Steam Quality
Steam Quality Testing
It seems logical to me that if steam plays such an important part in ‘moist heat sterilization’, it would be a good idea to control and test the quality of it. There have been many discussions and articles written suggesting that to test the quality of steam is unnecessary. Well I couldn’t disagree more. My experience has shown devastating consequences of using steam as the medium for sterilization when it does not comply to steam quality acceptance criteria.
I’m not on my own in regard to this viewpoint, from a regulatory and advisory guideline point of view, BS EN 285:2006+A1:2008; PDA Technical Report No.1 Revised 2007 Validation of moist Heat Sterilization Processes: Cycle Design, Development, Qualification and Ongoing Control; HTM2010; and ISO 17665-2:2009 discuss steam quality and testing.
If steam quality is so important, what are the consequences of failure?
In relation to wet steam - Wet steam can cause wet loads, hinder steam penetration and increase the heating rate. Wet steam can also cause problems from a contamination point of view; path for microbial growth through wet bags, tearing of bags etc.
In relation to superheated steam - With superheated steam, the transference of latent heat and moisture condensation on the load can only continue until the load reaches the propagation temperature of the steam. Subsequently the heat transfer will be the same as that of a non-condensable gas such as air, and as only sensible heat can now be imparted, this will be very slow. No further moisture condensation is possible and so the load remains only partially saturated. In these conditions superheated steam is less lethal than dry saturated steam.
In relation to non-condensable gases - As for superheated steam, in addition remember that air acts as an insulator to spores and therefore inhibits sterilisation. Air and steam mixed result in the same pressure, but lower temperature than dry saturated steam, which will affect the lethality rate.
In Summary:
Where ever your organisation is based, you should assess the quality of the steam being used for ‘moist heat sterilization’.
How often? if you have never done this before, I would advise every month for a year to build up data and during the second year, every quarter and then assess the situation based on risk. If the Pure/Clean Steam Generator (PSG/CSG) is serviced the steam should be tested on the PSG/CSG before and after intervention. At some stage in the autoclave/’Steam in Place’ system life cycle, intervention will have to be made into the steam supply; at these times the steam quality should be tested.
Please contact me for advise on how to test the steam, or if you are already testing but struggling with the results. If you are planning on installing or making changes to a system, I can advise you on Steam Headers, test points, test equipment etc.
I look forward to hearing from you.
