DECONTAMINATION
Emma Barrett
standard, EN 285, Sterilization – Steam sterilizers – Large sterilizers.
Integral or ‘built-in’ Bowie & Dick Tests
As mentioned before, the name of this device is misleading because these are not Bowie Dick challenge devices, but air detectors built into steam sterilisers. There is no independent challenge associated with these built-in devices. The test is integral to the steam steriliser and so is not independent to the control system. They are used on an empty cycle every day that the steriliser is used. They often work by using probes to measure temperature with a series of sensors placed in the chamber or the drain of the steam steriliser. There are no standards applicable to these devices, other than the requirements given in EN 285. Having identified the key characteristics of the different test devices, we can see that each has a different application in the routine control and testing of the efficacy of a steam steriliser, but what are the key arguments in deciding which of these tests should be adopted?
Standards To date, only the traditional chemical indicator-based Bowie & Dick test is covered by the European/International standards EN ISO 11140-3 and EN ISO 11140-4, as well as ISO 11140-5 for non-European countries.
A steam penetration test is required EN ISO 17665-1 states that a dedicated steam penetration test should be conducted at the commencement of each day. Therefore, a test that is not a steam penetration test does not meet this standard. An air detector, although useful, is not a penetration test and can be compromised by the position of the air leak, the presence and type of a load, and the chamber size.
The penetration challenge is a key attribute of the Bowie and Dick Test This challenge is designed to mimic the actual challenge of steam penetration into a steriliser load. This challenge must be demonstrated to be appropriate, hence the reason why the Bowie Dick test is closely aligned with the EN 285 small load thermometric test.
An independent test is a key attribute of the Bowie & Dick test Steam sterilisers already include independent monitoring (sensors that are independent of the steriliser control function) of the key cycle variables of time, temperature and pressure. The Bowie and Dick test is a test of steam penetration and the associated removal of air, that is independent of the steriliser control function.
An empty chamber is a key attribute of the Bowie & Dick test The presence of a load in a chamber may compromise steam penetration tests and air detectors because the load will act as a point of condensation, causing any air to migrate towards large masses, hence having the potential to disguise or hide pockets of air that may compromise the steam sterilisation efficacy.
When you consider these factors, it is easy to see why the Bowie Dick steam penetration test has maintained its position as a requirement in ISO 17665 and as an SSD manager’s go-to solution for steam steriliser validation for more than 50 years. A concerted approach of periodic validation, daily steam penetration testing with a Bowie Dick test at the commencement of each day, and use of an air detector for each cycle ensure the most rigorous yet cost-effective means of catching those critical fails to ensure correct sterilisation of medical devices and of course the consequent patient safety.
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Emma Barrett is the senior marketing manager for consumables at Steris. She has over 10 years’ international experience in healthcare and holds a Postgraduate Diploma in Professional Marketing. Previously a representative at the World Health Organization’s Private Organizations for Patient Safety (POPs), the Global Alliance for Prevention & Infection Control (GAPIC), Clean Hospitals and the Safer Disinfectants Network (SDN), she is passionate about infection prevention and improving hygiene standards to protect health and preserve life.
Richard Bancroft
Richard Bancroft is the science and technical director for Steris. He has over 30 years’ experience in sterilisation and is a Registered Authorising Engineer (Decontamination). He has a BSc Honours Degree in Applied Chemistry and is a Fellow of the Royal Society of Biology (FRSB). He has been involved in drafting of global sterilisation standards for over 25 years. He is an active member of many of standards committees, as well as chairman of ISO/TC 198, convenor of ISO/ TC 198 WG 6, convenor of CEN/TC 102 WG 7 and co-chair of AAMI/ST WG06.
CSJ AUGUST 2020
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