why the leakage rate of autoclave is NMT 1.3 mbar/min
To achieve effective steam sterilisation, dry saturated steam must contact the surfaces to be sterilised so that energy can be transferred.Most of the equipment we seek to contain vast quantities of air. If this air is not removed, then it can act as an insulating barrier between steam and equipment and thus compromise the sterilising process.
Thus, in the case of equipment sterilisation, the key to effective sterilisation is…
• total removal of air (and condensate)
• complete replacement of air by dry saturated steam
Air may be removed by a series of sub-atmospheric (negative) pulses, which draw out air by vacuum and then replace the vacuum with steam up to atmospheric pressure.
There are numerous ways of confirming effective air removal in autoclaves…
• a drain-mounted air detector
• the Bowie-Dick test (or equivalent)
• chamber leak rate test
The leak rate test quantifies vacuum chamber tightness and will detect leaks of >1.3 mbar/minute, a rate which would ruin the sterilization process. A failing Bowie Dick cycle usually caused by air intrusion or an “air in chamber” detector alarm must be rectified before any sterilisation cycles can be run.
Finally, it is common practice to carry out a chamber leak rate test at the beginning of each day, using an empty, dry, warm autoclave chamber. The chamber is evacuated and then isolated by closing all valves. The ability of the isolated chamber to hold that vacuum is then assessed.
A pressure rise of not more than 13mbar in 10 minutes is considered acceptable (see EN285).A greater rise indicates a leak on the chamber, for example due to a faulty door seal, which could permit entry of air to the chamber during the pre-sterilisation phase of the cycle.
Regards