Why To Autoclave Liquids With a Load Probe

Written by:Amit Gupta

In our previous Sterilization Cycles post on theF0 Cycle, we briefly reviewed the process for autoclaving liquids with a load probe. This post further discusses the benefits of using a load probe for sterilization validation.

A load probe is a temperature sensing probe located inside thelaboratory’s autoclave腔室。它的配置使用户可以将探针的尖端放置在被灭菌的负载中。通常，将其放置在最冷或最难进行消毒位置中。液体负荷中的最冷点是最大体积的中心（即2L烧瓶的中心）。同样，固体负载中的最冷点位于最密集的袋子或包装的中心。

Laboratory autoclaves without a load probe measure temperature at the chamber drain (the coldest point in a chamber) and account for sterilization time when the chamber reaches 250°F. The ambient chamber temperature, however, can often be higher than the temperature at the center of the load—a phenomenon referred to as “load lag”¹. This occurs because as steam condenses on a load, the heat must be conducted from the surface to the center of the load. While this is occurring, the load temperature “lags” behind the chamber temperature. If unaccounted for, a discrepancy between the chamber temperature and internal load temperature heightens the risk of non-sterilization.

When running asterilization cyclewith a load probe, the autoclave uses the load probe temperature reading as the primary control for the cycle. Therefore, if the cycle parameters are set for 30 minutes at 250°F, the sterilizer doesn’t start the 30 minute timer until the load probe senses a temperature of 250°F. The reason behind delaying the timer is a phenomenon referred to as load lag.

In order to guarantee sterilization is achieved, the load must reach at least 250°F (121°C) for a specified amount of time. For example, mostLB brothmust be sterilized for 15 minutes at 250°F. For loads that exhibit a large load lag (i.e., dense, solid loads or containers with greater than 500 ml of liquid), a load probe should be used to measure the temperature within the load itself.

Using a load probe ensures the load has been subjected to a temperature adequate for sterilization for the required amount of time.

[1] The size of any given load has a considerable impact on the amount of load lag. For example, a 500ml flask with 300ml of liquid will have a lower lag (i.e., the load will match the chamber temperature quicker) than a 1,000ml flask with 600ml of liquid.

Amit Gupta

Amit has over 15 years of experience engineering multi-disciplinary systems and brings his passion for engineering, innovation and quality to his work every day. Prior to joining Consolidated Sterilizer Systems in 2007, Amit worked on robotics at the Charles Stark Draper Laboratories. Additionally, he designed medical devices and scientific equipment such as novel catheters and DNA hybridization chambers for microarrays. A true engineer at heart, Amit enjoys breaking things just to figure out how to fix them; his love of tinkering even extends to assembling IKEA furniture. He graduated from the University of Pennsylvania with a B.S. in Mechanical Engineering and from MIT with an M.S. in Mechanical Engineering.

17 Questions to Ask Before Buying Your Next Autoclave

With so many models, sizes, options and components to choose from, how can you ever really know exactly what you need to make the most out of your investment?

These questions will help you to make informed decisions by outlining what is most important to consider and know about owning an autoclave.

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