The Setup and Optimisation of Air Detectors

Dec 5 / Chris Maughan


We have been busy this year supporting our customers across the UK, Europe and the USA with Air Detector Setup and Optimisation.

The increased interest in Air Detectors has stemmed from their inclusion in EU GMP Annex 1 as an alternative to the daily bowie dick test.

In this post we explain what air detectors are and how they can help provide an in process challenge device for your autoclave.

Why is air a problem in the sterilisation process?

The presence of Air or Non condensable Gases (NCGs) can prevent steam from penetrating load items, therefore inhibiting sterilisation. This is a critical factor in the efficacy of a steam sterilization process.

Typically weekly vacuum leak rate tests are performed to identify any leaks into the chamber. In addition daily bowie dick tests are performed to look for non condensable gases in the chamber from leaks and/or the steam supply.

Unfortunately both of these tests are performed in isolation of production loads. They are essentially a spot check on the performance of the steriliser.

In order to detect non condensable gases during a production cycle, we need to use an air detector.

What are air detectors and why do we use them?

Air detectors are a method of detecting non condensable gases within production cycles. They have mainly been used in Europe - predominately the UK and Ireland.

When setup correctly an air detector will fail a cycle on the presence of excessive non condensable gases which can be present from leaks, the steam supply or load items. Typically the air detector will abort the cycle to drying and 'Cycle Fail' will be printed on the control system printout.
Air detectors are normally located in a long thin tube off the drain line and are considered part of the chamber. The pipework is unlagged creating a worst case location for air to collect. In order to setup air detectors, known leaks are introduced to the chamber to determine the optimal setpoint for the system.

Why use an air detector?

Air detectors are an in process challenge device and the only method for identifying the presence of non-condensable gases within a production load.

Air detectors can be set up to fail with very low leaks, small enough to pass a vacuum leak rate test for example 1mBar/min.

How to set up air detectors and perform EN285 Thermometric Testing

The test methods for air detectors are detailed in EN285:

  • Small and Full Load Thermometric Test
  • Small and Full Load Air Detector Test
  • Air Detector Function Test


The testing helps ensure your cycle is robust enough to sterilise with a large leak into the chamber and the air detector is capable of detecting a leak.

How can we help?

We can help develop a cycle capable of passing EN285 Testing and optimise your air detector to detect very low leaks.

Setting up your cycle using EN285 delivers a robust and repeatable cycle. You can see this in the equilibration times recorded during validation. 

We can help provide training, consultancy or onsite service to setup your cycle and air detector. Please feel free to contact us to learn more at info@thermalcompliance.co.uk or call us on +441748327247

Autoclave Validation Training

Learn more about cycle design, EN285 and Air Detectors in our 3 day Advanced Autoclave Validation training course.
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