Auto calve is a process of sterilization by saturated steam under reduced pressure above 100@c. Steam sterilization is carried out in a pressure chamber called an autoclave.
Moist heating is done in an autoclave. It consists of a strong metallic chamber usually made of satin less steel. It has a cover fitted with a steam vent, a pressure and a safety value. Rubber gasket is fitted on the inner side of the lid, in order to make autoclave air tight.
The cover is closed with wing nuts and bolts. The electrically heated element is fitted at the bottom to heat the water to convert in to the steam. The perforated inner chamber is placed on the stand. The matreial is sterilized is loosely packed in to it.
An autoclave is a device used to sterilize equipment and supplies by subjecting them to high pressure saturated steam at 121 degC for around 15-20 minutes depending on the size of the load and the contents.
It was invented by charles chamberland in 1879, although a precursor known as the steam digester was created by densin papin in 1679. The name comes from Greek auto-, ultimately meaning self, and Latin clavis meaning key--a self-locking device.
The principle of the autoclave or steam sterilizers is that water boils when its vapour pressure equals that of the surrounding atmosphere.
When pressure is inside the closed vessel increases, the temperature at which water boils also increases. it is a better sterilizing agent than dry heat because the staturated steam has penetrative power.
Steam condensed to water and gives up to latent heat to that suraface when it comes in to contact with the cooler surface.
The energy available from this latent heat is considerable. For example 1600 ml steam at 100 @c and realese 518 cal of heat. The large reduction in the volume sucks in more steam in the area and the process continuous till the temperature of the surface is raised to that of the steam.
The water of the condensation is ensures moister conditions for killing of the exposed micro oraganisms.
Bacteria is intrincally more suspectible to moist heat as bacterial proteins coagulates rapidly and condensed water ensures moist conditions for killing the microbes present.
VARIOUS COMPONENTS OF AUTOCLAVE
Verticle or horizontal cylinder which is made of stain less steel or guemental in a supporting sheet iron case.
By srew clamps and air tight by a suitable washer the lid or the door is fastened.
The autoclave is on its lid or upper side a discharge tape of air and steam, a pressure valve and a pressure guage and a safety valve that can be sent to blow of at any desired pressure.
Heating is done by gas or electricity.
The domastic pressure cooker serves as a minature autoclave and may be used for sterilizing small articles in clinics and smaller estabilshments.
- A sufficient quantity of water is poured in to the chamber after removing the perforated chamber. The level of the water is adjusted in such a way that it does not touch the bottom of the perforated chamber.
- The material is packed in the perforated chamber. The lid is than closed with the wing nuts and bolts. The autoclave is a switched on to heat the water. The vent is opened and safty valve is setted the required pressure.
- Whem steam starts coming out from the vent and it continuous for 5 mins and it is then closed. It indicates that air has been removed. The steam pressure starts raising and it comes to the desired pressure.
- Therefore 10 lbs per square inch with coresponding temperature 121@c after the stated period, switch of the autoclave. Allow it to cool to about 40 @c before opening the vent. When whole of the steam inside the autoclave is removed, the lid is opened and the sterilised material is taken out.
TYPE OF THE AUTOCLAVE
- Simple laboratory autoclave
- Transporatble bench top autoclaves
- Large simple autoclave
- Downward displacement laboratory autoclave
- Media preparators
- Multi purpose laboratory autocalve
- Other autoclave
- High security autoclave
- Porous load sterilizers
- Low temperature steam
- Autoclaves are widely used in microbilogy, medicine, podiatry, tattooing, body piercing, veterinary science, mycology, dentistry and prosthetics fabrication. They vary in size and function depending on the media to be sterilized.
- Typical loads include laboratory glassware, other equipment and waste, surgical instruments and medical waste.
- Sterilization is the total destruction of all forms of life, including bacterial spores. It is best done with heat, either dry heat in an oven, or steam under pressure.
- Iti used in sterilizing of surgical dressings and surgical instruments.
- It is used to sterilize the containers and closures.
- It is used in the sterilizing the majority of official injections which can withstand the pressure of 15 lb per square inch for 30 mins.
- A notable growing application of autoclaves is the pre-disposal treatment and sterilization of waste material, such as pathogenic hospital waste.
- A new generation of waste converters is capable of achieving the same effect without a pressure vessel to sterilize culture media, rubber material, gowns, dressing, gloves, etc.
- To cure composites and in the vulcanization of rubber autoclaves are also widely used. The high heat and pressure that autoclaves allow help to ensure that the best possible physical properties are repeatably attainable.
- A medical autoclave is a device that uses steam to sterilze equipment and other objects. This means that all bacteria, viruses, fungui and spores are inactivated. However, such as those associated with creutzfeldt jakob disease, may not be destroyed by autoclaving at the typical 134 degC for three minutes or 121 degC for 15 minutes
- Steam autoclaves are advantageous as insulated metal contraptions providing intense heat and moisture to decontaminate objects and/or waste, according to the Environmental Protection Agency (EPA).
- Autoclave destory micro organisms more efficiently than dry heat and hence the materials is exposed to a lower temperature for a shorter period.
- It is used for sterilization of a large number of official injections.
- Equipments or parts of rubber and plastic such as nylone and PVC can be withstand the temperature and the pressure required for sterilization.
- A large quantity of materials can be sterilized in one batch using a big autoclave.
- It is unsuitable for sterilisation of powders and oils.
- It cannot be used for sterilisation of articles which get spolied at 115 - 116 @c for 30 mins such as plastics and injections.
- Mehta RM, Pharmaceutics-I: sterilisation (1996), Page no: 204 - 205.