operational qualification

How To Validate an Autoclave: Operational Qualification (OQ)

Every laboratory strives for consistency and repeatability in its sterilization processes. But this doesn’t come easily. In order to ensure your autoclave operates efficiently it’s critical that you validate the sterilization process and verify that the equipment is working safely and properly. This is known as Operational Qualification (OQ), and it’s one of the most important validation tests you can run on your steam sterilizer.

In a previous post we reviewed one of the first phases of a typical validation process: Installation Qualification. In this blog we’ll explain why Operational Qualification is another crucial step in validating your autoclave.

What is Operational Qualification (OQ)?

Simply stated, the OQ process verifies that the autoclave meets the desired and intended performance standards of the lab. OQ testing examines the autoclave’s ability to run the sterilization process correctly and repeatedly while also responding appropriately to error conditions. OQ testing typically includes the following tests:

  • Empty chamber temperature mapping
  • Simulated load chamber temperature mapping and, if required, verification of sterilization efficacy using biological indicators (BI)
  • Alarm conditions and expected results

Operational Qualification (OQ)- process of obtaining and documenting evidence that installed equipment operates within predetermined limits when used in accordance with its operational procedures [ISO/TS 11139:2006]

Equipment Capabilities and Specifications

In general, the operational requirements for a sterilizer are detailed in a User Requirement Specification (URS). The URS defines the required performance, parameter limits, accuracy, prevision, ancillary functions, and standards to which the equipment’s performance must meet. It is the basis of OQ and can be written by the customer or may be the manufacturer’s specification that the user accepts.

Autoclaves have specific critical process parameters:

  • Temperature setpoint range and control
  • Temperature uniformity throughout the chamber and load
  • Pressure range and control
    • For prevacuum sterilizers: air evacuation capability, including depth and control of vacuum setpoints
    • For any sterilizer: the capability to achieve saturated steam pressures given the temperature setpoint and control range.
      • It may also include evacuation and pressurization rate control
  • Exposure time (and other dwell phase) control

Successful cycle execution requires that these parameters are achieved repeatedly and with predefined precision. If the machine must comply with a specific standard (ISO 17665, PDA Technical Report 1, PDA Technical Report 48, EN 285), the accuracy and precision of the process parameters will be specified in the standard.

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Equipment Testing

OQ validation generally includes both empty chamber and loaded chamber temperature mapping for all cycle types that the facility runs (eg., gravity, liquid, pre-vacuum, etc). If an autoclave has the capability to run a cycle but it is not currently used, the facility does not have to test it since the validation for that cycle can always be run at a later date.

Empty Chamber Testing

Empty chamber temperature mapping is performed to verify and document that the temperature range delivered throughout the empty autoclave is within required specifications. Interestingly, temperature mapping an empty chamber can create more of a challenge than testing a fully-loaded chamber because the load’s thermal mass aids in providing temperature homogeneity and limiting overshoot.

Empty-chamber testing is done with temperature datalogging probes. Temperatures should be measured at a minimum of five locations in the chamber (plus at a point adjacent to the controlling temperature sensor in chambers up to 800 liters). More sensors provide a more-detailed analysis of temperature profile.

Examples of acceptance criteria are:

  • chamber temperature -0/+3°C relative to setpoint
  • chamber temperature range over all dataloggers at any given time ≤2°C

Pressure datalogging should also be performed only if pressure is a controlled parameter.

Simulated Load Testing

OQ validation must also test simulated loads that mimic the real loads a laboratory plans to run. These loads may be solid, liquids, glassware, medical devices, in short, anything that would normally be sterilized. For simulated load testing, ensure that at least three of the items in each load are being monitored for temperature and biological indicator (i.e. place the probe and BI right next to or on top of the load).

Diverse items processed in a specific cycle type may be tested together, however, their temperature and indicator (see below) data should be evaluated independently. Therefore, if mixed loads are to be tested, at least three of each item type should be included, and arrayed throughout the sterilizer chamber, not all adjacent to one another.

Simulated load testing may also include biological and/or chemical indicator testing. For overkill cycles, half-cycle testing (the cycle has exposure duration of half the normal exposure time) should be carried out for these cases. Biological indicators must have a 106 population of G. stearothermophilus spores for validation testing of steam sterilization. If chemical indicators are used, a Class 4 or 5 indicator is required. Class 6 indicators are only suitable for full-cycle testing, since they are not expected to show a complete cycle in less exposure time.

Alarm Testing

Here is sample list of alarms that should be tested during an OQ validation:

Alarm/ Interlock Action Expected Results Method & Actual Results
Recycle Alarm Simulate recycle alarm (Alarm occurs when temperature falls below sterilization temperature setpoint for 1 minute or more during the sterilize phase of a cycle) Buzzer sounds, alarm message printed, and steam supply to chamber is shut off and chamber exhausts
Over Temperature Alarm Simulate over temperature alarm (Alarm occurs when chamber temperature exceeds setpoint by x°C) Buzzer sounds, alarm message printed, and steam supply to chamber is shut off and chamber exhausts
Time Limit Alarm Simulate time limit alarm (Alarm occurs when temperature is not achieved within 1 hour of cycle start) Buzzer sounds, alarm message printed, and steam supply to chamber is shut off and chamber exhausts

Ancillary Items to Test

The method used to activate the alarm must be documented and should simulate the process error that would cause it to take place. The actual result must be identical to the expected result in order for it to “pass” the OQ validation.

Other unit-specific items that should be tested include, but are not limited, to:

  • Switches to prevent steam from being admitted to the chamber with the door unsealed.
  • Interlocks to ensure that, in a double-door unit, both doors cannot be opened at the same time in normal operation.
  • For units with dual transducers, the transducers must read within a specified amount of one another during exposure phase.

Operational Qualification provides documented proof that the autoclave can execute the required processes and that its safety and ancillary features work properly.

These capabilities must be demonstrated in the unit’s final location of operation with it’s final utilities connected.

If you have additional validation questions or any questions related to autoclaves in general, please contact us for more information. Also, stay tuned for future posts on How to Validate an Autoclave.

(Written by: Jonathan A. Wilder, Ph.D., Stericert div. of H & W Technology)

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