Sterilization Equipment

The usual way to sterilize cages, bottles, lids, and other material necessary for laboratory animal care that can withstand high temperatures is to use an autoclave. An autoclave is a pressure vessel that uses a combination of above atmospheric pressure and live steam to generate temperatures above boiling. A complete sterilization cycle for nonliquid materials typically includes several cycles of high vacuum followed by live steam injection to rid the chamber of air, the high temperature and pressure sterilization cycle, typically 120°C (250°F) for 20 min or 135°C (275°F) for 15 min, followed by time for steam withdrawal, pressure equilibration, and cooling. High vacuum autoclaves are far more effective and more practical than gravity autoclaves in the laboratory animal environment. In addition, "clean steam" generated from domestic water (not necessarily as high a quality as pharmaceutical grade "clean steam") should be used in the autoclave to avoid contaminating the cages, etc., with chemical additives (typically filming amines used to coat the boiler and steam pipes to reduce corrosion) normally put in steam boilers. Amines from live steam damage polycarbonate and add an avoidable variable to the animal's environment.

For effective sterilization, the material being autoclaved needs to be not wrapped, wrapped with materials that are not airtight, or the wrapped with the wrapping partially open to allow the vacuum

Figure 8.24 A robot stacking clean bedded cages four at a time after having picked the cages off of the indexing tunnel washer belt in back of the robot and placing them under a bedding dispenser that is pneumatically fed from a larger bedding storage hopper located near the dock where bedding is received. The cages are being stacked on special carts that rest on rails, all designed to precisely align the stacks of cages. On the soiled side, an identical combination of robot, carts, and rails are used to load soiled cages onto the tunnel washer belt after the robot dumps the soiled bedding into a hopper, from where it is pneumatically transported to a disposal container outside the facility.

Figure 8.24 A robot stacking clean bedded cages four at a time after having picked the cages off of the indexing tunnel washer belt in back of the robot and placing them under a bedding dispenser that is pneumatically fed from a larger bedding storage hopper located near the dock where bedding is received. The cages are being stacked on special carts that rest on rails, all designed to precisely align the stacks of cages. On the soiled side, an identical combination of robot, carts, and rails are used to load soiled cages onto the tunnel washer belt after the robot dumps the soiled bedding into a hopper, from where it is pneumatically transported to a disposal container outside the facility.

cycle to extract the air and to prevent the creation of air pockets that impede sterilization. Autoclave chamber sizes used in animal facilities vary considerably from ones that will hold only a few cages to ones that will hold three, four, or even more racks of cages. When planned for use in an infectious containment facility or a rodent barrier facility where routine husbandry relies on the sterilization of cages, it is essential to carefully calculate output capacity, which is dependent on the size of the autoclave chamber and the autoclave cycle times. Pit-mounted floor loading bulk autoclaves large enough to hold one or more cage racks are commonly used in biocontainment and barrier facilities (Figure 8.25). For productivity calculations, a cycle time of 1 h 30 min should be used to determine the number of cycles possible in a typical workday. Such heavy use of autoclaves increases maintenance downtime. If money and space is available, two autoclaves are preferred.

Autoclaves used for infectious and containment purposes should have two doors so that materials can be passed through. The autoclave may be located in the cage sanitation area, either between the soiled and clean sides, or between the clean side and the "sterilized" equipment storage area. The ideal location is as an integral part of the infectious containment (Figure 8.7) or rodent barrier area of the facility where cages, etc., can be autoclaved into or out of the area, thus eliminating the need to wrap the cages, etc., for transport between the area of the facility where used and the autoclave.

Materials that may not withstand the high temperatures of autoclaving may be sterilized with gases such as para-formaldehyde, ethylene oxide, and chlorine dioxide. Irradiation is commonly used for sterilizing feed and bedding.

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