Moist-heat sterilization temperature

Respirator parts Moist heat (autoclave) Moist heat (low- temperature steam, or hot water at 80°C) Sterilization Disinfection Sterilization by steam where possible Chemicals not recommended may be microbiplogically ineffective, may present hazard to patient safety by compromising the safety devices on the machine... 

Aseptic BPS machines are subject to steam-in-place sterilization following standard CIP cycles. The SIP cycles are routinely measured by thermocouples located in fixed positions along the product pathway. Validation of SIP cycles should be carried out to demonstrate that consistent sterilization temperatures are achieved throughout the equipment to prove that the system can be effectively sterilized. Validation should also identify suitable positions for routine use, or justify the fixed probe positions already in place. The SIP validation is generally carried out with the help of additional thermocouples and should include the use of biological indicators (appropriate for moist heat sterilization). Test locations should include areas which may be prone to air or condensate entrapment. An accurate engineering line drawing of the system to aid identification of suitable test locations and document test locations selected should be available. 

For dry-heat temperatures other than 170°C, Fh values are used. The Fh concept is comparable to the Fq concept for moist heat sterilization and references lethality to equivalent times at 170°C. Fh values are shown in units of minutes or seconds, and the calculations of Fh use the same equations as the calculations of Fq. The only difference is that a z value of 20° C is substituted for 10°C.t ... 

Moist-heat sterilization is achieved when water vapor (or, more generically, moist heat, i.e., a suitable combination of temperature and humidity) at a definite temperature is introduced or generated (even indirectly) at the level of the micro-organisms to be inactivated and is maintained in such conditions for a definite time. As explained in detail hereafter, moist-heat sterilization proceeds as an inverse logarithmic progression. Therefore, only a treatment of infinite duration provides absolute certainty that all micro-organisms have been inactivated. 

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. 

Clearly, if D is 1.0 at 121°C, it is 0.1 at 131°C and 10 at 111°C. In other words, the value of D decreases or increases by a factor of 10 when the temperature increases or decreases by 10°C. The algorithm z is defined as temperature coefficient of moist-heat sterilization, i.e., the number of degrees of sterilization temperature that causes a 10-fold variation of D or of the sterilization rate. Depending on the micro-organism... 

This is certainly the most widely used and most versatile moist-heat sterilization method. Accordingly, it is widely used not only for sterilization of pharmaceutical products but also for laboratory and hospital sterilization and for the treatment of medical devices. Nonetheless, it has significant limitations, especially in pharmaceutical use, which are described later. The sterilizing medium is obviously pure pressurized saturated steam. The word saturated means that the steam is in thermodynamic equilibrium with its liquid form (water) at the temperature being considered. 

However, the steam must entrain the smallest possible amount of condensate. The term steam dryness fraction defines the amount of condensate entrained by the moist steam. A dryness fraction of 0.95 means that lOOg of moist steam consist of 95 g of dry saturated steam plus 5 g of condensate, which is (or should be) at the same temperature the steam. A dryness fraction of 0.95 is considered the lower limit of adequacy for moist-heat sterilization. 

Sterilization by moist heat usually involves the use of steam at temperatures in the range 121-134°C, and while alternative strategies are available for the processing of products unstable at these high temperatures, they rarely offer the same degree of sterility assurance and should be avoided if at all possible. The elevated temperatures generally associated with moist heat sterilization methods can only be achieved by the generation of steam under pressure. 

As with sterilization by saturated steam, thermal damage to biological systems as a result of dry heat sterilization processes is a function of absorbtion of heat energy. Inactivation of microorganisms is by oxidation. The kinetics of oxidation and population death approximate to first-order reactions, but they are significantly different from the processes of coagulation of cellular proteins found with moist heat sterilization in that they require far higher temperatures and proceed more slowly. 

Moist heat sterilization is achieved by exposure to saturated steam under pressure in a suitably designed chamber. In these circumstances there is an exact relationship between the steam temperature and pressure, but the pressure is used solely to obtain the temperature required and otherwise contribute nothing to the sterilization process. The time, temperature and pressure must be used to control and monitor the process. 

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. 

Heat is the most widely used means of sterilization, which can be employed for both liquid medium and heatable solid objects. It can be applied as dry or moist heat (steam). The moist heat is more effective than the dry heat, because the intrinsic heat resistance of vegetative bacterial cells is greatly increased in a completely dry state. As a result the death rate is much lower for the dry cells than for moist ones. The heat conduction in dry air is also less rapid than in steam. Therefore, dry heat is used only for the sterilization of glassware or heatable solid materials. By pressurizing a vessel, the steam temperature can be increased significantly above the boiling point of water. Laboratory autoclaves are commonly operated at a steam pressure of about 30 psia, which corresponds to 121°C. Even bacterial spores are rapidly killed at 121 °C. 

Moist-heat autoclaves operating with counterpressure are sterilizers capable of controlling the pressure of their sterilizing medium independently of its temperature. They are used essentially for the terminal sterilization of solutions. 

Moist heat offers the advantage of greater effectiveness at low temperatures. The thermal capacity of steam is much greater than that of hot air. Spores and vegetative forms of bacteria may be effectively destroyed in an autoclave employing steam (121°C) under pressure (ISpsig) for 20 min or (27psig at 132°C), for 3 min. The lag time to complete exposure of the material to be sterilized is important. 

For heat treatment, a D-value only refers to the resistance of a microorganism at a particular temperature. In order to assess the influence of temperature changes on thermal resistance a relationship between temperature and log D-value can be developed, leading to the expression of a z-value, which represents the increase in temperature needed to reduce the D-value of an organism by 90% (i.e. 1 log cycle reduction Fig. 20.2B). For bacterial spores used as biological indicators for moist heat (B. stearotbermopbilus) and dry heat (B. subtilis) sterilization processes, mean z-values are given as 10°C and 22°C, respectively. The z-value is not truly independent of temperature but may be considered essentially constant over the temperature ranges used in heat sterilization processes. 

In heat sterilization processes, a temperature record chart is made of each sterilization cycle with both dry and moist heat (i.e. autoclave) sterilizers this chart forms part of the batch documentation and is compared against a master temperature record (MTR). It is recommended that the temperature be taken at the coolest part of the loaded sterilizer. Further information on heat distribution and penetra-... 

Hoxey EV, Soper CJ, Davies DJG. 1985. Biological indicators for low temperature steam formaldehyde sterilization Effect of defined media on sporulation, germination index and moist heat resistance at 110 degrees C of bacillus strains. J Appl Bacteriol 58 207-214. 

Sterilization by moist heat is suitable only for water-wettabie materials and aqueous solutions. Both temperature and pressure should be used to monitor the process. The temperature recorder should normally be independent of the controller, and there should be an independent temperature indicator, the reading from which is routinely checked against the chart recorder during the sterilization period. For sterilizers fitted with a drain at the bottom of the chamber, it may also be necessary to record the temperature at this position, throughout the sterilization period. There should be... 

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