Steam Autoclaves
Overloading Sterilizer - The quantity of instruments placed within the sterilizer chamber should not exceed the manufacturer's recommended capacity. Tabletop sterilizers, which are most frequently used in individual and group practices, have a relatively small chamber and are easy to overload. Instruments, bagged or otherwise, should not be loaded in such a manner as to inhibit the free flow of steam around them.

Interruption of Sterilization - Cycle Interruptions most frequently occur to retrieve a specifically required instrument. Effective sterilization in steam sterilizers is a specific function of time, temperature and pressure (saturated steam). If any of these parameters is compromised, sterilization failure is likely.

Time - For most steam sterilizers running at 250 degrees Fahrenheit (121 degrees Celsius), a 20-minute cycle is adequate. That 20-minute cycle should begin at the time the sterilizer reaches operating temperature and pressure. So, it is important to allow adequate warm-up time (normally, 5-10 minutes) before starting the timing of the cycle. There are some steam sterilizers, commonly referred to as "rapid- cycle" or "flash" sterilizers, which may have a shorter cycle time (3.5 to 8 minute cycle).

Temperature - Most steam sterilizers operate in a range between 250-270 degrees Fahrenheit. Any lower temperature may be inadequate to achieve sterilization.

Pressure should be 15-30 psi (pounds per square inch). A frequent reason for loss of pressure is an inadequate seal of the sterilizer door gasket. The gasket may need to be cleaned with common dish washing detergent or it may need to be replaced. A "hissing" sound coming from the sterilizer door may be an indication that the gasket is not sealing properly.

Venting is the process, which during the warm-up time, prior to the actual sterilization cycle, cool air is displaced within the sterilizer chamber by pressurized saturated steam. This process is achieved via a valve commonly referred to as a "bleeder valve". If this valve is not cleaned regularly, sterilization failure can occur. While the sterilizer temperature gauge may indicate that adequate sterilization temperature has been reached, there could be "cool" spots within the sterilizer chamber. The procedure for cleaning this valve should be described in the sterilizer owner's manual.

Water - Only distilled or deionized water should be used in autoclaves for purposes of sterilization and maintenance related cleaning. Water, other than distilled water, may be too corrosive or cause a build up of mineral deposits that can impair the function of the sterilizer.

Chemical Vapor Sterilizers (Chemiclaves^®)
Chemical vapor sterilizers, generally, are operated in a fashion similar to autoclaves. The difference is that a solution, which has its own reservoir, is used as an additive to the distilled water for purposes of sterilization in chemical vapor sterilizers. (The primary ingredient of this solution is denatured alcohol). This solution reduces the corrosive, dulling effect water has on instruments. The chemical vapor solution is introduced into the sterilization chamber through what is commonly called a metering valve. Like autoclaves, overloading and cycle interruption of chemical vapor sterilizers are common reasons for sterilization failure.

Time - 20 minutes is the normal cycle time for chemical vapor sterilizers. Again, it is important to allow adequate warm-up time before starting the sterilization cycle.

Temperature - Most chemical vapor sterilizers operate at the upper end of between 250-270 degrees Fahrenheit (121-131 degrees Celsius).

Metering Valve - This valve on chemical vapor sterilizers is the device that meters the appropriate amount of chemical vapor solution that is introduced into the sterilizer chamber. If the valve is not maintained and cleaned regularly, sterilization failure can occur. The owner's manual should describe how to properly service this valve.

Dry Heat Sterilizers
As with autoclaves and chemical vapor sterilizers, overloading or cycle interruption are common causes for sterilization failure with dry heat sterilizers.

Time - For most dry heat sterilizers a cycle time of 1 hour from the time the sterilizer reaches operating temperature is recommended. There are some dry heat sterilizers that have a shorter cycle time.

Temperature - Most dry heat sterilizers operate at 350+ degrees Fahrenheit.

Dentronix® - This brand of dry heat sterilizer operates via heat transfer. The racks within the sterilizer chamber get hot and, in turn, transfer heat to the instruments. For purposes of spore testing, it is necessary for the spore strip to be in direct contact with metal. It is recommended that the spore strip either be tied to a plier handle with ligature wire or paper clipped to a rack within the chamber. Some models of the Dentronix have a built-in holder for the bacterial spore strip.

Newer Sterilizers
Some of the newer sterilizers on the market, particularly the flash or rapid cycle sterilizers, are so automated that it is difficult to determine precisely why sterilization failure may have occurred. Most frequently, it is simply recommended to immediately retest the sterilizer. If a second, consecutive failed spore test occurs, we normally recommended that you examine the loading techniques and review your owner's manual to see if you are following the operating and maintenance procedures properly. The next step would be to have the sterilizer serviced by a qualified technician.

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