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Infectious Animal Carcass Sterilization

Most state laws in the United States make no distinction between autoclaves and "rotary autoclaves" with regard to laws governing the use of this equipment for processing medical waste. The rotary autoclave was developed, in part, because of the need for improved sterilization performance compared to stationary autoclaves.

The following paragraph is from a research paper titled Medical Waste Treatment (by the Research Triangle Institute in 1989) and is located in a section that discusses steam sterilization.

"While steam sterilization may be useful for pathological wastes and animal carcasses, USEPA notes that for aesthetic reasons these wastes should be incinerated or otherwise rendered unrecognizable before final disposal. Generally, it is not recommended to treat pathological waste, animal carcasses or body parts by steam sterilization. In an experiment where guinea pig carcasses were autoclaved, a period of time in excess of eight hours was required for the center of the waste load to reach sterilization temperature. In addition for aesthetic considerations, steam sterilization for large, solid objects is not a practical method."

Thus, the result of processing an animal in an autoclave is simply a "baked" animal that may, or may not, be sterile.

The following paragraph is from an abstract of a presentation by Dr. Larry J. Thompson and Dr. Ira L. Salkin at the 42nd Annual Biological Safety Conference in October of 1999 (for ABSA). Their presentation was the result of testing in New York to determine the ability of the Rotoclave® to process frozen animals (parts).

"The treatment and destruction of pathological waste by the Tempico Rotoclave® was evaluated utilizing legs and heads of adult cattle and horses (weight of 60-115 pounds). Vials containing 6 log 10 spores of Bacillus stearothermophilus were implanted into the cortex of the femur and sealed in place, under muscle and skin, with wire. The heads were disarticulated at the lower cervical vertebrae and vials of spores implanted in the cerebellum area of the skull via the ventral aspect of the atlanto-occipital joint. Muscle and skin were sutured closed over the vial implants and in so doing, the atlanto-occipital joint was returned to its natural position." [The animals were then frozen before being placed in the Rotoclave®Process times shorter than 75 minutes did not achieve total destruction of the animals, however:] ……. "Based on these studies we conclude that effective treatment and destruction of the pathologic waste evaluated in the present investigations could be achieved by exposing the legs and skulls for 75 minutes at 45 psi within the Tempico Rotoclave®. However, a sufficient volume of non-pathologic waste materials should be included with the pathologic waste to absorb any free liquid remaining after the treatment cycle."

The non-pathologic waste materials discussed in the abstract could be dry animal bedding, cardboard, paper (such as hospital records), or cloth. This dry material will help control the moisture released when the animal flesh is hydrolyzed in the Rotoclave®. A typical load of hospital waste with 10% pathology waste does not require any additional dry materials.

State laws, in the United States, do not prohibit attempting to sterilize animal carcasses in a standard autoclave. However, as noted in the first discussion, achieving sterilization temperature in an autoclave may be impractical due to time constraints. By comparison, the rotary autoclave is able to start with large, frozen animal parts and achieve 6 log 10 destruction of Bacillus stearothermophilus in a relatively short time. The difference between animal parts and human parts is a matter of esthetics. Many states prohibit treatment of human remains in an autoclave and this is understandable because most of these laws were written before the invention of the rotary autoclave. It is hard to envision that such a major difference exists between two very similar pieces of equipment, but the differences are real.