Humid-heat sterilization is used in hospitals to sterilize the surfaces of various appliances by dry saturated steam via pressure, such as hollow items or packaged items. The heat generated by the condensation of steam wrapped the items in the sterilizer, eliminating microorganisms simply. The result is irreversible damage to cells through blood clotting.
Sterilization loads used for humid-heat sterilization must be non-heat-sensitive, such as reusable medical equipment, dental instruments, simple surgical instruments, textiles or surgical instruments with cavity, etc. Humid-heat sterilization requires at least 3 minutes of sterilization at 134°C and 3bar or at least 15 minutes of sterilization at 121°C and 2bar.
Humid-heat sterilization has a good sterilization effect on pharmaceutical and other related products. It is a widely used sterilization method that using saturated steam to sterilize pharmaceutical equipment, products and reagents. Because steam will release latent heat when it condenses on sterilization loads which it is a kind of energy saving process.
Sterilization loads that use humid-heat sterilization are usually non-heat-sensitive loads, such as reusable medical instruments, dental instruments, simple surgical instruments, textiles, or surgical instruments with cavity. Whether the vacuum is properly pumped affects the whole sterilization effect, because the lack of vacuum will result in the limited ability of steam to penetrate into the cavity of the instrument.
Steam sterilization process
The advantages of the steam sterilization process include non-toxicity and ease of control. Drying, air removal, steam contact, time, humidity, temperature and pressure are all the key parameters of the sterilization. Temperature and pressure are the most critical factors of the sterilization. According to EN285’s requirements of measurements. It should meet an accuracy of +/ -0.5 ° C at the sterilization temperature and a pressure of +/ -1.6% in the scale range of 0 to 4bar.
Time is a very important factor of the sterilization. Because bacteria do not die immediately, that is why it takes the least amount of time to kill them. Time is closely related to temperature, because the killing effect (death value/lethality value) depends on both time and temperature.
The insecticidal effect is the lethal dose, sterilization for 15 min at 121℃ and 3 min at 134℃ has the same lethal dose.
If the sterilization loads can withstand higher temperatures, choosing 134°C can save a lot of time. The asepsis assurance level (SAL) must be taken under consideration when selecting the lethal value required, as it is usually defined as aseptic, approximately 1/1,000,000, depending on the application. This means that only one in a million bacteria will survive after sterilization.
Before operating, in order to ensure conditions for saturated steam, air must be removed from the sterilization chamber and sterilization loads, this is accomplished by a vacuum system that provides a series of vacuum pulses.
Technically speaking, it is impossible to completely remove the air of the chamber and sterilization loads. Insufficient air removal, vacuum leakage or poor steam quality and the presence of too much non-condensing gas all may lead to the failure of the sterilization.
In order to ensure that enough stored energy is transferred to the sterilization loads by condensation. It is very important that the steam directly contact to the contaminated surface of the sterilization loads. On the contrary, steam stored much more energy than in dry air or water at the same temperature. And this is why saturated steam is the preferred solution that people will choose for sterilization.
It is usually accomplished the proper and complete drying by applying a vacuum to the chamber at the end of the cycle. It is vital that the sterilization loads are sufficiently dry before leaving the chamber, as it may lead to re-contamination if not dry enough.
Temperature and pressure
The lethal value is related to temperature. Therefore, we can check the sterilizer according to the parameters. The pressure can be converted into a theoretical temperature when using a humid-heat sterilizer. And then compared the theoretical temperature with the actual temperature to evaluate whether the steam is saturated. The risk of bubbles that could threaten the sterilization process is eliminated.
The humidity of clean steam has a great influence on the destruction of proteins through denaturation (coagulation). Superheated steam (beyond its saturation temperature) must be avoided as it does not contain enough water to properly sterilize.