INSTRUMENT STERILISATION AND DECONTAMINATION
injected into the chamber to drive the formaldehyde into the load. After the formaldehyde exposure phase, further pulses of steam and air are injected into the chamber to remove the formaldehyde from the chamber and allow desorption from the load. Formaldehyde is a toxic vapour, and must therefore be handled carefully to avoid operator exposure. Loads should not smell of formaldehyde when removed from the chamber. Generally, thermally labile medical
devices which will not tolerate high temperatures, but will tolerate exposure to steam, can be sterilised by LTSF. Care must be taken to ensure that complex shapes, cavities, and lumen, are exposed for sufficient time to allow formaldehyde penetration.
Sterilisers Formaldehyde sterilisers are supplied as free-standing units, or fully installed, complete with centrally supplied services (steam, compressed air, and power etc). Chamber sizes vary from 150 to 500 litres. Generally they do not need to be located in specially ventilated rooms, but precautions must be taken to avoid exposure of operators to formaldehyde vapour. The formalin liquid must also be handled using appropriate personal protective equipment.
Choice of sterilisation process The vast majority of medical devices decontaminated in a Sterile Services Department will be manufactured from heat-tolerant surgical stainless steel, and can therefore be sterilised using a high- temperature saturated steam sterilisation process (see Figure 1 and Table 2). Most SSDs will have a bank of porous load saturated steam sterilisers ranging in size from 500 to 1000 litre chamber capacity. It is unlikely that a hospital SSD will
become involved in sterilising large quantities of thermally sensitive single-use medical devices, this being carried out by industry. However, it is possible that an SSD may be required to sterilise a reusable heat-sensitive medical device, such as a specialist endoscope, in which case the hospital must make some key decisions about how. The first consideration is what sterilisation processes are recommended in the medical device manufacturer’s instructions. These must be rigorously followed. The second consideration is: will the item or load need to be sterilised frequently? If not, then the use of an external commercial contract sterilisation company may be an economically appropriate choice. Alternatively, another SSD which already has the required sterilisation technology can be approached.
Purchasing options If it is decided to purchase an LTS system,
then one of the three aforementioned technologies are worthy of consideration, since these are the most common in use today. Others are clearly available (see Figure 1), and although there is considerable choice, the supplier’s ability to support the installation must be thoroughly investigated. Of the three choices described above (VH2O2, EO, and LTSF), consideration must be given to the steriliser characteristics, such as maximum loading capacity in terms of weight and size of load, restrictions on materials which can be processed, cycle times, operating costs, and servicing and validation requirements. The total cycle time must be considered; not only the sterilisation stage, since aeration of loads after processing can take several hours to reduce sterilisation residuals to a safe, acceptable level (regulations will apply). Whether the steriliser needs to be
installed in a special area with specific ventilation requirements should be considered, since the cost of installation and operation will add to the initial purchase costs. Is the steriliser free- standing, or does it require installation into a permanent position with supporting services such as ventilation, extraction, steam, compressed air, mains water, drainage etc, all of which will add capital installation costs?
Investigate abatement methods Most LTS systems utilise a toxic gas or vapour, and so the purchaser should thoroughly investigate what abatement methods are included in the steriliser technology, and what safety precautions are needed to avoid operator exposure. The user should also bear in mind additional environmental and personal monitoring requirements, such as alarm systems which sound if the sterilising gas concentration exceeds safe environmental limits. Similarly, discharge of toxic waste into the environment as gas or liquid waste through the drainage systems must be investigated, since there will be national and local regulations governing such discharges. Once a thorough analysis is made of the
purchase, installation, validation, routine testing, and operating requirements and costs, a sound decision can be made. When having to make such decisions the advice of the Authorising Engineer (Decontamination) and members of the Infection Prevention and environmental and occupational safety teams should be sought.
n Author’s note: This article is part is of the work being undertaken by an ad hoc working group from the Decontamination Professional Expert Communication Forum (DPECF) to revise the MAC manual.
Dr Brian Kirk
Dr Brian Kirk, MD, Brian Kirk Sterilization Consultancy Group, UK, is qualified as a Pharmacist, and holds a Masters Degree in Pharmaceutical Analysis and a PhD in Pharmaceutical Sterilisation Technology. His Doctoral research involved investigations into the application of computer technology for modelling chemical reactions, and the inactivation of bacterial spores in steam sterilisation processes and monitoring and controlling steam sterilisers; work for which he received the 1985 annual award for best submitted paper to the Parenteral Drug Associations Journal. He worked for over 10 years in the NHS as a quality control pharmacist for a hospital pharmaceutical sterile supply manufacturing department, gaining Qualified Person status. Joining 3M Health Care in 1989 as a development scientist for sterilisation monitoring products, he then became the Scientific Affairs and Education manager for Western Europe. Throughout his career Brian has had special responsibilities for monitoring the development of national, European, and international sterilisation standards, and as a result he is a member of a number of BSI, CEN, and ISO committees responsible for developing standards for chemical and biological sterilisation indicators and steam, ethylene oxide, and vaporised hydrogen peroxide sterilisers and sterilisation processes. He is the convenor of ISO TC 198 working group 3, Moist heat sterilization. A regular conference presenter, he has published a number of peer-reviewed articles, and is a Fellow of IHEEM and an IHEEM- registered Authorising Engineer (Decontamination). A visiting honorary associate professor at the University of Nottingham, he founded Brian Kirk Sterilization Consultancy Group after leaving 3M in April 2019.
October 2022 Health Estate Journal 39
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