Autoclave temperature

Autoclave temperature is the sterilization temperature inside an autoclave and is commonly 121°C or 134°C, depending upon the items to be sterilized

Autoclave temperature is the sterilization temperature inside an autoclave and is commonly 121°C or 134°C, depending upon the items to be sterilized. This article discusses autoclave temperature, how it is maintained, some common problems and finally, the calibration of autoclave temperature.

Autoclave temperature is defined as the temperature inside an autoclave at which sterilization occurs. The items to be sterilized are held at this temperature before being unloaded from the autoclave.

The ability of a temperature for effective sterilization is determined scientifically and experimentally and remains fixed under normal operating conditions. Additionally, regulatory bodies also review the compliance of autoclave temperature during their routine inspection.

Autoclave temperature is set as a function of time, i.e. temperature should remain for a specified time. When items are held for a specific time, only then is the sterilization successful, and items are allowed to be unloaded from the autoclave for further processing

If, on the other hand, the autoclave temperature not does not remain for a specified time, sterilization will not be successful. The process must be discarded, and it is repeated.

What is the value of the Autoclave temperature?

Recommended autoclave temperature is 121°C for 15 minutes. Another temperature commonly used is 134°C for 3 minutes.

The above temperature and time relationship is demonstrated based on the lethality of steam, defined as steam’s ability to kill microorganisms and another bioburden. 

Various studies and calculations have demonstrated that if the autoclave temperature is 121°C for 15 minutes or 134°C for 3 minutes, the autoclave can effectively achieve the required sterility level.

How is the Autoclave temperature managed inside an autoclave?


The heat source in an autoclave is steam, which is used to achieve the desired temperature. Naturally, the steam temperature is around 100°C, which under normal conditions cannot generate a temperature greater than 100 °C. To make it able to generate a temperature above 100°C, the steam pressure is increased.

The temperature inside an autoclave is directly proportional to the steam pressure, i.e. more significant the steam pressure, the higher the chamber temperature and vice versa. The increased pressure increases the ability of steam to generate a temperature greater than 100°C.

So for an effective autoclave temperature, steam pressure plays the primary factor in achieving and maintaining the desired temperature levels.

If steam enters the autoclave without the desired pressure, the temperature will not achieve its desired level. 

For processes requiring 121°C, the approximate steam pressure is 15 PSI or 1 bar.

Common problems related to autoclave temperature


Let’s discuss some common problems related to autoclave temperature and how to solve these.

Damaged temperature sensor

An autoclave’s temperature sensor often becomes damaged for many reasons, mainly due to hitting or mishandling during the loading and unloading of items. If damaged, the temperature sensor can stop measuring the temperature or erratically perform temperature measurement.

How this problem can be solved?

This problem can be solved by replacing the damaged temperature sensor or, if possible, repairing it. After repair or replacement, the central controller must verify its correct measurement.

A damaged autoclave temperature sensor can disturb the temperature readings of an autoclave

Misplaced Temperature sensor

 Temperature sensors are installed at specific locations with hooks attached to the walls of the autoclave. They are carefully installed in such a position that they do not touch any hot surface. Additionally, their position is precisely selected to cover the entire chamber.

A misplaced autoclave temperature sensor can also cause errors in temperature readings


Suppose the temperature sensor’s position is misplaced or changed and touches any items, chamber wall or hot surface. In that case, the temperature measurement will differ from the actual temperature inside an autoclave.

How this problem can be solved?

This problem can be rectified by inspecting the sensor’s position every time before loading the items into the chamber. If sensors are displaced from their actual positions, they can be immediately corrected, effectively rectifying the problem related to sensor placement.

Control temperature sensor 

The control temperature sensor is the sensor the controller uses to determine the autoclave temperature. While other sensors are in the chamber, the main controller only controls autoclave temperature.

This sensor is installed at the coolest point, typically in the drain, where the temperature is achieved in the last compared to the entire chamber.

Any problem with the drain, such as accumulation of water, steam or condensate, will result in erratic temperature measurement. 

How this problem can be solved?

Problems related to the control sensor can be solved by ensuring a smooth flow of water or condensate through the drain by removing the cause of the blockage. It will prevent the accumulation of steam, condensation or water in the drain and also prevent it from affecting the temperature measurements.

Damage to the temperature probe

Probe is a standard wire that connects the sensor to the man controller. It is a metallic conductor that adds to the actual temperature value due to resistance and electrical relationship. For a given probe, the main controller compensates for the resistance – electrical characteristics and displays the actual temperature value.

However, if the temperature sensor or its insulation is damaged, it will affect how the controller senses the temperature value.

How this problem can be solved?

Problems related to the probe can be solved by carefully inspecting it. If any damage is detected, it is immediately replaced or rectified.

Connection problems.

The connection of the temperature sensor with a controller plays a vital role in determining the autoclave temperature. Problems, such as loose connection, can drift the reading on the controller from the actual value. Additionally, rust on the connectors also negatively impacts the measurement value and subsequently affects the temperature and sterilization process.

How this problem can be solved?

The problem of loose connections can be solved by tightening the connectors. Additionally, if connectors develop rust, they can be removed by using contact cleaners.

Calibration of autoclave temperature sensor 

Calibration is a necessary process and a maintenance technique for autoclaves. It is also a regulatory requirement, and regulatory bodies review calibration procedures during their routine inspection.

Calibration is a process where the output of a measuring device, in this case, the temperature sensor, is compared to the standard reference value. If the difference between the output of a standard and the required temperature sensor remains within acceptable limits, calibration is said to be passed. If, on the other hand, the difference remains outside the acceptable limits, calibration fails. In this case, the temperature sensor must be repaired or replaced.

Temperature Calibration is performed by simulating a known temperature value. The temperature sensor (to be calibrated) is then subjected to the simulated temperature value, which is then compared with the simulated temperature. If the difference remains within the acceptable limits, the calibration is said to be passed or otherwise failed.


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