Autoclave steam sterilization device: components of the device-method of sterilization-its advantages-disadvantages-method of maintenance-components of the device

First - the use of steam-under-pressure sterilization:

To sterilize aqueous solutions and other materials that are damaged by heat, a special device called an autoclave is used.

**A pressure device designed to heat aqueous solutions above their boiling point to reach sterilization and was invented by Charles Chamberland in 1879

** It is filled with wet steam at a pressure higher than atmospheric pressure, so sterilization can be reached at a temperature higher than the boiling temperature of the water.

The materials are sterilized by autoclave at a temperature of 121 ° C for 15 minutes using steam under a pressure equal to approximately 1.2 kg/cm2.

At this temperature, the most heat-resistant microorganisms die when exposed to this temperature for a short period of time.

Note that some types of germs can withstand the temperature of boiling water for several hours.

It was believed that exposure to autoclave temperature for 15 minutes was sufficient to kill all microorganisms.

A temperature of 121.6 can be reached inside the autoclave at a pressure of 1.2 kg/cm2

Provided that all the air is expelled from inside the sterilizer so that all the pressure generated inside the sterilizer is due to the pressure of water vapour (under normal conditions and at standard pressure

Water cannot be heated to more than 100°C in open containers

Additional heating will cause it to boil and generate steam but will not raise the temperature of the water.

but when heating water in sealed containers that do not leak, such as an autoclave

It is possible to heat water to higher temperatures, when the vessel is heated, the pressure rises due to the constant volume of the vessel ("ideal gas law") and the boiling point of water rises)

At the beginning of sterilization, all the air that occupies the interior of the sterilizer must be expelled by the steam resulting from heating, and sterilizers are provided with special valves to expel the air,

Where the valves are left open after closing the sterilizer

After starting the operation, and when the water boils inside the sterilizer, the steam replaces the air, expelling it from the aforementioned valve

It is inferred that all the air has escaped from the sterilizer by the exit of a continuous, uninterrupted stream of steam from the valve.

After the air is expelled, the valve is closed and the pressure is allowed to rise until it reaches 1.2 kg/cm2

And sterilization is usually done at this temperature for 15 minutes, then the heat source is separated

The sterilizer is left to cool gradually until the pressure drops to the normal atmospheric pressure level

Then he opens the sterilizer

It is forbidden to open the sterilizer before the pressure drops to the normal atmospheric pressure level

Not getting rid of the air completely from the sterilizer leads to insufficient heat treatment for sterilization

Because the presence of air reduces the temperatures that can be reached.

Continue to continuously generate steam in it.

Modern autoclaves, many of which now organize the sterilization process automatically, are equipped with equipment on their doors

Allow it to be opened before lowering the device to the desired level

The standard rate of sterilization is (120°C) within (15 minutes).

The temperature rose to 134 degrees Celsius.

Time reduces to 3 minutes Moist heat sterilization, the ideal way to sterilize sheets and fabrics.

Wet heat sterilization is one of the most important sterilization methods for the following reasons:

1. Maintain the required temperature throughout the sterilization period.

2. The ability of pressurized steam to permeate into the pores of the objects to be sterilized.

3. It needs less heat than dry air sterilization, as hot steam has the ability to kill germs more and faster than dry hot air used in an electric oven.

Factors affecting the sterilization process by pressurized steam:

1. the heat :

The internal spores of bacteria are highly heat-resistant forms of life, and the fatal temperature can only be reached when the steam is pressurized, and a temperature of 121 ° C is sufficient for this purpose if it continues for the appropriate period of time.

2. Humidity:

_ Bacterial protoplasm coagulation (proteins, enzymes, etc.) at moderate temperatures requires moisture.

If moisture is not available, the heat needed to assemble the protein increases greatly

The higher the temperature of the steam, the drier it will be. Therefore, the temperature and exposure time required for sterilization will increase to approximately the state of hot air sterilization (170°C for an hour).

** If the temperature of the steam is higher than necessary, and accordingly, the overheated steam may lose some of its efficiency as a factor in killing microbes, in addition to the fact that the increase in temperature may be harmful to the materials being sterilized.

3. Pressure:

The pressure has no effect on the sterilization process over the range used by the autoclave

However, pressure is only required to bring the steam to a temperature above 100°C.

4. the time:

The time required for the steam to pass through and to heat the materials to the required sterilization temperature.

Even when the required temperature is reached, germs are not killed all at once. The death rate is constant at a certain temperature and for each unit of time during which microbes are exposed to the killing agent

A certain percentage of microbes die. Usually, the killing of endogenous spores of living, thermophilic bacteria takes 11-12 minutes at a temperature of 121°C (humid heat).

5. trapped air:

The cold air inside the sterilizer is two or more times heavier than steam at the sterilizing temperature

**. If the air is not allowed to escape, layers of air and steam will form inside the sterilizer

Because air and steam are slow to mix, the temperature difference between the upper and lower layers will be very large, and even if the air is mixed with steam, the resulting heat may be less than the required one.

_ Hence the importance of complete replacement of air by steam.

** If the thermometer reading on the steam exit hole reaches 100 ° C, this means that all the air in the autoclave has been removed.

6. The nature of the materials to be sterilized:

In general, the bulky and impermeable materials need to be sterilized for a longer time

Therefore, it is more appropriate to sterilize the materials in the smallest suitable containers.

For example:

We find that sterilizing 5 litres in five beakers, each of which has a one-litre capacity, is better than sterilizing them in one beaker of 5 litres capacity.

The flasks should be closed with cotton lids and, if necessary, plastic or other lids

It must be held in place loosely to allow air to escape and steam to enter easily

Also to avoid pots exploding or clogs expelled while the steam is running.