Central Service - Issue 5/2013
- What's New in Standardisation: Declaration of conformity
- Acceptance through competence: DGSV Congress in Fulda
- Amendment of acceptance criteria used for assessment of cleaning efficacy
- Central Service Editorial Board: new members
B. Fiedler, J. Steinke:
Investigation of ultrasound-induced microbial emission into the room air from contaminated ultrasonic baths
The use of ultrasound to clean medical devices is considered to be a method that is gentle on materials and has already been well established in practice. That all ultrasonic baths should be equipped with a lid to prevent danger to operating personnel is something that has often been expressed. Potential inhalation of microorgansims released into the air from the contaminated water is thought to present a hazard. By counting the particles and measuring the content of living organisms, it was possible to demonstrate under the test conditions, reflecting everyday practice, that the air above highly contaminated ultrasonic baths did not contain a significantly higher microbial count than that measured at a distance of 80 cm away. Whether the ultrasonic bath was, or was not, equipped with a lid, was operated with or without ultrasound and heating, or with detergent and disinfectant agents was unimportant in this regard.
instrument processing ultrasonic bath aerosol generation airborne microbial count occupational health and safety
FROM THE FIELD
Y. Uetera, K. Kishii, H. Yasuhara, K. Moriya, N. Kumada, H. Tanno:
Reverting colour change of Bowie-Dick test indicator caused by an air leak into the chamber of prevacuum autoclave
The prevacuum autoclave with a 196-liter jacket-type chamber was installed in November 2006 with a pure steam generator and reverse osmosis (RO) plant. Pure steam was produced from RO water and supplied to the chamber. The autoclave was designed so that the controlled jacket temperature was 1.0 °C lower than the chamber temperature.
The autoclave had passed the Bowie-Dick test until July 2009 using identical test packs. The unused yellow indicator turned blue/purple uniformly, and the colour remained unchanged after the test.
In August 2009, the «reverting colour change» phenomenon began to occur on used indicators. The indicator turned blue/purple uniformly at the end of a test cycle. Two days later, the blue/purple colour reverted to the original yellow.
The test pack manufacturer suggested some possible causes of this phenomenon: unacceptable levels of non-condensable gases (NCGs) in the steam supply, the presence of «wet» steam in the chamber, minute air leaks into the chamber etc. The steam quality was then evaluated. A vacuum leak test was also performed. A warm-up cycle was omitted for the leak test because the jacket was always warmed by the steam.
The levels of NCGs did not exceed 3.5 % in the pure steam. The leak rates ranged from 0. 31 to 0.57 mbar/min when the «reverting colour change» occurred. In October 2012, our maintenance engineer detected an air leak in the pipework. After the repair, the leak rate decreased to 0.18 mbar/min, and the «reverting colour change» has ceased to occur.
The same Bowie-Dick test packs were also tested in the two other autoclaves with a 196-liter chamber. In this case the controlled jacket temperature was 1.0 °C higher than the chamber temperature. Both autoclaves passed the Bowie-Dick test without the «reverting colour change». The leak rates ranged from 0.18 to 0.98 mbar/min. The leak test was performed without a warm-up cycle because the jackets of the autoclaves were always warmed.
Various factors may affect the performance of indicators in the Bowie-Dick test. It seems likely that this is an illustrative case report to consider the causes of a «reverting colour change» in the Bowie-Dick test.
Bowie-Dick test chemical indicator reverting colour change air leak
20 YEARS OF CENTRAL SERVICE
Indicators and sterilization control