The increasing concern for health, safety and hygiene necessitated the invention of various means of sterilization. One significant means of sterilization is the autoclave, which is used for sterilizing all kinds of medical and laboratory instruments prior to use. It is also used for rendering all biohazardous substances and infectious wastes sterile before disposal.
What Is an Autoclave?
The autoclave was invented by Charles Chamberland in 1879. It is designed on the principle of a pressure cooker, using supersaturated steam under pressure for sterilization. The body of an autoclave is made of steel. It can withstand great pressure and a high temperature. A simple autoclave is provided with a vent to allow the inside air to escape while the chamber gets filled with superheated steam. It is also provided with a thermometer and pressure gauge to monitor the temperature and pressure inside the autoclave chamber. However, more technically advanced versions of steam autoclaves are also provided with vacuum pumps.
An autoclave uses steam under pressure as a sterilizing agent to kill microorganisms. When the autoclave is packed and ready, it is switched on. As the water inside the autoclave chamber starts to boil, steam begins to fill up the chamber. As more and more steam is generated, it causes the air inside the chamber to evacuate from the vent. Eventually the entire autoclave chamber is filled with supersaturated steam. Steam under pressure attains much higher temperature than under normal conditions, and this increases its sterilizing ability and its penetration power.
Standard Operational Settings
The time that is required to kill a particular amount of microbial population is known as the thermal death time (TDT). Greater temperature reduces the TDT, while lower temperature in the autoclave chamber increases the TDT. Usually, a shorter TDT is preferred, which means that the temperature attained must be very high. However, the TDT increases for larger loads of materials that need sterilization. Hence TDT depends on temperature, pressure as well as the load amount. Usually 121ºC and 15 PSI pressure is employed. But if the loads are lesser, 115ºC and 10 PSI pressure are required. If the loads are higher, 132ºC and 27 PSI pressure are often necessary.
The supersaturated steam used for sterilization in an autoclave ensures quicker heating and deeper penetration of steam. It kills microorganisms due to coagulation of vital proteins and enzymes in its body. It is capable of killing all forms of microorganisms, including protozoa, bacteria, fungi, algae and even viruses. Moist heat can even penetrate the microbial spores that are resistant against all other forms of sterilizing agents and kill them.
An autoclave is used in hospitals to sterilize surgical instruments, dressings and also before discarding toxic or infectious medical wastes. Tattoo parlors and skin-piercing clinics also use an autoclave to prevent spreading infections through needles used for piercing. An autoclave is also used in the manufacture of dyes.
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