Vacuum Leak Test (VLT), Acceptance Criteria and its Importance in Pharmaceuticals

Vacuum leak test is performed to check any leakage in autoclaves. This test is also called chamber integrity test. In VLT, first vacuum is applied inside the chamber and then wait for the vacuum to reach at set vacuum point then hold the vacuum for required time and when hold time completed vacuum breakage occures. After that check the results whether autoclave leakage is within the limits or not.
As per HTM 2010 guideline VLT should be performed on weekly basis. But it is good to perform VLT on daily basis becasue this is very critical test which define the integrity of the chamber. If there is any leakage in the autoclave chamber or leakage is exceeding the limits it means there might be chance of entering non sterile air inside the chamber. When vacuum break happens, air enter inside the chamber through the 0.22 micron filter which is located on the unloading side of the autoclaves. There is no chance of contamination because sterile air enters inside the chamber after filtering through 0.22 micron filter. But if air enter inside the chamber from any other connectivity of the chamber other than the filter, non sterile air would enter inside the chamber and it could contaminate the sterilized load.
Acceptance criteria for VLT: As per HTM 2010 VLT should be not more than 1.3 mbar per minute. But in printouts of some autocalves the acceptance criteria mentioned is 0.013 bar and not showing whether this vacuum leakage limit is per minute or per 10 minute. That might cause confusion for the operator. To clear this confusion, I am explaining this concept and it would be easy for you to understand.
For example:
Vacuum at hold time start: X
Vacuum at hold time end:  Y
Actual leakage: X-Y=Z per minute and if we check leakage for 10 minutes then Z X 10 gives you the result for vacuum leakage per 10 minutes.
HTM 2010 says that acceptance criteria is NMT 1.3 mbar per minute
Some autoclave print outs give the results as 0.013 bar
1 bar = 1000 mbar = 0.001 bar per minute or 0.010 bar per 10 minutes
so, 1.3 mbar per minute or 0.0013 bar per minute or 0.013 bar per 10 minutes.
It means the acceptance criteria mentioned by some autoclave vendors in their printouts is 0.013 bar per 10 minutes which is having the same meaning of 1.3 mbar per minute as mentioned in HTM 2010 guideline.


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