Porous load autoclaves usually control by either temperature or pressure. Assuming that all air has been removed from the autoclave chamber prior to the sterilisation phase the temperature and pressure should correlate. The theoretical temperature can be correlated by the pressure recorded by using steam table for example http://www.spiraxsarco.com/Resources/Pages/Steam-Tables/saturated-steam.aspx 

Control of temperatures and pressures within the autoclave should fall within the control set points and correlate to steam tables. If excursions are identified then there are several potential route causes: 

• Calibration – Has this been performed recently and the correct off sets applied?
• Superheated Steam – Perform Steam Quality Testing Superheat test.
• Localised Dry Heat – High temperatures are often seen by thermocouples placed on paper and mop heads. This is caused by paper absorbing the moisture from the steam. We recommend placing a Biological Indicator in these locations to confirm kill.
• High Jacket Temperature – If your autoclave is jacketed the temperature of the jacket should be lower than the autoclave control temperature.
• High Temperatures in Vessels – Often referred to as Adiabatic Expansion or the Venturi Effect, as the steam expands entering the vessel the temperature increases.

​It is important to remember that high temperatures in an indication of dry heat, steam sterilisation is an effective method of sterilisation because of the moisture. Utilising dry heat as a sterilisation method requires much higher temperatures and extended hold times for example depyrogentation tunnels.

If you need any assistance with autoclave validation or steam quality testing please contact us.

Data loggers come in all shapes and sizes utilising different sensing technology from thermocouples to PT1000 sensors. The price and quality of these data loggers varies dramatically and the selection of sensor should be considered prior to perform a temperature mapping study.
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• Will the selection of the data logger impact the results of the temperature mapping study?
• Could a freezer pass with one data logger type and fail with another?

We selected various calibrated data loggers with internal and external probes and placed them adjacent to each other in a -20°C Freezer. The graph below shows a snapshot of the results, comparing an external sensor logger to an internal sensor logger.

From the graph you can clearly see the temperature fluctuations of the freezer in the external sensor. The internal logger however does not record the same extreme temperatures. The air within the sensor acts as a buffer, effectively buffering the temperature fluctuations.
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If you’re writing a risk assessment into the temperature mapping of your controlled temperature environments, consideration should be given to the sensors used to perform the mapping. Will the buffering effect of internal sensor impact the accuracy of your mapping exercise?

If you would like to read our full report on sensor selection and probe buffering please contact us.

Seasonal variations in weather can impact temperature and/or humidity control of warehouses. In order to ensure the stability of your warehouse it is recommended you perform summer and winter temperature maps.

In the UK and Ireland meteorological winter is between 01 December and 28 February. Meteorological summer is between 01 June and 31 August. So you should ensure your winter and summer maps fall between these periods.

​We typically perform winter and summer maps over 7 days, this is to ensure the mapping includes changes in shift patterns, workflow etc. We can work to your own onsite protocols or generate bespoke protocols including the identification of sensor locations, risk assessments and validation requirements.

If you'd like to more please visit our temperature mapping services page or contact us for more information.