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Autoclave Overview

Learn the purpose and limitations of autoclaves, types of cycles, and procedures for safe and effective autoclaving.

Purpose

Autoclaving, sometimes called steam sterilization, is the use of pressurized steam to kill infectious agents and denature proteins. This kind of "wet heat" is considered the most dependable method of sterilizing laboratory equipment and decontaminating biohazardous waste.

Other decontamination methods—dry heat, ultraviolet or ionizing radiation, and liquid, gas, or vapor disinfection—are not a proper substitute for autoclaving or incineration before disposing of biohazardous material. Autoclaves do not remove chemical contamination.

Operating procedures

When used properly, autoclaves are safe and highly effective. Autoclaves use saturated steam under pressure of approximately 15 pounds per square inch to achieve a chamber temperature of at least 250°F (121°C) for a prescribed time—usually 30–60 minutes.

In addition to proper temperature and time, prevention of entrapment of air is critical to achieving sterility. Material to be sterilized must come in contact with steam and heat.

Using an autoclave requires caution and adherence to strict regulatory and operational requirements. For operating procedures, read:

Autoclave cycles

There are 2 basic autoclave cycles:

  • Gravity or "fast exhaust"
  • Liquid or "slow exhaust"

Both cycles and the materials appropriate for each cycle are described below.

Cycle

Materials

Description

Gravity or "fast exhaust"

Dry goods, glassware, etc. This cycle charges the chamber with steam and holds it at a set pressure and temperature for a set period of time. At the end of the cycle, a valve opens and the chamber rapidly returns to atmospheric pressure. Drying time may also be added to the cycle.

Liquid or "slow exhaust"

Liquids This cycle prevents sterilized liquids from boiling. Steam is exhausted slowly at the end of the cycle, allowing the liquids (which will be super-heated) to cool.

Sterility monitoring

Chemical indicator (e.g., autoclave tape) must be used with each load placed in the autoclave. However, use of autoclave tape alone is not an adequate monitor of efficacy. Autoclave sterility monitoring must be conducted at least monthly using appropriate biological indicators (Bacillus stearothermophilus spore strips) placed at locations throughout the autoclave.

The spores, which can survive 250°F for 5 minutes but are killed at 250°F in 13 minutes, are more resistant to heat than most, thereby providing an adequate safety margin when validating decontamination procedures. Each type of container employed should be spore tested because efficacy varies with the load, fluid volume, etc.

Help UCSD get the lead out!

Some brands of autoclave indicator tape may contain lead. Learn more about possible high levels of lead in autoclave tape, how to properly dispose of it, and lead-free alternatives.

Notice: Disposal of hazardous waste using sinks, intentional evaporation, or as regular trash is against the law. Campus laboratories must abide by strict state and federal waste disposal requirements. You may be held liable for violations of applicable laws.