Department of Biology
The sterilization of materials using steam and pressure is a dependable procedure All autoclaves operate on a time/temperature relationship; increasing the. STERILIZER, TEMPERATURE, PRESSURE, TIME. Steam autoclave, C ( F), 15psi, 15min. unwrapped items, C ( F), 30psi, 3min. lightly wrapped. The extra pressure in an autoclave means that water boils at a temperature higher than its normal boiling point—roughly 20°C hotter—so it.
Condensation will continue to occur so long as the temperature of the condensing surface is less than that of steam. This allows for rapid heating of surfaces, penetration of dense materials, denaturing proteins and microorganism sterilization. Thermal Death Time Thermal death time TDT is used to determine how long it takes to kill specific microorganisms at a specific temperature and specific suspension. Let it suffice to say that death rate is directly proportional to the concentration of microorganisms at any given time.
If you increase the temperature of your sterilization process, this has the effect of decreasing thermal death time. Lowering the temperature increases thermal death time. Higher temperatures for shorter periods of time are preferred.
Use of a Steam Autoclave
Beyond temperature and time, thermal death time is affected by the materials being sterilized. For example, oily materials slow down steam penetration and therefore increase thermal death time. Materials that are highly acidic or basic tend to decrease thermal death times. Thermal death times are available for a number of microorganisms and specific suspensions they may be in. Keep in mind that thermal death time may not be accurate but a good place to start. Autoclaving is accepted as being the most effective and most efficient way of sterilization.
Moist heat autoclaves work on a time and temperature relationship. Higher temperatures are important for more rapid killing of microorganisms.
Longer sterilization times are required for larger loads, large liquid volumes, and dense materials.
Temperatures and pressures most often used in a moist heat autoclave are degrees C at 10 psi pounds per square inchdegrees C at 15 psi and degrees C at 27 psi. Moist heat autoclaving works well for glassware, biological mediasurgical dressings, biohazardous waste and much more.
Pressure and Temperature Pressure and temperature affect boiling. Water boils when the water molecules contains enough energy to escape the liquid and form water vapor or what is called steam above it.
As the water gets hotter, water molecules contain more energy and can more easily escape the liquid. On the other hand, pressure is important as well. The higher the pressure above the water, the more difficult it is for the water molecules to break free of the liquid and vice versa.
Consider going up in altitude. The higher you go, the lower the atmospheric pressure. Boiling water at this higher elevation occurs at a lower temperature because it takes less heat to boil the water.
It is much easier for liquid water to go into water vapor because the pressure above the liquid is much less. In fact, if you were on top of Mount Everest, water boils at around 70 degrees C not degrees C. The boiling point of water at one atmosphere sea level, mmHg is degrees C. Raising or lowering the pressure by around 28mmHg changes the boiling point by 1 degree C.
Vapor Pressure In the case of a closed container such as an autoclave, the process of evaporation will continue until there are as many molecules returning to the liquid as there are escaping. When this occurs, the vapor is said to be saturated. At higher temperatures, more water molecules can escape and the corresponding saturated vapor pressure is greater. In the case of an open container, vapor pressure is actually a partial pressure along with the other components in the air above.
How does a steam autoclave work?
In this case, the temperature at which the vapor pressure is equal to the atmospheric pressure is referred to as the boiling point. Summary Steam autoclaves use high pressure and high temperature steam to kill pathogens. In order for the steam autoclave to be effective, the materials to be sterilized must be saturated with steam. Sterilization refers to absolute destruction of all microorganisms that are present in fluids, on surfaces of materials, in medication and culture media.
Steam sterilization works by denaturing proteins. Denaturing proteins involves protein coagulation which is a change in the conformation of the protein rendering it inactive. Basically the steam autoclave is a pressure cooker that uses steam under pressure as its sterilizing agent. Providing stove-top or solar autoclaves to rural medical centers has been the subject of several proposed medical aid missions. Paper and other products that may be damaged by steam must also be sterilized another way.
In all autoclaves, items should always be separated to allow the steam to penetrate the load evenly. Autoclaving is often used to sterilize medical waste prior to disposal in the standard municipal solid waste stream.
How does a steam autoclave work? - Certoclav
This application has become more common as an alternative to incineration due to environmental and health concerns raised because of the combustion by-products emitted by incinerators, especially from the small units which were commonly operated at individual hospitals. In dentistry, autoclaves provide sterilization of dental instruments according to health technical memorandum HTM According to HTM, instruments can be kept, once sterilized using a vacuum autoclave for up to 12 months using sealed pouches.
Many medical-grade autoclaves are therefore limited to running regulator-approved cycles. Because they are optimized for continuous hospital use, they favor rectangular designs, require demanding maintenance regimens, and are costly to operate.
A properly calibrated medical-grade autoclave uses thousands of gallons of water each day, independent of task, with correspondingly high electric power consumption.
In research[ edit ] A cylindrical-chamber pass-through autoclave Most medical-grade autoclaves are inappropriate for research tasks. General-use non-medical often called "research-grade" autoclaves are increasingly used in a wide range of education, research, and industrial settings including biomedical research where efficiency, ease-of-use, and flexibility are at a premium.
Research-grade autoclaves may be configured for "pass-through" operation. This makes it possible to maintain absolute isolation between "clean" and potentially contaminated work areas. Research-grade autoclaves—which are not approved for use sterilizing instruments that will be directly used on humans—are primarily designed for efficiency, flexibility, and ease-of-use.
They rely on efficient cylindrical pressure-chamber designs, are intended for intermittent use, and have highly customizable programmable controls.
Inthe Office of Sustainability at the University of California, Riverside UCR conducted a study of autoclave efficiency in their genomics and entomology research labs, tracking several units' power and water consumption. Please help improve this section by adding citations to reliable sources.
Unsourced material may be challenged and removed. March Learn how and when to remove this template message Sterilization bags often have a "sterilization indicator mark" that typically darkens when the bag and its contents have been adequately processed. Comparing the marks on an unprocessed bag L and on a bag that has been properly cycled R will reveal an obvious visual difference.
There are physical, chemical, and biological indicators that can be used to ensure that an autoclave reaches the correct temperature for the correct amount of time.
If a non-treated or improperly treated item can be confused for a treated item, then there is the risk that they will become mixed up, which, in some areas such as surgery, is critical.
Chemical indicators on medical packaging and autoclave tape change color once the correct conditions have been met, indicating that the object inside the package, or under the tape, has been appropriately processed. Autoclave tape is only a marker that steam and heat have activated the dye. The marker on the tape does not indicate complete sterility. A more difficult challenge device, named the Bowie-Dick device after its inventors, is also used to verify a full cycle.
This contains a full sheet of chemical indicator placed in the center of a stack of paper. Biological indicators contain spores of a heat-resistant bacterium, Geobacillus stearothermophilus.