Pressurized steam, sterilization

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-... 

An empirical rule-of-thumb is often used in the design of sterilisation processes which uses the principle of substantial overkill to design a readily validated make-safe process. The MRC Working Party reports on pressure-steam sterilizers are often quoted as the intellectual source of the much-used sterilisation standard of saturated steam at 121.1 °C for 15 minutes. This treatment is widely regarded as giving a sufficient margin of safety in yielding a sterile product irrespective of the type and initial... 

Working Party on Pressure Steam Sterilizers (1959). Sterilization by Steam under increased Pressure. A Report to the MRC, Lancet (i), 425-435. 

Steam (qv) sterilization specifically means sterilization by moist heat. The process cannot be considered adequate without assurance that complete penetration of saturated steam takes place to all parts and surfaces of the load to be sterilized (Fig. 1). Steam sterilization at 100°C and atmospheric pressure is not considered effective. The process is invariably carried out under higher pressure in autoclaves using saturated steam. The temperature can be as low as 115°C, but is usually 121°C or higher. 

The most widely used sterilization method ia the food industry is moist heat. The heat is usually suppHed by high pressure steam, but because most foods already contain moisture the role of steam is to heat the food to the required temperature. The cooking and sterilization processes can frequendy be combined into one. The food may be sealed into impervious containers of glass, metal, or plastic film and undergo terminal sterilization, or it may be presterilized in batches or in a continuous operation and then filled into a presterilized container. The latter process is called sterile filling. 

Fluoro-l 13,17ot-Dihydroxy-21-Acetoxy-1,4-Pregnadiene-3,20-Dione A medium consisting of 1% dextrose hydrate, 2% cornsteep liquor of 60% solids and Kalamazoo tap water was adjusted to pH 4.9 with sodium hydroxide. The medium was steam sterilized at 15 pounds pressure for 30 minutes, cooled, and then inoculated with a 24-hour growth, from spores, of Septomyxa affinis, ATCC 6737. The medium was agitated, sparged with sterile air at the rate of one-tenth volume of air per volume of medium per minute. At the end of 24 hours of fermentation at room temperature, the pH was about 7.4. 

Table 20.2 Pressure-temperature relationships and antimicrobial efiScacies of alternative steam sterilization cycles... 

The relationship between temperature and pressure holds true only in the presence of pure steam adulteration with air contributes to a partial pressure but not to the temperature of the steam. Thus, in the presence of air the temperature achieved will reflect the contribution made by the steam and will be lower than that normally attributed to the total pressure recorded. Addition of further steam will raise the temperature but residual air surrounding articles may delay heat penetration or, if a large amount of air is present, it may collect at the bottom of the sterilizer, completely altering the temperature profile of the sterilizer chamber. It is for these reasons that efficient air removal is a major aim in the design and operation of a boiler-fed steam sterilizer. 

Steam sterilizers, or autoclaves as they are sometimes known, are stainless steel vessels designed to withstand the steam pressures employed in sterilization. They can be (i)... 

One can see by the complexity of these types of manufacturing procedures that much care and attention to detail must be maintained by the manufacturer. This sterile manufacturing procedure must then be validated to prove that no more than 3 containers in a lot of 3000 containers (0.1%) are nonsterile. Ultimately, it is the manufacturer s responsibility to ensure the safety and efficacy of the manufacturing process and the absence of any adverse effect on the product, such as the possible formation of substances toxic to the eye, an ever-present possibility with gas sterilization or when using ionizing radiation. For ophthalmic products sterilized by terminal sterilization (sterilization in the final sealed container, e.g., steam under pressure), the sterilization cycle must be validated to ensure sterility at a probability of 106 or greater. 

The technical problems to be solved are two fold All parts must be steam-sterilized and no abrasion can be tolerated in the chamber. For this the manufacturers offer various solutions in that the pressure plate is ... 

Steam sterilization is at presenzt the most used method [2.15] for freeze drying plants. It requires a temperature of +121 °C for 10 to 30 min, and thus the plant must be pressure-tight up to 2.5 bar. 

The resistance to moisture, hot water and pressurized water vapour is good, with no hydrolysis. The polyarylketones can withstand multiple steam sterilizations. 

The resistance to moisture, hot water and steam is good, with no hydrolysis. The polyetherimides can withstand multiple steam sterilizations. After 10 000 h in boiling water, a PEI retains 95% of its tensile strength. PEI resists repeated cycles of exposure to pressurized steam alternating with periods of vacuum at room temperature. 

Steam sterilization is limited in the types of medical waste it can treat, but is appropriate for laboratory cultures and/or substances contaminated with infectious organisms. The waste is subjected to steam in a sealed, pressurized chamber. The liquid that may form is drained off to the sewer or sent for processing. The unit is then reopened after a vapor release to the atmosphere, and the solid waste is removed for further processing or disposal. One advantage of steam... 

Tanks with vent hlters must be designed for pressures of -20 kPa and +100 kPa and must be equipped with a rupture disk. Tanks for hot loop and steam sterilizable line must be designed to withstand steam sterilization (121°C). A steam jacketed sterile vent hlter must be used to avoid condensation in the hlter and the vent hlter housing temperature controlled. The tank for hot storage is steam jacketed and insulated for temperature maintenance. Minimum instrumentation shall include level indication, temperature recording controller, pressure gauge, and pressure relief valve. 

A temperature control system. Although operating under pressure, temperature is the controlling factor in steam sterilization. The modern temperature controller is made up of several key elements to sense, record, and react. These are discussed in a later section. 

The condenser housing is round and horizontal with vacuum- and pressure-resistant design for the freeze-drying and steam sterilization processes. The condenser is slanted toward the drain ports. 

UHT milk differs from pasteurized milk mainly in the heat treatment employed for sterilization. Usually UHT milk is heated at 130° to 150°C for 2 to 8 seconds and is then aseptically packaged. In the final heating stage, steam is injected directly into the milk, or the milk is infused into a steam chamber, followed by flash evaporation to remove added water (steam). An alternative procedure, the indirect method, involves heating milk across a stainless steel barrier, using high-pressure steam as the heating medium (Mehta 1980). 

For many years, pressurized steam(autoclaving) at 120 °C for 30 minutes has been the basic method for sterilizing instruments and decontaminating materials. When autoclaving is not possible, as is the case with lensed instruments and materials containing plastic and rubber, ethylene oxide— diluted with either fluorocarbon or carbon dioxide to diminish explosive hazard—was used at 440-1200 mg/L at 45-60 °C with 30-60% relative humidity. The higher concentrations have been used to increase penetration. 

Autoclave sterilization is one of the most difficult common sterilization environments for a medical adhesive, and it is commonly used in hospitals and health care facilities for reusable devices. Autoclaves sterilize with high-pressure steam. Temperatures inside the sterilization chamber typically can reach 130°C with pressures above ambient. Certain adhesive systems, such as polyurethanes, may show hydrolytic degradation in such environments especially after multiple cycles. Epoxies perform the best under multiple autoclave exposures. However, on certain substrates, light-cured acrylics and cyanoacrylates will also perform fairly well. 

When carrying out cell disruption operations it is often necessary to provide cooling of the cell concentrate due to the high pressures developed in the equipment. An additional consequence of high-pressure operation is that cell disruption equipment can generate aerosols which may be undesirable, particularly for biologically hazardous organisms. In these cases, the ability to steam sterilize the equipment is required, for decontamination, and some type of secondary containment may also be required, such as an isolator or a contained area within a facility to which access is controlled. 

Heating of radioactive solutions, particularly under elevated pressure (e.g., steam sterilization), is also a matter of safety. In order to avoid any contaminated air to escape if a container or a seal is broken, autoclaves used for radioactive solutions should be placed inside negative-pressure sealed units. Autoclaves used for sterilizing high-energy y-emitting radiopharmaceuticals should in addition be supplied with proper lead shielding. 

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