Question
Discuss about autoclave and its uses.
Answer
An autoclave is the standard device for moist heat sterilization under pressure, the most reliable and widely used sterilization method in medical/laboratory practice.
Principle: water boils at a temperature dependent on the surrounding pressure — raising pressure above atmospheric raises the boiling point of water, so steam generated under pressure reaches temperatures well above 100°C. At 15 lbs/sq inch pressure, steam reaches 121°C; held for 15–20 minutes, this combination of high temperature, moisture, and pressure kills all microorganisms, including the most heat-resistant bacterial spores, by denaturing and coagulating their proteins.
Construction: a double-walled chamber; steam is generated (either within the chamber from an internal water reservoir, or supplied from an external boiler) and admitted into the chamber, displacing air (air is a poor heat conductor and must be fully evacuated — via a discharge/exhaust valve or, in modern models, a vacuum pump — for the set temperature to be reliably achieved throughout the load); a pressure gauge, safety valve, and thermometer/temperature sensor monitor conditions; a timer controls the holding period, after which the steam is released and the chamber allowed to cool before opening.
Standard cycle: 121°C at 15 lbs/sq inch for 15–20 minutes (longer for larger loads or when treating rubber goods).
Uses: sterilization of surgical instruments, dressings, culture media, glassware, rubber goods (gloves, tubing), and laboratory/hospital waste. Not suitable for materials damaged by heat/moisture (some plastics, sharp cutting-edge instruments that may be blunted, or oils/powders that steam cannot penetrate).
Sterility monitoring: chemical indicators (autoclave tape that changes colour, Bowie-Dick test for effective air removal/steam penetration) and biological indicators (spore strips of Geobacillus stearothermophilus, which must show no growth after processing) confirm that true sterilizing conditions were achieved throughout the load, not just that the machine ran.