Benchtop sterilizers operate on the principle of gravity displacement: steam is introduced from the top, forcing cooler air out through a vent at the bottom. The displaced air is replaced by saturated steam, and the latent heat released by this steam is used to sterilize the items. The following outlines the operating procedures and precautions for benchtop sterilizers:
I. Operating Procedures for Benchtop Sterilizers
(1) Add an appropriate amount of water to the sterilizer, place the items to be sterilized inside, secure the lid, and tighten the screws symmetrically.
(2) Begin heating the sterilizer to generate steam. When the pressure gauge reading reaches 33.78 kPa, open the exhaust valve to release the cold air. Once the pressure gauge needle drops back to zero, close the exhaust valve.
(3) Continue heating. As the pressure within the sterilizer rises to the required level, adjust the heat source to maintain the target steam pressure for the duration appropriate for the specific items being sterilized. Afterward, turn off the heat source (or disconnect the power) and allow the unit to cool down naturally. Once cooled, slowly open the exhaust valve to release any remaining air before opening the lid to retrieve the items.
II. Precautions for Benchtop Sterilizers
(1) Items to be sterilized should not be packed too tightly.
(2) Cold air must be thoroughly evacuated; otherwise, the sterilizer will fail to reach the required temperature, compromising the sterilization process.
(3) Do not attempt to release pressure rapidly after sterilization. Doing so could cause liquids inside containers to boil violently, potentially dislodging stoppers, leading to spills, or even causing containers to burst. The lid should only be opened once the internal pressure of the sterilizer has returned to atmospheric pressure. (4) The cotton plugs of test tubes or flasks should be wrapped with oil paper or kraft paper to prevent condensation from entering.
(5) To ensure the effectiveness of sterilization, it should be checked periodically. A common method involves placing sulfur powder (melting point 115°C) or benzoic acid (melting point 120°C) into a test tube and subjecting it to a sterilization cycle. If the substance melts, it indicates that the temperature inside the autoclave has reached the required level, confirming reliable sterilization. Alternatively, indicator tape (containing a temperature-sensitive agent) can be applied to the outer packaging of the items being sterilized; a change in the color of the indicator confirms that the sterilization process was effective.
III. Application of Benchtop Sterilizers
As a standard sterilization method, processing items at 101.33 kPa for 15–20 minutes is generally sufficient to achieve sterilization. This method is suitable for all items that can withstand high temperatures and moisture, such as standard culture media, physiological saline, clothing, gauze, and glassware.
Benchtop medical sterilizers have a wide range of applications; they are used in healthcare facilities, medical aesthetic clinics, and similar settings to sterilize medical instruments, dressings, glassware, and liquid culture media. This is a common sterilization technique in microbiological experiments. The method operates on the principle that the boiling point of water increases as steam pressure rises.