Sterilization superheated

The objective in packaging cool sterilized products is to maintain the product under aseptic conditions, to sterilize the container and its Hd, and to place the product into the container and seal it without contamination. Contamination of the head space between the product and closure is avoided by the use of superheated steam, maintaining a high internal pressure, spraying the container surface with a bactericide such as chlorine, irradiation with a bactericidal lamp, or filling the space with an inert sterile gas such as nitrogen. 

The critical parameters of steam sterilization are temperature, time, air elimination, steam quaUty, and the absence of superheating. Temperature and time are interrelated, as shown in equation 8. The success of steam sterilization is dependent on direct steam contact which can be prevented by the presence of air in the chamber. The abiUty of steam to heat a surface to a given temperature is considerably reduced by the presence of air. Air elimination, therefore, is regarded as an absolute parameter. If the required amount of air has not been eliminated from the chamber and the load, no combination of time and temperature results in complete sterilization. 

Superheated steam results when steam is heated to a temperature higher than that which would produce saturated steam. The equiUbrium between hquid and vapor is destroyed, and the steam behaves as a gas. It loses its abiUty to condense into moisture when in contact with the cooler surface of the article to be sterilized. This process resembles dry-heat sterilization more than steam sterilization and, under ordinary time—temperature conditions for steam sterilization, does not produce stetihty. 

If the temperature of dry saturated steam is increased, then, in the absence of entrained moisture, the relative humidity or degree of saturation is reduced and the steam becomes superheated (Fig. 20.5). During sterilization this can arise in a number ofways, for example by overheating the steamjacket (see section 4.2.2), by using too dry a steam supply, by excessive pressure reduction during passage of steam from the boiler to the sterilizer chamber, and by evolution of heat of hydration when steaming... 

Other heating equipment. Autoclave used for sterilization can be used to achieve superheating condition at 120°C. For higher temperature heating, a domestic pressure cooker, or a plastic steamer may be used. Some commercial laboratory pressure cookers have been designed for AR-IHC with controlled temperature. A water bath can be used to achieve lower temperature heating condition. 

The compressed ethylene and a peroxide initiator (catalyst) enter the autoclave reactor. An autoclave is any vessel that can be closed up and maintain pressure at elevated temperatures. In chemical applications, the ongoing reaction inside the autoclave generates heat and/or pressure. (When a doctor or dentist sterilizes his instruments in his office,. he uses an autoclave that generates superheated steam.)... 

Autoclave. A vessel used for heating, cooking, or sterilizing by exposure to superheated steam under pressure. 

Replacing sterilizers that operate by one set of principles with sterilizers that operate by another principle (e.g., substituting a gravity displacement steam process with a process using superheated water spray). 

Moist-heat sterilization is achieved when a suitable combination of temperature and humidity can be introduced (or indirectly generated) at the level of the micro-organisms to be inactivated. The classic way to achieve this is by means of pressurized saturated steam at the temperature of 121°C (250°F). However, other sterilizing media (e.g., superheated water or a steam-air mixture) are also frequently used to obviate certain problems that pure steam may pose. Sometimes the load is rotated inside the chamber of the sterilizer to achieve particular results. 

Current pharmaceutical production practice uses substantially three moist-heat sterilization processes 1) pressurized saturated steam 2) superheated water and 3) steam-air mixture. Process 1 is the traditional multipurpose process, which obviously uses pure pressurized saturated steam as sterilizing medium. Processes 2 and 3 are so-called counterpressure processes they were introduced in pharmaceutical production practice approximately 20 years ago and, respectively, use a spray superheated water and a homogeneous... 

Fig. 9 Two superheated water spray autoclaves with a chamber capacity of approximately 4m, with a rotating load and sliding double doors. The man-machine interface of the process controller is not shown. The automated loading/unloading systems, frequently used with large sterilizers to allow faster loading and unloading operations, are shown instead. (Adapted from Ref.t l.)...

Sterilization by saturated steam is only effective for particular combinations of temperature and time in the absence of air. Permanent records of pressure should also be inspected as part of routine batch release. Deviations from the known equilibrium that exists for steam between temperature and pressure may be indicators of superheating. Inspection of the pressure traces of the preliminary phases of sterilization cycles may reveal faulty steam or vacuum valves, which could impact upon sterility assurance. Piesterilization temperature traces are often too messy to be meaningful in these phases of sterilization cycles. This is due to differences between hot and cold starts, differences in temperature between probes in one part of the load and another, etc. 

For porous loads, two other monitoring techniques are in use to give assurance of sterility where there is a risk of air entrainment, superheating, etc. These are the Bowie-Dick test pack and the Lantor Cube. It should be emphasized that these are used in rather special applications and would be of little significance to fluid loads or nonporous solid loads. 

Sterilizability is of essential importance when the pol5mier is used in medical applications. Steam sterilization is preferred over chemical sterilization and radiation sterilization. Steam sterilization consists of a treatment of the membrane with superheated steam of >110°C for 30 min. Steam sterilizable membranes include poly(ether imide), PES and poly-(vinylidene fluoride). 

Superheated steam drying permits pasteurization, sterilization, and/or deodorization of food products. 

It may be noted that the sorption capacity of organic sorbents can be improved significantly (up to 40%) when in relatively small (5% to 10% w/w) mixture with salt or lactose (Tutova and Kuts, 1987). Another method of improving sorption capacity is drying with internal steam generation. Figure 12.17 depicts a sterilizer for granular peat in which the sterilization process takes place by water vapor evaporated from the peat and superheated due to heat supplied by indirect steam. In addition to the steam-heated jacket of a... 

The most reliable method for the sterilization of culture media and culture solutions has proved to be that of treatment with superheated steam in an autoclave (superheated steam sterilizer) at 121 C, which corresponds to 1 bar over atmospheric pressure, for 20 to 30 minutes. The operating conditions quoted by the manufacturer must be observed when using an autoclave. 

In comparison to high-pressure steam sterilization, dry heat is relatively inefficient and is usually reserved for sterilizing (or drying previously autoclaved) glassware. In the absence of superheated water, organic materials take longer to be inactivated even at much higher operational tempera-... 

---