Autoclaves must be used properly to effectively decontaminate potentially biohazardous materials. The following elements all contribute to autoclave effectiveness.

  • Temperature: Adequate chamber temperature is at least 121°C (250°F).

  • Time: Adequate autoclaving time for biohazardous waste is a minimum of 45 minutes, measured after the temperature of the material being sterilized reaches 121°C and 15 psi pressure. The more densely arranged the autoclave load, the longer it will take to reach 121°C in the center of the load.

  • Contact: Steam saturation of the load is essential for effective decontamination. Air pockets or insufficient steam supply will prevent adequate contact. To ensure adequate steam contact, leave autoclave bags partially open during autoclaving to allow steam to penetrate into the bag.

  • Containers: Use leak-proof secondary containers for items to be autoclaved. Place plastic bags inside a secondary container in the autoclave in case liquids leak out. Plastic or stainless steel containers are appropriate secondary containers. Make sure plastic bags and pans are autoclavable.

  • Indicators: Autoclave tape indicators can only verify that the autoclave has reached normal operating temperatures for decontamination. Most chemical indicators change color after being exposed to 121°C, but cannot measure the length of time spent at 121°C. Certain chemical indicators (such as SterigageTM) verify that the autoclave reached adequate temperature for a specified length of time. However, biological indicators such as Geobacillus stearothermophilus spore strips verify that the autoclave cycle is performing properly and will kill microorganisms.

    • Use a chemical indicator in every load to monitor the effectiveness of individual autoclave runs (temperature only).

    • Once a month, use a biological indicator (such as Geobacillus stearothermophilus spore strips). Bury the indicator in the center of the load to validate adequate steam penetration. Keep a log book to record the results.


Autoclave Safety

Autoclaves are classified as pressure vessels. All autoclaves with an internal capacity of 5 cubic feet or larger must be inspected at least annually according to Iowa Code. Repairs to most autoclaves on campus are done by Facilities Planning & Management (FP&M).

Because an autoclave uses saturated steam under high pressure to achieve sterilizing temperatures, proper use is important to ensure operator safety. Prevent injuries when using the autoclave by observing the following rules:

  • Wear heat resistant gloves, eye protection, closed toed shoes and a lab coat, especially when unloading the autoclave.

  • Prevent steam burns and shattered glassware by making sure that the pressure in the autoclave chamber is near zero before opening the door at the end of a cycle. Slowly crack open the autoclave door and allow the steam to escape gradually.

  • Allow items to cool for 10 minutes before removing them from the autoclave.

  • Never put sealed containers in an autoclave. They can explode. Large bottles with narrow necks may also explode if filled too full of liquid.

  • Never put solvents, volatile or corrosive chemicals (such as phenol, chloroform, bleach, etc.), or radioactive materials in an autoclave. Call EH&S at (515) 294-5359 if you have questions about proper disposal of these materials.

Inspect your autoclave components regularly. If you find a problem, notify your area mechanic. Do not operate an autoclave until it has been properly repaired.