Autoclave Safety

Autoclaving is a widely used process for the decontamination of biomedical waste(s). Medical waste is defined as any of the following materials:

  • Cultures and stocks of infectious agents and associated biologicals, including laboratory waste, biological production wastes, discarded live and attenuated vaccines, culture dishes, and related devices.
  • Liquid human and animal waste, including blood, blood products and body fluids, but not including urine or materials stained with blood or body fluids.
  • Pathological waste.
  • Sharps.
  • Contaminated wastes from animals that have been exposed to agents infectious to humans, those being primarily research animals.

Before disposal in the landfill, decontamination by autoclaving is necessary to prevent the potential spread of disease and to maintain proper sanitation. Most biohazardous/biomedical waste is currently disposed of in orange biohazard bags that have a built-in heat indicator ("AUTOCLAVED"). The letters darken to signify that the load has been autoclaved. However, the chemical indicator does not guarantee that the autoclave reached the right temperature and pressure to properly decontaminate the biomedical waste(s).

During routine autoclave inspections, the autoclaves should be run under different operational conditions. To simulate a real biohazard load when one is not available, a mock load may be used consisting of paper towels inside a biohazard bag. Checking procedures include placing indicators such as "Therma-log" S Steam Sterilization Integrator or the "BBL-Autoclave Control Kilit" ampule, both inside and outside the biohazard bag.

Because decontamination requires a significant amount of heat and steam, we suggest adding the amount of water indicated in the table below to help the process before closing the bag. The added water will create a saturated steam atmosphere which will help when autoclaving closed bags.



 9x17 in. (23x43 cm.)

 1/4 cup     60 ml

 14x19 in. (36x43 cm.)

 1/2 cup   120 ml

19x23 in.  (48x58 cm.)

 1 cup     250 ml

 25x35 in. (64x89 cm.)

 2 cups   500 ml



Another preferred way to autoclave your biohazardous/biomedical wastes is by leaving the bag open (with the recommended amount of water). This leaves a clear route for the heat and steam to enter and circulate into the bag. However, this also adds a risk of potential exposure to the biomedical waste when preparing to autoclave, and possible leakage during the decontamination process. Whichever method you prefer, open or closed bag, you need to follow the recommendations to guarantee that complete decontamination occurred without any occupational exposure. To reduce potential leakage, a shallow pan, preferably metal, can be used to place your biohazard load into.

In addition, it is essential to autoclave materials for at least 40 minutes at the standard 121 degrees centigrade and 15 psi for complete decontamination of biohazardous wastes if you use a single bag. If various bags are combined into one large bag, all bags must contain sufficient amounts of water. The time for autoclaving this type of load should be at least 60 minutes.
Excerpt from "Safe Science" (May 1995)  a publication of Michigan State University (ORCBS).