Sue Springett, commercial manager of hygienic equipment and furniture supplier Teknomek, looks at the pros and cons of different cleaning methods

When specifying furniture and fittings consideration should be given to the intended cleaning methods used. Picture courtesy of Oxford BioMedica

Cleaning is an essential part in the day-to-day running of any cleanroom areas or high-care lab or facility. Both fixtures and fittings need to be clean. However, choosing the wrong method can unnecessarily prolong the cleaning process or even reduce the lifespan of equipment. With many options available and so much equipment to keep hygienic, it can be hard to know what is right for any given context, and with the growing popularity of single-use (pre-sterilised) consumables, how much is necessary.

Historically, a “simple” wash down combining a lot of meticulous hard work with diluted cleaners has often been deemed sufficient. As long as all areas of a cleanroom could be reached with a clean cloth or brush, that was generally considered good enough. A modern auditor would not necessarily agree. A further downside was the time this takes. Add up the hours taken each day, week, month or year and the considerable cost to the business soon becomes apparent.

Yet there are competing influences at work: the risk of an audit failure makes each clean-down business critical, while the drive to reduce operating costs demands that new techniques that could aid smarter, compliant working, are investigated.

Intelligent design to remove dirt traps — such as folds, ledges and gaps — from specialist furniture has helped to reduce clean-down times. However, industry hygiene standards have become increasingly rigorous over the years to the extent that an entirely manual approach is now insufficient, regardless of how well considered a cleanroom design and support equipment may be. This means specialist techniques must be used.

Automated deep cleaning

The first option to consider is also one of the best established; the autoclave. It rose to prominence in Louis Pasteur’s own research into sterilisation in the mid nineteenth-century and it is partly thanks to the autoclave that we now enjoy the benefits of vaccination and pasteurisation. The autoclave is now a piece of kit that can be found in almost any lab or cleanroom environment. Ranging in size from the humble stovetop to airliner-size, autoclaves are non-toxic and do not produce harmful by-products. The most useful features of the autoclave are its efficiency and the wide range of products that it can sterilise.

Autoclaves are particularly popular due to their suitability for deep cleaning re-usable items. Depending on the size of model, an autoclave can be used to sterilise numerous pieces of equipment, such as lab instruments and utensils, in a single cycle. Larger items, such as anti-bacterial matting can also be run through autoclaves, as can some storage systems and even specialist furniture such as chairs and stools that can be dismantled for sterilisation as required.

A typical scenario for the use of an autoclave would be bug-hunting situations in which all bacteria or spores have to be 100% neutralised. Steam has a high-energy transfer capacity, which makes it a safe bet for neutralising micro-organisms. From an operations perspective, using wet heat is also significantly quicker and uses less energy than dry heat sterilisers.

The downsides of this approach are its ferocity and that it is a wet heat. An autoclave operates at 121°C (249°F) and this means being very careful about what equipment can be subjected to the autoclave process. Being effectively a steam cleaner, the steam can also risk damaging the contents, so it is essential that the material of the product being autoclaved is confirmed as having enough resilience. Stainless steel in both 304 and 316 grades can comfortably withstand sterilisation in an autoclave. However, less robust materials, such as plastics, polyethylene or silicon, may not survive or may be deformed.

Stainless steel in grades 304 and 316 can comfortably withstand being autoclaved

Although autoclaves can be fairly expensive to run, they can free the operator’s time, giving them the option to work elsewhere during the sterilisation process. Generally speaking, having the option to re-use equipment is considered the greatest benefit and this outweighs the running costs – as long as the items are tough enough to withstand the repeated sterilising process.

The autoclave has been a standard feature in this industry for decades and for good reason. This technology’s longevity speaks for itself, as does the fact we continue to see new autoclavable products being introduced to the market. The autoclave is a safe and versatile option for use in numerous scenarios to support the hygiene routines required.

Radiation-based sterilisation techniques, e.g. UV or gamma radiation, can offer an effective alternative to autoclaving for destroying micro-organisms and can be used on a broader range of materials, including plastics and even adhesives. A further advantage of sterilisation via gamma radiation is that it does not produce heat or moisture, nor leave any residue.

The gamma sterilisation process uses Cobalt 60 radiation to kill bacteria by breaking the covalent bonds of bacterial DNA. A downside being it does the same to any DNA, which could pose a risk to certain products and/or employees. There are other significant practical disadvantages to radiation-based methods. Primarily this comes down to the size of the kit to be sterilised, UV lamps have a limited radius and items to be sterilised using gamma radiation must be bagged. This places a limit on the size of equipment that can be treated. That said, gamma sterilisation has become a more popular option in line with the growing use of disposable consumables that come pre-packaged in plastic.

Chemical world

The third option commonly used for cleanroom applications is chemical sterilisation. This is most typically chlorine or hydrogen-based. Vapourised Hydrogen Peroxide (VHP) is becoming particularly popular for on-site sterilisation. Clearly, this will have some bearing on what furniture can be used: 316 grade stainless steel is the safest option as its higher nickel content, backed by the addition of molybdenum, brings an increased corrosion resistance to the steel.

VHP is a sensible choice for equipment that cannot withstand the highest temperatures of an autoclave or can be damaged by irradiation. Furthermore, it has a low cycle time compared to other methods. A full sterilisation in a VHP chamber can take under half an hour.

Despite the many benefits, the key drawback to the use of chemicals for sterilisation comes down to health and safety. Even short-term exposure to higher concentrations of oxidants can be extremely hazardous. As such, the design for facilities using chemical sterilisation techniques have to incorporate specialist — and expensive — ventilation systems.

Although VHP is not nearly as carcinogenic as chlorine-based equivalents and its only residue is water, it is still classified as dangerous to human health because it irritates the eyes and throat (the OSHA guideline is 1ppm averaged over and 8 hour shift).

The best sterilisation technique is a moot point in certain segments of the industry, as the trend towards single-use consumables grows. The use of pre-sterilised and disposable equipment is undoubtedly a sensible strategy for decreasing contamination risks for some applications. However, other businesses need to take account of the environmental considerations of this “throwaway” culture, as well as the expense and impracticality for businesses that demand the most rigorous sterilisation regimes or regularly need to sterilise larger items, such as furniture.

Similarly, while VHP is the quickest and most efficient way to sterilise in a single treatment, it may not always be best for the business. The additional costs in staff training and the time for ventilation post-VHP may also make this option less attractive.

There are pros and cons to any methods; so a simple rule of thumb is to design the cleanroom around the cleaning/sterilisation techniques that the application will most typically require.

Regardless of what regime is finally settled upon, it is worth remembering that hygiene standards do not start and end at the cleanroom. An audit can be failed in any part of a facility, so rather than getting caught up in the detail, the end goal should always be to instigate and maintain an overarching culture of good hygiene.

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