The Vacuum Leak Test (VLT), Acceptance Criteria, and Pharmaceutical Applications

Vacuum Leak Test for Autoclave:

  • To check for leakage in autoclaves, vacuum leak tests are conducted.
  • “The Chamber Integrity Test” is another name for the Vacuum Leak test.
  • In (Vacuum Leak test) VLT, a vacuum is initially applied within the chamber, followed by a wait for the vacuum to reach a predetermined set point, a holding period during which the vacuum is maintained, and finally, vacuum breakage.
  • Check the results afterward to see if the autoclave leakage was within the acceptable range.
  • According to the Health Technical Memorandum 2010 (HTM 2010) standards, VLT should be done once per week. (Full form of HTM is Health Technical Memorandum)
  • However, it is advisable to carry out VLT on a daily basis because this is a very important test that determines the chamber’s integrity.
  • There is a possibility that non-sterile air will enter the autoclave chamber if there is any leakage there or if the allowed amount of leakage is exceeded.
  • When a vacuum break occurs, air enters the chamber through a 0.22-micron filter that is situated on the autoclaves’ unloading side.
  • As sterile air passes through a 0.22-micron filter before entering the chamber, there is no danger of contamination.
  • However, if air entered the chamber through any other chamber connector than the filter, non-sterile air would enter and potentially contaminate the sterilized load.

Acceptance criteria for Vacuum Leak Test (VLT):

  • As per Health Technical Memorandum 2010 (HTM 2010) standards Vacuum Leak Test (VLT) should be not more than (NMT) 1.3 mbar per minute.
  • However, some autoclave printouts specify the acceptance requirement as 0.013 bar without specifying whether the vacuum leakage limit is per minute or per 10 minutes. The technician can become confused as a result.
  • Here is the clarity:.

For example:

  1. Vacuum at hold time start: A
  2. Vacuum at hold time end:  B
  3. Actual leakage: A-B= Z per minute
  • The result for vacuum leakage per 10 minutes is given by Z X 10 (Result for Leakage for 10 min.)
  • As per HTM 2010, the Acceptance criteria is NMT 1.3 mbar per minute
  • Some autoclave printouts suggest the results as 0.013 bar
  • 1 bar is equal to 1000 mbar or 0.001 bar per min. or 0.010 bar per 10 min.
  • so, 1.3 mbar per min. or 0.0013 bar per min. or 0.013 bar per 10 minutes.

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