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To Autoclave, or Not to Autoclave…

Read the examination of the autoclave environment that all components of an autoclave load must endure. If you’d like to skip down to the list of what can and cannot be autoclaved, click here.

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Withstanding Elevated Pressures

At the foundational level, autoclaves use steam (high temperature) under pressure to create a sterile environment by killing pathogens inside the autoclave chamber by the completion of the sterilization cycle. Creating this environment requires a tremendous amount of pressure in the chamber. A key component to understanding what can and cannot be autoclaved is whether or not the material can withstand the pressure of an autoclave’s sterilization cycle.

Pressure ramping required to remove entrapped air, a common barrier to proper sterilization, will ramp to over 30 PSI inside the chamber. This pressure creates a net difference of over 15 PSI when compared to standard atmospheric pressure of 14.7 PSI. To better conceptualize the amount of pressure, the simple pressure exerted on the autoclave door for the most common autoclave door sizes:

Chamber Size	Chamber Pressure	Amount of Force (Chamber Door)
10″ cylindrical (common tabletop)	15 PSI	1,178 lbs.
20″ x 20″	15 PSI	6,000 lbs.
26″ x 26″	15 PSI	10,140 lbs.
24″ x 36″	15 PSI	12,960 lbs.
26″ x 63″	15 PSI	24,570 lbs.

According to the CDC, the two most common sterilization temperatures are 121°C (250°F) and 132°C (270°F). It is essential to understand that special cycles, dependent upon the material load type, load sensitivity to temperature, and pathogen danger level, maximum cycle temperature could differ slightly. However, changes to the temperature parameter are not low enough to change the list of autoclavable items.

With that foundation, let’s take a look at some material make-up of low-density polyethylene (LDPE) and high-density polyethylene (HDPE). Both of these types of plastic are commonly used to make plastic containers and bins that are not rated as autoclave safe. The reasoning is simple. According to material selection platform SpecialChem, LDPE has a melting point between 105°C (221°F) and 115°C (239°F) and HDPE has a melting point between 120°C (248°F) and 140°C (284°F). While these are just two examples, it points to the chemical limitations of materials that are not suited for the temperatures inside of an autoclave chamber during a sterilization cycle.

Damage to the Sterilization Load and Autoclave Chamber Floor

At this pressure and temperature, load containers and instruments are likely to fail and ruin the load being sterilized. Not only can this disrupt the sterilization process inside the laboratory as the autoclave is cleaned and inspected, but the ruined material, glassware, and instruments could also cost hundreds or even thousands of dollars to replace. In addition, this could cause damage to the inside of the chamber and could void the manufacturer’s warranty on the autoclave chamber.