Autoclaves for Medical Waste


Autoclaves are closed chambers that apply heat and sometimes pressure and steam, over a period of time to sterilize medical equipment. Autoclaves have been used for a century to sterilize medical instruments for re-use. Surgical knives and clamps, for instance, are put in autoclaves for sterilization.

For medical waste that will be disposed of, autoclaves can be used as heat treatment processing units to destroy microorganisms before disposal in a traditional landfill or further treatment. Autoclaves are a batch process, not a continuous one. Autoclaves are "chemical free" and that appeals to many stakeholders in a complex waste management environment.

Autoclaves are best for wastes that are unlikely to combust or give off substantial off-gas. While incinerators can be built with pollution abatement systems, autoclaves are smaller and it is not economical to unit make a treatment system for vapors emitting from the unit.

Autoclaved medical waste is usually compacted after it cools down. The compaction process may include shredding before the compression. The compaction process reduces the volume of the treated waste significantly.

One problem with autoclaveautoclaves is that the process can aerosolize chemicals present in the waste, leading to the potential for release of materials you would prefer to not release. This can pose a hazard to human operators and to some extent the environment – even though the facility HVAC system may take much of the brunt. It is possible this aerosolized material will deposit on surfaces in ductwork or countertops and floors in your facility – much as what happens in a kitchen. Aerosolized grease is the source of much grime in kitchens.

Are autoclaves a substitute for incineration? Yes, to a large extent. Autoclaves can be used to process the large bulk of infectious waste produced at a hospital or clinic. Autoclaves come in a wide range of sizes and capacities. If you have steam in your facility, you can hook it up to a steam autoclave. Other autoclaves produce steam by electric heating.

Physical Configuration

Autoclaves are metal vessels in a cylindrical shape. This shape is better suited to high pressures than rectangular boxes. During operation the pressure inside the vessel is higher than the ambient pressure. There is a door on the end, and the words "auto" and "clave" mean automatic locking due to high pressure, but for safety reasons most are also sealed manually from outside.

Small autoclaves are electric - they run on the building’s power. Large ones sometimes use steam. Designs include autoclaves with external jackets or with internal heating pipes. Borrowing from incineration technology the word “retort” is sometimes used to refer to the autoclave chamber.

Larger autoclaves often operate under vacuum or a steam atmosphere. Pre-vacuum (or high-vacuum) autoclaves have a pump that is used to evacuate air after the chamber is sealed but before heating. Gravity-displacement autoclaves work by injecting steam into the chamber and thereby driving out the air that was present.

Operating temperature is typically 250 to 280 degrees F. Follow the autoclave manufacturer’s instructions and learnings from treatments of previous batches. Batch time is up to 30 minutes.

Operating Considerations

Autoclaves are basically dumb hot chambers and with a combination of time and temperature you can sterilize pretty much anything, so there is a temptation to put all sorts of medical waste in it. While autoclaves were first used (over a century ago) to sterilize medical instruments so they could be reused, when people started worrying about infectious waste they were throwing away, the autoclave was sitting there and able to accomplish the disinfection/sterilization needed.

Modern medical waste management systems incorporate autoclaves for processing of waste cultures, sharps, gauzes, bandages, and more. Sometime surgery waste and plastic and metal waste contaminated with blood or other bodily fluids are put into autoclaves.

Autoclave Cycle Time

The process design of any waste management system must consider the cycle time of the autoclave. Total cycle time includes

  • Time for operators to place waste in unit.
  • Heat up time - to achieve target temperature
  • Cooking time – time spent at target temperature
  • Cool down time
  • Removal time for operators to open autoclave once it has cooled sufficiently and to removed waste and put it into packaging for storage until transport.

The cycle time of an autoclave cannot be modified. Attempts to cut corners will result in safety violations. These include violation of the time-temperature protocol for waste sterilization and openingautoclave the autoclave before it has cooled sufficiently, endangering human operators.

Validation of Autoclave Efficiency

Periodically, operators must run spore tests to ensure disinfection efficacy. The autoclave manufacturer may recommend a frequency or the appropriate authority might specify how often confirmation with a spore test is required. For instance, the state of West Virginia requires a spore test every 40 hours of operation.

Your regulatory authority may require you keep a log of autoclave activity - date, time of batch processing, what is put into the autoclave (including mass), and confirmation that you have checked the autoclave tape after each use (a checkbox or initials is probably ok). Calibration of temperature and pressure should be done in accordance with manufacturer’s recommendations and the dates and results of calibration should be recorded in the log. Dates and results of spore testing should also be logged. Even if the regulators do not require a log book, it is a good idea to keep one.

Your state or local authority may also require regular checking of the autoclave mechanics by an external and independent inspector.

Treatment Limitations

Remember, the purpose of the autoclave is primarily to destroy micro-organisms. Burning off of small amounts of combustible material may occur, especially in a dry system where there is available oxygen. But don’t put stuff in autoclaves you expect might undergo a chemical reaction in any bulk. Don’t put volatile materials in the autoclave or hazardous organic waste. And don’t expect an autoclave to have any effect on radioisotopes.

What can’t you put in an autoclave? You can’t put in RCRA hazardous waste. You can’t put in heavy metals and expect them to be not hazardous when they come out.

Could pathological waste - human tissue - be treated in autoclaves? No. Human and animal flesh has lower thermal conductivity than metal, so a longer time in the autoclave would be required than for surgical instruments of comparable size. There is also a concern that autoclaved pathological waste may contain low levels of radioactive material or cytotoxic compounds that has survived the heat. In any case the rules and norms in most parts of the world call for incineration of pathological waste.

Some material on deisgn of management processes.