AUTOCLAVE: – An autoclave is a pressure chamber used to carry out industrial processes requiring elevated temperature and pressure different to ambient air pressure. Autoclave are used in medical application to perform sterilization, and in the chemical industry to cure coatings, vulcanise rubber and for hydrothermal synthesis. Autoclave was invented by Charles Chamberland in 1879.The name comes from greek auto- self, and latin clavis- key, a self- locking device.
STERILIZATION:- Sterilisation can be defined as any process that effectively kills or eliminates transmissible agents (such as fungi, bacteria, viruses) from surface, equipment, foods, medications or biological culture medium.A sterility assurance level (SAL) of 10^-6 means that there is less than or equal to one chance in million that particular item is contaminated or unsterile following sterilization process.
The standard temperature and pressure of an autoclave processes conducted at high temperatures for short time periods are preferred over lower temperatures for longer times. Some standard temperatures/ pressures employed are 115^°C/10 psi, 121^°C/ 15 psi, and 132 ^°C/27psi. (psi=pounds per square inch). After loading and starting the autoclave, the processing time is measured after the autoclave reaches normal operating conditions of 121^°C (250°F) and 15 psi pressure, NOT simply from the time we push the “on” button.
The different tests are follows for qualification of autoclave are: –
Vacuum leak test
Bowie-dick test
Heat distribution study

• Empty chamber
• Loaded chamber

Heat penetration study
VACCUM LEAK TEST: – This test is used to verify the leakage in sterilization chamber during vacuum hold time when the sterilizing chamber is empty.
Procedure: – Ensure that the chamber temperature is stable at ambient and compressed air is on with high pressure and ensure that gasket lubrication is proper and switch provided on panel board. Start the vacuum leak rate test cycle and observe the pressure in the pressure gauge of steam sterilizer and cycle allow the pressure to drop down. Machine will close all the valves connected to the chamber and stop the vacuum pump and note the time and pressure (P1). Wait for stabilization period of 5 minutes (±10 second) and note down the pressure again (P2) and Wait for another 10 minutes (± 10 second) and note down the pressure third time (P3). Return to atmospheric pressure and continue to run for next cycle where vacuum leak rate should not be more than acceptance criteria.
Acceptance criteria: – Vacuum leak rate should be NMT 0.013 bar / 10 minutes.
Frequency: – Run the test for 3 consecutive cycles at the time of Initial Qualification.
BOWIE DICK TEST: – To ensure that the vacuum pulses applied before the sterilization hold period are sufficient to remove the entrapped air or non-condensable gases so as to facilitate the event and rapid steam penetration into all parts of load and maintaining this condition during sterilization holding time.
Procedure:-Place the Bowie Dick test paper on the bottom shelf of the sterilizer just above drain point (100 mm over the drain). Air removal study shall be performed in empty chamber by placing the Bowie Dick test paper. It consists of standard paper pack and indicator sheet Start the cycle by pressing enter key After the cycle is over open the door from control area side and take the sterilized test paper from the autoclave and check the indicator paper for uniform color change As Bowie Dick test paper is designed to simulate the garment pack, it used to test the efficiency of the air removal from the steam sterilizer. Three cycle of air removal study shall be performed (initially) by using fresh indicator paper. This test shall be performed by using Bowie Dick test cycle. To fulfill the maximum exposure requirement, the sterilization cycle shall have 17 minutes at 121°C to 123°C sterilization period.
Place the Bowie dick indicator approximately 100 mm to 200 mm above the sterilization chamber base.
Acceptance criteria:- The Bowie dick indicator should show uniform colour change (Yellow to Brown / black) after the cycle. No change or no uniform change or air entrapment (bubbles) spot on the test sheet indicates inadequate air removal from the sterilization base chamber.
HEAT DISTRIBUTION STUDIES (EMPTY CHAMBER):- To verify the temperature uniformity throughout the chamber and to locate the cold spot in Empty Chamber.
Procedure:- Insert 16 no of temperature sensors inside the chamber through the validation port of sterilizer. Seal the port with silicon sealant to ensure that no steam leakage during operations of sterilizer. Fix all the probe at different location in the sterilizer so that sensors do not touch the metallic surface of the chamber. Connect the temperature sensors to the data logger, which can scan and print the actual temperature and pressure at different locations.
After completion of sterilization cycle check the thermograph in the data logger for attaining set temperature and pressure during the sterilizing hold period. If any deviation observed repeat the cycle after taking necessary correction.
Acceptance criteria:-Temperature distribution within the chamber must be between 121°C to 123°C at all location during the sterilization period (dwell time).
There should not be any slowest heating point (cold spot) in the autoclave chamber and equilibrium time should not be more than 30 second.
HEAT DISTRIBUTION STUDIES (LOADED CHAMBER):- To verify the temperature uniformity throughout the chamber and to locate the cold spot in loaded Chamber.
Procedure:- Insert 16 no of temperature sensors inside the chamber through the validation port of sterilizer. Seal the port with silicon sealant to ensure that no steam leakage during operations of sterilizer. Fix all the probe at different location in the sterilizer so that sensors do not touch the metallic surface of the chamber. Load the article as per loading pattern in the autoclave chamber. Loaded chamber heat distribution study shall be performed separately for all loading patterns. One cycle shall be performed for each loading type for loaded chamber heat distribution study. Connect the temperature sensors to the data logger, which can scan and print the actual temperature and pressure at different locations.
After completion of sterilization cycle check the thermograph in the data logger for attaining set temperature and pressure during the sterilizing hold period. If any deviation observed repeat the cycle after taking necessary correction.
Acceptance criteria:-Temperature distribution within the chamber must be between 121^°C to 123^°C at all location during the sterilization period (dwell time).
There should not be any slowest heating point (cold spot) in the autoclave chamber and equilibrium time should not be more than 30 second.
HEAT PENETRATION STUDIES:– In order to verify sterilizing temperature has been reached in each load subjected to moist heat sterilization, it is necessary to conduct heat penetration studies. This study is conducted to ensure that the coolest unit within a pre-defined loading pattern (including minimum and maximum loads) will consistently be exposed to sufficient heat lethality (minimum “F0”).
Procedure:- Insert 16 no of temperature sensors inside the chamber through the validation port of sterilizer. Seal the port with silicon sealant to ensure that no steam leakage during operations of sterilizer. Fix all the probe at different location in the sterilizer so that sensors do not touch the metallic surface of the chamber. Load the article as per loading pattern in the autoclave chamber. Loaded chamber heat distribution study shall be performed separately for all loading patterns. Arrange the load as specified keep at least 15 biological indicators and 10 thermo chemical indicators shall be used for each cycle. Load placed at the identified cold points must have indicator and temperature sensor in all three runs. One biological indicator and thermo chemical indicator along with external temperature sensor shall be placed at drain point in all three cycles. Perform the sterilization by operating the program specified for each load type as per standard operating procedure and start the data logger and steam sterilizer simultaneously. After the sterilization cycle is completed, stop data logger and open the sterilizer and take out the biological indicator and thermo chemical indicator from load and send to microbiological lab for testing. The biological indicator shall aseptically inoculate into sterile soybean casein digest media (SCDM) and incubated at 55 – 60^oC and liquid load at 35 – 39^oC for 7 days and check the thermochemical indicator for the compliance as per manufacturer recommendation for colour change (i.e. Brown). Take out temperature chart/data logger and inbuilt temperature recorder, report of biological indicator. Check against acceptance criteria for compliance and determine the Fo value and compare against acceptance criteria. Take out external temperature sensor from the chamber and perform vacuum leak rate test.
Acceptance criteria:-Temperature distribution within the chamber must be between 121^°C to 123^°C at all location during the sterilization period (dwell time).
Sterilization temperature should be maintained for NLT 15 minute for minimum 10 thermo couple during hold time. Biological indicator (Geobacillus stearothermophillus) should show complete sterilization (i.e. no growth after incubation).
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Reference links
http://www.dcvmn.org/IMG/pdf/example_pq_for_autoclave.pdf
https://consteril.com/operational-qualification/