A steam autoclave is a device designed to sterilize cultures, media, surgical instruments and medical waste. Autoclaves will sterilize on the basis of:

  • Length of time in the cycle
  • Temperature
  • Contact
  • Pressure
  • Steam

Important Information

Need to Autoclave?

Unless otherwise stated, at Stanford University autoclaving materials prior to medical waste disposal is NOT necessary. Exceptions to this are users of BSL – 3 biohazardous agents.

An autoclave is suitable for the treatment of certain types of medical waste but not all types. The following items of medical waste must not be autoclaved:

  • Items of medical waste which are mixed with volatile chemical solvents or radioactive materials (this waste must be handled as either chemical waste or radioactive waste)
  • Pathological waste (pathological waste is handled as follows: animal carcasses are placed in a red bag and taken to the pathological waste freezers in the Research Animal Facility; human body parts are placed in a red bag and disposed of as medical waste without autoclaving.)

The following items of medical waste can be autoclaved:

  • Microbiological waste such as cultures of human or animal specimens from medical or pathological 118 Stanford University Biosafety Manual laboratories
  • Cultures and stocks of microbiological specimens
  • Waste contaminated with biohazardous materials such as contaminated paper towels or contaminated surgical gloves

Considerations for effective autoclaving:

  • Do not overload the autoclave bag. The autoclave steam and heat cannot penetrate to the interior of an overloaded bag. The outer contents of the bag will be sterilized but the inner part of the bag will essentially be unaffected by the autoclave cycle
  • Do not put sharp objects, such as broken glass that can puncture the bag
  • Do not overload the autoclave
  • Do not mix autoclave bags and other items to be autoclaved in the same autoclave cycle. Liquid media requires a shorter cycle, often 15- 20 minutes while autoclavable medical waste requires a minimum of 30 minutes in order to be effectively sterilized
  • To help ensure non-variability of sterilization, try to use a consistent loading pattern of materials within the autoclave (amount of material and location within autoclave)
  • Record autoclave conditions achieved for each cycle that is used to decontaminate medical waste. Validate autoclave effectiveness once every month (test strips are a recommended method and easily available). Retain records in an accessible location

Safety considerations for autoclave attendants:

  • Wear personal protective equipment including heat-resistant gloves, goggles or safety glasses and a lab coat.
  • Use caution when opening the autoclave door. Allow superheated steam to exit.
  • Use caution when handling a bag in case sharp objects have been inadvertently placed in the bag. Never lift a bag from the bottom of the bag to load into the chamber. Handle the bag from the top.
  • Watch out for pressurized containers. Superheated liquids may spurt from sealed containers. Never seal a container of liquid with a cork that may cause a pressurized explosion inside the autoclave.
  • Agar plates will melt and the agar will become liquefied. Avoid coming in contact with this molten liquid. Use a secondary autoclavable tray to catch any potential leakage from the bag that would otherwise leak into the autoclave.
  • Glassware may crack or shatter if cold liquid comes in contact with this superheated glassware. If glass breaks in the autoclave, use tongs, forceps, or other mechanical means to recover the fragments; make certain that the autoclave has been cooled down to avoid surface burns.
  • Use an absorbent liner for glass vessels containing liquid. Never put autoclave bags or glassware directly in contact with the bottom of the autoclave.

To autoclave waste, follow the below procedures:

  • Place waste as generated in an autoclavable red bag
  • Put autoclave tape loosely around the top of the bag and place the bag in a secondary container such as an autoclave pan
  • Set the cycle for 30 minutes, 121 degrees F at 20 PSI (or alternate required conditions depending on waste)
  • Document the conditions achieved during the cycle
  • After autoclaving, the autoclaved red bag must be disposed of as red bag waste

A variety of factors must be taken into consideration prior to purchasing an autoclave; additional information concerning autoclave purchases is available on the web at: https://ehs.stanford.edu/reference/autoclave-safety