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Home > Evaluation & Reports >
Autoclave v. Rotoclave® by Dr. Gary Braedt of the University of New Orleans

Department of Biological Sciences

New Orleans
Louisiana 70148
(504) 286-6307
(504) 286-6121 FAX

December 4, 1995

Terrance Placzek
Tempico Medical Processing Co., Inc.

251 Highway 21 North
Madisonville, LA 70447-0428

Dear Mr. Placzek:

Upon your request, I have prepared the following brief analysis comparing the relative effectiveness of the Rotoclave®versus a stationary autoclave for the purpose of processing of Regulated Medical Waste ("Red Bag" waste).

Autoclaves are of two general types. The gravity displacement type uses a release valve to expel the air/steam mixture below a certain temperature; the pre-vacuum type creates a vacuum before pressurized steam is introduced into the vessel. Both methods lead to replacing air in the chamber with steam at a preset temperature and pressure, usually at or above 250° F and 15 psi. Saturated steam under pressure is necessary to achieve sterilization because endospores and some viruses can withstand boiling water for periods of 20 hours or more. The Rotoclave® uses the latter method and maintains a temperature of 275° F and 45 psi making it capable of sterilizing the hardiest of bacterial endospores.

Sterilization in an autoclave depends upon steam coming in direct contact with the contaminated material, or raising the temperature of a liquid or semi-liquid mass to at least 250° F. Dry heat requires a much higher temperature and longer incubation time to affect sterilization, hence thermal conduction of heat to a solid object without steam contact does not readily lead to sterilization. Sterilization is also time-dependent; usually 15-20 minutes at 250° F suffices.

Since steam sterilization requires that the steam directly contact the contaminated material, it is crucial that all of the air in the vessel be replaced by steam, and that the containers within the vessel be open to the steam. Air pockets result in "cold spots", which is to say, in steam that is at a lower temperature than expected for the pressure attained. Two research reports suggest that the contents of sealed polypropylene bags, i.e. Red Bags, do not reach 250° F during a 50 min cycle. Thus, in a stationary autoclave, Red Bag contents most likely are not rendered sterile. Stationary autoclaves also suffer from air pockets ("cold spots") that are a function of the geometry of the introduced load. The "cold spots" result from the vessel’s contents interfering with the evacuation of air and efficient circulation of the introduced steam, resulting in pockets of trapped air. Objects within these "cold spots" often are not sterilized. Furthermore, the volume of a liquid or semi-solid mass greatly influences the time required to raise the mass to a temperature required for sterilization. Thus, in addition to the problem of inadequate steam penetration, the mass within a Red Bag may preclude sterilization of its contents within a standard operating time.

The Rotoclave® solves these problems by physically disrupting the integrity of sealed containers. That is, Red Bags are ruptured and their contents uniformly distributed throughout the Rotoclave® vessel.

The vanes in the processor have been designed so that the vessel’s rotation forces a near random mixing of all of the material in the vessel. Should there be "cold spots", the constant rotation and displacement of materials will insure that the entire contents will reach the desired temperature for a time sufficient to guarantee sterilization. Thus, neither load geometry nor volume affect the ability of a Rotoclave® to achieve sterilization.

To achieve a result with a stationary autoclave similar to that of the Rotoclave®, the Red Bags would, at the least, have to be opened before treatment. This procedure would place the operator at risk due to aerosolization of the Red Bag contents. Additionally, opening of Red Bags would introduce potential pathogens into the hospital environment, both directly into the atmosphere and indirectly via the operator’s clothing. In any case, given the volume within most Red Bags, it is not clear that simply opening them would guarantee sterilization of their contents due to the mass of the material involved. The final product of an autoclave, therefore, is likely to contain pathogens. This places the downstream handlers at risk, including truckers and landfill operators. Furthermore, since the wastes most likely will spend some time in a dumpster before hauling, it is likely that contaminated leachate will escape the dumpster and re-enter the hospital via foot traffic and aerosolization. The risk of release of pathogens form non-sterile Red Bag contents is exacerbated if the contents are shredded before disposal.

Compliance with federal, state and local regulations in the future will require, where they do not already, a guarantee of effective sterilization of Red Bag waste. This can easily be achieved with a Rotoclave® by introducing vials containing Bacillus stearothermophilus spores into the vessel in perforated steel containers. By this assay, the Rotoclave® has achieved complete sterilization in testing involving thousands of samples. A similar analysis for an autoclave would require introducing vials of B. stearothermophilus spores into the center of a "typical" Red Bag mass. Results from placing spore vials in an autoclave outside of Red Bags will overestimate the apparent ability of the autoclave to sterilize the Red Bag contents since, as discussed, Red Bags trap air producing a "cold spot". The opening of Red Bags to place spore samples inside is an undesirable operation for reasons of operator safety. However, not to do so will lead to the dangerous conclusion that autoclaving results in the uniform sterilization of medical waste, when this most likely is not the case.

Many landfills require that medical waste be unrecognizable to be acceptable. Since Red Bags are deformed, but not destroyed during processing in a stationary autoclave, this result is not achieved. The Rotoclave®, however, disrupts Red Bags rendering them essentially unrecognizable. At the same time, during processing the volume of the waste is reduced by about 50%. A further reduction in volume, to about 20% of the original, is achieved by post-processing shredding and grinding. For this latter process to be safe and efficient, two criteria must be met. The first is that the material be sterile to prevent the spread of pathogens. Secondly, the Red Bag contents must be conspicuous to allow the operator to sort out objects that will damage the shredder and/or grinder. A stationary autoclave, unlike the Rotoclave®, fails both of these two criteria since not all of its product is likely to be sterile, and the Red Bag contents are not made conspicuous.

In summation, it is my opinion that the Rotoclave® is far superior to a stationary autoclave. Given the risk, it is my belief that nothing short of sterilization of Red Bag Medical Waste is sufficient to guarantee the public safety, and the Rotoclave® is the only product on the market that will reliably accomplish this goal. I am obviously favorably impressed with your product and believe that the Rotoclave® is the best product on the market for the processing of Regulated Medical Waste.

Gary Braedt, Ph.D.
Assistant Professor/Coordinator of the Microbiology Program
University of New Orleans


This report does not constitute an endorsement by the University of New Orleans, or the State of Louisiana. It was prepared by Dr. Gary Braedt in the capacity of an independent consultant, and he bears full responsibility for its accuracy and reliability.