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SOP for Autoclave Validation and Challenge Testing

This SOP describes the methods and step-by-step procedures for autoclave validation and challenge testing.

  • Validation testing is undertaken initially when new equipment is installed, and whenever significant changes are made to the equipment, waste or process.
  • Routine challenge testing is undertaken to assure effective disinfection is maintained.
  • Challenge tests are used to validate waste disinfection by autoclaving to achieve the STAATT level III standard by inactivation of G. stearothermophilus spores at ≥ 4 Log10 reduction.
  • The ability of new autoclaves to disinfect laboratory waste should be tested and validated after commissioning has been completed. Thereafter, routine testing should be undertaken to assure effectiveness of disinfection to acceptable standards. This should take place weekly, until four consecutive tests are successfully completed and thereafter it can be decreased to every two weeks.
  • Bowie-Dick tests are used to detect any failure in the air extraction in pre-vacuum autoclaves, particularly those operating at 134°C. The tests are carried out on an empty machine at the start of the day. Bowie-Dick tests are not designed to show whether the machine is capable of sterilizing properly, but instead indicate a specific mechanical fault.


This SOP refers to all personnel who are trained and authorized to use the autoclave, as well as those responsible for maintenance. All training must be documented, updated regularly and filed. Because the autoclave is a pressure vessel that is governed by legal requirements in most countries, local regulations may prescribe the frequency and scope of certain inspections and maintenance activities and who may be able to undertake them. The department manager is ultimately responsible for ensuring the autoclave is available for use.

Materials and Equipment
  • Personal protective equipment (PPE)
  1. Latex gloves
  2. Thick, elbow-length, heat-resistant gloves
  3. Safety glasses
  4. Lab coat
  5. Safety shoes
  • The following documentation must be made available for any operation of or maintenance undertaken on the autoclave:
  1. Instruction Manual
  2. Autoclave Maintenance Log
  3. Autoclave Validation and Challenge Test Log
  4. Autoclave Operation Log
  5. Permit to Work

Hazards and Safety Concerns
  • There are several hazards associated with the use of autoclaves:
  1. Substantial heat and pressure generated by the autoclave
  2. Heat from steam, hot liquids and other materials, including containers, the autoclave chamber and door
  3. Falling items e.g., heavy containers of waste being put into/removed from autoclave
  4. Infectious waste, including untreated waste and waste from a failed treatment cycle
  5. Sharps, when glassware has broken or has been placed in bags rather than puncture-proof containers
  • Do not touch the sides or back of older autoclaves; they have little or no heat shielding and may cause burns.
  • Do not stack or store combustible materials (e.g., cardboard, plastic materials) or flammable liquids next to the autoclave.
  • Never autoclave materials that contain toxic agents (e.g., disinfectants), corrosives (e.g., acids, bases, bleach, phenol), solvents or volatiles (e.g., ethanol, methanol, acetone, chloroform), or radioactive materials.


Validation Testing Procedures
  • Validation is carried out when an autoclave is installed or after any major servicing or change in the waste streams. The purpose is to find an effective disinfection cycle for each type of waste to be processed.
  • Validation must be conducted by an experienced operator or engineer. Procedures are similar to those for challenge testing (Refer to UNDP-GEF, 2010) but may include a degree of trial and error to find the best possible cycle for each waste stream.
  • Fake or surrogate waste is recommended during validation as a safety precaution because many of the cycles during the trial-and-error phase will not result in the correct conditions for disinfection and would consequently expose staff to unnecessary risks.
  • Steam integrators can be used during the trial-and-error phase of the validation to give a rapid indication of whether conditions are met.
  • Once a suitable cycle has been identified, disinfection must be confirmed using self-contained biological indicators (SCBIs). Three passes in a row must be achieved before the cycle can be validated. If any fail, a more rigorous cycle or improved waste loading and containment should be considered to make sure there is a sufficient margin of safety for routine operation.
  • Wherever possible, the engineer responsible for validation will then oversee a number of tests using SCBIs with the autoclave being used by the usual operator and with real waste, to make sure that the operator is achieving the expected level of passes.
  • If a cycle seems suitable during validation, but is not resulting in consistent pass tests during routine challenge testing, then it must be reviewed.

Challenge Testing Procedures
  • Run the autoclave at normal operating conditions processing typical waste during the test.
  • Use the same containers or bags as usual, which are sealed in the normal manner.
  • Check the appearance of and the expiry date of the SCBIs or steam integrators for use in the test. If the liquid in the SCBIs is cloudy or has changed color, do not use.
  • Check the biological indicator details (organism, concentration and d-value) and record the batch number of the SCBIs to be used.
  • Place the test vial in the waste bags/containers where treatment is most difficult, in terms of waste type (such as waste with voids) and location in the autoclave (for example, at the bottom, near the door in horizontal autoclaves). If deemed necessary, up to three SCBIs may be placed in different bags or containers in different parts of the autoclave.
  • Set aside a control vial from the same batch as the test at room temperature for the duration of the autoclave run, for incubation with the test vial (typically 24 hours at 55-60°C).
  • Record all test results in the Autoclave Validation and Challenge Test Log, including observations of the condition of the test vial after autoclaving.
  • Following a test failure, every autoclave run must include one or more test vials, until three tests are successfully completed. Thereafter, testing can resume weekly, until four consecutive tests show No Growth and then the testing can revert to every two weeks.
  • If two or more consecutive tests fail, the autoclave operation, including waste handling and containment should be reviewed. It may be necessary to have the autoclave checked by an experienced engineer or the manufacturer. Any faults found should be rectified. If this does not solve the problem, the validation should be repeated.

Reporting and Recordkeeping
  • Autoclave operator shall record validation and challenge test activities in the Autoclave Validation and Challenge Test Log as indicated.
  • Autoclave operator shall report any test failures immediately to the waste manager or laboratory manager as appropriate, for an investigation into the cause and action to be taken to prevent a recurrence.

Related Documents
  • Infectious Waste Autoclave Operation, Testing and Maintenance - Guidance
  • Autoclave Operation ─ SOP
  • Autoclave Operation Log
  • Autoclave Validation and Challenge Test Log
  • Autoclave Inspection and Routine Maintenance - SOP
  • Audit Checklist: Autoclave Operation


Revision History

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